The Experts below are selected from a list of 1989 Experts worldwide ranked by ideXlab platform
Dennis L Corwin - One of the best experts on this subject based on the ideXlab platform.
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evaluation of soil salinity Leaching Requirement guidelines
Agricultural Water Management, 2011Co-Authors: J Letey, Glenn J Hoffman, Jan W Hopmans, Stephen R Grattan, Donald L Suarez, Dennis L Corwin, J D Oster, Christopher AmrheinAbstract: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.
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Leaching Requirement for soil salinity control steady state versus transient models
Agricultural Water Management, 2007Co-Authors: Dennis L Corwin, J D Rhoades, J SimunekAbstract:Water scarcity and increased frequency of drought conditions, resulting from erratic weather attributable to climatic change or alterations in historical weather patterns, have caused greater scrutiny of irrigated agriculture’s demand on water resources. The traditional guidelines for the calculation of the crop-specific Leaching Requirement (LR) of irrigated soils have fallen under the microscope of scrutiny and criticism because the commonly used traditional method is believed to erroneously estimate LR due to its assumption of steady-state flow and disregard for processes such as salt precipitation and preferential flow. An over-estimation of the LR would result in the application of excessive amounts of irrigation water and increased salt loads in drainage systems, which can detrimentally impact the environment and reduce water supplies. The objectives of this study are (i) to evaluate the appropriateness of the traditional steady-state method for estimating LR in comparison to the transient method and (ii) to discuss the implications these findings could have on irrigation guidelines and recommendations, particularly with respect to California’s Imperial Valley. Steady-state models for calculating LR including the traditional model, which is an extension of the original U.S. Salinity Laboratory LR model, WATSUIT model, and water-production-function model were compared to transient models including TETrans and UNSATCHEM. The calculated LR was lower when determined using a transient approach than when using a steady-state approach. Transient conditions and the influence of preferential flow did not have as significant an effect on lowering the LR as salt precipitation for a representative study of the Imperial Valley using Colorado River water (EC = 1.23 dS/m) for irrigation. A valley-wide LR of 0.08 for a crop rotation of alfalfa/ alfalfa/alfalfa/alfalfa/wheat/lettuce, as calculated by both WATSUIT and UNSATCHEM, was concluded to be the most reasonable estimate for the entire Imperial Valley as compared to a LR of 0.13 by the commonly used traditional method. The reduced LR for the Imperial Valley would result in a diminished drainage volume of approximately 1.23 � 10 8 m 3 (i.e., 100,000 ac-ft). The most significant conclusion derived from the comparison is that the use of the traditional steady-state model for estimating LR needs to be reevaluated.
Christopher Amrhein - One of the best experts on this subject based on the ideXlab platform.
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evaluation of soil salinity Leaching Requirement guidelines
Agricultural Water Management, 2011Co-Authors: J Letey, Glenn J Hoffman, Jan W Hopmans, Stephen R Grattan, Donald L Suarez, Dennis L Corwin, J D Oster, Christopher AmrheinAbstract: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.
J Simunek - One of the best experts on this subject based on the ideXlab platform.
