Continuous ridges with film mulching improve soil water content, root growth, seed yield and water use efficiency of winter oilseed rape

• Continuous ridges with film mulching (M3) improved soil water content and promoted roots growth.
• M3 obtained the highest seed yield and water use efficiency.
• M3 was an optimal cultivation pattern for winter oilseed rape in arid and semiarid areas.

Limited water resources and low water use efficiency (WUE) have limited the increase in yield of winter oilseed rape (Brassica napus L.) in northwestern China for a long time. In order to determine an optimal cultivation method for increasing seed yield and improving WUE, field experiments were conducted to study the effects of various ridge-furrow and film-mulching planting patterns on soil water content, root distribution, seed yield, and WUE for three growing seasons from 2012 to 2015. Winter oilseed rape was planted in four patterns: flat planting without film mulching (CK), flat planting with film mulching (M1), ridge-furrow planting with film mulching on both ridges and furrows (M2), and ridge-furrow planting with film mulching on continuous ridges (M3). The results showed that M3 was the best at increasing soil water storage to a depth of 1.0 m after rain or irrigation and at maintaining much higher soil water content in the 0–0.3 m soil layer at the late growth stage. M3 produced the shortest taproots, but the largest taproot diameter and dry weight at both the seedling and pod-filling stages in all the three growing seasons. M3 also induced significantly more lateral-root proliferation in the 0–0.1 and 0.1–0.2 m soil layers without much reduction of lateral-root mass density in the 0.2–0.3 m layer in comparison to M1 and M2. Seed yield and WUE were the highest and evapotranspiration (ET) was the lowest in M3 in all the three growing seasons. Average seed yield was 70.0, 41.1, and 15.0% higher and average ET was 23.6, 14.3, and 9.4% lower in M3 than in CK, M1, and M2, respectively, thus improving WUE by 121.9, 64.5, and 26.8%, respectively. These results suggested that M3 was the best mulching and planting treatment for improving soil water storage, root growth, seed yield, and WUE. M3 may thus be the optimal mulching and planting pattern for the cultivation of winter oilseed rape in arid and semiarid areas.