Efeitos da degradação da terra nas substâncias húmicas de solos no cariri paraibano

Abstract

The soil compartment stores about three times more carbon compared to the atmosphere, therefore, maintaining the soil's organic carbon stock is of paramount importance for soil quality. Soil organic matter (SOM) is a sensitive thermometer of soil degradation, and in semi-arid regions, changes caused by anthropogenic interference generate losses in carbon stock, as well as in the quality and quantity of SOM. Therefore, this study aimed to evaluate the effects of anthropogenic actions on the total organic carbon stock as well as humic substances, regarding the fractions of fulvic acid, humic acid and humin under different land use systems in Cariri Paraíba. The research was carried out in areas with different land uses in the municipality of Sumé PB. Three areas were selected: a forest area (AM) in the process of natural regeneration for 10 years, a degraded area with a history of soil removal for the construction of landing strips and an area cultivating annual species (AC), with corn and bean. Samples were collected at depths of 0 to 5, 5 to 10 and 10 to 20 cm in which soil organic carbon was determined, calculating its stock (ECOS) and the carbon content of humic substances (fulvic acid, humic acid and humin) through the chemical fractionation of organic matter. The highest ECOT in the 0 to 5 cm layer were observed in the forest (2.36 g kg-1 ) and cultivation (2.33 g kg-1 ) areas, while the Technosol area presented the lowest values (0. 95 g kg-1 ). The cultivation area had the highest TOC stocks in layers from 5 to 10 cm (4.43 g kg-1) and from 10 to 20 cm (2.96 g kg-1), respectively. These results are associated with management with the addition of organic fertilizers. The C content contained in humic substances (SHs) ranged from 0.5 to 36.7 g kg-1, with the highest values associated with the soil in the cultivation area in the three layers evaluated. The humin fraction was predominant in all layers evaluated in the three areas, related to the greater recalcitrance and complexity of this organic compound in the soil. The cultivation area (AC) presented the highest averages of the humin fraction (3.67 g kg-1) in all layers. The lower ECOT and humin fraction in the Technosol area is due to the imbalance in the input and output of organic waste. Degradation significantly reduces carbon levels and stocks in different soil layers and in the humin fraction, this is due to the imbalance in the entry and exit of organic waste in this area. Higher levels of total organic carbon occur in the humin fraction in the corn (Zea mays L.) and bean (Phaseolus vulgaris L.) cultivation area, mainly in the 5-20 cm layers. in comparison to other areas studied, and the insolubility of the humin fraction, which forms compounds of greater complexity.