Characteristics of soil CO2 emission and carbon balance under long-term fertilization in red soil

Diurnal variation of soil respiration affected by fertilization was investigated with the static dark chamber method and gas chromatograph technique at the long-term experiment in red soil, and the contribution of root respiration was detected by root exclusion method. NEP was calculated for estimating carbon sequestration intensity. The results show that there are significant seasonal variations of the soil respiration rate and bulk respiration rate as the crop growth and temperature raise in wheat and maize growth seasons in all treatments. The accumulation amount of soil respiration and bulk respiration in the maize growth season is greater than that in the wheat growth season. The accumulation amount of soil respiration and bulk respiration of the NPKM treatment is the largest in the wheat and maize growth seasons, and is higher than those of the other treatments significantly (P0.05). The accumulation amounts of soil respiration and bulk respiration of the NP and NPK treatments are the second, and those of the CK and NK treatments are minimum. The mean ratios of root respiration to total soil respiration in the wheat growth seasons and maize growth seasons are 7.6 %17.4 % and 4.7 %16.6 %, and the contribution ratio of rhizospheric respiration of the NPKM treatment is largest in all treatments. Soils are sinks of atmospheric CO2 under the NPKM and CK treatments. Compared to other treatments, organic and inorganic fertilizer combination (NPKM) has a stronger carbon sink function, therefore the NPKM is reasonable fertilization in red soil.