Plant and soil boron in relation to boron deficiency in lucerne

Abstract

Plant and soil samples were collected from 91 stands of lucerne (M. sativa L.) in the main growing areas of New Zealand. In 39 samples of lucerne with B deficiency symptoms in the field, B concentration in whole shoots ranged from 5-17 ppm with lesser concentration in upper than in lower portions of the plants. B concentration in non-deficient plants ranged from 17-64 ppm with equal distribution or greater concentration in upper than in lower portions. Available soil B was determined by hot water (HWS B) and ammonium acetate (NH4Ac B) extractions. HWS B was a better indicator of available B than NH4Ac B because average HWS B values were lower in soil under deficient than under non-deficient plants; however, NH4Ac B did not distinguish clearly between the 2 groups, and HWS B was correlated with B concentration in plants but NH4Ac B was not. It was not possible to define a critical value for available soil B, nor was there any improvement in correlation between plant and soil B by using soil from below the surface rather than topsoil. Plant analysis was more reliable than soil analysis in diagnosing B deficiency in lucerne but there was no advantage in using only the apical portion rather than whole shoots.