Parameters and Characteristics of Alkalization of Sodic Soil in Da′an City

Primary parameters of sodic soil in Da′an City,including exchangeable sodium percentage（ESP）,sodium adsorption ratio（SAR）,total alkalinity,pH,soil salt content,etc.were determined for analysis of characteristics and vertical distribution of alkalization in the profile.Results show 1) Na⁺ and HCO^-₃ are the major soluble ions in the soil with the former accounting for 80 percent or more of the total cations and the latter for（75%-85%） of the total anions.And NaHCO₃ is the primary cause of aggravated soil alkalization.2) The soil layer located at the depth of（20-80） cm in the soil profile is an apparent alkalized soil layer,with ESP>（25%-30%）;pH>10.3;and salt content>6.0 g·kg^-1.The characteristics of soil alkalization tend to be weaker in other soil layers in the profile.3) Soil ESP rises with soil salt content and total alkalinity,and positively correlated with SAR（r=0.711,n=40,P<0.000 1）.Based on precipitation and groundwater data available,causes of the salinity distribution pattern in the soil profile were discussed at the end.