Cover Crops and Green Manures - wamis.org

Cover Crops and Green Manures

Cover Crops and Green Cover Crops and Green ManuresManures

Feed the Soil and Cool the Planet

Ray R. WeilUniversity of Maryland

USA

Feed the Soil and Cool the PlanetFeed the Soil and Cool the Planet

Ray R. WeilRay R. Weil

University of MarylandUniversity of Maryland

USAUSA

“Cover” or “green manure” crop:“Cover” or “green manure” crop:

• Grown mainly for soil improvement…rather than for harvest.

• Ideally grown in time and space where grains and other food crops are not possible.

• Grown mainly for soil improvement…rather than for harvest.

• Ideally grown in time and space where grains and other food crops are not possible.

Use plants to increase the quality and food production capacity of the soil

while decreasing greenhouse gases. •

• Add organic carbon to soil.• Add fixed nitrogen (if legume).• Recover nutrients from subsoil.• Improve nutrient availability & use efficiency• Enhance soil physical, chemical and

biological properties

•• Add organic carbon to soil.Add organic carbon to soil.

•• Add fixed nitrogen (if legume).Add fixed nitrogen (if legume).

•• Recover nutrients from subsoil.Recover nutrients from subsoil.

•• Improve nutrient availability & use efficiencyImprove nutrient availability & use efficiency

•• Enhance soil physical, chemical and Enhance soil physical, chemical and biological propertiesbiological properties

Soil Organic Carbon:Soil Organic Carbon:Accumulation = Gains Accumulation = Gains -- LossesLosses

••HarvestHarvest

••OxidationOxidation

••ErosionErosion

••LeachingLeaching

TillageTillageTillage

C gainsC gains

Equilibrium level Equilibrium level of SOC attainedof SOC attained

Soil Organic Carbon StockSoil Organic Carbon Stock

C LossesC Losses

•Roots

•Straw&Leaves

•Mulches

•Manures

•Composts

•Roots

••Straw&LeavesStraw&Leaves

••MulchesMulches

••ManuresManures

••CompostsComposts

Key differences are in the roots!

Soil Soil organic organic carbon carbon

SOCSOC

COCO22

RootsRoots

RhizoRhizo --depositiondeposition

Animal feedAnimal feed

FuelFuel

Shoot residuesShoot residues

Harvested part (grain)Harvested part (grain)

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

Soil C contentSoil C content

Soi

l Dep

th, m

Soi

l Dep

th, m

22

11

00

> 90% of the data is here.> 90% of the data is here.

> 60% of the > 60% of the carbon is here.carbon is here.

Leaching and

re-adsorption of dissolved

organic carbonDOC

Leaching and

re-adsorption of dissolved

organic carbonDOC

Roots

and

rhizo-

deposition

Roots

and

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.

Nutrient cycling by Acacia albida (syn. Faidherbia albida) in African agroforestry systems

0 1 2 3 4 5 6Site

0.000.020.040.060.080.100.120.140.160.180.20

Tot

al S

in m

aize

pla

nts,

%

Under canopyBeyond canopy V8 stage maize

From Weil and Mughogho(1993)

Example of deep root effects on enhanced nutrient recovery

Example of Example of deep root deep root effects on effects on enhanced enhanced nutrient nutrient recoveryrecovery

0

25

50

75

100

125

Soi

l dep

th

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

•Deep Phosphorus brought to surface

•Bound phosphorus made available

Capture of Deep Soil N After Grain Crop HarvestCapture of Deep Soil N

After Grain Crop Harvest

0

20

40

60

80

100

120

140

160

180

Soi

l Dep

th, c

m

0 2 4 6 8 10Nitrate-N, mg/kg

Oliseed RadishForage radishControl

Hayden Fall '03

+

**ns

ns

**

****

ns

nsns

*

**

Dean and Weil, 2009 (in press)

Fertilizer Fertilizer applied in Mayapplied in May

Previous year’s fertilizer

~ 150 kg N/hataken up by cover crop from “N deficient”sandy soil.

~ 150 kg N/hataken up by cover crop from “N deficient”sandy soil.

Wheat was harvested in July. Cover crops grew from August thru November

Data taken 8 months after cover crops were killed.

No-till - residues left on surface Tilled - residues incorporated

Fungal-feeding Coslenchus sp.

nematode

A single rape or rye crop altered soil food web from bacterial-dominated to fungal, thus influencing nutrient cycling. Gruver, Weil, Zasada, Sardanelli, and Momen (submitted to J. of Applied Ecology).

A single rape or rye crop altered soil food web from A single rape or rye crop altered soil food web from bacterialbacterial--dominated to fungal, thus influencing nutrient dominated to fungal, thus influencing nutrient cycling.cycling. Gruver, Weil, Zasada, Sardanelli, and Momen (submitted to J. of Applied Ecology).

