One option for coping with the high soil salinity levels caused by saline, shallow groundwater conditions along the west side of the San Joaquin Valley is to convert from sprinkler or surface irrigation methods to drip irrigation. Experiments in commercial fields revealed that subsurface drip irrigation of processing tomato (Lycopersicon esculentum Mill. var. esculentum) is highly profitable under these conditions compared with other irrigation methods. The experiments also showed that little or no field‐wide leaching occurred, based on the conventional or water balance approach to estimating the leaching fraction (LF), yet soil salinity measurements showed considerable leaching around the drip lines. Actual LFs could not be calculated because LF, soil salinity, soil water content, and root density all varied with distance and depth around the drip lines. Therefore, we conducted a numerical modeling study using the HYDRUS‐2D computer simulation model to evaluate leaching with drip irrigation under saline, shallow groundwater conditions for different amounts of applied water, water table depths, and irrigation water salinity, described by the electrical conductivity of the irrigation water (ECiw). Results showed that LF values ranged from 7.7 to 30.9% as applied water amounts increased from 60 to 115% of the potential evapotranspiration (ETpot) for the ECiw = 0.3 dS m−1 irrigation water, even though the water balance method showed no leaching for applied water amounts equal to or smaller than ETpot The spatially varying soil wetting patterns that occur under drip irrigation caused the localized leaching, which was concentrated near the drip line.
Enviroscan soil moisture sensors like the one shown, that monitor on a continuous basis, provide more information that can be valuable. Monitorina soil moisture hebs refine irriaation manaaement U v
Reducing tillage and maintaining crop residues on the soil surface could improve the water use efficiency of California crop production. In two field studies comparing no-tillage with standard tillage operations (following wheat silage harvest and before corn seeding), we estimated that 0.89 and 0.97 inches more water was retained in the no-tillage soil than in the tilled soil. In three field studies on residue coverage, we recorded that about 0.56, 0.58 and 0.42 inches more water was retained in residue-covered soil than in bare soil following 6 to 7 days of overhead sprinkler irrigation. Assuming a seasonal crop evapotranspiration demand of 30 inches, coupling no-tillage with practices preserving high residues could reduce summer soil evaporative losses by about 4 inches (13%). However, practical factors, including the need for different equipment and management approaches, will need to be considered before adopting these practices.
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