Water–Nitrogen Coupling Effect on Drip-Irrigated Dense Planting of Dwarf Jujube in an Extremely Arid Area

Abstract

Hami, Xinjiang, is located in an extremely arid region and jujube is the main economic crop. It is important to adopt dwarf and close-planting technology under drip irrigation and to optimize water and fertilizer management to improve jujube yield and quality. Local 12-year-old jujube trees were treated using two factors of irrigation and fertilization. Three irrigation amounts (520, 700, and 880 mm) and three fertilization levels (248, 318, and 388 kg/hm2) were set up in plot experiments. The root system, yield, and quality of jujube were monitored under different irrigation and nitrogen application combinations. The effects on water use efficiency (WUE), nitrogen partial factor productivity (PNP), and economic benefit were analyzed. The water and fertilizer coupling effect of dwarf closely planted jujube was studied by combining multiple regression and spatial analyses. The yield, quality, economic benefits, WUE, and PNP of jujube were significantly affected by irrigation and fertilization. Multiple regression and spatial analyses showed that the highest yield was for irrigation of 700 mm and a nitrogen rate of 340 kg/hm2. For the maximum net benefit, irrigation was 806 mm and nitrogen was 388 kg/hm2; correspondingly, for the highest total sugar, values were 688 mm and 362 kg/hm2; for vitamin C, they were 622 mm and 376 kg/hm2; for PNP, they were 880 mm and 256.57 kg/hm2; and for WUE, they were 520 mm and 388 kg/hm2. A comprehensive evaluation of each index showed that the acceptable irrigation amount for yield, quality, WUE, and net benefit of ≥85% of the maximum value was 600–628 mm, and the nitrogen application rate was 360–372 kg/hm2. This study provides guidance for the scientific management of water and fertilizer in the drip irrigation and fertilization process of local jujube trees.