Tillage intensity effects on soil properties and crop yields in a long-term trial on morainic loam soil in southeast Norway

Many tillage studies focus primarily on grain crops, whereas other important agricultural crops receive little attention. This paper presents yield results for various crops grown in the tenth to sixteenth year of a long-term tillage trial on loam soil in southeast Norway. Traditional plough tillage was compared with deep and shallow tine cultivation and with minimum tillage, and the residual effects of tillage were measured in the seventeenth and eighteenth years. Soil bulk density, air permeability and other soil conditions were found to be favourable for crop growth on all treatments in the tenth year. The yield levels of cereals (Hordeum vulgare L., Triticum aestivum L. and Avena sativa L.) and potatoes (Solanum tuberosum L.) showed consistent increases of 2–8% with declining tillage intensity, whereas yields of fodder beet (Beta vulgaris L.) were highest after plough tillage. The latter result was thought to be due to lower soil temperatures under reduced tillage. Yields of brassica crops were greatly affected by tillage intensity, owing to a marked reduction of clubroot (Plasmodiophora brassicae Wor.) infection with reduced tillage. Average yields for these crops were 23%, 52% and 59% higher with deep tine cultivation, shallow tine cultivation and minimum tillage, respectively, than with plough tillage. The effects were particularly dramatic in the case of fodder rape (Brassica napus L. ssp. oleifera Sinsk. f. biennis Reichb.) and cabbage (Brassica oleracea L. var. capita L.). Liming raised the yields of some brassica crops but did not influence the effect of tillage.

Soil acidity was measured twice during the trial period and again in the second residual year, and showed values which were 0.1–0.3 pH units lower with reduced tillage than with plough tillage. This rules out the conclusion that the effect of tillage on clubroot was associated directly with acidity. Positive residual effects of reduced tillage systems were found on the yields of both brassicaceous and gramineous crops. Reduced tillage intensity may thus be recommended for all crops studied, with the exception of fodder beet, on morainic loam soils of southeast Norway.