Updated: Oct 12
The NIWA climate outlook indicates that we will continue with the La Niña weather pattern for the rest of the summer. La Niña weather patterns always make for more challenging irrigation seasons due to more frequent rain events, warmer temperatures, but fewer ‘hot-days’. They are the seasons when you receive the biggest payback from closely monitoring your irrigation scheduling, which also minimises the risk of nutrient leaching.
Given this we thought it would be useful to touch on the current available options to monitor soil nitrogen and the challenges and opportunities of these.
There are a couple of proven commercial sensors on the market that can measure Volumetric Ion Content (VIC) and/or Electrical Conductivity (EC) of the soil. While these sensors cannot directly provide a direct measurement of the concentration of nitrate and ammonium ions in the soil, they can be calibrated to provide a measure of overall soil fertility, the distribution of nutrients down the soil profile, and therefore an indication of soil nutrient leaching events.
An example of this would the Sentek TriSCAN soil moisture probe that is widely used overseas in orchards and vegetable crops for this purpose. Primary Insight is currently in the process of calibrating this sensor for the common Canterbury soils.
There are some promising new soil nitrogen sensor technologies nearing commercialisation that will potentially become available for the 2023-24 season but more likely for 2024-25. However, the cost-benefit of these is yet to be proven.
Regardless of whether soil nitrogen sensors appear on the market in the future or not, one key consideration is how useful will they be? We have doubts around their value in a grazed pasture scenario due to the ‘urine patch effect’. A North Island study that looked at the number of sampling points required to get a representative leaching value under dairy pasture using drainage flux meters (small lysimeters) came up with the answer of ‘lots’ due to soil and urine patch spatial variability.
Given this, installing a single point sensor in a paddock will not be that useful unless cows can be taught to strategically urinate around the sensor! In the case of cropping, while there are less variables at play, a single sensor will still likely be challenging to obtain useful data from. Where these sensors potentially have application is in conjunction with remote sensing, ground-truthing hyperspectral imagery.
Remote sensing will be the way forward for obtaining more frequent measurement of soil nitrogen. However, until reliable, cost-effective, and user-friendly remote sensing technologies appear on the market, the best way to get a measurement of soil nitrate levels is still to take a soil test, and supplement this with the quick-N test during the growing season, obviously ensuring you follow the soil sampling protocols for both!
The team at Primary Insight would like to wish all irrigators a Happy Christmas and look forward to working with you in 2023.