Cover crops affects soil nitrogen fractions and maize responsiveness to nitrogen in the Cerrado region

Abstract

Cover crops affects soil nitrogen fractions and maize responsiveness to nitrogen in the Cerrado regionNitrogen (N) is the most required nutrient for the major crops and is globally consumed. The soil N dynamic involves losses and transformations, for example, leaching and denitrification, respectively, which makes the N fertilization management more complex and costly. The rational use of N fertilizers is one of the strategies to minimize economic and environmental impacts. The soil potentially mineralizable N estimation, or the readily mineralizable N estimation, can be used in N fertilizer recommendation to account the contribution of the organic N fraction in crop nutrition, adopting a pratical and simple method. Depending on the management, especially in no-tillage systems, which has crop rotation as one of its pillars, the main crop will present a different response to N-fertilizer depending on the previous crop. The study was carried out in a long-term experiment in Cerrado biome with maize as first-crop (rainy season) and leguminous and non-leguminous cover crops as secondcrop (off-season). The evaluations performed were: i) chemical and biochemical indices associated with N mineralization that correlates with maize productions component such as grain yield; (ii) the Illinois Soil Nitrogen Test (ISNT) as a tool to quantify the readily mineralizable N, testing different concentrations of the alcaline extraction, aiming to improve the correlation with maize components production in tropical agroecosystems; (iii) contribution of rotation systems with cover crops on maize yield and the effect in N accumulation in maize compartments (stalk + straw, cob + husk, and grains), N fertilizer recovery and N use efficiency using the 15 N stable isotope technique. The long-term experiment is located in Planaltina-DF in a Typic Haplustox (clayey texture) since 2010, in a randomized block design with subdivided plots, in which the plots are represented by nine cover crops and fallow (control) and subplots are represented by N managements (with or without N topdressing). Soil enzymatic activity and ISNT 0.5 M NaOH were the indices that showed correlation with maize yield. This is an indication that the indices are sensitive to quantify the variation on soil organic N and the maize responsiveness to N, with potential to adopt in N fertilizer recommendation for the crop. There was an increase in maize grain yield in maize-cover crops rotation systems in two seasons (2018/2019 and 2019/2020), but the N accumulation in maize compartments, the 15 N fertilizer recovery and N use efficiency did not differ from the control (fallow). The results shows that the benefits of the introduction of cover crops in rotation with maize are not only related to N cycling and other nutrients, but different ecosystem services that allows an increase in crop yield. The results indicate the potential of adopting indices to estimate readily mineralizable N and the maize response to N fertilization.