Identification of current research intensity and influence factors of agricultural nitrogen loss from cropping systems

Abstract

A large number of studies related to agricultural nitrogen (N) losses have been conducted in recent decades worldwide. However, determining if specific N loss pathways are under-researched or over-researched for different country-crop combinations still remains uncertain. The objective of this study was to provide an estimate of crop-specific research deficits or excesses for global cropland ammonia volatilization, nitrous oxide emission, and N leaching from 2001 to 2015 from simulations with the DeNitrification-DeComposition (DNDC) model and zero-inflated Poisson model integrated with bibliometric metrics (i.e., numbers of publications and researchers). In addition, some major influencing factors affecting cropland N loss patterns were also evaluated. Our analysis showed that corn, wheat, rice, and legumes have received substantially more research focus than other crops due to their greater N losses. Greater amounts of research were always evident in China, the United States, and Australia for cereals; in China, India, the United States, and Japan for rice; and in the United States, Brazil, China, Argentina, and India for legumes. These countries are major crop producers that spend large monetary sums on research and development. Some country-crop combinations, such as millet across the globe, cassava and sorghum in tropical countries, and legumes in Europe, show greater research deficits due to the lower level of economic development or due to agricultural policies in the countries where these crops are produced. Tillage method is sometimes considered the most sensitive driver for various N loss pathways. However, the amount of tillage research tended to be slightly lower than research on climate factors and fertilization. Our results support the urgent need for prioritizing the allocation of agricultural research focus and resources not only with regard to country-crop combinations but also with respect to measures for mitigating N loss in order to enhance environmental and agricultural sustainability.