SOIL ARSENIC EFFECTS ON CANOLA SEEDLING GROWTH AND ION UPTAKE

Authors: COX, M - MISSISSIPPI STATE UNIV.; Kovar, John

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Recently, Louisiana producers have become interested in growing canola as a rotation crop on well-drained soils where cotton is normally planted. Unfortunately, crop plants have varying degrees of tolerance to arsenic (As) compounds, and since a common contact herbicide used in cotton production contains As, canola may not grow well on these soils. To determine if soil As would influence canola growth, we conducted an experiment in a controlled-climate chamber, using three soils with histories of cotton production (Commerce silt loam, Rilla silt loam, and Sterlington silt loam) and three As application rates. Seedlings grown in both the Commerce and Sterlington soils absorbed more As when it was added to the soil. In the Rilla soil; however, As uptake did not change. Arsenic addition had no measurable effect on short-term plant growth; however, As toxicity symptoms appeared on the leaves of plants in all treatments where As had been applied. Results of this study suggest that canola can be adversely affected by soil As. Louisiana growers will benefit from the knowledge that canola planted on soils that have had a recent application of any As compound can be adversely affected.

Technical Abstract: Elevated levels of As often found in soils used for cotton (Gossypium hirsutum L.) production may limit growth and yield of canola (Brassica napus L.). This study was conducted to: 1) determine how soil-applied As affected shoot and root dry weights, root length density, As uptake and tissue concentration, and total water use of canola; and 2) evaluate the influence of soil As on P uptake by and tissue concentration of canola seedlings. An experiment was conducted in a controlled-climate chamber, using three soils with histories of cotton production (Commerce silt loam, Rilla silt loam, and Sterlington silt loam) and three As application rates (0, 5, and 10 mg/kg). Four 14-day-old canola seedlings were planted in 3-L pots containing 2.5 kg (oven-dry-weight basis) of each soil. After 14 days, whole plants where harvested. Arsenic uptake by seedlings grown in both the Commerce and Sterlington soils increased when 5 mg As/kg were added, but did not increase with further As addition. In the Rilla soil, As uptake did not change with As addition. Arsenic tended to remain in the roots, rather than being translocated to the shoots. Arsenic addition had no effect on shoot and root dry weights, root length density, or total plant water use in any of the soils; however, As toxicity symptoms were evident on leaves of plants in all treatments where As had been applied. Phosphorus uptake by the canola seedlings tended to decrease as soil As increased, but P concentration in tissue was not affected. A decrease in shoot P:As ratios in plants grown in Commerce and Sterlington soils indicated competition between these ions. Results of this study suggest that canola could be adversely affected if grown on soils with a recent As application.