Abstract: Based on the three-year field experiment in wheat/rape field in the Hexi Oasis Irrigation Area, the values of soil respiration rate were estimated with the EGM-4 soil respiration measurement system under different fertilizer application levels and ways and crop residue returning to field. The results showed that, throughout the observation period, the maximum value of soil respiration rate (152.06-199.58 mg·m^-2·h^-1) occurred in late August, and the minimum one (12.67-19.01 mg·m^-2·h^-1) occurred in mid-October. The curve of daily variation of soil respiration rate was unimodal, the maximum value occurred during the period of 12:00-14:00, and the minimum value appeared around 4:00. The soil respiration rate was significantly reduced under high crop stubble harvest without till, especially during the rape growth period. The soil respiration rate was significantly decreased under the different fertilizer application levels and in the case that N and P fertilizers were reduced by 15%. Under the treatment measures in the experiment, there was an extremely significant positive correlation between soil respiration rate and soil temperatures at soil layers of 5 cm and 10 cm in depth and also the soil moisture content at soil layer of 30 cm in depth. Furthermore, the correlation of soil respiration rate with soil moisture content in soil layer of 0-30 cm was higher than that with soil temperature. There was a negative correlation between soil respiration rate and soil porosity, but their correlation was not significant.

Key words: soil respiration rate, wheat, rape, fertilizer application level, rop residue returning to field, Shiyang River, Gansu Province