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Indirect N 2 O emissions from agricultural nitrogen (N) leaching and runoff in water bodies contribute significantly to the global atmospheric N 2 O budget. However, considerable uncertainty regarding this source remains in the bottom-up N 2 O inventory. Indirect N 2 O emission factor associated with N leaching and runoff (EF 5 ; kg N 2 ON per kg of NO 3 - -N) incorporate three components for groundwater and surface drainage (EF 5g ), rivers (EF 5r ), and estuaries (EF 5e ). The 2006 IPCC default EF 5 value was based on a small number of studies available at the time. Here we present the synthesis of 254 measurements of EF 5 , dissolved N 2 O, and nitrate from 106 studies. Our results do not support the further downward revision of EF 5g by the IPCC and suggest an upward revision of EF 5g of 0.0060. The emission factors for groundwater and springs (0.0079) was higher than that for surface drainage (0.0040). The emission factor for lakes, ponds, and reservoirs was 0.0012, whereas that for rivers was 0.0030, and a combined EF 5r was 0.0026. Estimated EF 5r and EF 5e (0.0026) values from the study were close to the current IPCC default values (0.0025 each). We estimated an updated default EF 5 value of 0.01 for the refinement of IPCC guidelines., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Biochar has been widely recommended as an effective soil amendment for reducing nitrous oxide (N2O) emissions and nitrogen (N) leaching. However, the effects of biochar application to Lei bamboo plantations on soil N2O emissions and N leaching remain unclear. These effects on soil N2O emissions and N leaching were investigated in the present study using five treatments applied with the same amount of N: rice husk at 10 t ha−1 (10H) and 30 t ha−1 (30H), biochar at 10 t ha−1 (10B) and 30 t ha−1 (30B), and no additions (control, CK). Both the 10H and 30H treatments significantly increased cumulative N2O emissions compared to the CK treatment, with an increment of 0.78 and 2.20 kg N ha−1, respectively. The 30B treatment significantly reduced cumulative N2O emissions by 0.90 kg N ha−1, whereas the 10B treatment had no significant effect. The reduction in N2O emissions following the high-rate biochar addition was probably due to the increased pH and the total abundance of nosZ I and nosZ II genes. The 30H treatment significantly increased nitrate N (NO3−–N) and dissolved organic N (DON) leaching by 38% and 170% respectively compared to the CK treatment, and had the largest N loss via N2O emissions and N leaching, while the 30B treatment had the lowest N loss. Partial least squares path modeling revealed that soil chemical properties [ammonium nitrogen (NH4+–N), NO3−–N, DON, dissolved organic C (DOC), total N (TN), soil organic C (SOC), and pH] dominantly affected soil N2O emissions, while the total abundance of denitrifying genes (nirS, nirK, nosZ I, and nosZ II) were the key factors involved in reducing NO3−–N leaching. There was a strong positive correlation between cumulative N2O emissions and N leaching loss, which may be related to excessive N surplus in the soil. Our results suggest that the replacement of rice husk by its biochar at a high-rate would reduce the risk of N2O emissions and N leaching loss effectively from Lei bamboo forests in subtropical China. [ABSTRACT FROM AUTHOR]

Abstract Indirect N 2 O emissions from agricultural nitrogen (N) leaching and runoff in water bodies contribute significantly to the global atmospheric N 2 O budget. However, considerable uncertainty regarding this source remains in the bottom-up N 2 O inventory. Indirect N 2 O emission factor associated with N leaching and runoff (EF 5 ; kg N 2 O N per kg of NO 3 −−N) incorporate three components for groundwater and surface drainage (EF 5g), rivers (EF 5r), and estuaries (EF 5e). The 2006 IPCC default EF 5 value was based on a small number of studies available at the time. Here we present the synthesis of 254 measurements of EF 5 , dissolved N 2 O, and nitrate from 106 studies. Our results do not support the further downward revision of EF 5g by the IPCC and suggest an upward revision of EF 5g of 0.0060. The emission factors for groundwater and springs (0.0079) was higher than that for surface drainage (0.0040). The emission factor for lakes, ponds, and reservoirs was 0.0012, whereas that for rivers was 0.0030, and a combined EF 5r was 0.0026. Estimated EF 5r and EF 5e (0.0026) values from the study were close to the current IPCC default values (0.0025 each). We estimated an updated default EF 5 value of 0.01 for the refinement of IPCC guidelines. Graphical abstract Image 1 Highlights • We summarized 254 field data on indirect emission factor from N leaching and runoff. • Mean emission factor (EF) for ground water and surface drainage (EF 5g) was 0.0060. • Mean EF for lakes, ponds & reservoirs, and rivers (EF 5r) was 0.0026. • Mean EF for estuaries (EF 5e) was 0.0026. • Combined EF (EF5) was 0.01, higher than IPCC 2006 default EF (0.0075). We summarized 254 field datasets and estimated indirect N 2 O emission factor from leaching and runoff of agricultural N (EF 5) of 0.01, higher than IPCC 2006 default EF (0.0075). [ABSTRACT FROM AUTHOR]