Effects of substituting biogas slurry for chemical nitrogen fertilizer on soil organic nitrogen and bacterial communities in coastal paddy fields
LI Rui;ZHANG Xun;YANG Yang;TANG Yi-fan;SHEN Jian-hua;HAN Jian-gang;College of Biology and the Environment, Nanjing Forestry University;Co-Innovation Center for Sustainable Forestry in Southern China, Nanjing Forestry University;COFCO Jiajiakang (Jiangsu) Co., Ltd.;
【Objectives】We studied the effects of biogas slurry on soil organic nitrogen(SON) mineralization in paddy fields and its relationship with the change in soil microbial community. 【Methods】The field trials were conducted on Jiangsu coastal rice fields in 2017. Four levels of biogas slurry N application were set with constant total nitrogen input(225 kg/hm~2) at 0%, 33%, 66% and 100%(BS0, BS33, BS66, BS100). After 3 years of continuous treatment(2019), soil samples were collected to determine the mineralization characteristics of SON. The content of total hydrolyzable N, non-hydrolyzable N, ammonium N, amino acid N, amino sugar N,unknown N in SON and the structure of bacterial composition were analyzed.【Results】BS66 treatment recorded higher soil potential mineralizable organic N(N_0)(39.7%) than BS0 treatment. Both amino acid N and non-acid hydrolysis N contents increased with biogas slurry application(P0.05). BS66 treatment had a higher increase in amino acid N(39.2%) and and BS100 had a higher increase in non-acid hydrolysis N(73.9%) than BS0 treatment. The substitution of fertilizers with biogas slurry increased the relative abundance of Chloroflexi and Actinobacteria, and decreased the relative abundance of Nitrospirae(P0.05). The bacterial genera exhibited a varying response to substituting fertilizers with biogas slurry. As the ratio of biogas slurry to chemical fertilizers increased, the relative abundance of Subgroup＿6＿unclassified increased and Subgroup＿17＿unclassified decreased.The relative abundance of KD4-96＿unclassified decreased under BS33 treatment and increased under BS66treatment and BS100 treatment; Subgroup＿7＿unclassified had a relative abundance ≥1% due to the replacement of chemical fertilizer with biogas slurry. The results of RDA showed that soil N_0 and Thermodesulfovibrionia＿unclassified had a significant negative correlation(P0.01), non-acid hydrolysis nitrogen had a positive correlation with Subgroup＿6＿unclassified(P0.05), and a significant negative correlation with Betaproteobacteria＿unclassified(P0.05).Amino acid nitrogen and Proteobacteria＿unclassified, amino sugar nitrogen and KD4-96＿unclassified were all positively correlated(P0.05). The unknown nitrogen and Desuslfarculaceae＿unclassified were significantly negatively correlated(P0.05).【Conclusions】The substitution of biogas slurry for chemical fertilizers changed the structure of the soil microbial community, increased soil nitrogen storage capacity, improved soil nitrogen mineralization potential, and enhanced soil nitrogen supply capacity.