ESPACIALIZAÇÃO DE CARACTERÍSTICAS GRANULOMÉTRICAS E QUÍMICAS EM SOLO HIDROMÓRFICO IRRIGADO

Abstract

The understanding of spatial variability of hydromorphic soils used in agriculture contributes to improve its management and a better use of correctives and fertilizers. In this sense, this paper aimed to characterize spatial dependence, spatialize chemical and granulometric attributes, and find the ideal number of samples in hydromorphic soil on surface and subsurface irrigation area in the Luís Alves’s Irrigation Project from Araguaia Municipality, Tocantins State, Brazil. The experiment comprised an area of 1.84 ha, where a soil sampling was collected at depths of 0.0-0.1 and 0.1-0.2 m, in a sample mesh of 10 x 10 m, totaling 432 composed samples, in October 2016. The evaluated attributes were pH in water, H+Al, MOS, Ca, Mg, Al, P, K, CTC, V%, Cu, Fe, Zn, Mn and granulometry. Descriptive statistics mean, median, minimum, maximum, coefficient of variation (CV), standard deviation, asymmetry, kurtosis, Komorogov-Smirnov normality test, and Pearson's correlation were applied. The spatial dependence of the data was initially evaluated using semivariance. The semivariograms were calculated and adjusted to theoretical models and the data were cross-validated. Then, ordinary kriging interpolation was carried out. The area texture was classified as sandy clay loam and loam to 0.0-0.1 and 0.1-0.2 m, respectively. The CV of the attributes ranged from 3.3% for pH (0.0-0.1 m) to 149.07% for Cu (0.1-0.2 m). The P, K, Fe, and Mn elements showed high levels in the studied soil. For all granulometry and chemical attributes evaluated, spatial dependence varied from moderate (24%) to strong (76%). The research data were most adjustable to the Gaussian model (47% of attributes), followed by exponential (29%) and xvi spherical (23%). The Mg, K, Cu, and Mn nutrients show great spatial homogeneity. The ideal number of subsamples for each composite sample was 19 for granulometry and macronutrients in the 0.0-0.1 and 0.1-0.2 m layers, excluding Al, P and K for the last layer, and 28 subsamples for the micronutrients studied for both layers, except Cu and Zn in the layer 0.1-0.2 m. New studies in the area can be carried out using sample grid with sampling space of 20 m, based on the results from the 0.0-0.1 m layer. The northern region differs from the southern region with regard to pH (H2O), Al, H+Al, CTC, and Fe