There’s a lot more to creating a stale seedbed than just tilling up the ground. Knowing the grass weeds that need to be controlled is the first thing that should be known about the field in question.
Some weed seeds should in fact be left on the soil surface. Once you know the problem you’re dealing with you can decide what method to use and what depth to cultivate down to.
Stale seedbeds can help to reduce grass weed problems by allowing the seeds to germinate and be controlled using glyphosate before the next crop is planted.
Depth of cultivation for black-grass control
The depth you cultivate to will have an effect on the percentage of the weeds which emerge and the length of time it takes those weeds to germinate.
Research from ADAS in the UK shows that where the ground is barely tilled at the top, 90% of black-grass seeds will emerge.
When tilled to 2cm, 89% of the seeds will emerge. A full breakdown of the depths and percentage emergence are listed below.
Data source: ADAS
Once the ground is tilled below 4cm the percentage emergence decreases dramatically.
According to Teagasc, sterile brome, great brome and cereal volunteers should all be shallow tilled to encourage germination.
What not to till
At a recent grass weeds event held in Co. Kilkenny, Teagasc stated that some bromes – meadow, soft and rye – should be left on the soil surface for a month after harvest.
Wild oat seeds should be left on the soil surface for as long as possible in the autumn. Oilseed rape seed which was lost out of the combine should also be left on the soil surface for four to six weeks. This will avoid the seeds becoming dormant.