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Fluid Journal : Fluid Journal 2005-2007
Winter 2006 Foliar Boron Bumps Cotton Yields Dr. James R. Woodruff Summary: In southeastern cotton, an average yield increase of 21 lbs/A lint was obtained with foliar applications of 0.5 lbs/A boron (B) where leaf tissue B was less than 40 ppm before first flower. There was no evidence of need for greater than 0.5 lbs/A of foliar-applied B. Where leaf tissue B exceeded 125 ppm, cotton yield reductions were observed. Southeastern study shows that at leaf boron levels below 40 ppm at first flower, foliar boron applications improved cotton yields. Fluid Journal 1 The interpretation of boron (B) soil tests and plant analyses is a major key to answering the question of the probability of crop yield response to fertilization. Today, we have excellent, precise chemical tests for B in soils and plants. There is a need to focus on interpretation of the test results. The standard micronutrient advisory of university agronomists during the early 1960s was, "Don't recommend a micronutrient unless a need can be demonstrated." This advice presented a difficult problem. At that time, agricultural laboratories performed no routine B analyses for soil or plant tissue and there were no established interpretations for crop need although it was reported that hot water extraction for available soil B and plant B analyses were useful indices for B need in corn. Over the past half century, progress has been made through the establishment of critical and sufficiency leaf tissue B levels for major crop plants. Also, among the 13 state laboratories in the southern region, nine can determine B upon request. Three laboratories routinely measure B on all soil samples and most private laboratories now determine soil B, thanks to the use of the Mehlich extraction of B, which correlates well with hot water B extraction and to B measurement with inductively coupled plasma atomic emission spectra detection instruments. Crop responses to B fertilization have been reported on most major southern field, forage, fruit, and vegetable crops. Much of this past work can be reviewed in two publications: Boron and Its Role in Crop Production (C.R.C. Press, Inc, Boca Raton, FL, Mortvedt, J.J. and J.R. Woodruff, 1993, Technology and application of boron on fertilizers for crops, pp. 157-183; In U.C. Gupta [ed.]) and Boron in Soils and Plant Nutrition (2002, U.S. Borax, Inc.). Since cotton occupies the largest southern acreage routinely fertilized with B, this report will focus on cotton responses to B. Early work Much of the earliest soil fertility work with B on cotton began before and during the 1960s. Prior to those years, soil tests for B were not routinely performed. Thus, B fertilization was not practiced, resulting in many soils in the southern region being low in B. However, when studies began, cotton yield responses to B were observed on a number of sites. Not all test sites showed an increase in yield where B was applied but enough responses were observed that most mid-South and southeastern states began to routinely recommend 0.5 to 1 lb/A of B annually. Points learned from the early studies of cotton response to B were 1) yield response of cotton to B fertilization was related to B concentrations in cotton leaf tissue, 2) B concentration in cotton leaf tissue was related to soil test B, and 3) where cotton responded to B application, soil test B levels were less than 0.2 ppm and leaf tissue B was below 20 ppm. Recent history During the mid-'70s, administrators of land grant universities, the USDA- ARS, and the fertilizer industry, prompted partly by the environmentalist Figure 1. Regional cotton leaf B concentration versus percent relative cotton yields, 1996 through 1998.
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