Soil Fertility in Organic Systems Jake Mowrer, PhD Assistant Professor and Extension Specialist Soil Nutrient and Water Resource Management
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:[email protected]:979-845-5366Office:348A Heep CenterEducation:MS Soil Chemistry University of GeorgiaPh.D., Soil Fertility/Soil Chemistry, University of Georgia
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