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.