| Abstract: | Abstract Hot water extraction (HW) is time‐consuming, highly variable, and losing popularity as the standard method for estimating plant‐available boron (B) in soil. Proposed alternatives are not widely used and guesstimation is replacing assessment at many soil test facilities. Mehlich 3 is increasingly promoted as a universal extractant, and diethylenetriaminepentaacetic acid (DTPA)–sorbitol and pressurized hot water (PHW) are effective and comparable to hot water extraction but also simpler and easier. Mehlich 3 B extraction has been compared mainly to hot water extraction. Because Mehlich 3 usage would be limited to neutral to acid soils, this study used a limed acid Darco loamy fine sand (loamy, siliceous, semiactive, thermic Grossarenic Paleudult) 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 on Darco soil from which alfalfa yield response has already been related to hot water, DTPA–sorbitol, and PHW is reported. The purpose was to determine the efficiency of Mehlich 3 B extraction compared to hot water, PHW, and DTPA–sorbitol in these B‐fertilized soils. Mehlich 3–extractable B significantly correlated with the rate of B application to incubation, greenhouse, and field soils and with B concentration and total B uptake in alfalfa in a greenhouse experiment. However, yield responses to B application were not observed in the greenhouse study. In the field where B response to B application was observed, Mehlich 3–extractable B did not correlate with alfalfa yield, whereas hot water and pressurized hot water did. In considering Mehlich 3 for B extraction, be aware that some older inductively coupled plasma (ICP) models may have significant drift when B is measured in Mehlich 3 extractant. In the current study, this problem was overcome with a new model instrument. Although effective in estimating B levels imposed on soils by fertilizer application, Mehlich 3 could not predict yield and thus cannot currently be recommended as a “universal” extractant to include B. |
