Mineralizable nitrogen and maize responsiviness in crop rotation systems in Cerrado

Abstract

Nitrogen (N) is the nutrient required in high amounts by crops and is the widely applied worldwide. The estimate of soil's N potential of mineralization is importante for better the eficciency of nitrogen fertilization, regarding that the soil is the principal source of the nutrient for plants. However, include the soil's mineralizable N in methods of fertilizer recommendation is not yet used because the difficult to quantify. The Illinois Soil Nitrogen Test (ISNT), a method to estimate the mineralizable N by the alcaline extraction with NaOH, highlights as a promisse method. Posterior studies have evidenced that the method extracts a fixed ammount of organic N and, therefore, do not represent the labile fraction.The hipothesis of this study is that the extraction with NaOH used in ISNT method upperestimates the soil's N labile fraction. The objective is to evaluate the mineralizable N in summer maize rotation with cover crops (grasses, legumes and cruciferous), using chemical and biological methods, with emphasis on variation of NaOH's concentration in ISNT method. The evaluation will include: shoot dry matter, productivity and accumulation of N in maize, chemical methods (ISNT with 0,25, 0,5, 1,0 and 2,0 mol L-1 NaOH and permanganate oxidizible C), biological (aerobic incubation and ²-glucosidase and celulase enzymes) and N fertilizer recovery by maize (15N isotope tecnicque). The inovation of this propose is the partnership with Embrapa Cerrados, that has na long-term experiment with summer maize rotation with ten species (grasses, legumes and cruciferous), with and without N fertilizer. Preliminar results indicates that the difference in responsiveness to N by corn depending on rotation with cover crops. The evaluations in the experiment will be the indices to estimate N mineralizable on soil that can correlate with the maize response to N in field conditions. The new topic aborded in this study is the pursuit to a practical method toestimate the soil's N mineralizable that can be used in the future in nitrogen fertilization recommendation to maize. (AU)