LONG-TERM EXPERIMENT WITH STRAW MANAGEMENT, STUBBLE CULTIVATION, AUTUMN AND SPRING PLOWING ON A CLAY SOIL IN SE NORWAY

Autumn vs. spring ploughing, stubble cultivation and straw management were investigated in a factorial field experiment on a clay loam at Tune in S.E. Norway. The experiment was started in the autumn of 1963 and was completed in the autumn of 1984. The main crops were barley (Hordeum vulgare L.) and oats (Avena sativa L.). Autumn ploughing gave significantly higher yields, 420 kg ha-1 higher on average, than spring ploughing. The combination spring ploughing/no stubble cultivation/incorporated chopped straw treatment have a yield decrease of 608 kg ha-1 year-1 as compared with autumn ploughing/no stubble cultivation/burnt straw. Incorporation of straw by stubble cultivation in combination with autumn ploughing was the best management practice as far as yields are concerned. The seedbed in spring was finer in the autumn ploughed soil because of the effect of freezing and thawing. Stubble cultivation had little effect when the soil was ploughed in autumn. To avoid yield depression after spring ploughing it was important to incorporate the straw by stubble cultivation in autumn. Stubble cultivation depressed the infestation of couch grass (Elytrigia repens L. Nevski). Burning straw resulted in higher yields when the soil was ploughed in spring and also reduced infestation of weeds. The positive effect of burning on yield was especially clear on spring ploughed soil without stubble cultivation. After 19 years of ploughing in cereal straw, aggregate stability and organic matter content in the soil had increased as compared with burning. The increase in organic matter was 0.3%. Other physical properties were not influenced by straw management.