I was on a farm walk last week where the value of over-wintered stubbles was discussed. It was acknowledged that crop treatments pre-harvest would have an impact, but assuming that pre-harvest dessicants were not used, what is the feed value from weed seeds? It was suggested that many of the seed bearing weeds would have been cut by the combine, therefore leaving relatively few in the base of the crop. Again, this can vary greatly depending on soil type, weather etc, but are there certain plants that produce large amounts of seed? It was also suggested that stubbles provide a good habitat (e.g. cover through the winter), and that is why they can attract large numbers of birds.
Does anyone have any thoughts on this?
Hi Bruce
The evidence shows that weedy stubbles support more birds and that areas with more stubbles through the winter have lower rates of declines of birds such as skylarks and yellowhammers, so weed seeds seem to be a critical factor. There is also evidence that stubbles which do not receive pre-harvest desiccants or post-harvest herbicides provide more seeds and support more birds.
Although growing weeds may get chopped by the combine, I suspect that they are not killed by harvesting, especially those with a sprawling growth-form. They will then have a flush of growth after the combine has removed the competition from the crop.
Important weed groups for birds include polygonums, chickweed, fathen, charlock and annual meadow grass, which all produce plenty of seeds. The cover provided by stubbles may be an added advantage, but clean stubbles can be as empty of seed-eating birds as winter wheat crops.
Stubble quality is very highly linked to the preceeding crop, herbicide regime including use of pre harvest glyphosate plus the long term cropping history of fields. As part of a project examining the quality of cirl bunting stewarship stubbles the RSPB found that stubbles following low input barley provided highest numbers of weed seeds when compared to standard stewardship or conventionally grown barley or wheat stubbles. The stubble weedness was highly correlated with bird numbers as well as the important weed groups highlighted by Richard. The project however did show that there was variation between fields in similar management regimes.