ABSTRACT
Salt- Affected Areas ...................................................................................... 144 8.4.1 LR: Steady-State vs. Transient Approach ......................................... 144
8.5 Caveat ........................................................................................................... 146 Acknowledgments .................................................................................................. 146 References .............................................................................................................. 146
EXECUTIVE SUMMARY
Water scarcity is an identifying feature of arid and semiarid regions of the world, causing water conservation to be a constant consideration in these areas. Due to the unpredictability and scarcity of natural precipitation in arid and semiarid regions, irrigation is essential for maintaining crop productivity. In general, irrigation and soil salinization go hand in hand, particularly in the arid zones of the world. Water conservation on arid and semiarid soils must be done with constant and careful consideration of the distribution of salinity across the landscape and through the soil profile. Salinity is of concern because it causes a significant decrease in crop productivity due to osmotic and toxic ion effects on plant growth. However, soil salinity can be managed through leaching and the application of various soil amendments. The fieldscale management of soil salinity is best handled with knowledge of its spatial and temporal distribution. Ideally, water conservation on irrigated agricultural lands is best achieved by applying irrigation water where, when, and in the amounts needed to adequately leach salts and to meet the crop’s water needs. This is not easily done since water content and salinity are highly variable both spatially and temporally across a field and through the root zone. The goal of site-specific irrigation, however, is to account for within-field variation of water content and salinity. Field-scale salinity measurement and mapping protocols have been developed by Corwin and his colleagues at the U.S. Salinity Laboratory in Riverside, California. These protocols utilize advanced information technologies (i.e., geophysical techniques measuring apparent soil electrical conductivity [ECa], geographic information system [GIS], geostatistics, spatial statistical analysis, and spatial statistical sampling designs) to map the spatiotemporal distribution of soil salinity for management applications. These protocols and technologies also have the potential to map soil water content and texture in most instances. The goal of this chapter is to provide an overview of the approach for delineating site-specific irrigation management units (SSIMUs) from the field-scale characterization of soil salinity, water content, and textural distributions using advanced information technologies. Guidelines, special considerations, protocols, and strengths and limitations are presented. Maps of SSIMUs provide irrigation management information to ameliorate crop yield reduction on salt-affected soils with minimal irrigation water requirements. Land resource managers, water conservation specialists, farmers, extension specialists, and Natural Resource Conservation Service field staff are the beneficiaries of field-scale maps of soil salinity, water content, texture, and SSIMUs, which can be used for crop selection, irrigation and salinity management, and remediation. These tools are important to provide adequate water for crop production while protecting soils from excessive salinization that will degrade soil quality and impair future productivity.
