Modelling the effects of saline water use in agriculture (original) (raw)
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Modeling the effects of saline water use in wheat-cultivated lands using the UNSATCHEM model
Irrigation Science, 2012
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. Communicated by J. Ayars.
A dynamic model of salinization on irrigated lands
Ecological Modelling, 2001
A dynamic simulation model of salt accumulation on irrigated lands is presented. The original version of the model is part of a large-scale socio-economic model of irrigation-based regional development. The model introduced in this paper is a systemic one in the sense that it integrates four major sub-processes of rootzone salinization: irrigation, drainage, groundwater discharge and groundwater intrusion. It provides a comprehensive and general description of the long-term process of salt accumulation in lowlands under continuous irrigation practice, where irrigated lands are annually increased. Analysis of the model and simulation results reveal, under what conditions the salinity reaches alarming levels and with what strategies it can be controlled. For instance, in situations where the mixing of drainage water into irrigation water supplies is high, rootzone salinity quickly reaches alarming levels. More importantly, in this setting, the typical strategy of increasing the drainage in order to control the salinity level yields unprecedented exponentially growing salinity levels, a catastrophic result for the agriculture. The model structure can represent the basin wide salinization process on different geographical settings in agricultural development. In general, the model provides an experimental simulation platform, which can be used by the policy makers in the long term strategic management of large scale irrigation development projects. The model can also be of interest to the students and learners in teaching and research, in the related fields of environmental sciences.
2014
Irrigated agriculture faces serious problems of soil salinization in the arid and semi-arid regions of the world. Tunisian saline soils occupy about 25% of the total irrigated area. In this study, the irrigated area of "Diyar El Hujjaj" in Tunisia was considered when sea water intrusion and a salinisation of the aquifer were observed. As a result, many pumping wells and farms have been abandoned. An expensive surface fresh water transfer from more than 100 Km was done and a mixture between aquifer salty water and surface water is common practice. In this paper, SaltMod model was used to simulate and analyze the soil salinity evolution under several water management scenarios. The first one was a new practice (simultaneously growth of strawberry and pepper). The others concerned the soil salinity evolution under crops rotation compounded by irrigated high value crops, fallow and rainfed crops using an alternative water supply options: groundwater, surface water and a mixture of surface water and groundwater. Results show that in using only groundwater, simulated soil salinity reaches its peak of about 12 dS m-1 when average salinity as high as 9 dS m-1 was recorded, and then decreases significantly to a level of 2 dS/m when surface water is applied. However these conditions are not usually met in the study area conditions as the crop water requirement is fairly difficult to be satisfied by surface water irrigation. The new farming practices option using mixture of surface and groundwater could be sufficient to keep soil within an acceptable range of salinity level of about 2.5 dS/m and 5 dS/m during the first and the second year respectively. Under the case study conditions, using the mixture of groundwater and surface water could be a viable alternative for irrigation with an agriculture practices including crops rotation, fallow and/or rainfed crops. Thus, to assure the agricultural success in areas at high risk of salinity, it appears indispensable to control the economical factors relating to the interaction between land attribution and irrigated area management and study the feasibility of the water desalination for agriculture particularly for crops of high added value.
Optimisation of agricultural water management in arid and semi-arid regions requires the availability of watersalinity crop production functions. A two-year experiment was conducted in the northern Golestan province of Iran to assess the water-salinity production function of wheat. The treatments in the experiment consisted of four levels of irrigation water, i.e. 50 (W1), 75 (W2), 100 (W3) and 125 (W4) % of crop water requirement, and four levels of water salinity, respectively 1.5 (S1), 8.5 (S2), 11.5 (S3) and 14.2 (S4) dS m À1 . The plots were arranged in a randomised complete block design with three replications and water quantity as main plot treatment and water quality as subplot treatment. The data were analysed using linear, quadratic, Cobb-Douglas and transcendental functions, complemented with an economic analysis. The results indicate that for the given climate-soil conditions, transcendental functions best predict wheat yield under both water and salinity stress conditions. Yield reduction caused by a unit increase of matric potential is found to be larger than that caused by a unit increase of osmotic potential. The marginal rate of technical substitution indicates that each one of the two factors studied, namely soil salinity and water supply, can be substituted with the other in a wide range in order to achieve equal amount of yield.
