Indicadores de qualidade do solo em unidades de referência produtiva de noz-pecã sob diferentes sistemas de manejo

Abstract

Increased production of Pecan nut (Carya illinoinensis) in Brazil and the need for a more sustainable cultivation system highlight further studies on the effects of different production systems on soil quality. Thus, the general objective of this study was to evaluate the cause-effect relationship between quality attributes of different soil types, under different management systems, and soil health in pecan orchards in southern Brazil. The study was carried out in 15 pecan orchards located in 11 municipalities of RS. Four soil samples were collected in each orchard, in the 0-10 cm layer in the projection of the plant canopy. Total organic carbon (TOC), microbial biomass carbon (MBC), basal respiration (RB), 𝛽-glucosidase (BETA), arylsulfatase (ARIL), particle size, pH, H+Al, sum of bases (V%), CEC, and soil P, K, Ca, Mg, S, Zn, Cu, B, and Mn contents were determined. A principal component analysis (PCA) was applied to define which variable(s) were most important for the variability of the analyzed data. Redundancy analysis (RDA) was applied to relate the influence of the explanatory variable or variable to the biological indicators in the soil. The microbial (qMic), metabolic (qCO2), and mineralization (qM) quotients were also analyzed. In addition, soil health was assessed using a combination of the Comprehensive Assessment of Soil Health (CASH) approach and the four-quadrant model (4QM). Multivariate analyses showed that there is variability in management within each orchard, which hindered the verification of the first hypothesis. PH correction management proved to be important, especially with variables associated with fertility, such as Ca, CEC and base saturation. The biological indicators TOC and RB stood out more than the other chemical and physical variables. TOC and BETA positively correlated with most macro and micronutrients and CEC, showing their influence on nutrient cycling and fertility processes. In addition, TOC, RB and MBC were shown to be influenced by soil type and management practices. Orchards in sandier soils and with non-conservationist management have lower TOC, RB and MBC, reflecting loss of fertility and lower soil dynamism. Likewise, the highest quotient values were in orchards with cover crop management, agroforestry system and animal grazing, and this input of organic residues influenced the greater efficiency of microorganisms in transforming organic matter into nutrients available in the soil. The integration of the CASH and 4QM methodologies was efficient in assessing soil health in orchards. Organic, agroforestry and cover crop systems showed greater soil health, confirming the second hypothesis of the study. In addition, the analysis indicated soils in the process of degradation that require management review.