The magazine for certified Soils - Agronomy

SOILCOMPACTION

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The magazine for certified crop advisers, agronomists, and soil scientists

July–August 2011

&SoilsAn American Society of Agronomy publication

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Extraordinary OpportunityThe Golden Opportunity Scholars Institute, a program of the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, matches undergraduates with scientist-mentors during the ASA–CSSA–SSSA International Annual Meetings. The program en-courages talented students to enter the agronomy, crop, and soil sciences, cultivate networks, and succeed in their careers.

Extraordinary Support You can help support young scientists with a monetary gift to the Golden Opportunity Scholars Institute. The program is now international and promises to become even more diverse in the future so make your pledge today to keep the future of agronomy, crop and soil sciences strong!

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ContentsContentsVolume 44 | Issue 4 | July–August 2011

Crops & Soils, the magazine for certified crop advisers, agrono-mists, and soil scientists, is published bimonthly (January– February, March–April, May–June, July–August, September– October, and November–December) by the American Society of Agronomy. Visit us online at www.agronomy.org/publications/crops-and-soils.

Magazine staffDirector of Science Communications: James Giese

([email protected] or 608-268-3976)Director of Certification Programs: Luther Smith

([email protected] or 608-268-4977)Managing Editor: Matt Nilsson ([email protected]

or 608-268-4968)Lead Writer: Madeline FisherProofreader: Meg Ipsen

Advisory boardFredrick F. Vocasek, Servi-Tech Laboratories, Dodge City, KS (chair)Howard Brown, GROWMARK, Inc., Bloomington, ILCharles Russell Duncan, Clemson Extension Service, Manning, SCSusan Fitzgerald, Fitzgerald and Co., Elmira, ON, CanadaDale F. Leikam, Kansas State University, Manhattan, KSLisa Martin, Martin and Associates, Pontiac, ILLarry Oldham, Mississippi State University, Mississippi State, MSJames Peck, ConsulAgr Inc., Newark, NYKim R. Polizotto, Potash Corp. of Saskatchewan, Greenfield, INGeorge Simpson, Jr., Yara North America Inc., Beaufort, NCDale L. Softley, Forensic Agronomy/Consultant, Lincoln, NEHarold Watters, Ohio State University Extension, Raymond, OHJohn W. Zupancic, Agronomy Solutions, Sheridan, WY

Contributions/correspondenceCrops & Soils welcomes letters, comments, and contributions, published on a space-available basis and subject to editing. The deadlines are February 15 (March–April issue), April 15 (May–June issue), June 15 (July–August issue), August 15 (September–October issue), October 15 (November–December issue), and December 15 (January–February issue). Call 608-268-4968 or email [email protected]. For general inquiries not related to Crops & Soils, please call 866-359-9161 or email [email protected].

AdvertisingContact Alexander Barton ([email protected] or 847-698-5069) or visit www.agronomy.org/advertising.

Postage/subscriptionsCrops & Soils (ISSN 0162-5098) is published bimonthly by the American Society of Agronomy. Send address changes to Crops & Soils, 5585 Guilford Rd., Madison, WI 53711-5801 (for the U.S.) or IBC Mail Plus, 7686 Kimble St., Units 21 & 22, Missis-sauga, Ontario L5S1E9 Canada (for Canada). Subscriptions are $21/year (U.S.) and $47/year (international). To subscribe, visit www.agronomy.org/publications/subscriptions, call 608-268-4961, or email [email protected].

The views in Crops & Soils do not necessarily reflect endorse-ment by the publishers. To simplify information, Crops & Soils uses trade names of some products. No endorsement of these products is intended, nor is any criticism implied of similar products that are not mentioned.

agronomy.org/certifications | soils.org/certification July–August 2011 | Crops & Soils magazine 3

FeatureSoil compaction can reduce farm yields and profits. While a number of factors contribute to compaction, such as farm machinery weight and traffic, rain, and tillage, it is fundamentally a biological problem caused by a lack of actively growing plants and active roots in the soil. This month’s feature examines the biology of soil compaction and ways to reduce it.

11 New Research | Rescue nitrogen applications for corn.

12 Regulatory News | Time to re-think CRP allocations.

14 Certification | Online courses for agronomy and soils profession-als. Plus, CEU and career opportunities abound this fall in San Antonio.

22 Tales from the Pits | The tale of the wayward email.

24

Meet the Professional | Meet Don Schmidt.

26

New Products

27 Self-Study CEUs | Compost rates for optimum yield in organic crop production (1 CEU in Nutrient Management) and reducing the variability in potato yield (1 CEU in Crop Management).

4

Earn CEUs this fall in San Antonio. See p. 18.

4 Crops & Soils magazine | July–August 2011 American Society of Agronomy

Feature

SOILCOMPACTION

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agronomy.org/certifications | soils.org/certifications July–August 2011 | Crops & Soils magazine 5

By James J. Hoorman, Extension Educator, Cover Crops and Water Quality, Ohio State University Extension, Columbus; João Carlos de Moraes Sá, Soil Organic Matter and Fertility Specialist, University of Ponta Grossa, Ponta Grossa, Brazil; and Randall Reeder, Extension Agricultural Engineer, Food, Agricultural, and Biological Engineering, Ohio State University Extension, Columbus

Soil compaction can reduce farm yields and profits. While a number of factors contribute to compaction, such as farm machinery weight and traffic, rain, and tillage, it is fundamentally a biological problem caused by a lack of actively growing plants and active roots in the soil. This month’s feature examines the biology of soil compaction and ways to reduce it.

Editor’s note: The following article is being reprinted with permission in a slightly modified format from the Ohio State University Extension. The original document can be viewed here: http://ohioline.osu.edu/sag-fact/pdf/0010.pdf.

Soil compaction is a common and constant prob-lem on most farms that till the soil. Heavy farm machinery can create persistent subsoil compaction (Hakansson and Reeder, 1994). Johnson et al. (1986) found that compacted soils resulted in: restricted root growth, poor root zone aera-tion and poor drainage that results in less soil aeration, less oxygen in the root zone, and more losses of nitrogen from denitrification.

Subsoil tillage has been used to alleviate compaction problems. Subsoilers are typically operated at depths of 12 to 18 inches to loosen the soil, alleviate compaction, and increase water infiltration and aeration. Subsoiling usually increases crop yields, but the effects may only be tempo-rary as the soil re-compacts due to equipment traffic. Some no-till fields never need to be subsoiled, but in other no-till fields, deep tillage has increased yields especially if equip-ment traffic is random. When subsoiling removes a hard pan, traffic must be controlled or compaction will reoccur. If a hard pan does not exist, equipment traffic generally will create one (Reeder and Westermann, 2006).

If the soil is subsoiled when the soil is wet, additional compaction may occur. In a loamy sand, Busscher et al.

(2002) found that soil compaction increased with time, and cumulative rainfall accounted for 70 to 90% of the re-compaction due to water filtering through the soil and the force of gravity. The fuel, labor, equipment, and time to subsoil makes it an expensive operation. Subsoiling in dry conditions requires even more fuel (Reeder and Wester-mann, 2006). Two other factors that affect soil compaction are rainfall impact and gravity. In soils that have been tilled, both the velocity of the raindrop impact on bare soil and natural gravity combine to compact soils.

Low organic matter levels make the soil more susceptible to soil compaction. Organic residues on the soil surface have been shown to cushion the effects of soil compaction. Surface organic residues have the ability to be compressed, but they also retain their shape and structure once the traf-fic has passed. Like a sponge, the organic matter is com-pressed and then springs back to its normal shape. However, excessive traffic will break up organic residues, and tillage accelerates the decomposition of organic matter. Organic residues in the soil profile may be even more important than surface organic residues. Organic matter (plant debris and residues) attached to soil particles (especially clay particles) keeps soil particles from compacting. Organic matter binds microaggregates and macroaggregates in the soil. Low organic matter levels make the soil more susceptible to soil compaction (Wortman and Jasa, 2003).

In the last hundred years, tillage has decreased soil or-ganic levels by 60%, which means that approximately 40%


of soil organic carbon stocks are remaining (International Panel on Climate Change, 1996; Lal, 2004). Carbon pro-vides energy for soil microbes, is a storehouse for nutri-ents, and keeps nutrients recycling within the soil. Humus or old carbon (>1,000 years old) is the most stable carbon and binds soil microparticles together to form microaggre-gates. Humus is not water soluble, so it stabilizes micro-aggregates and is not readily consumed by microorgan-isms. Humus is more resistant to tillage and degradation than active carbon.

Active carbon (plant sugars, polysaccharides, and glomalin) is consumed by microbes for energy. Active carbon is reduced with tillage but is stabilized under natural vegetation and no-till systems using a continuous living cover. Active carbon is part of the glue that binds microaggregates into macroaggregates and insulates the macroaggregate from oxygen. Soil porosity, water infil-tration, soil aeration, and soil structure increase under natural vegetation and no-till systems with continuous living cover. Increased soil macroaggregation improves soil structure and lowers bulk density, keeping the soil particles from compacting.

Microaggregates and macroaggregate formation

Microaggregates are 20–250 μm in size and are com-posed of clay microstructures, silt-size microaggregates, particulate organic matter, plant and fungus debris, and mycorrhizal fungus hyphae. Roots and microbes combine microaggregates in the soil to form macroaggregates. Macroaggregates are linked mainly by fungi hyphae, root fibers, and polysaccharides and are less stable than mi-croaggregates. Macroaggregates are greater than 250 μm in size and give soil its structure and allow air and water infiltration. Compacted soils tend to have more microag-gregates than macroaggregates (Fig. 1 and 2).

Glomalin acts like a glue to cement microaggregates together to form macroaggregates and improve soil structure. It initially coats the plant roots and then coats soil particles. Glomalin is an amino polysaccharide or glycoprotein created by combining a protein from the mycorrhizal fungus with sugar from plant root exudates (Allison, 1968). The fungal “root-hyphae-net” holds the aggregates intact, and clay particles protect the roots and hyphae from attack by microorganisms. Roots also create other polysaccharide exudates to coat soil particles (see Fig. 2 and 3).

The contribution of mycorrhizal fungi to aggregation is a simultaneous process involving three steps. First, the fungus hyphae form an entanglement with primary soil particles, organizing and bringing them together. Second, fungi physically protect the clay particles and organic debris that form microaggregates. Third, the plant root

and fungus hyphae form glomalin and glue microaggregates and some smaller macroaggregates together to form larger macroaggregates (see Fig. 4).

