Abstract
Nitrification inhibitors were applied in September 1980, after ploughing of a grass ley, to prevent formation of NO~3β~N which could be lost by leaching and denitrification. Laboratory tests indicated that nitrapyrin or etridiazole at 1 ΞΌg g soil^β1^ and dicyandiamide (DCD) at 10 ΞΌg g^β1^ could inhibit nitrification by approximately 40%, compared with untreated soil, for 10 weeks at 10Β°C. In the field, nitrapyrin, etridiazole and DCD had little effect on NH~4~ and NO~3~ levels in the soil throughout autumn and winter. In April uptake of mineralised N by wheat was greater in plots treated with DCD (but not with nitrapyrin or etridiazole) than in untreated plots. Spring fertiliser N applications (35 or 70 kg N ha^β1^) increased ear numbers, as did the two rates of all inhibitors except etridiazole. At harvest, grain and straw yields were increased by both rates of DCD with and without fertiliser N in spring, but there were no consistent increases from nitrapyrin or etridiazole. The mean increases in N uptake by wheat grain plus straw were 12 and 15% for 5 and 20 kg ha^β1^ DCD respectively. DCD could be of use in preventing losses of NO~3~βN, particularly in situations where large amounts of N may be mineralised during autumn and would be liable to loss prior to crop uptake.