Effect of Pretreatment on Loss of Nitrogen‐15‐labelled Fertilizer Nitrogen from Waterlogged Soil During Incubation

Soil preparation treatments (field‐moist, intact cores; oven‐dried, intact cores; and oven‐dried, crushed, screened soil) greatly influenced fertilizer nitrogen loss under waterlogged conditions in the laboratory. Nitrogen (300 pp2m) as 15 N‐labelled calcium nitrate was added to samples from selected horizons of Drummer silty clay loam (Typic Haplaquol) and they were subsequently covered with water and incubated for 0, 4, 8, 16, and 32 days. Samples of upper (above 51 cm) soil horizons were incubated at 21°C while those from deeper horizons were incubated at 18°C. Oven‐drying and crushing of the soil during preparation increased fertilizer nitrogen loss. Only 34% of the fertilizer nitrogen disappeared from field‐moist, intact soil cores while approximately 90% disappeared from both oven‐dried, intact cores and crushed screened samples. Maximum rate of dentrification of fertilizer nitrogen in field‐moist, intact cores was 3.58% of the applied nitrogen per day. This rate was approximately one‐third of that in the oven‐dried, intact cores and one‐ninth of that in the oven‐dried, crushed samples. Apparently oven‐drying and crushing soil samples increased the accessibility of the energy source for the denitrification process. However, crushing apparently did not increased the quantity of energy since total nitrogen losses after 32 days were similar for both oven‐dried, intact‐ and oven‐dried, crushed samples.