Addressing Nitrate N Leaching in Twizel: Insights from Soil Scientist Dr Gordon Rajendram and Allan Piercy from Agraforum New Zealand

The Wairepo Catchment Group and the Omarama Stream Water Users Group of Mackenzie Country recently hosted a presentation titled “Advancing Sustainable Agriculture in New Zealand.” The event featured Dr Gordon Rajendram, a soil scientist and independent consultant, and Allan Piercy, managing director of Agraforum New Zealand. Held on 29 April 2024 in Twizel. The talk emphasised the urgent need to reduce nitrate N leaching by half to maintain farming consents, given the region’s low rainfall, cold winters, and predominant dairying, cattle and sheep farming. In order to farm sustainability in this area, there needs to be a whole catchment approach.

Dr Rajendram explained that the area’s soils, with an Anion Storage Capacity (ASC) averaging around 15% and low Cation Exchange Capacity (CEC), are not conducive to retaining nutrients. This results in significant leaching losses, especially with higher stocking rates and cattle grazing on pastoral land. Nutrient loading rates in urine patches can be as high as 600-900 kg of nitrogen and potassium, which penetrate below the pasture root zone and leach into waterways.

 In any 1 year 28% of the paddock is covered in dung and urine at a 3 cow per hectare stocking rate.

Twizel experiences low annual rainfall, averaging around 700 mm, and cold temperatures, with winter lows often dropping below freezing. “These conditions hinder nutrient retention and increase the likelihood of leaching. The region relies on irrigation, which is vital for pasture production”. Dr Rajendram emphasised the importance of water availability for effective farming and practical solutions such as using biochar/humates (pure carbon source) to bind nitrogen and other nutrients, use of stand off pads/herd homes to reduce urination events on paddocks or reducing cattle/cow numbers to mitigate environmental impacts. If for instance the cattle were on stand off pads or a herd home for half a day, the nitrate leaching into water ways will reduce by half of what it is at present.

Rajendram et al 1996 Cation and Anion leaching (Article link)

Dr. Rajendram explained that if pure carbon such as Biochar was used and was incorporated into the soil to achieve an approximate 10% biochar/90% soil ratio, it would reduce nitrate leaching down to zero. Any farmer can make biochar from Wilding pines which is a pest in the Mackenzie basin. Rajendram explains that Trevor Richards of Biochar NZ gave a practical demonstration on a Twizel farm on making biochar in pits using Wilding pines.  

 Allan Piercy’s Contributions from Agraforum New Zealand

Following Dr Rajendram’s presentation, Allan Piercy discussed Agraforum New Zealand’s role in providing solutions to nitrate N leaching. Piercy introduced several key products designed to enhance pasture production while reducing fertiliser dependency. A highlight of his talk was El-I-Tech’s Biodynamic N, a product that facilitates biological nitrogen fixation, significantly reducing the need for synthetic fertilisers.

Piercy emphasised that integrating these products into nutrient management plans can significantly reduce nutrient leaching and improve soil health. Other notable products mentioned included:

  • EnviroCal: Improves soil structure and water penetration, enhancing drought resistance.
  • ComCat: Activates plants’ root growth and defence mechanisms, increasing stress resistance and improving crop/product growth.
  • ZumSil: Enhances phosphate and mineral uptake, improving soil texture and water retention.

“Our products offer a practical solution to nutrient management challenges, helping farmers reduce leaching and improve soil health for long-term sustainability.” – Allan Piercy, Managing Director of Agraforum New Zealand

Agraforum New Zealand’s focus on sustainable farming practices ensures that their solutions not only address immediate nutrient retention issues but also contribute to long-term soil health and productivity.

These insights and solutions provide a comprehensive approach to tackling the nitrate N leaching challenge in Twizel, ensuring sustainable and productive farming practices. For more information on Agraforum New Zealand’s products, visit Agraforum New Zealand Products.

Contact Dr Gordon Rajendram

021 466077

Contact Agraforum New Zealand

Mobile: 0274 485 159

Contact Phillip Quay

027 458 7724

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