Limited irrigation and planting densities for enhanced water productivity and economic returns under the ridge-furrow system in semi-arid regions of China

In the semi-arid regions of China, ridge-furrow (RF) planting system is being gradually implemented, in order to improve the soil moisture status and water utilisation efficiency. This study aimed to improve the efficiency of the RF system by investigating the effects of three planting densities (L: 52,500 plants ha−1; M: 75,000 plants ha−1; H: 97,500 plants ha−1) and four kinds of limited irrigation modes (NI: no irrigation; IV: irrigation at the vegetative stage with 11 leaves; IS: irrigation at the silking stage; and IVS: irrigation at the vegetative and silking stages). Maize (Zea mays L.) plants mainly consumed the top surface of (0-60 cm) soil water, whereas the deep layer (120-200 cm) of soil moisture was less affected under the RF system, and the average soil water storage of 0-60, 60-120, and 120-200 cm decreased by 58.7, 39.1, and 7.1 mm, respectively, during the entire growth period. Limited irrigation at the vegetative and silking stages had a positive effect on biomass, leaf area index, and evapotranspiration, but did not significantly increase grain yield, water use efficiency (WUEG), irrigation WUE (IWUEG), and irrigation water productivity (IWPG). The average data obtained over two years showed that medium planting density with limited irrigation at the silking stage (M-IS) treatment significantly increased WUEG, IWUEG, and IWPG by 5.7, 98.5, and 92.6%, respectively, compared with those in the M-IVS treatment. Economic benefit analysis also showed that M-IS treatment resulted in greater net profit (2313.3 USD ha−1). Thus, the M-IS treatment could be a suitable planting model for improving maize grain yield, economic benefit, and water use in the semi-arid regions of China.