Coal combustion residue for crop productivity in the semiarid US High Plains

Carbon (C) amendments can enhance crop productivity, particularly in semiarid regions. Understanding the potential interference of C amendment with herbicide efficacies is essential to informing the practice. An experiment was conducted in western Nebraska in 2016–2018 to evaluate the effects of coal combustion residue (CCR) and herbicides on crop yields and weed density in the dry bean (Phaseolus vulgaris L.)–maize_db (maize [Zea mays L.] following dry bean)–sugarbeet (Beta vulgaris L.)–maize_sb (maize following sugarbeet) rotation. All crop phases of the rotation were present each year and received CCR at varying rates (0, 3.3, 6.6, 13.1, and 19.7 Mg C ha⁻¹) in spring 2016. Overall, CCR did not have consistent beneficial effects on crop yields. There were trends for yield benefits with CCR application compared to no-CCR plots in dry bean (p = 0.066) and sugar beet (p = 0.155) in 2017 and maize_db in 2018 (p = 0.222). In 2016, among no-herbicide treatments, the treatment with the highest CCR rate had a greater maize_sb yield (16.2 ± 0.1 Mg ha⁻¹) than the rest of the CCR treatments, including the control. The CCR application did not adversely affect herbicide efficacy in weed control. However, in 2016, among plots where herbicide (saflufenacil + dimethenamid-p) was applied, the CCR treatment (6.6 Mg C ha⁻¹) had lower maize_sb yield than the control. Future research should consider factors such as application rates, methods, and timing to assess the potential adverse effects of C amendments on herbicide efficacies.