A recent meta-study by the Swiss-based Research Institute of Organic Agriculture (FiBL) that drew on 57 systematically selected international publications involving 149 pairwise comparisons found that:
- soils farmed organically contain, on average, 59 percent more biomass from microorganisms; and
- these microorganisms are up to 84 percent more active than those in conventionally treated agricultural soils.
Other key findings of the FiBL meta-study included that:
- microbes in organic soils have significantly more active metabolisms than those in conventionally farmed agricultural soils, resulting in speedier conversion of organic matter, such as compost, into plant-available nutrients;
- the positive impact of organic farming methods on soil microbial activity is increased significantly when they take place in warm, dry climates;
- using organic fertiliser increases the number and activity levels of soil microbes;
- adopting diverse crop rotation schedules, with the inclusion of legumes in the rotation, positively impacts soil microbial numbers and activity levels; and
- organic farming methods have a positive effect on both soil pH and soil carbon levels, which in turn have a beneficial impact on soil microbes.
Offsetting lower yields on organic farmsLarge quantities of microbial biomass, coupled with an ‘active’ soil life, should provide good base conditions for achieving high crop yields. Despite this, yields on organic farms are, on average, 20 percent lower than comparable crops grown via conventional farming methods. Lower yields on organic farms result, for the most part, from:
- a lack of adapted varieties available to organic producers; and
- organic farmers’ (necessary) avoidance of chemical plant-protection agents, synthetic herbicides and fertilisers.
An ongoing challenge for organic producers is to find effective ways to compensate for these lower yields.
Mounting evidence suggests that organic farming systems using adapted varieties produce more stable yields in drought conditions. Moreover, the higher biomass that accumulates in organically farmed soils has a positive impact on the environment: soils treated organically typically contain more humus, which aids in the sequestration of harmful greenhouse gas carbon dioxide (CO2), helping to mitigate climate change.
Read the original FiBL study on microbial biomass: Lori, Martina; Symnaczik, Sarah; Mäder, Paul; De Deyn, Gerlind; Gattinger Andreas (2017). 'Organic farming enhances soil microbial abundance and activity - A meta-analysis and meta-regression'. PLOS ONE. July 12, 2017.
Check out this video, in which FiBL's Professor Dr. Urs Niggl talks about soil fertility in organic agriculture.
Get more information on this study and on the work of FiBL: contact Martina Lori from FiBL's Department of Soil Sciences, or Helga Willer, Communication officer, at FiBL Switzerland, or visit the official FiBL website.