More Than Just Cover

Ray Weil

Professor of Soil Science

Cover Crops as Multipurpose Tools for Soil Quality

In fact using cover crops, changes everything!

Resource efficiencyBiological diversity

Soil quality

• Whatever you call them, these crops grown for the soil can do a lot more than just prevent erosion.

“Cover crop”, “Green manure”, “Catch crop”

Plan

ting

Cover crops can utilize otherwise wasted resources

The sun shines, the rain falls and microbes work 12 months a year, but this typical mid-west grain farm captures only 3-4 months of this activity.

November

July August

JuneSeptember October

Har

vest

Maize crop canopy

captures sunlight,

nutrients, water, carbon

Senescence &

Dry-down

1. Cool season grasses

2. Cool season Legumes

3. Cool season Brassicas

4. Warm season grasses

5. Warm season legumes

6. Warm season broadleaves

Cover Crops Liberate Farmers from Market Dictates on What to Plant

Cover crops change everything!

Soil organic matter

Soil organic matter

NematodesNematodes

Food web

activity

Food web

activityLabile CLabile C

Soil Aggregation

Soil Aggregation

Nitrogen fertility

Nitrogen fertility

Weed suppression

Weed suppression

Soil water

Soil water

Soil temperature

Soil temperature

Cover crops

Cover crops

Enhanced crop

growth

Enhanced crop

growthBio-drillingBio-drilling

Soil CoverSoil CoverReduced

erosion loss

Reduced erosion lossIncreased

infiltration

Increased infiltration

Nutrient capture (N, P, S, K, etc)

Nutrient capture (N, P, S, K, etc)

Rhizobial associations

Rhizobial associations

P- fertilityP- fertility

Reduced evaporation

Reduced evaporation

Reduced leaching loss (N)

Reduced leaching loss (N)

Mycorrhizal associations

Mycorrhizal associations

Alternate drill rows of rye and radish

Alternate drill rows of Sudex and radish

Pure radish

After trying single cover crops, you may want to try simple mixtures.

Plan your cover crop as carefully as your cash crops.

What do you want a cover crop to do?

What is your niche and growing window?

Farmers are good at figuring out ways to extend their cover crop planting window!

Cover Crop Treatment

Crop or Soil Parameter No Rye Rye

Soybean plant, kg ha-1 5275.5 ** 5995.1

Soybean yield, kg ha-1 2704.8 * 3054.9

Active C mg kg-1 624.2 ** 661.7

C respired in 2 days, mg kg-1 213.1 ** 255.0

Total organic C g kg-1 17.90 ns 19.06

Mineralizable N mg kg-1 82.01 ** 101.81

Stable aggregates % 60.40 ** 69.40

Overall Means of 6 sites in MD and PA with 2 to 6 years of rye cover crop in corn – soybean rotation.

Even a simple rye cover crop can make a measurable difference to your soil

Data taken 8 months after cover crops were killed.Fungal-feeding

Coslenchus sp. nematode

A single rape or rye cover crop changed the soil food web from bacterial to fungal-dominated.

A single rape or rye cover crop changed the soil food web from bacterial to fungal-dominated.

Gruver, Weil, Zasada, Sardanelli, and Momen 2010 (J. of Applied Ecology).

Earthworms and cover crops work together.

Key differences are in the roots!

Soil organic carbon

SOC

Soil organic carbon

SOC

CO2CO2

RootsRoots

Rhizo-depositionRhizo-deposition

Animal feedAnimal feed

FuelFuelShoot residuesShoot residues

Harvested part (grain, fruit, leaves)Harvested part (grain, fruit, leaves)

100 kg C as leaves ~ 15 kg SOC 1 year after incorporation.100 kg C as roots ~ 30 kg SOC 1 year after incorporation.

Soil C content

So

il D

ep

th, m

2

1

0

> 90% of the data is here.

> 60% of the carbon is here.

Leaching and

re-adsorption of dissolved

organic carbonDOC

Leaching and

re-adsorption of dissolved

organic carbonDOC

Rootsand

rhizo-deposition

Rootsand

rhizo-deposition

Much more effort is needed to study deep soil C

Much more effort is needed to study deep soil C

SOC in deep layers tends to have low C/N and slow turnover times.

SOC in deep layers tends to have low C/N and slow turnover times.

