Establishment of oilseed rape in the presence of cereal straw

Summary

A ban on straw and stubble burning is proposed by the Government to come into effect after the 1992 harvest.

There is a need to develop more suitable techniques for establishing rape in the presence of chopped straw, particularly after wheat on the heavier soils. The short interval between wheat harvest and rape sowing precludes the use of all except shallow cultivations on most of these soils. Light loams present few problems following ploughing. Medium loams are more suited than clays to ploughing before rape but the better option in dry conditions is often cultivation rather than ploughing.

Techniques of establishing oilseed rape by broadcasting seed into the standing cereal crop were investigated at Boxworth (clay) and at Rothamsted (silty clay loam with flint) in harvest years 1986-89. In both series, the effects of bailing and removing straw and leaving chopped straw on the surface were tested, and at Boxworth the chopped and spread straw was also incorporated; treatments were modified slightly each year. Some systems gave good results in some years. Further work is required to assist in improving the consistency of a system requiring the minimum of cultivation.

Variable results were found in ADAS surveys of 24 fields in which crops were established by broadcasting seed into standing wheat crops. However the farmers considered the advantages of reduced cultivation costs and timeliness of sowing to be important.

In the few comparisons of ploughing and tine cultivation for straw incorporation prior to drilling rape, the former treatment usually gave the higher yield but the trials were not on the very heavy or difficult soils.

In 1990 six farmers were interviewed about their method of rape establishment where straw had not been burnt. The systems adopted were to a large extent influenced by soil texture. All of the farmers considered it critical to do the primary cultivation as soon as possible after the cereal harvest and to conserve moisture by using a roll or landpacker immediately.

It is recommended that support be given for further work on developing methods of establishment of rape where straw has not been burnt, particularly on heavy soils, and for studies of the interaction of the presence of straw upon nitrogen requirement and slug damage.