Effects of soil temperature on nitric oxide emission from a typical Chinese rice–wheat rotation during the non-waterlogged period.

Abstract Measurements of nitric oxide (NO) emission from a typical Chinese rice–wheat rotation are continuously made during the non-waterlogged period by using an automatic system based on static chamber techniques. A positive correlation exists between NO emission and soil moisture content when surface soil temperature is > 20 °C. The diurnal variability in NO emission is characterized with day-peak, night-peak and irregular patterns, which are in close association with wheat growth. The diurnal NO emission under the day-peak pattern is correlated with the simultaneously observed surface soil temperature, whereas that under the night-peak and irregular pattern is dependent on surface soil temperature at 7 ± 2 and 3 ± 2 h before NO observation, respectively. The effect of soil temperature on NO emission is well described by F = α·e β·T , where F is NO flux, T soil temperature, and α and b empirical coefficients. The parameter Q 10 ; that is, the change in NO emission per 10 °C soil temperature, is correlated with the rates of fertilizer-N application. An approach orientated from the Arrhenius equation, &formm101;&formm102;, is developed in order to predict diurnal NO emission, where T K is the daily average soil temperature, ΔT K the deviation of soil temperature from the daily average, E a the apparent activation energy, R the gas constant, t a given time within the one-day cycle, t delayed time for appearance of the diurnal NO emission peak, and k an empirical coefficient. Based on the results, the authors recommend that intermittent measurement of NO emission from a similar ecosystem would be best taken around 17:00. The molar ratio of NO/N2 O over the non-waterlogged period is > 1 when soil moisture content was less than the field capacity, suggesting that NO emission was mainly derived from nitrification under this condition. [ABSTRACT FROM AUTHOR]