Benefits and trade‐offs of replacing synthetic fertilizers by animal manures in crop production in China: A meta‐analysis

Abstract

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.

Societal benefits of halving agricultural ammonia emissions in China far exceed the abatement costs

“…(3) Practical applicability: measures with current limited applicability due to technical, political or obvious social barriers in China, were excluded, for example, soil testing has been ruled out in this study due to high costs for the small farm size and high spatial and temporal variability, although it is an effective measure to optimize fertilizer use in the US and Europe where farm sizes are much larger. (4) Limitations: measures that likely and significantly reduce agricultural productivity (crop yield or animal productivity) were adopted with caution, for example, the full substitution of synthetic fertilizers by manure decreases the yield of upland crops and lowland rice by 9.6% and 4.1%, respectively 53 ; and low crude protein (LCP) feeding should only be adopted to an applicable level to avoid undermining animal productivity and welfare. Besides, LCP is mainly applicable to indoor animals (pig, poultry, and dairy).…”

Manure combined with chemical fertilizer increases rice productivity by improving soil health, post-anthesis biomass yield, and nitrogen metabolism

“…Changes in net photosynthetic rate(3,10,17,24, and 31 days after anthesis (DAA)) during grain-filling period during in the early (A) and late growing season (B) under combined organic and inorganic N fertilizer application. Vertical bars represent the standard error of the mean.…”

Agriculture Green Development: a model for China and the world

“…Also, as they are the primary producers providing raw materials for industry, these systems are treated as fundamental to the stability and sustainable development of the country [34] . In principle, the two systems should be coupled so that crop system provides almost all the materials for feeding livestock, and receives and uses the excreta from the livestock as part of the nutrient supply to crops [30,35] . Uncoupled or unmatched animal-crop systems will increase the risks of environmental pollution from emission of pollutants from the livestock system, which could be used as valuable nutrients for crop production [36] .…”