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PUR Lab Key figures: Soil macro-biodiversity in tropical areas

A study conducted by the PUR Lab, in partnership with the UNA University from Honduras, shows that cocoa agroforestry systems can increase soil macro-biodiversity by four times.

“A single gram of soil may contain millions of individuals and several thousand species of bacteria”. (FAO, 2014).
“A single gram of soil may contain millions of individuals and several thousand species of bacteria”. (FAO, 2014).

What is soil macro-biodiversity?

Soil organisms (beetles, spring-tails, mites, worm, spiders, ants, nematodes, fungi, bacteria, etc.) are essential to soil fertility and plants growth. They step in determinant phenomenon for soil fertility: nutrient cycling, decomposition of organic matter, soil structuring, carbon sequestration and regulation of greenhouse gas emissions.

Soil biodiversity is very sensitive to crop management: utilization of fungicides, pesticides, soil tillage, mono-cropping and intensive fertilization affect soil biodiversity and its ecological functionalities. A dead soil is an unproductive soil!

“Soil’s host a quarter of our planet biodiversity” (FAO, 2014). It is one of the world’s most complex and diversified ecosystem.

How do we measure soil macro-biodiversity?

Since early 2015, we are working with a local university in Honduras (Universidad Nacional de Agricultura) and cocoa farmers involved in the reforestation project. We use an ISO normalized method (ISO 23611-5:2011): the Tropical Soil Biology and Fertility (TSBF) method.

– We extract a 19 cm3 soil cube in each sample spot, with 5 repetitions per studied plot.
– We identify and count the different macro-organisms. The key figures are the number of individuals and the diversity of species.
– The sampling is repeated on different land uses: full sun, agroforestry, reforested area and secondary forest. Then we can assess the effects of land use on macro-organisms’ population.

Key figures

Three species of soil macro-organisms were studied (Scolopendra, Phyllophaga and Lumbricus). They are key players for:
– Organic matter decomposition (Lumbricus and Phyllophaga);
– Predation on potential pest species (Scolopendra and Phyllophaga);
– Soil structuring (Lumbricus).

PURLAb-Soil macrobiodiversity-purprojet

Our study shows that there are almost 4 times more Scolopendra, Phyllophaga and Lumbricus in agroforestry and reforested systems than in full sun system.

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