Optimizing forage allowance for productivity and weed management in integrated crop-livestock systems

Weeds are a major constraint on food and feed production, and the excessive use of herbicides to control them is a global concern for food security, human health, and environmental sustainability. Under no-tillage systems, cover crop residues provide a physical barrier to weed emergence that reduce weed infestations and reliance on herbicides. In integrated crop-livestock systems, cover crops provide fodder to grazing animals, adding an additional source of revenue for farmers; however, grazing can cause a trade-off because it reduces biomass during the cover crop season and residues left on the soil surface in the next cash crop, which may increase weed infestation. In the current study, it was hypothesized that there is an optimal cover crop forage allowance during the grazing period that maximizes beef production while retaining enough cover crop biomass and residue to minimize weed infestations and maintain grain yield of the subsequent cash crop. Therefore, the effects of cover crop (mixed black oat + Italian ryegrass) forage allowances (based on sward height) during the winter grazing period on weed infestations, beef production, and soybean grain yield during the next summer season were evaluated. The experiment was conducted in several commercial fields involving two experimental protocols (one short-term and one long-term experiment) in Southern Brazil, and the results demonstrated that a moderate forage allowance in winter cover crops (i.e., maintaining 17.8cm of winter grazed cover crop sward height) reduced weed infestations and increased soybean and beef production when compared with a lower forage allowance (i.e., <10.7cm of winter grazed cover crop sward height) or a higher forage allowance (i.e., >17.8cm of winter grazed cover crop sward height). Therefore, the current study provides evidence that it is possible to optimize forage allowance to sustainably intensify arable cropping systems using winter cover crops for direct grazing.