Studies On The Principles Of Water And Salt Movement AndSecondary Salinization In Songnen Plain

Being a part of the North-east Great Plain, the Songnen Plain covers 4.97 millions hectares. It is one of the main yielding zones of commercial foodstuff in China. Because of special geographical, climatic and hydrographical conditions, secondary salinization has been always hampering the local agricultural development, especially which has been aggravated by irrigation cause during the past decades. At present, the area of saline-soil has accounted to 1.116 millions hectares, and there are still about 5.33 millions hectares confronting hidden salinization .The aim of project is to forecast and predict secondary salinization on the basis of the studies on the principles of water and salt movement .The results as follows:1. By studying the features of water and salt movement in the Songnen Plain, we can make the following conclusions: (1) In the soil profiles at the depth from 0 to 30 cm, salt content, Na+, HCO3" and pH are the highest at the layer of 20 ~30 cm. A tendency that salt is moving towards the soil surface with the increase of cultivated years has been proved. (2) The accumulation of salt is decreasing fast with the increase of underground water level in despite of cultivated or deeper layers. (3) Different ways of irrigation cause different types of dynamic changes of underground water. Under ground water table varies from 60 to 160 cm under the condition of well irrigation, variance being 100 cm; underground water table varies from 16 to 168 cm .variance being 150 cm under the condition of canal irrigation.(4)In terms of ways of irrigation drainage ,the way of combination of irrigation and drainage is better than the way of single irrigation.2. The prediction and forecast of secondary salinization in the Songnen Plain, Under the condition of well irrigation, salt content of ll.Omg/kg is accumulated in cultivated layer annually, and at this rate, severe secondary salinization will be happened in 40 ~80 years, and medium secondary salinization in 1~40 years. Under the condition of canal irrigation, salt content of 17.0mg/kg is accumulated in cultivated layer annually, and severe secondary salinization will emerge 30-60 years, and medium secondary salinization will emerge 1~30 years.3. It is feasible to establish model of predicting and forecasting secondary salinization by applying Artificial Neural Net. It is comparatively accurate to describe the occurrence and development of secondary salinization according to ANN model.4. The improvement of saline soil by organic manure. In this pajt, the relation between organic and salinization and improvement of salinization byorganic manure are attached importance on. (1) Physical quality of cultivated soil is improved by organic manure, with organic increasing by 56.0g/kg, soil porosity increasing 6.0% and infiltration rate arising8.3%. Improvement of physical quality contributes to desalinization. (2) Salt content decreases by 38mg/kg. (3) Soil fertility is enhanced and yield of rice is increased by 12.9%.5. The classification of hidden secondary salinization. On the basis of the salt content of soil from surface to the depth of 2 m and the Standards of National Classification of Secondary, hidden secondary salinization in Songnen Plain is classified as five levels: unsalinization, light hidden secondary salinization, medium hidden secondary salinization, severe hidden secondary salinization and secondary salinization.6. The ways of preventing and curing secondary salinization. (1) Underground water table must be controlled in order to prevent the salt in deeper soil moving towards soil surface. (2) Organic manure should be scatter to improve physi-chemical quality and enhance soil fertility to increase rice yielding. (3) It is also necessary to construct field safeguarding forest and perform integrated control.