Adding well rotted manure

I have sandy soil that hasn't been touched for 20 years, I've had to pickaxe it to break it up to remove all the Ivy roots. I have added 3 tons of rotted manure (4inch sitting on the top) and am full of expectation for next season when I turn it in and have tomatoes the size of medicine balls. BUT, that lovely ol' manure won't last forever, somehow, leaf mould/ manure etc all seem to vapourise into nothing a few years down the line. How long do you think it'll last before I have to repeat the process?

 

If you can repeat the process or at least add some more each year, eventually you will see a huge improvement in the soil’s structure and moisture retention ability.
I grow a lot of tomatoes in my greenhouse, ( most summers, not this 1! are not warm enough to have much success growing them outside in Scotland). The tomatoes are grown in soil beds in the greenhouse, the beds get manure every autumn. Approx 5 x stacked builders barrow for a bed 3ftx20ft if that gives you an idea of how much I use. With the very good summer I am up to my neck in tomatoes and because of so much manure in the soil, despite the heat,I only need to water every other day.

 

Thank you all for your responses, to be honest, buying manure every 2 years makes for very expensive vegetables! fertilizer is waaay cheaper

 

How long your soil retains nutrients from your manure will also be influenced by how you treat your soil. If there is something growing on it you will get some protection of the soil from the plants. The leaves and top growth of the plants stop rain drops directly striking the soil and let rain water seep more slowly into the soil and with the plant roots will slow nutrients being washed out of your soil. In dry climates bare ground can also lead to some of the best soil being simply blown away as dust. The plants will also themselves build up organic material and this contains nutrients that will be cycled back into the soil when these plants die. Building up your soil with organic material is a much healthier way to grow your crops than just adding chemical fertilisers as these will not contribute much to developing the soil life that helps natural nutrient cycling with fungi that help plant roots and living elements that help control plant pests and improve the soil structure.

Deep rooting plants like comfrey can be used to make your own fertiliser and organic mulch and green manure crops can be grown in the times available in between crop plants to help build up organic material in your soil. Compost can be easily made from your garden and kitchen waste and added back to the soil and nitrogen fixing crops like beans and peas can be important as this is one of the more soluble nutrients that is easiest to have washed out of your soil. Leaving soil bare will lead to your soil nutrient levels degrading much faster so I don't think it is possible to give a good answer to your question without knowing how you intend on managing your plot.

Happy gardening!