Carbon Footprint under Kiwifruit
The capacity for storing carbon under kiwifruit vines
A group of soil scientists from several research organisations recently set out to quantify the storage of carbon both above and below ground in kiwifruit orchards, and to quantify the carbon footprint of kiwifruit production.
They conducted a survey of 40 kiwifruit orchards in the Western BOP, and assessed the carbon footprint of the orchard phase of kiwifruit production. They found no significant differences in the carbon footprint between orchards under conventional and organic management. The carbon footprint of the variety Hort16A was significantly higher than that of Hayward. This is mainly the result of the significantly higher amounts of fertilisers applied to Hort16A compared with Hayward.
They took soil samples down to 1m in around 64 orchards, most in the Bay of Plenty, but also in other major kiwifruit growing areas. They found that there was substantial sequestration of carbon into the soil, which varied between agro-ecological zones and were explained by differences in soil types, climatic differences between regions, as well as the time that a given site has been under its present land use.
They also compared two adjacent blocks of kiwifruit that had been established 10 and 25 years earlier. Soil samples down to 50 cm showed no difference in carbon stocks, but when they sampled down to 1 metre they found that the older block had 6 tonnes per hectare more carbon. This equated to an annual carbon sequestration rate of 400 kg C/ha.
Not content with that they went deep-C drilling – down to 9 metres on a different orchard location. They sampled the 30 year orchard and compared it with an area just over the fence, which had been in pasture over that period.
They found that the orchard had sequestered 6.3 tonnes of carbon per hectare per year more than the pasture, and estimated that the actual sequestration rate was 6.8 t/ha/year. This is a very significant amount. If taken into account in the calculation of the carbon footprint of a New Zealand kiwifruit landed on a UK supermarket shelf, it reduces that footprint by over 40%!
Horticulture and pastoral farming have long been accused of making major contributions to global warming through the use of fossil hydrocarbons in the forms of synthetic fertilisers, pesticides, and fuels for cultivation, maintenance, harvesting, processing and transportation of food products. Northern hemisphere markets have become concerned about greenhouse gas emissions and food miles, and consumers are being urged to buy local and help save the planet. Growers are encouraged to reduce the carbon footprints of their products, or in other words, to reduce the greenhouse gas emissions associated with the production of their goods.
In NZ, the previous government proposed levying carbon taxes on horticulture and farming from 2015 as part of the nation’s commitment to the Kyoto Protocol, and although the present government has rescinded the legislation many people believe it has merely been postponed.
What none of the “expert” government advisers in either hemisphere have taken into account is the sequestration of atmospheric carbon into orchard soils as a result of many decades of consistent management. In fact, the most widely used international standard for assessing the carbon footprint of goods and services, PAS 2050, specifically excludes changes in soil carbon, although there are indications this may change in the new ISO standard 14067 for carbon footprints.
The team sampled around 40 orchards in the Western Bay of Plenty that provides 85% of New Zealand’s kiwifruit harvest. Samples were collected at various depths down to 1m. Preliminary testing had shown that there was no significant difference between samples in the vine rows or between them. Orchards included certified organic as well as conventional integrated management types, and Hort 10A as well as Hayward. They also conducted a survey of these 40 kiwifruit orchards for the assessment of the carbon footprint of the orchard phase of kiwifruit production. In this survey they collected information on all management operations associated with high greenhouse gas emissions, including pest and disease management, soil management, weed control and fertilisation.
Around 24 other orchards, which are all growing the variety Hayward under integrated management, were sampled in other kiwifruit growing regions – Northland, South Auckland, Waikato, Eastern Bay of Plenty, Gisborne, Hawkes Bay and Motueka. Findings included:
- A significant difference in the carbon footprint between Hort16A and Hayward varieties mainly because of the significantly higher amounts of fertilizers applied in Hort16A compared with Hayward.
- No significant difference in the carbon footprint between orchards under integrated and organic management.
- Hot-spots for the carbon footprint of the orchard phase of kiwifruit production were related to fertilisers and compost and the associated greenhouse gas emissions.
- Carbon content increased with the age of the orchard, but this was only significant below 50 cm depth
- A considerable variation between regions in the amount of carbon, ranging from 40 to 600t/ha.
- The greatest carbon sequestration was in Northland and South Auckland and the least in Napier and Motueka. The observed differences may reflect differences in the soil types dominating in those regions, plus climatic differences between regions, as well as the time that a given site has been under the present land use, and systematic management differences between regions (e.g. irrigation).
- A positive correlation between the clay content of the soil and the amount of carbon stored probably because the clay forms complexes with the carbon and physically protects it from mineralisation.
- The Kyoto Protocol that specifies sampling to 30cm is inadequate to do justice to orchard soils. Much carbon was found between 30 and 100cm and beyond. In fact, only about 35% of the carbon in the top 9 metres of kiwifruit soils was located in the top 30 cm soil.
Allister Holmes, Research Manager for PlusGroup, says that the findings are very valuable for Zespri and proves that its sustainability focus is justified. “Perennial horticulture crops like kiwifruit are actually growing soil rather than degrading it, and this is important from a climate change point of view. Kiwifruit orchards are sequestering carbon and helping to reduce greenhouse gases,” he says. “If that soil carbon is taken into account in the calculation of the carbon footprint of a New Zealand kiwifruit landed on a UK supermarket shelf, it reduces that footprint by over 40%. We estimate that New Zealand kiwifruit orchards sequester about 0.9 million tonnes of carbon annually. This has a value on the carbon market of somewhere between $1.5m and $7m. Certainly it should be recognised as a marketing plus and as an offset for any future carbon tax.”