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Title: Evaluation of soil salinity leaching requirement guidelines

Author
item LETEY, JOHN - University Of California
item HOFFMAN, G - University Of Nebraska
item HOPMANS, J - University Of California
item GRATTAN, S - University Of California
item Suarez, Donald
item Corwin, Dennis
item OSTER, J - University Of California
item WU, L - University Of California
item AMRHEIM, C - University Of California

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2010
Publication Date: 3/1/2011
Citation: Letey, J., Hoffman, G.J., Hopmans, J.W., Grattan, S.R., Suarez, D.L., Corwin, D.L., Oster, J.D., Wu, L., Amrheim, C. 2011. Evaluation of soil salinity leaching requirement guidelines. Agricultural Water Management. 98:502–506.

Interpretive Summary: To prevent the deleterious buildup of salts in the root zone of crops, additional water beyond that needed by the plant is required to leach salts from the soil profile. The leaching requirement (LR) is a concept that establishes the minimum amount of water that is needed to remove salts from the root zone and yet maintain crop productivity at a high level. In the past, the means of estimating the LR was based on a set of conditions, referred to as steady state conditions, which rarely actually exist in the real world. The real world is more dynamic and transient state conditions predominate. 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 LR based on steady-state analyses need to be revised. The workgroup concludes that the present guidelines over estimate the leaching requirement and the negative consequences of irrigating with saline waters. This finding is of particular value to water resource management agencies, irrigation district managers, and farmers with limited water supplies since it reduces the recommended volume of water necessary to leach salts to maintain crop yield. Concomitantly, drainage volumes are reduced.

Technical 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 over estimate the leaching requirement and the negative consequences of irrigating with saline waters. This error is particularly large at low leaching fractions. This is a fortuitist finding because irrigating to achieve low leaching fractions provides a more efficient use of limited water supplies.