Soil microbial activity and community composition as influenced by application of pig biogas slurry in paddy field in southeast China

A 6-year field experiment was conducted to assess the effects of biogas slurry (BS) application on rice yield, soil nutrients, soil microbial activity (MicroResp (TM)) and community composition (16S rRNA gene sequencing) in paddy field in southeast China. The experiment included five treatments: (1) 270 kg N ha(-1) from urea (mineral fertilizers only, MF); (2) 135 kg N ha(-1) from urea and 135 kg N ha(-1) from BS (BS1); (3) 270 kg N ha(-1) from BS (BS2); (4) 405 kg N ha(-1) from BS (BS3) and (5) 540 kg N ha(-1) from BS (BS4). Results showed that no significant differences were found in average rice yield between the MF and BS treatments (BS1-BS4). Both soil available phosphorus (AP) and soil available potassium (AK) increased with an increasing application rate of BS. The average substrate-induced respiration was significantly higher in the treatment with lower rate of BS (BS1 and BS2) than in other treatments and then decreased with increasing application rate of BS. Soil microbial communities were affected by BS application. Chloroflexi, Proteobacteria and Acidobacteria were the dominant bacterial phyla across all soil samples. The BS application resulted in a relative abundance of Nitrospirae 2.6-3.7 times than that in MF. Our results also indicated that AP and AK were the two main factors affecting soil microbial activity and community. Overall, the results suggest that the replacement of chemical fertilizer with BS may be an alternative management practice for improving soil quality, soil fertility and nutrient balance in paddy field.