Effects of Nitrogen Sources on Primary and Secondary Production from Annual Temperate and Tropical Pastures in Southern Brazil

Improvements in nitrogen use efficiency can be achieved through fertilizer management strategies that capitalize on nutrient synergies. However, limited research on synergies between nitrogen, sulfur, and calcium complicates understanding causal links and developing sustainable management. In this regard, the effects of different nitrogen sources on productivity and nitrogen use efficiency in Italian ryegrass (Lolium multiflorum Lam.) and pearl millet (Pennisetum glaucum (L.)), along with their impacts on forage quality and secondary production, were investigated. Treatments included: Urea (46% N), ammonium nitrate (NH4NO3; 32% N), ammonium nitrate supplemented with calcium and sulfur (NH4NO3 (+), 27% N + 5% Ca + 3.7% S), and control treatment with no N application. The application of fertilizers that combine nitrogen with calcium and sulfur enhances primary production in both winter and summer pastures. Fertilization with NH4NO3 (+) increased nitrogen use efficiency by 125% in Italian ryegrass compared to NH4NO3. However, within the framework of rotatinuous grazing management principles, optimizing plant nitrogen use efficiency does not necessarily lead to a better forage quality or animal performance. These findings highlight that using fertilizers that promote synergies among nutrients, such as the combination of nitrogen with calcium and sulfur, can bring benefits to the sustainability of pasture-based livestock production systems.