Defining factors which affect the cultural and chemical control of brome species in winter cereals
About this project
In the first project on Bromus sterilis funded by HGCA (Orson, 1997), there was some evidence that small numbers of the seed survived in a viable ungerminated condition for longer in clay soils compared with lighter soils. Although an extensive experiment had been set up at one site to test whether this was so, using two populations differing in dormancy status which were sown either in a clay or sandy silty clay loam soil, too few seeds were recovered after eight months burial for any robust conclusions to be drawn. A further experiment devised, to determine the survival ofungerminated viable seeds in the same two soil types.
In addition to test if survival of ungerminated viable seed depended upon the drainage/aeration of the soil, B. sterilis seeds of a "medium dormancy" status were buried in soils differing in pore size.
Now that straw/stubble burning is no longer permitted, there is a considerable residue of straw after harvest which needs disposal. It is often chopped, and then ploughed in, which gives rise to two main questions with regard to B. sterilis control. Firstly, what effect does the chopped straw have on the germination of the seed pre-incorporation and, secondly, are there any post-burial effects? Within this project the first question was addressed by ADAS, Boxworth, while IACR-LARS investigated the second question using a micro-plot technique.
In the first project, when seed of a range of populations of B. sterilis differing in dormancy status (from low to high) were exposed throughout the winter on the soil surface (i.e. exposed to light, moisture and low temperatures) and then recovered the following spring, it was found that all populations had been induced into dormancy.
When recovered and placed in the dark, a condition in which they would normally germinate, germination was very slow. Whether burying seeds that had been induced into dormancy by exposure on the soil surface would lead to their long term survival in an ungerminated viable condition in the soil was not known. In the current project a further experiment was set up to test this latter hypothesis.
Little was known concerning the dormancy/germination behaviour of either Bromus commutatus or Bromus hordeaceus ssp. hordeaceus when this project was started. It was considered essential to obtain such information, so that a control strategy could be formulated, particularly as there was evidence of increasing incidence of both species in cereal crops in the eastern countries ofEngland. A total of 25 populations of B. hordeaceus ssp. hordeaceus and 20 populations of B. commutatus were collected during the course of the project, grown under common environmental conditions at Long Ashton and then tested for germination behaviour in the laboratory. Selected populations were tested outdoors in six mini-plot experiments to determine their germination and longevity behaviour in the field, particularly in relation to timing of autumn burial.
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