Spatial and Temporal Distribution of Salinity in Drip Irrigated Tomatoes in Central California

In California processing tomato production systems, quality and quantity of irrigation water is highly variable, so irrigation management is a critical component of sustainable production. Influence of irrigation regimes on yield and soil salinity were assessed in California drip irrigated processing tomatoes from 2010 to 2012. The irrigation regimes compared in the study were the following: a) grower treatment at > 100% ET, b) 80 and 60% ET at 65 and 95 days after transplant, respectively and c) 60 and 40% ET at 65 and 95 days after transplant, respectively. Water with low levels of salinity, and the same beds and tape were used for each treatment throughout the study. Yield was determined for each treatment based on 122 m-long beds harvested mechanically into a scale-equipped trailer and were unaffected by the irrigation treatments, with the exception of a 11.8 mt/ha reduction in yield in the plots with the most severe irrigation reduction in 2012. Substantial quantities of sub-surface moisture were mined during all seasons, which contributed to the overall good condition crop condition in the deficit treatments. No significant change electrical conductivity or chloride level was observed relative to irrigation treatments, but variability was very high. The position of increased salinity levels within the soil profile was often associated with the center of the bed at depths of 3160 cm, which could present challenges for the crop since there is substantial rooting in that zone. Annual overhead water plotted against the change in soil EC levels revealed a significant negative correlation between water quantities and salinity accumulation. While a drip-applied leaching fraction with high quality water may aid in salinity management, under the conditions of this study, a better use of high quality water for leaching would be through sprinklers.