Temporal and spatial variation of soil physical properties in alfalfa grassland under film mulching in northwest desert irrigation region

As a measure to increase soil temperature, conserve soil moisture, and increase available nutrients, film mulching (FM) has been generally and successfully used for crop cultivation. In this paper, using a crop without FM as a control (CK), the effects of FM on soil physical properties in an alfalfa field were studied in the second, third, and fourth year of the crop. The annual means of soil pH in the second and fourth year in the 0 to 20 cm depth soil layer in FM treatment were significantly decreased, and were 2.7% and 2.6% lower than those in CK. The annual mean values of water-soluble salt and Na+ content in FM treatment increased at first and then decreased over time, as they did in each soil layer depths. Both of the values in FM treatment were inferior to those in CK. FM significantly decreased the water-soluble salt content in May of the second year in the 0 to 20 cm depth soil layer by 62.9% compared with CK. The Na+ content in August and October of the fourth year in the 0 to 20 cm depth soil layer and in August of the second year in the 20 to 40 cm depth soil layer in FM dropped by 36%, 37%, and 39.5%, respectively, compared with that in CK. To a certain but statistically insignificant degree, FM increased the available nitrogen, available phosphorus, available potassium, and organic matter content in different years and in different soil layer depths.