In order for glomalin to be produced, plants and mycorrhizal fungi must exist in the soil together. Glomalin needs to be continually produced because it is readily consumed by bacteria and other microorganisms in the soil. Bacteria thrive in tilled soils because they are more hardy and smaller than fungi, so bacteria numbers increase in tilled soils. Fungi live longer and need more stable conditions to survive. Fungi grow bet-ter under no-till soil conditions with a continuous living cover and a constant source of carbon. Since fungi do not grow as well in tilled soils, less glomalin is produced and fewer macroaggregates are formed, which can result in poor soil structure and compaction. Thus, soil compaction is a biological problem

Feature

Fig. 1. (a) Macroaggregate components—schematic illustration; (b) mechanical disturbance by tillage dis-rupts macroaggregates and exposes soil organic mat-ter (SOM) protected within the aggregate to microbial attack; (c) decrease of SOM within the aggregates due to microbial attack causes dispersion of clay particles, clay microstructure, and silt+clay microaggregates. Illustration courtesy of João Carlos de Moraes Sá.


related to decreased production of polysaccha-rides and glomalin in the soil. Soil compaction is due to a lack of living roots and mycorrhizal fungi in the soil.

In a typical corn–soybean rotation, active roots are present only a third of the time. Adding cover crops be-

tween the corn and soybean crops increases the presence of active living roots to 85 to 90% of the time. Active roots produce more amino polysaccharides and glomalin be-

cause mycorrhizal fungus populations increase due to a stable food supply.

Surface and subsoil tillage may physically break up hard pans and soil compaction temporarily, but they are not a permanent fix. Tillage increases the oxygen content of soils and de-creases glomalin and amino polysac-

Fig. 2. Hierarchy of soil aggregates. Illustration republished with permission fromThe Nature and Properties of Soils, 14th ed., Brady and Weil (2008), Fig. 4.15 from p. 137.

Fig. 3 (below, left). Roots, fungi hyphae, and polysaccharides stabilize soil macroaggregates and promote good soil structure. Photo by João Carlos de Moraes Sá. Fig. 4 (below, right). A microscopic view of an arbuscular mycor-rhizal fungus growing on a corn root. The round bodies are spores, and the threadlike filaments are hyphae. The substance coating them is glomalin, revealed by a green dye tagged to an antibody against glomalin. Photo by Dr. Sara Wright and Dr. Kristina Nichols (USDA-ARS).


charide production by reducing plant root exudates and mycorrhizal fungus populations. Soil compaction is a re-sult of the lack of active roots producing polysaccharides and root exudates and a lack of mycorrhizal fungi produc-ing glomalin. In a typical undisturbed soil, fungal hyphae are turned over every five to seven days, and the glomalin in the fungal hyphae is decomposed and continually coats the soil particles. Disturbed soils have less fungi, more bacteria, and more microaggregates than macroaggre-gates. Heavy equipment loads push the microaggregates together so that they can chemically bind together, com-pacting the soil. Macroaggregate formation improves soil structure so that soil compaction may be minimized. Thus, soil compaction has a biological component (see Fig. 5).

Cultivation of soils, heavy rains, and oxygen promote the breakdown of mac-roaggregates, which give soil structure and soil tilth. Farmers who excessively till their soils (for example, heavy disking or plowing) break down the soil structure by breaking up the macroaggregates, injecting oxygen into the soil, and de-pleting the soil of glomalin, polysaccharides, and carbon. Greater than 90% of the carbon in soil is associated with the mineral fraction (Jastrow and Miller, 1997). Glomalin and polysaccharides are consumed by flourishing bacteria populations that thrive on high oxygen levels in the soil and the release of nutrients in organic matter from the till-age. The end result is a soil composed of mainly microag-gregates and cloddy compacted soils. Soils composed mainly of micro-aggregates prevent water infiltration due to the lack of macropores in the soil, so water tends to pond on the soil surface. Farm fields that have been ex-cessively tilled tend to crust, seal, and compact more than no-till fields with surface crop residues and a living crop with active roots to promote fungal growth and glomalin production.

An agricultural system that combines a continuous living cover (cover crops) with continuous long-term no-till is a system that closely mimics a natural system and should restore soil structure and soil productivity. A continuous living cover plus continuous long-term no-till protects the soil from compaction in five major ways. First, the soil surface acts like a sponge to help adsorb the weight of heavy equipment traffic. Second, plant roots create voids and macropores in the soil so that air and water can move through the soil. Roots act like a biologi-cal valve to control the amount of oxygen that enters the soil. The soil needs oxygen for root respiration and to sup-port aerobic microbes in the soil. However, too much soil oxygen results in excessive carbon loss from the aerobic microbes consuming the active carbon. Third, plant roots supply food for microorganisms (especially fungi) and burrowing soil fauna that also keep the soil from compact-ing. Fourth, organic residues left behind by the decaying plants, animals, and microbes are lighter and less dense

Feature

What is a clod?Many farmers complain that their soil is cloddy and

hard to work. Clods are man-made and do not usually exist in the natural world. Bricks and clay tile are formed by tak-ing wet clay from the soil and heating and drying the clay. When farmers till the soil, they perform the same process by exposing the clay to sunlight, heating and drying the clay until it gets hard and turns into a clod. Tillage also oxidizes the soil and results in increased microbial decom-position of organic residues. Organic residues keep clay particles from chemically binding. Clay soils that remain protected by organic residues and stay moist resist turning into clods because the moisture and organic residues keep the clay particles physical-ly sepa-rated.

Organic residues act like sponges, absorb-ing water and soil nutrients and cushion-ing soil particles. Clods act like bricks, re-sisting water absorption and making soils hard and compacted. Photo by Jim Hoorman.

Fig. 5. Tillage disrupts the macroaggregates and breaks them into microaggregates by letting in oxygen and releas-ing carbon dioxide. Photo by João Carlos de Moraes Sá.


Building soil structureBuilding soil structure is like building a house.

Mother Nature is the architect, and plants and mi-crobes are the carpenters. Every house needs to start out with a good foundation like bricks (clay, sand, and silt) and cement (cations like Ca++, K+). When a house is framed, various sized wood timbers, rafters, and planks are used to create rooms (represented by the various sized roots in the soil). Wood and roots give the house and the soil structure, creating space where the inhabitants (plants, microbes, and soil fauna) can live.

Wood in a house is held together by various sized nails (humus) and lag screws (phosphate attaches organic residues to clay particles). A house has braces to add stability (nitrogen and sulfur provide stability to organic residues) and a roof to control the temperature and moisture. In the soil, a deep layer of surface resi-dues controls oxygen and regulates water infiltration and runoff. A roof insulates the house and regulates the temperature just like surface residue on the soil surface keeps the soil temperature in a comfortable range for the inhabitants (microbes and plant roots). Houses need insulation and glue to keep them togeth-er. Root exudates form polysaccharides and glomalin (formed with mycorrhizal fungus) to insulate the soil particles and keep the soil macroaggregates glued together. If the roof on a house is destroyed, moisture and cold air can enter the house and rot out the wood and dissolve the glues.

In the soil, organic matter decomposes very quickly when tillage, excess oxygen, and moisture either break down the glues (polysaccharides and glomalin) or are easily consumed by flourish-ing bacteria popula-tions. Excess oxygen in the soil (from tillage) stimulates bacteria populations to grow, and they consume the polysac-

charides as a food source, destroying the soil struc-ture. With tillage, macroaggregates become microag-gregates, and the soil becomes compacted.

As every homeowner knows, houses need regular maintenance. In the soil, the roots and the microbes (especially fungi) are the carpenters that maintain their house, continually producing the glues (polysaccha-rides and glomalin) that hold the house together. Regu-lar tillage acts like a tornado or a hurricane, destroying the structural integrity of the house and killing off the inhabitants. Tillage oxidizes the organic matter in the soil, destroying the roots and the active organic matter, causing the soil structure to crumble and compact. If you remove wood supports and glue in a house, the house becomes unstable just like the soil does when you remove the active living roots and active organic residues (polysaccharides). Wood beams in a coal mine stabilize the coal mine tunnel like active living roots and healthy microbial communities give the soil structure to prevent soil compaction. Active roots and macroaggregates give soil porosity to move air and wa-ter through the soil in macropores. In an ideal soil, 50 to 60% of the soil volume is porous while in a degraded compacted soil, soil porosity may be reduced to 30 to 40% of the total soil volume. Compacted soil is like a decaying house turning into a pile of bricks, cement, and rubble.


than clay, silt, and sand particles, so adding organic residues to the soil decreases the average soil density. Fifth, soil compaction is reduced by combining microag-gregates into macroaggregates in the soil. Microaggregate soil particles (clay, silt, and particulate organic matter) are held together by humus or old organic matter residues, which are resistant to decomposition, but microaggregates tend to compact in the soil under heavy equipment loads. Polysaccharides and glomalin weakly combine microag-gregates into macroaggregates, but this process is broken down once the soil is disturbed or tilled.

SummarySoil compaction reduces crop yields and farm profits.

For years, farmers have been physically tilling and subsoil-ing the soil to reduce soil compaction. At best, tillage may temporarily reduce soil compaction, but rain, gravity, and equipment traffic compact the soil. Soil compaction has a biological component—it is caused by a lack of actively growing plants and active roots in the soil. A continuous living cover plus long-term continuous no-till reduces soil compaction in five ways. Organic residues on the soil surface cushion the soil from heavy equipment. Plant roots create voids and macropores in the soil for air and water movement. Plant roots act like a biological valve to control the amount of oxygen in the soil to preserve soil organic matter. Plant roots supply food for soil microbes and soil fauna. Residual organic soil residues (plants, roots, and microbes) are lighter and less dense than soil particles.

Soil compaction is reduced by the formation of macro-aggregates in the soil. Microaggregate soil particles (clay, silt, and particulate organic matter) are held together by humus or old organic matter residues and are resistant

to decomposition. Macroaggregates form by combing microaggregates together with root exudates like polysac-charides and glomalin (sugars from plants and protein from mycorrhizal fungi). Polysaccharides from plants and glomalin from fungi weakly hold the microaggregates together but are consumed by bacteria, so they need to be continually reproduced in the soil to improve soil struc-ture. Tillage and subsoiling increase the oxygen content in soils, increasing bacteria populations, which consume the active carbon needed to stabilize macroaggregates, lead-ing to the destruction of soil structure. Soil compaction is a direct result of tillage, which destroys the active organic matter, and a lack of living roots and microbes in the soil. Heavy equipment loads push soil microaggregates together so that they chemically bind together, resulting in soil compaction.

AcknowledgmentsThis fact sheet was produced in conjunction with the

Midwest Cover Crops Council (MCCC). The authors wish to thank Kim Wintringham (Technical Editor, Communi-cations and Technology, The Ohio State University) and Danita Lazenby (diagram illustrations).

ReferencesAllison, F.E. 1968. Soil aggregates—some facts and fallacies as

seen by microbiologist. Soil Sci. 106:136–143.

Brady, N.C., and R. Weil. 2008. The nature and properties of soils. 14th ed. Prentice Hall, Upper Saddle River, NJ.

