Carbono-¹³C de raízes e parte aérea de culturas de verão em frações físicas da matéria orgânica de dois solos de várzea

Abstract

Crop diversification in lowland areas in Rio Grande do Sul is incorporating sorghum (Sorghum bicolor) and soybean (Glycine max) into rotation system with irrigated rice (Oryza sativa). Little is known about the impact of these crop residues additions on carbon (C) stabilization in physical fractions of soil organic matter (SOM) in hydromorphic soils. The objective of this study was to understand the contribution of rice, soybean and sorghum crop residues to C accumulation in different physical fractions of SOM in two soils, with different textures. During 360 days, an incubation with rice, sorghum and soybean shoots and roots 13C enriched was carried out to evaluate crop residues C incorporation into SOM. The C incorporation and stabilization in the hydromorphic soils (Planossolo Hidromórfico Eutrófico gleissólico e Planossolo Hidromórfico Eutrófico arênico) were evaluated through physical fractionation method, based on size (> 250 μm, 250-53 μm and <53 μm). The crop residues, soils and physical fractions of SOM influenced C stabilization in the soil at the end of 360 days. Higher amounts of C were observed in >250 and <53 μm fractions. Planossolo Gleissólico was more efficient on C stabilization due higher sil and clay content. C stabilization from roots was higher in soybean and sorghum crops than rice. Soil texture did not influence roots C stabilization in fraction > 250 μm. For the fraction <53 μm, only soybean roots showed influence of soil texture on C stabilization , with higher C stabilized in Planossolo Gleissólico. The results indicate that the rice crop residues are important for a high C retention in hydromorphic soils, especially in the fraction <53 μm. The inclusion of soybean and sorghum crops in the lowland environment promotes a higher roots C stabilization in soil, being an important alternative for crop rotation with rice. The soil with higher silt and clay content presents a higher effectiveness of C stabilizationin the fraction <53 μm, mainly from shoots.