Response of Two Tomato Varieties to Varying Irrigation Levels

This field study was conducted in the inland region of the California Central Coast to compare the impact of five irrigation treatments with 4 field replicates on yield and quality of two organically grown tomato varieties, Early Girl (EG) and Brandy Wine (BW). The five treatments were set as percentages of evapotranspiration (%ET), 100, 75, 50, 25, and 12% ET. Initially, all plots were equally irrigated until pre-bloom stage when the different treatments were imposed. Plots of 12% ET treatment received no further water. EG yields for 12% and 100% ET were not significantly different, while for the same 12%ET irrigation treatment, BW had a 50% drop in economic yield. Fruit size, however, showed more complicated trends. Across irrigation treatments, BW produced 87 to 97% of its fruit in the extra large (XL) category and virtually its entire yield in the combined category of large to XL. At 12% ET treatment, EG produced 20% XL fruit and 69% small fruit. The remaining water treatments resulted in 54-60% of the fruit produced in the combined categories XL and L. Generally there was good red color development in BW fruit as indicated by low Hue values. Red color development was slightly less in fruit from treatments 25 and 12% ET. In contrast, the external color of EG fruit was similar in all irrigation treatments. BW fruit dry matter content (% dry weight) was the same (5.3-5.4%) in fruit from the 50, 75 and 100% ET treatments. It was significantly higher as water input decreased to 25 and 12% ET (5.5 and 5.6%, respectively). Soluble solids followed a similar trend as dry weight, but differences among treatments were relatively small (4.5% at 100%ET to 4.9% at 12%ET).. The % dry weight of EG fruit in the 12, 25, and 50% ET treatments was significantly higher (6.0%) than in fruit from the well-watered plots (5.6%). EG soluble solids followed a similar pattern (5.2% at 100%ET to 5.7% average for 50,25, 12%ET). EG tomatoes were less acidic as irrigation ET decreased (0.44% vs 0.36% Titratable acidity) while there were no differences in acidity of BW tomatoes (0.37% average T.A.).