Impacts of agricultural practices on soils
What effects will cropping practices have on the biological fertility of soils? A properly functioning soil operates on its 3 pillars: physical, biological, and chemical. The holistic soil approach allows understanding the interactions between these 3 aspects of soil (Holistic soil approach).
Achieving fertile soil requires a strong and functional biological fertility pillar (Soil biological activity).
To obtain a strong biological pillar it is enough to consider the impact of practices and the climate/soil couple on living organisms. Soil life development is based on the simple respect of 2 fundamental principles: respect for the habitat (shelter) and the cover (food source). It is very simple: feed these organisms and respect the integrity of their habitats.
Agricultural practices will have direct and/or indirect effects on habitats and/or food sources. Among the most impactful practices are:
Tillage
An increase in soil biological activity is observed when tillage is reduced. This is particularly true for large organisms. Indeed, they are the first impacted by tool passes which can either kill them or limit their movement by creating a compacted layer (which appears with any tool pass and not just with ploughing) that constitutes an obstacle. Endogeic earthworms are particularly affected by intense and frequent tillage with population reductions of up to more than 80% compared to soil with low tillage intensity and very occasional ploughing.
Fertilization
A direct effect is observed through the modification of chemical balances in the soil solution which affects microbial diversity. However, fertilization also indirectly impacts the soil because a well-fertilized crop produces a lot of biomass and can provide more organic matter to the soil.
Crop rotation
Soil organisms cannot tolerate the absence of root activity or abundant organic matter. Thus, periods of bare soil and absence of organic matter input (more or less fresh through crop residue return or cover crops or manure application) are very important stress factors. Systems including grassland are generally very beneficial to biological activity, as this period of continuous soil cover allows populations to regenerate after 3 or 4 years of cropping which have considerably reduced the number and diversity of living organisms.
Use of phytosanitary products
There are still relatively few studies on the effect of pesticides on soil organisms, but overall there are 2 effects:
- Direct, which kills organisms during product application, with quite counterintuitive observations such as herbicides affecting arthropods like ground beetles.
- Indirect, via degradation molecules of phytosanitary products which affect hormonal activity. Thus, a decrease in earthworm fertility exposed to several molecules such as mancozeb, carbofuran, or carbendazim has been noted (Cluzeau, 2008).
