13.2 Estimation of irrigation water requirement in paddy field
To calculate the irrigation water demand in Boro rice field in the study area, monthly
averaged rainfall and temperature data for the time period 1961–1990 is used. It
is found that potential evapotranspiration (PE) in the study area starts to exceed
precipitation (P) in the month of November and continues up to April. This means
that soil moisture deficit starts to buildup in November. The amount of water
required to replenish the soil moisture in the month of December is considered as
the water required for land preparation. The map of soil water required for land
preparation is shown in Fig. 5. The figure shows that the water required for land
preparation varies between 114 and 128 mm in the study area.
The sub-district scale map of percolation and seepage losses from the rice field
computed from soil composition map is shown in Fig. 6. The Seepage and Percolation
losses vary between 280 and 669 mm in the study area. The losses are higher in the