The soil N cycle: new insights and key challenges

Abstract

Abstract. The study of soil N cycling processes has been, is, and will be at the centre of attention in soil science research. The importance of N as a nutrient for all biota; the ever-increasing rates of its anthropogenic input in terrestrial (agro)ecosystems; its resultant losses to the environment; and the complexity of the biological, physical, and chemical factors that regulate N cycling processes all contribute to the necessity of further understanding, measuring, and altering the soil N cycle. Here, we review important insights with respect to the soil N cycle that have been made over the last decade, and present a personal view on the key challenges of future research. We identify three key challenges with respect to basic N cycling processes producing gaseous emissions:1. quantifying the importance of nitrifier denitrification and its main controlling factors; 2. characterizing the greenhouse gas mitigation potential and microbiological basis for N 2 O consumption; 3. characterizing hotspots and hot moments of denitrification Furthermore, we identified a key challenge with respect to modelling: 1. disentangling gross N transformation rates using advanced 15 N / 18 O tracing models Finally, we propose four key challenges related to how ecological interactions control N cycling processes:1. linking functional diversity of soil fauna to N cycling processes beyond mineralization; 2. determining the functional relationship between root traits and soil N cycling; 3. characterizing the control that different types of mycorrhizal symbioses exert on N cycling; 4. quantifying the contribution of non-symbiotic pathways to total N fixation fluxes in natural systemsWe postulate that addressing these challenges will constitute a comprehensive research agenda with respect to the N cycle for the next decade. Such an agenda would help us to meet future challenges on food and energy security, biodiversity conservation, water and air quality, and climate stability.

Spatial Distribution of Nitrous Oxide (N2O) in the Reloncaví Estuary–Sound and Adjacent Sea (41°–43° S), Chilean Patagonia

“…Sanford et al (2012) suggested that nondenitrifying populations with a broad range of metabolisms and habitats are potentially significant contributors to N 2 O consumption, therefore controlling N 2 O emissions. However, the mechanisms and controls of N 2 O consumption in soil are not clear, and various biochemical routes have been identified in addition to the classical reduction of N 2 O during denitrification (van Groenigen et al 2015); these routes include dissimilative reduction, a direct assimilatory N 2 O fixation via nitrogenase (Vieten et al 2008;Farías et al 2013). Recently, Wu et al (2013) reported a significant N 2 O consumption occurring under aerobic conditions, with a rising N 2 O consumption with increased soil moisture content, and the complete blockage of N 2 O consumption with the sterilization of oxic soil.…”

Nutritional characteristics of marandu grass (Brachiaria brizantha cv. marandu) subjected to inoculation with associative diazotrophic bacteria

“…Although the use of nitrogen fertilizers contributes to the increase in pasture production (Boddey et al, 2000;Palmer et al, 2014), their use have limited efficacy because of the complex steps in the nitrogen cycle which occurs in the soil, and which can result in the loss of the fertilizer after its application (Van Groenigen et al, 2015).…”

Are There Arid Land Soilscapes in Southwestern Europe?

“…Soils are self-organized heterogeneous porous media essential for supporting life within the Earth system, as they control the hydrological and biogeochemical cycles, among other biospherical services (Keesstra et al, 2012;Billings et al, 2015;Brevik et al, 2015b;de Graaff et al, 2015;Köchy et al, 2015;van Groenigen et al, 2015). The Iberian Peninsula has a long history of soil use.…”