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Irrigating grazed pasture decreases soil carbon and nitrogen stocks

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posted on 2023-05-03, 15:09 authored by Paul Mudge, Frank Kelliher, Trevor Knight, Denis O'Connell, Scott Fraser, Louis Schipper
The sustainability of using irrigation to produce food depends not only on the availability of sufficient water, but also on the soil’s ‘response’ to irrigation. Stocks of carbon (C) and nitrogen (N) are key components of soil organic matter (SOM), which is important for sustainable agricultural production. While there is some information about the effects of irrigation on soil C stocks in cropping systems, there is a paucity of such studies in pastoral food production systems. For this study, we sampled soils from 34 paired, irrigated and unirrigated pasture sites across New Zealand (NZ) and analysed these for total C and N. On average, irrigated pastures had significantly (P < 0.05) less soil carbon (C) and nitrogen (N) than adjacent unirrigated pastures, with differences of 6.99 t C ha1 and 0.58 t N ha1 in the uppermost 0.3 m. Differences in C and N tended to occur throughout the soil profile, so the cumulative differences increased with depth, and the proportion of the soil C lost from deeper horizons was large. There were no relationships between differences in soil C and N stocks and the length of time under irrigation. This study suggests SOM will decrease when pastures under a temperate climate are irrigated. On this basis, increasing the area of temperate pasture land under irrigation would result in more CO2 in the atmosphere and may directly and indirectly increase N leaching to groundwater. Given the large and increasing area of land being irrigated both in NZ and on a global scale, there is an urgent need to determine whether the results found in this study are also applicable in other regions and under different land management systems (e.g. arable).


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© 2016 John Wiley & Sons Ltd.


  • English

Does this contain Māori information or data?

  • No



Journal title

Global Change Biology




Mudge, P. L., Kelliher, F. M., Knight, T. L., O'Connell, D., Fraser, S. & Schipper, L. A. (2017). Irrigating grazed pasture decreases soil carbon and nitrogen stocks. Global Change Biology, 23(2), 945-952. doi:10.1111/gcb.13448

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