Soil Carbon and Nitrogen Dynamics Following Application of Pig Slurry for the 19th Consecutive Year II. Nitrous Oxide Fluxes and Mineral Nitrogen

Abstract

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 N 2 O emissions. Soil surface N 2 O fluxes ( F N2O ) were measured 36 times in 1 yr. Nitrous oxide concentration profiles, soil NH + 4 ‐ and NO − 3 ‐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 yr) 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, P 2 O 5 , and K 2 O. Denitrifying enzyme activity, soil N 2 O 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 yr 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 (up 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 NO − 3 ‐N for denitrification. The effects of PS on F N2O were mostly limited to the 30 d following application, with low fluxes (<10 ng m −2 s −1 ) during the rest of the measurement period. Total N 2 O–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%).