cover crops provide much more than just cover
DESCRIPTION
This presentation was the Keynote address for the Innovative Farmers of Ontario (Canada) in February 2014. Some slides may not work as well as intended without their animations.TRANSCRIPT
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…