Agroscope, FiBL, University of Bern

Can Effective Microorganisms Influence Green-Manure Decomposition?

Although effective microorganisms (EM) are frequently used to shallowly incorporate green manures (cover crops) in the field, almost no scientific research has been conducted on them to date. This study simulated the decomposition of green manures with EM in the laboratory.

Why EM with green manures?

Green vegetation is the ideal soil cover for preventing erosion and nutrient losses, which is why winter-hardy cover crops are the best option for bridging the period between two main crops from a soil-protection perspective. Ploughing-in a green intercrop in spring can be a challenge, however, since the risk of second growth is relatively high. This applies in particular to organic farms that have embraced no-till. In such systems green manures are often only incorporated shallowly, to promote soil life with the rapidly decomposable plant material (‘surface rotting’ system). However, environmental conditions in spring vary a great deal from year to year, and cold and damp conditions in particular can inhibit the decomposition of plant biomass. The incompletely decomposed smeary plant biomass can therefore make seedbed preparation substantially more difficult. The use of EM attempts to accelerate the decomposition of the incorporated plant biomass whilst promoting soil life and humus formation.

Effects of EM on soil parameters

An in-depth laboratory experiment was conducted into the effects of adding EM to support surface rotting. In early May we brought a portion of both the top layer of soil and the plant material of a patch sown with rye and vetch into the laboratory and simulated the rotting process under controlled conditions at 12 °C.

The processes with and without EM both exhaled the same amount of carbon dioxide, suggesting the same microbial activity in both processes. The addition of EM did not affect the solubility of nutrients and trace elements in the soil, nor did it influence microbial biomass. Moreover, genetic analyses of the soil microbiome showed that the processes with and without EM did not differ in terms of their microbiological composition. Seven days after the addition of EM to the soil, lactic acid bacteria were the only identifiable EM components; however, this effect was negligible at a normal rate of application (120 litres/ha), and only measurable at 100 times this application rate. The study therefore found no evidence that the addition of EM influenced the decomposition of green manure materials.


  • The addition of EM produced no consistent effects on microbial activity in the soil.
  • No differences were found between the processes with and without EM in terms of nutrient and trace-element solubility.
  • Only very minor differences were found in the microbial composition of the two processes.
  • Lactic acid bacteria, the primary constituent of EM, were detected in the soil, but only at a substantially increased application rate.
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