University Of Tasmania
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Use of optical sensor technology to reduce nitrogen fertiliser inputs on dairy farms

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conference contribution
posted on 2023-05-23, 09:46 authored by James HillsJames Hills, McLaren, D, Karen Christie, Richard RawnsleyRichard Rawnsley, Taylor, S
Nitrogen (N) is one of the most widely applied nutrients to dairy pasture in Australia and New Zealand, with an average annual application of around 230 kg N/ha/year. Dairy cattle generally excrete 75 to 80% of the N they consume, with the N loading within a urine patch potentially reaching 1000 kg N/ha. The annual mean urine patch coverage is estimated to be approximately 20-25% of the area of an intensively managed dairy pasture. Urine deposition zones are often visible due to the more intense greenness and increased biomass of these zones. The grass colour and biomass differential provides an opportunity for optical sensors to detect these N rich zones. Smart-N technology, developed by Mackenzie Research Group in New Zealand, uses optical sensors (WeedSeeker®) to detect N rich zones in order to avoid application of liquid N to these areas. This study explored the use of the Smart-N technology on four commercial dairy farms in Tasmania. On each farm six plots of between 0.25 and 1.0 ha each were selected, giving three replicates of each treatment. Treatments included liquid urea-ammonium nitrate (UAN) fertilizer applied using the Smart-N technology (SN) and UAN applied without the Smart-N technology (control). Repeated applications (between 2 and 6) occurred at each site. Averaged across all sites and applications, the mean N application rate for the control treatment was 21.2 ± 0.6 kg N/ha which was significantly (P < 0.05) higher than the SN treatment, 12.9 ± 0.8 kg N/ha. Averaged across all sites the mean average pasture growth rate was 33.2 ± 2.4 kg DM/ha/day for the control treatment and 34.4 ± 2.5 kg DM/ha/day for the SN treatment, which did not significantly (P > 0.05) differ from each other. This study has indicated that significant N fertiliser savings are possible through the adoption of the Smart-N technology without compromising pasture growth rate, although further work is required to validate these findings. For the average Tasmanian farm, it is estimated that the Smart-N technology has the potential to save approximately 8 t of N per annum. This equates to a potential greenhouse gas abatement of approximately 50 t CO2-e. Assuming that the adoption of the Smart-N technology satisfied the requirements as a Carbon Farming Initiative method and at a carbon price of $23 per t CO2-e, the potential CFI income is $1,150.


Publication title

Proceedings of the 6th Australasian Dairy Science Symposium


J Roche




Tasmanian Institute of Agriculture (TIA)


Australasian Dairy Science

Place of publication

New Zealand

Event title

6th Australasian Dairy Science Symposium

Event Venue

Hamilton, New Zealand

Date of Event (Start Date)


Date of Event (End Date)


Rights statement

Copyright 2014 Australasian Dairy Science Symposium

Repository Status

  • Open

Socio-economic Objectives

Sown pastures (excl. lucerne)

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