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How does recycling of livestock manure in agroecosystems affect crop productivity, reactive nitrogen losses and soil carbon balance? Longlong Xia, Shu Kee Lam, Xiaoyuan Yan, and Deli Chen Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 02 Jun 2017 Downloaded from http://pubs.acs.org on June 3, 2017
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How does recycling of livestock manure in agroecosystems affect crop
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productivity, reactive nitrogen losses and soil carbon balance?
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Longlong Xiaa,b,c, Shu Kee Lamb, Xiaoyuan Yan a*, Deli Chenb*
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a.
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Chinese Academy of Sciences, Nanjing 210008, China.
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b.
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University of Melbourne, Victoria 3010, Australia.
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c.
State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science,
School of Agriculture and Food, Faculty of Veterinary and Agricultural Sciences, the
University of Chinese Academy of Sciences, Beijing 100049, China
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*
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Xiaoyuan Yan, Phone: +86 25 86881530, Fax: +86 25 86881000, Email:
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[email protected] 14
Deli Chen, Phone: +61 3 83448148, Fax: +61 3 83445037, Email:
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[email protected] Corresponding author:
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Abstract:
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Recycling of livestock manure in agroecosystems to partially substitute synthetic
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fertilizer nitrogen (N) input is recommended to alleviate the environmental
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degradation associated with synthetic N fertilization, which may also affect food
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security and soil greenhouse gas (GHG) emissions. However, how substituting
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livestock manure for synthetic N fertilizer affects crop productivity (crop yield; crop
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N uptake; N use efficiency), reactive N (Nr) losses (ammonia (NH3) emission, N
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leaching and runoff), GHG (methane, CH4; and nitrous oxide, N2O; carbon dioxide)
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emissions and soil organic carbon (SOC) sequestration in agroecosystems is not well
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understood. We conducted a global meta-analysis of 141 studies and found that
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substituting livestock manure for synthetic N fertilizer (with equivalent N rate)
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significantly increased crop yield by 4.4% and significantly decreased Nr losses via
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NH3 emission by 26.8%, N leaching by 28.9% and N runoff by 26.2%. Moreover,
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annual SOC sequestration was significantly increased by 699.6 and 401.4 kg C ha−1
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yr−1 in upland and paddy fields, respectively; CH4 emission from paddy field was
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significantly increased by 41.2%, but no significant change of that was observed from
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upland field; N2O emission was not significantly affected by manure substitution in
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upland or paddy fields. In terms of net soil carbon balance, substituting manure for
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fertilizer increased carbon sink in upland field, but increased carbon source in paddy
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field. These results suggest that recycling of livestock manure in agroecosystems
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improves crop productivity, reduces Nr pollution and increases SOC storage. To
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attenuate the enhanced carbon source in paddy field, appropriate livestock manure 2
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management practices should be adopted.
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Key words: substituting manure for fertilizer; crop productivity; reactive nitrogen
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losses; greenhouse gas emissions; carbon sequestration; agroecosystems
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TOC
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Introduction
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Despite its critical role in feeding global population, the use of synthetic fertilizer
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N causes a cascade of adverse impacts on the environment (e.g., air pollution and
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freshwater eutrophication) through the release of reactive N (Nr) from agricultural
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soils1-4. Synthetic N fertilization may increase soil carbon sequestration5, but the
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increase in CO2 sink could be largely offset or even overweighed by N stimulation of
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CH4 and N2O emission from agricultural soils6-8. Better N management in crop
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production is therefore critical for addressing the triple challenges of food security,
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environmental degradation and global warming9-11.
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Globally, annual production of livestock manure N has reached nearly 100 Tg
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N12 and recycling of this large amount of manure N in agroecosystems to partially
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substitute synthetic N fertilizer (substituting manure for fertilizer, and hereafter) may
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help address the above-mentioned triple challenges3,
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fertilizer is beneficial for improving soil properties and subsequently crop yield14-16.
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The responses of yield to substituting manure for fertilizer may vary with crop species
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and the proportion of manure N substitution17-19, but few studies have conducted a
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comprehensive assessment on these responses.
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. Substituting manure for
Substituting manure for fertilizer generally alters Nr losses through regulating crop N uptake and soil N transformation20,
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, and may result in a better
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synchronization of crop N demand with N supply17, 22, thereby increasing crop N
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uptake and likely decreasing Nr losses23. Moreover, substituting manure for fertilizer
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increases the input of C substrates into soil, which may stimulate mineral N 5
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immobilization and therefore reduce N substrate that is subjected to loss as Nr24. The
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effects of substituting manure for fertilizer may vary with Nr species (e.g., NH3
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emission and N leaching)23. This highlights the importance of simultaneously
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assessing the responses of various Nr losses (NH3 emission, N leaching and runoff) to
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the substitution of manure for fertilizer.
