Livestock in diverse cropping systems improve weed management and sustain yields whilst reducing inputs

Intensive cropping systems select for a low diversity of weeds tolerant of chemical control, leading to persistent weed-crop competition and declining biodiversity. Crop rotation can mitigate this by introducing variable filters on the weed community through increasing management diversity. In this study, we investigate the effect of integrating livestock into no-till crop rotations to complement chemical weed control. We analysed 12 years of weed seedbank data from a trial of eight rotation systems with different crop sequence diversities, of which four included grazed forage phases. Linear mixed models and ordination were used to assess how weed abundance, diversity, and community composition responded to management filters, defined in terms of levels of disturbance strength and diversity (grazing and herbicides), and resource availability and diversity (inorganic fertilizers, legumes, and manure). Grazed rotation systems had less herbicide applied than ungrazed rotation systems, and had the lowest weed abundance and highest weed diversity. Herbicides and grazing apply contrasting selection pressures on weeds, and this combination was more effective in reducing weed pressure than increasing herbicide quantity or mode-of-action diversity. Lower resource availability and higher nitrogen source diversity in grazed systems may have further reduced weed abundance and promoted diversity. Crop sequence diversity also reduced weed abundance and promoted weed diversity, indicating that variable crop-weed interactions can enhance weed management. In addition, yields in the main cash crop (wheat) were highest where crop diversity was highest, regardless of whether the system contained grazed phases. Synthesis and applications. Diverse rotation systems produced high yields, and the inclusion of grazed forage phases maintained these yields at lower applications of herbicides and fertilizers: integrated livestock can therefore improve the sustainability of no-till systems. The role of grazing as a filter imposing a contrasting selection pressure to other weed control options could be further explored to improve weed management in different farming systems.