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Calcium Stimulation of Ammonium Absorption and Growth by Beet

Texas Agric. Exp. Stn., Texas A&M Univ., 1380 A&M Cir., El Paso, TX 79927

^* Corresponding author.

Inefficiency in N use by plants contributes to environmental degradation. We examined the use of Ca²⁺ as a means of increasing NH⁺₄ absorption in beet (Beta vulgaris cv. Detroit dark red). Ammonium absorption was measured in greenhouse and field studies. In the greenhonse, beet plants received full-strength nutrient solutions with Ca²⁺: NH⁺₄ molar ratios (MR) of 0, 0.25, 0.5 and 1.0 (Ca²⁺:NH⁺₄) and a NO^-₃ check. Absorption of ¹⁵NH⁺₄ was monitored over a 30-h period. The field production trials occurred over 3 yr on a calcareous Saneli silty clay loam [clayey over sandy or sandy-skeletal, montmorillonitic (calcareous), thermic Vertic Torrifluvent]. The ¹⁵NH⁺₄ absorption study showed the greatest plant weight at the molar ratio (MR) of 1.0 in tops (except in seedlings) and at 0.5 in bulbs. In seedlings, a biomass reallocation occurred in the root-bulbs from the tops. In both the intermediate and mature growth stages the weight of roots, tops and bulbs greatly increased. In the ¹⁵NH⁺₄ absorption studies N concentrations were unchanged or decreased as the Ca²⁺ concentrations increased, but total N increased. Seedling bulb-root weight increases were apparenlly metabolite transfer from tops. The intermediate and mature beet plants showed increases in total N. In the greenhouse growth test, vegetative matter increased in excess of 300% at the MR of 0.5 over the check (MR:0). Growth of beet in the 0.5 MRtr eatment exceeded that on the NO^-₃ comparison by 14%. In field testing at a MR of 0.25 (CaCl₂:urea), yields increases averaged 26% over 3 yr when compared with urea alone.

Received for publication May 10, 1993.