SLOW-RELEASE FERTILISERS IN PEAT-SAND COMPOSTS
A number of materials which supply either nitrogen, or a combination of nitrogen, phosphorus and potassium, in slow-release forms are now available, and some of the results of experiments on their use in peat-sand composts are presented here.
Until recently the only fertilisers which in any way offered a slow release of nitrogen were hoof and horn, dried blood and other similar organic materials. Hoof and horn has been the standard source of applied nitrogen in the John Innes composts since their introduction 30 years ago, and more recently it has been used in peat and peat-sand composts. Using large scale factorial experiments designed to supply information on the base fertiliser requirements of peat-sand composts, Bunt (1) has shown a significant interaction between the rates of application of hoof and horn, superphosphate and lime (calcium carbonate and Dolomite limestone) and plant growth. A large interaction between the safe rates of application and the season was also shown, with a marked depression in plant growth from certain rates and combination of fertilisers occurring in winter. The toxicity was largely attributed to the very high accumulation of ammonium ions and free ammonia released from the hoof and horn with an accompanying rise in pH.