​Conservation agriculture and soil fertility

Soil can be viewed as the heart of the farm: the centre through which matter and energy circulate. It provides a habitat for countless animals, protozoa, fungi and microorganisms, and supports the plants that feed people and animals. Living, healthy soil processes crop residues and livestock manure and acts as a natural filter that purifies water.

Soil fertility therefore depends primarily on creating the best possible conditions for soil organisms, maintaining an appropriate soil reaction (pH), ensuring a favourable balance between water and air, and providing an optimal and well-balanced nutrient supply. Agricultural practices must support crop growth without damaging soil vitality or fertility. Measures that improve soil structure and increase soil organic matter are among the most important steps towards lasting improvements in soil quality.

Crop residues and organic matter in the upper soil layer are particularly important because they stabilise soil aggregates, improve infiltration and reduce erosion. These conditions can be achieved by applying organic fertilisers or compost, using shallow conservation tillage and retaining at least part of the crop residues on the soil surface. Experience shows that conservation tillage systems in which at least 30% of the soil surface remains covered with crop residues bring significant changes in soil physical and chemical properties after several years.

The bulk density of the upper layer increases, the proportion of medium-sized pores rises and the proportion of macropores falls. Consequently, plant-available soil water capacity can increase by 15–40%. The number of biopores larger than 1 mm, created by earthworms and decaying roots, also increases. Crop residues at the surface, together with vertically oriented biopores, improve water infiltration. More rainfall therefore remains in the field and less runs off the surface.

Infiltrated water moves more slowly through the soil profile because the hydraulic conductivity of conservation-tilled soils is lower due to their higher density. Although these soils are denser, their structure is more stable. The upper 10 cm contain more stable macroaggregates larger than 200 µm, improving soil aeration. Surface residues also soften the impact of heavy rainfall, helping to prevent erosion and the lateral loss of nutrients and pesticides.

Crop residues reduce evaporation and keep the soil beneath them cooler, by an average of about 3°C. Together with greater plant-available water, this can significantly increase soil biological activity during summer and reduce drought stress. Drying and rewetting also occur more gradually, so the soil cracks less and loses less water from deeper layers through cracks.