Abstract: Gravel-sand mulch is a protective farming technique with a history of 300 years in the Loess Plateau of the Northwest. It has the effects of water storage, water retention, temperature increasing, alkali pressing and soil retention. As the mulch area increases year by year, studying the soil respiration in the gravel-sand mulch farmland system helps to understand the impact of ground mulch conditions on CO₂ flux and soil health. However, little is known about the changes in soil respiration and the main influencing factors under the mulch. In Gansu province, the soil respiration of long-term gravel-sand mulched farmland (12 years) was measured by using the LI6400 soil respiration system. The relationship between the environmental factors, the physical and chemical properties of the soil and the diurnal variation of the soil respiration was analyzed. The results showed that: (1)The diurnal variation of soil respiration was consistent with the change of temperature, and it was unimodal, and the peak of the soil respiration after gravel mulched was (16:00-17:00), which was obviously lagging behind the bare ground (14:00-15:00), and the peak value decreases with the increase of the mulch thickness; (2) the temperature of the soil surface layer (in the depth of 10 cm) is a significant power function relation with the soil respiration (P<0.01), and the gravel mulch reduces the temperature sensitivity index (Q₁₀) of the soil respiration, and the mulched Q₁₀ is 1.78-2.87 and 1.70-1.96; (3) after the gravel mulched, the soil respiration at night is improved, the daily accumulated carbon emission of the soil respiration is obviously improved, and the carbon emission of the thickness of 11 cm (GM11) in the mulch treatment is 2.00 g·m^-2 and 0.90 g·m^-2, respectively, as the mulch thickness increases, 15% and 18%, respectively, compared with the bare ground (CK). (4) The soil water, pH and soil respiration accumulated carbon emission were positively correlated with the soil characteristic factors, and the organic matter, the alkali-hydrolyzable nitrogen, the available phosphorus and the conductivity were negatively correlated with the carbon emission of the soil respiration.

Key words: gravel-sand mulch, soil respiration, soil respiration temperature sensitivity index