Effects of incorporating different amounts of straw on growth, diseases and yield of consecutive crops of winter wheat grown on contrasting soil types

Three experiments on winter wheat, each lasting 5 years and on different so il types, were used to test the effects of incorporating different amounts of straw, mainly to determine the importance of achieving uniform distribut ion to avoid adverse effects on grain yield. Decreases in crop growth and/o r grain yield as a consequence of incorporating straw were detected in the first year. The decreases were much larger in one experiment where straw wa s imported and applied to soil that had been fallowed for 12 months before sowing the wheat than in the other two where the straw was incorporated fol lowing the harvest of a winter wheat crop. Tn the subsequent 4 years, incor porating up to 20 t straw/ha had no significant effects on grain yield but there were some significant effects on concentrations and uptakes of N, P a nd K, especially on the heavier textured soils. The effects on crop growth and yield that were detected in the first year on each site are tentatively attributed to decreases in available N representing that which was require d to support the decomposition of the incorporated straw. The relative lack of significant effects in subsequent years seems to imply that a significa nt proportion of this N was remineralized relatively quickly. and thus avai lable to support the decomposition of the straw that was incorporated in th e second year and. after further recycling, in the years after that. Eyespo t, caused by the fungus Pseudocercosporella herpotrichoides, was decreased by incorporating straw but there were few; significant effects on other dis eases. The results provide a generally reassuring message for farmers in su ggesting that on most, if not all, soils there is little cause for concern about the consequences of incorporating even large amounts of wheat straw b efore sowing a further crop of winter wheat.