THE SAMPLING STRATEGY FOR THE ESTIMATION OF DAILY AVERAGE SOIL N2O FLUX BY STATIC CHAMBER METHOD.

Gas samples were sampled routinely once per day using the static chambers manually, regardless if there is any difference in the diurnal N₂O flux patterns among different sampling dates. Based on nine diurnal N₂O emission patterns collected during different emission periods (high, moderate and low) from incubation experiments in East China, the optimal sampling time and possible sampling strategy of daily N₂O fluxes in different emissions periods were discussed. Generally, N₂O emission presented an obvious diurnal variation characteristic, but the diurnal variation were slightly different in peaking time and daily deviation between the pulse and non-pulse periods. Statistics analysis showed that the optimum single sampling time in high, moderate and low emissions periods would be 22:00 h, 22:00 h and 12:00 h, respectively. An improved routine sampling strategy (IRS) with two samplings were presented, and performed better in daily average N₂O fluxes estimation than the routine sampling strategy (RS) and optimum single sampling strategy (SS). By using IRS, the double sampling times are different in low emission period to that in high and moderate emission periods. With a sampling fixed at 10:00 h in daylight, the IRS is more convenient than stochastically double sampling strategy (DS), which is not practical because of its inconsistent sampling time among all three emissions periods. Thus, it is feasible to get a more accurate daily average N₂O flux by adding a reasonable sampling to the routine sampling method, but the added sampling times are different between pulse and non-pulse emission periods. [ABSTRACT FROM AUTHOR]