Long-term changes in organic matter stocks and quality in an Oxisol under intensive vegetable cultivation

Abstract

Changes in carbon (C) and nitrogen (N) reserves reflect the impacts of land use and management. The objective was to evaluate the changes in organic matter stocks and quality in an Oxisol under intensive vegetable cultivation in the Brazilian Cerrado region. Four areas were selected: one under Cerrado vegetation (CV) and three under vegetable production with 15 (VG15), 20 (VG20) and 30 (VG30) years of cultivation. Soil samples were collected for the determination of total C (TC) and total N (TN) in soil organic matter fractions and the biochemical composition of particulate organic matter (POM) and mineral-associated organic matter (MOM). The smallest C stocks were observed on VG30, whereas the CV area had the highest values. The TN stocks were similar across treatments. The levels of labile C decreased with cultivation time. Increases and reductions in carbohydrate and lignin ratios in POM and MOM occurred in VG15 and VG20, respectively, with POM being more sensitive to changes in land use. There was greater similarity between VG15 and VG20, but differences between CV and VG30. There was a correlation between higher labile reserves (labile C and carbohydrates) and areas with shorter land use and between Cmic and agricultural use for 30 years. There was also a negative correlation between soil nutrients and the total and MOM C and N contents as well as the MOM carbohydrate levels, and there was also a negative correlation between Cmic and TC. The intensive use of Oxisols promoted a reduction in soil organic matter stocks and altered their quality.