Effects of water regulation methods on soil salt, nutrient content and its distribution in overlying saline wasteland

Drip irrigation with its characteristic of applying water at low discharge rate and high frequency over a long period of time can maintain constant and high soil water contents in the root zone, and reduce salinity in soil water by leaching, particularly near the drip emitters. Recently, numerous studies have evaluated the use of different levels of soil matric potential (SMP) to trigger drip irrigation in arid and semiarid regions and have successfully reclaimed saline and saline-sodic soils. However, very few studies have explored soil nutrients during the reclamation process under drip irrigation and hence understanding of nutrients in saline-sodic soil under drip irrigation is limited. A three-year experiment was carried out to investigate the soil salt and nutrient variation in saline wasteland during reclamation under drip irrigation in inland and arid region. The experiment included five treatments in which the SMP thresholds at 20 cm depth were controlled at -5, -10, -15, -20 and -25 kPa. The treatments were replicated three times in a completely randomized block design. The results showed that the soil electrical conductivity (ECe) and sodium adsorption ratio (SAR) in 0-40 cm layer decreased significantly after three years of reclamation and the soil in -5 kPa treatment had the highest decreasing rate. By the end of the third cropping season, the ECe for -5 and -10 kPa treatments had reduced from 47.0 to 5.3 and 8.1 dS/m, respectively, which were in the range of the threshold salinity of cotton. The changes in SAR with time were similar as those of ECe. After the third irrigation season, the SAR, relative to the initial level, decreased by 40%-75% for the five treatments. Comparing with the initial value, soil available N, P, K, total N, P, and organic matter had a significant (P