There is increasing research out there to show that the spreading of wastes and by-products to land- e.g. anaerobic digestate, compost, gypsum, and sewage sludge can provide an agronomic benefit and improve soil condition. Recent studies undertaken by WRAP have shown that the readily available nitrogen content of digestates from AD plants is higher than pig and cattle slurry. Composts do not provide quite the same nutrient benefit, however applications over a number of years was shown to lead to significant increases in soil organic matter.
These materials may also provide a farm business with the opportunity to diversify and can complement the use of manufactured fertilisers. For example sewage sludge has a lower readily available phosphorus content than inorganic fertiliser; however the phosphorous within the sludge is released over a longer period of time leading to a more consistent supply of the nutrient.
Like everything though, it is vital when deciding whether to spread these materials to land to ask the right questions. Most importantly, is it suitable for the conditions of your land, does the crop need it, has the material been properly treated, and will it provide benefit. The Landspreading Checklist provides a helpful summary of some of the initial questions to ask.
Case studies
Stephen Temple, who farms 500 acres of mixed arable and grassland for his dairy herd, diversified his business by installing an AD plant in 2009 and spreading the digestate (classified as a by-product) to land. He has demonstrated how the growth of maize for AD production is being managed appropriately to become an integral part of a successful crop rotation.
Read more here.
Russell Toothill, farming a mixed arable and livestock enterprise in South Yorkshire, uses compost derived from biodegradable waste products as a soil conditioner to improve soil organic matter content. Farming adjacent to the Humber Estuary has meant his soils are very light and sandy and this organic matter build up is crucial for retaining nutrients and moisture, ultimately helping to improve yields.