Thermal time and precipitation dictate cereal rye shoot biomass production

Authors: CRESPO, CECILIA - Orise Fellow; O'Brien, Peter; Ruis, Sabrina; Kovar, John; KASPAR, THOMAS - Retired ARS Employee

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2024
Publication Date: 6/18/2024
Citation: Crespo, C., O'Brien, P.L., Ruis, S.J., Kovar, J.L., Kaspar, T.C. 2024. Weather factors affecting cereal rye shoot biomass production and its implication on corn silage and soybean yields. Field Crops Research. 315. https://doi.org/10.1016/j.fcr.2024.109473.
DOI: https://doi.org/10.1016/j.fcr.2024.109473

Interpretive Summary: Cover crops are a valuable tool to reduce some of the negative effects of corn and soybean production in the Midwestern United States. Cover crops are plants that are grown during times of the year that corn and soybean are not growing in an effort to reduce soil erosion and nutrient losses while suppressing weeds and helping soil organisms. The benefits of cover crops normally increase with higher amounts of cover crop biomass. However, the amount of time for the cover crops to grow is often limited by two factors: the growing season of corn and soybean, and weather conditions. Data from a 13-year experiment was examined to determine what weather conditions are most important in determining total cover crop biomass. The experiment included cover crops grown either every year or every other year in a crop rotation of corn silage and soybean. Overall, it was found that cover crops planted after corn silage harvest produced much more biomass that cover crops planted after soybean. This higher biomass was mostly due to the longer growing season for the cover crops because they could be planted earlier after corn silage harvest. When the effect of weather conditions was split between fall and spring, it was found that fall weather conditions were more important for cover crops grown after soybean, while spring weather conditions were more important for cover crops grown after corn silage. Importantly, it was found that cover crops only reduced corn or soybean yields in one year of the 13-year experiment. These results are important for farmers, researchers, and crop advisors because it will help them make the best decisions about how and when to plant cover crops, and increasing cover crop adoption across the Midwestern United States will make agricultural systems more sustainable and resilient.

Technical Abstract: Context: Maximizing 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. Objective: We evaluated: i) if growing degree days (GDD) and precipitation affect rye (Secale cereale L.) cover crop shoot biomass, ii) if GDD and precipitation impact shoot biomass differently as rye planting date, previous crop, or cover crop planting frequency (every year vs every other year) varies, and iii) the influence of rye cover crop on soybean [Glycine max (L.) Merr.] and corn silage yields. Methods: In a 13-year field study in a corn silage-soybean rotation, we assessed rye biomass and main crops yield when rye was planted after one or both of the main crops every year. Results: Rye after silage produced 1.98 Mg ha-1 more shoot biomass than rye after soybean. Thermal time (expressed as growing degree days, GDD) had a greater impact than precipitation on the shoot biomass of rye cover crop. A threshold of 800 GDD (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 GDD (below 800 GDD) after soybean and by spring GDD and precipitation after corn silage. Rye cover crop inclusion did not decrease corn silage and soybean yields in 12 out of 13 years. Conclusion: Fall GDD below a threshold may limit the maximum potential for spring rye cover crop growth, but spring GDD or precipitation may prevent maximum growth from occurring when exceeding 800 GDD. 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. Implications: Cropping systems that allow a rye cover crop to be planted early enough to accumulate 800 GDD in the fall have the best potential for high cover crop biomass production.