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Fluid Journal : Fluid Journal 2005-2007
Winter 2006 Fluid Journal 2 movement, demanded that those of us responsible for interpreting soil test reports and making fertilizer recommendations show our data and documentation of crop response to nutrients. Although soil fertility workers now have confi dence that most current interpretations of soil and plant analysis data are generally valid based on experience from research and extension activities in the field, they often feel hard pressed to show definitive yield response data. Agronomic and biological sciences, not being exact sciences, lean heavily on experience as well as numerical measurements. Those engaged in soil fertility research in the field have experienced difficulty showing immediate yield responses to nutrients other than nitrogen, making it difficult to document and predict nutrient needs. This has been true for major nutrients, and especially true for micronutrients, including B. Current data Using the modern tools of soil and plant analyses, the validation of current B recommendations is quite possible. Figure 1 shows 36 comparisons of cotton leaf B concentration versus relative percent cotton yields, illustrating how we can justify our present interpretation of cotton need for B. The Mitscherlich yield response curve clearly fits the range of leaf tissue B generally interpreted as the sufficiency range (Georgia uses 20 to 60 ppm B). The fact that a significant B yield response was obtained within this range (Georgia, 1997) suggests that B fertilization might be beneficial even where leaf tissue B concentration falls within the sufficiency range. The use of relative yield permits the combining of data from many locations or for many years into a single plot. Figure 2 shows cotton yield versus cotton leaf tissue B response. Superimposing the Tennessee data on Figure 2. Tennessee cotton leaf B concentrations verus percent relative yield, 1996 - 1998 the response curve generated by a South Carolina, Georgia, and Virginia regional study shows how the Tennessee data fit the same response curve. Table 1 presents a summary of the combined data across years and locations from the South Carolina, Georgia, and Virginia regional cotton study. Conclusions drawn from regional study: • An average yield increase of 21 lbs/A lint was obtained with foliar application of 0.5 lb/A of B where leaf tissue B before first flower was less than 40 ppm B • There was no evidence of need for greater than 0.5 lb/A of B foliar applied (split into three 0.166 lb/A increments at first flower, two weeks after, and four weeks after first flower) • When cotton leaf tissue exceeded 125 ppm (five weeks after first flower), cotton yield reductions were observed • Average lint yield increase of 21 lbs/A was exceeded in Georgia, where a 69 lbs/A increase was obtained by the applications of B, raising leaf tissue B from36to5ppm • Economically, even if cotton price was 40 cents/lb, a half-pound of B costing $2.50 would produce a return of $8.40 from 21 lbs of lint, and a net return of $5.90 (or 236%) on the B investment. Future approach Soil test B was less than 0.5 ppm at Figure 3. Alfalfa tissue B correlation with soil test B.
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