ENVIRONMENTAL AND AGRONOMIC MANAGEMENT STRATEGIES FOR IMPROVING TOMATO PRODUCTION IN SALT-AFFECTED SOILS OF THE SAN JOAQUIN VALLEY, CA

Production of processing tomatoes (Solanum lycopersicum L) is a major challenge in salt-affected soils of western San Joaquin Valley (SJV). Environmental and agronomic strategies need to be implemented to improve yields and reduce salt built-up in the root zone. Such strategies include acidifying the irrigation water to reduce soil pH and implementing fertigation of important nutrients, such as calcium, to improve their availability to plants. In this study, we evaluated the environmental and economic benefits of irrigation water acidification and calcium (Ca) fertigation on the yield and quality of processing tomatoes grown in saline soils, incidence of blossom end rot (BER-a physiological disorder attributed to Ca deficiency), plant calcium levels and soil chemical properties. The experiment was conducted during a two-year period in a conventional processing tomato field in Kettleman City, CA. The four fertilizer/acidification treatments were (1) ammonium nitrate (AN-20), (2) urea sulfuric acid (US-15) + AN-20, (3) calcium ammonium nitrate (CAN-17) and (4) calcium thiosulfate (CTS) + AN-20 which were replicated four times. A randomized complete block design was utilized and each treatment plot consisted of 5 beds of 300-ft length. In year 1, fertilizer treatments had a significant effect on the yield of tomatoes. Yields were highest under the calcium thiosulfate (CTS) treatment. Plants treated with CTS+AN-20 had 10 to 15% greater total and marketable yield as compared to tomatoes receiving the other fertilizers. In year 2, no significant yield differences were observed among the treatments. Plants treated with CTS exhibited the lowest incidence of BER in both years. Correlation analysis indicated that elevated sodium (Na) and Sodium Adsorption Ratio (SAR) in soil had a negative effect on tomato yields and contributed to greater incidence of BER in both the seasons, regardless of fertilizer treatments. Results suggest that efforts should be directed towards soil Na amelioration using management practices such as proper irrigation methods and gypsum application rather than using Ca fertilizers only.