PLOWING AND ROTARY CULTIVATION FOR CEREAL PRODUCTION IN A LONG-TERM EXPERIMENT ON A CLAY SOIL IN SOUTHEASTERN NORWAY .1. SOIL PROPERTIES

Rotary cultivation to 10 cm depth versus mouldboard ploughing to 25 cm depth at two rates of nitrogen application (50 and 100 kg ha(-1)) wer e investigated in a factorial field experiment on a clay soil at Tune in southeastern Norway. The experiment was started in the autumn of 19 76, and the measurements discussed in this paper were made in 1989. Th e main crops were spring barley (Hordeum vulgare L.) and spring oats ( Avena sativa L.). The soil structure was measured by volumetric relati ons, aggregate stability and cone penetrometer resistance in the soil after 13 years with rotary cultivation and ploughing. The soil structu re had improved on the rotavated soil with regard to plant growth requ irements and erosion control. Aggregate stability was about 15 g per 1 00 g greater on rotavated as compared with ploughed soil. This could b e explained by the increased content of organic matter in soil which h ad not been ploughed, but only rotavated for 13 years. The content of organic matter had on the average increased by 0.06 g per 100 g year(- 1) in the top layer (0-5 cm) in rotavated soil, and had remained const ant in ploughed soil. The penetration resistance was similar for rotav ated and ploughed soil for the upper 15 cm. The soil physical paramete rs were measured at one level of applied nitrogen (100 kg ha(-1)). The pH had decreased 0.006 units per year in the upper 20 cm after rotary cultivation as compared with ploughing. In this experiment the drop i n pH was not an effect of nitrification. Available phosphorus and avai lable potassium were significantly greater in the top layer (0-5 cm) i n rotavated soil. The difference in available potassium between plough ed and rotavated soil had remained relatively constant since 1980, whi le the difference in available phosphorus had increased. Soil pH and n itrate concentration were affected by nitrogen fertilization.