When compost reduces soil pathogens

According to the WHO (World Health Organization), outbreaks of foodborne illnesses associated with the consumption of fresh produce have become a major public health concern. The WHO estimates that 600 million people worldwide, or about one in ten people, fall ill every year after consuming contaminated food, and 420,000 die from it. According to a study published in Journal of Applied Microbiology, “More than 80% of infections are responsible for most of the three pathogens: Listeria monocytogenes, Salmonella enterica and Escherichia coli. . They are sequentially caused by listeriosis, salmonellosis, and food poisoning, caused by the secretion of toxins secreted by certain strains of Escherichia coli bacteria and known as Shiga-toxins.

Biological modification between environment and health benefits

The study states that “The recent outbreak of foodborne illnesses has caused American farmers to reevaluate their practices. In particular, fear that the amendment (Eg operations intended to improve soil physical properties, by adding fertilizer) Can introduce food borne pathogens into the fields and promote their survival in the soil. In fact, this fear has prompted farmers to reduce or eliminate the application of manure of animal origin. “.

At the core of this study is Naresh Devarajan, a doctoral student at the University of California, and his team of researchers. For 27 years, he conducted an experiment aimed at comparing the effects of biological and conventional soil management on the suppression of food-borne pathogens. In fact, they measured how poultry litter and / or crops are composted – “green” manure that covers the soil in the absence of the crop – affecting the ability of agricultural soils to suppress disease pathogens. Food origins, such as Listeria and Salmonella.

This study has shown that organic soil management, through organic amendment, will improve soil quality. Green waste, for example, can increase soil organic matter, prevent nutrient leaching, and increase nitrogen content. All this is also necessary for proper growth of plants. Compost, on the other hand, also has a beneficial effect on soil health: in fact, it improves biomass, as well as microbial activity and diversity.

More manure and less pathogens

Actually, according to Naresh Devarajan and his associates, “Soil germs compete for space and resources (For example, carbon, nitrogen and other nutrients, editor’s note) With foodborne pathogens, and therefore can be prevented from retaining pathogenic bacteria. Therefore, greater soil microorganism diversity is often associated with less survival of foodborne pathogens in the soil. Thus, organic amendments (eg compost and cover crops) can […] Increase soil diversity and microbial activity, which can act as competitors or antagonists and reduce the survival of pathogens ”.

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Compost also helps increase organic matter, as well as, for example, the concentration and retention capacity of nutrients such as organic carbon. By adding nutrients to the soil, compost limits the growth and survival of pathogens that can cause food-borne illness in the long run. Indeed, after ten and thirty days of incubation, researchers showed that soils containing more macronutrients and micronutrients were more likely to suppress salmonella.

In contrast, soil without compost, after incubation for ten days at 20 ° C, retained four to five times more salmonella than soil amended with compost. In addition, traditional soil, which is soil with fertilizers, but without manure or naturally without fertilizers, will have fewer micronutrients than other treatments at harvest time. Thus, manure of cattle and compost of cover crops may work as an alternative to chemical fertilizers used in traditional agriculture.

Short term effectiveness

However, according to this work, the effects of treatment worsened as bacterial communities changed during the growing season (local weather conditions allow normal plant growth). Even though the study showed a decrease in Salmonella And listeria is more important in the two compost treatments than the two treatments that did not receive compost at the beginning of the vegetative period. All treatments eventually changed to give the same level of Salmonella and Listeria suppression at harvest time.

Soils with very different management histories are widely equivalent in their ability to suppress Salmonella and Listeria at the time of harvesting.

© Naresh Devarajan.

Therefore, the use of compost or cover plants will not be directly at the origin of the spread of pathogens that can cause foodborne diseases. Conversely, in the short term, these organic farming techniques will be even more beneficial for soils and their microbiota than chemical farming practices. Therefore, even though the presence of pathogens does not differ significantly between traditional and organic farming at the time of harvesting, the use of compost and cover crops has many benefits in terms of human health. Respect for soil and environment. Therefore the ideal would be to develop ecologically responsible practices that keep pathogens limited to the crop.

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About the Author: Abbott Hopkins

Analyst. Amateur problem solver. Wannabe internet expert. Coffee geek. Tv guru. Award-winning communicator. Food nerd.

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