Optimal Irrigation of Cotton via Real-Time Adaptive Control

This project has demonstrated the implementation of adaptive control systems at commercial cotton cropping sites. The control simulation framework VARIwise has been used for the simulation and development of irrigation control strategies. The framework potentially provides site-specific irrigation volumes and timing to be determined in autonomous irrigation, either for uniform or variable-rate irrigation application. \n \nField evaluations of the control strategies were conducted on siphon and centre pivot irrigation systems in Jondaryan, QLD utilising a weather, soil and plant sensors, control strategies and irrigation control hardware. The siphon and centre pivot irrigation trials produced yield improvements of 11% and 7% respectively, and water use reductions of 12% and 4% respectively. Higher water reductions were achieved in surface irrigation systems than overhead irrigation systems because of the larger volumes of irrigation water applied. Adoption of these irrigation control systems would provide improved and automated irrigation management and labour savings to the industry. \n \nAn on-the-go plant sensing system was developed to estimate plant density, plant height (for leaf area index calculation), flower count (for square count calculation) and boll count, as required to calibrate the industry crop production model OZCOT for the control strategy operation. This sensing system was standalone and platforms were developed that enabled mounting to on-farm vehicles (e.g. moped) and irrigation machines. The centre pivot irrigation trial indicated that plant data input was preferable to soil data input for model-based irrigation control strategies. \n \nThere is limited control hardware currently commercially available for surface irrigation, and commercial variable-rate solenoid-based irrigation adjustment hardware is available for centre pivots and lateral moves. For the purposes of the field evaluations in this project, an irrigation control hardware system was developed that was independent of the irrigation system. This was based on adjusting the flow rate using a remotely controllable ball valve and servomechanism and could be installed in-line with siphons and droppers on irrigation machines. \n \nOver 90% of the Australian irrigated cotton industry uses surface irrigation. Further enhancements to the system would entail investigating the spatial resolution of irrigation application adjustment for both surface and overhead irrigation systems. This would potentially determine the data requirements of surface irrigation control systems, reduce the sensors requirement (leading to reduced cost of the system) and increase the practicality and uptake of the final system. In addition, the control strategies could be extended to consider fertiliser application in surface irrigation systems, as the efficiency of the fertiliser application is expected to be related to the efficiency of the irrigation application.