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Substituting manure for fertilizer can also affect SOC accumulation through
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supplying exogenous C input to soil25, which may also enhance soil microbial
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activities and stimulate soil CO2 emission26-28. Likewise, the growth of methanogenic
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populations in flooded paddy field may also be stimulated by the extra C supply and
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consequently release more CH429, 30. However, the response of substituting manure for
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fertilizer on CH4 emission from upland field remains unknown. Another knowledge
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gap is how substitution of manure for fertilizer affects N2O emission from agricultural
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soils. Through affecting the C and N availability for the processes of nitrification and
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denitrification, substituting manure for fertilizer can regulate N2O production and
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emission from soils17, 31. While a number of measurements have been reported, there
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has been no systematic assessment of the overall effects of substituting manure for
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fertilizer on CH4, N2O and CO2 emission, and SOC sequestration in agroecosystems.
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Here, using a global meta-analysis of 141 studies, we evaluated the overall
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effects of substituting manure for fertilizer on crop productivity (crop yield; crop N
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uptake; N use efficiency, NUE), Nr losses (NH3 emission, N leaching and N runoff),
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GHG (CH4, N2O and CO2) emissions and SOC sequestration in agroecosystems.
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Responses of these variables to manure substitution were then evaluated against crop 6
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species, manure type and substitution rate. Effects of substituting manure for fertilizer
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on the net soil carbon balance were also evaluated for upland and paddy fields. In the
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end, the underlying causes of different responses of variables to manure substitution,
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and the implications of the findings were discussed.
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Materials and methods
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Data collection. This meta-analysis is based on studies that evaluated the effects of
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substituting manure for fertilizer on crop productivity, Nr losses, GHG emissions and
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SOC sequestration in grain and vegetable cropping systems. Several databases were
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employed to search relevant peer-reviewed studies published before August 2016,
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including Web of Science, China National Knowledge Infrastructure database,
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SCOPUS, CAB Abstracts and Google Scholar. Studies included in this analysis had to
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meet the following criteria. First, species and amounts of applied manure, cropping
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system and experimental durations had to be clearly stated. Second, manure type was
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restricted to livestock manure and animal-excreta dominated farm yard manure. Third,
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the control (synthetic N fertilization) and treatment (substituting manure for fertilizer)
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had equal total N rate. Fourth, the substitution rate, defined by manure N input/total N
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applied, had to be reported.
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Fifth, studies were restricted to field, lysimeter and pot studies with crop growth.
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Means and samples size must be provided for the control and treatment plots.
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Multiple observations conducted in the same experimental site over sampling years
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were averaged. The observation methods of various GHG emissions and Nr losses
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should be widely-adopted. Specifically, GHG emissions should be measured by the 7
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static chamber technique32, NH3 emission by the dynamic chamber method or
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micrometeorological method23, and N leaching and runoff by lysimeter method or
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suction cap24. In addition, when evaluating the response of SOC sequestration, studies
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with experimental durations less than 3 year were excluded to avoid a short-term
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noise33. A total of 141 peer-reviewed studies were finally selected across the world
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(Supporting Information (SI), Figure S1).
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Evaluated variables. Effects of substituting manure for fertilizer were evaluated by
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the following three categories with 11 variables, including (1) crop productivity: crop
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yield, crop N uptake and N use efficiency (NUE); (2) Nr losses: NH3 emission, N
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leaching and N runoff; (3) GHG (CH4, N2O and CO2) emissions and SOC
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sequestration (SOC content and SOC sequestration rate). N2O is both a species of
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GHG and Nr, and here its responses are reported under the category of GHG. Crop N
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uptake refers to total aboveground N uptake for grain crop, while it denotes the total
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N uptake by yield, stem and leaves for vegetable crop. The NUE, referring to total N
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recovery efficiency, was calculated by dividing the difference in crop N uptake in
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plots with and without fertilization by total fertilizer N rate.
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The emission of CO2 refers to soil respiration, which includes microbial and root
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respiration. In the studies where SOC sequestration rate (SOCSR) was not directly
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reported, the rate was estimated by the following equation16, 34:
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SOCSR (kg C ha−1 yr−1) = (SOCDt– SOCD0) / T
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where SOCDt and SOCD0 refer to SOC density (kg C ha−1) in final and initial years of
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the experiment, respectively, which was calculated using equation (2). T refers to the 8
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experimental duration of substituting manure for fertilizer (year).
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SOCD = SOC × ρ × H × 10−1,
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where SOC is soil organic carbon content (g C kg−1); ρ is soil bulk density (g cm−3)
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and H is the sampling depth. In studies where ρ was missing, it was estimated using
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following equation35:
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ρ= –0.0048 × ln SOC + 1.377
(2)
(3)
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Effects of substituting manure for fertilizer were further categorized, according
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to crop species (grain crop and vegetable crop, Table S1 in SI), manure type (fresh
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and composted manure) and substitution rate (Rs, manure N input/total N applied)
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(Rs≤25%, 25
