Partial root-zone irrigation (PRI) is an irrigation technique to save irrigation water without much yield reduction. We investigated if the benefits of PRI on physiology, fresh fruit yield, fruit quality and water use efficiency (WUE) of pot-grown tomato could be modified by different calcium (Ca) levels in the greenhouse. Three irrigation methods, i.e. conventional irrigation (CI), alternate partial root-zone irrigation (APRI, alternate watering on both sides of the pot) and fixed partial root-zone irrigation (FPRI, fixed watering on one side of the pot), and five Ca levels in solution, i.e. 0, 0.3, 0.5, 0.8 and 1.0% of Ca supplied as calcium chloride, were designed. Results show that PRI reduced more transpiration rate than photosynthetic rate, which led to higher leaf WUE. APRI enhanced root activity, increased fresh fruit yield of tomato slightly and WUE on fresh yield greatly. APRI increased the contents of VC and soluble sugar in fruits by 12.6 and 4.5% but decreased organic acid content in fruits by 5.3%, so APRI increased the ratio of sugar/acid and improved fruit quality greatly. However, FPRI reduced fresh fruit yield and quality to some extent. Suitable concentration of Ca fertilizer can increase photosynthetic rate, fresh fruit yield, WUE on fresh yield and fruit quality. Thus APRI with suitable concentration of Ca fertilizer is a water-saving, quality-improving and practical irrigation technology. In this study, APRI with 0.8% of Ca supplied as calcium chloride is the best treatment.
