American J. of Engineering and Applied Sciences 2 (1): 133-138, 2009 ISSN 1941-7020 © 2009 Science Publications Corresponding Author: Anongrit Kangrang, Faculty of Engineering, Mahasarakham University, Kantharawichai, Maha sarakham, 44150, Thailand Tel: +66-43-754316 Fax: +66-43-754316 133 A Varied-Utilized Soil Type in Linear Programming Model for Irrigation Planning Ounla Sivanpheng, Anongrit Kangrang and Alongkorn Lamom Faculty of Engineering, Mahasarakham University, Maha sarakham, Thailand Abstract: Problem statement: Optimal crop pattern with maximum profit is important information for irrigation planning using optimization model. Crop yield, crop water requirement, man power, production cost and physical soil type are required to the search model. A consideration varied-utilized soil type directly influences to the profit of obtained crop pattern. Approach: The objective of this study is to find an optimal crop pattern for irrigation planning in a varied-utilized area of the Van Vieng Phi irrigation project, Khammouan province, Central Region of Lao PDR. An allocation Linear Programming (LP) model was applied to find the optimal crop pattern in dry-season (November- April). The considered irrigation project was divided into several sub-areas, based on suitable soil type of each crop representing the varied-utilized character. The existing suitable soil type of each crop was used to represent the varied-utilized in term of water requirement and crop yield for each sub-area. The records of seasonal flow from pump station, requested and actual implementation of irrigation area, crop water requirements, evaporation, percolation and effective rainfall were used for this illustrative application. Results: The results have shown that the net benefit of varied-utilized character and unvaried-utilized character (existing consideration) were obvious difference. The obtained crop pattern of the proposed model corresponded to the suitable soil type for cultivation crops. Furthermore, the results presented that the proposed model gave higher net benefit than the existing unvaried-utilized character. Conclusions/Recommendations: The consideration several sub-areas of irrigation project based on suitable soil type in LP model can be represented the varied-utilized character. The proposed LP model is appropriately for finding the optimal crop pattern for irrigation planning. Key words: Optimization model, linear programming, irrigation planning, crop pattern INTRODUCTION An allocation of limited available resources is one of the classical problems in water resources management. In particular, given the total available resources for example water, soil, land area and manpower, one would like to know what proportion of the available resources should be given to each considered crop in an irrigation project in order to maximize the total profit of agricultural activities. With optimization techniques available; such as Linear Programming (LP), Dynamic Programming (DP) and Genetic Algorithm (GA), it is LP model that is more popular because of the proportionate characteristic of the allocation problems. The formulation of the LP model to the problems usually assumes that crop water requirement and crop yield of all soil types in the considered project be homogeneous value for all seasons. Unfortunately, the assumption often leads to serious error in the optimal solution of the crop pattern. In Lao PDR, improving performance of irrigation planning for an operation and maintenance project is an obvious issue for agricultural development and water resources management. The Vang Vieng Phi Irrigation scheme is a Pump Irrigation System, which located in Se Bangfai district about 45 Kilometers south of Thakhek, Khammouan province. The irrigation scheme is designed for an irrigation service area of 1,086 hectares during the wet season and 1,070 hectares during the dry season. Record of irrigated area from 2000-2007 presented that the scheme had been irrigating an average of 229.55 hectares during the dry season or a 21.45% of the dry season design area. The highest dry season irrigated area is recorded in crop year 2006-2007--359.74 hectares or 33.62% and the lowest in 2004-2005--121.79 hectares or 11.38%. The record shows that the dry season irrigated area had been increasing from crop year 2000-2001 to 2002-2003 but this started decreasing from then to 2003-2004 and increased again from crop year 2005-2006 to 2006-