Teores de Fe, Mn, Zn e Cu em solos e cana-de-açúcar : reserva, disponibilidade e concentração na planta

Abstract

The potential of micronutrient fertilization for sugarcane in Northeast Brazil may be underestimated due to the limited data on the available and reserve concentrations of these elements in soils. In this context, the objective of this work was to determine the available and potentially available concentrations of Fe, Mn, Zn and Cu in soils and the nutritional status of sugarcane in plantations in Pernambuco and Paraíba states. We sampled 56 sites distributed in three predominant geological contexts: igneous-sedimentary basin; clay-sandy sediments and gnaissic-migmatitic complex. Samples were selected according to vinasse application (with and without) and soil variability. At each site, 10 single samples were taken at two depths (0.0-0.2 and 0.2-0.4 m) to form a sample composed of each depth. For plant sampling, leaf +3 was collected in 10 plants per area to form the composite sample, in plants at the fifth month of age. Soil micronutrients were evaluated for the potential reserve by the 3051a method and the availability by the Mehlich-1 method. The Fe, Mn, Zn and Cu contents were also determined in the leaves. The results were evaluated by descriptive and multivariate statistics. On average, 70% of the soils presented levels of Fe and Zn available above 30 mg kg-1 and 1.5 mg kg-1, respectively. Soils developed in the clay-sandy sediment environment had low Mn availability, with 67% of the samples presenting Mn concentrations below 6 mg kg-1. Except for soils of the igneous-sedimentary basin, low Cu availability was verified in the studied soils. About 50% of the samples had levels below 0.8 mg kg-1 of Cu. No significant difference was identified in the micronutrients levels according to the management of fertilization (with and without vinasse). The plants presented adequate levels of Fe and Cu whereas the Mn and Zn leaf contents were below adequate. The Mn and Zn presented greater potential of response to the fertilization of sugarcane. Most of the soils presented lower Fe, Mn, Zn and Cu than the reference soils in the study region, indicating that there is a reduction of these micronutrients in soils cultivated with sugarcane. There is a great variation of the micronutrient reserve contents in the studied soils, mainly for Mn.