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

Author(s)

Raíssa de Araujo Dantas

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2023-09-05

Examining board members

Rafael Otto; Arminda Moreira de Carvalho; Eduardo Mariano

• Advisor: Rafael Otto

Abstract

Nitrogen (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 practical 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 second-crop (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 15N 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 15N 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. (AU)

• FAPESP's process: 19/00978-7 - Mineralizable nitrogen and maize responsiviness in crop rotation systems in Cerrado
• Grantee: Raíssa de Araujo Dantas
• Support Opportunities: Scholarships in Brazil - Doctorate