Sustainability Analysis of Nitrogen Use Efficiency in Soybean-Corn Succession Crops of Midwest Brazil

Abstract

Nitrogen (N) is abundant in the atmosphere as N2, which is converted into reactive forms (Nr) for plant assimilation. In pre-industrial times, atmospheric N2 conversion to Nr balanced Nr reconversion to N2, but 20th-century human activity intensified this conversion via synthetic fertilizers, biological N2 fixation, and fossil fuel burning. The surplus of Nr detrimentally impacts ecosystems and human well-being. This study aimed to assess the N use efficiency in the soil–plant system of the soybean-corn succession (SPSS,C) in Mato Grosso and Mato Grosso do Sul, Brazil’s midwest. We estimated N macrofluxes in SPSS,C and identified key agro-environmental indicators. Between 2008 and 2020, the yearly sowed area for the SPSS,C increased by 3.3-fold (currently 7.3 million ha). The average annual input of net anthropogenic Nr, average annual N balance, and N loss in SPSS,C was estimated to be ~204 kg [N] ha−1, 57 kg [N] ha−1, and 30 kg [N] ha−1, respectively, indicating persistent N accumulation and loss. The average results of the agronomic efficiency and N retention indicator in the SPSS,C was 0.71 and 0.90, respectively. Modest N use efficiency results reflect N loss effects. Despite these limitations, there are opportunities in SPSS,C for management strategies to reduce N loss and enhance efficiency.