Spatial and temporal variations in soil water and salt in arid areas before and after irrigation

Spatial and temporal variations in soil water and salt contents of arid farmlands in Qitai County, Xinjiang was investigated before and one week, 3 weeks after irrigation through profiles sampling. The results showed low soil water contents (15.25%~16.70%) in all soil layers before irrigation, with moderate to weak spatial variability. Salt content in the upper 40 cm soil layer was strongly variable, while that in the lower soil layer was moderately variable. One week after irrigation, soil water and salt contents in the soil layers (except for the 0~20 cm soil layer with weak variability) remained unchanged, but their coefficients of variation dropped. Salt content variability in the upper soil layer changed to medium and strong. Average water content in the profiles increased by 10.51%, with a desalting rate of 8.94%. The rates of water increase (118.48%) and desalting (20.86%) in the 0~20 cm soil profile were the highest. On the other hand, the rates of water increase (40.54%) and desalting (-6.93%) were lowest in the 100~120 cm soil layer. Compared with the one week post-irrigation condition, variation in water and salt contents in the soil layers (except for the 80~100 cm soil layer) remained unchanged three week after irrigation. However, the coefficient of variation for water content increased while that for salt decreased. Average water content along the soil profile decreased by 5.20%. The rate of water loss (36.47%) in the surface 0~20 cm soil layer was highest while that (7.31%) in the 80~100 cm soil layer was lowest. The rate of salt accumulation (4.55%) in the surface soil was about 12 times that in the 20~40 cm soil layer. While desalting still occurred below the 40 cm soil layer, that in the 40~80 cm soil profile decreased. Desalting rate (9.03%) in the 80~120 cm soil layer increased.