Dinámica del nitrógeno en maíz posterior a cultivos de servicio invernales

In recent decades, agricultural intensification in Uruguay has generated negative effects on the soil and environment, such as erosion, loss of biodiversity, and contamination from agrochemicals. In this context, cover crops (CC) have emerged as a key tool for more sustainable agriculture, thanks to their ability to improve soil health and provide ecosystem services. The hypotheses of this thesis were: (1) that CCs consisting of grass-legume mixtures maintain high productivity and good residue quality in different environments; and (2) that CCs including legumes improve nitrogen (N) dynamics in the soil compared to long fallows or CCs without legumes, which can be measured through variations in soil nitrate (N-NO₃⁻) levels. The general objective was to study the effect of different winter CCs on N dynamics. The specific objectives were: (1) to evaluate biomass production, N contribution, and the C/N ratio of different CCs; and (2) to quantify N-NO₃⁻ availability according to the winter predecessor at different stages of the maize crop cycle. Over two years, a network of four experiments was established in two locations, each with a randomized complete block design with nesting. Each experiment included five treatments: Avena byzantina (pure grass), chemical fallow (control), Vicia villosa (pure legume), Avena strigosa + Vicia villosa (mixture), and Avena byzantina + Vicia villosa (mixture). Biomass production, N content, and N-NO₃⁻ release were evaluated. The results indicate that CCs incorporating Vicia villosa captured more N and had a lower C/N ratio, promoting a faster and more sustained release of N into the soil. Compared to pure Vicia villosa CCs, mixtures produced more biomass but with a higher C/N ratio. The percentage of Vicia villosa in the biomass of the mixture was a determining factor in soil N-NO₃^- levels throughout the maize cycle. Grasses generated more biomass but had a higher C/N ratio, leading to N immobilization in the soil and lower soil N-NO₃^- levels. It is important to highlight that considering agroclimatic variability and field history, along with proper CC management, is crucial for optimizing N use efficiency and contributing to the sustainability of the agricultural system.