Using near-continuous measurements of N2O emission from urine-affected soil to guide manual gas sampling regimes

Nitrous oxide (N2O) fluxes are influenced by fluctuating soil temperature and external factors such as rainfall events. Therefore, sampling time, frequency of sampling after nitrogen (N) application and weather interactions are critical when determining cumulative N2O losses and associated emission factors. Using automated chambers, three short-term field trials were conducted to measure N2O fluxes from urine-affected pasture in southern New Zealand to determine the influence of soil temperature and light on diurnal N2O variation and the effect of sampling frequency on estimated cumulative N2O losses. Diurnal N2O flux patterns were often interrupted by rainfall events, but when present they were mainly driven by fluctuations in soil temperature at 02 cm depth. Mean daily N2O fluxes occurred between 10:0012:00 h and 18:0021:00 h. Analysis of all data, including rainfall-affected periods, showed that gas sample collection three times a week between 10:0012:00 h provided zero bias in calculated cumulative emissions when compared with those based on frequent, 2-hourly, flux measurements. To account for resource limitations in field campaigns for estimating cumulative N2O emissions, an alternative approach is to sample two times a week, when fluxes can be expected to be large (e.g. first 46 weeks following urine deposition on to pasture), with additional sampling following significant rainfall. This latter approach produced an average bias of +4%, but ranged from 3 to +18%.