Background  The drought and steep slopeland in the loess region of western Shanxi is one of the areas where the vegetation restoration has been very difficult in China due to little precipitation but high evaporation.Varied techniques(infiltration bag, high-pressure water gun, etc) have been applied for increasing the seedling survival rate, but they have shortcomings.

Methods  Here we designed a low-cost water-supplying bag, and studied the forestation effect of infiltrating irrigation via it.We carried out surface infiltrating irrigation test with acid blue in setting different water supplying amount(1, 2, 3, and 4 liter) and reforestation test in setting different infiltrating irrigation aperture(0.22, 0.45, and 1.20 μm) of water-supplying bag in Caijiachuan Watershed.Meanwhile we measured the track of acid blue, soil moisture content, seedling survival rate and growth in different test treatments to explore the relationship between wetted soil volume and water-supplying amount and the effect of water-supplying bag in different infiltrating irrigation aperture.

Results  1) The wetted soil of infiltrating irrigation was approximate half ellipsoid.The maximum vertical infiltration depth was greater than the maximum horizontal wetting radius, and they increased with the increasing of water-supplying amount and soil moisture content.Wetted soil volume and water-supplying amount were in power relationship.2) We carried out the infiltrating irrigation test with water-supplying bag from April 1 to May 20, 2015.We found that infiltrating and irrigating the plantation with the medium-aperture water-supplying bag, soil moisture content increased from 15.02% to 18.90%, and then stayed around 19.07%.Infiltrating and irrigating the plantation with the big-aperture water-supplying bag, soil moisture content increased rapidly from 15.02% to 19.55%, and then decreased to 7.17%.Watering 1 liter water to the plantation every 5 days, soil moisture content stayed around 17.28%.Infiltrating and irrigating the plantation with the small-aperture water-supplying bag, soil moisture content decreased from 15.02% to 6.15%.For the plantation without treatment, soil moisture content decreased from 15.02% to 5.06%.3) After the growing season(April to October, 2015), watering 1 liter water to the plantation every 5 days and infiltrating and irrigating the plantation with the medium-, big-and small-aperture water-supplying bag, seedling survival rate were 86.7%, 90.0%, 73.3% and 63.3%, respectively.Compared with plantation without treatment, they increased by 26.7, 30.0, 13.3 and 3.3 percentage points, seedling height growth were 10.8, 10.6, 7.5, and 6.9 cm, respectively, compared with plantation without treatment, they increased by 92.86%, 89.29%, 33.93% and 23.21%.Watering 1 liter water to the plantation every 5 days and infiltrating and irrigating the plantation with the medium-aperture water-supplying bag were more effective in improving soil moisture content and promoting seedlings survival rate and growth, however, infiltrating and irrigating the plantation with the medium-aperture water-supplying bag saved 11.20 tons of water per hectare than watering 1 liter water to the plantation every 5 days.

Conclusions  Infiltrating and irrigating the plantation with the medium-aperture water-supplying bag is recommended in planting for drought and steep slopeland in the loess region of western Shanxi.