Project Summaries

09-520GA  Project Manager: E. M. Barnes


George Vellidis, V. Liakos, G. Harris, R. Hill and H. Henry, University of Georgia

During the 2010, 2011, and 2012 growing seasons, we conducted research to evaluate the feasibility of variably applying side-dress N on cotton. We have used the GreenSeeker® sensing system as the basis for measuring the status of the cotton crop. The GreenSeeker measures light reflectance from plants in the red and near infra-red wave bands and uses this information to calculate vegetation indices (VIs). VIs are mathematical ratios of reflectance data. The most commonly used VI is the NDVI (Normalized Difference Vegetation Index). Under most circumstances, NDVI is highly correlated with plant biomass.

A uniform application of fertilizers is inefficient as it does not consider field variability. During the last decade, variable rate application (VRA) has become increasingly popular. At both study fields, the experimental design consisted of two variable rate application strategies (VRA1 and VRA2) and a control. The fields were divided into nine 6-row strips allowing 3 replicates of the VRA treatments and 3 replicates of the control. The design was not randomized. Rather the strips were assigned to a repeating pattern (VRA1, Control, VRA2) to allow for direct comparison of adjacent VRA and Control treatments. This was done primarily because the fields were terraced and not all the strips were immediately adjacent to each other and we wished to avoid excessively complicating the comparisons with distance-induced variability.

The two VRA treatments (VRA1 and VRA2) used in this study differed primarily in the amount of N applied to the areas of the field with the highest vigor (high NDVI). The results show that applying more N to the high vigor areas (VRA2) resulted in higher overall yields and higher levels of profitability compared to the control. The VRA1 treatment resulted in lower overall yields, much lower use of N, but the same level of profitability as VRA2. The same pattern was observed during 2011 in a field immediately adjacent to Field 1. Profitability is not always associated with the highest yield and cotton producers should focus on this factor more than on yield.


Project Year: 2012

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