Effect of hairy vetch cover crop on maize nitrogen supply and productivity at varying yield environments in Southern Brazil

Cover crops play a critical role on conservation and sustainable agriculture due to their well-documented benefits on both soil and crop productivity. Inclusion of legumes (e.g., hairy vetch, Vicia villosa Roth) in the farming system can reduce the nitrogen (N) fertilizer needs for cereals such as maize (Zea mays L.) crop while maintaining or increasing its productivity. The aims of this research study were to quantify the effect of hairy vetch as a cover crop on: i) successor maize yield under varying yield environments (YEs) and fertilizer N rates, and ii) maize N status [N uptake, N nutritional index (NNI), and N fertilizer replacement value (NFRV)] at flowering time. Two field studies were carried out in Southern Brazil under varying YEs. The factors investigated were: YE (low, medium, and high), hairy vetch cover crop (with and without), and fertilizer N rate (0, 60, 120, 180, and 240 kg N ha^-1). Under the combination of low YE and low fertilizer N rates (0-60 kg ha^-1) with previous vetch, maize displayed the largest yield response and an improvement in its N status. The NNI determined at maize flowering was an efficient index of the vetch effect, increasing delta maize yield response (yield with- minus without-vetch) as the NNI reduced, with more than 10% delta yield response with NNI below 0.85. The NFRV of the hairy vetch represents potential N savings of 151 kg N ha^-1 for the LYE, 95 kg N ha^-1 for the MYE and from 59 to 45 kg N ha^-1 for the HYE depending on the tested fertilizer N rate. The N coming from the legume cover crop in addition to the N fertilization was critical for supplying N to maize and boosting productivity across all YEs.