Evaluation of soil salinity leaching requirement guidelines

Abstract

Water for irrigation is a major limitation to agricultural production in many parts of the world. Use of waters with elevated levels of salinity is one likely option to meet the supply of increased demands. The sources of these waters include drainage water generated by irrigated agriculture, municipal wastewater, and poor quality groundwater. Soil salinity leaching requirements that were established several decades ago were based on steady-state conditions. Recently transient-state models have been developed that potentially can more correctly predict the dynamics of the chemical-physical-biological interactions in an agricultural system. The University of California Center for Water Resources appointed a workgroup to review the development of steady-state analyses and transient-state models, and to determine whether the current recommended guidelines for leaching requirement based on steady-state analyses need to be revised. The workgroup concludes that the present guidelines overestimate the leaching requirement and the negative consequences of irrigating with saline waters. This error is particularly large at low leaching fractions. This is a fortuitous finding because irrigating to achieve low leaching fractions provides a more efficient use of limited water supplies.

Modeling the effects of saline water use in wheat-cultivated lands using the UNSATCHEM model

“…These results suggest that consideration of rainfall would produce lower leaching requirements or higher permissible EC iw , thus allowing farmers to use either less irrigation water or water with lower quality (Letey et al 2011;Isidoro and Grattan 2011). Data collected from the wheat-cultivated land of the Fars Province indicate that the average wheat yield increases by about 900 kg ha -1 in those years, for which annual rainfall is 50 % above its long-term mean (Cheraghi and Rasouli 2008).…”

“…Steady-state and transient water flow and solute transport models are the two main classes of currently available models for the assessment of salinity management. Steadystate models, which assume steady-state water flow through the soil profile and constant soil solution concentrations at any point of the root zone at all times, are not suitable for irrigated lands under saline conditions (Letey and Feng 2007;Corwin et al 2007;Letey et al 2011). A large number of transient flow and transport models, including UNSATCHEM (Š imůnek et al 1996), SWAP (van Dam et al 1997), HYDRUS-1D (Šimůnek et al 2008), and HYSWASOR (Dirksen et al 1993), among many others, have been developed to simulate integrated effects of climate, soil, and plants.…”

A Site-sPecific Agricultural water Requirement and footprint Estimator (SPARE:WATER 1.0)

“…Recently, Letey et al (2011) and Corwin et al (2007) reviewed steady-state and transient models. In general, transient models (Corwin and Waggoner, 1991;Simunek and Suarez, 1993) are very complex, aiming at capturing physical and chemical processes, and thus require a large amount of input parameter.…”

Soil, Water and Crop Management for Agricultural Profitability and Natural Resources Protection in Salt-Threatened Irrigated Lands

“…Transient-state models calculate lower soil salinities than steady-state models (Corwin et al, 2007). This fact makes the leaching requirements calculated with transient-state models to be lower than the leaching requirements calculated with steady-state models (Corwin et al, 2007;Letey et al, 2011). The implementation of the time variable as simple monthly steps in the SALTIRSOIL_M model has suffice to have soil salinities very similar to those calculated with other more complex and data-demanding transient-state models.…”