Effects of nitrification inhibitors on uptakes of mineralised nitrogen and on yields of winter cereals grown on sandy soil after ploughing old grassland

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Abstract
An old grass sward on a sandy loam soil (Cottenham series) was ploughed‐down in summer 1981 and winter wheat, winter oats and winter wheat respectively were grown on the site for the next 3 years. Nitrification inhibitors (dicyandiamide (DCD), nitrapyrin or etridiazole) were applied to the seedbed in all 3 years. In spring, the cereals were given 0, 35 or 70kg N ha−1 as “Nitro‐Chalk”. Inhibitors had little effect on the amounts or distribution of mineralised nitrogen in the soil profile or on the uptake of mineralised nitrogen during autumn and winter. Much mineralised nitrogen was leached during the autumn and winter 1981/82 and 1982/83, but amounts of available mineralised nitrogen were sufficient to meet the crop requirements. In these 2 years nitrogen fertiliser decreased yields and inhibitors had no consistent effect on yields or nitrogen uptakes. In 1984, winter wheat responded to spring‐applied nitrogen fertiliser, while DCD or nitrapyrin increased yields and nitrogen uptakes. There was no evidence that yield increases were due solely to the increased availability of mineralised nitrogen caused by the inhibition of nitrification.