Carbon Storage (Sequestration)

Avocado orchards have a significant capacity to remove CO2 from the atmosphere and sequester (store) it in the soil.  All plants can do this, but trees are the most likely to sequester large amounts of CO2.  This is the basis of buying carbon offsets in many situations.  The CO2 emissions that come from your car, household or overseas holiday are offset against CO2 that can be absorbed by trees from the atmosphere and sequestered in the soil.  Usually for companies to claim these offsets the trees have to be guaranteed to be in place for 100 years or the stored CO2 in the soil will be returned to the atmosphere.  Avowest has been growing avocado trees for nearly 40 years and we have no intention of stopping. 

Modelling of carbon sequestration in orchards has not been carried for many types of tree crops.  Encouraging results have been found with many crops that have been tested.  Old kiwifruit vines in New Zealand have been shown to store 190 tonnes of carbon per hectare more than pasture1.  A vineyard in Orange has been shown to have a positive carbon input of 69 tonnes per year2.  Apple production systems in New Zealand could be considered as carbon sinks due to their net sequestration of CO2 3.  Studies in Italy showed the potential of apple, citrus, olive and peach orchards to sequester carbon.4

Image result for carbon sequestration model trees soil

Unfortunately modelling of carbon storage has not been carried out with avocado.  We can see from own our own observations though that this is occurring.  The soils on which most of Avowest’s avocados are grown on are very sandy and in their original state contain less than 1% organic matter.  Soils are the largest terrestrial sink for carbon on the planet. 

Carbon adding
Soil change from carbon adding

Above are pictures of soil that our avocado trees have been adding carbon to from the atmosphere.

Below is what the soil started off as. 
The difference in stored organic carbon is obvious.

Before Carbon storage

At Avowest our farming techniques allow carbon to sequestered in two ways.  Firstly, our trees do what all trees do naturally.  Living roots release sugars and other exudates to encourage their microbial environment, including supporting mycorrhiza.  In a healthy Californian soil an estimated 20,000 km of hyphae, or fungal filaments, were found beneath every square meter of soil5.  This has been referred to as the wood wide web.  Also as tree roots die the carbon that is within them is more likely to stay in the soil than to be released back into the air. 

WOR – Whole Orchard Recycling

The second thing Avowest does to encourage carbon sequestration is to use whole orchard recycling (WOR).  All prunings from our trees are mulched on site.  These prunings are broken down first by fungal and then bacterial populations returning carbon to the soil.  WOR affect deep soil profile and dissolved organic carbon is an important product.  Not only is the carbon content of the soil increasing but leaching is likely to be lowered with better retention of the orchard’s nutrients.

This is mulched on site with a forestry mulcher.

Forestry Mulcher
Terex

When it’s all finished it looks like this.  The carbon dioxide that was absorbed by the trees and pruned off can now add to the organic matter content of the soil.

A tree in a forest

A University of California project with almonds has shown that WOR increased carbon stored in the soil between 5.8 to 8 tonnes per hectare (Wolff and Guo, 2019)


Other greenhouse gas emissions

Orchards that use any form of nitrogen fertiliser (including organic forms) can emit a potent greenhouse gas called nitrous oxide (N2O).  This has a global warming potential 300 times greater than carbon dioxide (CO2).  The emissions of nitrous oxide are greatest when either applied excessively, or to waterlogged and compact soil.  At Avowest are fertiliser applications are applied at low doses when our trees need the nitrogen.  We are also careful to avoid over irrigation which is not just a waste of water but also a potential source of greenhouse gas emissions


References

  1.  Gentile, RM and Perie, E and Muller, K and Deurer, M and Mason, K and van den Dijssel, C and Clothier, BE and Holmes, A and Hardie, M and McLaren, SJ, Quantifying the potential contribution of soil carbon to orchard carbon footprints, Acta Horticulturae, 17-22 August 2014, Brisbane, Australia, pp. 461-466. ISSN 0567-7572 (2016) [Refereed Conference Paper]
  2. Goward J. and Whitty M., 2014 Estimating and Predicting Carbon Sequestration in a
    Vineyard using Precision Viticulture Techniques.  Proceedings of the 19th Association of Public Authority Surveyors Conference (APAS2014)
    Pokolbin, New South Wales, Australia, 31 March – 2 April 2014
  3. Page, Girija. (2011). Modelling Carbon Footprints of Organic Orchard Production Systems to Address Carbon Trading: An Approach Based on Life Cycle Assessment. HortScience: a publication of the American Society for Horticultural Science. 46. 324-327.
  4. Scandellari, F, Caruso,G, Liguori, G., Meggio, F., Palese, A. M; Zanotelli, D; Celano, G; Gucci, R., Inglese, P., Pitacco, A. and Tagliavini, M A 2016.  Survey of carbon sequestration potential of orchards and vineyards in Italy.  European Journal of Horticultural Science. 81. 106-114. 10.17660/eJHS.2016/81.2.4.
  5. Velasquez-Manoff, Moises (2018-04-18). “Can Dirt Save the Earth?”. The New York Times. ISSN 0362-4331. Retrieved 2018-04-28.

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