Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 13, issue 17
Biogeosciences, 13, 4975–4984, 2016
https://doi.org/10.5194/bg-13-4975-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 13, 4975–4984, 2016
https://doi.org/10.5194/bg-13-4975-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 09 Sep 2016

Research article | 09 Sep 2016

Long-term nutrient fertilization and the carbon balance of permanent grassland: any evidence for sustainable intensification?

Dario A. Fornara1, Elizabeth-Anne Wasson1, Peter Christie2, and Catherine J. Watson1 Dario A. Fornara et al.
  • 1Agri-Food & Biosciences Institute (AFBI), Newforge Lane, Belfast, BT9 5PX, UK
  • 2Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China

Abstract. Sustainable grassland intensification aims to increase plant yields while maintaining the ability of soil to act as a sink rather than sources of atmospheric CO2. High biomass yields from managed grasslands, however, can be only maintained through long-term nutrient fertilization, which can significantly affect soil carbon (C) storage and cycling. Key questions remain about (1) how long-term inorganic vs. organic fertilization influences soil C stocks, and (2) how soil C gains (or losses) contribute to the long-term C balance of managed grasslands. Using 43 years of data from a permanent grassland experiment, we show that soils not only act as significant C sinks but have not yet reached C saturation. Even unfertilized control soils showed C sequestration rates of 0.35 Mg C ha−1 yr−1 (i.e. 35 g C m−2 yr−1; 0–15 cm depth) between 1970 and 2013. High application rates of liquid manure (i.e. cattle slurry) further increased soil C sequestration to 0.86 Mg C ha−1 yr−1 (i.e. 86 g C m−2 yr−1) and a key cause of this C accrual was greater C inputs from cattle slurry. However, average coefficients of slurry-C retention in soils suggest that 85 % of C added yearly through liquid manure is lost possibly via CO2 fluxes and organic C leaching. Inorganically fertilized soils (i.e. NPK) had the lowest C-gain efficiency (i.e. unit of C gained per unit of N added) and lowest C sequestration (similar to control soils). Soils receiving cattle slurry showed higher C-gain and N-retention efficiencies compared to soils receiving NPK or pig slurry. We estimate that net rates of CO2-sequestration in the top 15 cm of the soil can offset 9–25 % of GHG (greenhouse gas) emissions from intensive management. However, because of multiple GHG sources associated with livestock farming, the net C balance of these grasslands remains positive (9–12 Mg CO2-equivalent ha−1 yr−1), thus contributing to climate change. Further C-gain efficiencies (e.g. reduced enteric fermentation and use of feed concentrates, better nutrient management) are required to make grassland intensification more sustainable.

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This study demonstrates that intensively managed agricultural grasslands can sequester significant amounts of carbon in soils, especially under long-term applications of cattle slurries. There is also evidence that soil carbon sequestration can contribute to offset between 9 % and 25 % of total greenhouse gas emissions associated with the management of permanent grassland. However, to make livestock-based grassland systems more sustainable, further carbon-gain efficiencies are required.
This study demonstrates that intensively managed agricultural grasslands can sequester...
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