| Yinchuan plain which is an important industrial and agricultural base is situated in the north of Ningxia Hui Autonomous Region. Serious soil salinization due to long time flood irrigation is greatly restricting the development of agricultural in the plains. In this paper, based on the analysis of the collected data of hydrological, meteorological, hydrological, water resources development, water quality and soil soluble salt, the systematic study of the balance between groundwater and salt was made in addition to the influencing factors of soil salinization. Reasonable infiltration and drainage project was established for providing scientific basis for the elimination of the of soil salinization. Main contents and conclusions of the study are as follows:1. A comprehensive analysis of the study area on topography, hydrological and geological conditions and groundwater recharge, runoff and discharge conditions were made. Based on the analysis, the recharge items of the groundwater balance were determined as agricultural irrigation infiltration, precipitation infiltration, flood loss, canal seepage and lateral runoff. Discharge items were considered as gutter drainage, groundwater discharge to the Yellow River, groundwater exploitation and groundwater evaporation.2. The water budget equation was established. Considering the close hydraulic connection between unconfined aquifer and confined aquifer, the computation was unified on the unconfined aquifer and confined aquifer. During the balanced period of the study area the total groundwater recharge is 23.757×108m3/a, among which over 60% of groundwater recharge is from canal seepage. The total discharge capacity is 23.658×108m3/a; and groundwater evaporation is the main discharge factor. The relative balance difference was 0.42%, indicating that groundwater in the study area is basically in equilibrium.3. Based on the water balance calculation, the salt balance equation was established. The cumulative amount of salt and ions were calculated in combination of water quality data. During the balanced period of the study area, the total recharge capacity of salt is 1179664.69t/a, the total discharge amount of salt is 1048421.25t/a, and the salt product is 131243.44t/a. More than 55% of salt leakage is from the canal supply, while artificial salt mining and drains discharge are the major drainage ways. In study area, the total cumulative amount of ions is 129070.08t/a, among which Ca2+, HCO3-, SO42-in the study area are in the accumulation state, Mg2+, Na+, Cl- in the plain are in the discharge state.4. Based on the calculated results of salt balance, the relationship between TDS and groundwater salinity was analyzed, which indicated that the salinity of the groundwater greatly affected TDS. The relation among groundwater TDS, burial depth and soil salinity were further studied, the results showed that the soil salinity is higher and soil salinization is more serious with shallower groundwater table and higher TDS condition.5. After the Analysis of the soluble salt data and water quality data, ions affecting soil salinization are mainly Mg2+, Na+, Cl-and SO42-. Assume salt balance is exist, ratio of canal seepage water (Wc) and the discharge of drain (Wd) is 2.36, the ratio of canal seepage permeability coefficient (q) and the discharge coefficient of drain (δ) is 0.47. At present, the two ratios are 3.94 and 0.73 respectively which are higher than the ratios of salt balance. The results show that the plain is currently in a salt accumulative state base on which some measures for the improvement of soil salinization were proposed.
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