Interactions of straw disposal methods and direct drilling or cultivations on winter wheat (Triticum aestivum ) grown on a clay soil

A field experiment was started in 1979 on a clay soil to compare effects of baling to leave stubble only, chopping and spreading straw or burning on the yield of winter wheat (Triticum aestivum). Results are reported for the period 1982–1988 with occasional references to earlier years. The crop was either direct drilled or sown after incorporation of straw or ash by cultivation to depths of 5, 15 or 25 cm. Tine cultivation was used until 1983 then replaced by ploughing. Averaged over a nine-year period, direct drilling into chopped straw caused a one-third reduction in yield compared to direct drilling where the straw was burnt. Over the same period, 5 cm deep straw incorporation resulted in one-fifth less yield compared to crops after burning. From 1985 to 1988, ploughing to 15 or 25 cm resulted in respectively 1 and 9% less yield if straw was incorporated rather than burnt. There was no evidence that these reductions were a consequence of consistent differences in pests or diseases. Temporary (1 year) burning after seven years of incorporating chopped straw increased average yield on tillage treatments by 17%. On this soil, ploughing at least to 15 cm is recommended to improve reliability of crop establishment. The average yields obtained from the straw returned treatments indicates that it was the presence of straw rather than the amount that most influenced yield.