In the past, organic vegetable crops in Iceland were fertilised mainly with mushroom compost (1.9 % N). However, due to the contamination with conventional chicken manure this fertiliser is to be replaced. Thus, substitutes are urgently needed.

Plant compost (0.9 % N), composted animal residues (1.9-2.6 % N), residues from the fish industry (10.9 % N), grain legumes (4.3 % N) and commercial organic fertilizers (216 mg N/l) have been tested in a pot experiment with perennial ryegrass (Lolium perenne L.). Fertilizers (800 mg N) were mixed into a greenhouse soil (0.6% N_t, 6.8% C_org) and dry matter yield was observed and plant N utilisation over the time investigated.

A fertilizer application resulted in comparison to the unfertilized control in a higher DM yield. The yield increase was higher with fertilizers with a high N content. The composted animal residues were comparable to mushroom compost. The time course of the apparent N utilization of ryegrass differed strongly depending on the organic fertilizer used. The cumulative fertilizer-N uptake of ryegrass was highest for Pioner complete 6-1-3^®, fishmeal and clover. A medium apparent N utilization of ryegrass (40-50%) was achieved for chicken compost and fababean. The cumulative fertilizer-N uptake was lowest for plant, sheep, cow and horse compost as well as for the reference fertilizer mushroom compost. The prohibition of mushroom compost should not really effect the organic vegetable growers as there are at least equal (composted animal manures) or even better fertilizers (e.g. fishmeal) on the market.