By Claire Robinson
Glyphosate is turning up in manure-based fertilizers used by gardeners and organic and conventional growers and the residues can ruin yields of tomatoes and other sensitive crops, new research from Finland shows.
The scientists were prompted to do the research based on an incident in Finland where a commercial tomato grower suspected poultry manure fertilizer of damaging their commercial organic tomato production.
The grower company commissioned testing, which revealed high levels of glyphosate residue in the poultry manure fertilizer they had used.
To test the possibility that glyphosate residue damaged the crop, the scientists compared results from two manure-based fertilizers produced in Europe and marketed for professional horticultural use.
The first (“G fertilizer”) was the original fertilizer tested by the tomato grower and was shown to contain glyphosate residue at a level of 0.94 milligrams per kilogram (mg/kg). The control fertilizer underwent similar testing and was found to have 0.23 mg/kg glyphosate.
As manure-based fertilizers, both products were marketed as suitable for use in certified organic crop production, but this does not mean the manure is from certified organic livestock.
To test the fertilizers, the scientists grew 72 Encore variety tomato plants for 14 weeks in a climate-controlled greenhouse according to the practices of the commercial grower.
The scientists found that the total harvest of tomatoes grown with the fertilizer with the higher level of glyphosate residue was 35% smaller, and the yield of first-class tomatoes was 37% lower than that of the control fertilizer with the lower glyphosate level.
In their paper, the scientists explain:
“Except for the glyphosate content, the two fertilizers were substantively similar. Hence, the difference in tomato production between the two treatments can reasonably be attributed to the glyphosate residue present in a commercial fertilizer marketed (at the time) as suitable in certified organic horticultural production including for tomatoes.”
As part of the study, to ascertain awareness and potential contamination mitigation measures, the researchers contacted five fertilizer companies, two farming organizations, a feed company and two government organizations working on nutrient cycling and agricultural circular economy.
Two of the five fertilizer companies identified poultry manure as a source of glyphosate contamination. Companies with awareness of pesticide residues reported interest in establishing parameters for pesticide residues.
Where does the glyphosate in poultry manure come from? While the authors of the paper do not address this question, two sources immediately come to mind: pre-harvest “desiccation” (dry-down) of feed grains by the spraying of glyphosate-based herbicides; and the spraying of these same herbicides onto genetically modified, or GM glyphosate-tolerant corn and soy, which will be commonly used in poultry feed worldwide.
Bakery waste too toxic for fertilizer
A disturbing detail in the study is the finding by one fertilizer producer that herbicide residue in bakery waste is too high for fertilizer production — illustrating that regulatory limits on permitted pesticide residues in foodstuffs alone do not ensure that products can be safely recycled into the food system as fertilizer.
If bakery waste is too toxic for plants, what effects are the bakery products having on humans who eat them?
Glyphosate residues have ‘negative impacts on crop production’
The authors conclude their paper:
“The extent of glyphosate contamination of recycled fertilizers [i.e., manure or compost-based fertilizers] is unknown, but this study shows that such contamination occurs with negative impacts on crop production.
“Lack of testing and regulation to ensure that recycled fertilizers are free from harmful levels of glyphosate or other pesticides creates risks for agricultural producers. The issue is particularly acute for certified organic producers dependent on these products, but also for sustainable transitions away from mineral fertilizers in conventional farming.”
Another pesticide industry-created headache
The research adds yet another pesticide industry-created headache to the longstanding one involving the herbicide aminopyralid, which regularly turns up in animal manure and is persistent enough to severely damage or kill plants grown with contaminated manure.
Victims of aminopyralid damage include the author of this article and, very probably, the British author, broadcaster and vicar Peter Owen Jones, who, on a quest to live a simple life in line with the principles of St. Francis, found his home-grown tomato crop ruined by herbicide-contaminated horse manure (see around 13:34 minutes into the video linked).
On another scale of outrage altogether is the ongoing tragedy in the U.S. of dicamba herbicide drift from dicamba-tolerant GM crop fields killing and damaging millions of acres of non-tolerant crops and wild plants, including trees.
These examples raise the question of how long society will be prepared to tolerate such chemical trespass and damage to our vital food crops.
It also suggests that there is a commercial need for certified pesticide-residue-free or low-pesticide-residue fertilizers, with a premium paid to suppliers who guarantee that they have not used persistent agrotoxins in their production processes.
It does, however, seem manifestly unfair that organic growers should have to pay that premium. A fairer system would be to force the polluters to pay via a tax on their pesticide products.
Originally published by GMWatch.
Claire Robinson is an editor at GMWatch.org, a not-for-profit organization that keeps the public informed about GM foods and crops and their associated pesticides.