Busscher, W.J., P.J. Bauer, and J.R. Frederick. 2002. Recompac-tion of a coastal loamy sand after deep tillage as a func-tion of subsequent cumulative rainfall. Soil Tillage Res. 68:49–57.

Hakansson, I., and R.C. Reeder. 1994. Subsoil compaction by vehicles with high axle load-extent, persistence and crop response. Soil Tillage Res. 29(2–3):277–304.

Jastrow, J.D., and R.M. Miller. 1997. Soil aggregate stabilization and carbon sequestration: Feedbacks through organomineral associations. p. 207–223. In R. Lal et al. (ed.) Soil processes and the carbon cycle. CRC Press, Boca Raton, FL.

Johnson, B.S., A.E. Erickson, and A.J.M. Smucker. 1986. Allevia-tion of compaction on a fine textured soil. ASAE Paper No. 86-1517. ASAE, St. Joseph, MI.

Lal, R. 2004. Soil carbon sequestration impacts on global climate change and food security. Science 304:1623–1627.

Reeder, R., and D. Westermann. 2006. Environmental benefits of conservation on cropland: The status of our knowledge. p. 26–28. In M. Schnepf and C. Cox (ed.) Soil management practices. Soil and Water Conservation Society, Ankeny, IA.

Wortman, C., and P. Jasa. 2003. Management to minimize and reduce soil compaction. NebGuide G896. University of Nebraska Extension, Lincoln.

Feature

Five ways soil organic matter resists soil compaction1. Surface residue resists compaction. Acts like a sponge

to absorb weight and water.

2. Organic residues are less dense (0.3–0.6 g/cm3) than soil particles (1.4–1.6 g/cm3).

3. Roots create voids and spaces for air and water.

4. Roots act like a biological valve to control oxygen in the soil.

5. Roots supply exudates to glue soil particles together to form macroaggregates and supply food for microbes.


New Research

Rescue nitrogen (N) applications to a stand-ing corn crop may be necessary when wet conditions prevent preplant or timely sidedress N applications or when the loss of previously applied N is suspected due to excessive moisture after application. Nitrogen loss is generally associated with excess rainfall causing leaching, denitrification, or ammonia volatilization. However, crop injury when N is broadcast-applied may counteract the yield benefits of a rescue N application.

Previous research has shown that corn can respond with increased yields from N applications at late vegeta-tive growth stages. Numerous studies have shown that excellent yield responses and often full yield may be obtained with N application times ranging from V6 to tasseling, although yield tends to decline the longer the N application is delayed.

When rescue N applications are called for, producers will need to decide what N source to apply and how to apply it for the greatest yield response. Ready availability of equipment and N source are important factors, but the effect of N application method and source on yield response also needs to be part of this decision. There are several factors that may influence corn yield response to different rescue N sources or application methods.

In a recent report in the Soil Science Society of America Journal, a group of researchers from the University of Mis-souri determined the effect of corn height, N placement, and source on injury and yield response. The group evalu-ated five site-years of research on the impact of broadcast and between-row placement of ammonium nitrate, urea ammonium nitrate (UAN), urea, and urea plus N-(n-butyl) thiophosphoric triamide (NBPT), a urease inhibitor, at about 150 lb/ac either pre-plant or when the corn was 12, 24, 35, or 47 inches tall.

The visual injury for broadcast-applied N sources was then ranked with urea being equal to urea plus NBPT, urea and urea plus NBPT being less than ammonium nitrate, and ammonium nitrate being less than UAN seven days after treatment.

The researchers found that injury depended on plant height. Leaf injury resulted in reduced yield when UAN or ammonium nitrate was broadcast on corn that was 24, 35, or 47 inches tall.

Broadcast urea or urea plus NBPT caused minimal crop injury and effectively supplied N to the corn crop. Application of NBPT-treated urea increased yield 229 lb/ac averaged across timings when compared with urea alone. Application when corn was 12 inches tall pro-duced the highest yields, but excellent yield response to rescue N was obtained at all application heights.

The optimal application height for N fertilizer was at about 12 inches tall, regardless of placement (averaged across site-years and N sources). Grain yields were similar for broadcast and between-row N placement when ap-plied pre-plant or on corn that was 12 or 24 inches tall.

Yields decreased slightly, however, with between-row ap-plications and steeply with broadcast applications when applied to taller corn.

Overall, the researchers believe that the placement and source of N should be considered when rescue N applica-tions are made to corn that is greater than 12 inches tall.

Adapted from the Soil Science Society of America Journal article, “Rescue Nitrogen Applications for Corn” by K.A. Nelson, P.C. Scharf, W.E. Stevens, and B.A. Burdick. Soil Sci. Soc. Am. J. 75:143–151.

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The USDA recently announced acceptance of 2.8 million acres into the Conservation Reserve Program (CRP), bringing total enrollment to 29.9 million acres. Under the 2008 farm bill, taxpayers are paying to set aside up to 32 million acres of American farmland designated as environmentally sensitive land. As we approach the 32-million acre limit and the next farm bill, it’s time to talk candidly about the number of acres we are idling in CRP. I think we all know that. With world population growing, more middle class citizens seeking better diets, and technology advancing, it’s time to re-think CRP allocations and consider bringing some of that land back into production.

Nearly 20 million CRP acres will expire over the next five years, making this a logical and painless time to re-examine our acreage-idling policies. Traditional market forces are calling for those acres to be brought back into

production, and unless USDA takes extraordinary steps, the market should be able to outbid Uncle Sam for the best acres.

Looking toward the next farm bill, we need to once again ask: What is the highest and best use of land cur-rently planted to vegetative cover under CRP? For a CCA, this is a pretty logical and straightforward decision. If the agriculture budget is going to be on the chopping block, should limited conservation dollars be directed to support

working lands or to idle land? Today’s answers will differ from those of 25 years ago when CRP was born.

We need to plan today to feed the additional two bil-lion people expected to be on the planet by 2050. Some land that is currently idle could produce crops, and it should. Some land could produce grass and forage for livestock to feed people, and it should.

A 10-10-10 approachI propose that we reallocate the 30 million acres cur-

rently in CRP roughly in thirds. I think of it as a 10-10-10 approach.

By definition, to be eligible for CRP, all of the land cur-rently under contract was at one point under cultivation and should have been highly erodible, but in fact, all of it is not. CRP regulations require that the land must have been farmed during at least four years from 2002 to 2007 or be part of a riparian buffer. In most cases, CRP acres were not the most fertile fields, but that land nevertheless was planted and produced crops.

Some 10 million acres or so covered by CRP are indeed fragile, highly erodible land, and keeping this land out of production provides high environmental benefits. This land is better suited for riparian or wetland buffers, filter strips, grass waterways, or contour grass strips. Keep-ing vegetative cover on this marginal land keeps soil on the ground and out of our waterways. We need to main-tain protection on these acres, and they should remain in CRP. Future CRP enrollments should be surgical in approach—complementing working lands.

Roughly another 10 million acres are best suited for grassland or forage crops. While the land would be marginal for commodity crop production, it can be used for grazing or producing hay and biomass, providing a positive contribution to the food, fiber, and fuel chain.

By Bruce I. KnightConsultant for the ASA and ICCA programs Washington, DC

CRP allocationsTime to re-think

“... it’s time to talk candidly about the number of acres we are idling in CRP. ”

Regulatory News


We need to move it from fallow ground into production of needed feed, fiber, and fuel. At the same time, for the wildlife community, we can preserve nesting and pollina-tor habitat as we do under the current CRP. This will in fact stabilize the haphazard emergency haying and graz-ing rules that are used today to access this forage even in nonemergency years.

The remaining 10 million acres can be responsibly managed to again produce crops to feed people, and we should encourage farmers to do so. Even record harvests will not dampen the need for additional grain in the years ahead. The advances in no-till technology and precision agriculture over the past 25 years permit us to farm this land responsibly. The services of a CCA can help guar-antee that this land can optimize yields while limiting environmental risk. In fact, the most reliable information compiled by the USDA suggests that more than eight mil-lion acres idled under CRP today are prime farmland and probably should never have been in the program.

American farmers have done a tremendous job in providing food to feed our nation. USDA Secretary Tom

Vilsack points out that our people spend only 6 or 7 cents out of every dollar to pay for the food we eat. That’s good news for consumers. But populations around the world are expanding, and we need to release acres from CRP to allow U.S. producers to meet expanding food needs. In fact, if we don’t do it, other countries will be forced to convert fragile prairies and forests to farmland to produce food.

I recognize this is a controversial proposal, especially in light of USDA’s addition of 10% more land to CRP just this past month. My proposal will startle some in both farm and conservation communities. However, I think this 10-10-10 proposal has multiple benefits. Farmers can re-sponsibly return more land to production, increasing their incomes, taxpayers will see lower bills for land retirement, and customers here and abroad will have access to more food.

Changing CRP has a lot of benefits, especially in light of the budget and food security concerns that will surely arise during consideration of the next farm bill. It’s time to put the future of CRP on the table.

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This fall, ASA and SSSA will be expand-ing their online course offerings. ASA has been offering its Fundamentals in Applied Agronomy course for the last several years, and both ASA and SSSA have been offer-ing online, educational seminars. The target audiences are agronomy and soil science professionals who are (or would like to be) certified or licensed (CCA, CPAg, CPSS, and CPSC). The response has been favorable, so we are adding additional courses to the menu of options, which are outlined below.

ASA CoursesFundamentals in Applied Agronomy is an introduc-

tory crops and soils course designed for practitioners who want to build their knowledge and skills in the topics that are most needed for a CCA. Upon completion of this 12-week, two-hours-per-week online course, participants should have a fundamental knowledge of soil and water, nutrient management, pest management, and crop man-agement. Topics include:

• basic soil physical and biological characteristics

• resource conservation

• irrigation

• drainage

• water quality

• soil and tissue analysis and interpretation

• fertilizers and other nutrient sources

• soil pH and liming

• pest identification, sampling, and control

• cropping systems

• planting practices

• crop growth and development

• harvest

• storage

• managing production risk

ASA is also offering the following three five-week, two-hours-per-week online courses:

Biotech Basics. Covers introduction to genetics—DNA and the genetic code, traditional plant-breeding tech-niques, plant breeding by genetic engineering, regulation and acceptance of GMOs, and review of products in the marketplace or new products in development.

Precision Agriculture. Covers precision farming basics, GPS and GIS, guidance systems and on-the-go equipment, collecting site-specific information (soil sampling, remote sensing, yield monitors, electrical conductivity, variable-rate technology), nutrient and soil management, seeding, pest management, and spatial data analysis/precision farming economics and adoption.

