Effects of permanent raised beds on soil salinity in oasis irrigation districts

Shortage of water resources and soil salinization threaten oasis agriculture ecosystem health and stability, which are the two big problems in sustainable agricultural development in arid oasis irrigation areas. While there is need to adopt new irrigation technologies in these regions, such actions could break up the balance of soil water and salt. This could eventually cause secondary soil salinization of farmlands that will in turn decrease farmland productivity. To develop new water-saving irrigation technologies, prevent secondary soil salinization and ensure sustainable agricultural development in irrigated arid oasis areas of Northwest China, it is important to resolve existing conflicts between the adoption of water-saving irrigation technology and the control of secondary soil salinization. Thus an experiment was conducted in spring wheat fields from 2005 to 2010 to monitor soil salinity characteristics under conventional tillage (CT), fresh raised-bed (FRB), permanent raised-bed (PRB) and zero-tillage in flat fields (ZT, control). The results showed that soil salt content increased from sowing to harvest under FRB by 83.3% in the 020 cm, 77.2% in the 2040 cm, 47.6% in the 4060 cm and 84.0% in the 60100 cm soil layers. For the same layers under PRB treatment, soil salt content increased by 62.6%, 46.3%, 28.2% and 103.6%, respectively. Main salt accumulation zone under furrow irrigated FRB and PRB treatments was the 060 cm soil layer. However, main salt accumulation was the 100160 cm soil layer under flood irrigated ZT and CT treatments while there was alternative soil desalination and accumulation in the 0200 cm soil profile. Soil salt content in the 060 cm soil layer decreased with decreasing irrigation while it increased with decreasing irrigation in the 60200 cm soil layer. Soil salinity in root-layer soil depth (0200 cm) was significantly greater from first irrigation to harvest under PRB treatment than under FRB treatment. There was soil salt accumulation in the 6080 cm soil layer under FRB treatment and in the 4060 cm soil layer under PRB treatment. Soil salinity was significantly greater under ZT than CT treatments in the 0100 cm soil layer. Following normal irrigation, soil salinity became redistributed in the middle and surface of beds under FRB treatment. Soil salt migration from the edge to the center of the beds was most notable under PRB treatment. Ridge tillage and bed farming significantly increased salt accumulation in the soil profile. With increasing number of years of cropping and irrigation, salt increasingly migrated and accumulated in the middle of the beds. Thus a fraction of the irrigation water leached salts from ridges/beds and from the soil profile. There was need for at least one irrigation to be larger than normal (over the top of the beds) to enhance redistribution of salts below root-zone soil layer.