November 2024

Dr Gordon Rajendram, a leading New Zealand soil scientist, highlights that, as New Zealand transitions from spring into summer, responsible phosphorus management is more crucial than ever. Phosphorus is a key nutrient for plant growth, but improper use can lead to harmful nutrient run-off. With regular irrigation approaching and rainfall peaking in late spring, Dr Rajendram underscores the need for proactive steps to minimise phosphorus pollution in waterways, protecting ecosystems and supporting sustainable farming. The Role of Phosphorus in Eutrophication In New Zealand’s waterways, phosphorus from fertiliser run-off is a significant contributor to eutrophication—a process that accelerates algae growth and depletes oxygen in water, harming aquatic life. Research shows that when phosphorus levels are unchecked, algae thrive, leading to toxic conditions for fish and other organisms. In fact, around 76% of streams in New Zealand are phosphorus-limited, meaning they are particularly sensitive to excess phosphorus inputs (McDowell, Larned, & Houlbrooke, 2010). Dr Rajendram notes that farmers’ efforts to mitigate phosphorus run-off can make an immediate difference to water health, particularly in catchment areas where excess phosphorus has historically led to water quality issues. Effective Phosphorus Management Practices Farmers can mitigate phosphorus run-off by tailoring fertiliser application to soil needs and monitoring soil nutrient levels through regular testing. This approach prevents over-fertilisation, conserving resources and limiting nutrient loss into waterways. One effective solution is to use less water-soluble phosphorus fertilisers, which release nutrients more gradually, giving plants more time to absorb them and reducing the risk of run-off. Additionally, applying phosphorus in alignment with crop growth cycles, such as in early spring, maximises plant uptake, further minimising the potential for nutrient loss. Dr Rajendram advises: “We all have a duty to balance productivity with environmental responsibility. By carefully managing phosphorus use and establishing buffer zones around waterways, we can protect the integrity of New Zealand’s rivers and lakes for future generations.” Buffer zones—areas of vegetation between farmland and water—are highly effective in trapping nutrients before they reach water systems. Additionally, cover cropping helps stabilise soils, reducing erosion and supporting long-term soil health, which naturally limits phosphorus loss. Towards a Sustainable Approach in Phosphorus Management Dr Rajendram underscores that responsible phosphorus management is essential for New Zealand’s environmental future. By adopting practices that limit phosphorus discharge, farmers can play a vital role in reducing eutrophication risks. McDowell et al. (2016) suggest that both regulatory and voluntary approaches are crucial to sustaining good water quality across regions, offering a way forward that respects both productivity and the environment. References – McDowell, R. W., Larned, S. T., & Houlbrooke, D. J. (2010). Nitrogen and phosphorus in New Zealand streams and rivers: Control and impact of eutrophication and the influence of land management. *New Zealand Journal of Marine and Freshwater Research*, 44(4), 985-995. https://doi.org/10.1080/00288330909510055 – McDowell, R. W., Dils, R. M., Collins, A. L., Flahive, K. A., Sharpley, A. N., & Quinn, J. (2016). A review of the policies and implementation of practices to decrease water quality impairment by phosphorus in New Zealand, the UK, and the US. *Nutrient Cycling in Agroecosystems*, 104, 289-305. https://doi.org/10.1007/s10705-015-9727-0 For more information, please contact: Contact Dr Gordon Rajendram 021 466077 rajendram@xtra.co.nz www.gordonrajendramsoilscientist.co.nz Contact Media PA phillip@mediapa.co.nz 027 458 7724 www.mediapa.co.nz

Dr Gordon Rajendram, a leading New Zealand soil scientist and consultant for sustainable farming, explains that even slight overuse of fertiliser can result in nutrient imbalances, water pollution, and long-term soil damage. “Even if over-fertilisation isn’t a crisis now, farmers must focus on efficiency and sustainability. Applying only what is necessary protects the land and the environment,” he says. Fertilisers contain key nutrients like nitrogen (N), phosphorus (P), and potassium (K), which are vital for plant growth. However, if these nutrients exceed crop requirements, they can leach into groundwater or wash into nearby water bodies. Nitrogen, in particular, poses a risk as it transforms into nitrates, which can contaminate both groundwater and surface water. High nitrate concentrations not only threaten aquatic ecosystems but can also make drinking water unsafe, particularly in rural areas dependent on groundwater sources. Dr Rajendram stresses that “soil testing is key in modern agriculture; applying excess fertiliser may seem beneficial initially, but it can lead to nutrient imbalances and soil acidification, which ultimately harms crop yields.” When excess nutrients disrupt soil pH, beneficial microorganisms that help plants absorb nutrients and resist diseases are negatively impacted. This degradation compromises soil structure and reduces its ability to retain moisture, making crops more vulnerable to drought. In addition to environmental risks, excessive fertiliser use results in a reliance on chemical inputs, increasing farming costs. Over time, continuous over-fertilisation can lead to an accumulation of salts in the soil, which harms plant roots and reduces crop resilience. This dependency threatens both farm productivity and profitability. To mitigate these risks, Dr Rajendram advises using precision farming techniques. “Farmers can improve both yield and sustainability by adopting best practices, such as soil nutrient testing and targeted fertiliser application,” he recommends. Technologies like GPS-guided fertiliser application allow for targeted delivery, ensuring crops receive what they need without excess. By prioritising balanced nutrient management, Dr Rajendram believes that farmers can achieve optimal yields while protecting the health of their soil and the environment. Implementing these practices ensures that fertilisers contribute positively to crop productivity while safeguarding the long-term viability of the land. For more information, please contact: Contact Dr Gordon Rajendram 021 466077 rajendram@xtra.co.nz www.gordonrajendramsoilscientist.co.nz Contact Media PA phillip@mediapa.co.nz 027 458 7724 www.mediapa.co.nz