Denitrification losses from 15N‐labelled calcium nitrate fertilizer in a clay soil in the field

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Abstract
SUMMARY: Calcium nitrate fertilizer containing 92.3 atoms % excess nitrogen‐15 was applied on 5 May 1981 at a rate equivalent to 100 kg N ha−1 to a clay soil in southern England cropped to winter wheat. Samples of the soil gases were collected frequently during the following 3 weeks. The soil oxygen concentration declined to 5% after 60 mm rain. A maximum of 1.5 ± 0.5 atom % N‐15 enrichment in labelled N2 gas (29N2) was detected in the soil atmosphere on 28 May. Total denitrification losses, calculated from air‐filled pore space and rates of gas loss from the soil estimated using a Fick's law approximation, were 9.5 kg N ha−1 with a daily rate of 0.30 ± 0.07 kg N ha−1. Estimated total losses were greater than 30 kg N ha−1, 93% in the form N2, but the estimation depends on several assumptions about the amount of double labelled gas (30N2), rates of gas diffusion and flux.