SALTIRSOIL (SALTs in Irrigation SOILs) is a soil salinisation model able to make accurate predictions of soil salinity, sodicity and alkalinity at soil water saturation using no more information than that obtained during most regular land surveys. It is a deterministic, static and functional (capacity-type) process-based model composed in turn of two main modules. The first one calculates the soil water balance through the year, and hence the soil solution concentration factor with regard to the irrigation water. Next, the irrigation water major ion composition is multiplied by this factor and then, the second module, called SALSOLCHEM, calculates the major inorganic ion composition of the soil solution at equilibrium with soil calcite and gypsum at the soil CO 2 partial pressure. The SALTIRSOIL algorithms were verified by simulating two horticultural crop developments in a fine to medium texture heavily calcareous soil under a semi-arid Mediterranean climate. The quotients of elect...
SIMULATION OF SOIL WATER AND SALINITY DISTRIBUTION UNDER SURFACE DRIP IRRIGATION
Irrigation and Drainage, 2013
Higher crop production and better water use efficiency are usually achieved with surface drip irrigation as compared to traditional surface irrigation methods. Increasing competition for fresh water also means a greater use of brackish water in agriculture. For this reason, the effects of soil hydraulic properties, initial soil moisture content (θ i ), and irrigation regime on soil water and salinity distribution under surface drip irrigation (DI) with brackish irrigation water were investigated. Model simulations were performed using the HYDRUS-2D/3D model assuming tomato crop in saline soil. Simulation scenarios were conducted including sand, loamy sand, and sandy loam soils, together with daily and alternate-day irrigation regimes. Two θ i values were considered in the simulations. Results revealed that the effect of the irrigation regime on wetting patterns differed according to the soil's hydraulic properties, while the effect of the initial soil moisture content disappeared after a few days. The irrigation regime and θ i value did not display any significant effect on soil salinity distribution. Higher soil salinity occurred along the soil surface by the end of the simulation period. The higher soil salinity was more close to the emitter in sand as compared to loamy sand and sandy loam. Water balance calculations showed that as the initial soil moisture content increased, the free drainage component increased. However, the irrigation regime and initial soil moisture content did not affect the evaporation rate and root water uptake rate. RÉSUMÉ L'augmentation de la production agricole et la meilleure efficacité de l'utilisation de l'eau sont habituellement obtenus avec l'irrigation goutte à goutte comparé aux méthodes traditionnelles d'irrigation de surface. La demande croissante pour l'eau douce implique une plus grande utilisation des eaux saumâtres en agriculture. Pour ces raisons, nous avons étudié l'impact des propriétés hydrauliques du sol, humidité initiale du sol (θ i ) et le régime de l'irrigation sur l'eau du sol et la distribution de la salinité sous irrigation goutte à goutte (DI) avec une eau saumâtre. En supposant que les sols salins sont cultivés en tomate, des modèles de simulations ont été réalisés en utilisant HYDRUS-2D/3D. Les scénarios de simulation ont été effectués pour des fréquences d'irrigations journalières et un jour sur deux et ce sur des sols sableux, sablo-limoneux et limono-sableux. Deux valeurs de θ i ont été prises en compte dans les simulations réalisées. Les résultats ont révélé que les effets du régime d'irrigation sur le mode d'humidification du sol diffèrent selon les propriétés hydrauliques du sol, alors que l'impact de la teneur en eau initiale du sol n'a plus lieu après quelques jours. Le régime d'irrigation et la valeur de θ i n'ont pas d'effet significatif sur la distribution de la salinité des sols. La salinité élevée du sol est observée à la surface du sol à la fin de la période de simulation. La salinité élevée du sol était plus proche de l'émetteur dans le sol sableux que dans le cas des sols sablo-limoneux et limono-sableux. Les calculs du bilan hydrique ont montré que l'augmentation de l'humidité initiale du sol engendre une augmentation de l'eau drainée. Cependant, le régime d'irrigation et l'humidité initial du sol n'ont pas d'effet sur le taux d'évaporation et d'absorption de l'eau par les racinaires.
