Abstract:
In Sri Lanka, farmers prefer to grow paddy because it is their staple food. The most common reason given for the shortfall is the lack of sufficient irrigation water to rescue crop when the rainfall is lean. The lack of irrigation water is dependant of two aspects. One is the lack of storage and the other is the poor water management. Out of the two, the latter is considered very important because it is an activity that can be easily influenced from the first day of recognition. Therefore, the aim of this study is to carry out a systematic case study application demonstrating the potential to investigate the possibility of increasing land and water productivity through the management of crop types (Paddy, green gram, soya bean and cowpea) grown in each season. Irrigation department guidelines were used for computation of irrigation demand, evapotranspiration requirements and selection of the value of crop growth stages, crop factors and land preparation for Maha season and Yala season with 105 days and 135 days duration for paddy and OFC respectively. Land preparation water requirement, farm loss and the project efficiency were assumed as uniform inputs for all spatial units. Reservoir water balance model based on Irrigation Department guideline was applied to determine the smallest capacity of reservoir that would be required for cultivation of the largest required irrigable area for a pre-determined cropping pattern and intensity for both seasons. After computation of irrigation demand and reservoir water balance modeling, it was found that in all four options, full command area (100%) could be cultivated while in Yala season this result differs as follows. In option 1, paddy was considered for 16% of the command area, while in option 2 this cultivation could be as 10 % of the command area paddy and 28% of the command area green gram. In option 3 and option 4, the cultivable areas were found as 10% for paddy along with 19% for soya beans and 10% for paddy along with 21% for cowpea respectively. Consequently, the second option in which 10 % of the command area was considered for paddy and 28% of the command area for Green Gram was found as a best option to be practiced under Labunoruwa Irrigation Tank in order to increase the water productivity.
