Nitrogen cycling and management focusing on the central role of soils: a review

Abstract

Soil is a hotspot of the terrestrial nitrogen (N) cycling. Nitrogen is an indispensable component of fertilizers for producing crops in agricultural soils and is a macronutrient for natural soils driving the food chain, including microbial activities in terrestrial ecosystems. Humans acquired the technology of artificial N fixation during the early 20th century and used the fixed N for fertilizer and industrial materials. Artificial N fixations have amounted to ca. 150 Tg N yr–1 in recent years, surpassing terrestrial biological N fixation. Consequently, a large amount of reactive N (N compounds other than dinitrogen) is lost to the environment, inducing various forms of N pollution and threatening human and environmental health. This review aims to highlight future research on N cycling and management from the soil science perspective based on the author’s experience. The review covers the following themes: N processes to be elucidated preferentially in agricultural soils, interactions between soil and N cycling in the polar regions storing a large amount of organic matter and susceptible to climate change, and N management at national and international scales focusing on how soils are treated.