Winegrowers Supplies - Soil Preparation
Ideally, in the Summer the year before planting, it is a great advantage to sub-soil. It is important to do this when the ground is at it's driest and hardest. Find a local contractor who has a large twin-leg sub-soiling implement with fins (an attachment for a powerful tractor). This should go down to around 22" and crack open the subsoil, allowing air and rain to penetrate. Sub-soil the whole field in two directions at right angles.
In late autumn or early winter the ground should be deep-ploughed (8" to 9"), leaving enough time for the turned-in grass/weeds to break down before the soil is thoroughly rotovated in March. Spraying with glyphosate to kill the grass/weed roots before ploughing is often done, but it is possible to carry out the ploughing without first spraying, providing there is enough time for the grass/weeds to break down and die naturally; organic growers have to use this method.
Preparing the ground before winter allows one to get a stable structure from the combined effects of frost and rain.
The soil should only be worked if it is dry, else one risks compaction.
Avoid deep ploughing of the soil in springtime, since this creates an unstable structure which dries out badly. Weeds need oxygen to decompose, so late preparation risks creating an asphyxiating environment for the young vines.
Any grass/weeds remaining in mid-February should be sprayed off with glyphosate. Finally
the soil should be rotovated in late-March, a Shakaerator is a particularly good machine for this.
A crumbly soil, fine and well aerated, will favour the take-up of the plants.
Plan to plant up/down the slope, rather than in a precise N-S direction, this allows much easier working long term than if there is a slight cross-slope. If a cultivator is used with vines planted on a cross-slope then a series of 'terraces' build up and the soil level tends to rise around the vines on the lower side; if the soil rises above the graft then the scion can form its' own roots and eventually the plant will die.