Nitrogen Fertilizer Efficiency Determined by the 15N Dilution Technique in Maize Followed or Not by a Cover Crop in Mediterranean Chile

Abstract

Nitrogen (N) in a maize crop is a determining yield factor, but its negative impact on the environment is also known. Therefore, it is necessary to propose mitigation strategies that allow an improvement in the N fertilizer efficiency (NFE), such as the use of cover crops (CC) and the adjustment of the fertilizer dose. The objective of the study was to determine NFE using 15N isotopic techniques and nitrate (NO3−) leaching in a maize–fallow versus a maize–CC rotation with optimal and excessive doses of N in the Mediterranean area of Chile. The treatments were a combination of crop rotation (maize–fallow versus maize–CC of Lolium multiflorum) with the optimal dose of N (250 kg ha−1) or excessive dose (400 kg ha−1). We found that the optimal dose of maize–CC rotation contributed to reducing the losses of N by leaching and improving the NFE. Using the optimal dose decreased the dissolved inorganic N (DIN) emission intensity by 50% compared to the excessive doses. Even if grain yield was higher (19 t ha−1) when applying the excessive N dose, the NFE (28%) was lower than when applying the optimal dose (40%). In the maize–CC rotation with optimal dose, yield was 17 Mg ha−1. The excessive N dose generated higher DIN content at the end of the maize season (177 kg N ha−1). In conclusion, replacing the traditional autumn–winter fallow in the maize monoculture with a CC with optimal N dose contributed to improving NFE and reducing N leaching in a Mediterranean agricultural system. Consequently, it is a strategy to consider as it has positive advantages in soil and N management, helping to reduce diffuse pollution of surface and groundwater bodies.