There’s a reason agronomists and Extension educators are constantly urging growers to have their soil tested. Sometimes it contains things they definitely do not want in their crops.
Consider root crops especially. The part of the plant that’s in the soil is the part consumers will eat. If those roots absorb bad nutrients, they get passed along.
A team of researchers from the Departments of Plant, Soil & Microbial Sciences; Microbiology, Genetics & Immunology; and Chemistry at Michigan State (Chenxi Li, Aaron Sue, Andrew Huang, Qianqian Dong, Hui Li, Keith MacRenaris, Thomas V. O’Halloran, Kurt Steinke, Zachary Hayden, Ray Hammerschmidt and Wei Zhang) worked together to look at the effect of soil amendments on the uptake of four particularly not-good elements in carrots.
The team noted that the toxic metals (TMs) arsenic (As), cadmium (Cd), chromium (Cr) and lead (Pb) in carrots (and other crops) are a serious food safety concern. Even in trace amounts, these TMs can cause much larger problems.
The objectives of their study were to develop a method to assess the uptake of TMs in crops; to identify optimal soil amendments with the overall benefits of decreasing crop uptake of TMs, especially in carrots; and revealing correlations among TM uptake and/or translocation in carrots.
Genetically, translocation occurs when a chromosome breaks and the (typically two) fragmented pieces re-attach to different chromosomes. This can lead to issues in the carrots themselves.
Using the highly productive ‘Canberra’ carrot variety, the researchers grew the carrots for 25 days, until they reached growth stage 1. Four different amendments were added to carrots – composts (dairy compost and poultry compost); liming (gypsum and lime); minerals (organic matter-rich Leonardite and Zeolite); and pyrogenic materials (biochar and wood ash) – to see what affect each would have on TMs. There was also a control group with no amendments added.
The carrots were grown in a polyethylene tubes. After the 25-day growing period, the bulk soil, rhizosphere soil, carrot root and shoot samples were collected. A mass spectrometry test was used to measure TM concentrations.
When looking at root concentrations of TMs, gypsum decreased the concentrations of As, Cd and Cr in roots. Wood ash increased Cr concentration, however. Zeolite decreased Cd concentrations.
When looking at translocation, biochar increased the translocation of Cr. Gypsum increased the translocation of As, Cd and Cr. Wood ash increased the translocation of Cr. Zeolite decreased the translocation of Cd and Pb.
Additionally it was found that the root uptake of Cd reduces the translocation of that same TM. High root concentrations of Pb tended to decrease the translocation of As as well.
What this study found is that there is no silver bullet for TMs. “It is challenging to mitigate the uptake of these TMs in carrots with a single soil amendment,” the research team noted. “No soil amendment significantly decreased the uptake of these TMs in carrots. However, the effect of multiple soil amendments in combination on carrot uptake of TMs should be further investigated.”
