Fertigation Strategies to Optimize Tomato Production In Salt-Affected Soils

Growers in the Central Valley of California are transitioning to higher value crops and more efficient irrigation systems to maximize production yields.  Particularly, growers facing low returns from cotton under flood irrigation practices are now growing vegetable crops, such as tomatoes, using drip irrigation system.  However, such transition poses new challenges, primarily in heavy clay soils affected by saline-sodic conditions.  Such problems include the sensitivity of vegetable crops to salinity and their susceptibility to diseases and calcium deficiency. Therefore, the challenge is to increase soil calcium availability to plants and reduce soil pH in the root zone in order to ensure maximum crop yield and quality.  Hence, the objective of this study was to evaluate the effects of four fertigation practices on tomato yield, incidence of blossom-end rot (BER), and total soluble solids (Brix index).  The experiment was conducted in Central California on a Lethent silty clay soil with salinity ranging from 2 to 8 dS/m within the 0-1 ft depth.  Processing tomatoes were transplanted in 2009 and direct-seeded in 2010.  The following four fertigation treatments were compared: 1) urea ammonium nitrate (UAN), referred to as the control and commonly used in Central California, 2) water acidification using Urea Sulfuric Acid (US-15), 3) calcium ammonium nitrate (CAN), and 4) calcium thiosulfate (CAT).  All treatments were applied through a sub-surface drip system and replicated four times in a randomized complete block design.  Results of the first year study conducted in 2009 indicated that tomatoes fertigated with CAT produced the highest yield (66.2 tons/acre; p<0.002).  However, no significant yield differences were observed among treatments in 2010 with the average being 37.49 ± 10.39 tons/acre.  Fertigation strategies significantly affected the incidence of BER in both years.  Overall, there was a higher incidence of BER in 2010 when compared to 2009.  Tomatoes grown in soils subjected to acidification had higher incidence of BER when compared to tomatoes grown with CAT.  Total soluble solids did not differ with any fertigation treatment with an average Brix index of 6.5^o in 2009 and 5.5^o in 2010.