Effect of plastic film mulch on soil moisture and salt dynamics under saline water irrigation in coastal saline soils

Filed experiments were conducted to study the dynamics of soil moisture and salt under saline water irrigation and plastic film mulching in coastal saline soils in spring in Haixing County, Hebei Province. Two field sites were selected—Xiaoshan Town with original soil moisture content ≥ 20% and Haixing Farm with original soil moisture content < 20%. A total of 6 treatments were designed for Xiaoshan Town, involved saline water irrigation at March 29^th and April 13^th with and without plastic film mulching, and plastic film mulching only, with no irrigation without plastic film mulching as the control. The treatments in Haixing Farm were CKN (no irrigation without plastic film mulching) and SE+PMN (saline water irrigation with plastic film mulching). The irrigation water was ponded from the drainage ditch along the field with salinity of 12.12 g·L^-1 and 11.53 g·L^-1 for Xiaoshan Town and Haixing Farm, respectively. The irrigation amount was 180 mm in both sites. Oil sunflower was planted after irrigation. Results showed that soil salt content in plough layer significantly reduced under saline water irrigation and plastic film mulching. The earlier the application of the treatment, the better the salt leaching effect obtained. Moreover, salt leaching effect was affected by the original soil water content. A better salt leaching effect was observed in Haixing Farm, and the average salt leaching depth was 40 cm. This ensured the normal growth of oil sunflower, with germination rate and yield of 73.9% and 920 kg·hm^-2, respectively. Soil salt content decreased from 1.93% before irrigation to 0.32% at harvest stage of oil sunflower, with mean salt leaching rate of 84.07%. For the Xiaoshan Town experimental site, however, water was infiltrated through soil macro-pores and it was difficult for salt to leach out from soil micro-pores. Thus water infiltration at the rate of saturated hydraulic conductivity, which led to slow leaching rate and shallower leaching depth of soil salt. High soil salinity was maintained at sowing of oil sunflower limited its' normal growth and therefore no yield was obtained. In the research, soil salinity in plough layer reduced effectively through saline water irrigation and plastic film mulching in spring. This provided a suitable soil water and lower salinity for the normal germination of crops in coastal saline soils.