Soul arsenic effects on canola seedling growth and ion uptake

Elevated levels of arsenic (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 i) determine how soil-applied As affected the shoot and root dry weights, root length density, As uptake and tissue concentration, and total water use of canola and ii) evaluate the influence of soil As on phosphorus (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(-1)). Four 14-day-old canola seedlings were planted three in 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(-1)). 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 were harvested. Shoot and root tissues were dried and analyzed for As and P. Arsenic uptake by seedlings grown in both the Commerce and Sterlington soils increased when 5 mg kg(-1) As were added, but did not increase with further As addition. In the Rilla soil, As uptake did not change with As addition, possibly due to the lack of change in soil solution As 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 grownin 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 fresh As application.