Nitrogen of summer culture residues in physical fractions of organic matter of two lowland soils

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES Rio Grande do Sul has about 20% of its total area of soils with hydromorphic characteristics, denominated lowlands suitable for rice cultivation (Oryza sativa) irrigated by flooding. In order to mitigate damage caused by rice monoculture, new crops such as sorghum (Sorghum bicolor) and soybean (Glycine max) have been cultivated in these areas. Considering different qualities of cultural residues, a change in the availability of nitrogen (N) present in soil organic matter (SOM) is expected. The aim of this study was to understand the influence of cultural residues of rice, soybean and sorghum on the dynamics of N in different physical fractions of the MOS in two soils of lowlands with different textures, using the technique of isotopic marking of 15N. Simulating an agricultural year, an incubation of the cultural residues of rice, soybean and sorghum enriched with 15N isotope in the soils Planossolo Hidromórfico Eutrófico gleissólico and Planossolo Hidromórfico Eutrófico arênico during 360 days, and at 180 days thereafter the soil was flooded. The remaining N of the plant residues was quantified at 30,180 and 360 days after the beginning of the incubation. The N destination from the residues in the soils was evaluated in the whole soil and after the physical fractionation of the MOS based on the particle size (> 250μm, 250-53μm and 250 μm, 250-53 μm e