Examination of remote sensing applications for monitoring growth of cotton and application rates of mepiquat chloride

Management of vegetative growth is an important part of cotton production. Cotton is a perennial plant with indeterminate growth characteristics that is grown as an annual under agriculture cropping systems. As a result, reproductive and vegetative growth occur simultaneously on the plant causing competition for photosynthetic products and an influence on yield. Plant growth regulators (PGR) such as mepiquat chloride are an essential tool used in cotton production for controlling excess vegetative growth. Application timing and rate selection of PGR's can be complex and an important factor for maintaining an optimum fruit load in relation to vegetative growth. Currently, there is no standardized way to schedule and select PGR rates. However, some plant monitoring techniques such as height-to-node ratio, plant height, main stem nodes, and nodes above white flower have been used to schedule and assign rates. The problem with these plant monitoring techniques is that growth measurements are time consuming and require intensive sampling. Remote sensing has the ability to acquire information about the vegetative growth and development of cotton without coming into contact with it. Utilizing this technology is an effective and timely means to spatially monitor differences in vegetative growth. Within a cotton field, vegetative growth is often diverse due to many variables such as soil fertility, moisture availability, soil type, etc. Currently, in cotton production systems PGR are generally applied in a constant rate broadcast fashion regardless of vegetative growth. This application strategy can result in over treatment to areas not requiring any, and/or insufficient application in high growth areas. The utilization of aerial remote sensing can be used to make site-specific PGR management decisions within a spatially diverse field in an attempt to maximize cotton yield. The results of this study indicate that lower seed cotton yields occurred when constant rate broadcast application was compared to site-specific variable-rate applications based on normalized difference vegetation index (NDVI). These results suggest that seed cotton yields can be influenced if a constant rate of PGR is applied to cotton regardless of its growth. The results also indicated other field topography variables such as elevation and soil conductivity can influence cotton yield. These variables in addition to NDVI showed to be important for the design and construction of site-specific PGR application maps in order to achieve a higher degree of precision.