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 depth (mouldboard plough) were compared at two nitrogen application rates (50 and 100 kg ha(-1) in a factorial experiment on a clay soil at Tune in southeastern Norway. The experiment was established in the autumn of 1976. Changes in soil properties after 13 years of treatment are discussed in a first paper (Borresen, T. and Njos, A., 1993. Soil Tillage Res., 28: 97-108). In this paper quantity and quality of yields and weeds infestation during 14 years are discussed. The main crops were barley (Hordeum vulgare L.) and oats (Avena sativa L.). Rotary cultivation yielded 200 kg ha(-1) more on average than ploughing. Particularly in years with dry early summer, rotary cultivation gave significantly higher yields compared with ploughing. The nitrogen content in the cereal increased when grown on rotavated soil. The total uptake of nitrogen 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 ha(-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 infestation 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 glyphosate for 5 years during this period to control the couch grass and other perennial weeds.