Indicadores de qualidade do solo em sistemas de produção agrícola em solos arenosos

Abstract

In tropical sandy soils of Western São Paulo State, soil quality responds strongly to land use and the degree of soil disturbance. This study compared five soil management systems: Pasture, Pasture-ILP, Crop-ILP, Pivot irrigation, and Forest, aiming to identify sensitive sustainability indicators. The approach integrated chemical fractions of soil organic matter (SOM) with microbiological and enzymatic indicators. The objective was to discriminate among management systems and support monitoring and decision-making. The study was conducted at Fazenda Ybyeté Porã, in Rancharia, São Paulo State, Brazil, on sandy soils, predominantly Ultisols and Oxisols, from May 2022 to May 2023. SOM was assessed by chemical fractionation into fulvic acid (FA), humic acid (HA), and humin (HU), in addition to biological indicators: soil respiration, microbial biomass carbon (MBC), qCO2, and enzymatic activities (FDA, dehydrogenase, β-glucosidase, arylsulfatase, and phosphatase). Management systems and soil depths (0–10 and 10–20 cm) were compared using ANOVA and integrated multivariate analyses of the attributes. In the conclusions, in 2022 FA (labile fraction) was the most sensitive chemical attribute, ranging from 0,87 to 4,30 g kg−1, with the highest values under Pasture (4,30) and Pivot irrigation (3,89). HA (more stable fraction) was higher under less disturbed systems, particularly Pasture (1,75 g kg−1) and Forest (1,15 g kg−1), and lowest under Pasture-ILP (0,55 g kg−1). HU (most recalcitrant fraction and an indicator of long-term carbon sequestration) highlighted better performance of systems with lower soil disturbance: in 2022, Pasture showed the highest HU at 0–10 cm (8,04 g kg−1) and maintained vertical stability in 2023 (5,69 g kg−1 at the surface and 5,62 g kg−1 at depth); in contrast, Crop-ILP exhibited reduced stabilization, dropping to 2,73 g kg−1 at 10–20 cm, suggesting an effect of soil disturbance. Biological indicators reinforced this pattern: in 2022, soil respiration was highest under Pasture (0,12 mg CO2 hora−1) and lowest under Crop-ILP (0,026 mg CO2 hora−1). In 2023, MBC was highest under Pasture (181,76 mg C g−1 soil), followed by Forest (172,93 mg C g−1), whereas the lowest values occurred under Pivot irrigation (87,47 mg C g−1) and Crop-ILP (84,56 mg C g−1). In 2022, arylsulfatase activity was consistently highest under Pasture (230,8 µg PNP g−1 soil h−1), while Pivot irrigation showed the lowest activity (43 µg PNP g−1 soil h−1). Overall, a positive association was observed between conservation-oriented management (reduced soil disturbance), higher carbon contents in humified fractions, and greater biological activity. Pasture emerged as the best treatment for promoting soil quality, while Pasture-ILP and Crop-ILP were intermediate and promising alternatives for sandy soils in Western São Paulo State. The combined use of SOM chemical fractionation (FA, HA, and HU) with enzymatic and microbial indicators provides a robust toolkit for monitoring and decision support in production systems.