Nitrogen Fundamentals and Management. Covers nitrogen basics and the nitrogen cycle, nitrogen soil and tissue testing, nitrogen nutrient sources and fertilizers, nitrogen application methods, spatial management, on-the-go management, and nitrogen recommendations and economics.

SSSA CoursesFundamentals in Soil Science is an introductory soil

science course designed for practitioners who want to build their knowledge and skills in the topics that are most needed for the field of soil science. Upon completion, participants should have a fundamental knowledge of soil chemistry and mineralogy; fertility; physics; genesis,

agronomy and soils professionalsOnline courses for

By Luther SmithDirector of Certification Programs ASA and SSSA [email protected]

Certification


soils.org/education

agronomy.org/education

morphology, and classification; biology and biochemistry; and land use management. This is a 12-week, two-hours-per-week online course that begins in August 2011.

Soil and Water Management is a six-week, 90-minutes-per-week course with two versions: one with an agriculture focus and one with an urban or environmental soils focus. Each course will cover NPDES, conser-vation measures, ero-sion/sediment control, fate and transport of nutrients and pesticides, and surface/ground water connections.

Selected Topics in Applied Soil Science covers soil chemistry and mineralogy; soil fertility; soil physics; soil genesis, morphology, and classification; soil biology and biochemistry; and land use management. It is a six-week, 60-minutes-per-week course with multiple presenters centering on the topics above aimed at a target audience of soil scientists and environmental consultants. There will also be six-week sessions focused on agricultural, urban,

environmental, and wetland soils. Learning objectives will guide instruction and evaluation and are based on the ap-plication of soil science principles using problem-solving case discussions with an advanced understanding of soil science.

To learn more and to register, please visit www.soils.org/education or www.agronomy.org/education.

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Newly certifiedThe following list includes newly certified individuals and those who have added additional certifications.This list is alphabetized by surname within each state/province.

CanadaAlbertaClements, Andrew, Okotoks, AB

(CCA-PP)Hanneson, David, Airdrie, AB (CCA-

PP)Loney, Michael, Morinville, AB

(CCA-PP)Rempel, Andrea, Vermilion, AB

(CCA-PP)

British ColumbiaWarkentin, Paul, Ladysmith, BC

(CCA-NW)

ManitobaBaron, Heather, Swan River, MB

(CCA-PP)Doelger, Christian, Beausesour, MB

(CCA-PP)Newton, Scott, Neepawa, MB (CCA-

PP)Weir, Michael, Miami, MB (CCA-PP)

New BrunswickSavage, Bryan, Grand Falls, NB

(CCA-AP)

Nova ScotiaMargarit, Sebastian, Malagash, NS

(CCA-AP)Schurman, Marc, Auburn, NS (CCA-

AP)

OntarioCoghlin, Kyle, Atwood, ON (CCA-

ON)Guindon, Gilles, St. Isidore, ON

(CCA-ON)Macpherson, Bradley, Belmont, ON

(CCA-ON)

Sebben, William, Strathroy, ON (CCA-ON)

SaskatchewanBertoia, Phillip, Eatonia, SK (CCA-

PP)Bruce, Jesse, Moose Jaw, SK (CCA-

PP)Currah, Janina, Canwood, SK (CCA-

PP)Wall, Jeff, Maidstone, SK (CCA-PP)

United StatesArizonaMeen, Arthur, Douglas, AZ (CCA-

AZ)

CaliforniaAlpers, Kyle, Salinas, CA (CCA-CA)Bailey, Michael, Paicines, CA (CCA-

CA)Fien, Brian, Tulare, CA (CCA-CA)Giannini, Christopher, Nipomo, CA

(CCA-CA)Graber, David, Merced, CA (CCA-

CA)Grainger, Justin, Greenfield, CA

(CCA-CA)Gray, Eryn, Santa Maria, CA (CCA-

CA)Kashefi, Kion, Modesto, CA (CCA-

CA)Lanini, Lon, Salinas, CA (CCA-CA)Machlitt, David, Camarillo, CA

(CCA-CA)Madrid, Thomas, Gonzales, CA

(CCA-CA)Maloney, Daniel, Santa Maria, CA

(CCA-CA)Needham, Edward, Visalia, CA

(CCA-CA)Olivera, James, Santa Maria, CA

(CCA-CA)Orosco, Frank, Oxnard, CA (CCA-

CA)Pisani, Karen, Solvang, CA (CCA-

CA)

Rice, David, Santa Maria, CA (CCA-CA)

Rivers, Jimmy, Paso Robles, CA (CCA-CA)

Rover, John, Lincoln, CA (CCA-CA)Ruiz, Robert, Santa Maria, CA

(CCA-CA)Sandberg, Rick, Fresno, CA (CCA-

CA)Sheller, Eric, Visalia, CA (CCA-CA)Stanger, Trenton, Woodland, CA

(CPAg)Vanherweg, Nicolas, San Luis

Obispo, CA (CCA-CA)Weber, Nathaniel, Salinas, CA

(CCA-CA)Whitney, Mary, Hughson, CA (CCA-

CA)Widle, Charlie, Santa Maria, CA

(CCA-CA)Wilhelm, Nikohles, Merced, CA

(CCA-CA)Wilk, Cristopher, Durham, CA

(CCA-CA)Williams, Elizabeth, Nipomo, CA

(CCA-CA)

FloridaAdair Jr., Robert, Vero Beach, FL

(CCA-FL)Malek, Aaron, Lehigh Acres, FL

(CCA-FL)Moore Jr., James, Clewiston, FL

(CCA-FL)Pullen, Esther, Dover, FL (CCA-FL)

GeorgiaMullis, Mandel, Eastman, GA (CCA-

GA)

HawaiiManning, Grant, Kunia, HI (CCA-

HI)

IdahoHedler, Lance, Troy, ID (CCA-NW)Klingler, Ryan, Sugar City, ID (CCA-

NW)


Renfrow, Matthew, Kendrick, ID (CCA-NW)

Robison, Darius, Rexburg, ID (CCA-NW)

IllinoisConner, Shawn, Springfield, IL

(CCA-IL)Gerdes, Craig, Greenville, IL (CCA-

IL)Griesbach, Rick, Davis Junction, IL

(CCA-IL)Heimerdinger, Earl, Pearl City, IL

(CCA-IL)Howell, John, Red Bud, IL (CCA-IL)Spray, Andrew, Browns, IL (CCA-IL)Tyson, Shaun, Mt. Pulaski, IL (CCA-

IL)Webster, Mallory, Pontiac, IL (CCA-

IL)

IndianaKessinger, William, Elwood, IN

(CPAg)

IowaHammes, Bradley, Wilton, IA (CCA-

IA)Nelson, Grant, Denison, IA (CCA-

IA)Schirm, Dustin, Garrison, IA (CCA-

IA)

KansasFrise, John, Great Bend, KS (CCA-

KS)Hatcher, Bryan, Goodland, KS

(CCA-KS)McKinnis, Kent, Hutchinson, KS

(CCA-KS)Noellsch, Adam, Manhattan, KS

(CCA-KS)Russell, Garrett, Courtland, KS

(CCA-KS)Schulle, Darrell, Udall, KS (CCA-KS)Smith, Michael, Girard, KS (CCA-

KS)

KentuckySaxton, Charles, Bowling Green, KY

(CPAg)

MaineFitzpatrick Peabody, Erica, Houlton,

ME (CCA-NR)

MarylandMetz, Christopher, Cordova, MD

(CCA-CB)

MichiganDarke, LaVern, Shelby, MI (CCA-MI)Goetsch, William, Greenville, MI

(CCA-MI)Nelson, Stacie, Traverse City, MI

(CCA-MI)Robinson, Ryan, Mason, MI (CCA-

MI)Wilson, Benjamin, Perrinton, MI

(CCA-MI)

MinnesotaBray, Guy, Long Prairie, MN (CCA-

MN)Gehling, Timothy, Truman, MN

(CCA-MN)Kuehl, Eric, St Cloud, MN (CCA-

MN)Schabert, Beth, Cleveland, MN

(CCA-MN)

MississippiMcPherson, James, Inverness, MS

(CCA-MS)

New YorkBiltonen, Michael, Trumansburg, NY

(CCA-NR)Crooke, Nathan, Geneva, NY (CCA-

NR)Frisbee, Gideon, Walton, NY (CCA-

NR)Kingston, James, Elba, NY (CCA-

NR)Severson, Keith, Marcellus, NY

(CCA-NR)

Wright, Alexandra, Greenwich, NY (CCA-NR)

North DakotaMortenson, Timothy, Devils Lake,

ND (CCA-IA)

OklahomaMaisonnave, Roberto, Kingfisher, OK

(CCA-OK)Teels, Glen, Okemah, OK (CCA-OK)

OregonSinn, Scott, Salem, OR (CCA-NW)

TexasBaccus, Mark, Whiteface, TX (CCA-

TX)Barnes, Joe, Plainview, TX (CCA-

TX)Boedeker, Kryl, Plainview, TX (CCA-

TX)Burson, Garry, Lockney, TX (CCA-

TX)Cerny, Brent, Midfield, TX (CCA-

TX)Fischer, Sammy, Victoria, TX (CCA-

TX)Gheer, Landon, Plainview, TX (CCA-

TX)Odom, Bruce, Lubbock, TX (CCA-

TX)Seeton, Jana, Richmond, TX (CCA-

TX)

VirginiaWightman, Brett, Edinburg, VA

(CCA-CB)

WashingtonGroen, Steven, Lynden, WA (CCA-

NW)Munn, Derrick, Prosser, WA (CCA-

NW)


This fall, join the American Society of Agronomy (ASA), Crop Science Society of America (CSSA), and Soil Science Society of America (SSSA) at the 2011 Interna-tional Annual Meetings, October 16-19, in San Antonio, TX. We welcome the Canadian Society of Soil Science (CSSS) to our meetings this year as we meet under the theme, “Fundamental for Life: Soil, Crop, and Environ-mental Sciences.” Visit www.acsmeetings.org/program to view the program, search the schedule, or browse by day and Section/Division.

Earn CEUsMore than 3,000 poster and oral papers will be pre-

sented in sessions throughout the week, covering such topics as nutrient management, soil and water manage-ment, integrated pest management, crop management, and professional development. Certified professionals can attend the paper sessions and self-report their CEUs following the meeting. CCAs may only receive CEUs for structured oral presentations; open poster sessions do not qualify for CCA CEUs. Self-reporting forms are available online at www.certifiedcropadviser.org, www.agronomy.org/certifications, and www.soils.org/certifications.

