Uma abordagem teórico-metodológica da capacidade de campo

Abstract

Field capacity is one of the most cited soil physical quantities, being relevant for the management of agricultural systems. In the search for alternatives to the estimation of field capacity, several researchers have proposed methods based on dynamic and static criteria. The evaluation of these methods in a range of textural classes of soils is of paramount importance for more frequent uses prospects. Considering the hypotheses that The field capacity for a particular soil textural class is exclusively associated with an equivalent pore diameter, the D-threshold, which separates the structural and textural porosities, That the inverse modeling of water redistribution, because it is based on physical processes, accurately simulates the water dynamics in the soil and, therefore, also does it for field capacity of the soil in situ, the objectives of this study were: 1) estimate the equivalent pore diameter (D-threshold) that defines the field capacity in each textural class of soil in situ and, with the change of bulk density, from changes in its water characteristic curve; 2) estimate the moisture in the field capacity in each textural class of soil in situ and with the change in bulk density, from changes in its water characteristic curve; 3) estimate the moisture in the field capacity in each soil textural class from inverse modeling. For purposes of obtaining the moisture corresponding to the field capacity in situ, experiments were carried out with instantaneous profile in five soil textural classes. For estimating the field capacity and the D-threshold based on the change in pore volume, soil water characteristic curve considering two situations: before and after compaction. The simulation of water dynamics through Hydrus-1D, to obtain the moisture corresponding to the field capacity occurred with the measured values of matric potential in situ. Correlation and regression analyzes were performed and Student's t-test (at 5% significance) was applied to compare the D-threshold values and the parameters of the van Genuchten model (s, r, α e n) obtained by the field methods and the change in pore volume. The moisture data corresponding to the field capacity were analyzed in a completely randomized design with three treatments (field method, change in pore volume and the inverse modeling method) and five replicates. For the comparison of means the Dunnett test was applied at 5% significance considering the field method as the control. It was concluded that: 1) the moisture in the field capacity in each soil textural class is not exclusively associated with a single equivalent pore diameter, the D-threshold, not confirming the hypothesis assumed in this research; 2) the inverse modeling accurately estimates the moisture in the field capacity regardless of the textural class of soil and 3) the protocols that are based on soil water dynamics should preferably be used for the estimation of field capacity over methods based on static criteria.