COMPARISON OF SOIL TESTS FOR ASSESSING BORON TOXICITY TO ALFALFA

Three soils from Colorado that varied in texture and organic matter (OM) content were treated with sodium borate (Na//2B//4O//7 multiplied by (times) 10H//2O) at rates of 0, 10, 20, and 40 mg B kg** minus **1 soil. Alfalfa (Medicago sativa, 'Ladak', 'Rambler', 'Riley', and 'Agate') was planted in the soils in the greenhouse and cut twice at the 30% bloom stage. Plant tissue digests and soil extracts (ammonium bicarbonate-diethylenetriaminepentaacetic acid left bracket AB-DTPA right bracket , saturation, hot water, and mannitol-CaCl//2) were analyzed for B using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Alfalfa yield was significantly ( alpha equals 0. 01) reduced with increased B application rate in the Ascalon sandy loam and Ulysses loam soils.