Simulation modeling of irrigation requirements for sugarcane production in Sindh Province, Pakistan

Over-irrigation and poor internal drainage of soils in the Indus basin of Pakistan have resulted in waterlogging and salinity problems, severely affecting agriculture. These problems may be solved by subsurface drainage or more efficient irrigation water management. Since drainage system installation is relatively expensive Pakistan, efficient irrigation management practices e.g., irrigation scheduling and on-farm water management are cheaper alternatives.A soil water simulation model, SWAP93, was used to evaluate the effects of water stress on crop yield, water use efficiency (WUE) and crop water use in sugarcane [Saccharum officinarum L.]. This information was used to determine water management practices, which can reduce salinity and waterloggingDrainage fluxes and evapotranspiration simulated by the model were compared with those measured in drainage lysimeters (water tables controlled at 1.5 m and 2.25 m from the soil surface) for 1989 and 1990. Drainage fluxes were overestimated, and evapotranspiration underestimated. The model's original grass-based evapotranspiration (ET) was changed to an alfalfa-based one, resulting in a better estimation of drainage fluxes and ET.The effects of soil water balance, simulated by the SWAP93, on the crop yield, WUE and crop water use were assessed using twelve irrigation treatments consisting of four irrigation amounts (1800, 1650, 1200 and 900 mm) factorially combined with three irrigation intervals (7, 10 and 15 days) for seven years of climatic data.Crop yields increased linearly with irrigation of 1200 mm during the growing season, Crop yield, ET and WUE were not significantly different for irrigation amounts ranging from 1200 to 1800 mm. When the total applied water was above 1400 mm, the crop yield showed a plateau. This maximum yield was reached because irrigation water was remained in the soil profile or percolated into deeper layers at high levels of irrigation application.For a 7-day irrigation interval, the 1200 mm treatment showed water deficits during the middle of the growing season, whereas for 10- or 15-day irrigation intervals, water deficits were negligible.A 3rd degree polynomial relationship between cumulative irrigation amount and drainage fluxes was developed, allowing a daily estimation of irrigation amount for a given percolation or capillary rise. This relationship can be used to optimize irrigation amounts, and evaluate their impacts on percolation losses.From the results of this simulation study, it was predicted that the 1200 mm---15 irrigation application treatment (15 day interval) was best for irrigation scheduling to reduce salinity and waterlogging