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

Abstract

Waters of poor quality are often used to irrigate crops in arid and semiarid regions, including the Fars Province of southwest Iran. The UNSATCHEM model was first calibrated and validated using field data that were collected to evaluate the use of saline water for the wheat crop. The calibrated and validated model was then employed to study different aspects of the salinization process and the impact of rainfall. The effects of irrigation water quality on the salinization process were evaluated using model simulations, in which irrigation waters of different salinity were used. The salinization process under different practices of conjunctive water use was also studied using simulations. Different practices were evaluated and ranked on the basis of temporal changes in rootzone salinity, which were compared with respect to the sensitivity of wheat to salinity. This ranking was then verified using published field studies evaluating wheat yield data for different practices of conjunctive water use. Next, the effects of the water application rate on the soil salt balance were studied using the UNSATCHEM simulations. The salt balance was affected by the quantity of applied irrigation water and precipitation/dissolution reactions. The results suggested that the less irrigation water is used, the more salts (calcite and gypsum) precipitate from the soil solution. Finally, the model was used to evaluate how the electrical conductivity of irrigation water affects the wheat production while taking into account annual rainfall and its distribution throughout the year. The maximum salinity of the irrigation water supply, which can be safely used in the long term (33 years) without impairing the wheat production, was determined to be 6 dS m -1 . Rainfall distribution also plays a major role in determining seasonal soil salinity of the root zone. Winter-concentrated rainfall is more effective in reducing salinity than a similar amount of rainfall distributed throughout autumn, winter, and spring seasons.

Cyclic use of saline and non-saline water to increase water use efficiency and soil sustainability on drip irrigated maize in a semi-arid region

“…No significant increase in soil salinity was observed under fresh water application. Rasouli et al (2013) evaluated the effects of saline water irrigation in wheat-cultivated lands in Iran. The study revealed that rainfall distribution played a key role in creation of soil salinity profile during the growing season, and off-season winter rainfall was more effective in salt leaching than a similar amount of rainfall distributed throughout winter, spring, and autumn seasons.…”

Modeling the effects of different irrigation water salinity on soil water movement, uptake and multicomponent solute transport

“…is attributed to significant leaching of Ca 2+ and Mg 2+ from the surface layer and continuous desorption of exchangeable Na + . Rasouli et al (2013) used model UNSATCHEM to predict EC sw in a field experiment with winter wheat and varying irrigation water salinities. They obtained RMSE values that ranged from 0.52 to 1.01 dSm -1 and from 1.60 to 2.13 dSm -1 for the validation period, with irrigation water salinities of 6.5 and 11.5 dSm -1 , respectively.…”

“…Adoption of suitable salinity control measures requires determination of salt and water movement through the soil profile and prediction of crop response to soil water and soil salinity, subject to various climatic, soil and agronomic factors (Rasouli et al, 2013). Mathematical models that consider and integrate various climatic, crop, and edaphic factors have been suggested as useful tools for assessing the best management practices for saline conditions (Gonçalves et al, 2006;Ramos et al, 2011).…”

Simulation of root water uptake under combined soil moisture and salinity stress

“…The flow to individual roots is ignored and the overall root system is assumed to extract water from each point of the root zone. While the complete insight into the physical process of root water uptake was not required and therefore the determination of soil and plant parameters were more empirical (Feddes, 1988;Zhuang et al, 2001, Lekakis et al, 2011;Rasouli et al, 2013).…”