More soil-plant matching recommended

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By Communications Staff
Thursday, August 6, 2009
Add pressure from urban sprawl and shrinking cropland to a growing demand for locally produced fruits and vegetables, and it's tempting to bring marginal land into food production.
 
The good news, according to a recent University of Western Ontario research study, is that growing vegetables on mildly contaminated soil can be safe. But the finding comes with a caution – different crops can accumulate contaminants differently, so a matching of soil type with a particular plant may be called for.
 
“Much more attention needs to be paid to the match between the specific crop and the characteristics of the soil in which it will be grown, even if the soil is not considered contaminated,” says University of Western Ontario biologist Sheila Macfie, who co-authored the study with master’s student Hollydawn Murray and honours student Karen Thompson.
 
The research was funded through Macfie’s Natural Sciences and Engineering Research Council (NSERC) Discovery Grant, and by NSERC and private sector contributions to the Metals in the Human Environment Strategic Network.
 
The researchers planted carrots, radishes, lettuce, soybeans and wheat on three Canadian field soil types, using a commercial potting mix for comparison. The researchers looked at the concentrations and types of metals in the original soils and then at the metal amounts in the edible parts of the plants when they were harvested.
 
The most mobile element was cadmium, which can be very toxic, so farmers need to pay particular attention if it is present, says Macfie.
 
Another significant result she says was that the accumulation of metal depended much more on the crop species raised than the type of soil.
 
Carrots were particularly efficient at concentrating cadmium, lead and zinc, a finding that has appeared in other studies, she says. Next, were the radishes and lettuce, which had high concentrations of cadmium and zinc. The seeds of wheat had the highest concentrations of copper.
 
The researchers found biovailability of metal to the plants was greatest in soils that combined a high metal content with a low content of organic matter.
 
Putting this and similar studies together will allow regulatory agencies to determine risk factors for different combinations of crop and soil planting, the researchers say.
 
"We currently base standards for metals in soils on the concentration of metal in the bulk soil," says Ms. Murray.
 
"This does not factor in how much is bound up and unavailable to plants. Our study shows that, if the metal is available even in soil considered uncontaminated by present standards, the consumer may be at risk if the wrong plant is grown. On the other hand, if the metals are not readily bioavailable, vegetables grown in a mildly contaminated soil are likely to present a low risk to human health."
 
The study with tables is showing metal concentrations in plants in each soil type has been published in the current issue of Botany.

Article source: Natural Sciences and Engineering Research Council
 

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