I have come across several cases recently of the Environment Agency refusing to allow Deployments to spread processed wastes because there was “too much nitrogen” present. The Nitrogen would, in composts and organic wastes, be present substantially, if not completely, as organically bound N. In a grassland or direct-drilled arable soil, that might release as little as 1 or 2 % of the total Nitrogen in that soil, to ground water per annum. (That might be just enough to keep the weed in a trout steam growing at a natural rate.) At the other extreme, in a much-cultivated clay soil, the release of N might reach 10%, and in a much cultivated sandy soil, maybe 15 % per annum. Now, to be economic, if the farm did then not have composts made from “wastes”, and used ammonium nitrate, then the percentage of N lost to groundwater would be between 30 and 60 or even a bit higher (85%) on an irrigated sandy soil.
The point is this. Read the research. Recycled wastes spread as well made compost are generally safe to add to farm land at any N content, without limit on quantity added. Don’t believe the research? Try common sense; when Vermuyden drained the Fens some 300 years ago, it was, and remains, possible to grow a crop (probably the best crop in the UK) every year, without ever adding any N fertiliser in any year for 300 years. By the way, some of these Fen soils were 10 or 12 m deep when first drained (the N reserves were enormous) and the dykes and Norfolk Broads were not full of green slime and dead fish.
If the human race is to survive, we have to recycle wastes to land.
Bill Butterworth, Land Research Ltd 18th May 2018