Don't Waste a Kilo: Why Spring Fertiliser Plans Should Start With Test Results, Not Habit By Dr Gordon Rajendram

As Canterbury moves through September, the region is reaching the tail end of its highest risk period for nutrient loss. The window between April and October is when nitrate leaching below the root zone typically occurs, and as a soil scientist working across New Zealand, this is exactly the point in the season when I want farmers reading their soil and pasture test results closely, rather than defaulting to last year's fertiliser programme.

At this point in the season, soil test results across Canterbury properties often show real variation between paddocks, particularly in Olsen P, sulphate sulphur levels and residual soil nitrate. A wet winter affects nutrient retention differently from paddock to paddock, which means a single farm-wide fertiliser plan can easily leave some areas short while oversupplying others. Soil testing alone, however, only tells half the story.

In my view, pasture testing needs to sit alongside soil testing, not replace it. Soil results show what nutrient reserves sit in the ground, while pasture testing shows what the plant is actually taking up, and where deficiencies are already appearing in growth. Used together, the two give a far more accurate picture of where spring inputs will have the greatest effect and where spend would otherwise be wasted.

That accuracy matters more this spring than most. Global fertiliser markets remain unsettled, with pricing tied closely to international energy costs and supply pressures rather than the steadier patterns farmers have relied on in past seasons. For Canterbury dairy farmers already working within the 190kg nitrogen per hectare cap, the priority is no longer simply how much nitrogen or phosphate goes on, but how precisely it is placed.

My message for spring planning is straightforward. Rather than repeating last year's application programme out of habit, use this year's soil and pasture results to build a plan specific to current paddock conditions. With fertiliser costs under pressure and nutrient loss limits tightening, the farms that get the most from every kilo applied this spring will be the ones basing decisions on current test data rather than routine.

For Canterbury farmers finalising their spring fertiliser plans, I recommend completing both soil and pasture testing first, and letting those results, not last season's invoice, set the programme.
 

For more information, please contact:

Dr Gordon Rajendram
Soil Scientist
Phone: 021 466 077
Email: rajendram@xtra.co.nz
Web: https://www.gordonrajendramsoilscientist.co.nz

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