Sensor-based estimation of cotton plant height: Potential for site-specific plant growth management

Abstract. Current crop production technology provides control of chemical application of production inputs with exceptional field resolution, positioning accuracy, and the capability to generate real-time data to track machine efficiency, input use, ambient conditions, etc. To take full advantage of the real-time application control capabilities of modern technology, these control systems must be interfaced with electronic sensors to monitor plant conditions on-the go. In contrast to the level of sophistication in hardware and software used in application control, the development of soil/plant sensors still lags behind. Experimental work at the University of Arizona has shown the potential of displacement sensors and GPS-RTK systems to generate plant-height (PH) information from moving platforms. Sensor analog signals and GPS field elevation data were combined using an algorithm developed specifically to estimate plant height. Field trials in Maricopa, AZ in the Summer of 2012, included varietal differences (columnar and bushy types), planting densities (25, 50, and 75k plants/acre), and irrigation management (75 and 50% of water depletion) with measurements taken during the period of rapid growth. Data analysis is currently under way to compare sensor-based PH data with manual measurements. An extension of the experimental work is being directed at generating real-time data of cotton height:node ratio (H:N), by estimating the number of nodes as a function of heat-unit accumulation. Discussion of technology capable of generating sensor-based PH data includes measurement accuracy, performance parameters such as machine field capacity, and integration to control systems. Cotton H:N information has been shown to be a figure of merit for management of plant growth regulators (PGR), therefore technological development in this area can lead to automatic variable-rate application algorithms of plant growth regulators which will improve plant growth management of irrigated cotton.