Arsenic Phytotoxicity on a Plainfield Sand as Affected by Ferric Sulfate or Aluminum Sulfate
1972
Steevens, D. R. | Walsh, L. M. | Keeney, D. R.
Repeated use of arsenic (As) salts in orchards, cotton, and tobacco fields occasionally has caused phytotoxicity. A study was initiated to evaluate the effect of periodic applications of sodium arsenite (NaAsO₂) which has been used extensively as a defoliant to kill potato vines in Wisconsin commercial potato fields. Sodium arsenite was applied in 1967 to a Plainfield sand at rates varying from 45 to 720 kg As/ha. In 1970, these field plots were subdivided and treated with ferric sulfate [Fe₂(SO₄)₃] and aluminum sulfate [Al₂(SO₄)₃] to attenuate As toxicity, planted to peas (Pisum sativum L.) and potatoes (Solanum tuberosum L.), and yields compared with those obtained in earlier investigations. Arsenic toxicity persisted over a period of four cropping seasons. Pea yields on As-treated soil tended to be higher with an application of Fe₂(SO₄)₃ and lower with an application of Al₂(SO₄)₃, although yields generally were not significantly changed by either material. Potato yields were not affected by application of Fe₂(SO₄)₃, therefore, neither Fe₂(SO₄)₃ or Al₂(SO₄)₃ were effective at the rate used in reducing toxicity. Potato tuber peelings contained up to 53.7 ppm of As, but regardless of treatment, the tuber flesh did not exceed 1 ppm. Ferric sulfate or Al₂(SO₄)₃ did not have a consistent effect on the concentration of As in potato peelings or tuber flesh. The As content of As-treated soil increased in the subsoil but decreased in the plow layer during four cropping seasons. The increase in subsoil As was found to a depth of 38 cm and 68 cm for treatments of 90 and 180 kg As/ha and 720 kg As/ha, respectively. Even considering the downward movement, all of the As applied in 1967 as NaAsO₂ was not accounted for in the soil profile (0–83 cm).
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