Crop Rotation and Nitrogen Fertilizer on Nitrate Leaching: Insights from a Low Rainfall Study

The intensive use of agricultural fertilizers containing nitrogen (N) can increase the risk of nitrate (NO3−) leaching. However, little information exists regarding its interaction with other factors that influence NO3− leaching, such as no-tillage, which is associated with different crop rotation schemes. The objective of this study was to quantify the leachate NO3− concentration and load below the root zone in two different crop rotations under no-tillage, with and without mineral N fertilizer. The experiment was conducted in a no-tillage area in Brazil between 2018 and 2020. The factors were two crop rotations (diversified and simplified) and two N fertilization managements (with and without N fertilizer). The soil solution was collected with suction lysimeters (1 m depth), the NO3− concentration (mg L−1) was spectrophotometrically determined, and the NO3− load (kg ha−1) was calculated from the volume of water drained and the NO3− concentration. The results were categorized into 24 evaluation periods. NO3− leaching was extremely low due to low rainfall throughout the experiment, with no significant differences between the factors and treatments. In the presence of N fertilization, leaching was substantially greater when rainfall increased, and vice versa. No significant difference was observed between the crop rotation schemes, except for one period in which the simplified soybean rotation exhibited high leaching. The evaluated treatments showed less NO3− leaching during the four periods when grass species were cultivated, indicating the importance of grasses in rotation systems.