COMPARISON OF MEHLICH-1 AND MEHLICH-3 EXTRACTABLE SOIL BORON WITH HOT-WATER EXTRACTABLE BORON

The standard hot water extractant for soil boron (B) was compared with two extractants currently in use by routine soil testing laboratories, Mehlich-1 (M-1) and Mehlich-3 (M-3). If routine extractants could be used for B, it would save the time and expense required for a separate extraction. Six states (Delaware, Maryland, Virginia, North Carolina, South Carolina, and Georgia) each selected 100 soil samples sent by growers to their State laboratories which were analyzed for routine properties (pH, P, K, Ca, Mg, and organic matter) and B by M-1 or M-3. The samples were then analyzed for hot-water B (HWB) using a plastic pouch procedure and inductively-coupled plasma emission spectrometry (ICP). M-3 extracted more B than M- 1, and the correlation coefficients for M-3 B with HWB were higher (r = 0.82**) than were M-1 with HWB (r = 0.74**). Correlations of soil properties with M-1 and M-3 B were higher than with HWB, but none were notable with two exceptions. Extractable Ca was positively correlated with M-1 and M-3 B for four states, and the weight per volume of soil was negatively correlated with HWB for five states. The negative correlation reflected the lower B holding capacity for the coarser-textured high-volume-weight soils compared to that of the fine-textured low-volume-weight soils. The correlation data shows that M-1 and M-3 can be used as a substitute for HWB, particularly at M-1 and M-3 B levels above 0.5 mg/dm3.