Soil Fertility in Organic Systems - Texas A&M AgriLifeagrilifecdn.tamu.edu/samuelzapata/files/2017/04/022317...Soil Fertility in Organic Systems Jake Mowrer, PhD Assistant Professor

Soil Fertility in Organic Systems

Jake Mowrer, PhDAssistant Professor and Extension SpecialistSoil Nutrient and Water Resource Management

I. Know your soil

II. Fertilizers for Organic Systems

III. Cover Crops and Soil Fertility

IV. Soil Test Recommendations

Outline

I Soil

Four Principal Components of Soil

Air (gases)

Water (liquids)

Minerals

Organic material

I Soil

Putting it all together

Soil components create a ‘structure’

I Soil

https://websoilsurvey.sc.egov.usda.gov/App/WebSoilSurvey.aspx

I Soil

I Soil

Improve soils friability by looseningtight clays, help sands hold morewater, and add nutrients

• Fresh plant materials• Animal Manures• Green Manures• Composts

Tilling soils to 8 - 12” lets veggieroots go deeper

• Moist but not wet• Winter for spring

planting• Incorporate and

distribute amendments

I Soil

O2 CO2

N2 O2

CO2N2

H2O H2OH2O

Plant vegetables on raised beds• Provides furrows for irrigation• Allows air to enter the soil• Allows water to drain away from roots• Helps plants through periods of high (& low)

rainfall

I Soil

Organic Farming • Production system managed to respond to site-

specific conditions• Integrates cultural, biological, and mechanical

practices• Fosters cycling of resources• Promotes ecological balance• Conserves biodiversity

II Fertilizers

‘Measure to Manage’

II Fertilizers

How can we evaluate soil fertility?

The soil testKey to nutrient management

Ideally - this extractant should mimic the plant root exudate to best estimate the availability of nutrients at the soil root interface.

II Fertilizers

‘Measure to Manage’ Liebig’s Barrel

II Fertilizers

II Fertilizers

II Fertilizers

Phosphorus in soils

H2PO4-

H2PO4-

HPO4-2

HPO4-2

Plant Available FormsPrimary orthophosphate (H2PO4

-)Secondary orthophosphate (HPO4

-2)

Functions in plantsEarly growth & root formationReproduction & fruiting

Movement in soilImmobileCan accumulate if applied in excess

II Fertilizers

Plant Available FormsPotassium ion (K+)

Functions in plantsWater-use efficiencyDisease resistanceCold hardiness

Movement in soilMarginally mobile (depends on clays)Does not volatilize

Potassium in soils

K+

K+

K+

K+

II Fertilizers

Organic Fertilizer Sources

Animal manures • Recycles materials • Broad nutrient content (N, P, K, Ca, Mg, S, Micros)• Unbalanced & require analysis

II Fertilizers

Organic Fertilizer Sources

Vermicompost/ worm castings• Relatively low in nutrients but still good

Meals

• Alfalfa 3- 1- 2• Blood 13- 1- 0.5• Fish 9- 4.5- 0• Bone 2- 20- 0• Kelp 1- 0- 4

II Fertilizers

Organic Fertilizer Sources

Rock Phosphate• Very slow release mined product• 28% P2O5

Compost & Yard Waste• Low in macros but deliver micros• Recycling practice

Green Sand & Granite Meal• K sources mined products

III Cover Crops

What is a cover crop?

Crop integrated into periods between

cash crops to provide ground cover and

green manure, promoting living roots

and dynamic exchange of nutrients and

biology continuously throughout the

annual growing cycle

III Cover Crops

SARE 2014-2015 Cover Crop Survey

Who is planting cover crops?

Small Farmers Large Farmers

III Cover Crops

Who is planting cover crops?

Small Farmers Large Farmers

III Cover Crops

Who is planting cover crops?

75% Corn

68% Soybean

<1% Cotton

SARE 2014-2015 Cover Crop Survey

III Cover Crops

Who is planting cover crops?

SARE 2014-2015 Cover Crop Survey

III Cover Crops

III Cover Crops

Benefits of Cover Crops1. Agronomic Benefits

• Soil erosion (wind and water)

• Reduction in pollution

• Increasing nitrogen (legumes)

• Scavenging nutrients (cereals)

III Cover Crops

Benefits of Cover Crops2. Soil Functionality

• Increase soil organic matter (SOM)

• Improved water infiltration

• Diversification in cropping system

• Dynamic nutrient cycling

III Cover Crops

Benefits of Cover Crops3. Biotic Pressure Reduction

• Early season weed control (physical

barrier)

• Inhibition of weed germination

(allelopathy)

• Insect pressure reduction

III Cover Crops

Soil conservation – erosion preventionIII Cover Crops

Water conservation

Stobart Morris (2015) The impact of cover crops on yield and soils in the New Farming Systems programme

