Improving Avocado Production Through Soil Health

A simple soil biology approach increases fruit weight and quality

Healthy soil is the foundation of healthy plants. A trial on an avocado farm near Childers demonstrated that improving soil biology through the use of Humic Acid and Liquid Sea Minerals resulted in heavier fruit, higher sugar levels, and improved soil conditions.

The trial showed that feeding the soil ecosystem improved plants' access to nutrients, resulting in an 11% increase in harvested fruit weight compared with untreated trees.

Note: Bio-Booster was not used in this trial.

The Trial

The trial was conducted on a commercial avocado farm near Childers, Queensland, using the Sheppard avocado variety.

Three rows of trees were treated with:

• Humic Acid: 15 L/ha
• Liquid Sea Minerals: 5 L/ha

The products were applied through the under-tree irrigation system, allowing the treatments to be delivered directly into the soil around the root zone.

Applications were made on:

• 3 October 2018
• 29 November 2018
• 26 February 2019

The treated rows were located in the centre of a field, with the adjoining rows on either side used as untreated control areas for comparison.

Improvements in Soil Condition

By 8 May 2019, noticeable differences were observed in the treated area.

The soil around the treated trees felt:

• Softer
• More friable
• Wetter compared with the untreated rows

This assessment was made independently by two farm workers and two trained agricultural consultants, who all agreed there was a noticeable improvement in soil condition.

These observations suggested increased soil moisture retention and improved soil structure, both important factors for healthy root growth and nutrient availability.

Increased Fruit Weight at Harvest

At harvest, the difference between treated and untreated trees was measured.

The average bin weight from the control rows on either side of the treated area was:

416 kg per bin

The 10 bins harvested from the treated rows averaged:

460 kg per bin

This represented an increase of approximately 11% in fruit weight.

For the grower, this meant more marketable fruit from the same area of land.

Higher Brix Readings Indicate Improved Plant Health

Plant sugars are produced in leaves through photosynthesis, the remarkable process where plants use sunlight, water, carbon dioxide and minerals to create energy in the form of sugars.

This process depends on a wide range of nutrients being available to the plant.

Leaf sugar levels were measured using a refractometer on:

• 2 April 2019
• 8 May 2019

The treated trees recorded Brix readings approximately 10% higher than the adjacent untreated trees on both occasions.

Brix measures dissolved sugars in plant sap and is often used as an indicator of plant vitality. Higher Brix readings can be associated with:

• Improved plant health
• Better fruit flavour
• Increased nutrient density
• Greater plant resilience

Healthy plants are generally better able to resist environmental stresses and are less attractive to many insect pests.

Creating a Positive Soil Cycle

Plants do more than take nutrients from the soil. Through photosynthesis, they produce sugars, and a portion of these sugars is transported through the roots into the soil to feed beneficial microorganisms.

These soil organisms, in turn, help:

• Release nutrients for plant uptake
• Improve soil structure
• Increase soil carbon levels
• Improve water-holding capacity

This creates a positive cycle:

Healthy soil biology → healthier roots → stronger plants → better fruit → more plant sugars returned to the soil

By supporting this natural relationship between plants and soil life, growers can build long-term soil fertility rather than relying only on external inputs.

Economic Return

The cost of the treatment was approximately $200.

The additional production achieved an estimated return of around $600, while also contributing to longer-term improvements in soil condition.

This trial highlights an important principle of regenerative gardening and farming:

Feed the soil, and the soil will help feed the plant.

Healthy soil biology provides the foundation for productive plants, nutritious food and a more resilient farming system.

Refractometer note

A refractometer is a simple instrument used to measure the concentration of dissolved substances, including sugars, in plant sap. The reading is expressed as degrees Brix (°Bx).