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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 Presentation
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Taking Cover Crops to the Next Level with Mixtures – Focus on C:N Ratios
Charlie WhiteCrop Management Team
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
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?
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
• 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
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
Nitrogen supply: N is released from cover crop residues by microbial decomposition
Fava Bean Residues Sorghum – SudangrassResidues
Ryegrass Residues
Red Clover Residues
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
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
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
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
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
C:N ratio of a cover crop can be managed through species selection, management timing, and species mixtures
Triticale
Annual Ryegrass
Early boot stage
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
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
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
Vining legumes make a better companion with grasses
Rye Hairy VetchRye + Hairy Vetch
+ Canola
Study by Denise Finney, PSU Graduate Student
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
•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
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