Does irrigation increase the storage of carbon in soil under temperate managed pastures?

3 September 2020

The growing demand for meat, wool and dairy products has resulted in increased use of fertiliser and irrigation to enhance pasture production. Understanding the responses of soil organic carbon to these pasture management practices is needed to assess their role in contributing to or mitigating further increases in atmospheric carbon dioxide concentrations.

Scientists at Plant & Food Research, Lincoln University and Manaaki Whenua – Landcare Research conducted a study on Lismore silt loam soil collected from a dryland lucerne (Medicago sativa L.) pasture on the Ashley Dene Research and Development farm in Lincoln, Canterbury. The main objective was to measure the effect irrigation has on the distribution of photosynthate carbon (photosynthesis derived-carbon) within the plant-soil system. This study was motivated by the lack of data available on this subject from grazed pastures in temperate climates.

Continuous non-radioactive isotope 13-carbon dioxide (13CO2) pulse labelling of temperate perennial ryegrass (Lolium perenne L.) and white clover pasture (Trifolium repens L.) was applied to two treatments that simulated irrigated and dryland management.

The researchers observed no differences in accumulation of new photosynthate carbon (13C) in soil between the irrigated and dryland treatments – despite the irrigated treatment having significantly increased above-ground pasture productivity and reduced root biomass.  However, the irrigated treatment had reduced 13C in rhizosphere soil, and increased 13C in the 53–250 µm and < 5 µm soil size fractions compared with the dryland treatment. These results indicate the importance of the scale at which soil processes occur, and can be used to improve models to predict more accurate soil organic carbon cycling under temperate managed pastures.

This research was funded by the New Zealand Government to support the objectives of the Livestock Research Group of the Global Research Alliance on Agricultural Greenhouse Gases.

 


Journal reference:

Carmona CR, Clough TJ, McNally SR, Beare MH, Tregurtha CS, Hunt JE 2020. Seasonal irrigation affects the partitioning of new photosynthate carbon in soil. Soil Biology and Biochemistry 143. https://doi.org/10.1016/j.soilbio.2020.107751