Objectives The various types of green manure crops have differing effects on soil physicochemical properties, as well as microbial activity. We studied the effects of different winter and summer green manure patternson soil quality in terms of soil microbial metabolism and nutrient limitation.

Methods A three-year field experiment was carried out in Guizhou Institute of Soil and Fertilizer, and the used winter green manure crop were Orychophragmus violaceus L. (O) and Vicia sativa (V), and summer green manure crop were Guizotia abyssinica (G), and Vigna umbellata (P). The winter-summer combination patterns included O-G, O-P, V-G, and V-P. Soil samples at 0−20 cm depth were collected at the blooming period of winter green manures in the third year. Soil enzyme activities, soil microbial biomass carbon, soil microbial biomass nitrogen and soil microbial biomass phosphorus were measured. Soil enzyme stoichiometry characteristics, and the contribution of various soil factors to soil quality indices were calculated.

Results All the green manure patterns affected soil pH, total nitrogen, microbial biomass nitrogen, microbial biomass phosphorus , β-glucosidase and acid phosphatase significantly. The soil microbial community as a whole was limited by the availability of corbon and phosphorus in all treatments. There was no significant difference in carbon limitation among treatments, and the O-G (Orychophragmus violaceus L.-Guizotia abyssinica) had the least phosphoru limitation, which was significantly reduced by 2% compared to the V-P (Vicia sativa-Vigna umbellata). Soil pH, available phosphorus, and dissolved organic carbon were the main drivers of soil enzyme activities and soil microbial nutrient limitation. Soil pH had a negative effect on soil enzyme activity (P<0.05). Soil organic carbon, total nitrogen and total phosphorus contents had a positive effect on soil enzyme activity but a negative effect on microbial carbon limitation. Soil enzyme activities had a positive effect on microbial carbon utilization and were mainly regulated by acid phosphatase.

Conclusions The winter and summer green manure rotation patterns lead to significantly different soil pH, total nitrogen, microbial biomass nitrogen, microbial biomass phosphorus, β-glucosidase and acid phosphatase. The winter green manures have significant interaction on the microbial phosphorus and carbon limitation, and the rotation patterns of winter and summer green manures have significant interaction on the soil quality index. The V-G pattern (Vicia sativa-Guizotia abyssinica) shows the lowest soil microbial phosphorus limitation and exhibits the highest soil microbial carbon utilization and soil quality index, therefore it is an optimal pattern for rapid soil fertility enhancement.