In 2018, Oklahoma State University conducted a study at the McCaull Research and Demonstration farm in Northern Texas County, OK to assess corn yield response to pre-plant applied nitrogen with varying irrigation rates. While yield data was ultimately the metric used by the OSU to provide estimates of economic returns on nitrogen and irrigation trials, TerrAvion aerial imagery was used as a supplemental tool to evaluate the performance of the trials. The OSU study offered TerrAvion the opportunity to test our high-resolution imagery, in a controlled study, against yield data as a crop performance meter. The results of the study in relationship to TerrAvion imagery is described below.
Pre-plant nitrogen trials
The Oklahoma State study was conducted on a 125-acre pivot. For the nitrogen part of the research, pre-plant nitrogen was applied at rates of 100 (yellow color in image to the right), 150 (green), 200 (blue), 250 (red), and 300 (pink) pounds per acre. The applications were made in three replicated strips around the pivot. Zero anhydrous ammonia check strips (light green) were placed towards the center of the field. Yields in the fertilized areas ranged from 210 bushels per acre with 100 pounds nitrogen acre to 245 bushels per acre with 300 pounds nitrogen per. The check strip which received only 12 pounds nitrogen per acre produced an average yield of 168 bushels per acre.
TerrAvion NDVI imagery (above image on the left) correlates to the yield results for the nitrogen trials. The lowest applied rates of 100 and 150 pounds per acre exhibit the lowest NDVI values (red and yellow colors), while the 250 and 300 pounds per acre strips exhibit the highest NDVI values (purple and blue colors). The 200-pound zone shows crop vigor in between the high rates and lower rates (green color).
In addition to the nitrogen trials, the OSU group also applied variable rates of irrigation to test the yield impact of various levels of rainfall. Irrigation was applied at 1-inch (red color in image above in the center), 1.25-inch (yellow) and 1.5-inch (green) application rates. The amount of irrigation water applied was manipulated for each treatment by adjusting pivot speed, slower for a higher water application rate and faster for a lower rate.
The thermal image (above on the right) does show the larger irrigation amount in the blue colored areas, which correlate well with the green and yellow areas in the center image. The study conclusion was that there was no difference in yield response among the various irrigation treatments, but if you look closely in the TerrAvion NDVI imagery to the left, you can see that there is some vigor variation corresponding to the different rates of irrigation. High-resolution NDVI imagery is capable of detection small rates of variation that are not evident in yield data or to the naked eye. For this reason, high-resolution NDVI imagery can provide valuable insights for evaluation the performance of inputs.
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