Fertiliser demonstration

Fact sheet 2025

What was done

In conjunction with the KI Landscape Board, a demonstration was established on a property at Roo Lagoon to evaluate the performance of various fertilisers in addressing plant nutritional health. On the 31 July 2024, Neutrog Prolifer8 and single super phosphate (SSP) were spread at 125kg/ha by a local contractor as illustrated in Figure 1. On the 1 August, a foliar liquid fertilizer called the Australian Soil Planners (ASP) Autumn brew was foliar applied by motorbike at water rate of 140L/ha (meant to be 100L/ha = $80/ha).

Treatments

ASP: Liquid fertiliser containing calcium, phosphorous (as micronized guano), magnesium, sulphur, nitrogen as ammonium, zinc, copper, boron, selenium, cobalt, manganese, boron and fermented kelp.

SSP: single super phosphate - 8.8P, 11S, 21Ca

NeutrogProlifer8: pelletised biologically activated, phosphate boosted fertiliser, coated with microbes that liberate and solubilise phosphate, fix nitrogen and improve plant resilience.

1.75N, 6P, 1.15K, 0.55S, 17Ca, 0.85Mg, 0.004Mn, 0.003Zn

Control: Nothing

A background soil test of the paddock was performed in May 2024, the results of which can be found in Table 1.

Table 1. Key background soil test measurements, May 2024

Two months after the fertiliser application, sap tests which are akin to a blood test in humans, were taken from each of the zones to determine the plant nutritional status. The results can be seen in Table 2.

Table 2. SAP test results - species: sub clover, 30 September 2024

• Green cells are the highest measurement for each nutrient.
• Red numbers indicate the measurement was below desirable levels.

What happened

Being a paddock demonstration there is a lot of variability so please to interpret with a bit of caution.

The total phosphorus reading of 439 is a reflection of the high phosphorous buffering index (PBI) of the soil. In other words, the soil has a high tendency to adsorb phosphorus on the soil particles locking it away from root access. In light of this high PBI, the adjusted Colwell Phosphorus target is ~38, meaning that the soil phosphorus level is below optimum.

SAP Tests

• The sap test of the control showed low sulphur, copper, iron and manganese.
• All treatments lifted sulphur levels into desirable range.
• ASP and Prolifer8 increased copper levels into the desirable range. This was despite Prolifer8 not containing copper in the analysis.
• ASP and the Proflier8xSSP treatment increased manganese into the desirable range.

All treatments lifted iron levels but the iron levels were still insufficient (no treatments applied iron). KI soils contain a lot of iron but it is in the oxidized/rust (Fe3+) form thus it is not physiologically available to the plant. The plant will take it up, but it cannot use it because it is oxidized. Plants need the reduced form (Fe2+).