Impact of ploughless soil tillage on yield and soil quality: A Scandinavian review

Ploughless soil tillage impacts on yields and selected soil quality parameters is reviewed from the Scandinavian countries of Denmark, Finland, Norway and Sweden. Soil conditions as well as climatic conditions vary widely, this resulting in variations in the length of the growing season, which is very short in the northern part of Scandinavia. The success of reduced tillage and direct drilling depends on the crop species as well as on the soil type and the climatic conditions. The best results seem to be obtained on the heaviest clay soils, which is the most difficult soils to prepare with conventional soil tillage methods. Satisfactory yields were obtained after ploughless tillage in winter wheat (Triticum sp.), winter oil seed rape (Brassica sp.) and late harvested potatoes (Solanum tuberosum L.). The influence of crop rotations and preceding crops in ploughless tillage systems for small grain cereals has received relatively little attention. Also, fertilization of reduced tilled crops has received too little attention, but it seems that nitrogen cannot compensate for sub-optimal tillage. One of the most striking effects of ploughless tillage is the increased density of the soil just beneath the depth of tillage. Increased soil density decreased the volume of macropores (>30–60 μm) and increased the volume of medium pores (30–0.2 μm), but the volume of small pores (<0.2 μm) was only little affected by soil tillage. Increased soil bulk density reduced the air-filled porosity, the air diffusivity and the air permeability as well as the hydraulic conductivity, and sometimes the root development. More plant residues were left on or near the soil surface after ploughless tillage, which led to lower evapotranspiration and higher content of soil water in the upper (0–10 cm) soil layer. It also led to lower soil temperature, and more stable soil aggregates which provided better protection of the soil against erosion. Nutrients and organic matter accumulated near the soil surface after ploughless tillage, and in the long run the soil reaction (pH) declined. Nearly all species of earthworms increased in number in ploughless tillage. The leaching of nitrogen seemed to increase with more intensive cultivation, particularly when carried out in autumn.