Taking Cover Crops to the Next Level with Mixtures – Focus on C:N Ratios

1. Taking Cover Crops to the Next Level with Mixtures – Focus on C:N Ratios Charlie White Crop Management Team

2. 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

3. 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

4. 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

5. 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

6. Nitrogen retention: N acquisition strategy of cover crops affects nitrate leaching Anion Exchange Resin Capsules Austrian Winter Pea Red Clover vs.

7. Nitrogen supply: N is released from cover crop residues by microbial decomposition Red Clover Residues Fava Bean Residues Sorghum – Sudangrass Residues Ryegrass Residues

8. 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

9. 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

10. 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

11. 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

12. 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

13. C:N ratio of a cover crop can be managed through species selection, management timing, and species mixtures Triticale Annual Ryegrass Early boot stage

14. 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

15. 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

16. Managing C:N ratio in legume-grass mixes: Red clover is a poor competitor Red clover plus increasing seeding rates of triticale

17. Vining legumes make a better companion with grasses Rye + Hairy Vetch + Canola Rye Hairy Vetch Study by Denise Finney, PSU Graduate Student

18. Vining legumes make a better companion with grasses Study by Denise Finney, PSU Graduate Student

19. 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

20. 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