Abstract
Water retention in soil is used in many agronomic and environmental applications, but its direct measurement is time-consuming and expensive. Therefore, pedotransfer functions (PTFs) are alternatives to obtain this information faster and more economically. The objectives of this study were to generate and validate PTFs to estimate the water content at potentials of -33 kPa (field capacity) and -1500 kPa (permanent wilting point) for different soil classes from the central-south portion of Rio Grande do Sul State. The physical and chemical analyses database from soil surveys of the Celulose Riograndense Corp were used. The database is composed of particle size distribution (coarse and fine sand, silt and clay), soil organic matter, and water content data at the above mentioned potentials, besides other information concerning the behavior of the soil classes at field conditions. Firstly, the data were stratified by soil classes and depths, and then 70% of the data were separated for PTF generation and 30% for validation. PTFs were generated for each specific soil class and also general PTFs which were not stratified by soil class, by means of stepwise multiple regression. In most situations, PTFs for a specific soil class showed a better fit than the general PTFs. Proper adjustment of the data showed that the water retention values at potentials of -33 kPa and -1500 kPa can be estimated for the soils from the central-south portion of Rio Grande do Sul State that do not have such analyses through the use of PTFs.
Highlights
Water retention by soils is used in projects involving water availability for plants, such as irrigation and drainage projects, hydric stress, movement of solutes in the soil etc. (OLIVEIRA et al, 2002, MICHELON et al, 2010; NEBEL et al, 2010)
Examples of pedotransfer functions (PTFs) can be seen in: Balland et al (2008) who proposed equations to estimate the water retention and the hydraulic conductivity from the particle size distribution and organic matter of the soil for a wide variety of soils in Canada; Khodaverdiloo et al (2011) who generated PTFs to estimate the water retention in the soil at various potentials for soils derived from limestone in Iran; and Tomasella et al (2000) who used various soil survey data in Brazil to generate PTFs to predict the water retention parameters of the van Genuchten equation and to estimate the water retention; among other works as in Oliveira et al (2002), and Piedallu et al (2011)
The water content was estimated at potentials of -33 kPa and -1500 kPa, which correspond, respectively, to the water content at field capacity (FC), considered the upper limit of the range of water availability to plants, and the permanent wilting point (PWP), considered the lower limit of water availability to plants (EMBRAPA, 1995)
Summary
Water retention by soils is used in projects involving water availability for plants, such as irrigation and drainage projects, hydric stress, movement of solutes in the soil etc. (OLIVEIRA et al, 2002, MICHELON et al, 2010; NEBEL et al, 2010). Laboratory problems, delays and inaccuracy can often occur (OLIVEIRA et al, 2002). To overcome those difficulties, great efforts have been employed to determine pedotransfer functions (PTFs) for water retention estimative in soils. As in the great majority of the soil surveys (base for this research), the data concerning water retention came from disturbed samples. This aspect and the fact that the entries of data of generated PTFs are different from the ones generated here do not allow comparison of models. There is need to develop PTFs using simpler and cheaper data entry (DASHTAKI et al, 2010) as performed in this work
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