Short-term changes in total heavy metal concentration and bacterial community composition after replicated and heavy application of pig manure-based compost in an organic vegetable production system

A 4-month field experiment was conducted in an organic vegetable production system; two crops, Brassica chinensis and Cichorium endivia L., were cultivated successively and treated with 0 (CKC), 30 (PC1), 60 (PC2), or 120 (PC3) t ha−1 of pig manure-based compost. The replicated and heavy application of pig manure-based compost increased the total amounts of some heavy metals (Zn, Cu, Pb, and Cd) in the short term in soil. Despite the Shannon (bacterial diversity), Chao1 (richness), and evenness indices of different samples calculated after pyrosequencing analysis were similar, changes occurred in the bacterial community composition in soils amended with different rates of compost. The joint cluster and principal component analysis (PCA) indicated that heavy rates of compost may not change bacterial diversity in the short term and, in some cases, even produce a lower genetic diversity. The optimum rate, as well as the period, for compost application should be evaluated to promote the sustainable development of organic agriculture.