Cover Cropping in Soybean-Corn Rotation System: Economic, Agronomic, and Soil Fertility Impact

Planting winter-annual cover crops prevent soil erosion, reduces water runoff, and improves soil structure and soil quality. This research was conducted from 2017 to 2019 to evaluate the nutrient turnover of different species of cover crops in soils under different row crop production systems in Northeast and Central Louisiana. In Northeast Louisiana (Site 1, 2, and 3), treatments (cover crops and no cover crop) were arranged in a strip trial with three replications. At the Ben Hur Research Station, the treatments included three planting dates (September, October, and November) with [7 kg ha-1 of phosphorus (P) and potassium (K)] and without fertilization arranged in a split-plot randomized block design with four replications. Cover crop treatments produced significantly higher biomass yields than the no cover crop treatments across sites in 2018 but only at Site 3 in 2019. For most site-years with high biomass accumulation, the amounts of soil nutrients removed or scavenged by cover crops from the soil subsequently increased the levels of available nutrients in the soil. However, there was no difference observed on yields of the main crops nor net return. Cover crops planted in September produced 764 kg ha-1 (39%) and 1632 kg ha-1 (153%) more biomass than cover crops planted in October and November, respectively. Recovered nutrients were higher for September-planted cover crops than October and November-planted cover crops. Generally, cover crop biomass had a negative association with soil P and K nutrient content in most site-years. Main crop yields had weak positive associations at Site 1 in 2018 (r2 = 0.43), and Site 2 in 2019 (r2 = 0.16). A negative association was observed at Site 3 for both years (r2 = 0.23 and 0.17), and at Ben Hur Research Station (r2 = 0.5). This study demonstrated that planting dates had a more evident and consistent impact on cover crop growth and biomass accumulation than fertilizer treatments. In addition, positive impact on main crop yields and net returns were not observed suggesting that the improvement in soil fertility and crop productivity requires long-term adoption of cover cropping