Baker, J.M., T.E. Ochsner, R.T. Venterea, and T.J. Griffis. 2007. Tillage and soil carbon sequestration--what do we really know? Agriculture, Ecosystems & Environment 118:1-5.

Root system of a corn plant (field excavation by Weaver 1929) and the sampling depthsused in 140 comparative studies of tillage impacts on soil carbon. Scale in feet.

Researchers are no longer so sure that no-till increases total profile organic carbon.

Depth distribution of corn roots Distribution of C measurements

PlowedNo-till

Amount of soil carbon soil

But very few of the tillage comparison

included cover crops!

Cover crop roots build soil bio-physical quality

1.2% OM2.0% OM

A little extra organic matter goes a long way to stabilize aggregates and keep soil surface open.

More on biodrilling to fight compaction

in the break out session tomorrow!

Cover crops can improve structuredeeper in the soil

Spring oatresidues

• Soil temperature• Soil moisture• Weed pressure

Forage radishresidues

Cover crop surface residues influence:

19

Four stages of a unique cover crop

RyeForage Radish

Vegetation and residues dramatically suppress weeds and influence no-till

seedbed conditions.

Vegetation and residues dramatically suppress weeds and influence no-till

seedbed conditions.

Forage radish “film” during rapid decomposition

Effect of living rye v decayed forage radish on soil temperature at 5 cm

depth in April in Md.25

20

15

10

5

(o C)

Effect of living rye v decayed forage radish on soil water at

5 cm depth in April in Md.

Workable days (below 80% plastic limit)

Soil moisture at 5 cm after cover crop treatments, Clarksville Md 2013

Zoned cover crop mixtures

War

mer

, drie

r, hi

gh fe

rtility

, loo

sene

d pl

antin

g be

ds

Weed suppressive mulch in

wheel tr

acks

September Joel Gruver,

Western Illinois Univ.

Radish planted on 75cm (30”) centers with 3 rows of oats drilled in between.

26

photo by Joel Gruver, UWI

Like deep ripping and using a burn down herbicide in the planting row while mulching the inter-row

PLU

S ba

ndin

g fe

rtili

zer

S

Another major cover crop function:enhanced nutrient management

N

BCa

K

PReduce lossesEnhance availabilityAdd nitrogenRecover deep nutrients

Why use cover crops to manage nutrient loss?The environment• Nutrient leaching (N)• Runoff/erosion (P)

Farm profitability

P N

Source Price / kg N

Price / kg P

Urea $1.40

DAP $1.40 $2.75

Legumes Cost of seed, land, labor, lost crop

Dairy manure

? ?

Lake Erie

Blue = anaerobic processesBright green = N addition to soilDark olive = N losses to waterVery complex

as N occurs in • Solids• Liquids• Gases

Very complex as N occurs in • Solids• Liquids• Gases

The N CycleThe N Cycle

From Weil and Brady 2015 The Nature and Properties of Soils.

Inputs of N to soil organic matter as plant and animal residues.

Inputs of N to soil organic matter as plant and animal residues.

SOM

R-NH2

NH4+

Decomposition of residuesand release of N by mineralization.

Decomposition promoted by:• Good aeration• Warm

temperature• Easy to digest

carbon• Tillage

Decomposition promoted by:• Good aeration• Warm

temperature• Easy to digest

carbon• Tillage

Grass turns greener because Fairy ring fungi release N from SOM

Leachingloss

Conversion of N from soil organic matter to soluble mineral forms.

Organic matter

Soil organismsSoil organisms

NO2-

nitrite

NO2-

nitrite

NO3-

Nitrate

NO3-

NitrateNH4

+

Ammonium

NH4+

Ammonium

Oxidation of Ammonium to Nitrate

Nitrification needs:• Oxygen (aeration)• Warm temperature• Presence of nitrifiers

Nitrification needs:• Oxygen (aeration)• Warm temperature• Presence of nitrifiers

~4000 kg/ha ORGANIC Nitrogen

< 100 kg/ha Inorganic N/year• nitrate-N• ammonium-N• other forms (gases etc.)

In a soil with 2.5% organic matter, the top 30cm has:

Constantly

turning over!

Crop use of N and P

Crop Yield N P

Canola 3000 kg seed 119 19

Corn 9000 kg grain 133 25

Soybean 3100 kg grain 199 20

Wheat 3700 kg grain 69 13

To estimate N_P_K in harvest, use tool at https://plants.usda.gov/npk/main

Nutrient capture: nitrogen in fall

120-

80 = 40

150 kg N taken up by plants

150 kg N taken up by the cover crop

40 kg N missing from the upper 1 m of soil

Where did the other 110 kg N come from?

