Integrating soil water monitoring technology and weather based crop modelling to provide improved decision support for sugarcane irrigation management

• Soil water data were successfully integrated into weather based crop simulations.
• Simulation analysis identified cases of drought stress and poor crop husbandry.
• The integrated system enhances support for sugarcane irrigation management.

Various technologies exist to support scientific irrigation scheduling, each with its own strengths and weaknesses. Weather-based crop models are good at estimating evapotranspiration and future irrigation needs over large areas, while electronic soil water sensors are able to provide good estimates of soil water status at a given point. Synergy may be obtained by combining these technologies to enhance their usefulness for irrigation management. The objective of this study was to incorporate real-time field records of soil water status into a weather based sugarcane simulation system and to evaluate its use for supporting irrigation scheduling in 15 sugarcane fields in South Africa.Layered soil water status data from capacitance probes were converted to root zone available soil water content (ASWC) using linear scaling. Field specific calibration coefficients were derived from drainage and extraction patterns.An analysis of simulation outputs and observed cane yields suggested that yields were substantially below potential for seven out of the 15 fields. Two fields had prolonged periods of water stress due to under-irrigation, as reflected by the fact that yields from simulations based on measured soil water data were substantially below the potential yield. Yields in six fields were probably limited by poor husbandry as suggested by the fact that observed yields were well below simulated yields using measured soil water data.The system was demonstrated to commercial and small-scale farmers and extension officers during a series of workshops. The integrated system provides enhanced support for irrigation water management for sugarcane production. Farmers and extension specialists can understand the impact of irrigation practices on the soil water regime and its impact on crop growth and yield. This is a good basis for making adjustments to irrigation practices and for benchmarking crop performance and water use efficiency. It also has value for supporting irrigation scheduling decisions.