A pressurized hot water extraction method for boron

Abstract

Extracting boron (B) to predict plant availability in arid soils is a tedious soil test procedure, and an inexpensive, rapid alternative would be welcomed. This paper compares the results of tests conducted with pressurized hot water and conventional boiling hot water extraction of soil B. The time required for pressurized hot water extraction varied with each soil, but averaged 1.0 min per sample compared 10 min per sample for the standard boiling hot water technique. A Maxim EX-450 model espresso machine producing water at 90°C was used to extract B from 40 arid zone soils. Resulting aliquots were analyzed by ICP spectrometry. The measured values of B with pressurized hot water extraction were higher than with the boiling hot water extraction. There was a high and significant correlation between B values using the boiling hot water extraction and the pressurized hot water extraction [r=+0.83 (p=0.001)]. A regression equation y=0.12217+0.21155x (r 2=68) (y is mg kg− 1 boiling hot water extractable B and x is mg kg− 1 pressurized hot water extractable B) converts pressurized hot water readings to standard values already correlated with field response. Also tested were three espresso machines from different manufacturers (Krups, Mr. Coffee and Maxim) testing five widely divergent soils and found similar B extraction with each espresso machine. This pressurized hot water extraction procedure provides a much needed simplification for measuring B in soils, but currently the concentration must be determined with ICP rather than colorimetric measurement because of color interference.