Irrigation Cutback a Reliable Tool for Soluble Solids Improvement in Processing Tomato

Abstract

Soluble solids concentration (SSC) is a major quality factor for tomatoes (Lycopersicon esculentum Mill.) grown for processing. The effects of early irrigation cutback were investigated in a series of drip-irrigated field trials in California from 2000-03. Irrigation cutback was initiated from 4-7 weeks preharvest, with irrigation volume reduced to 30% to 70% of reference evapotranspiration. Early irrigation cutback was compared to full irrigation until cutoff 2-3 weeks preharvest. SSC was monitored from the initiation of deficit irrigation until harvest, with breaker-stage fruit sampled at approximately 10-day intervals; additionally, early-maturing fruits were tagged on the plant at breaker stage and retrieved at harvest for SSC analysis. Fruit yield, overall SSC, and brix yield (Mg·ha-1 fruit solids) were evaluated at commercial maturity. Fruit SSC increased in response to soil moisture stress, with late-maturing fruit as much as 2.0 °Brix higher than fruit maturing before significant moisture stress. However, once a fruit reached the breaker stage of maturity, its SSC did not increase regardless of subsequent soil moisture stress. Across field trials, yield decline resulting from early irrigation cutback was matched by a corresponding increase in overall SSC, resulting in equivalent brix yield in all test fields. We conclude that the early irrigation cutback provides a flexible tool for SSC management and that °Brix monitoring of breaker-stage fruit can augment soil moisture monitoring to tune irrigation management to field-specific conditions.