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Image-Based, Variable Rate Plant Growth Regulator applied by Air to California Cotton

Matthew Bethel, David Lewis, Susan White, Ted Sheely, Bruce Roberts, Roger Hewitt, Mechel Paggi, and Nick Groenenberg

ABSTRACT

Plant Growth Regulator (PGR) is commonly used in cotton plant management. When applied to the crop, it redirects plant growth from the vegetative leaves to boll production and as a result can increase yield. In the 2000 and 2001 growing seasons experiments were performed in Mississippi to study the effect of PGR application across different Normalized Difference Vegetation Index (NDVI) regions of a field. NDVI measurements were extracted from remotely sensed data acquired over the field. In the2000 experiment, the field was segmented into two types of treatment strips. One type received blanket applications of PGR according to traditional methods. The other treatment strips received no PGR. The treatment strips contained three different NDVI groupings to research if plants with different NDVI measurements respond differently to PGR. The 2001 experiment replicated the 2000 experiment, but added treatment strips as Spatially Variable plant Growth Regulator (SVPGR) applications to the design. The intent of this study was to determine if SVPGR application methods could be used as a technique to reduce PGR application costs and at the same time maintain or increase yields over the traditional (100%) method of applying PGR. The results of this research indicated that a cost savings of approximately 24% was realized in using the SVPGR method as compared to the traditional method.

In 2002, the image-based PGR application experiments were also conducted in the San Joaquin Valley of California. The San Joaquin Valley was chosen because of its different growing conditions from Mississippi, as well as the availability of a cooperating producer (Ted Sheely) and concurrent collaborative research on-going by USDA and University of California researchers at the farm. The 2002 PGR experiment incorporated plant height variance analysis following the PGR prescription application to determine any treatment effects on crop canopy management. The 2002 study experiment design consisted of three treatments; the untreated control, Site-Specific PGR (SSPGR), and Variable-Rate PGR (VRPGR). The SSPGR treatment consisted of strips that received two rates (0% and 100% of the scout prescribed rate for the field) of plant growth regulator based on the image data. The additional image-based treatment included in the experiment design, VRPGR, included five different PGR rates based on image analyses for those treatment strips. The results of the 2002 study (ITD Final Report, 2002) showed that the SSPGR treatment resulted in a 19% cost savings from using site-specific PGR applications as opposed to traditional (100%) applications of Pix. The results also showed that there was a 51% reduction in chemical applied with the SSPGR treatment with no adverse effect on yield. The comparison of the VRPGR and 100% applications of Pix indicated that VRPGR applications were, on average, 27% more costly. There was no statistical difference in plant height variance among the treatments, which indicated no negative impact on crop canopy management from using the image-based techniques.

The 2003 image-based PGR experiment incorporated the knowledge gained from the results of the 2002 study and attempted to implement new aspects to the experiment that would lead to more practical adoption of this technology in California. Specifically, the 2003 experiment included one image-based treatment that consisted of three rates based on the imagery and the field scout’s recommendations, and because of the practical limitations of the application of PGR by ground sprayer in an area dependant on furrow irrigation, the study was designed around the aerial application of the PGR prescription. A Pima cotton field was included in the 2003 study because of the large amount of cotton acreage in California devoted to this crop.





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Document last modified 04/27/04