Exclusion zones for variable rate nitrogen fertilisation in grazed dairy pasture systems in New Zealand

To assess the variability of total soil nitrogen (TN) on grazed and irrigated pastures, TN was quantified from spatially distinct “areas” within the paddock (irrigated and non-irrigated areas, around the gates, and around the troughs) on two dairy farms located in Canterbury, New Zealand. During soil sampling, each area was sub-divided and multiple soil samples were taken to ensure adequate spatial representation of each area. The results showed there were no differences in TN between the farms, but differences were detected between the paddocks (P < 0.001), largely due to the significant interaction between the areas (gates and troughs) in different paddocks (P < 0.001). The greatest variability in TN was around the gates, due to either much higher or lower TN near the entrance of the gates. The TN levels returned to concentrations that were similar to those in the surrounding pasture after 4 m distance from the gates. This study shows while TN concentrations are relatively consistent spatially within pastures, there is high variability in TN in proximity to some farm infrastructure, such as gates and troughs.