Optimizing High‐Residue Cultivation Timing and Frequency in Reduced‐Tillage Soybean and Corn

Abstract

Integrated weed management (IWM) practices are needed to prevent the development of herbicide‐resistant weeds and create more robust weed management programs. This experiment was conducted to determine the optimal timing and frequency of high‐residue cultivation in reduced‐tillage soybean [Glycine max (L.) Merr.] and corn (Zea mays L.) in Pennsylvania. Banded herbicides were applied at planting and high‐residue cultivation frequency ranged from one to three passes. A split‐plot assessed the effects of cover crop residue, either cereal rye (Secale cereale L.) in soybean or a hairy vetch (Vicia villosa Roth)‐triticale (X Triticosecale Wittm.) mixture in corn, on weed control and yields. Breakeven analyses were used to evaluate cultivation and cover crop costs. Two cultivator passes reduced weed biomass to 500 kg ha−1 or less and were needed to optimize weed control and prevent yield loss. No weed control or yield benefit was observed with three passes compared to two passes. Cover crop residues increased weed biomass and yield in dry years but suppressed weeds without influencing yields in wet years. In 1 of 3 yr, cover crop establishment costs were offset by 0.7 Mg ha−1 greater soybean yield with cereal rye residue than without. In 1 of 2 yr, a 0.8 Mg ha−1 greater corn yield with cover crop residue compared to none offset establishment costs only when legume N credit was substituted for urea fertilizer. This research confirms that banded herbicide application together with high‐residue cultivation can achieve yields similar to herbicide‐only programs while diversifying weed control tactics. New integrated weed management approaches are greatly needed in reduced‐tillage systems to help preempt the continued evolution of herbicide‐resistant weeds. High‐residue interrow cultivation following banded herbicide application at planting is an in‐season weed management program that combines mechanical and chemical weed control tactics. Under conditions of the experiment, two passes with a high‐residue cultivator achieved similar cash crop yield as a post‐glyphosate application in soybean and corn. Single‐pass treatments usually resulted in higher weed biomass and lower yields than two‐pass treatments, and no weed control or crop yield benefit was observed with three passes. Rolled cereal rye and hairy vetch–triticale cover crop residues increased soybean and corn yields, respectively, in dry years despite increasing weed biomass. Economic analyses indicated that the benefit to cash crop yield from cover crop residues will not likely exceed establishment costs in every year; however in dry years, residues can increase cash crop yield beyond breakeven levels. The higher seed cost of the hairy vetch–triticale used before corn was able to pay for itself if N provided by the hairy vetch was assumed to offset the cost of urea fertilizer.