An investigation was carried out into the potential of tylosin and terramycin fermentation wastes as fertilizers for tomatoes. Each waste was added at concentrations equivalent to 1 tN/ha to John Innes base compost. Each waste provided the sole source of nitrogen for the crop. Controls were set up with inorganic nitrogen applied at 1 tN/ha and 0·2 tN/ha, the quantity of nitrogen normally found in John Innes potting compost. Comparisons were also made between wet and dry terramycin waste. Each treatment was added to normal John Innes base compost and John Innes base minus one part peat, to determine the potential of antibiotic fermentation waste as a peat substitute. The size, weight and antibiotic content of the tomatoes produced were determined.

The use of antibiotic fermentation wastes delayed the onset of tomato production due to the slow release of nitrogen. Final yields were not significantly different from the control treatments except in the tylosin treatment which produced the highest yield, both in terms of weight and numbers, of all the treatments. The reduction in the amount of peat in the base compost only appeared to affect the control treatments, where a delay in the onset of tomato production was seen in the control low in peat. No antibiotic was detected in any of the tomatoes.