Matéria orgânica, fluxo de CO2 e índice Q10 em dois latossolos com texturas contrastantes sob diferentes usos no cerrado

Abstract

The different land use systems at Cerrado, with intensive use of land, brought direct consequences in relation to the chemical, physical and biological soil properties. The impacts of land use are rapid degradation and imbalance in the biological processes and nutrient cycling. Soil texture and seasonality can interfere in these processes. The objectives of this study were to determine the changes in the biochemical soil microorganism s metabolism in different agroecosystems in Oxisol of different textures, to evaluate the effects of seasonality on microbial activity and modeling CO2 efflux, and evaluate the sensitivity of soil microbes as a function of warming. The organic fraction, microbial biomass and extracellular enzymes (β-glucosidase, urease, acid phosphatase and FDA) were evaluated. Soil respiration, soil temperature and gravimetric soil moisture were assessed for 12 months in 2012. The precipitation and air temperature were also monitored. Laboratory bioassays were conducted to determine the C-CO2 released by static incubation with temperatures of 20, 25 and 30oC. Linear, quadratic and exponential models were applied to analyse how soil moisture influences at soil respiration. The soil temperature and soil moisture combination was modelled. Arrhenius and van\'t Hoff equations were applied to evaluate the sensitivity of respiration and microbial activity in relation to soil temperature. The land use system influenced at biochemical response of the soil, and the native Cerrado showed the highest values for the organic fraction of the soil, microbial biomass and enzyme activities compared to grassland and sugarcane. The CO2 emission showed no statistical differences only in relation to agroecosystem evaluated, regardless of soil texture, with higher values in the rainy season and declined at dry season. The models involving temperature and soil moisture better explained the soil respiration variations in sandyclayey- loam soil, especially in the area of grassland. There were no differences in the adjustment of the Arrhenius and van\'t Hoff´s equation parameters, being dependent on the land use and soil texture. Q10 index was significantly affected by land use and soil texture, with the lowest values obtained in the areas of sugarcane.