Optimizing irrigation frequency and amount to balance yield, fruit quality and water use efficiency of greenhouse tomato

Vegetable production in many countries relies on irrigation. While increasing irrigation amount normally improves yield, too much water could jeopardize fruit quality and comprise profit. Optimizing irrigation frequency and amount is thus essential to ensuring yield increase without compromising fruit quality. This paper presents a three-year (2011-2013) experimental study on responsive changes in yield, fruit quality and water use efficiency (WUE) of tomato grown in greenhouse to different irrigation frequency and amount under drip irrigation. The irrigation scheduling was based on accumulative evaporation (AE) measured from a standard 20 cm pan. Three irrigation frequencies were considered in which irrigation was resumed when AE was 10 mm (IA 20 mm (I-2) and 30 mm (I-3) respectively. Each frequency was associated with four irrigation amounts, which were 50% (K-cp1), 70% (K-cp2), 90% (K-cp3) and 110% (K-cp4) of AE respectively. Water consumption, yield characteristics and fruit quality of the plants in each treatment were measured. The three-year results show that for each irrigation amount, increasing irrigation frequency led to an increase in yield and WUE. Visual fruit-quality traits, including average weight, longitudinal and transverse diameter, increased with irrigation amount but not with irrigation frequency. It was found that a reduction in irrigation amount increased all other fruit quality characteristics except the sugar-organic acid ratio in 2013. Both yield and WUE increased asymptotically with irrigation amount before approaching their plateau when the irrigation amount reached 90% and 70% of AE respectively. While the yield was positively related to fruit size and negatively to soluble solid content, it was independent of WUE. The results from technique for order preference by similarity to ideal solution analysis revealed that among all treatments, I-1 +K-cp2 was the optimal in terms of best balancing yield, fruit quality and water use efficiency. Principal component analysis found that the comprehensive fruit quality score was closely related to the total soluble solids content.