Maize–fababean rotation under double ridge and furrows with plastic mulching alleviates soil water depletion

Double ridge and furrows with plastic mulching (PM), an effective drought-resistant farming technology, has been widely used in the semi-arid areas of China, and increased crop yields by more than 30%. However, where this technology has been applied in successive years, the annual balance of soil water has been affected and the risk of soil desiccation exacerbated. A 6-year field experiment had been conducted on the semiarid Loess Plateau to find a new mode of ecological security and economic efficiency under PM conditions. The two treatments were (i) PM with continuous maize cropping (PM-C) and (ii) PM with maize–fababean rotation (PM-R). The vertical variation of soil water along profile and the interannual variation of soil water, cumulative water consumption, biomass and yield, benefit and water economic yield were investigated. The results showed that the depth of soil water consumption of PM-C was extended downward by 60 cm from 2009 to 2014, but it did not vary in PM-R; the maximum depth of soil water consumption were 280 cm and 220 cm in PM-C and PM-R, respectively. Compared with the pre-seeding stage in 2009, soil water storage in the 0–300 cm depth in 2014-HA for PM-C decreased by 163.59 mm, comprising 5.21 mm in the 0–140 cm soil layer and 158.37 mm in the 140–300 cm layer. However, in the PM-R treatment, the soil water storage in the 0–300 cm depth in 2014-HA increased by 28.36 mm, resulting from an increase of 47.86 mm in the 0–140 cm soil layer and a decrease of 19.50 mm in the 140–300 cm layer. PM-R significantly improved crop water consumption in the post-flowering period, and the ratio of water consumption in post-flowering to total significantly increased by 19.54–51.09% (P < 0.05). The biomass and grain yield for PM-R were significantly lower than for PM-C, by 21.36 and 59.14%, respectively. However, there were no significant differences in benefit, mainly because the price of fababean was higher. The soil water depletion in 6 years of PM-R decreased significantly and therefore water economic yield was significantly higher than for PM-C. This suggested that PM-R alleviated the over-consumption of deep soil water and the water depletion depth, which caused by continuous maize cropping in PM-C, and so achieved significantly higher water economic yield by reducing soil water depletion and provided stable economic benefit. Consequently, PM-R represents a sustainable ecological, economic, secure and replicable planting mode.