Thermal time and precipitation dictate cereal rye shoot biomass production

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ContextMaximizing cover crop biomass production is key to agroecosystem service delivery. Cover crop biomass accumulation is particularly important in corn (Zea mays L.) silage cropping systems due to the high rate of crop biomass removal that leaves the soil surface mostly bare from early fall until planting the following spring. ObjectiveWe evaluated how weather factors affect rye (Secale cereale L.) cover crop shoot biomass in different rotations including corn silage and soybean [Glycine max (L.) Merr.] and their influence on soybean and corn silage yields. MethodsIn a 13-year field study in a corn silage-soybean rotation, we assessed rye biomass and main crop yields when rye was planted after one or both main crops every year. ResultsRye after silage produced 1.98 Mg ha−1 more shoot biomass than rye after soybean. Thermal time (expressed as growing degree days) had a greater impact than precipitation on the shoot biomass of rye cover crop. A threshold of 800 growing degree days (0°C base) in the fall was determined, above which final biomass was not limited by fall thermal time (R2=0.58). Rye biomass was most strongly affected by fall thermal time (below 800 growing degree days) after soybean and by spring growing degree days and precipitation after corn silage. Rye cover crop inclusion did not decrease corn silage and soybean yields in 12 out of 13 years. ConclusionFall growing degree days below a threshold may limit the maximum potential for spring rye cover crop growth, but spring growing degree days or precipitation may prevent maximum growth from occurring when exceeding 800 growing degree days. Planting rye cover crops in both phases of the rotation did not affect cover crop biomass or main crop yields and may hold a greater potential to protect the soil than planting after only one crop in the rotation. ImplicationsCropping systems that allow a rye cover crop to be planted early enough to accumulate 800 growing degree days in the fall have the best potential for high cover crop biomass production.