## Abstract

The main objectives of this review were to: (1) review different methods/techniques to assess gaseous N-losses from manure (2) review N-gaps, attributed to dinitrogen loss as the difference between directly measured N compounds summed as total N loss and indirectly measured N loss through a mass balance in livestock manure systems, and (3) provide approaches to close the N-gap. In literature, N-gaps run up to 80% of total N loss, this undermines N emission assessments and leaves a huge part of the emission unexplained. However, studies that measure N-gaps are scarcely available or are limited in their evaluation, hence more study is needed. Three approaches are introduced to research N-gaps: (1) measure N_{2} through a suggested Gas Flow Soil Core (GFSC) technique and compare the sum of all measured N losses with the indirect method, (2) assume N_{2} loss as being the N-gap and (3) include N_{2} as an estimate based on ratios from literature. In a hypothetical example for poultry manure, assumed values for measurement error of 50% and variance due to physical differences between the experimental units of 50% led to a total standard deviation of 131% in the N-gap. Variance of N-gap was reduced with 80% point when assuming 16 vessels compared to single vessel. Using literature-based-ratios to estimate losses of N compounds led to variation of N-gap from 0.06% initial N overestimation to 26% of initial N underestimation. Future research should address this variance and apply methods to measure N_{2} to close N-gaps.

Original language | English |
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Pages (from-to) | 179-199 |

Journal | Biosystems Engineering |

Volume | 229 |

DOIs | |

Publication status | Published - May 2023 |

## Keywords

- Dinitrogen (N) estimation
- Direct and indirect methods
- Gas-Flow-Soil-Core (GFSC) technique
- N loss and emission
- N-gap

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