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Fluid Journal : Spring 2018
18 The Fluid Journal Spring 2018 of N rate and S rate using N-S fluid fertilizers with varying N:S ratios. The treatment design for the second dataset was a 3X4 factorial design with three total N rates and four N:S fluid fertilizers. The three total N application rates were 60, 100, and 140 pounds N per acre and the four N:S fluid ratios were 32:0, 8:1 4:1 and 2.66:1. Fisher LSD mean separation procedure was used to detect treatment differences at a = 0.05 level of significance. Results and Discussion General comments. The 2017 growing season had more favorable weather for cotton production than 2016, particularly during the boll opening /defoliation period of the growing season. Yields in Virginia averaged over 1,100 pounds of lint per acre and were the second highest production year in Virginia’s history. Yields across all locations were high with the highest yields reported at the Southampton location in 2017. There was no substantial period when rainfall or soil moisture was limiting at any location. Due to seed availability of Phytogen 499 WRF, the variety planted across all locations in 2017 was Phytogen 450 W3FE. This variety was chosen due to its similar maturity and performance in the 2016 Virginia cotton official variety trials. However, this variety was variable in its performance across locations and its environment. Large differences were found in plant available nitrogen (PAN) (soil ammonium-N + nitrate-N) in the top 36 inches of soil at each location (Table 2). The Lewiston location had the highest PAN among the sites with 12.3 ppm ammonium N and 15.2 ppm nitrate N, which would be equivalent to 55 lbs. N per acre of PAN prior to planting at this site. This is over 50% of the recommended N rate for cotton in Virginia. Southampton had the lowest PAN of any location with an equivalent N rate of 14 lbs. N per acre prior to planting. Normalized Difference Vegetative Index (NDVI). Normalized difference vegetative index at TAREC was very similar to that measured in 2016. Differences in NDVI were more were more prevalent early in the growing season, differences becoming limited later in the growing season (Table 3). Once the cotton closed the row middles the biomass, with a handheld sensor, saturated NDVI, thus only the unfertilized control was significantly different from the fertilized treatments. Visually, some greenness differences were observed visually, however, the handheld sensor and/or NDVI was not able to differentiate the visual differences. A sensor mount on a UAV might be a better option for measuring reflectance on cotton, as the higher altitude will prevent sensor saturation due to a large canopy near to the sensor. Granular vs. Fluid N/S Formulations.