Evaluating salinity distribution in soil irrigated with saline water in arid regions
In arid and semi-arid regions, salinity is a serious and chronic problem for agriculture. A 3-year field experiment in the arid environment of Xinjiang, northwest China, was conducted to study the salinity change in soil resulting from deficit irrigation of cotton with non-saline, moderate saline and high saline water. The salinity profile distribution was also evaluated by an integrated water, salinity, and nitrogen model, ENVIRO-GRO. The simulated and observed salinity distributions matched well. Results indicated that after 3 years of cotton production, the average salinity in the 1.0-m soil profile was 336% and 547% of the original soil profile, respectively, for moderate saline and high saline water irrigation. If the practices continued, the average soil salinity (EC e ) in the 1.0-m soil profile would approach a steady level of 1.7, 10.8, and 14.7 dS m −1 , respectively, for the treatments receiving irrigation waters of 0.33, 3.62, and 6.71 dS m −1 . It was concluded that deficit irrigation of saline water in this region was not sustainable. Model simulation showed that a big flood irrigation after harvest can significantly reduce the salt accumulation in the soil profile, and that this practice was much more efficient for salinity control than applying the same extra amount of water during the growing season.
Water, 2020
In Tunisia, water used for irrigation is often saline, increasing the risk of salinization for soils and crops. In this study, an experiment was conducted on a tomato crop cultivated on a silty-clay soil irrigated with three different water qualities: 0, 3.5, and 7 dS•m −1. Experimental data were then used to calibrate and validate the Hydrus-1D model, which simulates water flow and salt transfer in soils. The successfully-calibrated and validated model was then used to study the combined effects of the soil osmotic and soil matrix potentials on root water uptake. The values of the root mean square error (RMSE), the coefficient of determination (CD), the modeling efficiency (EF), and the coefficient of residual mass (CRM) were close to their optimal values for both soil water content and soil electrical conductivity profiles, indicating the reliability of the model to reproduce water and salt dynamics. Relative yields (Y r), indirectly estimated using actual and potential root water uptake (transpiration), indicated that the multiplicative stress response model (using the S-shape model) satisfactorily simulates measured yields and reproduces the effects of irrigation with saline waters on crop yields. An alternative scenario using a reduction of water requirements by 50% was investigated to assess an irrigation method with considerable water savings. As the results show that relative yields, Y r , were only slightly reduced, the crop water requirements estimated by CROPWAT 8.0 must have been overestimated. The variation of the soil salinity in the root zone highlighted a high salinization risk in the short-term when water of 7 dS•m −1 is used for irrigation.
Revista de Ciências Agrárias, 2020
The control and mitigation of soil salinization and/or sodicization phenomena are considered one of the main challenges of irrigated agriculture. In Portugal, Leziria Grande of Vila Franca de Xira its a region with increased salinization and/or sodicization risks due to its costal location with tidal influence. The aim of this study was to evaluate soil water and salt dynamics in a irrigated Fluvisol with a crop rotation of maize and annual ryegrass, and to predict irrigation-induced risks of soil salinization. We first calibrated the Hydrus 1D model for predicting soil water flow and solute transport with observed field data, afterwards we predict future risks of soil salinization performing a scenario analyses considering irrigation with different water qualities (ECw of 1.5, 3 and 5 dS m-1). We observed that when the ECw increases to values of 5 dS m-1, the average solute concentration in the root zone rises to levels above the threshold tolerated by maize. Hydrus 1D successfully...