Nitrous Oxide Fluxes from Manure‐Amended Soil under Maize

Abstract Nitrous oxide (N 2 O) emissions by agricultural soils are influenced by farming practices. The application of manure to cultivated land modifies soil microbial activity by supplying additional quantities of C and N and changing soil physical and chemical properties. Nitrous oxide fluxes at the surface of a soil under maize ( Zea mays L.) amended with dairy cattle manure were measured from April to October 1993 using closed chambers. The manure application rates were 0, 56, and 112 Mg ha −1 corresponding to 0, 170, and 339 kg ha −1 of total N, respectively. Nitrate and NH + 4 were measured in soil samples obtained at the same time that gas flux measurements were made. Nitrous oxide concentrations in the soil profile were quantified by sampling soil air at depths of 5 and 15 cm using stationary air probes. On the manured plots 67% of the total N 2 O emitted during the growing season occurred during the first 7 wk following manure application. Fluxes of N 2 O occurred in episodes with maxima that ranged from 0.070 mg m −2 h −1 on the soil without manure amendment to 0.171 and 0.494 mg m −2 h −1 on soils that had received the low and high rates of manure, respectively. These high fluxes coincided with periods when NO − 3 ‐N levels and soil water contents were relatively high. Fluxes were highest the first day after manure application and returned to near pre‐application levels 7 d later. This episode was followed by short‐lived peaks of N 2 O flux that usually followed periods of rain. The absence of a strong correlation between N 2 O concentration in the soil profile and N 2 O flux at the soil surface suggested that high soil water content restricted gaseous diffusion in the soil and/or that a variable part of the N 2 O produced via denitrification was reduced to N 2 . The accumulated N 2 O‐N emissions at the soil surface of the manured plots over the snow‐free season amounted to 1% of the manure N that was potentially mineralizable during the experiment.