Changes of soil nutrients and microbial community diversity in responses to different growth environments and cultivation practices in 30 years

【Objectives】 With the elongation of vegetable cultivation,the soil bio-ecosystems will change greatly. Systematically research on the changes in soil nutrient availabilities and the microbial community will provide theoretical support for the sustainable vegetable production. 【Methods】 The soils consecutively used for vegetable production over 30-years under different growth environments and cultivation practices were chosen for the investigation. Double cucumber cropping followed by fallow in summer in greenhouse was used as control(CK), double cucumber followed by green soybean/peanut in summer (CS1), double cucumber cropping in plastics greenhouse (CS2), double cucumber in plastics greenhouse for the first 28 years and followed by two-years?? green leafy vegetables in open filed (CS3), and consecutive green leafy vegetables in the open filed (CS4) were used. The soil samples of 0-20 cm depth were collected in 2009, and the soil nutrient contents and microbial quantity were measured with conventional methods. The microbial community diversity was evaluated with the values of Average Well Color Development (AWCD), the utilization of six C sources with the principal component analysis (PCA). 【Results】 The AWCD values of CS1 was significantly higher than other treatments. Differences of carbon resources utilization were 32.9%, 33.61% and 32.21%, respectively at 96 h, 120 h and 144 h in principal component 1, and the CK was significantly different from others in principal component 1. The differences in carbon resources utilization were 14.2%, 15.96% and 16.42% at 96 h, 120 h and 144 h separately in principal component 2, and the CK was significantly different from the others at 96 h and 144 h. According to the weights of principal component 1 to 3, CS1, CS3 and CS4 had differences with CK and CS2 at 96 h and 144 h, respectively. The main carbon resources contributing to the difference in principal component 1 were amino acids, carboxylic, amine compounds, amino acids, and to the difference in PC2 were amines and polymers. The utilization of the six carbon sources was significantly different among the treatments. The utilization values of carboxylic acids, carbohydrate and polymers of CK and CS2 were lower than those in other treatments. Both microbial community diversity and evenness in CK and CS2 were significantly lower than those in other treatments. The ratio of bacteria/fungi (B/F) and the microbe quantity of CS3 and CS4 were significantly higher than those in other treatments. Compared with CK, the B/F value and microbe quantity of CS2 and CS4 were increased by 310.34%, 334.48% and 280.1%, 368.0%, respectively. The total N, available K, organic matter and NO3--N in CK were higher than those in other treatments, Compared with CK, CS1 reduced the accumulation of total N, organic matter, available K, NO3--N, NH4+-N by 41.46%, 50.26%, 51.47%, 26.72%and 54.11% separately. The total N, available P, available K and NO3--N in CS3 and CS4 were lower than those in other treatments. The total N and available nutrient had negative correlation with B/F, microbial quantity and microbial community diversity, and NH4+-N had significant negative correlation. 【Conclusions】 The continuous cropping of cucumber followed by fallow in summer in greenhouse for 30 years accumulates a lot of nutrients in soils, followed by green soybean and peanut increases the microbial diversity and reduces NO3--N contents. Continuously cropping of cucumber for 30 years in greenhouse has reduced the microbe community diversity. The consecutive cultivation of green leafy vegetables in open field for 30 years and in plastic greenhouse for 2 years improve the microbe quantity and reduce available nutrient contents in soils.