Led by AgResearch, research results were collated and proposals for model changes were made*. With the recent update of Overseer, the model will now reflect the effects of plantain’s plant composition on urine nitrogen excretion: less of the excreted nitrogen ends up in urine and urine patches have a lower nitrogen load due to a greater urine volume per animal per day. Depending on the proportion of plantain in the animals’ diet, this will reduce the N leached. Further research on soil processes is planned and may in future result in further updates of the model to also reflect those effects.
FRNL used the cultivar ‘Ceres Tonic’ in the various experiments. Other work suggests similar effects of ‘Agritonic’ but that differences between cultivars exist. New research is planned to develop a framework for verifying which other plant varieties possess the attributes that result in N leaching reductions.
In some regions, farmers will need to report their Overseer nitrogen leaching number to regulators. These regulators will have their own requirements for providing evidence or auditing farm management. The choice of plantain cultivar may be one aspect these regulators will want to verify. Additionally, the percentage plantain in the pasture will need to be entered in Overseer. DairyNZ is developing an easy to use approach to assess plantain content. This will be available as soon as testing is completed and Regional Councils agree that the results are acceptable for auditing purposes.
* The following reports document the process to determine the required model changes, the recommended model changes to reflect plantain and their effects on nitrogen leaching:
1. Integration report – evaluation of FRNL data against Overseer (April 2019)
2. Recommendations for implementation of plantain-based pasture in Overseer (Feb 2020)
3a. Plantain sensitivity analysis (April 2020)
3b. Testing of the Overseer plantain block model (July 2020)