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Valuable horticultural asset is up to 9 metres underground


20 November 2012

Researchers show one of our most valuable horticultural assets is up to nine metres underground

A research report released this month by PlusGroup Research provides an underground map profiling the organic carbon stores that lie in the soil deep below kiwifruit orchards in key growing regions across New Zealand.

“The findings of the report stand to challenge current thinking and orchard management practices across New Zealand’s perennial tree crop industries including avocado, pipfruit and summerfruits,” says Allister Holmes of PlusGroup Research. “This could potentially lead to significant financial benefits for growers and ecological benefits for New Zealand.”

In the first study of its type, undertaken within the New Zealand kiwifruit industry, researchers measured Soil Organic Carbon (SOC) and estimated the rate at which kiwifruit vines convert atmospheric carbon dioxide (CO2) to SOC in the process known as carbon sequestration.

SOC is a critical natural capital for primary producers. Soil rich in organic carbon provides growers with a natural advantage and numerous production benefits. The soil has a greater ability to store water and nutrients, highlevels of healthy microbial activity, and may contribute to the natural control of potential agricultural pests. High levels of SOC are known to improve soil drainage and enhance root penetration, ultimately protecting kiwifruit vines from the effects of both extreme wet and dry periods synonymous with climate change.

The research study investigated soil samples from 104 kiwifruit orchards across different kiwifruit growing regions of New Zealand. Both Hayward Green and Hort16A Gold orchards were sampled at various depths. The individual orchard management regimes were noted as well as the age of the blocks sampled.

Key findings of the study included:

• Northland orchards recorded the highest SOC and the lowest SOC readings were in Hawkes Bay

• Older, more established orchard blocks sequestered more carbon and at a higher rate than younger blocks

• Soil at a depth of nine (9) metres under a 30-year-old kiwifruit orchard carried a SOC level significantly higher than pasture soil at a depth of nine (9) metres

• Hayward Green kiwifruit caused significantly less greenhouse gas emissions per kg of fruit in the orchard phase than Hort16A Gold kiwifruit

• The New Zealand kiwifruit industry sequesters approximately 90,000 tonnes of carbon annually.

The results of thisstudy have immediate practical applications for New Zealand kiwifruit growers and future financial benefits. Kiwifruit growers are continually looking for ways to reduce orchard inputs, such as fertilisers and protective sprays, without compromising fruit quantity, quality, size, taste or storage life.

“By fully understanding the SOC profile of their orchard, a grower may be able to tailor orchard management practices to maintain and improve SOC, harnessing the natural water storage capability and the nutrient and microbial activity of the soil, in order to maximise orchard productivity and increase profitability,” says Allister.

In practical terms this may mean less nitrogen is applied across the orchard and lower irrigation volumes are required as more water is retained within the soil. Any increase in SOC will improve soil drainage, root penetration and help reduce soil compaction, especially critical in regions that have low levels of natural SOC, such asGisborne, Hawkes Bay and Motueka.

Ultimately, changing orchard management practices to increase carbon sequestration rates and SOC will deliver significant ecological benefits to surrounding land and downstream waterways, contribute to reducing the kiwifruit industry’s carbon footprint, and are likely to provide financial benefits to the grower in the long-term.

PlusGroup is currently working with a number of the growers involved in the study, providing them with a profile of the SOC on their own orchards and tailoring on-orchard management practices to increase carbon sequestration rates and boost SOC. These include such activities as deep soil penetration (sub-soiling) and the establishment of deep-rooted grass species below the kiwifruit canopy.

This study, led by PlusGroup Research and involving Plant & Food Research, has contributed valuable information to the international research fraternity by developing a research methodology for the collection and evaluation of soilsamples to meet the requirements of international guidelines for the assessment of lifecycle green house gas emissions – known as PAS 2050.

ZESPRI applied the PAS 2050 methodology to the calculation of carbon emissions across the lifecycle of kiwifruit production - from orchard gate to consumer plate. The inclusion of on-orchard carbon sequestration data completes the lifecycle and will now enable the carbon footprint of the New Zealand Kiwifruit Industry to be more accurately calculated.

The methodology of the SOC study is immediately applicable to other perennial tree crop industries such as avocado, pipfruits and summerfruits. A long-term approach toharnessing and enhancing SOC will contribute to the sustainability of orchards, the continued economic viability of the horticultural industries and the protection of the environment for future generations.

- Ends -

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