Soil Respiration In The Typical Farmlands In The North China Plain

Experimental studies were done at the Yucheng comprehensive experimental station of the Chinese Academy of Sciences during 2002-2003. Respiration of a pulverous sandstone soil was studied under cultivation of winter wheat, summer maize and cotton over a growth season and under fallow. The results indicated that diurnal variation of soil respiration rate showed a single peak in farmlands of winter wheat, double peak in farmlands of summer maize, both single peak and double peak in farmlands of cotton. In the winter wheat fields, soil respiration rate reached the highest at about 13 o'clock, and the lowest at about 4 o'clock in the early morning, and in the summer maize fields, soil respiration rate reached the highest at about 11:00~15:00 and 1:00~7:00 in the morrow, and the lowest at about 22:00-1:00, and in the cotton fields, soil respiration rate reached the highest at about 13 o'clock, and the lowest at about 4 o'clock in the early morning when it showed a single peak, and when it showed a double peak, the soil respiration rate reached the highest at about 15:00-17:00 and 22:00-1:00 in the morrow, and the lowest at about 4 o'clock in the early morning. The soil respiration rate of winter wheat, summer maize and cotton, showing a similar seasonal variation tendency with soil temperature. Among all treatments, the straw manure had the most distinct soil respiration, though soil respiration also increased slightly with increasing nitrogenous fertilizer. Soil respiration increased exponentially with increasing soil temperature, and the correlation of soil temperature at the depth of 5 cm was the best. This relationship was usually described with the Q10 model, which represented the sensitivity of soil respiration to temperature. Q10 was not a fixed value, it varied with the depth at which the temperature was measured and the depth of the active soil layer and soil temperature. At same time, the Q10 value decreased with increased soil temperature. Soil water content was another important factor influencing the soil respiration rate, but in this region, the relationship between soil respiration and soil moisture was poor, and no distinct rules was shown. Average net photosynthesis rate of winter wheat had a close relation with soil respiration rate, differences between them showed that photosynthetic uptake of CO2 was beyond emission of soil respiration during the period from return green to mature, and the farmland of winter wheat was a sink of CO2.