A sandy soil will hold about its own weight in water. A clay 2 or 3 times. A typical natural peat around 16 times!
A compost made from urban green waste will hold up to 10 times its own weight in water, maybe only 5 times if it is made from woody cuttings in winter (and it would have less N). However, compost made from urban green waste plus industrial wastes will (depending on the wastes used) hold 8 to 14 times its own weight in water and possibly a lot more NPK. Although the Environment Agency will restrict quantities, the truth is that the Fens, when Vermuyden drained them some 300 years ago, were up to 40 foot deep of almost pure compost. (Organic soils do not leak excessive N.) It is also true that high organic, well-composted soils, can halve cultivation energy inputs and reduce chemical spraying.
So, there really should be a national policy of maximizing urban waste recycling to urban farm land. Suggest get a copy of “Survival”, read it and send a copy to your MP.
Bill Butterworth, Land Research Ltd, 1 August 18