Diagnóstico da fertilidade do solo e do nível tecnológico de propriedades rurais no Triângulo Mineiro e Alto Paranaíba

Abstract

Triângulo Mineiro and Alto Paranaíba mesoregion (TMAP) is an important agricultural area in Minas Gerais State, Brazil, totally located in Cerrado biome. Currently, the majority of Brazilian agriculture is concentrated on Cerrado soils. These soils are highly weathered, leached and poor. Thus, the soil fertility management is crucial for exploration of the Cerrado. This work aimed to evaluate the soil fertility properties of 126 agricultural areas in TMAP region under different land uses and compare to native cerrado. Also, we assessed the farm level technology and the technical assistance for farmers to establish relationships with adoption of the best management practices and soil fertility properties. In each farm, topsoil samples (0-20 cm) were used to determine the following properties: pH; exchangeable Al, Ca, Mg and K; available P, B, Fe, Cu, Mn and Zn; organic matter; and cation exchange capacity. These soil properties were determined by conventional laboratory methods. Additionally, the same soil samples were characterized using a portable X-ray fluorescence spectrometer (pXRF). The pXRF results were correlated to conventional methods and used to obtain prediction models to estimate soil properties. Also, potential environmental pollutants were assessed via pXRF. Based on technologies available and adopted by farmers a technological development index (TDI) was calculated and the farm-level technology (high, medium, low and very low) was determined. In general, the soil acidity and Al3+ presence in agricultural soils were ameliorated due to liming practices. However, satisfactory contents of Ca and Mg were not observed. Increasing the soil organic matter is still a challenge. As a consequence, the cation exchange capacity remains low or medium. Satisfactory contents of micronutrients Fe, Cu, and mainly Zn and Mn were observed. Conversely, a generalized deficiency of B was detected, except in coffee areas. The adoption of best management practices was strong related to the economical level of farmers (farmer-employer or smallholders). Most of the TMAP farmers were classified at a medium and low technology level. In general, as the technological level decreases the adoption of best management practices and technical assistance for farmers reduce. As a consequence, the best soil fertility conditions were observed in high level farmers. The pXRF technology demonstrated to be a useful tool for fast chemical characterization of Cerrado agricultural soils. The total elemental contents obtained via pXRF corroborated the known mineral composition and geochemistry of Cerrado soils. Based exclusively on pXRF data the clay content was successfully predicted. Also, the available forms of P, Ca, Mn and Cu (and to some extent soil organic matter) were successfully predicted from pXRF results.