Evaluation of Commercial Aerial Imagery to Assess Variability of Height and Yield in Cotton (Gossypium hirsutum L.) Fields
Variable rate application of products can be applied based on the identification of vigor zones in cotton fields. Companies exist which acquire imagery, create vigor zones, and provide application maps for products based on the vigor zones. The accuracy of using commercially obtained vigor zones in semi-arid cotton growing areas, such as the southern High Plains of Texas was investigated, and compared with the value obtained by digitized soil maps, that are obtained at no charge by the Soil Survey Geographic Data Base of the USDA Natural Resources Service. Commercial aerial imagery was taken of nine cotton fields (six in 2006 and three other fields in 2007) by Wilbur-Ellis, using AgFleet version 3.0 in 2006 and by In Time Inc. in 2007. Vigor maps based on three zones were created by these companies and used to test whether the zones accurately represented differences in plant height in nine fields, and yield in five fields. Soil maps were overlaid over the imaged fields, and plant height and yield were compared among the different soil types. In general, yield differences were not adequately predicted by height differences in the fields. Vigor maps did adequately represent yield differences in 3 of 5 fields. Soil maps were related to yield differences in 3 of 5 fields. However, it was not intuitive which soils would be more productive based on their properties. There were several instances where soils with a shallow petrocalcic horizon yielded higher than areas of deep, calcium free soils. The use of commercially available imaging to identify vigor zones was successful in some fields, but in a number of situations it was not reliable. Producers should evaluate the technology on a case-by-case basis before using recommendations based on imagery for variable rate applications. Plant height was not necessarily a reliable method to identify vigor zones, so the use of a yield monitor may be the best method of identifying consistent management zones.