Theory And Application Of The Evaluation On Agricultural Soil Water Utility Based On Water Cycle Simulation

Currently, with the rapid development of social economy and growth of population, the contradiction between water supply and demand in agriculture has become a serious problem. For a long time, the pressure of food security has encouraged the farming practice in China with high multi-cropping index, complex rotation systems and strong human intervention. The characteristic of natural-artificial dualistic water cycle in farmland is becoming more and more significant. Based on the concept of dualistic water cycle, this paper analyzed water cycle of farmland influenced by modern agricultural technologies, and quantitatively simulated the movement of soil water in regional scale. Meanwhile, this paper also evaluated the soil water utility according to the evaluating index system. On a whole, the research in this paper plays an important role in maintaining high and stable yield in agriculture, popularizing water-saving technologies in agriculture and coping with agricultural water scarcity.In order to alleviate the conflict of between water supply and demand in agriculture, we should pay much attention to both increasing volume of available water and reducing water demand. In terms of increasing volume of available water, the potential of soil water in farmland should be fully developed. The storage in crop root zone can smooth the uneven temporal distribution of available water in farmland and alleviate agricultural drought and water shortage to some extent. In terms of reducing water demand, efficiency of agricultural water use should be fully improved. Through simulating and calculating soil water cycle process of farmland, the relationship between the volume of water stored in soil reservoir and water flux in soil layer could be analyzed, which could be the reference to take the relevant measures to exploit the potential of soil water, inhibit low-efficiency water flux and then improve the level of efficient utilization of agricultural water. Meanwhile, as to the farmland management measure, monitoring-soil-moisture-for-irrigation method should be popularized, in which, soil water simulation and calculation are of great importance.Based on extensive literature review, this study proposed the concept of water utility and the quantitative evaluation index system on farmland soil water use, and North China Plain was selected as the study area. The water cycle simulation and soil water utility evaluation model-MODCYCLE1.5was used to analyze water cycle process in the study areas, by which, the utility efficiency of soil water in the study areas was quantitatively evaluated. This paper mainly includes the following aspects:1) Based on the analysis of the motion path and exchange of soil water cycle in farmland, this paper put forward a new concept and new evaluation method of soil water utility in farmland. Through a thorough review of relevant researches, this article aimed to achieve efficient use of farmland soil water resources by inspecting the farmland water cycle on regional scale. And the distributed hydrological model was adopted as a tool to establish a new system for evaluation on efficient utility of soil water.2) Distributed hydrological model was used in this paper to simulate the soil water cycle in farmland. Combined with the characteristics of the hydrological cycle of farmland in North China Plain, the hydrological model-MODCYCLE was modified and improved to be MODCYCLE1.5, by which, the farmland soil water cycle in Handan City was simulated and analyzed. MODCYCLE1.5considers the basic characteristics of the farmland in the study area, and creates the database of soil properties using the measured data of lithology of soil in Haihe River Basin. And the other parameters in MODCYCLE1.5were also effectively calibrated, improving the accuracy of the simulation and the calculation.3) The simulated results were sufficiently verified from the following aspects: simulated soil moisture in15soil moisture monitoring stations, yearly water balance in the entire area, yearly runoff running out of the area and the simulated yield of crop. The results show that there is a good agreement between the estimated values and the observed values, which indicate that the model is reliable.4) This paper gave a new concept about the soil water utility in farmland. It holds that the soil water utility refers to the rational state of the resource attribute, spatial-temporal distribution attribute and function attribute of soil water in its development and utilization. This paper also put forward the evaluation index system based on the new concept, which included:1) the effective storage of soil water reservoir in the crop root zone;2) the variation of the empty storage of soil water reservoir in the crop root zone, which includes2subindexes, the annual average value of the empty storage and the variation coefficient of the empty storage within one year;3) the spatial and temporal matching status between water supply of the soil water reservoir and water demand of the crop, which includes2subindexes, the spatial matching index and the temporal matching index;4) the recharge efficiency and discharge efficiency of the soil water reservoir in the crop root zone.5) This paper quantitatively analyzed the indexes of soil water utility in different hydrological level years of Handan City. The results show that the soil storage capacity in the eastern plain area is larger than that in the western mountainous areas. However, the condition of water supply in crop root zone of the study area is not good, and the crops seriously suffer from water deficiency and water stress. In terms of temporal matching status between soil water supply and crop water demand, water is severely deficient in the tillering stage, shooting stage and booting stage of winter wheat. Therefore, irrigation is important for wheat growth in the study area. In terms of spatial matching status between soil water supply and crop water demand, the agricultural water scarcity in the east and middle parts of Handan City is serious. According to the results, the efficiency of soil water recharge in Handan City is high, which indicates that inefficient water loss in the recharging process of the farmland is not large, while the efficiency of soil water discharge is much lower, indicating that a large amount of soil water can’t be efficiently absorbed by crops.6) At last, the paper comprehensively evaluated the utility efficiency of soil water in different county districts. Results show that the comprehensive utility efficiency in the west mountainous part and the east plain part is higher than that in the middle part of Handan City. And this paper also proposed many measures to improve the utility efficiency of soil water based on the concept of temporal and spatial soil water management, which included changing planting structure, increasing the storage capacity in the crop root zone, applying monitoring-soil-moisture-for-irrigation method and popularizing water-saving technologies.