Modelling the Soil Water Balance of a Sugarcane Crop in Sindh, Pakistan with SWAP93

Abstract

The soil water balance was simulated for a sugarcane (Saccharum officinarum L.) crop grown at a site in Sindh, southeast Pakistan. Data from drainage lysimeters with a water table depth (WTD) set at 1.5 m or 2.25 m from the soil surface were used to calibrate the SWAP93 model. Surface irrigation, subirrigation and drainage were monitored in the lysimeters, and climatic data were collected at the site for day of the year (DOY) 46 to 289. SWAP93’s ability to predict soil water balance components such as net bottom fluxes below the plant root zone (i.e., drainage or capillary rise) and evapotranspiration was evaluated. Daily and cumulative drainage were overestimated for both WTDs over the season. However, if the simulation was stopped before the heavy rainfall of DOY 201–205 (approx. 200 mm), daily drainage for the 2.25 m WTD lysimeters and cumulative drainage for both WTDs were underestimated. This rainfall showed no effect on evapotranspiration estimates. Weekly and cumulative ET were both underestimated, suggesting that the ET computational method needed to be revised for the study region.