Biomassa microbiana, frações de carbono e fósforo orgânico de um latossolo húmico sob diferentes usos

Abstract

The soil organic matter (SOM) comprises the plant residues in various stages of decomposition, microbial biomass, roots and more stable fractions, the so-called humus. The SOM regulates several chemical, biological and physical processes in soil and it is considered a key indicator of soil quality. The replacement of natural vegetation by crops often results in changes in both the quantity and the quality of SOM. The magnitude of these changes varies with soil properties, climate, crops and soil management. Some parameters such as phosphorus and soil organic carbon are not always sensitive to soil changes. Therefore the distribution of P and C fractions are used to better assess the SOM quality. The work aimed to evaluate the changes in chemical characteristics of SOM fractions such as microbial biomass, as well as in P and c organic fractions of a Humic Oxisol under different uses in Pernambuco, Brazil. Soil samples were collected from five different environments (native forest, scrub submitted to sporadic fires, a 30-year pasture use, pasture for 25 years and annual crops) at four depths (0.0-2.5; 2.5-5.0, 5.0-7.5 and 7.5-10.0 cm). The pasture systems for 25 years and annual crops caused negative impacts on most of the parameters. The effect of fire on soil under secondary forest resulted in increased levels of Ca2+ and Mg2+ and decreases in the contents of labile fractions of organic carbon, especially in the superficial layer (0.0-2.5 cm). About humic substances, there was a predominance of C in the humin fraction, followed by fulvic and humic acids in all the soils. Most of the labile and moderately labile P was found in organic forms. It summed up 64 and 88% of total P fractions, being the greatest percentage observed for the soil covered with pasture for 30 years.