Impact Study On Salinizstion Of Nierji Irrigation Area And Control Countermeasure

The Nenjiang (Nierji) irrigation area, originated from the HadaTown in the north to the Songhua River in the south, and startedfrom the area along the Nen River to the low Songnen plain of themain Beiyin channel, with an irrigation area of 121033.3hm2, is alarge irrigation district diverting from the Nierji reservoir.The key issue of developing the irrigation area is whether thesoil salinity can be prevented effectively or not because the area isdistributed with the salinized soil. Therefore, to reseach theirrigation's effect on the soil salinity is very important. The researchis aimed for the present situation of earth, water and salinity basedon the data collected widely. The main conculsions ara asfollowings:1. The dry climit and semi-inwardflow area supplied by theWuwei River during the period of salinity accumulation in themodern times are the main reasons for the groud water and salinityof the soil in the area. The salinity is from the chemical runoffs ofthe river mainly mainly.2. Waterlogging and salinity back made by the soil freezingand thawing. The soil surface begins to freeze in the late Marchand finishes in the middle and late June, and this period is in thedry seasons as the spring and summer. The freezed water in thesoil is evaporated, and the salt accumulated in the freezed soil willevaporate with the water, concentrated in the land surface (salinityback). Due to the un-freezed layer, the freezing layer takes a roleof separating the water and form a freezed water layer, ifextra-irrigation or un-suitable diversion, not only can causewaterlogging but also the salt will be taken to the surface during thewater evaporation in the soil.3. The secondary salinity of the soil maybe occur in theirrigation area. Through the dynamic monitoring for the water andsalt of the soil we can know that:3.1Groudwater level: the groudwater level increases generallyafter freezing, compared with the situation before freezing, thegroudwater level increases quickly, the lasting time of high waterlevel are longer than before. The rainy period delays one month ormore. The peak of water level wihin one year occure more timesthan before, and water level increase quickly, the increasing curveis very sharp, and the curve of water level reduces gentallycompared with the increasing curve.3.2 Chemical and drynamic character of the groudwater: thedegree of groudwater mineralization increases, and the changing isdecided by the salt contents of the soil. The high mineralizationoccur in the rainy period, because as only the water level increasesto the part containing the salt the mineralization will increase. Afterfreezing, the water level will increase generally, and themineralization degree will increase obviously both in the rainy anddry period. The hightening of water level may dissolve the solubilitysalt in the layer containing high salt, and the mineralization of waterwill increase. If the high water level lasts long, the groudwater inhigh mineralization will cause the salinity accumulation on thesurface.3.3 Dynamic state of soil saltAfter freezing, the salt contents in the soil changes greatly, the saltaccumulation is very obvious and the ions increase too. When thetotal salt contents increase, HCO3-and Na+ increase with it.Sepecially, the two sides both have been taking the advantageswhen the total salts exceed 0.07%, which show that the solution ofsoil has large quantities of NaHCO3, and developing towards thealkalization stage. Therefore, the threat of secondary salinity is stillexisted.3.4 The soil salinity may be prevented. Through theexperimental observation, for many years, due to the strict controlover the irrigation, combination with the improvement measures,not only the secondary salinity didn't occur in the soil but also thesalt contents of the soil reduced, and the production also increases.The research concludes various measures against the soil salinity,and will take roles of preventing and guiding the soil salinity.In general, the key of preventing the secondary salinity of thesoil lies in the smooth drainage system.