Soil carbon and nitrogen dynamics following application of pig slurry for the 19th consecutive year:: II.: Nitrous oxide fluxes and mineral nitrogen

Agricultural soils often receive annual applications of manure for long periods. Our objective was to quantify the effects of 19 consecutive years of pig (Sus scrofa) slurry (PS) application to a loamy soil (loamy, mixed, frigid Aeric Haplaquept) on N2O emissions. Soil surface N2O fluxes (F-N2O) were measured 36 times in 1 yr. Nitrous oxide concentration profiles, soil NH4+- and NO3--N contents, denitrifying enzyme activity (DEA), and denitrification rate (DR) in soil were also determined to explain the variation in F-N2O. Long-term (19 Jr) treatments on continuous silage maize (Zea mays L.) were 60 (PS60) and 120 Mg ha(-1) yr(-1) (PS120) of pig slurry and a control receiving mineral fertilizer at a dose of 150 kg ha(-1) each of N, P2O5, and K2O. Denitrifying enzyme activity, soil N2O concentrations, and F-N2O (<25 ng m(-2) s(-1)) were low in the control plots receiving mineral fertilizer. Annual applications of PS to the soil for 18 Jr had positive residual effects on the DEA compared with the long-term fertilized control plots. Following PS application, there was a strong and rapid increase of F-N2O (np to 350 ng m(-2) s(-1)) on manured plots. The PS-induced F-N2O increased with increasing quantity of PS, probably as the result of a greater availability of NO3--N for denitrification. The effects of PS on F-N2O were mostly limited to the 30 d following application, with low nuxes (<10 ng m(-2) s(-1)) during the rest of the measurement period. Total N2O-N emissions represented 0.62, 1.23, and 1.65% of total N applied in control, PS60, and PS120 plots, respectively. These emission factors for the PS plots agreed with values previously suggested for N-fertilized soils (1.25%).