Effect of rainwater harvesting via plastic film-covered ridge on soil moisture in Medicago sativa grassland and water use efficiency

The productivity and water use efficiency of cultivated pastures are low in arid and semiarid areas of the Loess Plateau due to low annual rainfall and periodical deficit of soil moisture. In this study, the rainwater harvesting system via plastic film-covered ridge was applied in production of biennial Medicago sativa grassland in dryland. And the impact of ditch/ridge ratio and mulching patterns on the trends and use efficiency of soil moisture were determined. Results showed that rainwater harvesting by plastic film-covered ridge significantly improved soil moisture content in 0~20 cm soil at early stage of rainwater harvesting (from the middle ten-day of April to the first ten-day of June). It also greatly enhanced average soil moisture content in 0~120 cm soil at mid-late rainwater harvesting stage (from the middle ten-day of June to the last ten-day of September). During winter, rainwater harvesting via plastic film-covered ridge increased soil infiltration capacity and improved average soil moisture content in 20~120 cm soil. Further, the rainwater harvesting efficiency of plastic film-covered ridge was higher than that of compacted bare ridge. The moisture storage in 0~120 cm soil with rainwater harvesting via plastic film-covered ridge initially dropped, and then rose during the growth period of M. sativa. At late growth stage, soil moisture storage with rainwater harvesting via plastic film-covered ridge was evidently higher than that via compacted bare ridge. Average water use efficiency with plastic film-covered ridge was 34.91 kg·mm^-1·hm^-2, which was 2.25 times that of CK (flat field without ridge and mulch). Average water use efficiency with compacted bare ridge was 28.47 kg·mm^-1·hm^-2, which was 1.83 times that of CK. Average water use efficiency of plastic film-covered ridge increased by 22.62% compared with that of compacted bare ridge, and the highest ones were in plastic film-covered ridges with 60 cm/60 cm and 60 cm/75 cm ditch/ridge ratios.