A Bibliometrical Analysis of Status and Trends of International Researches on the Agronomic and Environmental Effects of Nitrogen Application to Farmland

The primary topics and trends in the development of research on the agronomic and environmental effects of nitrogen application,both in China and abroad,were analyzed to provide references and highlight opportunities for future research in the field of farmland nitrogen application. The Institute for Scientific Information( ISI) Web of Science database was used to retrieve Scientific Citation Indexed( SCI) papers published( 1957-2014) on the topic of "nitrogen fertilizer application", and literature relevant to "agronomic effects", "environmental effects ", and "appropriate nitrogen application"was extracted. The bibliometric method was used to analyze the main focus,research institutions,publishing journals,and citation indices of the publications in each research branch. A total of 7460 SCI articles on farmland nitrogen research were published during this period. Of these,2,773 were related to "agronomic effects",which mainly includedthe effects of nitrogen application on nitrogen use efficiency,soil organic carbon,and yields of wheat,corn,rice,and soybeans,as well as other crops. There were 1609 articles related to "environmental effects",which mainly included the effects of nitrogen application on ammonia volatilization,nitrification and denitrification,greenhouse gas emissions,nitrate leaching,groundwater quality,and other environmental topics. There were 408 articles were related to "appropriate nitrogen application ",which mainly covered the aspects of quantity of nitrogen fertilizer application and field nitrogen management. Most of the publications were by researchers affiliated to institutions in developed countries in Europe and North America; most of the publications in mainstream journals and the most highly cited publications were also by researchers based in developed European and American countries. However,research on farmland nitrogen application has developed rapidly in China,and some institutions,including the Chinese Academy of Sciences,China Agricultural University,Nanjing Agricultural University,and the Chinese Academy of Agricultural Sciences,have gradually become global leaders in this area. The bibliometric method can be used to analyze the primary topics and developmental trends in research on nitrogen application. Currently,investigation of the agronomic effects of nitrogen application is the main focus of research on nitrogen. Research on the environmental effects of nitrogen,especially the impacts of nitrogen loss on water qua