Non-organic artificial substrates such as rockwool and glasswool require a percentage of the applied nutrient solution (input) to run to waste. The percentage waste (run-off) varies throughout the year from over 40 % in spring to less than 15% in summer. This paper outlines the principles, implementation and four (4) years commercial experience of using re-circulated run-off in substrate grown tomato and rose crops in Guernsey. Guernsey has a land surface area of 63 km(2), which supports an average population of about 65.000 people. This rises to about 78.000 during the peak tourist periods in the summer months. During the 1960's about 350 ha of glass was in commercial production covering 1/15th of the land area, but by 1995 this had fallen to 183 ha, of which 32 ha use artificial substrates such as rockwool and glasswool. This reduced area has exposed sites of high nutrient soil loading and substantial leaching has occurred during periods of heavy winter rainfall. The whole of the Island is now considered to be a water catchment area, and over the past few years the States Water Board (SWB) have had increasing difficulty in collection suitable rain water from the surface streams to meet the needs of the Island's population. There is no provision for water abstraction from wells or boreholes, although the majority of the glasshouses have a sub-surface raw water source. The diary industry also import substantial quantities of nitrogenous fertilisers. This results in 78% of the collectable water having a relatively high nutrient content (Fig.1). The remaining 22% has nutrient levels well in excess of the current potable water maximums of 50 ppm for nitrates and 12 ppm for potassium. In 1994 an agreement was reached with the States Committee for Horticulture, SWB and the Guernsey Growers Association, and a Code of Good Horticultural Practice was produced. Part of this Code included a Run-off Management Plan (RMP). This comprises six sections; information; containment and collection; storage; re-cycling and disposal; monitoring and emergency contingencies. A flow diagram of the decision making process is outlined in Fig. 2.
