PLOWING AND ROTARY CULTIVATION FOR CEREAL PRODUCTION IN A LONG-TERM EXPERIMENT ON A CLAY SOIL IN SOUTHEASTERN NORWAY .2. YIELDS AND WEED INFESTATION

Rotary cultivation to 10 cm depth (rotavator) and ploughing to 25 cm d epth (mouldboard plough) were compared at two nitrogen application rat es (50 and 100 kg ha(-1) in a factorial experiment on a clay soil at T une in southeastern Norway. The experiment was established in the autu mn of 1976. Changes in soil properties after 13 years of treatment are discussed in a first paper (Borresen, T. and Njos, A., 1993. Soil Til lage Res., 28: 97-108). In this paper quantity and quality of yields a nd weeds infestation during 14 years are discussed. The main crops wer e barley (Hordeum vulgare L.) and oats (Avena sativa L.). Rotary culti vation yielded 200 kg ha(-1) more on average than ploughing. Particula rly in years with dry early summer, rotary cultivation gave significan tly higher yields compared with ploughing. The nitrogen content in the cereal increased when grown on rotavated soil. The total uptake of ni trogen in grain and straw was frequently greater on rotavated soil. On average the difference was as high as 5 kg ha(-1) in grain and 2 kg h a(-1) in straw. Loding increased and the grain percentage decreased if the solid was rotavated. Phosphorus, potassium, calcium and magnesium contents of the grain were not affected by the tillage system. The in festation of couch grass (Elytrigia repens L. Nevski) and other weeds was greater on the rotavated soil and more pronounced at the beginning of the experiment than in later years. It was necessary to apply glyp hosate for 5 years during this period to control the couch grass and o ther perennial weeds.