A comparative study to understand the impact of cultivation practices on biodiversity

The three systems studied are the following: direct-seeding mulch-based cropping systems, organic farming with tillage, conventional. No-till and contribution of fresh organic matter: 2 key factors conducive to micro-organisms.

Soil micro-organisms include all soil fungi and bacteria. They contribute to functioning of the soil through several ecological processes. They are the main biochemical transformers of organic matter in the soil. They recycle carbon and nutrients through their action as primary decomposers. Their action has an impact on soil structure. Through production of polysaccharides, they allow the connection between bacteria and soil particles. Finally, certain groups, such as rhizobium and mycorrhizae, can offer a direct benefit for plants through symbiosis.

Measuring total DNA levels in the soil is an indirect way of assessing microbial biomass. The first results show that the cultivation systems studied have significant impact on the quantity of microbial biomass present in the soil. Reducing tillage therefore appears to be a relevant lever to increase living biomass in the soil. As seen in DMC, not disturbing the surface and regularly contributing organic matter favours development of micro-organisms.

a=conventionnel / b=organic / c=DMC

The abundance of fungi is similar in conventional tillage or organic systems, and is significantly higher in direct-seeding mulch-based cropping systems. The fungus population is very sensitive to tillage: soil fragmentation provoked by tillage significantly impacts the continuity of mycelial networks of fungi and reduces their population.

The abundance of bacteria is linked to Corg levels. In direct-seeding mulch-based cropping systems, bacteria are favoured by the root system of cover crops and the concentration of carbon in the surface horizon.

 

Nematodes represent one of the most abundant taxa among soil invertebrates (between 200 and 20,000 individuals per kg of “ordinary” soil). Nematodes significantly contribute to nutrient cycles. They integrate and mineralise soil nutrients. They also stimulate populations of primary decomposers through predation.

Two services provided by increased soil biodiversity which are greater in direct seeding mulch-based cropping systems: increased fertility and better structural stability of soils

Micro-organisms and nematodes play an important role in at least three major ecological functions: carbon transformation, nutrient cycle, maintaining soil structure.

Bacterivorous nematodes excrete a significant proportion of the nutrients contained in the bacteria they eat and therefore make it possible to release these nutrients which are normally not accessible to crops. This is expressed by acceleration of the nutrient cycle and enhanced soil fertility.

More abundant mycelial network hyphae in DMC systems lead to higher secretion of polysaccharides by fungi. These sugars create a link between bacteria and soil particles and reinforce structural stability of the soil, thereby reducing its vulnerability to climate hazards.

The results of this study show that direct-seeding mulch-based cropping systems give rise to a more abundant food web in the soil, which is more mature and diverse than with tillage systems. These results also suggest a higher turnover of bacteria in conservation agriculture than in intensive agriculture. Some of the biological indicators used in this study have made it possible to emphasise several aspects of soil functioning in conservation agriculture and therefore appear to be relevant in assessing the quality of the soil for this type of agriculture: abundance of nematodes and quantity of microbial biomass.