Rye-soybean double-crop: planting method and N fertilization effects in the North Central US

Authors: Malone, Robert - Rob; O'Brien, Peter; HERBSTRITT, STEPH - Pennsylvania State University; Emmett, Bryan; KARLEN, DOUG - Retired ARS Employee; KASPAR, THOMAS - Retired ARS Employee; KOHLER, KEITH - Retired ARS Employee; Radke, Anna; LENCE, SERGIO - Iowa State University; WU, HUAIQING - Iowa State University; RICHARD, TOM - Pennsylvania State University

Submitted to: Renewable Agriculture and Food Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2022
Publication Date: 9/13/2022
Citation: Malone, R.W., O'Brien, P.L., Herbstritt, S., Emmett, B.D., Karlen, D.L., Kaspar, T.C., Kohler, K., Radke, A.G., Lence, S.H., Wu, H., Richard, T.L. 2022. Rye-soybean double-crop: planting method and N fertilization effects in the North Central US. Renewable Agriculture and Food Systems. 37(5):445-456. https://doi.org/10.1017/S1742170522000096.
DOI: https://doi.org/10.1017/S1742170522000096

Interpretive Summary: Double cropping, when two crops are grown and harvested in the same field in one year, may be a useful way to increase crop production without negative effects to the environment. We studied a double cropping system using a winter rye cover crop (CC) and soybean for two years in central Iowa. We found that fertilizing CC at a moderate rate economically increased biomass production compared to not applying fertilizer but also increased greenhouse gas emissions. Also, the CC took up more nitrogen than we applied with the moderate fertilizer rate, so it may be a tool to help reduce nitrogen losses. Adding higher rates of fertilizer did not lead to higher yields and made the practice more expensive. Our study shows some of the tradeoffs between crop production, environmental quality, and costs when double cropping. Our findings are important to producers, scientists, crop advisers, and policy makers trying to find the best agricultural management practices in the North Central U.S.

Technical Abstract: Double-cropping winter rye cover crops (CC) with soybean in the North Central U.S. could help with the global effort to sustainably intensify agriculture. Studies addressing the management of these systems are limited. Therefore, a field study was conducted from 2017 to 2019 in central Iowa, U.S. to evaluate winter rye CC biomass production, aboveground N accumulation, estimated economics, estimated within-field energy balance, and estimated greenhouse gas (GHG) emissions under three N application rates (0, 60, 120 kg N ha-1) and three planting methods (pre- and post-harvest broadcast and post-harvest drilling). Averaged over N rates, all planting methods resulted in >5.0 Mg ha-1 yr-1 rye aboveground biomass dry matter. Averaged over the two-year study and compared to unfertilized treatments, applying 60 kg N ha-1 produced 1.1 Mg ha-1 more aboveground biomass (6.1 v 5.0 Mg ha-1), accumulated 30 kg ha-1 more N in aboveground biomass (88 v 58 kg N ha-1), and led to 20 GJ ha-1 more net energy. Biomass production was not higher with 120 kg N ha-1 compared with the 60 kg N ha-1 rate. Even when accounting for an estimated 0.75 Mg ha-1 of above ground rye biomass left in the field after harvesting, more N was removed than applied at the 60 kg N ha-1 rate. The minimum rye prices over the two-year study needed for double-cropping winter rye CC to be profitable (breakeven prices) averaged $117 and $104 Mg-1 for the 0 and 60 kg N ha-1 rates, which factors in estimated soybean yield reductions in 2019 compared to local averages but not off-site transportation. GHG emissions were estimated to increase approximately 3-fold between the unfertilized and 60 kg N ha-1 rates without considering bioenergy offsets. While environmental tradeoffs need further study, results suggest harvesting fertilized rye CC before planting soybean is a promising practice for the North Central U.S to maximize total crop and net energy production.