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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.
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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 lbs N/ac Ryegrass + Red Clover Red Clover
How do cover crop species and mixes affect nitrogen management? 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
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
Nitrogen retention: N acquisition strategy of cover crops affects nitrate leaching • 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 Anion Exchange Resin Capsules Austrian Winter Pea Red Clover vs.
Nitrogen supply: N is released from cover crop residues by microbial decomposition Red Clover Residues Fava Bean Residues Sorghum – Sudangrass Residues Ryegrass Residues
With high N residues, microbes use some of the N , the rest goes to the soil as NH4+ “Mineralization” Decomposition Available Soil N NH4+ Nitrogen Nitrogen Carbon ~50% assimilated (Building blocks) Microbial Biomass Carbon Cover Crop Residues C:N = 10:1 C:N = 10:1 ~ 50% respiredas CO2 (Energy gain for the microbes) Atmosphere
With moderate N residues, microbes use all of the N Decomposition Available Soil N NH4+ Nitrogen Nitrogen Carbon ~50% assimilated (Building blocks) Microbial Biomass Carbon Cover Crop Residues C:N = 10:1 C:N = 20:1 ~ 50% respiredas CO2 (Energy gain for the microbes) Atmosphere
With low N residues, microbes use all of the cover crop N plus some soil N “Immobilization” Decomposition Available Soil N NH4+ Nitrogen Nitrogen Carbon ~50% assimilated (Building blocks) Carbon Microbial Biomass C:N = 10:1 Cover Crop Residues C:N = 40:1 ~ 50% respiredas CO2 (Energy gain for the microbes) Atmosphere
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
C:N ratio regulates N availability from cover crop decomposition Burndown Corn Yield (bu/ac) Cover Crop N content 40 lbs N/ac 140 lbs N/ac 70 lbs N/ac 10 24 16 Cover Crop C: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 April 16 Penn England Farm Central PA Cereal Rye Annual Ryegrass C:N = 17 C:N = 16 C:N = 23 Triticale
Managing C:N ratio in legume-grass mixes: Red clover is a poor competitor Red Clover 12 lbs/ac Ryegrass + Red Clover 10 lbs/ac + 12 lbs/ac Ryegrass 10 lbs/ac Cover Crop N 40 lbs N/ac 140 lbs N/ac 70 lbs N/ac 10 24 16 Cover Crop C:N
Managing C:N ratio in legume-grass mixes: Red clover is a poor competitor Red clover plus increasing seeding rates of triticale
Vining legumes make a better companion with grasses Rye + Hairy Vetch + Canola Rye Hairy Vetch Study by Denise Finney, PSU Graduate Student
Vining legumes make a better companion with grasses Study by Denise Finney, PSU Graduate Student
Conclusions 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
Thank You! Feel free to contact me for more information: Charlie White cmw29@psu.edu 814-863-9922 Funding for this work was provided by: USDA NRCS Conservation Innovation Grant USDA NIFA OREI Program