31 July 2001
Managing weeds and slumped soils after rape
Rape that was badly flooded out and subsequently had little grass weed control has been disced in good conditions and rolled with plenty of moisture present. How long will I need to wait before I have to accept that there will be a need to plough to put the high seed return to the bottom? These dead lifeless flooded areas – subsoil or shakerator?
Ideally, rape stubbles should be left undisturbed to allow the seed to chit on the soil surface. The same applies to black-grass (not so for brome – see previous answer).
I presume that the cultivation you have done was a shallow one – hopefully with moisture present, you will get a chit quite rapidly.
By ploughing down rape, however, you encourage the seed to go dormant and it will re-emerge in later years. But if you dont get a chit then ploughing will help control black-grass.
The bare patches may well need subsoiling if the soil has slumped and there is poor structure – dont mind how you do it but make sure that the depth is correct, just below the normal cultivation depth. You dont need to scrape the top of the drains thats called mole ploughing!
Wet holes need a strategy to bring them back into production. I will assume that these are normal wet spots that occur most years and not the Thames flooding every 3 weeks!
In my experience there is probably a background plough pan that is the main cause of the problem, which causes water from other parts of the field to run down to low parts, causing these flooded areas. So as the soil structure builds up in the other parts of the field, less water will be sent to the wet holes.
For this autumn I would if possible run a mole from these areas into a ditch or known drain. If not, then a run of the subsoiler just in these areas would do.
Then I would expect Nature to take its course – it would be best to leave them alone apart from normal cultivation operations.
As for the grassweeds, this year I would look to have two glyphosate applications onto these areas to reduce the seedbank. Over time the weed pressure will get less as the soil structure improves and water drains away faster.
The typical time frame would be 2-3 years. If you plough I think you would have a short term fix and no long term solution remember to think about what you may plough up.