The effects of mulching on soil microbial composition in gravel and sand mulched field have been studied. The experiment had been set up in spring of 2004, which included three experiments of  ① GSMF mulching layer composed by different diameters of gravel, ② GSMF mulching layer composed by different gravel thickness, ③ GSMF mulching layer composed by mixed gravels at different diameter. The soil bacteria, fungi, antinomycete and soil moisture had been determined in May of 2009. In the experiments, the measured layers were 0~1 cm, 1~2 cm, 2~4 cm and 4~20 cm. Results show that the soil moisture and the soil microbial quantity all increase when mulched by gravel and sand. It is especially beneficial to bacteria and soil moisture when mulched by smaller diameter gravels, while it is beneficial to actinomycete when mulched by bigger diameter gravels. When the gravel diameter is within 1~8 cm it is in favor of fungi developing. More than 50% fungi is distributed in 0~1 cm soil layer. It is optimum for microbial developing when the thickness of gravel-sand is in range of 7~9 cm.

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