POMEWEST PIPS 3

Orchard floor management 

FINDINGS FROM PIPS 3

During the PIPS 4 Profit Roadshow from 28–29 August 2024, orchard floor management and choice of beneficial plant species in the interrow was a good topic of discussion. Below is a summary of the PIPS 3 findings that may guide grower management for the orchard floor in 2024 and beyond.

Words Jennifer Riseley, Project Officer, Pomewest

FARMERS understand very well that an orchard is a system, with changes in one area influencing outcomes in others. At times, methods that improve yield productivity or lower financial costs are not always sustainable in the long term. The PIPS 3 project looked at ground cover options for the interrow and under tree that provide benefit to tree health, nutrition, water availability and orchard resilience, the demonstration site was Ladycroft Orchard in Manjimup.

Treatments included both interrow and under tree applications, applied in spring 2020 (see Table 1).

Living plants in the interrow and under the treeline brought a range of benefits:

• Shelter and food source for pollinating species of bees, flies and moths

• Pest and disease regulation, providing shelter for beneficial predators

• Weed suppression

• Nutrient cycling from rootzones reaching different depths

• Maintaining soil structure and chemical fertility

• Regulating soil and water quality

• Minimising erosion from rainfall or vehicle movements

Improvements to soil health can be measured in different ways:

• Texture

• Structure —impacts air exchange, water filtration, root growth

• Porosity —fine soils can hold more water than coarse soils

• Bulk density – indicates compaction, influenced by organic matter and influences nutrient uptake

• Water holding capacity

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Under-tree treatment planted with pollinator mix in PIPS 4 Profit.

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Under-tree treatment using compost in PIPS 4 Profit.

Findings

Of the under-tree treatments the following effects were seen on the soil:

• Compost treatment saw improved microbial carbon content, aggregate stability, bulk density, hydraulic conductivity, water infiltration, nitrate nitrogen, phosphorous, potassium.

• Grass/legume treatment saw improved bacterial diversity, highest microbial respiration, earthworm numbers, soil bulk density, hydraulic conductivity, less acidic pH, higher ammonium nitrate.

• Compost was generally higher in nutrient than the control and grass/legume mix. The trial saw a more neutral pH, higher organic carbon, less sodic, more organic carbon, more Phosphorus, more Potassium (in year one but not three), many times higher exchangeable Carbon, Magnesium, Manganese, Sulphur, Zinc.

Soil analysis results are summarised in Tables 2 and 3 showing the differences between 2021 and 2023.

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PIPS 4 Profit Demonstration Site, Ladycroft Orchard Manjimup.

Impact on tree growth and crop load

Treatments had no impact on tree growth, blossom density or crop load.

There were small differences in brix and dry matter, though this was inconsistent across seasons. Grass/legume plots saw higher firmness, more redness, slightly heavier fruit and slower conversion of starch to sugar. The compost treatment had the least redness and lighter fruit in the 2022 harvest, but heavier than the control in 2023.

In year two the compost plot saw slightly later leaf fall, perhaps due to higher soil nutrient, though changes are generally slower.

Considerations in the orchard

Under-tree plantings can become a fire hazard in summer if allowed to grow too long. Similarly, tall plants can allow pests access to the tree canopy so choose plants with a low habit or ensure you can mow regularly. Compost applications can become expensive if annual application is required, by year three during the PIPS 3 trial the initial nutrient differences from the compost application were no longer significantly different to other treatments as the product had been broken down. However, in 2024 when planting native ground covers for PIPS 4 Profit it was quite evident which bays had been treated compost previously as the soil was much more friable and easy to dig and plant.

Conversation during the August 2024 field walk highlighted concerns for possibly excessive nitrogen in spring/summer from clover mixes planted under pink fruit varieties.

PIPS 4 Profit will consider all facets of fruit quality including colour when assessing treatments.

Managing pests

Ground cover composition was found to impact arthropod diversity. The living mulch within tree-line encouraged predators like spiders and earwigs. Non-pest mites also increased where compost was applied. No fruit damage was seen from either treatment condition with inspections in December, January and March. Ground covers may also suppress ground dwelling pests in winter and woolly aphid in summer as the compost or tree-line mulch harbours ground dwelling predators. During the PIPS 3 trial it was difficult to allow plants to flower and set seed to see the full benefit of an interrow sward.

The PIPS 4 Profit project will further trial under-tree treatments analysing benefits to the soil as well as closely monitor impacts to tree health and fruit quality.


MORE INFORMATION

Jen Riseley, jen.riseley@dpird.wa.gov.au, (08) 9777 0185.