Abstract
Field capacity (FC) is a fundamental parameter in soil and water engineering and hydrologic modeling. Despite its relevance, the in situ determination of this parameter is not standardized and its determination by indirect methods is dubious. This study presents a method of calculation of in situ FC and its corresponding water suction (hFC), using the van Genuchten equation for water retention and the pedotransfer function by Ottoni Filho et al. (2016) for standardized in situ determination of FC. The methodology was applied to HYBRAS, a database of hydrophysical data for Brazilian soils with 1,075 soil samples from 15 Brazilian states. FC and hFC were confirmed to depend on textural class and pedogenetic origin (weathered and unweathered soils). Our analysis justified why FC must not be determined based only on a single predetermined water suction value. A simplified method is proposed for the management of irrigated soils through the determination of water suction in the root zone and the mode and confidence interval values of hFC corresponding to soil groups formed from textural classes and pedological nature. Various statistical calculations of FC and hFC are presented for these groups.
Highlights
According to the Soil Taxonomy (1975), a soil is characterized by an arrangement of pores formed by inorganic and organic matter that serves as a support to plants in the field
To evaluate the quality of the field capacity (FC) results calculated with Equation 6, we compared the FC measured in situ with the calculated FC of the 77 samples from HYBRAS mentioned in the explanation of Equation 10
The results demonstrated that Equation 6 estimated FC well, since root mean square error (RMSE) = 0.0255 cm3/cm3 (Equation 10) was not high and the Wilcoxon test showed that the measured FC was statistically indistinguishable from the calculated FC (p < 0.05), which indicates the inexistence of an estimation bias
Summary
According to the Soil Taxonomy (1975), a soil is characterized by an arrangement of pores formed by inorganic and organic matter that serves as a support to plants in the field It is an environment capable of having the air of its pores renewed with air from the atmosphere or filled with water. The main objective of its agricultural management is to provide optimum conditions for the development of plants with minimum impact to the environment In this context, the concept of field capacity (FC) was introduced by Veihmeyer and Hendrickson (1931, 1949) as the soil moisture that corresponds to the maximum capacity of the soil to hold water available for use by plants, characterized as the water content stabilized in the soil pores after the soil profile has been drained following an irrigation or rain event. This parameter has been largely used in hydrodynamic and hydrologic models involving soils (Kannan, White, Worral, &Whelan, 2007; Nasta & Romano, 2016; De Jong Van Lier, 2017), as well as in projects of irrigation and drainage systems and in water and soil management in general, including studies of groundwater recharge
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