Abstract: The moderate and severe saline-alkali land in Hetao irrigated area that is characterized by high underground water level,serious salt table accumulation and difficult crop growth.In this study,the effects of mulching film coverage early in the non-growth period,salt dynamics were investigated by planting sunflower bioassay for the submembrane farming layer during the growth period.The desalting effect of non-growing mulch on the underlayer is evaluated.The results showed that compared with the conventional pre-sowing mulching,film mulching in autumn of the previous year year and early spring mulching were significantly reduced in different growth periods.The seedling rate,plant height,stem diameter and disk diameter of sunflower were significantly increased.The desalting rates of 0-10 cm and 10-20 cm tillage layers under film mulching in autumn of the previous year were 21.54%and 19.63%higher than the rates under conventional film mulching,respectively.The average 0-20 cm desalination rate increased by 20.59%.The seedling rate of sunflower increased by 18%during the filling stage.Production increased by 58.1%.The desalting rates of 0-10 cm and 10-20 cm under early spring mulch were increased by 13.70%and 14.54%,respectively.The average 0-20 cm desalination rate increased by 14.12%.The seedling rate of sunflower increased by 16%during thefilling stage and production increased by 38.2%.

Key words: Saline-alkali soil;Mulching in non-growth period;Salt in farming layer