Wednesday, November 15, 2006

Mehlich-3 B Extraction from B-Treated Incubated or Cropped Soils of Texas Compared to Other Extractants.

Sara Redd1, Von Jolley1, Bruce Webb1, Amanda Shiffler2, and Vincent Haby3. (1) Brigham Young Univ, 275 WIDB, Provo, UT 84602-5183, (2) Idaho Falls R&E Center, 1776 Science Center Dr. Ste 205, Idaho Falls, ID 83402-1575, (3) Texas Agricultural Expt. Stn., PO Box 200, Overton, TX 75684-0200, United States of America

Hot water extraction (HW) is losing popularity as the standard B extractant and guesstimate is often replacing assessment within the soil testing community. Mehlich 3 is increasingly promoted as a "universal" extractant to include B. Boron extraction with DTPA-Sorbitol and pressurized hot water (PHW) is simpler, easier and comparable to the more time consuming and variable HW extraction. Limited comparison of Mehlich-3 B extraction to HW and no comparison to DTPA-sorbitol nor PHW extraction are available. The purpose of this study was to determine the efficiency of Mehlich-3 B extraction compared to HW, PHW and DTPA-sorbitol with soils fertilized with B. This study focuses on comparing B extraction methods on a limed acid Darco fine loamy sand soil from Eastern Texas to which 10 rates of B were applied followed by either incubation without plants or planting to alfalfa in greenhouse pots. Mehlich-3 extraction of soils obtained from a long-term experiment in Eastern Texas on which alfalfa yield response was previously correlated to B extracted by HW, DTPA-sorbitol and PHW is also compared. Mehlich-3 extractable B correlated with the rate of B application to soils in incubation, greenhouse, and field experiments and with B concentration and uptake of alfalfa in a greenhouse experiment. However, Mehlich-3 extractable B did not correlate with alfalfa yield in the field, while HW and PHW did. The combination of chemicals in the Mehlich 3 extractant caused drift and interrupted B measurement when analyzed on an older model ICP, but the problem was corrected by using a newer model ICP. Although Mehlich-3 extraction reflected rates of B application to soils, it did not predict yield response of alfalfa on a limed, acid soil and thus cannot be recommended as a universal extractant to include B without further study.