Roots and aboveground carbon and nitrogen inputs by black oats (Avena strigosa Schreb.) as affected by grazing and nitrogen in integrated crop-livestock system in subtropical Brazil

Aims Roots are important contributors to soil organic matter in pasturelands, yet in integrated crop-livestock systems (ICLs), the effects of grazing intensities are poorly understood. We investigated the effects of grazing intensities and nitrogen application to black oats pasture (Avena strigosa) on carbon and nitrogen additions, mainly by roots, into soil. Methods The ICL experiment in southern Brazil comprised no, moderate and intensive grazing of black oats pasture receiving 0, 75 and 150 kg N ha(-1). Root (0-30 cm) and aboveground biomass of black oats were assessed over two years, in a sequence of maize (Zea mays)-black oats-soybean (Glycine max)-black oats. Results Moderate grazing did not change the carbon and nitrogen additions by roots, but reduced the aboveground additions by 45-54%, compared to no grazing. Generally, the intensive grazing did not affect root or aboveground additions relative to moderate grazing, but in year of normal precipitation and supplied with 150 kg N ha(-1), it reduced root carbon and nitrogen addition by 11-22%. Nitrogen application had no clear effect on root additions, but increased the aboveground additions. Conclusions In ICL system, moderate grazing maintained carbon and nitrogen additions by roots of black oats, compared to no grazing, while nitrogen fertilization can be used to increase carbon and nitrogen aboveground additions.