RICE IN SRI LANKA - Water Management
Water requirement for land preparation
Land preparation consumes highest quantity of water during a cropping season, which could be reduced with dry land preparation (Kekulan or Manawary). However, majority of rice is cultivated with wet land preparation. Duration of land preparation determines the amount of water it requires. This depends on the land class and the weed infestation. For lowland land preparation water requirement is accounted for soil soaking, maintaining standing water and water losses.
Quantity of water required for soil soaking is determined by initial soil moisture content, surface conditions of the land and soil type, Maintenance of standing water is done after primary tillage to control weeds. When standing water is maintained, there could be losses via evaporation (E), seepage (S) and percolation. (P)
- Average rate of ‘E’ in a sunny day in the Dry Zone in “Maha” is about 3.5 mm and in “Yala” is about 6 mm,
- Average S & P rates of RBE soil is 7-10 mm/day and LHG soils is 3-4 mm/day
Therefore, Water requirement for maintaining standing water and keep the soil saturated need to meet S, P and E, which is higher when land preparation takes longer (usual minimum duration for conventional land preparation is two weeks). For e.g. for LHG – ~150 mm and for RBE – ~300 mm (dry zone).