Meeting highlightsCertified professionals working in the agronomic,

crop, soil, and related sciences can learn about the latest advances in production agriculture, network with col-leagues, view products and services in the exhibit hall, and attend professional development programs. Certified professionals are encouraged to attend ASA Section and Community business meetings, held throughout the week. View the program for more information. Professional soil scientists are invited to attend these sessions and presenta-tions on Monday, October 17:

Business Topics in Consulting

• Migrating From Public- to Private-Sector Soil Science Consulting

• Professional Career Opportunities in the Business of Soil Science Consulting

Ethics and Professional Practice

• Professional Soil Scientists’ Ethics Seminar

CSI: Critical Investigations—How Consulting Plays into Forensic Analysis

• Why Hasn’t Anybody Seen that Money Floating Down the River?

• Mysteries Unraveled

• Unique Interpretations Based On Soil Properties: Ground Squirrels as a Hydric Soils Indicator and Other ‘Tails’ from the Field

• Restoring and Managing Soils in Urban Areas

• So You Want to Be a Consultant

Soil Science Program Manager Dawn Ferris encour-ages consultants to attend these presentations and says certification/licensing is not a pre-requisite. “I would love to have consultants there as I think it would be a good networking opportunity and would help generate some candid discussions,” she says. “The sessions are open to anyone.”

SSSA 75th anniversaryIn addition to the technical

sessions, there will be several special events surrounding the celebration of the SSSA 75th an-niversary. These events include an SSSA informational display as part of the Society Center in the exhibit hall. On October 18, the SSSA plenary address will be held in the afternoon featuring author and journalist Chris Mooney, and that evening, there will be an SSSA awards and 75th anniversary reception outdoors.

Career opportunitiesIf you are looking for an employee or a job, tap into

the services of the Annual Meetings on-site Career Center. Open Sunday through Wednesday in the exhibit hall, the

1936–2011

Soil ScienceSociety of America75

this fall in San AntonioCEUs, career opportunities abound

Certification


center assists employers and employees with job oppor-tunities and facilitates interviews. For information, visit www.careerplacement.org or contact Leann Malison at 608-268-4949 or [email protected].

Meeting registrationRegistration for the Annual Meetings is available online

or by fax or mail. Register by September 7 to receive the early registration discount or by September 23 to receive

the pre-registration discount. Early registration by Sep-tember 7 is $445 for members of ASA, CSSA, or SSSA and $645 for non-members. After September 23, the regis-tration fee increases to $575 for members and $775 for non-members. Both one- and two-day rates are available. Members receive substantial registration discounts. In most cases, it costs less to join or renew and register for the Annual Meetings than it does to attend at the non-member fee. For more information, visit www.acsmeetings.org/register.


Technology is a wonderful thing;it allows us to be more productive and keep in touch with our clients on an almost real-time basis. Email and text messaging from smart phones have become the norm in our everyday work lives; however, they can also cause major problems if not used appropriately.

I hear a lot of comments that sound like this: “I don’t know how many times that I have had to talk to younger staff about appropriate email content.” This is not to imply that younger professionals are the only ones guilty of sending inappropriate emails or text messages, but those who grew up with the technology may have the tendency to use it more frequently without considering the con-sequences. Younger professionals also need to make the transition from using text messaging in their personal lives to their professional lives. That said, I would also submit

that we all need to think about how we use this technol-ogy on a professional level.

How many consultants out there have (or wanted to) email or text the following? “Mr./Ms. XXX is such an idiot. He/she does not even have a clue about soil science (LOL).” That sentence could be referring to a colleague, superior, a client, or perhaps even regulatory personnel. While it may seem like an innocent way to blow off some frustration at the time, consider what might happen next. Suppose that text or email gets forwarded onto other people, and then the next week you get a request for all documents and emails pertaining to the project. (After all, that email or text just called into question the methodolo-gies, analyses, and conclusions of that project, did it not?) That request is followed up by a trip into a deposition with the first question being “Have you ever called Mr./Ms.

By Dawn R. Ferris, Ph.D., PSS, and CPSSSoil Science Program Coordinator for the Soil Science Society of America; 608-819-3900 or [email protected] Twitter: @dferris_soils Blog: http://wiredsoils.blogspot.com

Email and text tipsRemember the following when preparing an email or text message:

1. Never text a client.

2. If you wouldn’t put it in a report, don’t put it in an email.

3. Obey the 24-hour rule: Always give yourself 24 hours to cool off before sending a reply email when the original email got you upset.

4. Review the email string and always include it when replying to emails.

5. Know who you are replying back to. A lot of times, your client’s boss could be on the dis-tribution list, and you want to always make your client look good in front of the boss.

6. Never text a client. (Yes, this was meant to be repeated!)

7. If in doubt, use the phone portion of your smart phone.

wayward emailThe tale of the

Tales from the Pits


XXX an idiot?” Not only is this hard to explain in a deposi-tion, but consider the working relationship you now have with Mr./Ms. XXX.

As an environmental consultant or consulting soil sci-entist, projects always tend to have the ability to go legal. As such, I always tend to take extra precautions when preparing emails that are going to be delivered to clients. However, now with the popularity of text messaging and smart phones, this is becoming more and more difficult, especially since everyone wants information and replies immediately. The one thing that has been lost with all of this “new” technology is the actual use of the telephone. As far as I know, most smart phones still have a phone component. Some of the shortest emails or text messages can be the most harmful.

For example, a short text message or email to a col-league or client talking about what “just got screwed up in the field” is probably not an incredibly smart thing to do. Can you imagine a competitor or, worse yet, an attorney getting that information? I cringe to think about how that deposition would go.

No one seems to be immune to this issue. Consider this example from one of my colleagues. “While waiting

to testify recently, I overheard a client’s lawyers getting hammered regarding an email that read, “Don’t get the records, make them work for it.” It was sent from a Black-berry and did not have the previous email. The previous email asked if a consultant was supposed to gather and copy the public records.” Oops! That was not an email that the lawyers wanted to go public.

The “tone” of an email is never clear and can be easily misinterpreted. Emails are easily forwarded—sometimes edited. If you inserted a “LOL” or smiley face on the end of a sentence to lighten the mood, did it get forwarded too? You never know. The bottom line is that your intent within the email and how you say it aren’t guaranteed to be picked up by subsequent readers. The same can be said regarding a text message.

The moral of this “Tales from the Pits” is to be aware of your email or text because no matter how you intended it to look, it has the potential to make you look bad, which in turn can backfire on your client and/or the company you work for. A little time spent thinking about the pos-sible consequences of an email or text will go a long way in saving you time and headaches later. Or in other words, 2alc b careful w txt and just use pots gr b4n.

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Like many a CCA, Don Schmidt grew up farm-ing, helping his family grow cash crops and raise a few hogs and dairy cows on a farmstead in southern Minneso-ta. But when time came to choose a career, the operation was too small to support him and all his brothers, Schmidt says. So he left to study soils, landed his first job at a co-op in northeast Wisconsin, and proceeded to become an integral part of the farm landscape there.

A crop consultant with nearly 35 years of experi-ence, Schmidt now writes nutrient management plans for some 30,000 acres in northeastern Wisconsin and Upper Michigan and handles the area’s largest dairy farms for his company, AgVentures, an ag supplier and consulting business based in Oconto Falls, WI. He has also worked with some farmers—and then their sons and grandkids as farms were passed down—ever since moving to the area around 1979.

But his longevity and the breadth of his territory are only part of the story. What makes Schmidt indispensable, says his associate of more than 20 years, Mike Mleziva, is his ability to absorb highly technical information—such as new regulations or the details of incentive programs—and convey it to farmers in practical terms they can work with.

“Don is our resident expert on state regulations and nu-trient management. He digs into it and he understands it, so he can explain it to his customers,” says Mleziva, gen-eral manager of AgVentures, where Schmidt is part of the “Enviro-Pros” sales and consulting team. “The best way I can describe Don is that he takes his time. He makes sure his customers understand what he’s talking about before he leaves them.”

Two of those customers are Leland and Ann Vande-Walle, owners of a “permitted” dairy farm near Crivitz, WI that must meet strict water quality standards because its herd exceeds 1,000 animals. For nearly 20 years, Schmidt has kept close watch over the operation, says the couple, helping with everything from crop scouting, soil sampling,

and pest management to regulatory permits and paperwork.

“Don is very conscientious and thorough in everything he does,” says Leland VandeWalle. “He does a good job of making sure we’re following all the guidelines we need to and keeps us up to date on new regulations, since we don’t have the time to keep up on those changes. If he does the same type of work for other farmers as he does for us, he is surely making a difference for dairy farmers in northeast Wisconsin.”

Schmidt didn’t necessarily set out to become a regional information resource on regulations. But he realized early in his career that agriculture, and especially dairy farm-ing, would be increasingly monitored by both state and federal agencies in the coming years. “So I thought I might as well get ahead of the curve, understand their thinking early on, and make sure the rules were livable for farm-ers,” he says.

Shortly after earning his CCA certification in 1994, Schmidt began promoting nutrient management planning, diving into the rules and developing good relationships with regulatory personnel at the county, state, and federal levels. Then “comprehensive” nutrient management plan-ning came along, an even more involved process that’s required of any dairy operation that wants to expand and become permitted. Schmidt now writes a large percentage of these plans for AgVentures’ clients. He has also spent a lot of time lately interpreting the NRCS’s Conservation Stewardship Program for farmers, he says.

Part of Schmidt’s devotion to this work stems from his analytical nature, Mleziva says. But another part comes from his desire to protect the region’s extensive water resources. The AgVentures headquarters are only 10 to 15 miles away from Green Bay on Lake Michigan, and the Menominee River flows through the region—a popular

Don Schmidt

By Madeline FisherLead WriterCrops & Soils magazine

Don SchmidtMeet the professional:

Meet the professional


fishing destination. The Crivitz area, too, sports many small lakes and vacation cabins. For all these reasons, Schmidt knows that dairy farming has to be compatible with recreational and water quality needs, Mleziva says.

“Don believes in agriculture. He understands it’s the livelihood of the farmer—and for him and me, for that matter,” he says. “But he also understands that we need to protect the environment, so that land continues to be available for farming.”

Still, what is always at the forefront in Schmidt’s mind is the farmer’s perspective, which is probably why he ex-cels at explaining technical information in terms farmers can easily grasp. When regulatory authorities first began announcing nutrient management standards, for example, Schmidt was quick to relate the new requirements to farm-ers’ age-old practices. “I told them, ‘You guys have been doing nutrient management your whole lives. If you had a hay field, you put a little less fertilizer on it; if you had a field that you put manure on, you added a little less fertil-izer. So, now we’re just getting a little more fine-tuned.’”

He tries to “watch out for farmers on other levels, too,” he says. He serves on the Wisconsin Crop Production As-

sociation’s legislative subcommittee on nutrient manage-ment, which keeps an eye on policy issues and helped re-write Marinette County’s manure ordinances so that they worked for both farming and residential communities. He also organized a letter-writing campaign on behalf of area farmers a couple of years ago when the state legislature was rewriting rules on agricultural runoff. Although it’s always hard to judge the impact of such efforts, he says, changes to the legislation were made that farmers were hoping for.

