Research On Assessing The Suitability Of Farmland Drainage Resource For Irrigation

In the region of water shortage, in order to meet the demand of crop growth during a tense period of lacking irrigation water, reuse farmland drainage for irrigation in a suitable way could avoid reduction of crop production, and relieve the tense contradiction between agricultural water demand and supply. However, farmland drainage not only contains nitrogen, phosphorus and so on, which are beneficial to crop growth, but also contains salt and heavy metal and other toxic and harmful substances. It is harmful to use farmland drainage for irrigation in an unreasonable way, causing a decline in crop yield and quality, the problem of soil salinization and pollution of groundwater environment, etc. At present, it is still a lack of abundant experience on long-term safety utilization of farmland drainage for irrigation. Due to insufficient understanding of the risk of reuse, there is a certain blindness in utilization of farmland drainage resources. It is badly in need of a normative guidance for irrigation reuse. This paper carrys out research on evaluation of the suitability of drainage water for irrigation, in order to provide guidance for reusing farmland drainage resources for irrigation in a scientific and reasonable way, avoid or mitigate adverse effects caused by utilization. This study selects arid and semi-arid regions under the threat of salinization as the object of research, first puts forward the connotation and evaluation index system of the suitability of reusing farmland drainage resource for irrigation, and then uses the fuzzy pattern recognition evaluation model based on analytic hierarchy process to evaluate suitability degree of five typical ditch water for irrigation in Ningxia Yinbei Irrigation District and analyzes the evaluation results.Through research mainly drawing the following results:(1) This research puts forward the connotation and evaluation index system of the suitability of reusing farmland drainage resource for irrigation, selects fuzzy pattern recognition model widely used in Hydropower Engineering and hydrology and water resources field, determines the standard value matrix of evaluation index system, uses the analytic hierarchy process (AHP) to determine the weights of each evaluation index, carrys out the actual evaluation of Ningxia Yinbei Irrigation District, making the suitability evaluation of reusing farmland drainage resource for irrigation from the concept into practice, from qualitative evaluation to quantitative evaluation.(2) Through analysis of the level characteristics value of drainage water quality and suitability, finding that the farmland drainage water quality is generally better in the latter period of irrigation in Yinbei District, In the meantime the level characteristics value of the suitability of reusing farmland drainage resource for irrigation tend to be smaller, and specific rules of suitability also vary between different years, but the suitability in the latter period of irrigation is better than the previous in general.(3) Analysis of the correlation between the level characteristics value of suitability and soil salinity increment shows that there is some correlation between them, the soil salinity is in a dynamic change process of salt deposition and desalting alternating with a slight salt accumulation trend, and draws that when the soil salinity increment is zero in the region under the condition of reusing farmland drainage water for irrigation,the critical level characteristics value of suitability is2.2.(4) Through comparative analysis between different regions, it is found that the conditions of Longhu and Yanzidun is suitable for utilization of farmland drainage resources; the farmland drainage is of poor quality in Qianjin Farm, only can be used as proper compensation irrigation in the case of relatively dry weather; more land are grow with rice in Nuanquan Farm, it is suggested that the Paddy-Upland rotation mode should be taken to regulate groundwater level under the condition of reusing farmland drainage water for irrigation.Based on the above findings, although utilization of farmland drainage for irrigation will cause slight salt accumulation in some region, as long as the better corresponding measures are taken, it will still be able to achieve the purpose of sustainable utilization.