Use of optical sensor to reduce nitrogen inputs to intensively grazed pastures

Nitrogen (N) is one of the most widely applied nutrients to dairy pasture in Australia and New Zealand, with an average annual application of 230 kg N/ha per year. Dairy cows generally excrete 75 to 80% of the N they consume, with the N levels within a urine patch potentially achieving concentrations equivalent to 1000 kg N/ha. Smart-N technology (SN), 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 SN technology on commercial dairy farms in Western Australia and Tasmania. On each farm six plots of between 0.25 and 1.0 ha each were established. Treatments included liquid urea-ammonium nitrate (UAN) fertilizer being applied using the SN technology and UAN applied without using the SN technology (control). In Tasmania, the mean N application rate for the control treatment, averaged across all sites and applications, was 21.4 ± 0. 4 kg N/ha, which was significantly (P 0.05) to the SN treatment at 32.3 ± 1.9 kg DM/ha.day. In Western Australia average pasture growth rates for the control treatment were 27.3 ± 4.9 kg DM/ha.day. The SN plots average pasture growth rate was 23.7 ± 4.7 DM/ha.day which was not significantly different from the control. This study has indicated that significant N fertiliser savings are possible through the adoption of the SN technology without compromising pasture growth rates.