Away from work, Schmidt is a dedicated youth edu-cator at his church and an accomplished cook of Cajun cuisine. And now that his kids have grown up, he’s been able to indulge in a youthful passion. His family in Minne-sota always had motorcycles, so a few years ago Schmidt bought himself a Harley. Now he regularly tools around the area, with his wife on the seat behind him.

There’s just one thing that puts the hobby somewhat at odds with his other passion: farming. “If she catches me looking at fields as we’re riding along,” Schmidt jokes, “she slaps me on the side of the head to concentrate on the road.”

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Crop and Soils 1_2 horizontal.psd 1 4/29/2011 12:35:08 PM


New ELISA tests for Bt proteins in hybrid seed corn

A new assay designed to confirm the absence or pres-ence of Bt-Cry1F and Bt-Cry34Ab1 proteins expressed in HERCULEX XTRA seed corn has been commercialized and is being offered by Agdia, Inc. Capable of detecting both analytes in the same test well, this new dual-protein ELISA (enzyme-linked immunosorbent assay) is said to re-duce labor and cost. A typical single-trait ELISA test takes approximately two hours, including preparation time. This ELISA for both traits has the approximate completion time as a single-trait assay.

The ELISA employs two specific antibodies, one for Cry1F and one for Cry34Ab1, allowing for the detection of two traits in a single test well. Typically, ELISA assays only allow for one detection per well. This dual detection is accomplished by the coating of two antibodies per well and by employing two specific color-indicating substrates.

The new assay is a complete kit, including specially coated ELISA plates, an enzyme conjugate, positive con-trols, and extraction and wash buffers.

Agdia offers a portfolio of validated, diagnostic tests as well as in-house testing services for identifying GMO/traits and detecting plant pathogens. For more information, see www.agdia.com, email [email protected], or call 1-800-622-4342.

Collaboration to accelerate crop improvement

DuPont and Biotique Systems, Inc. have entered into a research alliance to accelerate genetic discovery in agricultural crops. Under the agreement, Biotique will provide knowledge and access to its proprietary “TITAN”

solution for next-generation sequence management, marker analysis, and genotype to phenotype association as well as its “Make-Sense” intellectual property portfolio. DuPont business Pioneer Hi-Bred will have access to the platform for agricultural applications and will retain all intellectual property for its genetic information and crops produced as a result of the alliance.

The platform incorporates a number of methods, tools, and technologies. DNA sequence analysis allows crop breeders to better understand the structure and function of genes in plants and other living things. Recent improve-ments in sequencing technologies have increased the pace of sequence data accumulation by many orders of magnitude, and new information platforms are essential to translate this accumulated data into knowledge and then customer value. For more, see www.pioneer.com.

Beck’s hybrids to offer new seed brand

Beck’s Superior Hybrids, Inc., Atlanta, IN, announced that it will distribute Phoenix brand corn hybrids from Syngenta in its marketing area beginning with the 2012 growing season. The new seed brand will offer hybrids containing diverse genetics and trait technologies, such as Agrisure 3000GT and Agrisure Viptera 3111 trait stacks. The company will distribute the new Phoenix brand to growers in the eastern Corn Belt. For more information, see www.beckshybrids.com.

The New Products section is a service to our readers. To simplify information, trade names may be used. No endorsement of these products is intended, nor is any criticism implied of simi-lar products that are not mentioned.

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New Products


Although invaluable as fertilizer in tradi-tional agriculture, animal manure was largely perceived as waste in the decades following World War II due to the availability of inexpensive synthetic fertilizer. Height-ened awareness of the environmental consequences of over-fertilization refocused attention on manure utili-zation in the 1990s. In recent years, the rising cost of synthetic fertilizer has reinforced the idea that efficient use of manure, and compost derived from it, can have both economic and ecological benefits. The economic imperative to use manure and compost efficiently is perhaps greatest on organic farmland, where no synthetic fertilizer is used, but current approaches to organic fertil-ity management are based on meeting nutrient targets designed to maximize yield, not profit.

A fundamental result from agricultural production economics is that the fertilizer rate that maximizes prof-it—the economically optimal rate (EOR)—is less than the rate that maximizes yield because of diminishing returns with respect to additional fertilizer. In other words, as more fertilizer is added, at some point the cost of an ad-ditional unit of fertilizer exceeds the revenue gained from the additional yield. Within a single season, the slope of the yield response at the EOR equals the fertilizer/crop price ratio. When a fertilizer affects yield in the years after its application, however, the optimality criterion for the EOR must be modified. Intuitively, one can see

that carryover effects with a multi-year planning horizon change the EOR because even if the cost of an additional unit of fertilizer cannot be recouped in the current year, it can be paid off by carryover effects in subsequent years. Although the theory for EORs with fertilizer carryover is not well known, it has been used on occasion to account for the carryover effects of synthetic fertilizer. Because two of the main fertilizers used in organic agriculture—manure and compost—have pronounced carryover ef-fects, the theory is particularly important to organic crop production.

Figures 1 and 2 (next page), which are based on data from a certified organic dryland wheat–fallow system in northern Utah, illustrate the potential for carryover effects with compost. In the fall of 1994, compost was incorpo-rated before planting the winter wheat at several rates. This site was harvested in 1995, and that fall, the same experiment was conducted at an adjacent site, harvested in 1996. Figure 1 shows that in both years, the yield increased in response to the compost, but only up to a point, after which there was no further increase. The large yield difference between the two harvests reflects year-to-year variability in precipitation.

In the fall of 1996, after a year of fallowing, the first site was replanted with winter wheat, but no additional

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in organic crop productionCompost rates for optimum yield

Abbreviations: CC, cumulative carryover; EOR, economically optimal rate.

Earn 1 CEU in Nutrient Management by reading this article and completing the quiz at the end. CCAs may earn 20 CEUs per two-year cycle as board-approved self-study articles. Fill out the attached questionnaire and mail it with a $20 check (or provide credit card information) to the American Society of Agronomy. Or, you can save $5 by completing the quiz online at www.agronomy.org/certifications/self-study.


compost was applied. Figure 2 shows the 1995 and 1997 harvest data as a function of the compost applied in the fall of 1994. The yield increase due to the carryover effects of the compost in 1997 was comparable to the yield in-crease in 1995. These data and subsequent research at the site have confirmed that the carryover effects of compost can be detected for many years in dryland wheat.

Decay seriesOf the primary macronutrients (N, P, and K) in manure

and compost, N has the most pronounced carryover ef-fect. Compared with 70 to 100% of the total K and P, any-where from 0 to 50% of the total N is bioavailable within the season of application, depending on the materials and extent of decomposition. A N decay series describes what fraction of the total (or organic) N is available for plant up-take in the first, second, third, etc., years after application. Nitrogen decay series have traditionally been measured by comparing the yield in plots receiving manure with the yield in plots receiving N fertilizer. For example, a N decay series of 0.4, 0.2, … means that plots receiving 200 lb manure N/ac had the same average yield as plots re-ceiving 200 × 0.4 = 80 lb fertilizer N/ac in the first year. In the following year, provided no new manure was added,

the manured plots had the same average yield as unmanured plots receiving 200 × 0.2 = 40 lb fertilizer N/ac. In practice, a regression model is used to interpolate between the N fertilizer rates used in the experiment.

Even if a decay series is not fully known, it may be possible to estimate the cumulative carryover (CC) for a manure or compost. CC measures the cumulative fertilizing value in the years following an application relative to the fertilizing value in the first year. In principle, the CC encompasses

both nutritive and non-nutritive effects, but almost no quantitative information is known about the latter. Be-cause well-composted manures have a low N-fertilizing value in the season of application and release a greater proportion of their total N for plant uptake in the years after application, these materials are expected to have a higher CC than fresh manure. As an example of how the CC would be calculated based on N, consider a compost that releases 10% of its total N in the first year. If one credits 50% of the total N as eventually available for plant uptake, then the CC based solely on N would be (50 – 10)/10 = 4.

Case study: EOR for organic dryland wheat The real data in Fig. 1 and 2 were used to guide the

simulation of a dryland wheat system in northern Utah. In this simulation, compost was applied once every four wheat crops, which means once every eight years in the wheat–fallow system.

The EOR depends on both the CC, which was initially assumed to be 4 (see above), and the ratio between the price of compost (pu) and the price of wheat (py). In early

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Fig. 1 (left). Wheat yield response to compost. Data points indicate the individual plot yields for one site in 1995 (open circles) and a second site in 1996 (X’s). Quadratic-plateau models were fit for each site-year (solid lines) and for the average of the two site-years (dashed line). Fig. 2 (right). The carryover effect of compost in dryland wheat. The 1995 yields shown in Fig. 1 are replotted here (as X’s) along with the 1997 yields (open squares) from the same plots, as a function of the compost rate in 1994. The two responses are remarkably similar even though no new compost was applied to the 1997 crop.


2008, a commercial compost manufacturer in northern Utah quoted bulk prices equivalent to $125/dry ton for delivery to the farm site. That summer, the average price for food-grade, organic hard red wheat in the Upper Midwest was $540/ton, leading to a price ratio of pu/py = ($125/dry ton compost) ÷ ($540/ton wheat) = 0.23. By the summer of 2009, the price of wheat had fallen to $260/ton, which translates into a price ratio of 0.48.

Figure 3 shows the EOR for the Utah organic dryland wheat system at price ratios between 0.16 and 0.40. As the price ratio increases, the EOR decreases. This is intui-tive because the higher the price ratio, the lower the value of the wheat relative to the compost, and thus a larger increase in yield is needed to pay for an additional unit of compost. Since the slope of the yield response increases as the production level decreases (see Fig. 1), a rising price ratio pushes the EOR to lower levels of produc-tion. Because a quadratic model was used in Fig. 1, the relationship between the EOR and the price ratio in Fig. 3 is linear.

The three lines in Fig. 3 correspond to the 1995 (solid), 1996 (solid), and average (dashed) yield responses in Fig. 1. The slopes of the lines, which represent the sensitivity of the EOR to changes in the price ratio, vary

because of differences in the curvature of the three yield responses. The EOR based on the 1995 yield response is the least sen-sitive to changes in the price ratio because it had the highest curvature. For a less con-cave yield response, such as that observed in 1996, a larger decrease in compost rate is needed to effect the same change in the slope of the yield response, so the EOR becomes more sensitive to changes in the price ratio (the slope of the line in Fig. 3

increases). For each response, the EOR is zero above a critical price ratio, the value of which depends on the initial slope of the yield response.

