cover crops and green manures - wamis.org
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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
Volumetric Water Content Volumetric Water 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)
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
Volumetric Water Content Volumetric Water Content
No cover and No cover and radish plots radish plots exhibit most exhibit most extreme diurnal extreme diurnal temperaturestemperatures
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
Radish plots Radish plots have high EChave high EC
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
Volumetric Water Content Volumetric Water Content
No cover and No cover and radish plots radish plots exhibit most exhibit most extreme diurnal extreme diurnal temperaturestemperatures
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
Radish plots Radish plots have high EChave high EC
Rye + radish mix Rye + radish mix plots show high plots show high EC laterEC later
Sensors at Sensors at 7.5 cm in 7.5 cm in this examplethis example
(nitrate)(nitrate)
Managing soils to improve plants
plantssoils
Questions?Questions?
Think aboutThink about ……