Cinética intra-anual da matéria orgânica como um indicador da qualidade de sistemas de manejo em ambiente de terras baixas

Abstract

Conservation management systems contribute to the increase of the soil organic matter stock (SOM) and for the improvement of the soil, air and water quality. Scarce are the studies that evaluate the intra-annual dynamics of the SOM in low lands of the south of Brazil. I was aimed at to evaluate the seasonal variation of the stocks of SOM in the whole soil and in the free light fraction (FLL) in different cropping systems and manegement; ii) to quantify the SOM lability in different cropping systems and management in a Typic Albaquult. Soil samples were collected in the 0,000-0,025; 0,025-0,075; 0,075-0,125 and 0,125-0,175m depths, in four stations (summer, autumm, winter and spring), in three crop systems under no tillage Ryegrass (Lollium multiflorum Lam)+Trefoil (Lotus corniculatus)/Aside (Az+Corn/P); Ryegrass +White Clover (Trifolium repens)/Corn (Zea mays L.) (Az+Tr/M); Ryegrass /Soy(Glycine max L) (Az/Sj), and in an area of native pasture adjacent to the experiment. In the whole soil and in FLL, obtained by flotation in NaI 1,8g cm-3, it was quantified the TOC and TN pools by use of the dry combustion analyzer. The stocks of TOC and TN in the whole soil and in the FLL of the SOM it were affected for the season, especially in the surface layer. The FLL demonstrated larger sensitivity to the seaseness of the additions of crop residues to the soil comparatively to the whole soil. The intra-annual dynamics of the SOM it was affected directly by the process of addition of the crop residues. In the conditions of this study, FLL represented 20% of TOC in the soil maintained under native field and, on average, 14% in the cropping systems under no tillage.