Livestock manure contributes considerably to global emissions of ammonia (NH3 ) and greenhouse gases (GHG), especially methane (CH4 ) and nitrous oxide (N2 O). Various measures have been developed to mitigate these emissions, but most of these focus on one specific gas and/or emission source. Here, we present a meta-analysis and integrated assessment of the effects of mitigation measures on NH3 , CH4 and (direct and indirect) N2 O emissions from the whole manure management chain. We analysed the effects of mitigation technologies on NH3 , CH4 and N2 O emissions from individual sources statistically using results of 126 published studies. Whole-chain effects on NH3 and GHG emissions were assessed through scenario analysis. Significant NH3 reduction efficiencies were observed for (i) housing via lowering the dietary crude protein (CP) content (24-65%, compared to the reference situation), for (ii) external slurry storages via acidification (83%) and covers of straw (78%) or artificial films (98%), for (iii) solid manure storages via compaction and covering (61%, compared to composting), and for (iv) manure application through band spreading (55%, compared to surface application), incorporation (70%) and injection (80%). Acidification decreased CH4 emissions from stored slurry by 87%. Significant increases in N2 O emissions were found for straw-covered slurry storages (by two orders of magnitude) and manure injection (by 26-199%). These side-effects of straw covers and slurry injection on N2 O emission were relatively small when considering the total GHG emissions from the manure chain. Lowering the CP content of feed and acidifying slurry are strategies that consistently reduce NH3 and GHG emissions in the whole chain. Other strategies may reduce emissions of a specific gas or emissions source, by which there is a risk of unwanted trade-offs in the manure management chain. Proper farm-scale combinations of mitigation measures are important to minimize impacts of livestock production on global emissions of NH3 and GHG.

Recycling of livestock manure to agricultural land may reduce the use of synthetic fertilizer and thereby enhance the sustainability of food production. However, the effects of substitution of fertilizer by manure on crop yield, nitrogen use efficiency (NUE), and emissions of ammonia (NH3), nitrous oxide (N2O) and methane (CH4) as function of soil and manure properties, experimental duration and application strategies have not been quantified systematically and convincingly yet. Here, we present a meta‐analysis of these effects using results of 143 published studies in China. Results indicate that the partial substitution of synthetic fertilizers by manure significantly increased the yield by 6.6% and 3.3% for upland crop and paddy rice, respectively, but full substitution significantly decreased yields (by 9.6% and 4.1%). The response of crop yields to manure substitution varied with soil pH and experimental durations, with relatively large positive responses in acidic soils and long‐term experiments. NUE increased significantly at a moderate ratio (<40%) of substitution. NH3 emissions were significantly lower with full substitution (62%–77%), but not with partial substitution. Emissions of CH4 from paddy rice significantly increased with substitution ratio (SR), and varied by application rates and manure types, but N2O emissions decreased. The SR did not significantly influence N2O emissions from upland soils, and a relative scarcity of data on certain manure characteristic was found to hamper identification of the mechanisms. We derived overall mean N2O emission factors (EF) of 0.56% and 0.17%, as well as NH3 EFs of 11.1% and 6.5% for the manure N applied to upland and paddy soils, respectively. Our study shows that partial substitution of fertilizer by manure can increase crop yields, and decrease emissions of NH3 and N2O, but depending on site‐specific conditions. Manure addition to paddy rice soils is recommended only if abatement strategies for CH4 emissions are also implemented.

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