The optimum ridge-furrow ratio and suitable ridge-covering material in rainwater harvesting for oats production in semiarid regions of China

Drought, water loss and soil erosion are the main factors limiting agricultural production in semi-arid regions of China. A field study was conducted to determine (1) the runoff efficiencies of different ridge widths (30, 45 and 60 cm) covered with different materials (common plastic film, biodegradable mulching film and manual compacted soil) and (2) the effects of different ridge-furrow ratios (30:60, 45:60 and 60:60) and ridge-covering materials on soil water storage, topsoil temperature, hay yield, grain yield and water use efficiency (WUE) of oats in ridge-furrow rainwater harvesting (RFRH) system at the Dingxi Agri-meteorological station, during 2 consecutive years of 2012 and 2013. Average runoff efficiency was 18%, 20%, 22%, 71%, 77%, 83%, 76%, 77% and 84% for SR30, SR45, SR60, BMR30, BMR45, BMR60, CMR30, CMR45 and CMR60 (SR, BMR and CMR were ridges with compacted soil, covered with biodegradable mulch film and common plastic film, respectively, and subscript numbers 30, 45 and 60 stand for ridge widths (cm)) over 2 years, respectively. The field experiment using oats as an indicator crop showed that mulching materials and ridge widths had distinct effects on topsoil temperature on the top of the ridges, but not in the bottom of the furrows. The soil water storage in the 140 cm depth of soil at the bottom of furrows increased with increasing ridge widths and in the order of CMR ≈ BMR > SR > FP (FP was the flat planting). The total precipitation was 414.4 mm in 2012 and 448.8 mm in 2013, which were higher than the average of rainfall (388.1 mm), leading to a significant increase of hay and grain yield in CMR, and an equivalent of hay and grain yield in BMR compared with FP in most cases. In the SR system, the positive effects of rainwater harvesting could not compensate for the negative effects of planting area reduction resulting in decrease in hay and grain yield. Compared with FP, the average grain yield decreased by 19%, 27% and 34% for SR30, SR45 and SR60, and increased by 6%, 4%, 1%, 12%, 9% and 6% for BMR30, BMR45, BMR60, CMR30, CMR45 and CMR60 over 2 years, respectively. The WUE of SR, BMR and CMR was 1.31, 1.41 and 1.47 times greater than that in FP over 2 years, and increased with increasing ridge width. The optimum furrow width was 32-38 cm for CMR and was 30-34 cm for BMR. Future study is needed to investigate the impact of RFRH on crop production, WUE and economic benefit under different precipitations, soil types, slopes and plant species using biodegradable mulching materials.