Objective The aims were to investigate the impact of long-term plastic film mulching and organic fertilizer application on soil moisture content and water use efficiency in rain-fed potato farmlands in semi-arid regions.

Method Relying on a 10-year continuous long-term positioning experiment at the National Soil Quality Monitoring and Testing Station, the crops were grown once a year without irrigation, representing a typical rain-fed agricultural area in dryland. Two covering methods were set: full plastic film mulching (PFM) with micro-grooves on ridges (F) and flat planting without mulching (L), moreover, four fertilization levels were set: ① combined application of chemical and organic fertilizers (NPKM), ② sole application of organic fertilizer (OM), ③ sole application of chemical fertilizer (NPK), and ④ no fertilization (CK).

Result The results indicated that the dynamic changes of soil moisture content in potato fields were jointly influenced by precipitation, fertilization, PFM and growth periods. Long-term PFM and organic fertilizer application significantly increased the moisture contents in the 0-100 cm soil layer. The treatments with organic fertilizer application (NPKM and OM) had higher moisture contents than those with sole application of chemical fertilizer and no fertilization. PFM was superior to flat planting without mulching. PFM and organic fertilizer application significantly affected the water consumption of potatoes, which was closely related to the growth period and precipitation. The total water consumption was F > L. Under the same covering method, the total water consumption in the OM treatment was higher than that in the NPK treatment but lower than that in the NPKM treatment. The water use efficiency (WUE) of F was significantly enhanced by 81.3%-133.7% compared with L treatment. Under PFM, the WUE of OM and NPKM was increased by 42.3% and 7.4% compared with the NPK treatment. The yield of F treatment was increased by 78.2%-159.2% compared with L treatment. Under PFM, the yield of OM and NPKM was increased by 44.7% and 17.3% compared with the NPK treatment, and by 123.3% and 80.9% compared with the CK treatment.

Conclusion Under the condition of the loess soil in the hilly and gully region of the northwest, through a 10-year continuous PFM and fertilization located experiment, PFM and organic fertilizer application could significantly improve the soil moisture and water use efficiency of potato farmlands in the years with seasonal water shortage. Considering the effects of water storage, soil moisture conservation, and crop yield increase, PFM combined with sole application of organic fertilizer (F-OM) is the optimal treatment.