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Leaching Requirement for soil salinity control steady state versus transient models
Agricultural Water Management, 2007Co-Authors: Dennis L Corwin, J D Rhoades, J SimunekAbstract:Water scarcity and increased frequency of drought conditions, resulting from erratic weather attributable to climatic change or alterations in historical weather patterns, have caused greater scrutiny of irrigated agriculture’s demand on water resources. The traditional guidelines for the calculation of the crop-specific Leaching Requirement (LR) of irrigated soils have fallen under the microscope of scrutiny and criticism because the commonly used traditional method is believed to erroneously estimate LR due to its assumption of steady-state flow and disregard for processes such as salt precipitation and preferential flow. An over-estimation of the LR would result in the application of excessive amounts of irrigation water and increased salt loads in drainage systems, which can detrimentally impact the environment and reduce water supplies. The objectives of this study are (i) to evaluate the appropriateness of the traditional steady-state method for estimating LR in comparison to the transient method and (ii) to discuss the implications these findings could have on irrigation guidelines and recommendations, particularly with respect to California’s Imperial Valley. Steady-state models for calculating LR including the traditional model, which is an extension of the original U.S. Salinity Laboratory LR model, WATSUIT model, and water-production-function model were compared to transient models including TETrans and UNSATCHEM. The calculated LR was lower when determined using a transient approach than when using a steady-state approach. Transient conditions and the influence of preferential flow did not have as significant an effect on lowering the LR as salt precipitation for a representative study of the Imperial Valley using Colorado River water (EC = 1.23 dS/m) for irrigation. A valley-wide LR of 0.08 for a crop rotation of alfalfa/ alfalfa/alfalfa/alfalfa/wheat/lettuce, as calculated by both WATSUIT and UNSATCHEM, was concluded to be the most reasonable estimate for the entire Imperial Valley as compared to a LR of 0.13 by the commonly used traditional method. The reduced LR for the Imperial Valley would result in a diminished drainage volume of approximately 1.23 � 10 8 m 3 (i.e., 100,000 ac-ft). The most significant conclusion derived from the comparison is that the use of the traditional steady-state model for estimating LR needs to be reevaluated.
Paramjit Singh Minhas - One of the best experts on this subject based on the ideXlab platform.
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Saline water management for irrigation in India
Agricultural Water Management, 1996Co-Authors: Paramjit Singh MinhasAbstract:Much (32–84%) of the ground water surveyed in different Indian States is rated either saline or alkali. Because of the continental monsoonal climate, the basic principles of saline water management need some adaptation, e.g. providing for a Leaching Requirement is not appropriate when the growing season for post-monsoon winter crops starts with a surface-leached soil profile, because it would increase the salt load. High salinities during the initial stages of growth are particularly harmful. Further, if benefits are to be gained from frequent saline irrigation, the amount of water applied per irrigation needs to be reduced. This is not possible with most widely practiced surface irrigation methods, but can be achieved with sprinkler and drip methods. However, in India the large-scale use of such systems is not yet technically or economically feasible. Another management goal is simultaneously to encourage the utilisation of carried over rainwater in the soil profile/shallow watertables. Tolerance limits of crops to the use of saline water in different agro-ecological regions of India are available, and have been observed to vary with soil type, rainfall and anionic/cationic constituents of salinity. Multi-location trials on the appropriate use of saline and non-saline water reveal the benefits of irrigating with non-saline canal water during the initial stages of growth, as well as cycles of saline and non-saline water during the pre-sowing irrigation period. Monsoon-induced salt Leaching decreases with increasing clay content, SARiw, and is enhanced with increasing chloride salinity. Additional doses of phosphorous to alleviate the effects of chloride toxicity, and the use of organic materials to enhance the efficiency of applied nitrogen are recommended under saline-irrigated conditions. Contrary to the general belief that soils irrigated with high-SAR saline water may regain their infiltration capacity when the electrolytic concentration of ingoing water is greater than the flocculation value, irreversible reductions are induced under cyclic saline-rainwater infiltration where sub-soil layers, ingressed with clays from the plough layer, control steady intake rates. Thus, the use of gypsum (SARiw > 20) is advocated. Gypsum is also needed for soils irrigated with saline water with an Mg:Ca ratio > 3 and rich in silica. Other cultural practices, such as furrow planting, increasing the plant density and post-seeding irrigation in crops like mustard, also prove useful. Water-quality standards which were too conservative have been replaced by site-specific guidelines where factors such as soil texture, rainfall and crop tolerance have been given due consideration.
J Letey - One of the best experts on this subject based on the ideXlab platform.
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evaluation of soil salinity Leaching Requirement guidelines
Agricultural Water Management, 2011Co-Authors: J Letey, Glenn J Hoffman, Jan W Hopmans, Stephen R Grattan, Donald L Suarez, Dennis L Corwin, J D Oster, Christopher AmrheinAbstract: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.