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Copper Toxicity in Snapbeans (Phaseolus vulgaris L.)¹

ABSTRACT

A 2-year field experiment was conducted to determine whether Cu applied for pathogen control could accumulate to a level that would be toxic to snapbeans (Phaseolus vulgaris L.). Copper sulfate and Cu(OH)₂ were applied at rates varying from 0 to 486 kg/ha Cu on a Plainfield loamy sand to approximate 1, 3, 9, and 27 years of fungicidal treatment. Correlation and regression analyses were used to compare the amount of Cu extracted from the soil by 3 extraction procedures (0.1N HCI, EDTA, and DTPA) with crop yield and the concentration of Cu in snapbean tissue.

Rates of up to 54 kg/ha Cu had no deleterious effect on the yield of snapbeans in either year. Slight yield decreases were noted when the rate of Cu exceeded 130 kg/ha, and a marked reduction in yield occurred when 405 kg/ha of Cu as Cu(OH)₂ or 486 kg/ha of Cu as CuSO₄ was applied. Yield decreases were similar the 1st and 2nd years after Cu application, indicating that Cu toxicity was not being ameliorated over a 2-year period of time. Soil Cu and yield were highly correlated for each of the extraction methods. Based on the regression equations, a significant yield depression was obtained when HCI or DTPA-extractable Cu exceeded 20 ppm, and when EDTA-extractable Cu exceeded 15 ppm. Soil Cu extracted by each extraction procedure was highly correlated with Cu in the leaf tissue, especially for the immature first trifoliate leaf. Yield reductions were noted when the Cu concentration in the seedling trifoliate increased from 20 to 30 ppm, and severe toxicity was observed at tissue concentrations in excess of 40 ppm Cu.

Key Words: available soil Cu • Cu extractants • nutrient uptake

¹ Contribution from the Department of Soils, University of Wisconsin, Madison, Wis. 53706. Research supported by the College of Agricultural and Life Sciences (Project no. 1027), University Wisconsin, Madison, and by the Green Giant Co., LeSueur, Minn.

² Professor, Visiting Extension Specialist (University of Maine), and former Research Assistant (now Research Agronomist, Green Giant Co., Dayton, Ore.), respectively.

Received for publication September 17, 1971.