Whereas the sensitivity of the EOR to changes in the price ratio is linear for a quadratic yield model (Fig. 3), the curves in Fig. 4 illustrate the nonlinear dependence of the EOR on CC. Below a certain threshold, the EOR is zero because the carryover effects are not sufficient to cover the cost of even the first unit of compost. As the CC increases above this threshold, the EOR first increases but then passes through a maximum and eventually decreases.

The presence of a maximum, which is somewhat counterintuitive, is the result of two competing effects. As the CC increases, a lower marginal revenue in the season of application can be tolerated because of the additional revenue generated by carryover, which tends to increase the EOR. On the other hand, the rate increase needed to achieve a higher fertility state decreases as the CC increases, which tends to lower the EOR.

Discussion and conclusionsThe objective of this research has been to develop

and apply a method for calculating the EOR of compost

Fig. 3 (left). The effect of the compost/wheat price ratio on the eco-nomically optimal rate (EOR). The EOR is plotted for the case where compost is applied once every four crops in a wheat–fallow rotation (for CC = 4). The solid lines are based on the yield response in 1995 and 1996, and the dashed line is for the average yield response. Fig. 4 (right). The effect of cumulative carryover (CC) on the EOR. All three curves are based on the average 1995/1996 yield response, for different values of the compost/wheat price ratio (pu/pY) in units of tons wheat/dry tons compost.


that properly credits its pronounced carryover effects. The results were formulated to capture essential aspects of the agronomy and economics, but additional layers of complexity could be added. For example, the price of wheat can vary depending on protein content, which is in turn affected by the level of fertility. With sufficient data to model the effect of compost rate on wheat protein con-tent, this relationship could be included in the calculation of compost EORs.

This article has considered the problem of optimizing the compost rate for a given cropping system, but in real-ity, there is interplay between the design of the cropping system and the choice of an optimal rate. In any location, there are likely to be several feasible rotations for which a myriad of factors need to be considered, including envi-ronmental and economic sustainability. Such comparisons should be made after optimizing the compost rate along the lines indicated. Systems in which the EORs are so high as to warrant concern about phosphorus accumula-tion should be avoided when alternatives of comparable

profitability and enhanced environmental protection are available.

In the case study of dryland organic wheat, it was shown that the EOR decreases as the compost/price ratio increases, and the EOR exhibits a maximum with re-spect to the CC. The EOR for compost sold by one of the region’s main composting facilities was predicted to be zero, although there is considerable uncertainty in this conclusion because there was a lack of empirical data for carryover in organic systems. Compared with conven-tional agronomic systems, the gap between the maximum-profit and maximum-yield approaches in organic systems may be wider due to the high cost of organic fertilizers. Experimental studies are needed to explore this issue and to improve the efficiency of organic fertility management.

Adapted from the Agronomy Journal article, “Economi-cally Optimal Compost Rates for Organic Crop Produc-tion” by J.B. Endelman, J.R. Reeve, and D.J. Hole. Agron. J. 102:1283–1289.

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1. The fertilizer rate that maximizes yield is ________ the rate that maximizes profit.

q a. less than

q b. greater than

q c. equal to

q d. unrelated to

2. When the carryover effect of a fertilizer is neglected, the slope of the yield response at the EOR is _____ the fertilizer/crop price ratio.

q a. less than

q b. greater than

q c. equal to

q d. unrelated to

3. When the carryover effect of a fertilizer is taken into account, the optimality criterion for the EOR must be modified. Why is this particularly important in organic crop production?

q a. Because manure has unpredictable effects.

q b. Because compost has different effects during a drought.

q c. Because compost has pronounced carryover effects.

q d. Because manure can leach nitrogen into surface waters.

4. At a site in northern Utah in the fall of 1994, compost was incorporated before planting winter wheat, and the crop was harvested in 1995. When that same site was replanted in 1996, the carryover effect of the compost on the yield in 1997 was

q a. non-existent.

q b. as large as the effect in 1995.

q c. twice as large as the effect in 1995.

q d. half as large as the effect in 1995.

5. For a compost where 20% of its total N is bioavailable in the first year and 60% of the total N is eventually available for plant uptake, what is its cumulative car-ryover?

q a. 1

q b. 2

q c. 3

q d. 4

6. There can be considerable year-to-year variability in dryland wheat yield, primarily due to differences in

q a. the available light.

q b. the price of fertilizer.

q c. the price of fuel.

q d. the amount of precipitation.

7. The ratio between the price of wheat and the price of compost affects the EOR. Specifically, as the price ratio increases, the EOR

q a. decreases.

q b. increases.

q c. remains the same.

q d. doubles.

This quiz is worth 1 CEU in Nutrient Management. A score of 70% or higher will earn CEU credit.

DirectionsAfter carefully reading the article, answer each ques-tion by clearly marking an “X” in the box next to the best answer. Complete the self-study quiz registration form and evaluation form on the back of this page. Clip out this page, place in an envelope with a $20 check made out to the American Society of Agronomy (or provide your credit card information on the form), and mail to: ASA c/o CCA Self-Study Quiz, 5585 Guilford Road, Madison, WI 53711. Or you can save $5 by completing the quiz online at www.agronomy.org/certifications/self-study.

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July–August 2011 self-study quizCompost rates for optimum yield in organic crop production (no. SS 04157)

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8. In Fig. 3, the EOR is more sensitive to changes in the price ratio for the yield response in 1995 than for the yield response in 1996. Why?

q a. The price of wheat was higher in 1996.

q b. The price of compost was higher in 1996.

q c. The curvature of the yield response was larger in 1996.

q d. The curvature of the yield response was smaller in 1996.

9. The EOR exhibits a ______ with respect to cumulative carryover.

q a. minimum

q b. plateau

q c. maximum

q d. zero-response

10. For a cumulative carryover of 3 and price ratio of 0.3, the EOR in Fig. 4 is

q a. 0.

q b. 2.

q c. 4.

q d. 6.

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Potato yield is a product of the interaction be-tween genetic yield potential and the external production environment. The soil production environment can fur-ther be subdivided into chemical (macro- and micronutri-ents) and biophysical components. Soil matrix properties determine retention of moisture, facilitation of gas ex-change between the soil and the aerial environment, and the ability to sequester carbon through different bonding mechanisms. Soil nutrients are intensively managed by commercial growers during the entire potato production cycle. As such, biophysical characteristics of the soil are expected to have a greater role than chemical proper-ties in accounting for potato yield heterogeneity. This is particularly relevant to the poorly structured coarse soils where the majority of potatoes are grown in North America. If a dominant role for soil biophysical properties is ascertained, soil structure remediation recommenda-tions are available for potato production on sandy soils.

Soil structure is an important link in the functioning of the soil–plant–atmosphere continuum and is expected to impact crop yield performance. It influences soil mois-ture status and aeration as well as ionic exchange in the soil colloids. Aggregate stability is directly related to soil structure in terms of physical function to support crop growth, and thus is an excellent indicator of soil quality status. The ability of the potato plant to utilize available nutrients and moisture can be hampered by a non- optimum internal plant condition (e.g., presence of

disease or insect infestation) leading to reduced pho-tosynthesis and ultimately reduced yield. There is a considerable body of literature that positively correlates near-infrared reflectance with disease prevalence as well as environmental stress in plants.

A recent study reported in Agronomy Journal was conducted to quantify potato yield heterogeneity in a commercial production environment and determine predictive soil and plant spectral properties for tuber yield spatial analyses. The study was conducted at two commercial potato production fields managed by the same farm operator and designated as Fields A1 and A2, sampled in 2003 and 2004, respectively. The fields were located in Vestaburg, Montcalm County, Michigan. All field operations were left to best management practices developed by the cooperating commercial grower over the years.

Precipitation in the study area was documented using records from the nearby Montcalm Research Farm weath-er station. Annual precipitation for both years was below the 135-year average. Supplemental irrigation water application is the industry standard and was performed in these fields based on soil water content determination through the hand-feel method conducted by an experi-enced irrigator. A center-pivot irrigation system covered each field, rotating 360° in 24 hours and applying about 1.9 cm of moisture each rotation. Fields A1 and A2 are both composed of a Mancelona loamy sand with a slight

Earn 1 CEU in Crop Management by reading this article and completing the quiz at the end. CCAs may earn 20 CEUs per two-year cycle as board-approved self-study articles. Fill out the attached questionnaire and mail it with a $20 check (or provide credit card information) to the American Society of Agronomy. Or, you can save $5 by completing the quiz online at www.agronomy.org/certifications/self-study.

in potato yieldReducing the variability


slope, and about three quarters of Field A2 is composed of a complex of Gladwin loamy sand and Palo sandy loam. The soil complex in Field A2 is somewhat poorly drained.

Historical soil sample data taken from the fields were used to formulate the sampling design. Soil was tested for percent organic matter, phosphorus, potassium, magne-sium, calcium, pH, cation exchange capacity (CEC), and zinc. Soil samples for water-stable aggregate analyses were taken before harvest on Sept. 18, 2003 and Sept. 11, 2004 for Fields A1 and A2, respectively.

Spectral reflectance imagesAn Olympus 340R (Melville, NY) digital camera was

utilized to obtain red, green, and near-infrared spectral images at each of the grid points in Fields A1 and A2, on Aug. 31, 2003 and Aug. 28, 2004, respectively. The red, green, and near-infrared band images of the electro-magnetic spectrum were extracted using a photo-editing software (Photoshop, San Jose, CA) with a macro program to facilitate the processing of hundreds of pictures within a short time. The extracted green, red, and near-infrared band images were used as input to a geographic informa-tion software (IDRISI for Windows v1, Worcester, MA) to compute the mean average value of the image pixels (Fig. 1), as well as to generate different spectral ratios between the green, red, and near-infrared part of the electromagnetic spectrum through the overlay function. Unsupervised clustering into two groups using the cluster module of IDRISI was performed on the infrared com-posite image to produce a Boolean image, with 0 being non-vegetated areas and 1 being vegetated areas. Pixels with a 1 value in the image were counted and expressed as a percentage of the entire image pixels to represent per-

cent vegetated. A copy of the RGB (red-green-blue) and near-infrared images was multiplied with its correspond-ing Boolean image to segregate vegetation from non-vegetated areas, and the resulting image was classified as an adjusted spectral image. Spectral bands and ratios reported here can be distinguished based on the subscript, for example, Gadj, G/Radj, and R/IRadj were computed based on the adjusted images of the G (green), R (red), and IR (near infrared) bands. Use of an “unadj” subscript such as Gunadj, G/Runadj, and R/IRunadj were computed using non-adjusted digital images.

Potato yield responseThe mean total tuber yields for both fields were mod-

erately higher than those reported in 2005 from a variety trial conducted at the Michigan State University Montcalm Research Farm, indicating that the commercial manage-ment practices followed were effective.

