Low-Cost Soil Amendments to Reduce Cd Uptake By Crop Plants.

Cadmium (Cd) is a non-essential trace element that can present a human health risk. Elevated Cd concentrations in soil can arise from industrial activity as well as through the application of Cd-rich phosphate fertilisers. Cadmium is readily taken up by plants and can be transferred to grazing animals. In many agricultural systems, Cd concentrations in leafy vegetables and the offal products of grazing animals are at or above food safety standards. There is no practical means to remove Cd from contaminated soil. Therefore, there is an imperative to find a low-cost solution to reduce the plant Cd-uptake. We sought to determine whether low-cost soil amendments could fulfil this role. Batch experiments revealed that lignite coal and composts made from municipal green waste and animal residues combined with wood-waste sorbed >50 times more Cd than two agricultural soils between pH 4.5 and pH 7 and that sawdust, charcoal, and zeolite did not sorb significant amounts of Cd. Pot trials demonstrated that municipal composts applied at rates of 2.5% and 5% (w/w), reduced Cd uptake by spinach, lettuce, onions and potatoes by 20% to 60%. Lignite produced variable results, with plant Cd concentrations increasing in one soil, presumably due to acidification. Similarly, liming produced variable results. Besides reducing plant Cd uptake, municipal composts had little effect on the plant-uptake of other elements. Unlike lime or lignite, municipal composts significantly improved plant growth. Incubation studies followed by pot trials demonstrated that Cd sorption by composts and its effectiveness in reducing plant Cd-uptake persists for at least one year, even under warm, humid and high N conditions. We conclude that biological wastes, especially composts, are an underutilised resource that can not only reduce plant Cd-uptake but also improve plant production.