Soil Salinity Dynamics And Its Influencing Factors In Weibei Region Of Shaanxi Province

Weibei region is the second granary of Shaanxi province,but the problem of soil salinization is more prominent,this region has suffered from soil salinization,big waterlogging disasters,and high soil compaction for a long time.At present,the study of soil salinization in Weibei area mainly focuses on LuBotan,but the dynamic distribution and genesis of soil salinization in Weibei area are few,especially soil compaction structure of plow pan impacting the movement and distribution of salt in the soil profiles is not clear.Therefore,it is of great practical and scientific significance to study the soil salinization in Weibei area from the regional scale and to explore the influence of plow pan on soil water and salt movement.Soil samples from typical farmland in Weibei region were collected through 10 km×10 km mesh point method.In this study,soil salinity types and soil salinity spatial distribution in Weibei farmland were clarified,and the influence of soil physical properties on salt distribution in soil profile were revealed.The relationship between water,heat and salt in soil salinization was analyzed by location monitoring.Taking Luohui irrigation area and Jiaokou irrigation area as typical areas to analysis interannual dynamics of soil salinization.The relationship between soil salinization and soil bulk density on water and salt transport in the shallow groundwater area was discussed through the indoor simulation experiment.The main conclusions of this study are as follows:(1)The soil anions in the Weibei area of Shaanxi Province were dominated by Cl-and SO42-,the sulphate soil ratio was about 55.88%,the cation was mainly Na+,and the ratio of sodium salt was about 41.18%.Non-salinization and mild salinization soil were about 76.23%,and the soil salinity increased with the increase of soil depth,there was a risk of soil salinization.(2)Soil electrical conductivity showed a trend of summer> autumn> spring> winter in the high salinity area,and showed a trend of spring> summer> autumn> winter in low salinity area.The conductivity of high salinity area is affected by various factors,and the low salt content area is mainly affected by temperature and altitude.The effect of temperature on the conductivity of soil profile decreases with the depth of the soil,but the effect of water on the conductivity increases with the depth of soil.During the year,the effect of moisture on the conductivity is greater than temperature,when water range from 15% to 30%(equivalent to 11%~21% of water content),there had a significant influence of soil moisture on conductivity.(3)The area of soil salinization in the two irrigation areas showed an increasing trend in the past 10 years.The dynamics of soil salinization area in irrigation area was affected by irrigation and drainage measures.The irrigation area was the main influencing factor of soil salinization,and the area of soil salinization increased with the increasement of irrigation area.(4)Significant correlation was observed between soil texture and salt content only in 0-20 cm soil layer.The effect of soil physical properties on salt content not only found in the same soil layers but also in different soil layers,namely ectopic impact.And this impact was related to the degree of soil salinization.When salt content was lower than 1 g/kg,a power function relationship was observed between soil bulk density in 40-60 cm layer and salt content in 20-40 cm layer.An increasing function was observed between soil bulk density in 20-40 cm layer and salt content in 0-20 cm layer when salt content ranged from 2 g/kg to 4 g/kg.However,when salt content was higher than 2 g/kg,a decreasing function would be found between soil bulk density in 0-20 cm layer and salt content in 20-40 cm layer.A decreasing function was observed between water-stable aggregate and salt content,especially when salt content was higher than 2 g/kg.(5)Plow pan can prevent water and salt migration from bottom to top.With the increase of soil bulk density in the plow pan,a parabolic function relationship was observed between soil conductivity and soil bulk density.The critical value of the accumulation of salt in the plow pan is 1.60 g/cm3.For the groundwater shallow area,when the plow pan bulk density is greater than the critical value,the retention of plow pan is conducive to the prevention of salt water in the ground.When the plow pan bulk density is less than the critical value,may consider appropriate to break the plow pan,reduce the capillary effect,to prevent the salt taransport to surface soil.