In general, the climatic conditions in 2003 were conducive to potato production, and Michigan potato yield levels were higher by 1.5% compared with 2004. Precipitation in 2003 was well synchronized with potato growth stages and provided consistent moisture supply during the critical tuber bulking period of late summer, whereas 2004 had higher precipitation overall, but 50% below average late in the growing season. More than 80% of Michigan commercial potato fields, including the two monitored in this study, are provided supplemental irrigation through pivot systems. However, potato tuber is a high-moisture (75–80% moisture content), fresh com-modity product, and rainfall remains an important source of moisture with a significant influence on potato tuber yield.

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Fig. 1. Image acquisition, process-ing, and analyses involving an RGB (A) image and a near-infrared RGB image (B) being cropped (A1 and B1) to remove edge arti-facts, composited into IDRISI for Windows (A2, A3, A4; B2, B3, B4). Unsupervised clustering into two groups was performed on the near-infrared composite image (B5) to produce an image with 0 being nonvegetated areas and 1 being vegetated areas (B6). Pixels with a 1 value in the image were counted and expressed as a percentage of the entire image pixels to represent percent vegetated.


Spectral reflectancePotato spectral reflectance was

taken as a proxy for plant health in this study, since it is difficult to ac-count for all factors affecting potato yield. Digital images were taken at approximately the same time, Aug. 31, 2003 and Aug. 28, 2004 for Field A1 and A2, respectively, yet Field A1 had more reflectance in both the unadjusted and adjusted images for the green band (15 and 91%, respectively) compared with Field A2. The amount of red and near-infrared reflectance was higher in Field A2 than in Field A1 for the unadjusted images (48 and 80%, respectively). The higher level of red and near-infrared in Field A2 is presumably related to senescent plant tissues and vegeta-tion cover at less than 5% in A2 compared with 47% in A1. The significant difference in vegetation cover between the two fields may be due in part to growth and maturity patterns in the dry fall of 2004, as Field A2 was planted

nearly two weeks earlier than A1 (Apr. 29, 2004 vs. May 13, 2003), yet vegetation health by late August was poor. Field A2 had 33, 23, and 84% less rainfall in July, August, and September of 2004 compared with Field A1 rainfall in 2003. The combined effects of early planting and signifi-cant moisture stress could have accelerated senescence in Field A2. Figure 2 shows the typical vegetation cover in Fields A1 and A2 during sampling.

Fig. 2. Typical vegetation cover in Fields A1 (A) and A2 (B), when spectral images were taken in 2003 and 2004, respectively.


With vigorous, healthy vegetation, near-infrared light reflection should be high and a corresponding decrease will be observed as senescence begins. The interpretation of observed near-infrared values was confined to within study Fields A1 and A2 at a late stage in the growing season (tuber maturation phase, 110 days after planting in A1; 121 days after planting in A2) and not between fields. The red part of the electromagnetic spectrum is no longer absorbed by senescent plant tissues, causing an increase in the reflectance of this spectrum to be picked up by digi-tal imagery. In the current study, different spectral indices were positively correlated to potato yield: the unadjusted green, the green/red ratio, and the red/near-infrared spec-tral band or ratios in Field A1, and the red/near-infrared unadjusted ratio in Field A2.

Correlation analysesAs observed previously in the literature, soil texture

helped determine yield potential in the A1 field. Clay con-tent was positively correlated to tuber yield in this field; however, no similar relationship was found in Field A2. In a potato field study, researchers concluded that soil clay content was a driving factor in the formation of a well-aggregated soil and positively contributed to potato yield. In the current study, the influence of soil moisture on yield was consistent. It was positively correlated in both fields.

The experimental areas in both fields were purposively located so as to minimize the impact of micro-elevation, a factor that has been shown to markedly influence potato tuber yield. Micro-elevated areas in Field A1 with local-ized soil saturation late in the 2003 season may have led to detrimental effects on tuber growth, due to the known sensitivity of potatoes to oxygen deprivation. Indeed, the correlation values for Field A1 showed a positive relation-ship between elevation and yield. A year later, in Field A2, elevation did not have a significant relationship with yield. However, plants located at low topographical posi-tions may have benefited in this field—although this did not translate into detectable yield benefits—as soil mois-ture was negatively correlated to elevation in 2004.

The role of potassium in the growth and develop-ment of tubers varies with the intended market. Where the amount of solids is critical, as in processing potatoes, potassium needs to be monitored closely. Potassium promotes moisture accumulation in the tubers, resulting in decreased specific gravity, which influences market acceptability.

Yield predictorsBased on a SAS Proc Reg routine and variation infla-

tion factor behavior of the dataset, a total of 23 predic-tor variables were selected from the original pool of 42

for Field A1 while 21 predictor variables were selected from the original pool of 40 for Field A2. There were 15 common variables in both Fields A1 and A2 that did not contribute to multicollinearity. After the initial stepwise regression analysis was conducted on the selected pool of predictor variables, the analysis was repeated for a second time to determine if additional variables would contribute significantly to yield prediction. These additional predictor variables were hypothesized to be important for yield pre-diction and consisted of bulk density and infiltration rate for Field A1 and apparent electrical conductivity for Field A2. The final stepwise regression equation for Field A1 ac-counted for 67% of the potato yield variability. Physical, chemical, and spectral variables included in the equation were aggregate stability (mean weight diameter), topog-raphy, soil texture (the amount of clay), the unadjusted green band, and potassium level. Inclusion of infiltration rate and bulk density in the pool of predictive variables did not affect the variability explained, and neither one of these variables was included in the final regression equa-tion.

In Field A2, the stepwise regression initially included mean weight diameter, the red unadjusted band of the digital images, and the base saturation portion of hydro-gen, which together accounted for 44% of the observed potato yield variability. Inclusion of apparent electrical conductivity not only increased the explained variability to 60%, but it removed all of the identified yield predic-tors and replaced them with the green and red unadjusted band ratio and 250-μm water stable aggregate size frac-tion in the predictive equation.

The yield predictive models derived from commercial potato fields demonstrated the significant roles played by soil structure, specific spectral bands, and derived vegeta-tive index, as well as soil potassium status. These attri-butes proved critical for developing predictive regression models that could account for more than 60% of the yield variability observed. The inclusion of two proxies for soil structure (i.e., mean weight diameter and 250-μm water-stable aggregate) showed the significant contribution of soil structure to the positive dynamics of the soil, plant, and environment continuum, enhancing our understand-ing of how to reduce potato yield variability in a com-mercial context, where coarse-textured sites predominate. This study has relevance to environmentally friendly po-tato production as well; the findings are consistent with a need for soil structural geo-referenced information, given its indirect and direct effects on plant yield response.

Adapted from the Agronomy Journal article, “Potato Yield Variability across the Landscape,” by Edgar A. Po, Sieglinde S. Snapp, and Alexandra Kravchenko. Agron. J. 102:885–894.

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1. According to the article, soil matrix properties determine retention of moisture, facilitation of gas exchange between the soil and the aerial environment, and

q a. the pH of the soil.

q b. the interaction between soil nitrogen and carbon.

q c. the salinity and cation exchange capacity.

q d. the ability to sequester carbon through differentbonding mechanisms.

2. There is a considerable body of literature that positively correlates near-infrared reflectance with ___ as well as ___ in plants.

q a. senescence/root rot

q b. disease prevalence/environmental stress

q c. disease resistance/water use efficiency

q d. insect prevalence/shrunken tubers

3. With vigorous, healthy vegetation, near-infrared light reflection should be high and a corresponding

q a. increase can be seen as potato vines reach tubermaturity.

q b. decrease will be observed as senescence begins.

q c. decrease will be observed in the unadjusted green spectrum.

q d. increase in the absorption of the red part of the electro-magnetic spectrum will be seen.

4. In a potato field study, it was concluded that

q a. soil clay content was a driving factor in the formation of a well-aggregated soil and positively contributed to potato yield.

q b. soil clay content was a minor factor in the formation of a well-aggregated soil and did not contribute to potato yield.

q c. soil clay content was a negative factor in the formation of a well-aggregated soil and reduced potato yield.

q d. soil clay content was not a contributing factor in the formation of a well-aggregated soil and did not contrib-ute to potato yield.

5. Micro-elevated areas in Field A1 with localized soil satura-tion late in the 2003 season may have led to detrimental effects on tuber growth

q a. because of rot caused by poor drainage.

q b. caused by cold temperatures

q c. due to the oxygen deprivation.

q d. caused by high salinity.

6. Potassium promotes moisture accumulation in potato tubers resulting in

q a. increased specific gravity.

q b. low tuber set.

q c. knobby tubers.

q d. decreased specific gravity.

7. According to the article, what could have accelerated senescence in Field A2 of this study?

q a. The combined effects of late planting and too much moisture.

q b. The combined effects of too much potassium and poor aeration.

q c. The combined effects of early planting and common scab infestation.

q d. The combined effects of early planting and significant moisture stress.

This quiz is worth 1 CEU in Crop Management. A score of 70% or higher will earn CEU credit.

DirectionsAfter carefully reading the article, answer each ques-tion by clearly marking an “X” in the box next to the best answer. Complete the self-study quiz registration form and evaluation form on the back of this page. Clip out this page, place in an envelope with a $20 check made out to the American Society of Agronomy (or provide your credit card information on the form), and mail to: ASA c/o CCA Self-Study Quiz, 5585 Guilford Road, Madison, WI 53711. Or you can save $5 by completing the quiz online at www.agronomy.org/certifications/self-study.

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July–August 2011 self-study quizReducing the variability in potato yield (no. SS 04158)

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Self-Study Quiz Evaluation FormRating Scale: 1 = Poor 5 = Excellent

Information presented will be useful in my daily crop-advising activities: 1 2 3 4 5

Information was organized and logical: 1 2 3 4 5

Graphics/tables (if applicable) were appropriate and enhanced my learning: 1 2 3 4 5

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8. The red part of the electromagnetic spectrum is no longer absorbed by senescent plant tissues, which

q a. causes an increase in the reflectance of this spectrum to be picked up by digital imagery.

q b. causes a decrease in the reflectance of this spectrum to be picked up by digital imagery.

q c. causes a decrease in the G/Runadj ratio.

q d. cannot be picked up by digital imagery.

9. The mean total tuber yields for both fields in this study were moderately higher than those reported in a 2005 variety trial, indicating that

q a. there was better soil drainage in the current study.

q b. the university management practices followed in the 2005 study were flawed.

q c. the commercial management practices followed in the current study were effective.

q d. improving water management made a difference.

10. The yield-predictive models derived from commercial potato fields demonstrated the significant roles played by soil structure, specific spectral bands, and derived vegetative index, as well as soil potassium status. These attributes proved critical to developing predictive regres-sion models that could account for

q a. more than 60% of the yield variability observed.

q b. about half of the yield variability observed.

q c. 90% of the yield variability observed.

q d. one-third of the yield variability observed.

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