The response of microbial communities to N fertilizer varies depending on environmental and management-related factors. However, few studies have compared the effects of N fertilization on microbial communities under different agricultural management. We thus compared the biomass and composition of microbial communities in N-fertilized and unfertilized long-term (25 years) fields managed under conventional tillage with crop residue removal (CTR) and no-tillage with crop residue mulch (NTM) systems. Soil samples were taken in January 2011 and July 2012 at a depth of 0 to 10 cm, and phospholipid fatty acid (PLFA) profiles were measured. Fungal abundance was lower in N-fertilized soils than in unfertilized soils under both management systems at both sampling times. Bacterial abundance was lower in N-fertilized soils than in unfertilized soils under the CTR system, whereas no difference was observed between N-fertilized and unfertilized soils under the NTM system in January 2011. However, in July 2012, bacterial abundance was lower in N-fertilized soils than in unfertilized soils under both management systems. Principal component analysis of the PLFA profiles showed that N fertilizer had a significant effect on the PLFA composition under the CTR system but had less impact under the NTM system. These results suggest that (i) fungal biomass is negatively affected by N fertilizer regardless of management system; (ii) bacterial response to N fertilizer differs temporally between management systems, reflecting temporal changes in soil C content; and (iii) the NTM system mitigates N effects on the composition of soil microbial communities.
1Graduate School of Environment and Information Sciences, Yokohama National University, Yokohama, Japan.
2Department of Chemical Engineering, Faculty of Engineering, Tokyo University of Agriculture and Technology, Tokyo, Japan.
3Center for Regional Environmental Research, National Institute for Environmental Studies, Ibaraki, Japan.
4Department of Soil Science, University of Lampung, Bandar Lampung, Indonesia.
Address for correspondence: Dr. Toshiko Miura, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo, 184-8588, Japan. E-mail: email@example.com
Financial Disclosures/Conflicts of Interest: This study was supported in part by a grant-in-aid for the Global COE Program E03 for Global Eco-Risk Management from Asian Viewpoints and MEXT KAKENHI Grant No. 25220104 and Grant No. 25281053.