AgriGro Compost vs Single Super: Comparison Trial on Mixed Permanent Pasture

Trial Overview

This trial aims to compare plant responses to a single super application with those of a Bio Gro Agri-Gro compost. The application rates used were the area’s conventional super application rate and a compost application rate of the same economic value. Different rates of compost are also compared within the trial. The aim of this trial is to reduce the amount of phosphorus applied in a mixed permanent pasture by substituting single superphosphate with compost. The goal is for the compost to increase microbial activity in the ground, in doing so freeing previously unavailable phosphorus into the plant. Results showed that the compost samples showed a higher increase in pasture growth, increased minerals, as well as an increase in dry matter compared to single super. This Trial will continue in 2026, using a larger area to replicate this trial to increase the reliability, accuracy and validity of results.

AgriGro is a high-quality base compost designed for agricultural use.

Figure 1 (above): Image of Trial site, 10km out of Mount Gambier on the starting date of the trial (14/8/2025)

Purpose of Trial

Nitrogen is the most important element in the growth and production of plants in agricultural systems. Second to this is phosphorus. However, its complex relations with the soil make phosphorus fertilisers largely inefficient and cause growers to use large amounts to meet the plant’s needs.

Single super phosphate is a finite resource and very inefficient, particularly in calcareous soils, which are common in South Australia. Contrastingly, compost is a renewable resource, and despite relatively low levels of phosphorus, it offers other nutrients that single super does not, as well as microbial activity that may help cycling unavailable phosphorus from the soil to the plant.

This trial will examine the effects of substituting single superphosphate with compost on pasture growth and production.

Methodology

Trial Objectives

• Compare plant responses from different products of the same economic value.

• Assess how compost applications compare to conventional fertiliser inputs.

Location: 

• 10km south-east of Mount Gambier, South Australia. (Figure 1)

Crop Type

• Mixed permanent pasture

Timing

• Start date: 14/08/2025

• End date: 31/12/2025

Treatments

• Control – No compost applied

• Single Super Phosphate – Spread at 125kg/ha

• AgriGro – Spread at 1.6t/ha

• AgriGro Double Rate – Spread at 3.2t/ha

• AgriGro Half Rate – Spread at 0.8t/ha

Measurements

• Biomass – measured once, 6 weeks after application

• Feed quality – test on 1.6t/ha compost and single super treatments only

Spreading cost

• Conventional management in this area involves spreading 125kg of single super per hectare. Considering the cost of product, freight, and spreading, the cost of spreading 125kg of single super is the same as 1.6 t/ha of AgriGro compost.

Results

Figure 2: Graph comparing Product (X axis) to Dry Matter (Y axis)

• All treatments increased pasture growth, except the half-rate compost treatment.

• The single-rate application of compost increased pasture dry matter by 115kg/ha compared to the single super treatment.

• The double rate of compost had 266kg/ha more dry matter than the half rate.

• The compost applied at 3.2t/ha (double rate) was 35kg/ha less, and the 0.8t/ha (half rate) was 301kg/ha less than the compost spread at 1.6t/ha.

• The double rate does not appear to be economically viable, but this may be due to differences in pasture composition in this small plot design.

Table 1: Comparing Forage Quality Parameters in Single Super and Compost

• Dry Matter, Crude Protein and ADF remain relatively stable in both treatments.

• AgriGro compost has greater digestibility and ME than the single super sample. With both ME and digestibility increased, the feed conversion from pasture to livestock gains will be greater.

• NDF is higher in the compost sample than in the single super sample. With a higher NDF, feed intake may be limited as livestock feel fuller from less feed. With better feed digestibility and higher ME content, animal performance should not be limited. Stock rate should increase.

• WSC, fat, and ash appear to be higher in the single super sample than in the compost sample. Despite higher WSC and fat in the single super treatment, ME remains higher in the compost treatment.

This suggests that compost provides both valuable nutrients to the plant and enables more efficient nutrient uptake.

Table 2: Comparing Minerals in Single Super and Compost

• Interestingly, single super did not increase phosphorus levels in the plant and had a lower sulphur result, despite being a phosphorus and sulphur fertiliser.

• The compost sample shows higher levels of potassium, magnesium, sodium and sulphur. However, it does have lower levels of calcium.

• The compost treatment having higher levels of these minerals in the pasture provides a more well-balanced feed for livestock.

Key Findings

• Compost consistently delivers greater pasture growth than single super phosphate when both applied at an equivalent cost
  
  
• Compost samples also showed an increase in minerals and dry matter in comparison to single super
  
  
• Compost samples demonstrated a greater potential for improved livestock outcomes due to higher ME and NDF
  
  
• Compost samples overall improved the quantity and quality of pasture compared to the single super treatment

Summary

AgriGro compost consistently delivers greater pasture growth than single super phosphate when both are applied at an equivalent cost. As rates increase, pasture production generally rises as well, which is evident in the half and double rate compost treatments. Although the comparable and double rates don’t follow a perfectly linear trend. Even so, compost still improves both the quantity and quality of pasture relative to single super. While these gains may appear small at the plot scale, they become far more significant when applied across an entire paddock, given that the cost of the product and its application is the same. A larger trial will now be undertaken in 2026, and its results will be compared with this initial study to strengthen confidence in these findings.

This trial was conducted on small plots, so while the findings are useful, larger plots will be needed to produce more conclusive results. There were clear differences in pasture composition between plots, which is important to consider when interpreting the data. The single super and comparable rate compost treatments showed similar pasture composition. The half- and double-rate compost treatments also aligned closely, while the control plots contained a mixture of both compost compositions. For this reason, comparisons will only be made between plots with similar pasture composition to ensure fair and accurate interpretation. All data was collected on 12.09.25, with pasture biomass measured using a Grass Master Pro and feed quality analysed by Agrifood Technology Feed Test.

Contact us to learn more about Bio Gro agricultural soil amendments and how they can benefit your land and farming operation.