Tomato yield and water use efficiency - coupling effects between growth stage specific soil water deficits

To investigate the sensitivity of tomato yield and water use efficiency (WUE) to soil water content at different growth stages, the central composite rotatable design (CCRD) was employed in a five-factor-five-level pot experiment under regulated deficit irrigation. Two regression models concerning the effects of stage-specific soil water content on tomato yield and WUE were established. The results showed that the lowest available soil water (ASW) content (around 28%) during vegetative growth stage (here denoted theta(1)) resulted in high yield and WUE. Moderate (around 69% ASW) during blooming and fruit setting stage (theta(2)), and the highest ASW (around 92%) during early fruit growth stage (theta(3)), fruit development (theta(4)) and fruit maturity (theta(5)) contributed positively to tomato yield, whereas high WUE was achieved at lower theta(2) and theta(3) ( around 44% ASW) and higher theta(4) and theta(5) (around 76% ASW). The strongest coupling effects of ASW in two growth stages were between theta(2) and theta(5), theta(3). In both cases a moderate theta(2) was a precondition for maximum yield response to increasing theta(5) and theta(3). Sensitivity analysis revealed that yield was most sensitive to soil water content at fruit maturity (theta(5)). Numerical inspection of the regression model showed that the maximum yield, 1166 g per plant, was obtained by the combination of theta(1) (c. 28% ASW), theta(2) (c. 82% ASW), theta(3) (c. 92% ASW), theta(4) (c. 92% ASW), and theta(5) (c. 92% ASW). This result may guide irrigation scheduling to achieve higher tomato yield and WUE based on specific soil water contents at different growth stages.