Effects of deficit irrigation and partial root-zone drying on soil and plant water status, stomatal conductance, plant growth and water use efficiency in tomato during early fruiting stage

The effects of 'partial root-zone drying' (PRD), compared with full irrigation (FI) and deficit irrigation (DI), on soil and plant water status, plant growth and water use efficiency (WUE) were investigated in potted tomatoes (Lyeopersicon esculentum L., var. Cedrico) at the early fruiting stage. In FI the whole root system was irrigated daily close to pot capacity; in DI-70 and DI-50 70% and 50%, respectively, of the irrigation water in FI was applied to the whole root system; in PRD-70 and PRD-50 70% and 50%, respectively, of the irrigation water in FI was applied to one half of the root system, and the irrigated side of the plants was reversed when volumetric soil water content (theta) of the dry side had decreased to 6%. theta of FI was about 14%. theta of DI decreased during the first 4-5 days after the onset of treatment (DAT) and was about 7% and 6% thereafter for DI-70 and DI-50, respectively. theta of the wet side in PRD-70 declined during 3-6 DAT and was lower than that of FI by 4-6% thereafter. theta in both wet and dry sides of PRD-50 was slightly lower than that for PRD-70. After 5 DAT, midday leaf water potential was significantly lower in DI and PRD than in FI plants. FI plants had the highest leaf elongation rate (LER) among treatments. Given the same irrigation water, PRD and DI had a similar effect on LER. At eight out of fourteen instances FI plants had the highest stomatal conductance while DI-50 and PRD-50 had the lowest. No significant differences were found between treatments in plant leaf area and total top biomass. Compared to FI, WUE increased by 56%, 38%, 36% and 21 % in PRD-50, DI-50, PRD-70 and DI-70, respectively. PRD had higher WUE than DI given the same irrigation water. It is suggested that both DI and PRD are feasible water-saving irrigation strategies for tomato at the early fruiting stage.