J. D. Rhoades

Use of saline drainage water for irrigation: imperial valley study

Abstract It is contended that there is potential to expand irrigated agriculture through the increased use of saline waters for irrigation. Two kinds of evidence are given to support this contention. Literature is cited to document the successful use of saline waters for irrigation around the world, even when conventional management was employed. Results of a field test are presented to document the feasibility of facilitating the use of saline water for irrigation through the development of new crop/water management strategies and practices.

Intercepting, isolating and reusing drainage waters for irrigation to conserve water and protect water quality

Abstract Theoretical and conceptual evidence is given along with four case examples to show that a loss of usable water occurs in the total water supply when agricultural drainage waters are returned to the water supply, even when blending is carried out such that apparently safe limits of salt concentration are not exceeded in the final mixture. An alternative means of managing agricultural drainage waters is offered that provides a greater practical benefit to be derived from the total water supply than does blending.

Assessing irrigation/drainage/salinity management using spatially referenced salinity measurements

Abstract A unique technology-package for measuring the spatial distributions of salinity in irrigated soils and fields and for evaluating the appropriateness of some related irrigation-, drainage- and salinity control-management practices is described. This assessment technology is based on the use of: (1) geophysical-instrumental systems for intensively measuring bulk soil electrical conductivity and associated spatial coordinates; (2) statistical algorithms for site selection and salinity calibration; and (3) algorithms for data analysis and graphical display to facilitate interpretation. Results are presented to demonstrate some of the utility of the technology. Additionally, examples are given which show that much of the apparent chaos observed in the spatial pattern of soil salinity in irrigated fields is man-induced and related to such management practices as irrigation, drainage, and tillage.

Geostatistical Analysis of a Soil Salinity Data Set

Publisher Summary This chapter presents a typical geostatistical analysis of a data set representative of the diversity and complexity of data sets handled through GIs. There is much more to geographical (spatial) data analysis than performing elementary operations of overlay, merge, and split and then merely mapping data with somewhat arbitrary, eye-pleasing, spline algorithms. The data talk when their geographic interdependence is revealed; there is an essential third component to any two data values taken at two different locations in space or time-their relation is seen as a function of the separation vector linking these two locations. Pictorial and numerical models of patterns of space or time dependence allow us to go far beyond data locations into alternative (stochastic equiprobable) maps that depict the true complexity of the data while always preserving an assessment of uncertainty. This chapter also illustrates the toolbox aspect of geostatistics, presenting several alternative ways to reach the same goal and proposing cross-validation exercises to help the operator in his or her decision.

Production functions relating crop yield, water quality and quantity, soil salinity and drainage volume

Abstract Data from a long-term lysimeter experiment were used to estimate a set of production functions describing relationships between yield, water quantity and quality, soil salinity and drainage volume. The experiment simulated a variety of conditions prevailing in the San Joaquin and Imperial Valleys of California currently suffering salinity and drainage problems. Coefficients for the various estimated functions are statistically significant and the functions describe the relative effects of input water quality and quantity on yield, soil salinity, and drainage volumes for wheat, sorghum and tall wheatgrass. Possible use of these functions for decision making is discussed.

Reducing water quality degradation through minimized leaching management

Abstract The U.S.A. has adopted a policy of enhancing water quality and of conserving natural resources. The concept of minimized leaching has been advanced to help meet these goals by reducing salinity pollution from irrigated agriculture. It has received considerable attention by those concerned with management of water resources and is promoted by some as a generally applicable method for minimizing salinity pollution. This paper reviews the basis of the concept and identifies the conditions under which minimized leaching will and will not enhance water quality.