Effect of cover crop rooting on soil tilth.Effect of cover crop rooting on soil tilth.

Rye roots fail to Rye roots fail to penetrate a penetrate a compacted soilcompacted soil

“Biodrilling”“Biodrilling”

• No: no pass• Medium: one pass• Heavy: two passes

• No: no pass• Medium: one pass• Heavy: two passes

3 compaction levels:3 compaction levels:

For each pass Wt: 1.19*104 kgcontact area: 1600 cm 2 force: 7.44*10 4 N

For each pass Wt: 1.19*104 kgcontact area: 1600 cm 2 force: 7.44*10 4 N

Compaction Experiment Compaction Experiment (Don(Don ’’ t try this on your farm!)t try this on your farm!)

Soil properties after compaction treatments

Soil properties after compaction treatments

0

10

20

30

40

50

0 500 1000 1500 2000 2500 3000

Penetration resistance (kPa)

Dep

th (

cm)

Heavy

Medium

No

Soil strength and bulk density for different compac tion levels.

0

10

20

30

40

501.3 1.4 1.5 1.6 1.7 1.8

Bulk density (g/cm 3) D

epth

(cm

)

Heavy

Medium

No

Rye and Radish Cover Crops in Dec. after compaction

Forage Radish roots under no or heavy compaction

Note: the whole experimental site was disked to 8 cm (3 inches) to provide a suitable seedbed before planting cover crops.

Core-break method to determine at root numbers with depth.

Taking soil core to a depth of 60 cmTaking soil core to a depth of 60 cm Counting root numbers at Counting root numbers at the breakage facesthe breakage faces

Three cores per plotThree cores per plot

Differences of root numbers (per 32 cm2) at each depth are indicated by *; student t-test, a=0.05

Root penetration capability of 3 cover crop growing under heavy compaction Root penetration capability of 3 cover Root penetration capability of 3 cover crop growing under heavy compaction crop growing under heavy compaction

0

10

20

30

40

500 10 20 30 40 50 60 70

Roots

FR

rape

Rye

* ***

**

*** *

**

*

FR had 2 to 4 times roots as rye or rape

Roots Roots per 32 cmper 32 cm 22

Soi

l dep

th, c

mS

oil d

epth

, cm

Chen and Weil, unpub.

*

* Indicates significant differences in roots/m2 at each (P=0.05)

Means of 12 cores (3 cores per replication) in sandy soil at Hayden farm. Weil and Chen. 2007

0

10

20

30

40

50

60

Soi

l dep

th (

cm)

0 2000 4000 6000 8000Corn roots /m 2

0

10

20

30

40

50

600 2000 4000 6000 8000 10000 12000

Soybean roots /m 2

RyeNo-coverForage radish

Cover crop

Soybean, 2006Corn, 2005

***

**

****

*

*

*

Fall cover crop improves vertical distribution of crop roots the

following season.

Fall cover crop improves vertical distribution of crop roots the

following season.

More subsoil water use by maize after radish, regardless of compaction

Soi

l wat

er te

nsio

n (k

Pa)

Water use in subsoil (55 cm deep) under Water use in subsoil (55 cm deep) under corn in midcorn in mid --summer growing season.summer growing season.

HC = High Compaction, NC = No Compaction

5TE sensor (Decagon, Inc.) measures

1. Volumetric water content (capacitance/frequency domain technology)

2. soil temperature3. bulk soil electrical conductivity

5TE sensor (Decagon, Inc.) 5TE sensor (Decagon, Inc.) measures measures

1.1. Volumetric water content Volumetric water content (capacitance/frequency domain (capacitance/frequency domain technology)technology)

2.2. soil temperaturesoil temperature3.3. bulk soil electrical conductivitybulk soil electrical conductivity

5 cm

cc

cc

Volumetric Water Content Volumetric Water Content

Cover crop Cover crop effects on effects on biobio --chemical chemical and and physical physical properties properties monitored monitored with with capacitance capacitance sensors.sensors.

EC of soil porewater EC of soil porewater

Soil TemperatureSoil Temperature

Sensors at Sensors at 7.5 cm in 7.5 cm in this examplethis example

cc

cc

No cover and No cover and radish plots radish plots have same have same water contentwater content


No cover and No cover and radish plots radish plots exhibit most exhibit most extreme diurnal extreme diurnal temperaturestemperatures

No cover plots No cover plots have low EC have low EC (nitrate)(nitrate)





cc

cc







Radish plots Radish plots have high EChave high EC


cc

cc







Radish plots Radish plots have high EChave high EC

Rye + radish mix Rye + radish mix plots show high plots show high EC laterEC later


(nitrate)(nitrate)

Managing soils to improve plants

plantssoils

Questions?Questions?

Think aboutThink about ……

Documents

Cover Crops and Green Manures - wamis.org