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Fluid Journal : Fluid Journal 1993-1995
2 Fluid Journal Summer 1994 reports on research involving soil- applied K, but only a few on the usefulness of foliar-applied K. With the emphasis on lint quality, the effect of foliar K on lint quality may be of paramount importance. This article will cover a three-year study whose objective was to compare the effectiveness of foliar-applied KNO3 with soil-applied KCl in alleviating K deficiency and improving cotton yield and fiber quality. By the book At all sites, the recommended practices for high-yield cotton production for that particular state were followed. Five treatments consisted of: • no soil or foliar K • low-soil-K as preplant KCl, according to preplant soil tests • high-soil-K preplant (double the recommended level) • low-soil-K-plus-foliar-K • high-soil-K-plus-foliar-K Foliar rate was 10 lbs/A of KNO3 applied four times at 10- to 14-day intervals after first flower. Whenever KNO3 was added to treatments 4 and 5, 1.38 lbs/A of N were added to the other treatments as foliar urea to negate the possible effect of the added nitrogen in the foliar KNO3 treatments. Preplant soil test potassium levels in the upper six inches varied widely, from a low of 67 lbs/A in Georgia to a high of 829 lbs/A in College Station, Texas. Mixed returns 1991. Yield results were variable and significant differences occurred in only three of the twelve locations: Alabama, California, and North Carolina. The soil-added K treatments tended to increase yield (by an average of 150 lbs/A), compared to the untreated control at all except three locations: Georgia, Mississippi, and Texas (College Station). At these three locations, the untreated check gave the highest yield. The high-soil-K treatment showed only a slight (non-significant) increase in yield of 45 lbs/A, compared to the low-soil-K treatment. Low-soil-K-plus-foliar-K treatment tended to increase yield the most---by 200 lbs/A, compared to the untreated check and by 50 lbs/A compared to the low-soil-K treatment. Strangely, the high-soil- K-plus-foliar-K treatment decreased yield by 10 lbs/A, compared to the low-soil-K treatment, and by 60 lbs/A, compared to the low-soil-K-plus- foliar-K treatment. 1992. Significant differences occurred at six often locations: Alabama, Arkansas, Georgia, California, Tennessee, and Mississippi. The low-soil-K and high-soil-K treatments increased yields by an average of 100 to 200 lbs lint/A, compared to the untreated control. Foliar applications increased yields by an average of 230 and 332 lbs lint/ A, compared to the untreated control, and by 44 and 69 lbs lint/A, compared to the low-soil-K and high soil-K treatments, respectively. 1993. Significant differences occurred in three of twelve locations. The low-soil-K and high-soil-K treatments increased yields by an average of 40 and 99 lbs lint/A, compared to the untreated control. Foliar-K applications increased yields by an average of 140 and 97 lbs lint/A for the low-soil-K-plus-foliar-K and high-soil-K-plus-foliar-K treatments, respectively, compared to the untreated control. Foliar K applications increased yields by an average of 100 and 41 lbs lint/A, compared to the low-soil-K and high- soil-K treatments, respectively. Similar trends were observed for boll numbers and boll weight. The treatment means, averaged across twelve locations, are presented for all three years in Figure 1. Three additional treatments added in 1993 were: 1. foliar KNO3 without any soil- applied K 2. sidedressed KNO3, following a soil- applied KC1 preplant treatment 3. a plant growth regulator (PGR-IV), followed by foliar KNO3. The foliar treatment without initial soil-applied K was very disappointing. The sidedressed KNO3 was not much better than the control. The mean yield for PGR-IV plus foliar KNO3 over all locations gave the highest yield of all eight treatments. The possible reason is PGR-IV caused increased boll retention that the foliar KNO3 was then able to feed. More research needed While firm conclusions cannot be drawn at this time, foliar application of KNO3 appears to offer some potential for supplementing preplant soil applications of potassium fertilizer. The results have been variable and somewhat unpredictable. Significant yield differences, as stated earlier, have occurred about 40 percent of the time. It is clear that additional research will be required to understand the physiology of plant K requirements and soil buffering capacity. Dr. Oosterhuis is professor of crop physiology at the University of Arkansas.
Fluid Journal 1996-1998