15 August 2001
Guide me through lo-till after a grass ley
The best soil structure to be found on any farm is where the land has been in temporary grass. There may be problems with breaking up the turf, but some sort of zero-till or min-till system would help retain the structure. What problems would you envisage what would be the solutions?
Where grass leys form a break in arable rotations, this provides a period of structural stability. Earthworm numbers rise dramatically, especially in the second and subsequent years. This, along with the huge root biomass that leys produce, can greatly improve structure.
Where the leys have been grazed this will be better than where silage has been taken because the machinery causes some compaction.
There are also weeds to consider. Grass swards are very useful at depleting the weed seed bank. Seeds near to the surface will either germinate and get grazed, out-competed, cut and predated or they will simply become unviable.
Those ploughed down previously will also show some decline, but some persistent species benefit in terms of survival from the more stable (moisture, temperature, light etc.) conditions found deeper in the soil.
So, having depleted the surface of viable seeds and created a good structure, we do not want to plough up more seeds and destroy that structure!
However there a number of things to watch out for. To destroy the sward the best practice is to apply glyphosate after the third cut of silage or at the end of the grazing period.
Silaged swards can benefit from sub-soiling but some machines are better than others. My personal choice is Tim Howards machine as it hardly breaks the surface open. Even so, a pass with the rolls will rectify.
Mature frit fly larvae transferring from the ley to the establishing cereals can pose a major threat. I have never had the problem, but others have. Spraying off early reduces the Green bridge effect but does increase wheat bulb fly risk.
At your chosen drilling date, direct drill wheat into the grass stubble, ideally with slug pellets mixed with the seed. Do not be afraid to roll after to assist with slot closure.
The destruction of grass leys tends to release a flush of nitrogen as the organic matter decays. But this does not happen where you spray off and direct drill because the soil is not disturbed, so the opposite occurs and N can be short. I apply 25kg/ha post emergence with dramatic effects.
A final observation: Do not use this technique if your ley has shed seed at any time during the ley period. Viable grass seed on the surface in a crop of direct drilled wheat will germinate persistently throughout the year with consequences you do not wish to witness.
How do I know? Dont ask!!