AB‐DTPA and Mehlich III soil tests unable to predict copper available to creeping bentgrass1

Abstract

Copper (Cu) can be toxic to creeping bentgrass (Agrostis palustris ’Penncross') grown in sand‐based systems. Plant analysis is not always a reliable predictor of toxic levels of Cu in these sand‐based systems. Therefore, there is need for soil analysis to detect potentially toxic Cu concentrations in soil. The objective of this research was to determine the effectiveness of AB‐DTPA and Mehlich III soil tests to assess Cu availability to ‘Penncross’ creeping bentgrass grown in calcareous and silica sand/peat media. Samples of sand/ peat were removed from greenhouse pots, air dried, and Cu was analyzed by inductively coupled argon plasma spectrometry (ICAP/IRIS). Correlations were made between extracted Cu and Cu in the shoot and root tissue of the plant. The AB‐DTPA‐extractable Cu was 24% and 42% higher for the calcareous sand at the 400 and 600 mg kg‐1 Cu treatments, respectively, when compared with Cu extracted from the silica sand. The Mehlich III soil test extracted 25% more Cu at the 400 mg kg‐1 Cu treatment and 37% more Cu at the 600 mg kg‐1 Cu treatment from the calcareous as compared to the silica medium. Shoot and root tissue Cu concentrations were higher at all Cu treatment levels for plants grown in silica sand. Although correlations were significant between Cu extracted from both sands by the AB‐DTPA and Mehlich III soil tests and Cu in the shoot and root tissue of plants, these extractants were unsuccessful in determining Cu availability from the two sand medium. This research indicates a need for a soil test which can be effectively used to extract plant‐available Cu from sand‐based systems.