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Franklin Sustainability Project

Severe storms, such as in May 1996, resulted in widespread damage to property and infrastructure from the loss of soil from cultivated land in the Pukekohe area, south of Auckland. Apart from the damage to property, the off-site movement of soil resulted in sedimentation and ecological damage to the Manukau Harbour and the streams feeding into it, and the irreversible loss of a precious soil resource. As a result, the Franklin Sustainability Project was born to address issues of sustainable management in cropping systems in the area. Tony Thompson of the Auckland Regional Council discusses the achievements of the project so far.

The three-year multi-stakeholder Franklin Sustainability Project was established in 1997 to identify and promote best management practices amongst Franklin vegetable growers to protect water and soil resources.

The project involved financial and in-kind contributions from the Auckland Regional Council (ARC), Environment Waikato, Franklin District Council, VegFed, MAF, AGMARDT and the Pukekohe Vegetable Growers’ Association. The bulk of funding for the project came from the Ministry for the Environment’s Sustainable Management Fund.

Over the course of the project, workshops, field days, trials and demonstrations have been held to promote good practice amongst growers on fertiliser use, surface water management, irrigation, integrated pest management, and soil health. Regular newsletters have also been produced for distribution amongst the approximately 350 growers.

A number of good practices have been identified and trialled over the past three years. These have now been compiled into a set of guidelines called Doing it Right, which was officially launched in October 2000.

The soils of the Pukekohe, Pukekawa and Bombay areas of the Franklin District are some of the best in the country and are intensively cultivated for food production. They are of high agricultural and horticultural value because of their drainage characteristics, suitable texture, natural fertility and structural integrity under repeated cultivation. Such intensive cultivation does however pose potential adverse environmental effects, including off-site movement of soil and subsequent adverse effects on surface water quality.

Soil Loss

Protection of the soil resource of the district is paramount for ensuring its continued availability and versatility for the future. While the soil remains well aggregated and settles out readily in a water column, high intensity storm events, such as in May 1996 and January 1999, resulted in thousands of tons of topsoil being eroded and mobilised, a large proportion of which was lost off-site. This highlighted to both growers and resource managers the importance of implementing and maintaining surface-water management works such as silt-traps, contour-drains, raised access-ways and cut-off drains. The benching and contouring of headlands is also important for reducing the energy of storm water and retaining soil within the paddock.

Trials conducted by Landcare Research indicate wheel-track ripping could be one of the most effective tools and operations growers could perform to minimise the risk of soil loss. Compacted wheel-tracks act as impermeable conduits for concentrating storm-water flows, which often scour out the sides of furrows and seed-beds, resulting in substantial sheet and rill erosion.

Another lesson learnt from these storm events is to be sure that storm-water engineering and works are investigated and carried out at the catchment level. In many cases, growers downstream have suffered severe damage and soil loss as a result of drain over-flows and blow-outs.

Nitrates in Ground Water

Regular monitoring of two artesian springs, which provide indicative nitrate levels of the aquifer, reveal that nitrate levels are currently around 85ppm, well above the World Health Organization recommended drinking water level of 50ppm. Whilst the ARC is concerned about potential adverse effects on human health, surface water ecology and long-term sustainability, the wider industry concerns are for sustained and improved market access.

This aquifer is an unconfined system, and with intensive cultivation activities above it, there is a high risk of nitrate impact. Various studies indicate that the nitrate is primarily originating from the mineralisation of soil organic matter, and, to a lesser degree, directly from fertiliser. The decreased soil carbon levels — a result of repeated cultivation — exacerbate the transport of nitrates through the soil profile.

An important message therefore, for the growers and the industry, is the judicious use of fertiliser, i.e. better targeted rates, placement and timing of fertiliser application, but also the use of cover crops. The growing and ploughing-in of cover crops, such as oats or mustard, have a beneficial role in improving soil carbon (organic matter) levels, improving soil structure and “mopping up” excess nitrate. One challenge facing us is to encourage growers to put in cover crops over the winter period and have them plough the crop back in just prior to re-planting. By doing this, nitrates released from re-incorporation of the cover crop residue will be available to the following crop, and soil will be protected from erosion through the wettest time of the year. This however presents an increased risk for the grower in terms of weather and soil water conditions for cultivation. Nitrate leaching trials conducted during the Franklin Sustainability Project indicated that pre-winter crop/cover-crop incorporation and fertiliser use on winter vegetables pose the greatest risks to nitrate leaching.

The Future

Growers and stakeholders involved with the Franklin Sustainability Project have been successful in securing funding from MAF’s Sustainable Farming Fund to engage a field representative on behalf of the Pukekohe Vegetable Growers’ Association. The field rep will promote and encourage adoption of practices outlined in the Doing it Right guidelines, and facilitate discussion and greater awareness of resource management issues amongst growers in the district and beyond.

 

Contact for Enquiries

Amber Duncalfe
Editor - RM Update
Ministry of Agriculture and Forestry
PO Box 2526
Wellington
NEW ZEALAND

Tel: +64 4 894 0710
Fax: +64 4 894 0745
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