Grazing intensities affect weed seedling emergence and the seed bank in an integrated crop-livestock system

Integrated crop-livestock systems (ICLS) are widespread worldwide. Although weeds can result in several types of losses, essential information regarding weed seedling emergence and seed banks is lacking in these systems for integrated weed management planning. This study investigated the effects of different grazing intensities (no grazing and grazed swards maintained at 10-, 20-, 30- and 40-cm sward heights) on weed seedling emergence and seed banks in a winter cover crop during the 15th year of an ICLS experiment under no-tillage management in subtropical Southern Brazil. We hypothesized that low grazing intensities would reduce weed interference and weed seed banks size in an ICLS. We determined treatment effects on weed species richness, seed bank population density, and seedling emergence during winter and summer. Higher sward heights in the winter-grazed cover crop reduced the number of weed species, the density of emerged weed seedlings, and the weed seed bank size compared with the non-grazed control. With a sward grazing height of 10 cm, the seed bank contained an average of 3151 seeds m−2, and the weed population densities during the summer and winter were 11.8 and 21.7 plants m−2 greater, respectively, compared with the sward grazing height of 40 cm. Fifteen years after adopting low grazing intensities (30- and 40-cm sward heights) in the ICLS, the size of the weed seed bank was reduced by 42.1% compared with the non-grazed treatment. Decreasing the grazing intensity reduced the number of weed species, the density of emerged weed seedlings, and the weed seed bank density; therefore, integrated weed management strategies should consider minimizing grazing intensities in an ICLS.