Evaluation of the NH₄HCO₃‐DTPA soil test for assessing boron availability to wheat

Abstract

The NH₄HCO₃‐DTPA (AB‐DTPA), 1 MNH₄HCO₃, 0.005 M DTPA, pH=7.6, was proposed as a multi‐element extractant, for evaluating macro and micronutrients availability to plants. AB‐DTPA was also evaluated as a soil test, for assessing boron availability and toxicity to alfalfa. In a pot experiment, ten soils of Northern Greece were used to assess AB‐DTPA as an extractant of available boron to wheat (Triticum aestivum L., cv. Yecora), in comparison with hot water and saturation extract. Boron (B) was added as borax (Na₂B₄O₇*10H₂O) to the ten soils, at rates equal to 0, 3, and 5 mg B kg^‐1. Wheat was grown in pots containing the boron amended soils to the stage of tillering, and dry aboveground biomass, B concentration and B uptake by wheat were determined. AB‐DTPA extractable B was significantly greater than saturation extract and similar to hot water at each B application rate, and was correlated significantly with hot water (r=0.84), or with saturation extract (r=0.48). Extractable boron by all extractants, boron concentration in wheat and boron uptake were significantly affected by the soil x B application rate interaction. In assessing B availability to wheat using AB‐DTPA as a soil test, CEC should be included in the regression equation for B concentration, or pH for B uptake. However, the corresponding adjusted coefficients of determination for B concentration (adjusted R²=0.46) and B uptake (adjusted R²=0.48) were similar or lower to those of hot water (adjusted R²=0.45 and 0.60, respectively) and the saturation extract (adjusted R²=0.70 and 0.49, respectively), when the latter two soil tests were used in the regression equations without the inclusion of any soil property.