Caracterização química e funcional da matéria orgânica do solo e frações e formas de fósforo em diferentes sistemas de uso do solo

Abstract

Due to its importance in soils with a tropical climate, organic matter is considered an important indicator of soil quality. In addition to having a direct influence on the phosphorus (P) soil availability (P), especially in oxidic soils. The aim of this study was to evaluate changes in the chemical and functional structure of soil organic matter (SOM) and to evaluate how phosphorus forms depend on the soil mineralogy and the land use forms. Three systems were studied: no-tillage system (SPD), conventional tillage system (SPC) and permanent pasture (PA or P). An adjacent forest area was used as a natural soil condition. Total organic carbon (COT), oxidizable carbon determinate with potassium permanganate, total organic carbon (EstCOT) and total nitrogen (EstN) stocks, SOM chemical and densimetric fractions, natural 13C abundance were quantified, spectroscopic characterization using 13C-NMR CP / MAS in the humic acid (HA) fraction; phosphorus in equilibrium solution (P-rem), available phosphorus (PD), total phosphorus (PT) and 31P-NMR CP / MAS in humic acid (AH), in addition to the forms of iron and aluminum: soluble iron (Fe-S), iron dithionite (Fe-D), aluminum dithionite (Al-D), iron oxalate (Fe-O) and aluminum oxalate (Al-O). The results showed that in the forest area (F) high levels organic C (chemical and densimetric fractions) were quantified in superficial layer, and predominantly aliphatic HA were quantified. In SPD, despite the constant supply of biomass to the soil, there is a low occurrence of aliphatic structures in HA, indicating greater carbon mineralization. In the pasture area, there is the HA formation similar to those observed in the forest area. In the SPC, less incorporation of chemical and densimetric fractions, TOC and TN stock and the HA formation were found to be structurally different compared to the others. areas. It is possible to affirm that the more stabilized systems in tropical climate provide the formation of HA with compositional and structural similarity regardless of the carbon origin (C3 and C4). In SPD and SPC areas structurally different HA were observed in comparison to pasture areas and F. The results of Chapter II show that in the pasture area, the highest levels of iron forms (low and high crystallinity) were quantified. Higher levels of available P were quantified in the SPD and pasture area in all layers and higher levels of total phosphorus in 0-0.05 m layer, due to the higher toers of organic matter. The levels of P-Rem were low and similar in all areas, indicating a high buffer power of the soil. There was no relationship between P availability and soil Fe and Al forms. The spectra of 31P-NMR CP / MAS in the AH fraction showed a predominance of organic forms of P. The use with pasture favored the accumulation of P- diester. In the forest area there was the incorporation of nucleotides like sugars and in the areas of SPC and SPD, the structures of P-monoestrus accumulated in greater quantity. The higher cultivation intensity seems to favor the more recalcitrant organic P structures, indicating, therefore, that the cultivation systems with SPD and SPC provide the maintenance of less labile P form. The results of this study indicate that the use of the soil modifies the chemical and functional height of the SOM and the forms of Fe and Al, however there was no relationship between the forms of Fe and Al with the availability of P.