Disponibilidade de zinco e cobre pelos extratores HCl, MEHLICH-1, MEHLICH-3 e DTPA em solos do Estado da Paraíba

Abstract

Little has been done with the choice of micronutrients extractors in soil of the Paraíba state, prevailing the use of the Mehlich-1 extractor and the adoption of availability classes generated in other regions of the country. Thus, the objective of this work was to evaluate the performance of extractors HCl, Mehlich-1, Mehlich-3 and DTPA at pH 7.3 in the evaluation of the availability of Zn and Cu in representative soils of the State of Paraíba. Two experiments were carried out, one for each micronutrient, with treatments arranged in an 8 x 5 factorial scheme, corresponding to eight soils and five doses of Zn or Cu, in a randomized block design, with three replications. The experimental unit consisted of a plastic pot, containing 1.5 dm3 of soil and two sorghum plants (Sorghum bicolor L.) cv. BRS Ponta Negra. Materials from the subsurface layer of four more weathered soils (Red-Yellow Latosol - LA; Red-Yellow Argisol - PVA; Red Argisol - PV and Regolithic Neosol - RR) and four less weathered soils (Litholic Neosol - RL; Haplic Planosol - SX; Chromic Luvissol - TC and Haplic Vertisol - VX). Doses of 0.0; 1.0; 2.0; 4.0 and 8.0 mg dm-3 of Zn, in the form of zinc sulfate, and 0.0; 1.0; 2.0; 4.0 and 6.0 mg dm-3 of Cu, in the form of copper sulfate. The doses of Zn and Cu were incubated in the soil for fifteen days. In the same period, basic fertilization was carried out for tests in a greenhouse, without zinc and copper, with the other macro and micronutrients. After this incubation period, subsamples of 0.1 dm3 were taken to evaluate the levels of Zn and Cu by the extractors HCl, M-1, M-3 and DTPA, and the remaining soil volume was placed back in the pots for the cultivation of sorghum. At 45 days of cultivation, the production of root dry matter (MSR), shoot (MSPA) and total dry matter (MST) was analyzed, as well as the contents and accumulation of Zn and Cu in the shoots of the plants. The data obtained, analyzed statistically by analysis of variance, regression and correlation, allowed the following conclusions to be drawn: the Zn and Cu recovered by the extractors HCl, M-1, M-3 and DTPA increase linearly with increasing doses of these nutrients applied to soils; with the exception of M-1, there was little influence of the soil's buffering capacity. The extraction capacity of Zn and Cu from soils follows the following decreasing order: M-3 > HCl > M-1 > DTPA. With the exception of VX soil, the extractors HCl, M-1, M-3 and DTPA are highly correlated with each other. With the exception of PV and VX soils (M-3 and DTPA) and SX soil (none of the extractors), the four extractors are adequate to estimate the availability of Zn in the soil; on the other hand, the availability of Cu in soils LA, RR, RL and TC can be adequately evaluated by any of the four extractors, being the same inadequate in soils PVA, PV, SX and VX. The NC of Zn and Cu for extractors HCl, M-1, M-3 and DTPA are 3.4 and 0.95; 3.0 and 0.60; 5.9 and 1.45; 3.0 and 0.75 mg/dm3, respectively; with the exception of DTPA for Cu, there was little influence of the buffer capacity factor on the NC of Zn and Cu in the soils.