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

Ploughless soil tillage impacts on yields and selected soil quality paramet ers is reviewed from the Scandinavian countries of Denmark, Finland, Norway and Sweden. Soil conditions as well as climatic conditions vary widely, th is resulting in variations in the length of the growing season, which is ve ry short in the northern part of Scandinavia. The success of reduced tillag e and direct drilling depends on the crop species as well as on the soil ty pe 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 con ventional soil tillage methods. Satisfactory yields were obtained after plo ughless tillage in winter wheat (Triticum sp,), winter oil seed rape (Brass ica sp.) and late harvested potatoes (Solanum tuberosum L.). The influence of crop rotations and preceding crops in ploughless tillage systems for sma ll grain cereals has received relatively little attention. Also, fertilizat ion of reduced tilled crops has received too little attention, but it seems that nitrogen cannot compensate for sub-optimal tillage. One of the most s triking effects of ploughless tillage is the increased density of the soil just beneath the depth of tillage. Increased soil density decreased the vol ume of macropores (>30-60 mu m) and increased the volume of medium pores (3 0-0.2 mu m), but the volume of small pores (<0.2 mu m) was only little affe cted by soil tillage. Increased soil bulk density reduced the air-filled po rosity, the air diffusivity and the air permeability as well as the hydraul ic conductivity, and sometimes the root development. More plant residues we re left on or near the soil surface after ploughless tillage, which led to lower evapotranspiration and higher content of soil water in the upper (0-1 0 cm) soil layer. It also led to lower soil temperature, and more stable so il aggregates which provided better protection of the soil against erosion. Nutrients and organic matter accumulated near the soil surface after ploug hless tillage, and in the long run the soil reaction (pH) declined. Nearly all species of earthworms increased in number in ploughless tillage. The le aching of nitrogen seemed to increase with more intensive cultivation, part icularly when carried out in autumn. (C) 1999 Elsevier Science B.V. All rig hts reserved.