A depth of one meter is a long way to improve the soil. You might consider simply removing it with a backhoe, and replace with topsoil. If that is not possible, the amendment process will take a long time, so be prepared to wait at least a few months. See this link for more info http://www.umassgreeninfo.org/fact_sheets/plant_culture/improve_sandy_soils.html There are products now on the market that you add in and it soaks up and retains water, such as Lassinite, a brand name natural product, or one of the many synthetic water saving polymers.

One meter? WOW! Depending on the amount of land, this is a HUGE amount of soil treatment. I've no experience with really large projects. However, for small projects, like your flower garden, vegetable garden or new trees, I can help a little bit with my own experience. First of all, most gardens of any kind do no need a one meter depth treatment. But should you decide to do so, excavation of the soil and mixing or replacing with nutrient rich soil, fertilizers, and mulch will help. Keep in mind that excessive mulch may cause mold and fungus issues. A standard garden tiller will suffice to create the soil environment you need while doing this. Also, excessive digging may lead to water retention issues due to improper drainage, depending on the underlying soil composition. A high clay content under all this, for example, may mean you have created a swimming pool or bog in the affected area because the water cannot properly drain. I have dug to such depths in the planting of trees when I wished to encourage a rapid growth of both the root system and the tree itself in the early stages. Excavating nutrient poor and water impermiable clays and then filling in the hole using a good fill dirt/mulch combination resulted in a DRAMATIC growth in the first year or so, which lead to a tree which more rapidly established itself throughout the harder clays later.

here is a great bed builder Ingredients 40lbs of bagged topsoil 10lbs of compost 5lbs of bonemeal 1lb of epsom salts mix ingredients in a wheelbarrow spread a 2 to 3 inch layer over the entire site and top the bed with mulch. Then all you have to do is add the plants whenever you are ready