Rainfall harvesting on slopes using contour furrows with plastic-covered transverse ridges for growing Caragana korshinskii in the semiarid region of China

A rainwater harvesting system on slopes using contour furrows with plastic-covered transverse ridges designed to be used in small rainfall dominated areas of the semiarid loess region of China has been tested from 2001 to 2004. The system consisted of constructing contour furrows on the loess slope at a distance of 5 m with plastic-covered transverse ridges built in the furrows between shrubs of Caragana korshinskii. There were three treatments in the study: (1) plastic-covered ridge with gravel-mulched furrows (T1), (2) plastic-covered ridge with bare furrows (T2), and (3) control (no ridge and no contour furrow) (T3).The experimental results indicated that runoff from the natural loess slope was small and variable, and only produced from a few rainfall events with high intensity. Runoff efficiency averaged 13.8, 4.5, 1.4, and 0.4% in 2001, 2002, 2003, and 2004, respectively. However, the plastic-covered ridges accumulated runoff from most rainfall events, particularly from the light rains less than 5 mm. So the natural loess slope between the furrows and the plastic-covered ridges in the furrows can complement each other, i.e., the plastic-covered ridges induce runoff from small rainfall to the planted area, and the natural loess slope between the furrows concentrate runoff from heavy rainfall, thus improving rain use efficiency. The total runoff collected from both the natural loess slope and the plastic-covered ridges to the planted area in the furrows was 231, 143, 88, and 59 mm in 2001, 2002, 2003, and 2004, respectively. Soil moisture storage in the 200-cm deep soil layer was obviously higher for T1 and T2 than for T3, and C. korshinskii showed a significant improvement in growth for the T1 and T2 treatments. Therefore the combination of contour furrows and plastic-covered ridges as rainwater harvesting system may have a great potential development in the small rainfall dominated arid regions of China.