Improving nitrogen use efficiency in subtropical dairy systems – A modelling approach using POAMA and DayCent

Martin Labadz1, Clemens Scheer1, David W. Rowlings1, Beverly Henry1, William Parton2, Peter Hayman3, Oscar Alves4, Griffith Young4 and Peter Grace1

1 Institute for Future Environments, Queensland University of Technology, 2 George Street, Brisbane QLD 4000, Australia

2 Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523, United States

3 Government of South Australia, SARDI, 2b Hartley Grove, Urrbrae SA 5064, Australia

4 Centre for Australian Weather and Climate Research, Melbourne, Victoria, Australia


The DayCent biogeochemical model was used to assess the applicability of POAMA-2 weather forecasts to assist dairy farmers in future nitrogen fertiliser decisions. Simulated soil mineral nitrogen, water-filled pore space, and biomass was calibrated and validated against field measurements from a dairy farm in subtropical Queensland, Australia, for the season 2012/2013 with a ryegrass/kikuyu rotation. DayCent was able to predict water movement in the soil profile, soil nitrogen dynamics and biomass production; however, there were some discrepancies between simulated and measured mineral nitrogen content in the soil and biomass production. This study showed that combining weather forecasts with biogeochemical models as a decision support tool for farmers to estimate mineralisation and assess N fertiliser demand is a promising approach to avoid excessive nitrogen application for dairy cropping systems. However, there are still shortcomings in an accurate simulation of soil nitrogen turnover and plant nitrogen uptake, in particular in highly fertilised systems such as the one presented here. More confidence in the accurate representation of the complex nitrogen transformation processes on dairy farms in biogeochemical models is necessary to use weather forecasts as fertiliser nitrogen decision support tool.