Nitrogen management to reduce yield-scaled global warming potential in rice

•Rice yields increased similarly in response to urea- and manure-N.•Manure increased GWP by 60% relative to urea due to higher CH4 and N2O emissions.•Yield-scaled GWP with urea was lowest at N rate required to achieve maximum yield.•When manure was used as the N source, yield-scaled GWP was higher t...

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Bibliographic Details
Published in:Field crops research 2013-05, Vol.146, p.66-74
Main Authors: Liang, X.Q., Li, H., Wang, S.X., Ye, Y.S., Ji, Y.J., Tian, G.M., van Kessel, C., Linquist, B.A.
Format: Article
Language:English
Subjects:
CH4 and N2O
emissions
global warming
Global warming potential
grain yield
greenhouse gases
growing season
Manure
nitrogen
nitrogen content
nitrogen fertilizers
Oryza sativa
pig manure
pollution
Rice
risk
Urea
Yield-scaled emissions
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Summary:•Rice yields increased similarly in response to urea- and manure-N.•Manure increased GWP by 60% relative to urea due to higher CH4 and N2O emissions.•Yield-scaled GWP with urea was lowest at N rate required to achieve maximum yield.•When manure was used as the N source, yield-scaled GWP was higher than for urea. Fertilizer N is usually required to achieve optimal yields but when applied in excess there is increased risk of pollution, including higher greenhouse gas (GHG) emissions. Thus, optimal N management must consider both yields and environmental effects. Yield-scaled GWP (Global Warming Potential), which is the GWP (in CO2 equivalents) per Mg of grain yield, is a useful metric for evaluating management options where the goal is to achieve both high yields with minimal environmental burden. A 6-year field study was conducted to test the hypothesis that the lowest yield-scaled GHG emissions for rice occur when N is applied at optimal N rates for maximum yields, independent of the source of N applied. We tested this hypothesis for organic (manure) and inorganic (urea) N sources. The N rates and sources in each growing season were: 0, 90, 180 and 270kgNha−1 applied as either urea alone or pig manure combined with urea (where N was added as manure and supplied 60% of the total N rate). The N rates to achieve maximum yields (90 to 180kgNha−1 depending on year) were similar for both N sources. Seasonal CH4 and N2O emissions varied significantly between years but the magnitude of emissions was determined largely by N source. Across N rates, application of manure increased GWP by almost 60% relative to the urea treatments due to higher CH4 and N2O emissions. When urea was used as the sole N source, yield-scaled GWP (87kg CO2eq. Mg−1 grain) was lowest at optimal N rates for maximum yields. In contrast, when manure was used, yield-scaled GWP was higher than for urea and increased with increasing manure-N rates (from 104 to 171kg CO2eq. Mg−1 grain). The lowest yield-scaled GWP for manure was when no manure was applied – despite the low yields. Thus, when manure is used as an N source in flooded rice systems, over application should be avoided.
ISSN:0378-4290
1872-6852
DOI:10.1016/j.fcr.2013.03.002