Long-term application of manure over plant residues mitigates acidification, builds soil organic carbon and shifts prokaryotic diversity in acidic Ultisols

Addition of organic materials is believed to be a feasible practice for mitigating Ultisols acidification and loss of soil organic carbon (SOC). However, how organic materials mitigate acidification, affect SOC content and aggregation and shift microbial community structure requires further investigation. In this study, we used high-throughput sequencing of microbial DNA to evaluate the relationships between soil properties, aggregation and prokaryotic communities in soil subjected to 27 years of inorganic and organic fertilization. The field experiment included seven treatments: no fertilization (control), inorganic NPK fertilizer (I), inorganic NPK fertilizer plus liming (CaCO3) (IL), and inorganic NPK fertilizer plus peanut straw (IPS), rice straw (IRS), radish (IR), or pig manure (IPM). Amendment with NPK fertilizer plus pig manure more effectively increased soil pH, SOC, total nitrogen (TN), available phosphorus (AP) and dissolved organic carbon (DOC) compared with NPK fertilizer plus crop residues. IPM also increased the mass proportion of large macroaggregates (>2000 μm) from 7.8% in the control to 30.6% while it reduced effective diffusion coefficient of oxygen (DCo) from 12.58 × 10−6 m2 s−1 in the control to 2.81 × 10−6 m2 s−1. Application of pig manure increased prokaryotic diversity and altered prokaryotic community structure, while crop residues did not. Soil pH was the predominant factor influencing prokaryotic community structure. Bacillales and Clostridiales accounted for 47.5% and 21.4%, respectively of the indicator species in the IPM and the relative abundances of them were increased, compared with the other treatments. Furthermore, the relative abundances of Bacillales and Clostridiales were correlated with SOC, TN, AP and DOC, and negatively with DCo in the soil. Overall, our results suggest that application of NPK fertilizer plus pig manure rather than crop residues enhanced soil pH, improved SOC content and aggregation, increased prokaryotic diversity and altered community structure of prokaryote after 27-year fertilization.