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

Photogrammetry for assessment of pasture biomass

New tools are required to provide estimates of pasture biomass as current methods are time consuming and labour intensive. This proof-of-concept study tested the suitability of photogrammetry to estimate pasture height in a grazed dairy pasture. Images were obtained using a digital camera from one site on two separate occasions (May and June 2017). Photogrammetry-derived pasture height was estimated from digital surface models created using the photos. Pasture indices were also measured using two currently available methods: a Rising Plate Meter (RPM), and Normalised Difference Vegetation Index (NDVI). Empirical pasture biomass measurements were taken using destructive sampling after all other measurements were made, and were used to evaluate the accuracy of the estimates from each method. There was a strong linear relationship between photogrammetry-derived plant height and actual biomass (R²=0.92May and 0.78June) and between RPM and actual biomass (R²=0.91May and 0.78June). The relationship between NDVI and actual biomass was relatively weaker (R²=0.65May and 0.66June). Photogrammetry could be an efficient way to measure pasture biomass with an accuracy comparable to that of the RPM but further work is required to confirm these preliminary findings

Soil inorganic nitrogen in spatially distinct areas within a commercial dairy farm in Canterbury, New Zealand

For precision nitrogen (N) fertilisation of grazed dairy paddocks, soil N distribution needs to be quantified. It is expected that farm infrastructure will affect inorganic-N distribution due to its influence on cow grazing behaviour. Surface soil from four spatially distinct areas (main gate, water troughs, non irrigated and the remaining pasture) was analysed for soil ammonium-N (NH₄⁺-N) and nitrate-N (NO₃⁻ -N) from three paddocks (180 soil samples) on an irrigated commercial dairy farm in Canterbury, New Zealand. Variation between paddocks was higher for NO₃⁻ (P<0.001) than for NH₄⁺ (P=0.52). Differences between spatially distinct areas were detected for NH₄⁺ (P<0.001) but not for NO₃⁻(P=0.37), though there was variation in NO₃⁻ with distance from the gates and troughs. This study demonstrates methods for classifying spatially distinct areas of grazed pasture to quantify their influence on inorganic-N distribution. Further research is required to better understand variability