Use of nitrification inhibitors to improve recovery of mineralised nitrogen by winter wheat

Nitrification inhibitors were applied in September 1980, after ploughing of a grass ley, to prevent formation of NO3‐N which could be lost by leaching and denitrification. Laboratory tests indicated that nitrapyrin or etridiazole at 1 μg g soil−1 and dicyandiamide (DCD) at 10 μg g−1 could inhibit nitrification by approximately 40%, compared with untreated soil, for 10 weeks at 10°C. In the field, nitrapyrin, etridiazole and DCD had little effect on NH4 and NO3 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−1) 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−1 DCD respectively. DCD could be of use in preventing losses of NO3‐N, particularly in situations where large amounts of N may be mineralised during autumn and would be liable to loss prior to crop uptake.