A thesis submitted in partial. fulfilment of the requirement for the degree of Master of Engineering, School of Civil Engineering

Thesis (M. Eng.) - Asian Institute of Technology, 1994

Land use study was conducted in the Chao Phraya Delta in the first phase of this study to identify the components of diversified farming system including their spatial distribution over the delta by the conjunctive use of visual interpretation of satellite images (LANDSAT TM) and physical verification through extensive field visit. Based on the findings, a base map has been developed showing different land use units distinguished by the cropping pattern, crop calendar and land use elements. In the next phase, intensive study had been performed in 6 selected farms under the North Rangsit Irrigation Project to estimate the water requirement of citrus. Farmers' interview had also been taken to explore the water management and relevant agronomic aspects as well as to study the possibility of expansion of citrus farming in the same. This study reflects the existence of diversified farming in the Chao Phraya Delta having major components of aquaculture, vegetables and fruits. Among them fruit is concentrated in the central part of the delta. Especially citrus (orange) has come up replacing rice in the North Rangsit Irrigation Project. Citrus farming in this area has a special type of farm structure, termed as 'Bed and Ditch System', for maintaining well controlled on-farm water management. In normal situation water level is maintained close proximity to the plant root zone (about 50 cm below the top of the bed) with a permissible water level fluctuation of about 20 cm. This study reveals that flowering stage is the most susceptible one to water stress followed by fruit set & establishment stage. During the flowering stage whole day water application is necessary to ensure the full scale fruit setting and thereby yield. The frequency of water diversion from canal to garden varies from farm to farm over a wide range of 1 time/month to 12 times/month with an average value of 6 times/month. Average water requirement and the kc value for citrus in the dry season (January-May) has been estimated as 630 mm (4.2 mm/day) and 0.68 respectively. In consideration to water requirement and other relevant factors, this study divulges the promising possibility of citrus farming expansion in the Chao Phraya Delta.