taking cover crops to the next level with mixtures – focus on c:n ratios
DESCRIPTION
Taking Cover Crops to the Next Level with Mixtures – Focus on C:N Ratios. Charlie White Crop Management Team. What type of cover crop would lead to each result for corn yields and N leaching?. Ryegrass. Corn Yield Bu/ac. Corn Fertilizer. CC #2. CC #3. CC #1. Nitrate Leaching l bs N/ac. - PowerPoint PPT PresentationTRANSCRIPT
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Taking Cover Crops to the Next Level with Mixtures – Focus on C:N Ratios
Charlie WhiteCrop Management Team
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What type of cover crop would lead to each result for corn yields and N leaching?
Annual Ryegrass
No Cover Red Clover + Ryegrass
Red Clover100110120130140150160170180190200
0 lbs N/ac160 lbs N/ac
0
25
50
75
100
125
150 Chart TitleCC #1 CC #3
Corn
Yie
ldBu
/ac
Nitr
ate
Leac
hing
lbs N
/ac
CC #2
Corn Fertilizer
Ryegrass
Ryegrass + Red Clover
Red Clover
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Themes for today• N supply vs. N retention functions• Cover crop types
- grasses, brassicas, legumes
Mechanisms to learn about• N acquisition strategies• Decomposition and N release• Competition & synergies in mixes
How do cover crop species and mixes affect nitrogen management?
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Cover crop functions and species should be tailored to meet the needs and constraints of each farming system
Categories of nitrogen management objectives• Retain N against leaching• Supply N to the next crop• Both retain & supply N
Cover crop planting window affects species options• Late summer after small grain
– many species options• Early fall after corn silage
– still a few good options• Late fall after shell corn or beans
– only a couple species left
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• Grasses and brassicas only acquire N from the soil• Legumes can acquire N from the atmosphere so there is less
demand from the soil
Nitrogen retention: N acquisition strategy of cover crops affects nitrate leaching
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0
20
40
60
80
100
120
140
160
180
over
-win
ter N
leac
hing
(kg/
ha)
a
ab
bcc c
cd
de de de e e e
Red Clover vs.Austrian
Winter Pea
Nitrogen retention: N acquisition strategy of cover crops affects nitrate leaching
Anion Exchange Resin Capsules
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Nitrogen supply: N is released from cover crop residues by microbial decomposition
Fava Bean Residues Sorghum – SudangrassResidues
Ryegrass Residues
Red Clover Residues
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Decomposition
With high N residues, microbes use some of the N , the rest goes to the soil as NH4
+ “Mineralization”
Carbon
Nitrogen
~ 50% respired as CO2
(Energy gain for the microbes)
~50% assimilated (Building blocks)
Carbon
Atmosphere
Available Soil NNH4
+
Cove
r Cro
p Re
sidue
s Microbial Biom
ass
Nitrogen
C:N = 10:1
C:N = 10:1
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Decomposition
Carbon
Nitrogen
~ 50% respired as CO2
(Energy gain for the microbes)
~50% assimilated (Building blocks)
Carbon
Atmosphere
Available Soil NNH4
+
Cove
r Cro
p Re
sidue
s Microbial Biom
ass
Nitrogen
C:N = 20:1
C:N = 10:1
With moderate N residues, microbes use all of the N
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Decomposition
With low N residues, microbes use all of the cover crop N plus some soil N “Immobilization”
Carbon
Nitrogen
~ 50% respired as CO2
(Energy gain for the microbes)
~50% assimilated (Building blocks)
Carbon
Atmosphere
Available Soil NNH4
+
Cove
r Cro
p Re
sidue
s Microbial Biom
ass
Nitrogen
C:N = 40:1
C:N = 10:1
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C:N ratio regulates N availability from cover crop decomposition
• C:N below 20 – Nitrogen Mineralization – NH4+ produced
• C:N between 20 and 30 – Neutral Mineralization/Immobilization• C:N above 30 – Nitrogen Immobilization – NH4
+ and NO3- consumed
Cover Crop Species Typical Range of C:N
Clovers 9 – 12
Austrian Winter Pea 9 – 12
Soybean 12 – 15
Fava Bean 13 – 19
Canola 11 – 20
Radish 12 – 14
Cereal rye, triticale 9 – 40
Annual ryegrass 10 – 30
Oats 17 – 30
Sorghum Sudangrass 30 – 40
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C:N ratio regulates N availability from cover crop decomposition
Oct Nov Dec Mar Apr May Jun0
5
10
15
20
25
30
Red CloverNo CoverRed Clover + RyegrassRyegrass
Soil
Nitr
ate
(ppm
N)
Annual Ryegrass
No Cover Red Clover + Ryegrass
Red Clover100110120130140150160170180190200
0 lbs N/ac160 lbs N/ac
Corn
Yie
ld (b
u/ac
)
40 lbs N/ac 70 lbs N/ac 140 lbs N/acCover Crop N contentCover Crop C:N 24 16 10
Burn
dow
n
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C:N ratio of a cover crop can be managed through species selection, management timing, and species mixtures
Triticale
Annual Ryegrass
Early boot stage
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C:N ratio of a cover crop can be managed through species selection, management timing, and species mixtures
Annual Ryegrass
Triticale
Cereal RyeC:N = 16 C:N = 17 C:N = 23
April 16Penn England FarmCentral PA
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Managing C:N ratio in legume-grass mixes: Red clover is a poor competitor
Ryegrass10 lbs/ac
Ryegrass + Red Clover10 lbs/ac + 12 lbs/ac
Red Clover12 lbs/ac
40 lbs N/ac 70 lbs N/ac 140 lbs N/acCover Crop N Cover Crop C:N 24 16 10
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Red clover plus increasing seeding rates of triticale
Managing C:N ratio in legume-grass mixes: Red clover is a poor competitor
0 10 20 30 40 50 60 700
20406080
100120140160180
051015202530354045
Rock SpringsBig FlatsC:N Rock SpringsC:N Big Flats
Triticale Seeding Rate (lbs/ac)
Tota
l Cov
er C
rop
Biom
ass N
(lbs N
/ac)
C:N
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Vining legumes make a better companion with grasses
Rye Hairy VetchRye + Hairy Vetch
+ Canola
Study by Denise Finney, PSU Graduate Student
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Vining legumes make a better companion with grasses
Study by Denise Finney, PSU Graduate Student
Rye Rye + HV + Canola
Hairy Vetch0
20406080
100120140160180
0 lbs N/ac135 lbs N/ac
Corn
Yie
ld (b
u/ac
)Rye Rye + HV + Canola Hairy Vetch
Biomass N (lbs N/ac) 60 141 165C:N 42 16 9Nitrate Leaching (lbs N/ac) 1 3 23
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•Cover crop mixtures need to be tailored to specific farm goals and constraints•Grasses work well at retaining N against leaching• Legumes work best at supplying N to the next crop
- Low C:N ratio of legumes causes mineralization upon decomposition
•Cover crop mixes can balance N retention and N supply functions•Vining species of legumes work best in a mix with
grasses
Conclusions
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Thank You!
Feel free to contact me for more information:Charlie White
Funding for this work was
provided by:
USDA NIFAOREI Program
USDA NRCS Conservation
Innovation Grant
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