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Fluid Journal : Fluid Journal 2005-2007
Early Spring 2005 Fluid Journal 3 did not substitute for a preplant K application for optimal soybean production in this research. Foliar K may be a supplemental nutrient management practice when conditions reduce plant K uptake from soil. Second, carrier volumes required for foliar application of K2SO4 at rates shown to be effective in this research are generally impractical for most farm operations. Additional research was needed to evaluate crop response from more soluble K fertilizer sources that would have relatively lower salt indexes and possible compatibility with glyphosate. K with glyphosate Spray pattern. Compatibility tests of tank mixing K sources with glyphosate were conducted in 2003 with the highest rate of foliar fertilizer that could be mixed with glyphosate. Therefore, not all K sources were mixed at uniform K rates. A slight precipitate was formed when fluid 3-18-18 was tank mixed with Roundup WeatherMAX, while potassium thiosulfate (KTS) formed a viscous solid with Roundup WeatherMAX that was removed prior to the tank mixture application. A poor spray pattern was observed when 0-0-30 (potassium carbonate) was applied with Roundup WeatherMAX and the spray boom height was adjusted to compensate. Visual injury was primarily necrosis of leaves exposed to foliar application. For the high soil test K site located at the Greenley Center, all treatments except 0-0-30 had less than 10 percent soybean injury 3 and 7 days after treatment (DAT) with almost complete recovery 21 DAT (Table 1). Tank mixtures of 3-18-18 and 5-0-20-30 at rates of 12, 23, and 35 lbs/A of K2O with glyphosate injured soybeans more than the foliar fertilizer applied alone 3 DAT. This injury was still evident up to 21 DAT for some treatments and plant height late in the season was shorter than the untreated control (data not shown). The adjuvants present in Roundup WeatherMAX probably increased uptake of the foliar K causing increased injury. Grain yield. The weed-free soybean grain yield was 44 bu/A (Table 1). In the absence of Roundup WeatherMAX, 0- 0-30 increased soybean grain yield 5 bu/A when compared to the weed-free control at the high soil test K site located at the Greenley Center. At the low-to-medium soil test K site, foliar- applied 0-0-62 significantly increased soybean grain yield by 2 bu/A when compared to the weedfree control (data not shown). Conclusions. The first year results of these fi eld trials indicated the potential viability of mixing K sources with glyphosate, but also highlighted the importance of evaluating both crop K response and weed control to ensure grower acceptance of the practice. Potential concerns will be the initial foliar injury observed after spraying some of the foliar K sources, and the solubility limitations of certain K sources such as potassium nitrate and potassium sulfate, which would reduce flexibility in increasing foliar K application rates. In addition, soybean yield response to foliar K varied among the K sources and was much lower at both the high and low-to-medium soil test K field sites compared to the initial field site tested in 2001 and 2002. Our current research is comparing K sources for foliar fertilization at uniform K application rates with and without mixing with glyphosate at several field sites in the state of Missouri. Dr. Motavalli is assistant professor in the Department of Soil, Environmental, and Atmospheric Sciences, Dr. Nelson is research agronomist and assistant professor in the Department of Agronomy, Dr. Stevens is extension associate professor in the Department of Agronomy, and Mr. Phurahong is a research assistant in the Department of Soil, Environmental, and Atmospheric Sciences at the University of Missouri.
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