Clover

No cover

• Mulching of residue

conserves soil water

• Better infiltration rates =

less runoff = more water

captured

• Less nutrient loading on

adjacent water resources

III Cover Crops

Agronomic Benefits - cutting nitrogen costs

• Nitrogen benefit of legumes easiest to

quantify

• Often enough to justify adoption

• Cash crops recover 30 to 60% of N produced

• Allows reduction in applied (purchased) N

fertilizer (up to 80% of corn N needs)

III Cover Crops

Nodules in roots of cow pea (black-eyed peas)

where biological N-fixation occurs

Azotobacter, Bacillus, Clostridium, and Klebsiella spp. bacteria

III Cover Crops

Agronomic Benefits - cutting nitrogen costs

Hairy Vetch

• 150 lbs/acre N

• Boosts yields

• Reduces economic risk

• Overall profits higher in no-till

corn than following wheat

Hansen et al., (1993) Profitibility of no-tillage corn following a hairy vetch cover crop

III Cover Crops

Agronomic Benefits - cutting nitrogen costs

Red Clover

• 128 lbs / acre N

• Higher corn production than

corn - corn rotation

• Highest economic return

Stute and Posner., (1995) Legume Cover Crops as a Nitrogen Source for Corn in an Oat-Corn Rotation

III Cover Crops

Agronomic Benefits - cutting nitrogen costs

Sunn Hemp

• August to first frost biomass

improves corn production

• 90 lbs / acre N

• Warm season crop

Balcomb & Reeves., (2005) Sunn-Hemp Utilized as a Legume Cover Crop for Corn Production

III Cover Crops

Agronomic Benefits - cutting nitrogen costs

Non-Legumes

• Act as ‘catch crop’ to

scavenge nutrients (fibrous

roots)

• Prevent nitrate leaching

• Reduce N & P runoff

• Redistribute immobile P & K

Hoyt and Mikkelsen., (1991) Soil nitrogen movement under winter cover crops and residues

III Cover Crops

Agronomic Benefits – reduce herbicide needs

• Smother crop outcompetes

weeds for water and nutrients

• Canopy blocks light and

changes soil temperature

• Root exudates or compounds

inhibit weeds

• Safeguards human healthCereal rye

III Cover Crops

Agronomic Benefits – pest control

Predatory wasp

ladybug

Plotkin (1999) UCONN Proceedings NEVBC

III Cover Crops

Cover – no till

No-cover – no till

No-cover –tilled

Cover – tilledr2 = 0.7676

Agronomic Benefits – sustainability

• Living roots year round

• Increased organic matter in soil

• Arbuscular mycorrhizal fungi (AMF) benefits promoted

Boswell et al., (1998) Winter wheat cover cropping, VA mycorrhizal fungi and maize growth and yield

III Cover Crops

Area

2 dimensional spacePlanar

Volume

150 ft

29

0 f

t

150 ft

½ f

t

IV. Fertilizer Calculations

3 dimensional spaceMass

First: Some physics

IV. Fertilizer Calculations

Then: Some Math

• Soil test result in parts per million (ppm)

• Same as mg / kg

• Multiply ppm x 2 to get pounds per acre

IV. Fertilizer Calculations

Example: 95 lbs N

30 lbs P2O5

65 lbs K2O

IV. Fertilizer Calculations

Example: 95 lbs N

30 lbs P2O5

65 lbs K2O

Step 1: Find the nutrient recommendation ratio

Step 2: Select fertilizer(s) with appropriate ratio

Step 3: Divide lbs / acre recommended by percentage

nutrient to get lbs fertilizer applied

10 -3 - 7

1) 11-13-26-6 @ $381.14 / ton

P2O5: 30/0.13 = 230 lbs fertilizer K2O: 65/0.26 = 250 lbs fertilizer

250 lbs fertilizer x 0.11% N = 27.5 lbs / acre

Step 4: Multiply your acreage by lbs / acre recommended

If 270 acres, then. . . . . . . . . .

Go back to Step 2: Select fertilizer(s) with appropriate ratio

IV. Fertilizer Calculations

We still need 67.5 lbs N / acre

46-0-0 (urea) @ $425.00 per ton

Step 3: Divide lbs / acre recommended by percentage nutrient to get lbs fertilizer

applied

N: 67.5 / 0.46 = 147 lbs per acre fertilizer

20 tons urea + 34 tons 11-13-26-6

Total Price Tag = $22,000

Jake MowrerAssistant Professor and Extension SpecialistEmail:jake.mowrer@tamu.eduPhone:979-845-5366Office:348A Heep CenterEducation:MS Soil Chemistry University of GeorgiaPh.D., Soil Fertility/Soil Chemistry, University of Georgia

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