From deeper soil layers?

Soil v Cover Crop or Weed Nitrogen Contents in November

Data: Wang and Weil,unpublished

Dean, J.E., and R.R. Weil. 2009. Journal of Environmental Quality 38:520-528.

Last spring’s fertilizer

2 years ago fertilizer

No cover

Nitrate-N in 180 cm soilNo cover: 173 kg/haForage radish: 48 kg/haOilseed radish: 62 kg/ha

Loamy sand, Beltsville, MarylandAfter corn-wheat

1 2 3 4 5Seeding date, weeks after Aug. 20

1500

2125

2750

3375

4000

4625

5250

5875

6500

Sho

ot D

M,

kg/h

a

1 2 3 4 5Seeding date, weeks after Aug. 20

2.000

2.375

2.750

3.125

3.500

3.875

4.250

4.625

5.000S

hoot

tis

sue

N,

%

1 2 3 4 5Seeding date, weeks after Aug. 20

50

75

100

125

150

175

200

225

250

Sho

ot N

Up t

a ke ,

kg/

h a

Effect of seeding date on forage radish dry matter and N uptake. Means of 3 locations in 2007.

Shoot dry matter Tissue N conc. Shoot N uptake

Effect of seeding date on forage radish growth & nitrogen uptake in fallEffect of seeding date on forage radish growth & nitrogen uptake in fall

Means of 3 sites

A few weeks later planting reduces weed suppression and biodrilling

but not nitrogen capture.

Topsoil N tied up by rye

Nitrogen Capture by October-Planted Rye Cover Crop

2 10 15 50

September AprilMarchNovemberOctober

Large amounts of N lost

Timing is everything! – We need to get cover crops planted earlier!

Nitrogen Capture by Early Sept-Planted Radish Cover Crop

25 125 200

September AprilMarchNovemberOctober

N available to early planted cash crop?

N?

Some advantages of early planting and frost killing.

SoilMay 10th

Nutrient capture: nitrogen in spring

Soil

Nitr

ate

(0-2

0 cm

) Nitrate-N33 (kg ha-1)

increase from radish

Nitrate-N34 (kg ha-1)

increase from radish

N mineralization in springLounsbury and Weil 2013

Maize Response to Early Spring Nitrogen Release by Radish Cover Crop

Following rye

Following radish

• Deep P brought to surface & bound P made available

0

25

50

75

100

125

Soi l

depth

0 20 40 60 80 100 120 140Soil test P (Mehlich 3), mg/kg

Cereal ryeRapeseedOilseed RadishForage radishNo cover

ns

ns

ns

ns

ns

lsd 0.05

lsd 0.05

lsd 0.05

0

25

50

75

100

125

Soi l

depth

0 20 40 60 80 100 120 140Soil test P (Mehlich 3), mg/kg

Cereal ryeRapeseedOilseed RadishForage radishNo cover

ns

ns

ns

ns

ns

lsd 0.05

lsd 0.05

lsd 0.05

Silt loam, upper 120 cmIn 3rd winter of cover crop trts.

Silt loam, upper 120 cmIn 3rd winter of cover crop trts.

Increased available phosphorus in surface soil horizons

Cover crops can enhance topsoil fertility with more than just nitrogen

P Concentration around radish holes

White and Weil (2009)

Sulfate in Topsoil (0-20 cm)

Lounsbury and Weil 2013

Clarksville Wye

Calcium contents Phosphorus contents

Brassicas are exceptionally high in certain nutrients: calcium, phosphorus, sulfur , boron

Deep Soil Nutrients:

Neglected Resource under your feet?

Some Nutrient Capture Questions Needing Research

1. How big is the deep N pool in early fall ? 2. How does aerial seeding in Aug compare to

drilling in Oct?3. Can irrigation or seed coating ensure early

stands with aerial seeding? 4. Can on the spot nitrate N tests predict‐ ‐ ‐ need

for covercrop starter N? 5. Can ~15 lbs starter N allow covercrops to

capture 100 lbs of extra N?6. Can cash crops use the captured N (+P, K, S) in

spring?

Managing soils to improve plants

plants soils

Questions?Questions?

Think about…