Dynamics of Pig Slurry Nitrogen in Soil and Plant as Determined with ¹⁵ N

The fate of pig ( Sus scrofa ) slurry labeled with 15 N was investigated when applied on a clay soil (fine, mixed, frigid, Typic Humaquept) and a sandy loam (loamy, mixed, frigid, Typic Dystrochrept) cropped to maize ( Zea mays L.) in 2000 and to barley ( Hordeum vulgare L.) in 2001. The slurry was applied in spring 2000, and plant and soil samples were collected at 6 h (Day 1) and at Days 14, 42, 96, and 413 after application. The samples were analyzed for 15 N content in plant, in whole soil, and in soil NH 4 + –N, NO 3 − –N, organic N, and clay‐fixed N pools. Percentage 15 N recovery was >93% in both soils at Day 1 and decreased slowly thereafter. Rapid clay fixation of slurry 15 N occurred at Day 1, and was greater in the clay soil (34% of applied 15 N) than in the sandy loam (11%). At Day 96, less of the applied slurry 15 N was recovered in maize grown on the clay soil (29%), as compared with the sandy loam (50%). At the same period, the residual soil 15 N was mostly present as organic N and NO 3 − –N in the sandy loam, and as organic and clay‐fixed N in the clay soil. At Day 413, 15 N recovery in barley was about 3% of the initially applied N in both soils. The 15 N recovery was generally higher in the clay soil than in the sandy loam, but total 15 N recovery from the soil–plant system was similar for both soils. We conclude that soil type had little influence on the total 15 N recovery from the soil–plant system, but significantly influenced the fate of slurry N in the various soil pools and plant N uptake on the year of application.