Variabilidade espacial da qualidade físico-hídrica do solo de um sistema em produção agroecológica

Abstract

The knowledge of physical hydric soil quality indicators is crucial during planning and management of agriculture activities. Many articles had been written to identify and to correlate the physical hydric soil quality and crop production. However, the most part of the results are not reliable for mapping spatial variability, mainly in large areas. The objective of this study was to evaluate the feasibility of some indicators to map physical hydrical quality of soils in a research area with agroecological production system (SIPA). The study site was located in the municipality of Seropédica, Rio de Janeiro State, Brazil. It has an area of 6.24 hectares, with coverage of pasture and a rotation of crops in a small plot system. A regular square grid was applied for soil sampling and measurement of the following physical hydrical attributes, at 0.0 to 0.30m soil depth: Available water capacity (AWC), aeration porosity (AP), penetration resistance (PR), and water soil infiltration rate (WSIR). In each grid point, UTM coordinates and altitudes were determined using DGPS equipment. Undisturbed soil samples, at 0.0-0.10, 0.10- 0.20 and 0.20-0.30m soil depth, were collected to analyze water retention at 10kPa (FC - Field Capacity), 80kPa (limit of tensiometer reading) and 1500kPa (PWP - Permanent Wilting Point), soil bulk and particle density, and soil texture. From the moisture retention data it was estimated AWC (AWC = ?CC-?80kPa), the total porosity from soil densities (TP = p s r r 1- ), and the aeration porosity from total porosity and field capacity (AP = TP-FC). The WSIR was determined using a Permeameter IAC (Guelph modified), and the PR with a penectrometer of impact (Planalsucar model). The geoestatistics evaluation of spatial dependence of AWC, AP, PR and WSIR indicators, as well as the interpolation by ordinary krigging, was performed by the GEOESTA software. The spatial variability maps of the indicators were stored in a Geographic Information System (GIS), where the map classes were organized into: suitable, not restricted, and restricted for plant development. Thereafter, the maps were overlaid to generate the soil physical hydrical quality map. In general, all soil physical hydrical attributes presented significant correlation with altitude and clay and sand content, and also showed spatial dependence. The semivariograms varied in relation to the best fit model, Gaussian to altitude and clay content, spherical to AWC and AP, and exponential model to PR and WSIR. The integration in the GIS of the indicators AWC, AP, PR and WSIR showed to be technically reliable. Thus, this procedure may be used to map spatial variability of soil physical hydrical quality and also to detect the areas most vulnerable to physical degradation.