The contribution of nitrogen transformation processes to total N2O emissions from soils used for intensive vegetable cultivation

Abstract

The rapid expansion of intensively farmed vegetable fields has substantially contributed to the total N 2 O emissions from croplands in China. However, to date, the mechanisms underlying this phenomenon have not been completely understood. To quantify the contributions of autotrophic nitrification, heterotrophic nitrification, and denitrification to N 2 O production from the intensive vegetable fields and to identify the affecting factors, a 15 N tracing experiment was conducted using five soil samples collected from adjacent fields used for rice-wheat rotation system (WF), or for consecutive vegetable cultivation (VF) for 0.5 (VF1), 6 (VF2), 8 (VF3), and 10 (VF4) years. Soil was incubated under 50% water holding capacity (WHC) at 25°C for 96 h after being labeled with 15 NH 4 NO 3 or NH 4 15 NO 3 . The average N 2 O emission rate was 24.2 ng Nkg −1 h −1 in WF soil, but it ranged from 69.6 to 507 ng Nkg −1 h −1 in VF soils. Autotrophic nitrification, heterotrophic nitrification and denitrification accounted for 0.3-31.4%, 25.4-54.4% and 22.5-57.7% of the N 2 O emissions, respectively. When vegetable soils were moderately acidified (pH, 6.2 to ≥5.7), the increased N 2 O emissions resulted from the increase of both the gross autotrophic and heterotrophic nitrification rates and the N 2 O product ratio of autotrophic nitrification. However, once severe acidification occurred (as in VF4, pH≤4.3) and salt stress increased, both autotrophic and heterotrophic nitrification rates were inhibited to levels similar to those of WF soil. The enhanced N 2 O product ratios of heterotrophic nitrification (4.84‰), autotrophic nitrification (0.93‰) and denitrification processes were the most important factors explaining high N 2 O emission in VF4 soil. Data from this study showed that various soil conditions (e.g., soil salinity and concentration of NO 3 -or NH 4 + ) could also significantly affect the sources and rates of N 2 O emission.

Impact of the size of nitrogen fertiliser application rate on N₂O flux

“…The major N 2 O source is denitrification (Skiba et al 1997;Skiba, Smith 2000;Ruser et al 2001). High rate of N fertiliser application increases concern regarding N 2 O emissions from intensively farmed fields (He et al 2009;Pang et al 2009;Lin et al 2010;Zhu et al 2011). Although N 2 O emissions from the soil increase with the amount of N fertiliser (Eichner 1990;Bouwman 1996;Verma et al 2006;Jones et al 2007;He et al 2009;Pang et al 2009;Lin et al 2010;Mapanda et al 2011), there is still a lack of data for fertiliserintensive systems (Pfab et al 2012).…”

Nitrogen Transformations Associated with N2O Emissions in Agricultural Soils

“…If there was no leaching or loss via runofs, all available N will be adsorbed by plant roots and used for growth. However, nitriication and denitriication processes (both produce greenhouse gas N 2 O) also occurred between ammonium and nitrate N, causing new balance among diferent N components [2,4,7].…”

“…In addition to N input by anthropogenic activities, N output via crops harvest or human-induced runofs with irrigation could occur simultaneously in agricultural soils (Figure 1). Moreover, the complicated N transformations going on in soil ecosystems also account for large part of N output from soils [7]. For example, N mineralization associated with transforming organic N into inorganic N might induce more N leaching with runofs or underground water; nitriication process could increase N loss from soils via gas emissions [2,7,8] ( Figure 1).…”

“…Moreover, the complicated N transformations going on in soil ecosystems also account for large part of N output from soils [7]. For example, N mineralization associated with transforming organic N into inorganic N might induce more N leaching with runofs or underground water; nitriication process could increase N loss from soils via gas emissions [2,7,8] ( Figure 1). Thereby, understanding the process and mechanisms underlining N transformations in agricultural soils would be vital for more eicient fertilization practice and agriculture management.…”

Application of Nitrogen Fertilizers and its Effect on Timeliness of Fertilizers Decomposition Resulting in Lost of Nitrogen Through Nitrous Oxide Emissions from Soil

“…It was also concluded that application of high dose of nitrogen fertiliser resulted in the increase of concerns regarding to the N 2 O emissions from intensively farmed fields (Zhu et al, 2011;He et al, 2009;Pang et al, 2009;Lin et al, 2010;Šima, 2014). Although intensive research conducted by various researchers (e.g.…”