Estimation of water retention and availability in soils of Rio Grande do Sul

José Miguel Reichert,Reimar Carlesso,Dalvan José Reinert,Douglas Rodrigo Kaiser,Jackson Adriano Albuquerque,Felipe Lavarda Urach

doi:10.1590/s0100-06832009000600004

Abstract

Dispersed information on water retention and availability in soils may be compiled in databases to generate pedotransfer functions. The objectives of this study were: to generate pedotransfer functions to estimate soil water retention based on easily measurable soil properties; to evaluate the efficiency of existing pedotransfer functions for different geographical regions for the estimation of water retention in soils of Rio Grande do Sul (RS); and to estimate plant-available water capacity based on soil particle-size distribution. Two databases were set up for soil properties, including water retention: one based on literature data (725 entries) and the other with soil data from an irrigation scheduling and management system (239 entries). From the literature database, pedotransfer functions were generated, nine pedofunctions available in the literature were evaluated and the plant-available water capacity was calculated. The coefficient of determination of some pedotransfer functions ranged from 0.56 to 0.66. Pedotransfer functions generated based on soils from other regions were not appropriate for estimating the water retention for RS soils. The plant-available water content varied with soil texture classes, from 0.089 kg kg-1 for the sand class to 0.191 kg kg-1 for the silty clay class. These variations were more related to sand and silt than to clay content. The soils with a greater silt/clay ratio, which were less weathered and with a greater quantity of smectite clay minerals, had high water retention and plant-available water capacity.

Highlights

Plant-available water in the soil is essential for adequate crop growth and development and depends on the soil properties
The objectives of this study were: to generate pedotransfer functions to estimate soil water retention at different tensions based on measurable soil properties; to evaluate the efficiency of pedotransfer functions generated in other regions for the estimation of water retention in soils of Rio Grande do Sul (RS); and to calculate plant-available water capacity based on soil particle-size distribution of RS soils
Water retention is positively correlated with the clay content (Table 3), because this fraction favors the occurrence of micropores and menisci that generate capillary forces

Summary

Introduction

Plant-available water in the soil is essential for adequate crop growth and development and depends on the soil properties. Plant-available water is measured directly, by the determination of gravimetric soil water content in a laboratory drying-oven or by indirect methods, with equipments such as the neutron probe and reflectometers The accuracy of these methods is good, but they are very time-demanding or require the availability of expensive equipment, creating barriers to a large-scale use. To overcome these difficulties, some researchers have proposed mathematical models to estimate soil water retention (Meng et al, 1987; Arruda et al, 1987; Bell & van Keulen, 1995; van den Berg et al, 1997; Pachepsky & Rawls, 1999; Saxton & Rawls, 2006), known as pedotransfer functions or equations (pedofunctions). Pedotransfer functions may be generated when the particle size distribution, density, porosity and/or mineralogy of the soil are known (Rawls et al, 1991)

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