‘Added value fallows’ The use of customised cover cropping approaches within integrated grass weed management

Abstract

Concerns about soil health and sustainability have led to an increasing interest in and adoption of cover cropping approaches to both improve soil health and crop rotation performance. Alongside rotational diversity and the adoption of no-till or reduced cultivation, cover crops form the basis of conservation agriculture. At the same time, across the industry, there is increasing pressure from grass weed species, such as black-grass, Italian rye-grass, bromes and wild oats. This is as a result of the development of herbicide resistance (in some species) combined with a reduction in available herbicide active ingredients.

The increased adoption of systems with lower cultivation intensity, allied to increasing use of cover crops, could potentially exacerbate grass weed problems. Such systems can reduce the out-of-cropping opportunities for grass weed control (eg stale seedbeds and/or use of glyphosate for total weed control) and limit use of inversion to bury fresh weed seeds.

This project aimed to address this conflict to evaluate the risk/reward balance, specifically with regard to the use of cover cropping where black-grass pressures are high.

Although cover crops have value in the rotation, the research trials and modelling carried out as part of the project confirm that, in relation to the management of black-grass in arable rotations, cover crops should be seen as having a neutral or slightly negative effect on weed population dynamics. The potential negative effects can, nonetheless, be mitigated by careful management.

It is clear that other agronomic factors have far more significant effects on the population dynamics of grass weeds, such as black-grass, including: cultivation timing and type, use and timing of glyphosate outside of the crop, the date of crop establishment and the diversity of rotation.

Many of these agronomic variables are modified when cover crops are introduced and their effects can be confused or confounded with the direct effects of cover crops. This project has found that the direct effects of cover crops on black-grass are small – almost all the effect on populations in field trials could be explained by the underlying cultural control approach. Therefore, maximising the effectiveness of a cover crop strategy as part of a black-grass control strategy involves maximising the effectiveness of the underlying cultural control approach.

This project, therefore, concludes that cover cropping should continue to be considered as a support to the sustainable production of crops. However, the role of cover crops in modifying the population dynamics of black-grass should not be overstated.