Improving crop profitability by using minimum cultivation and exploiting grass weed ecology

Project Report No. 381

Improving crop profitability by using minimum cultibation and exploting grass weed ecology


S.K.Cook1, A.J. Swain2, J.Clarke1, S.Moss2, Z.Hughes2, J.Orson3, L.Powell3, A.Creasey3, K.Norman4 and J.Alford4

1ADAS Boxworth, Battlegate Road, Boxworth, Cambs. CB3 8NN
2Rothamsted Research, Harpenden, Herts. AL5 2JQ
3The Arable Group, Morely Research Centre, The Old Rectory, Morley, Wynmondham, Norfolk NR18 9DB
4Velcourt Group plc, Melbury Sampford, Dorchester, Dorset DT2 0LF



A range of controlled environment, glasshouse and small plot experiments were carried out between 2001 and 2005 to understand the cultural and environmental factors that influence black-grass seed dormancy and germination. Further field experiments, on large plots, assessed the relative importance of management and natural factors on black-grass populations.

A test was developed to determine dormancy level in black-grass seed collected in July. Controlled environment work indicated that temperature stress towards the end of seed maturation, irrespective of that during early stages of development, had the greatest impact on dormancy status. In black-grass, under field conditions, this critical timing was mid-June to mid-July. Lower seed dormancy was due to a combination of increased mean maximum (1.8°C) and mean minimum (1.4°C) temperatures over the long-term average for this period. In years with below-average temperatures, levels of dormancy were higher. It should be possible to provide regional forecasts of seed dormancy based on a relatively small number of samples.

The effect of a more-dormant population was to delay emergence of black-grass, compared to a lessdormant population by at least 6-8 weeks, even in the presence of adequate soil moisture. The moredormant population also had a greater proportion (up to 20%) of seeds still viable in the late autumn. The conclusions on dormancy in black-grass cannot be immediately applied to other grass species. There was greater variation in dormancy in Italian rye-grass, barren brome and meadow brome than black-grass, but in some, such as Italian rye-grass and barren brome, dormancy lasted a shorter time than for black-grass.

In the field in high dormancy years and in wet autumns, black-grass populations showed delayed emergence. Drilling after 20 October resulted in significantly lower black-grass populations. If drilling before 20 October, ploughing resulted in the greatest reduction of high black-grass populations. At every site however, ploughing resulted in lower populations than discing.

In low dormancy years, black-grass was able to emerge immediately, provided sufficient moisture was available. This resulted in higher populations in the stubble and lower populations in the crop when assessed before the post-emergence spray. For any given cultivation regime there were no significant differences between before/after 20 October drilling dates. However, if drilling before 20 October, ploughing resulted in significantly lower black-grass populations than discing before drilling or direct drilling. There was however a consistent trend – with discing, there were fewer black-grass present in the crop where cultivation took place immediately after harvest than before drilling. The long-term trials showed that management of black-grass populations was enhanced by the use of dormancy information, but the presence of a mixed grass-weed population made black-grass management more difficult.

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