Summary of: Using Humic Compounds to Improve Efficiency of Fertiliser Nitrogen

Schofield, Watt & Schofield (2013). On-farm trials, Fertilizer and Lime Research Centre.

On-farm work led by Dr Phillip Schofield, whose PhD is in soil microbiology and plant science, on a commercial dairy near Ashburton, testing whether adding humic compounds to nitrogen fertiliser grows more pasture per unit of nitrogen. Three trials over four years, on half-paddock plots, a paddock split down the middle with one treatment each side, under irrigation.

It tested three things: granular urea with and without a little humic acid; granular urea against dissolved (foliar) urea carrying humic compounds and biostimulants at a much lower N rate; and dissolved urea with and without humic added.

What the authors reported:

• Adding humic to granular urea grew about 9% more dry matter over a year, though they note this one was not statistically significant, the plot-to-plot variation was too high to be sure.
• The dissolved urea with humic and biostimulants grew roughly three times more dry matter per unit of nitrogen than granular. That treatment ran at far less N, so it’s an efficiency-per-kilo figure, not more grass overall.
• Adding humic to dissolved urea grew about 14% more dry matter, significant on four of five harvests, an extra 2,681 kg DM/ha over the trial.
• On the farm’s own records across the four years, nitrogen use fell from 250 kg N/ha to between 80 and 100 while measured pasture held or rose. The authors read this as maintaining production on about a third of the nitrogen.

How we’d read it: this is on-farm work from someone well qualified to run it, and it points in a direction a lot of farmers are exploring. A few things to hold in mind. The thing being tested is the humic compound, and where the big efficiency gain shows up, the foliar treatment also had biostimulants and a much lower rate, so several things changed at once and you can’t pin it on any one. It’s a single farm with one plot per treatment rather than a controlled replicated trial, so treat it as a strong lead, not proof. The “a third of the nitrogen” figure comes from the farm’s own four-year records, not a controlled comparison, so it carries everything that farm changed over that time. The leaching points are modelled, not measured here. The paper also discusses animal-health observations, which sit outside what we’ll comment on and aren’t something a fertiliser or machinery company can speak to, so we’ve left that for you and your vet.

Short version: humic compounds and foliar look promising here for growing more pasture per kilo of nitrogen, on one farm, with the humic doing much of the work and the rest of the system moving alongside it. Worth a read and worth trialling on your own place. Not proof you’ll get the same.