Ridge Runoff Effeciency And Effects Of Ridge-furrow Rainwater Harvesting On Alfalfa(Medicago Sativa) Production

Drought, water loss and soil erosion are main factors constraining agriculture and husbandry sustainable production in semi-arid Loess Plateau hilly regions. In order to improve field soil water content and to increase of rainwater resources utilization, and to find the optimum furrow-to-ridge ratio and a suitable ridge-mulching material for alfalfa production, field experiments were conducted to determine(1) Runoff efficiencies and threshold rainfalls of different ridge widths(30, 45 and 60 cm) mulched 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-mulching materials on soil water storage, topsoil temperature, growth characteristics, forage yield and quality and water use efficiency(WUE) of alfalfa in ridge-furrow rainwater harvesting system, with traditional flat planting(TFP) as a control, at the Dingxi Agri-meteorological station. The results were followed.Average monthly runoff efficiency(expressed as a ratio of runoff to rainfall received at the same period) were 12%, 13%, 15%, 59%, 65%, 73%, 66%, 65% and 73% for RCS30, RCS45, RCS60, RMBF30, RMBF45, RMBF60, RMPF30, RMPF45 and RMPF60(RCS, RMBF and RMPF were ridges with compacted soil, covered with biodegradable mulch film and common plastic film, respectively, and subscript 30, 45 and 60 refer to ridge widths(cm) all with 60 cm furrow width), respectively. Regression analysis indicated that correlation coefficients between runoff and amount of the rainfall were distinct higher than that between runoff efficiency and amount of the rainfall. Correlation coefficients between runoff and amount of the rainfall were 0.790, 0.803, 0.821, 0.981, 0.994, 0.980, 0.986, 0.990 and 0.992, respectively, for RCS30, RCS45, RCS60, RMBF30, RMBF45, RMBF60, RMPF30, RMPF45 and RMPF60, while correlation coefficients between runoff efficiency and amount of the rainfall were 0.570, 0.557, 0.530, 0.608, 0.537, 0.494, 0.542, 0.571 and 0.497. Threshold rainfalls for the same treatments were 4.2, 3.7, 3.2, 1.8, 1.1、0.43, 1.3, 1.6 and 0.64 mm.Ridge mulching had distinct effects on topsoil temperature at ridge tops, but not at furrow bottoms, and topsoil temperature at ridge tops increased with ridge width increasing. Topsoil temperature was in order of RMPF > RMBF > RCS > TFP. Compared with TFP, average increase topsoil temperature at ridge tops during alfalfa growing season was 0.9, 1.5, 1.6, 3.6, 4.1, 4.3, 3.9, 4.7 and 4.6℃, respectively, for RCS30, RCS45, RCS60, RMBF30, RMBF45, RMBF60, RMPF30, RMPF45 and RMPF60.Compared with TFP, average soil water storage in the 140 cm depth at the bottom of furrows increased 12.6, 19.1, 24.4, 21.2, 19.1, 34.0, 23.6, 32.6 and 41.2 mm, respectively, for RCS30, RCS45, RCS60, RMBF30, RMBF45, RMBF60, RMPF30, RMPF45 and RMPF60. There was no distinctive dry soil layer found within the root zone during the 2 years old of Alfalfa growing among ridge-furrow rainwater harvesting treatments.Ridge-furrow rainwater harvesting treatment increased Alfalfa crude protein content, but decreased Alfalfa neutral detergent fiber content and acid detergent fiber content. Compared with TFP, average Alfalfa forage crude protein content increased 4.9%, 11.7%, 11.6%, 12.3%, 15.8%, 16.1%, 11.4%, 13.8% and 16.8%, respectively, for RCS30, RCS45, RCS60, RMBF30, RMBF45, RMBF60, RMPF30, RMPF45 and RMPF60, while Alfalfa neutral detergent fiber content decreased 3.4%, 4.3%, 6.0%, 4.6%, 6.7%, 9.2%, 5.7%, 7.4% and 9.3%, and Alfalfa acid detergent fiber content decreased 3.9%, 5.5%, 7.4%, 6.4%, 7.7%, 9.9%, 7.5%, 9.4% and 10.7%.RMPF and RMBF increased forage yields, but RCS decreased forage yields, and forage yields decreased with ridge width increasing. RMPF, RMBF and RCS increased water use efficiency(WUE). Compared with TFP, forage yields decreased by 1%, 6% and13% for RCS30, RCS45 and RCS60, respectively, while WUE increased by 64%, 76% and 79%. Forage yields increased by 39%, 27%, 18%, 43%, 31% and 21% for RMBF30, RMBF45, RMBF60, RMPF30, RMPF45 and RMPF60, respectively, and WUE increased by 83%, 74%, 64%, 82%, 76% and 67%.Optimum furrow width was 35 cm for RMPF and RMBF in the ridge-furrow rainwater harvesting system with 60 cm width furrows for Alfalfa production, in this region that has an annual 427.6 mm rainfall. Biodegradable mulching film has similar effects on soil water conservation and temperature increasing as common plastic mulching film during early Alfalfa growing times(March-June). And Biodegradable mulching film can be degraded in natural conditions during late Alfalfa growing times(June-October), and is a suitable mulching material in ridge-furrow rainwater harvesting production.