Fert Options with Robin Boom Agronomic Advisory Services

 As the recipient of the Ray Brougham Trophy for 2018, Dr Ants Roberts, the chief scientific officer for Ravensdown, gave three lectures – at Ruakura, Massey and Lincoln – in August.

The Ray Brougham Trophy is awarded each year by the New Zealand Grasslands Trust to somebody who has made a significant contribution to pastoral agriculture in New Zealand.

Dr Roberts talk was entitled ‘Soil Fertility Finangling: A Curmudgeons View’. The talk itself can be viewed online at https://www.youtube.com/watch?v=4eCnFZ9Tros

In the last few decades there’s been a number of articles in the farming press on sustainable and regenerative agricultural practices by self-proclaimed experts, who are critical of conventional fertiliser practices.

In his talk Dr Roberts discussed a number of these ‘alternative’ approaches to soil fertility, yet which have failed to show merit when put through scientific rigour.

His criticisms included Fine Particle Application or liquification of mainstream fertilisers, the Base Saturation Cation Ratio theory – sometimes referred to as Albrecht theory – the use of humates to build soil organic matter levels, and dicalcium phosphate compared to using superphosphate and lime.

Fine particle application

With FPA he referred to trial work which showed that regardless of whether a product is sprayed on or applied in dry granular form, there is no difference in overall production – and it is the quantity of nutrient applied which determines the response.

The Base Saturation Cation Ratio theory was promoted by Dr William Albrecht from Missouri State University in the 1940s and 1950s. The theory is there is an ideal ratio of the positive elements –cations – calcium, magnesium, potassium and sodium which are attached to the negatively charged soil particles where calcium should make up 60-75 per cent, magnesium 10-20%, potassium 2-5% and sodium 0.5-5% of the exchange sites of the soil’s CEC (Cation Exchange Capacity). Later trial work showed there is no ideal ratio, but that these elements should be applied to the soil based on whether they were deficient or not using the SLAN method (Sufficiency Level of Available Nutrients) which we use here in New Zealand (MAF Units) for calcium, magnesium, potassium and sodium.

Overseas research showed that sufficiency levels are a better predictor of crop responses compared to using base saturation ratios. After Dr Roberts gave his talk in Hamilton I mentioned to him some recent research done by Dr Tim Reinbott of Missouri State University which he presented at the American Society of Agronomy and Soil Science Society of America annual conference last year. Dr Reinbott’s research showed that using the Albrecht system gave improved yields in corn and soya bean crops and that there were some soil health improvements using the Albrecht approach compared to the conventional fertiliser input approach.

Humates

For me personally, when advising farmers, I consider both base saturation ratios and sufficiency levels as I think there is some overlap in terms of production and quality and in the case of livestock, particularly dairy cows, that having correct calcium-potassium and magnesium-potassium ratios can improve animal health.

When it came humates, which are extracted from lignite and leonardite coal seams, Dr Roberts showed most of our soils already have large quantities of organic matter and soil carbon, and how adding a small amount of humate products (humic acid, fulvic acid and humin) would make very little difference.

He stressed the importance of trying to maintain good organic matter levels as it provides so many benefits including improved moisture and nutrient retention, reducing soil compaction and surface crusting, improving water infiltration, providing food and a valuable home for important soil micro-organisms and earthworms, preventing soil erosion and nutrient run-off, and improving the macro and micro porosity of the soil.

Blends

As for reverted and dicalcium phosphate fertilisers, Dr Roberts showed there was no greater value in using these compared to applying lime and superphosphate separately.  The only exceptions where dicalcium phosphate products could be more beneficial than superphosphate are the Pakihi sand soils of the West Coast, the podsol soils of Northland and raw peat soils in the Waikato where the Anion Storage Capacity is very low, and phosphorus is prone to leaching out, so having less soluble forms of phosphate might be advantageous.

Robin Boom, CPAg, member of the Institute of Professional Soil Scientists. Ph: 0274448764.