Spinach yield and nutritional quality affected by controlled soil water matric head

The yield and quality of spinach cultivar (Spinacia oleracea L. ‘Virginia’) in sandy soil are improved by controlling soil water within the rhizosphere. An automated irrigation system using by a buried-type electric tensiometer connected to electromagnetic valves was shown to control soil water accurately. The soil water matric head was maintained in the ranges h=−10 to −20 cm (treatment I), −20 to −30 cm (treatment II) and −30 to −40 cm (treatment III). According to commercial standards, treatment II could have yielded a lowest 20 days earlier than treatment I and III. The yield from treatment II was more than two times greater than that from the other treatments. Total ascorbic acid and sugar content, as well as the concentration of total N, P, K, Ca, Mg, and Na in the spinach of treatment II, were all significantly higher than those from the other treatments. The water use efficiency (g dry weight/l water) and net water use efficiency (g fresh weight/l water) were better for treatment III. Only the yield and quality of spinach from treatment II reached commercial standards.