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Soil salinity significantly limits citrus production in many areas worldwide. Although data on fruit yields in response to salinity are limited, they indicate that grapefruit, lemons, and oranges are among the most sensitive of all agricultural crops. Fruit yields decrease about 13% for each 1.0 dS m(-1) increase in electrical conductivity of the saturated-soil extract (EC(e)) once soil salinity exceeds a threshold EC(e) of 1.4 dS m(-1). Accumulation of excess Cl(-) and Na(+) can cause specific ion toxicities, but this problem can be minimized by selecting rootstocks that restrict the uptake of these ions. During the past two decades, numerous papers describing the agronomic and physiological responses of citrus to salinity have been published. This paper reviews these research reports and discusses differences in the response of citrus species to salt stress, the role of different rootstocks, the causes of salt injury, and the interactions of other environmental conditions or stresses with salinity.

As noted in previous chapters of this manual, the quality of irrigation water is an important factor in determining sustainability of agriculture on salt-impaired lands. For a number of reasons, the availability of lowsalinity irrigation supplies has led to (1) an interest in using alternative supplies, such as recycled wastewaters, and (2) innovative plant and water management strategies to mitigate the adverse effects of salt and specificion stresses these poor-quality waters may impose on plant growth, yield, and quality. A second motivating factor is the lack of suitable drainage outlets in many agricultural areas of the world. Drainage of irrigated lands is one of the requisites for sustaining agricultural productivity in a given region over the long term. Adequate drainage not only allows for better aeration in the crop rootzone but provides a means by which salinity and toxic elements can be managed and controlled. Reuse of drainage water for irrigation is one way of expanding the useable water supply while at the same time reducing drainage volume. This chapter provides a management perspective on (1) how plants respond to salinity and toxic elements (e.g., Na ϩ , Cl Ϫ , and B); (2) crop salt tolerance and the various factors that influence plant response to salinity; (3) the extent to which salinity affects crop yields and quality; and (4) management strategies to optimize yields by controlling soil salinity. It is not our intent to provide a comprehensive review of physiological effects of salinity crops. That topic is covered in detail in Chapter 6.

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