Changes in the cations composition of water from irrigation to drainage and leaching requirement of the Hetao Irrigation District, Inner Mongolia
2008
Akae, T.(Okayama Univ. (Japan)) | Nakao, C. | Shi, H. | Zhang, Y.
According to the calculated salt balance of the entire Hetao Irrigation District, the district is gaining 1.7 M ton of total dissolved salt annually. In spite of the fact, irrigation engineers and farmers assert that salinization of the district has improved in recent years. Furthermore, the LANDSAT image analyses show a recent decrease in the saline area. The first objective of this paper is to clarify the riddle in salt dynamics, by a systematic sampling and analysis of canal water, groundwater and soils. All of the water soluble and insoluble cations including exchangeable cations were analyzed. The results showed that most of calcium precipitated in the soil, consequently, sodium predominantly accumulated in the top layer and drained to the drainage canal water. The second objective is to propose a new leaching requirement based on sodium balance, LRsub(Na) and to apply it to the whole district. The estimated LRsub(Na) in 2005 was 0.12, which agreed with the present observed drainage fraction 0.11. It means that sodium balance of the whole district is almost attained at present time and that the new leaching requirement, LRsub(Na) indicates the actual salinization status of the district better than the conventional leaching requirement. Furthermore, risk of salinization was evaluated on each branch drainage canal block. The risk was found to be high in the central blocks.
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