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Quantifying the whole farm systems impact of nitrogen best practice on dairy farms: Milestone 7 report

Citation

Rawnsley, R and Harrison, M and Christie, K, Quantifying the whole farm systems impact of nitrogen best practice on dairy farms: Milestone 7 report, Dairy Australia, Hobart, Tasmania (2019) [Contract Report]


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Abstract

This milestone report details the activities of the Tasmanian Institute of Agriculture for the "Quantifying the whole farm systems impact of nitrogen best practice on dairy farms". The activities and outcomes reported in this report is work undertaken between June 2019 and November 2019. All activities undertaken have been modelling studies, and thus the results are simulated estimates. The University of Melbourne has entered into a funding agreement with Dairy Australia for this project and the project is being undertaken collaboratively between the University of Melbourne and the Tasmanian Institute of Agriculture.

The invited paper titled "Current and future direction of nitrogen fertiliser use in Australian grazing systems" (primary author R Rawnsley) is now published online as part of a Special Issue for Crop & Pasture Science with other invited papers from the Australian Grassland Association Conference, held in Launceston, Tasmania earlier this year. This paper was a review focusing on recent research aimed at understanding the complex interactions between climate, edaphic and farm systems management constraints in order to improve nitrogen fertiliser-use efficiency in dairy pasture systems in Australia. The authors reviewed a range of approaches to advancing best management practices, such as implementing of emerging technologies, alternative feedbase options and predicting soil mineralisation.

The paper titled "Simulated seasonal responses of grazed dairy pastures to nitrogen fertilizer in SE Australia: N loss and recovery" (primary author K Christie) was unsuccessful in being accepted for publication in its original form in Agricultural Systems, primarily due to misunderstandings around ‘perceived’ recommendations for high N fertiliser rates to achieve the pasture growth potential for some site exampled. The resubmitted paper has been reviewed, with the examiners recommending reconsideration following major review. At the time of submitting this milestone report, the paper is being amended and thus is not available to be included in this report.

A continuation of reviewing of the use of nitrification inhibitors to reduce nitrous oxide emissions and nitrate leaching within DairyMod was undertaken by Karen Christie. DairyMod (version 4.9.6) was used to model nitrogen (N) dynamics at Casino, northern NSW (Allansford, south-west Victoria reported in the previous milestone report). The nitrification inhibitor was applied either in autumn or spring with the same efficacy parameters to allow comparison between the two locations. In summary, the use of a nitrification inhibitor in spring was effective in reducing nitrous oxide and leached nitrate over the first 120 days post-application and over the full 12 month period. In autumn, the nitrification inhibitor was effective in reducing nitrous oxide emissions, relative to the control, both over the first 120 days as well as annually. Nitrate leaching increased slightly over the first 120 days when the nitrification inhibitor was activated. However, over the full 12 months, nitrate leaching declined, relative to the control. Pasture production increased when the nitrification inhibitor was activated, irrespective of the season of application. The findings from this study will be incorporated into future communications, such as reviewing of the Fert$mart manual, where applicable (see Appendix 1).

The results of the nitrification inhibitor, applied in spring and autumn at Casino was then compared to previous modelling by Karen for Allansford (milestone 6 report) to ascertain differences between locations and seasons. There was clear merit in applying a nitrification inhibitor at Casino, to increase pasture production and decrease N loss. However, the benefit of applying the nitrification inhibitor at Allansford was variable, with no change in pasture production, relative to the control, and variable results in terms of reducing nitrous oxide and nitrate leaching, depending on the season and the timeframe examined (see Appendix 2).

Karen Christie modelled Five sites throughout Tasmania to ascertain the effect of initial soil organic matter (OM) status and a range of N fertiliser inputs (10 to 50 kg N/ha.month in 10 kg increments) on pasture dry matter (DM) production and N dynamics. Achieving ∼ 20 t DM/ha.annum was possible at all five sites, irrespective of starting soil OM status, when modelled over a 40-year timeframe (1979-2018). A detailed examination of one site, Togari, examined the timeframe and N fertiliser rate required for a low OM status soil to achieve similar DM production to a high OM soil. The timeframe varied between > 100 years when applying 10 kg N/ha.month, compared with ∼ 15 years when applying 50 kg N/ha.month. This study then examined the effect of essentially ‘turning down the N input tap’. Reducing N fertiliser inputs from 50 to 40 kg N/ha.month reduced pasture production by 5%, while environmental N loss (sum of nitrate leaching, nitrous oxide denitrification and ammonia volatilisation) reduced by 24%, predominantly due to a 27% reduction in nitrate leaching.

Item Details

Item Type:Contract Report
Keywords:dairy, nitrogen, nitrate, ammonium, nitrous oxides, pasture, ryegrass, modelling, DairyMod
Research Division:Agricultural and Veterinary Sciences
Research Group:Agriculture, Land and Farm Management
Research Field:Farming Systems Research
Objective Division:Environment
Objective Group:Soils
Objective Field:Farmland, Arable Cropland and Permanent Cropland Soils
UTAS Author:Rawnsley, R (Dr Richard Rawnsley)
UTAS Author:Harrison, M (Dr Matthew Harrison)
UTAS Author:Christie, K (Miss Karen Christie)
ID Code:135816
Year Published:2019
Deposited By:TIA - Research Institute
Deposited On:2019-11-15
Last Modified:2020-03-26
Downloads:0

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