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Long‐term impacts of manure amendments on carbon and greenhouse gas dynamics of rangelands
Author(s) -
Owen Justine J.,
Parton William J.,
Silver Whendee L.
Publication year - 2015
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/gcb.13044
Subject(s) - greenhouse gas , environmental science , manure , soil carbon , rangeland , carbon sequestration , primary production , nitrous oxide , agronomy , carbon dioxide , manure management , fertilizer , soil water , agroforestry , ecosystem , soil science , ecology , biology
Livestock manure is applied to rangelands as an organic fertilizer to stimulate forage production, but the long‐term impacts of this practice on soil carbon (C) and greenhouse gas ( GHG ) dynamics are poorly known. We collected soil samples from manured and nonmanured fields on commercial dairies and found that manure amendments increased soil C stocks by 19.0 ± 7.3 Mg C ha −1 and N stocks by 1.94 ± 0.63 Mg N ha −1 compared to nonmanured fields (0–20 cm depth). Long‐term historical (1700–present) and future (present–2100) impacts of management on soil C and N dynamics, net primary productivity ( NPP ), and GHG emissions were modeled with DayCent. Modeled total soil C and N stocks increased with the onset of dairying. Nitrous oxide (N 2 O) emissions also increased by ~2 kg N 2 O‐N ha −1 yr −1 . These emissions were proportional to total N additions and offset 75–100% of soil C sequestration. All fields were small net methane ( CH 4 ) sinks, averaging −4.7 ± 1.2 kg CH 4 ‐C ha −1 yr −1 . Overall, manured fields were net GHG sinks between 1954 and 2011 (−0.74 ± 0.73 Mg CO 2 e ha −1 yr −1 , CO 2 e are carbon dioxide equivalents), whereas nonmanured fields varied around zero. Future soil C pools stabilized 40–60 years faster in manured fields than nonmanured fields, at which point manured fields were significantly larger sources than nonmanured fields (1.45 ± 0.52 Mg CO 2 e ha −1 yr −1 and 0.51 ± 0.60 Mg CO 2 e ha −1 yr −1 , respectively). Modeling also revealed a large background loss of soil C from the passive soil pool associated with the shift from perennial to annual grasses, equivalent to 29.4 ± 1.47 Tg CO 2 e in California between 1820 and 2011. Manure applications increased NPP and soil C storage, but plant community changes and GHG emissions decreased, and eventually eliminated, the net climate benefit of this practice.