Pathway to carbon neutral – whole orchard recycling in almond orchards (AL21000)
What's it all about?
This project is quantifying the impact of whole orchard recycling on the carbon footprint of an almond orchard, including the impact on carbon storage and turnover in the soil, soil greenhouse gas emissions and the carbon accumulation by the newly planted trees.
The information gathered through this project will support almond growers to integrate whole orchard recycling into their orchard redevelopment programs with clear expectations around carbon farming, changes in soil health, irrigation use efficiency and productivity improvements. It will also support the almond industry to improve their sustainability credentials, with the potential for whole orchard recycling to underpin practices that will allow the production of carbon neutral almonds.
Almond trees accumulate significant amounts of carbon (such as trunks, branches and roots) during their lifecycle. Unfortunately, when an orchard reaches the end of its commercial life this resources is traditionally managed through burning as part of the orchard redevelopment.
While burning rapidly clears debris from the site and can reduce pathogen load, it also releases a significant amount of carbon that could potentially be sequestered or at least incorporated to improve soil organic matter, fertility and help with it the establishment and productivity of the new orchard.
The alternative to burning the trees prior to replanting is described as whole orchard recycling. This is the pulverisation of the perennial portion of the almond trees and incorporation into the soil prior to replanting.
The project is also assessing any co-benefits from the orchard recycling such as more rapid orchard establishment and improved irrigation use efficiency and soil health and potential negative impacts such as increased pressure from soil pathogens and potential for nitrogen draw down.
Orchard establishment, and a series of experimental and communication activities have been completed.
The experimental trees were planted in August 2022, the primary cultivar was Non Pareil; which was planted in alternating rows with Shasta and Pyrenees. The trees were planted to overlay the three compost treatments – the recycled almond trees, a compost made from almond hulls and waste from a bioreactor and the untreated control. There were multiple sensors and sampling instruments installed, these included nine soil moisture probes (each probe was installed to a depth of 1.2 meters and the probes were replicated three times in each treatment) and an in line pressure sensor to track when irrigation was being applied. The soil and soil water sampling regime commenced, this included the use of soil water extractors (again three per treatment) to track nutrient movement and regular soil samples from the surface 30cm of the profile to track carbon concentration.
The trial design has been completed and the treatments successfully implemented. The trial has three treatments (recycled almond trees, almond hull compost and control) and six replicates. Each replicate is approximately 70m long (half a row). The trees were removed and chipped so the particles would pass through a 50mm screen. The recycled almond trees and almond hull compost were spread across the soil surface at a rate of approximately 50kg/m (65t/ha) and then scraped into a mound. Buffer rows, that will be planted with the pollinator trees, received recycled almond trees at approximately 60kg/m to account for the material that was not applied to the control or the compost treatments.
Sensing equipment has been purchased and is ready for installation after the trees have been planted in August 2022.
Initial (pre-tree removal) soil samples were collected in mid-January. A hydraulic soil corer was used to collect samples down to 60cm in the mid-row and under tree space for carbon analysis; these were divided into two depths for analysis (0-30cm and 30-60cm). An additional sample was collected to 30cm for pathology analysis. Tree and air samples have not been collected as the trees are yet to be planted.
This project is a strategic levy investment in the Hort Innovation Almond Fund