Silage corn uptake of sludge-applied zinc and cadmium as affected by soil pH

Liming is often recommended to control metal uptake in plants. In western Washington, where silage corn (Zea mays L.) is ofted fed to dairy cattle, studies were conducted to determine the effect of liming on the uptake of Zn, and especially Cd from land-applied sewage sludge. Two soils, a Sultan silt loam and a Puyallup fine sandy loam were amended annually for 2 y with anaerobically digested sewage sludge, and seeded to silage corn. Half of the plots were limed, which increased soil pH from 4.6 to 6.5 for both soils. In general, liming reduced Zn uptake in most corn tissues, whereas Cd uptake was generally unaffected. Concentration of Zn and Cd in corn leaves from both soils increased significantly with increased sludge rate. Liming significantly lowered leaf Zn, although leaf Cd was not significantly decreased by liming. In fact, at higher sludge application rates, leaf Cd was greater from limed than unlimed plots for the Puyallup soil in 1976. Kernel Zn and Cd concentrations for both soils generally increased with sludge rate. For the Sultan soil, kernel Cd concentration at silage harvest was similar, regardless of lime treatment, whereas Cd values for the limed Puyallup soil increased significantly over those from unlimed soil in 1976. For both soils, Cd and Zn concentrations followed the order: leaves > stover > cobs > kernels. Leaf and DTPA-extractable Zn/Cd ratios from limed plots were lower than those from unlimed plots. These results suggest that liming to pH 6.5, as recommended in a number of sludge application guides, would not reduce Cd uptake by corn in the soils studied.