Nitrogen mineralization related to light-fraction and hot-water extractable carbon in pasture and cropping soils

Mr Tord Ranheim Sveen1, Prof. Deli Chen1, Dr Helen  Suter1

1School of Agriculture and Food, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Victoria 3010, Australia, Melbourne, Australia

Nitrogen mineralization is an essential part of the soil nitrogen cycle, and solid knowledge of mineralization rates is crucial to optimize fertilizer application levels and avoid reactive nitrogen loading into the environment. However, mineralization rates will depend on climate- as well as management factors; most notably temperature, moisture levels and SOM contents. Here, we assessed the rate of nitrogen mineralization in soils of differing properties and land use in Southeast Australia and related these to the soils’ organic matter content through light fraction separation (LFOM) and hot-water extraction (HWC). Soil (0-100mm) was collected from 10 pasture- and 6 continuous cropping systems, with pastures grazed by dairy cows, and cropping systems consisting of 2:1 wheat and canola rotation. Rates of net mineralization were measured at three temperature (10, 20, 30°C) and three moisture levels (air dry, FC, 150% FC), after 14- and 28 days of aerobic incubation. Sampling was conducted at three times over the course of a year to incorporate seasonal differences. Preliminary results indicate soil moisture as the main limiting factor of nitrogen mineralization, with significantly higher mineralization rates in the group of pasture soils at higher levels of moisture conditions. At 150% FC, variation between soils increased for both groups, which is attributed to transient waterlogging conditions. The obtained mineralization rates are to be further correlated to LFOM and HWC.


Tord Ranheim Sveen is a Master’s student at the Office for Environmental Programs, The University of Melbourne. He received his BS (2015) degree from the University of Gothenburg in Sweden. Tord’s general area of interest lies in soil science with agricultural implications, and he is currently finishing his master thesis’ research project on nitrogen mineralisation related to soil organic matter in dairy pasture and cropping soils. After having graduated from his master’s in July 2019, Tord is looking to further deepen his knowledge in the field of soil science and is looking for suitable PhD opportunities.


7th International Symposium
Soil Organic Matter

6 – 11 October 2019

Hilton Adelaide

Adelaide, South Australia


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