Abstract: Over irrigation leads to deep percolation,which is one of the main pathways of water loss from drip irrigation field.Subsurface water retention technology (SWRT) can be used to effectively reduce the deep percolation and improve the water use efficiency.The objectives of this study were to determine the effects of irrigation volume and SWRT on soil moisture balance,cotton yield and water use efficiency in a drip-irrigated cotton field.The experimental was designed as 3×3 factorial with three irrigation volumes (340,440,and 540 mm) and three SWRT treatments (contrast,40 cm deep membrane and 60 cm deep membrane).Results showed that the soil moisture content (0-60 cm) and net soil water storage were significantly increased under the treatments of 40 cm and 60 cm deep membranes compared with that of contrast.Deep water percolation loss in soil layer deeper than 1 m was significantly increased with the increase of irrigation volume.Under 340 mm irrigation,there was no significant difference in deep water percolation loss among three SWRT treatments.Under 440 mm and 540 mm irrigation,the deep water percolation losses in the plots with 40 cm and 60 cm deep membranes were reduced by 64% and 72%,and 38% and 76%,respectively compared with those of contrast.Both the treatments of 40 cm and 60 cm deep membranes reduced significantly the evapotranspiration in the 340 mm irrigated plots.However,in the 540 mm irrigated plots,the 60 cm deep membrane treatment increased significantly the evapotranspiration compared with the contrast.In the 340 mm and 440 mm irrigated plots,the dry matter weight,yield,water use efficiency and economic benefits of cotton were significantly higher in the 40 cm and 60 cm deep membrane treatments than those in the contrast.But there were no significant differences between the 40 cm deep and 60 cm deep membrane treatments.In the 540 mm irrigated plots,the treatment of 60 cm deep membrane increased significantly the cotton dry matter weight and yield,water use efficiency and economic benefits.There was no significant difference between the 40 cm deep membrane and the contrast.Therefore,both the 40 cm and 60 cm deep membranes were suitable under low and moderate irrigation volumes (340 mm and 440 mm),and the SWRT of 60 cm deep membrane was preferable under high irrigation volume (540 mm).

Key words: drip irrigation, subsurface water retention technology, irrigation amount, cotton yield, water use efficiency