Ghosts of past pesticide use can haunt organic farms for decades

Date:
March 3, 2021
Source:
American Chemical Society
Summary:
Although the use of pesticides in agriculture is increasing, some
farms have transitioned to organic practices and avoid applying
them. But it's uncertain whether chemicals applied to land decades
ago can continue to influence the soil's health after switching
to organic management. Now, researchers have identified pesticide
residues at 100 Swiss farms, including all the organic fields
studied, with beneficial soil microbes' abundance negatively
impacted by their occurrence.



FULL STORY ========================================================================== Although the use of pesticides in agriculture is increasing, some farms
have transitioned to organic practices and avoid applying them. But it's uncertain whether chemicals applied to land decades ago can continue to influence the soil's health after switching to organic management. Now, researchers reporting in ACS' Environmental Science & Technology
have identified pesticide residues at 100 Swiss farms, including all
the organic fields studied, with beneficial soil microbes' abundance
negatively impacted by their occurrence.


========================================================================== Fungicides, herbicides and insecticides protect crops by repelling
or destroying organisms that harm the plants. In contrast, organic
agriculture management strategies avoid adding synthetic substances,
instead relying on a presumably healthy existing soil ecosystem. However,
some organic farms are operating on land treated with pesticides in the
past. Yet, it's unclear whether pesticides have a long-lasting presence
in organically managed fields and what the reverberations are to soil
life, specifically microbes and beneficial soil fungi, years after their application. So, Judith Riedo, Thomas Bucheli, Florian Walder, Marcel
van der Heijden and colleagues wanted to examine pesticide levels and
their impact on soil health on farms managed with conventional versus
organic practices, as well as on farms converted to organic methods.

The researchers measured surface soil characteristics and the
concentrations of 46 regularly used pesticides and their breakdown
products in samples taken from 100 fields that were managed with either conventional or organic practices.

Surprisingly, the researchers found pesticide residues at all of
the sites, including organic farms converted more than 20 years
prior. Multiple herbicides and one fungicide remained in the surface
soil after the conversion to organic practices; though the total number
of synthetic chemicals and their concentrations decreased significantly
the longer the fields were in organic management. According to the
researchers, some of the pesticides alternatively could have contaminated
the organic fields by traveling through the air, water or soil from nearby conventional fields. In addition, the team observed lower microbial
abundance and decreased levels of a beneficial microbe when fields had
higher numbers of pesticides in the fields, suggesting that the presence
of these substances can decrease soil health. The researchers say future
work should examine the synergistic effects of pesticide residues and
other environmental stressors on soil health.

========================================================================== Story Source: Materials provided by American_Chemical_Society. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Judith Riedo, Felix E. Wettstein, Andrea Ro"sch, Chantal Herzog,
Samiran
Banerjee, Lucie Bu"chi, Raphae"l Charles, Daniel Wa"chter, Fabrice
Martin-Laurent, Thomas D. Bucheli, Florian Walder, Marcel G. A. van
der Heijden. Widespread Occurrence of Pesticides in Organically
Managed Agricultural Soils--the Ghost of a Conventional Agricultural
Past? Environmental Science & Technology, 2021; 55 (5): 2919 DOI:
10.1021/ acs.est.0c06405 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/03/210303142622.htm

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