Dynamics and mineralisation of nitrogen in soil fertilised with brown coal-urea blends

Biplob K. Saha1*, Michael T. Rose2, Vanessa Wong3, Timothy R. Cavagnaro4 and Antonio F. Patti1

1School of Chemistry, Monash University, Clayton, Victoria, 3800, Australia

2NSW Department of Primary Industries, Wollongbar Primary Industries Institute, Wollongbar, NSW 2477, Australia

3School of Earth, Atmosphere & Environment, Monash University, Clayton, Victoria, 3800, Australia

4School of Agriculture, Food and Wine, The University of Adelaide, Waite Campus, South Australia, 5064, Australia

*Corresponding author. Email: biplob.saha@monash.edu


Increasing the efficiency of nitrogenous fertilisers is becoming more important due to detrimental effects of N loss on the environment. The addition of humic rich brown coal (BC) as an organic amendment can alter N cycling by reducing its losses in different ways. However, the effect of brown coal-urea (BCU) blends on N cycling is poorly understood. Therefore, a glasshouse incubation study was conducted to assess the effects of BCU blends on the transformation and transport of N in soil. Blending of urea with BC slowed down the fertiliser N release resulting in higher N retention over a longer period of time compared to urea. Over the two-month study, compared to urea, BCU blends generally suppressed total N2O and NH3 emissions by 31% and 43%, respectively. Incorporation of BCU blends in soil maintained significantly higher amounts of mineral and mineralisable N in soil compared to urea application only. This is supported by the leachate analysis data, which showed that less mineral N was leached from soil in the BCU blends compared to urea. The blends with higher proportions of BC had lower NH3 emissions and maintained higher mineral N in soil compared to the blend with lower proportion of BC. Moreover, addition of BCU blends increased the organic carbon content of soil. The overall results suggest that blending of urea with BC can strongly reduce N losses via leaching and gaseous emissions. As a result, greater amounts of fertiliser N will be available to crops over a longer time period, increasing the fertiliser N use efficiency and soil health.