Farm level decision support for sugarcane irrigation management during drought

A large portion of global sugarcane is produced under irrigation, and this often occurs in areas where water supply is not abundant or reliable. Crop management decisions during limited water supply are complex and require information on the impacts of irrigation strategies on crops and profitability. This paper describes the development of a computerized system to support farm level management of limited irrigation water for sugarcane production. The system comprises a daily crop and water balance model, an irrigation module and a gross margin calculator. The model calculates crop yield and survival for the current (Y1) and the next season (Y2), for multiple fields on a farm, for a given irrigation strategy and water supply/climate scenario. Irrigation strategies that can be explored include: (1) scheduling irrigation using growth phase specific soil water thresholds (SWT), and (2) postponing replanting and/or abandoning low potential fields. Farm gross margin is calculated from simulated yields and production costs at field level and takes into account re-establishment costs when crops fail. The system was applied in a case study for a hypothetical farm of 18 fields near Komatipoort, South Africa.. Four possible restricted water allocation scenarios were investigated, namely, a mildly and severely restricted allocation ("50% and 25% of the full allocation) over a 24 month and 12 month period. Results from the case study show that under most circumstances a SWT of 60% of plant available soil water capacity applied during the germination and stalk growth phases produced the best outcome. Reducing SWT to 30% during the tillering phase makes more water available for use on other fields, resulting in higher crop survival under severe restrictions. Abandoning low potential fields under severe water restriction limited financial loss in Y2, but reduced future productive capacity thereafter. Results suggest that the system produces realistic responses to irrigation applied and drought. It has the potential to aid strategic decision-making for irrigated sugarcane production during drought.