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Study of Applying Hydrologic Budget Model on a Field Scale Simulation of Soil Moisture
|關鍵字:||Hydrologic budget model|
馬可夫一階模式(Marcov Lag-one model)可以考慮三維資料中垂直方向之相關性與平面中存在的變異情形，在本文中則是指各土層水分含量在平面分佈上的平均值與標準偏差，以及上下相鄰土層的直線相關係數。在模擬時，由隨機變數的函數來掌握平面的統計特性。
The purpose of this study is to establish a hydrological budget model for the simulation of variance of soil moisture in southwest area of Taiwan. Parameters of climate data required are limited only to precipitation and evaporation, while those of the correlation of soil and crop are derived from field survey and simple statistics analysis. Meanwhile, attempt is made using Marcov Lag-one Model, that could well handle three- dimensional data of the horizontal moisture variance in soil layers and their vertical correlation, to formulate an one-dimensional model to present the three- dimensional distribution of moisture in a specific field soil. The hydrological budget model is based on the assumption that moisture content varying with time is equivalent to the water deficit(due to flow in and out)of root zone(60cm depth in a solum), while on the basis of planned drainage amount of water in field ,the amount of infiltration water is derived from the amount of precipitation minus run-off. In areas of southwest Taiwan, water movement in a solum and water supply to root zone by capillary water are observed linearly correlated with soil moisture content(W), i.e., G= Ka (W-Wfc), Ka indicating hydraulic conductivity constant and Wfc representing field capacity in situ. Field evaporation(ET)is obtained from crop coefficient(Kc)and potential evaporation(ET0), i.e., ET = Kc * ET0. Kc is a function according to change of time and defined as the crop coefficient curve, merged by four linear equations expressing crop coefficients of four commonly divided growth stages of corn. When at growth stage 1st, with leaf area index (LAI)smaller than 1 or cover rate of canopy still less than 10%, Kc is the value of the minimum constant. While at growth stage 3rd, with leaf area index larger than3 or cover rate of canopy attaining 70-80%, the maximum constant of Kc value is obtained. Essential for a hydrological budget model are parameters of Ka and Wfc, and data of precipitation and evaporation. Ka and Wfc can be acquired from field data at any growth stage as long as the range of soil moisture content is carefully considered. To study the simulation of soil moisture and secure the parameters for model, an irrigation timing experiment of spring crop of corn(draught period)was conducted in Chia-Nan area. The results indicate parameters of Kc, Ka and Wfc are readily available from field survey of the initial growth stage of corn(0-26 day, LAI<1)in Hsueh-Chia for the formulation and validation of model. Integrating parameters with data of precipitation, irrigation, evaporation and the crop coefficient curve, the soil moisture content of different treatments during the entire growth season can be simulated to get the linear relation between observed and simulated data. The correlation coefficients R2 of treatment A and B, 0.94 and 0.92, respectively, are both extremely significant. Analysis of the hydrological budget shows the precipitation of 273 mm in 1988 spring crop is sufficient to meet the demand of evaporation, which could even be 1.1 times its potential evaporation at the culmination of growth. The Marcov Lag-one Model enables consideration of three- dimensional data of the horizontal moisture variance in soil layers and their vertical correlation. The mean value and standard deviation of the horizontal distribution of soil moisture content in every soil layer are included and considered in this text. Furthermore, the coefficients of linear relation between neighbor layers are also calculated in the study. Random variables or numbers handle the characteristics of horizontal statistics, when simulating. Validation of the Marcov Lag-one Model is carried out with soil survey of field No.16 in Taiwan Agricultural Research Institute. It indicated under conditions of rain and irrigation the maximum variance coefficient of soil moisture content in field of 0.5 hectare was 15%, while that under conditions of partially wet and partially remain drought could reach over 40%. Through assessment of soil moisture content during the entire growing season, linear correlation was found between layers of 0-15 and 15-30 cm, and also between layers of 15-30 and 30-60 cm, with coefficients R2 of 0.7388 and 0.7406, respectively. Data generated from the Marcov Lag-one Model have advantages of maintaining population features of original soil layers and existence of linear relation between two neighbor layers. Therefore, on a large field scale, the Marcov Lag-one Model combined with Monte Carlo Method can be expected to handle the variance and distribution of soil moisture content in field, as long as the variance coefficient is large enough to locate the correlation between every two neighbor layers. Readjustment use of field land is quite crucial to sustainable agricultural development in Taiwan. It is convinced that facilities design of irrigation and drainage, fulfilling requirements for environmental protection, once introduced will spark great change in current environment of soil water. Long-term fallow is not only for ecology reason but contributes to more benefit of conservation of water resource than that of paddy. Quantitized assessment of such benefit is just made a start. As experiments have indicated, greenmanuring and pasturing on fallow land gained higher speed of biomass accumulation, also resulted in larger capacity of infiltration than upland rice and paddy.
|Appears in Collections:||土壤環境科學系|
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