Estoques e frações de carbono orgânico em latossolo sob plantio direto e preparo convencional no semiárido

Abstract

The removal of natural vegetation and the deployment of agricultural cropping systems cause direct impact on the storage of organic matter and its fractions in the soil. The conventional tillage system due to tillage, favors the oxidation and subsequent reduction of the carbon stock in the soil, especially in labile. On the other hand, the system of tillage, due to low mobilization, preserves soil cover. contributing to maintaining and increasing the stock of soil carbon. In semiarid, studies with such systems are scarce. The stocks of carbon and nitrogen of a Latosoil in the semiarid was evaluated under no-tillage (NT) and conventional tillage (CT) with distinct cover crop. The experiment used one plot with 18 x 18 meters by treatment: being two tillage systems and three crop succession, reaching six treatments (T) plus the common check, as follows: T1: NT, maize- fallow-bean-fallow; T2: NT, sorghum-fallow-bean-fallow, T3: NT, sunflower- fallow-bean-fallow, T4: CT, maize-fallow-bean-fallow, T5: CT, sorghum- fallow-bean-fallow, T6: CT, sunflower-fallow-bean-fallow; Common check: native forest (NF), at least 40 years without anthropic intervention. In the summer, performed crop succession and in winter, beans. After 2 years and 3 months, mulch and was evaluated, and soil samples were collected at 0.00 to 0.05, 0.05 to 0.10, 0.10 to 0.20 and 0.20 to 0.40 m depth for assessment of: total organic carbon (TOC), total nitrogen (TN), humic substances (HS) and its constituents (fulvic acid fraction (FAF), humic (FAH) and humin (FH)), stock of labile carbon (CL), non-labile (CNL) and water soluble carbon (CSA) and determination of indexes: humification (IH: humification index (FAH/COT), RH: reason humification: (HS/TOC), GP: degree of polymerization (HAF/ FAF), EA/FH: relationship between alkaline extract (FAF + FAH) and humin fraction) and carbon management (ICC: index of carbon compartment, L: lability, IL: lability index, and CMI: carbon management index).No-till systems promoted major storage COT, NT, carbon in HS, CL, CSA, carbon management index, than CT systems at 0.00 to 0.05 m of soil depth semiarid. At 0.05 to 0.10 m depth, the NT systems contributed to higher carbon storage in soil FAF and HAF, was also observed by the highest values of EA/FH compared to CT. At larger depth, a reduction of the influence of management systems on the concentrations and stocks of soil carbon. The cultivation of corn in NT contributed to higher storage of COT, CNL, NT, CL, SH in carbon in the 0.00 to 0.40 m, and CMI in the subsurface (0.10 to 0.20m), being more promising for the recovery of the stock of soil carbon than the other systems. The no-tillage system in semi-arid conditions promote in a short time (two years and three months) increase in soil earbon stocks, as improvement in the quality of soil organic matter, indicated by the values of GP.