Leading Hamilton Soil Scientist Dr Gordon Rajendram Urges Smarter Soil Science By New Zealand Farmers To Offset Spike In Global Fertiliser Costs
An escalation in global fertiliser prices due to the Iran war will force New Zealand farmers to rethink traditional input-heavy systems, according to one of New Zealand’s leading soil scientists, Dr Gordon Rajendram of Hamilton (pictured)
“The solution is a combination of using less fertiliser and also using better science to apply only what is truly needed,” Dr Rajendram said today.
A crucial starting point is soil and pasture testing. Dr Rajendram consistently emphasises that without accurate data, fertiliser programmes become guesswork.
“Comprehensive testing identifies nutrient deficiencies, soil pH, and retention capacity, allowing farmers to apply inputs precisely rather than broadly,” he says.
“This avoids over-application, which not only wastes money but can also lead to nutrient losses through leaching. In fact, testing is considered one of the most cost-effective steps in nutrient management, often representing a very small proportion of overall fertiliser spend while delivering significant savings,” Dr Rajendram said.
Beyond testing, there is growing evidence that many farms are applying more nutrients than required, particularly phosphate.
Dr Rajendram notes that some New Zealand soils can retain phosphate for several years, meaning annual applications are not always necessary. Shifting away from routine fertiliser programmes to a needs-based approach can significantly cut costs without impacting production.
“Nitrogen use is another area where efficiency gains can be substantial” he says.
“Rather than relying heavily on granular applications, more farmers are adopting targeted methods such as foliar spraying. This approach delivers nutrients directly to the plant, improving uptake and reducing the total amount required. Trials have shown that significantly lower nitrogen rates can achieve comparable pasture growth when applied in this way, highlighting a clear opportunity to reduce input costs.”
Soil condition itself also plays a major role. Maintaining optimal pH through liming improves nutrient availability and root development, meaning plants can access more of the nutrients already in the soil. Poor pH, on the other hand, limits growth and reduces fertiliser efficiency, effectively increasing the cost per unit of production.
While reducing synthetic inputs is important, Dr Rajendram also advocates for strengthening biological systems within the pasture. Clover remains a critical component, naturally fixing nitrogen from the atmosphere and reducing reliance on purchased fertiliser. However, he stresses that clover should be part of a broader, balanced system that includes diverse pasture species and well-managed soils. Excessive nitrogen use can actually suppress clover’s ability to fix nitrogen, reinforcing the need for moderation and balance.
“Ultimately, the shift is about moving from a fertiliser-driven system to a soil-driven one,” Dr Rajendram said.
As Dr Rajendram states: “Farmers are increasingly recognising that they may not need as much fertiliser as once thought. By combining accurate testing, targeted application, improved soil management, and biological inputs like clover, farmers can reduce costs, maintain productivity, and build more resilient farming systems in the face of ongoing global price pressures.”
About Dr Gordon Rajendram:
With more than three decades of experience in soil fertility, Dr Rajendram’s approach centres on improving efficiency, reducing waste, and unlocking the natural potential already present in the soil.
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