Processing tomato fruit quality: influence of soil water deficits at flowering and ripening

One way to reduce the production cost of tomato solids is to increase fruit solids at harvest time. In a field trial using 200-L containers the effects of early and late soil water deficits (treatments DE and DL) on fruit yield and quality were tested during either flowering or late fruit growth. The effect of standard irrigation, with water cut off during the 3-5 weeks before harvest (SC), was also compared with full-season irrigation (FS). Manual irrigation of containers twice per week replaced soil water loss, measured by time domain reflectometry. A rain shelter was used as needed. The duration of the DL treatment was 43 days, which was intended to equate to 60-70 days of slower root-zone drying by finer textured field soils. Soil matric potentials were as low as - 1500 kPa during both DE and DL. Fruit colour change was accelerated by DL; fruit were 97% red at harvest as against 89-93% for the other 3 regimes. Fruit yields of treatments other than DL were all near 93 t/ha. Yield of DL was reduced 38%, mainly due to 35% smaller fruit. Fruit quality parameters [soluble solids concentration (SSC), total solids, and titratable acidity] were similar in the 3 higher yielding regimes, but were much greater in the DL treatment. Fruit pH was also more favourable (i.e. lower) in DL. The SSC was 2.8 degrees Brix higher in DL, sufficiently so that soluble solids yield/ha was not significantly lower than other treatments. This occurred without a decrease in juice viscosity or consistency (Bostwick). Simple models were developed for predicting soil water deficit effects on fruit quality. There is clearly an opportunity for irrigation management to improve tomato processing quality and profitability.