Defining the critical period for irrigation of processing tomato (Lycopersicum esculentum Mill.)

The critical period (CP) for irrigating processing tomatoes spans from the beginning of blooming (BB) until eight weeks after blooming. Water stress greater than 90% of ETc in the CP affects yield and quality. The objective of this study was to evaluate the effect of water stress at the beginning and end of CP, increase efficiency in the use of water, and optimize yield and fruit quality. Trials were carried out during 1998-99 and 1999-2000 on a sandy loam typical Torrifluvent soil in Mendoza, Argentina. Furrows on a 0.2% slope were used for irrigation. Irrigation treatments were scheduled weekly and measured in terms of hours (h) after irrigation water reached the end of a furrow. Treatments in 1998-99 began at BB, with 6- and 4-week irrigations, 18 h each, plus in the last 2 weeks at 9 h each (treatments A and C, respectively); 6- and 4-week irrigations, 18 h each (treatments B and D); from BB 2 weeks of 9-h irrigations, then 4 and 2 week 18-h irrigations (treatments E and F, respectively). In 1999/2000, 9 h irrigations, beginning 2 weeks from BB, plus 3 weeks of 18 h irrigations, (treatment G); 3 weeks of 9-h irrigations, followed by 3 weeks of 18-h irrigations (treatment H), and finally, 4 weeks of 9-h irrigations plus 2 weeks of 18-h irrigations. Experimental design was in complete randomized blocks with five replicates. Data was analyzed by ANOVA and means separation was tested by Duncan an alpha level of 0.05. Harvest of plots started when 90% of fruits were reds. Soil humidity was monitored by tensiometers. and double-ring infiltrometer. Highest yields were obtained when no water stress was imposed during weeks 3-6 after BB (treatments A, B, and E). Treatments A and B were irrigated to excess during weeks 5-6 and 9-10. E was the most efficient treatment; it was irrigated with I ETc until week 6; during weeks 7-10 no irrigation was applied, and ETc was close to 0.4. CP was reduced to 30 days (adjusted CP) from the original 42 days. Irrigation treatments longer than 6 weeks resulted in softer fruits. CP for soluble solids was determined in weeks 5 and 6 after BB. Soil tensiometer use was satisfactory and no reduction of yield was detected below 51 cbars (kPa).