An emphasis of pasture first in respect to dairy farms is underpinned by legume pastures being a high quality and cheap form of feed for cows. So it’s no surprise that with a focus on pasture there is an accompanying focus on soil fertility to ensure pastures are given the very best opportunity to perform.

Despite our best efforts, soil fertility on dairy farms, whilst generally flat in topography, will also vary due to different soils, effluent applications, forage cropping, animal transfer through dung and urine, supplementary feed and fertiliser spreading.

Currently Whole Farm Soil Testing (WFST) provides the most detailed picture of this soil fertility variability by soil testing each paddock (or parts of paddocks) individually. Ravensdown has been offering WFST since 2011. Once you have identified which paddocks will benefit from maintaining/increasing soil fertility or withholding fertiliser across the farm, then variable-rate spreading technology can be used to ensure the farm is at its optimum soil fertility giving the opportunity for pastures to thrive. This benefit is not only about maximising the return on fertiliser spend but also about reducing excessive soil phosphorus (P) levels, which increases the risk of P loss to waterways. Managing soil fertility levels is important for farmers to manage this risk by withholding P fertiliser from high fertility areas. This can be significantly enhanced if they can be spatially defined accurately.

Building on the promise that AirScanTM technology is showing on hill country farms within the ‘Pioneering to Precision’ Primary Growth Partnership, Ravensdown has begun research to establish if similar benefits can be developed on dairy pastures between remote sensing imagery, plant nutrients and soil fertility. With a focus on soil phosphorous (Olsen P), the high resolution that the remote sensing imagery can achieve of 1m2 provides dairy farms with the potential to obtain soil fertility maps to a level of precision beyond what WFST can achieve. This has exciting implications when you extend this to the technology’s ability to cover large geographic areas in a short space of time (1,000ha an hour – conducting the equivalent of 10,000 soils tests per hectare) which means that multiple dairy farms will be able to be surveyed in a single day. 

The research programme for dairy pastures is into its second year, calibrating its collection of remote sensing imagery. Soil and plant samples from farms in Waikato, Taranaki, Manawatu, Canterbury and Southland make up a large dataset, encompassing the variation found within dairy pastures. This is critical to validating the robust relationships between remote sensing and soil fertility.

If the technology proves effective for predicting soil fertility across extensive and intensively managed pastures, then it offers huge potential for enabling variable-rate fertiliser strategies that will not only maximise the return on every fertiliser dollar spent but will equally improve our environmental footprint.