What the numbers actually say
Fertiliser prices are climbing and every farmer is asking the same question, do you cut back or keep investing. The reality is this is not a simple call and getting it wrong in either direction will cost you, which is why this decision needs to be driven by numbers rather than headlines or gut feel.
Nitrogen is still your cheapest feed
At $1,200 to $1,400 per tonne of urea and $10 per kg milk solids, nitrogen-grown pasture is still coming in at around 18 to 22 cents per kg DM, while replacement feed starts at around 40 cents at the gate and quickly climbs to 55 to 65 cents once you factor in carting, feeding out and wastage. That gap is significant and holds across most realistic payout and price scenarios.
On a 500 cow Canterbury dairy farm running 190 kg N per hectare, cutting nitrogen by half might save around $43,000 in fertiliser, but the lost milk production is worth somewhere between $50,000 and $70,000, which means the saving does not hold up once you look at the full system.
Phosphate and sulphur are a slow bleed
Phosphate decisions are more nuanced, but the principle remains the same, what you do not put on now will need to be paid for later, often more than once. A five percent drop in pasture production might not sound like much, but on an irrigated Canterbury flat running 12,000 kg DM per hectare, that loss is worth more than a full year of maintenance super at $700 per tonne, and while the margin tightens on hill country systems, it still does not stack up in most cases.
The bigger issue is the recovery, because once Olsen P starts to fall it takes two to three seasons of above maintenance fertiliser to rebuild, which means you are not just losing production in one year, you are creating a cost that carries forward.
When pulling back might make sense
This is where blanket decisions fall apart, because the right call depends entirely on where your farm is starting from. Olsen P changes everything, with farms sitting above 40 and carrying a strong fertiliser history having a genuine buffer that allows one season without maintenance phosphate to carry relatively low risk, while farms sitting at Olsen P 15 with a patchy history have no such buffer and any reduction simply accelerates decline.
System and production level matter just as much, with low production dryland systems at Olsen P above 25 being the clearest case where reducing spend can be justified, although even here the better approach is to reduce rather than stop completely. High production irrigated systems sitting below Olsen P 20 to 25 carry too much revenue risk to skip phosphate altogether, as the numbers simply do not support it.
Aerial vs ground spreading
Where the equation shifts
Most sheep and beef farms are not uniform, and the mix of terrain changes the economics more than most people account for. Ground spreading typically sits around $15 to $20 per hectare, while aerial application is often $40 to $50 per hectare depending on terrain and access, and on farms where a large portion requires aerial application, the saving from skipping fertiliser is higher in absolute terms.
That creates different decisions across the same farm, with steep hill country carrying higher spreading costs and lower production per hectare, which can justify reducing rates if savings are required, although the risk is that these soils often sit at lower Olsen P and recovery is slower. Rolling flats and downs tend to have lower spreading costs and higher production, meaning the revenue at risk is greater and the case for maintaining the programme is stronger.
If you are making cuts, the key is to be targeted rather than uniform across the whole farm.
If you reduce, reduce properly
A half rate is not a compromise, it is a strategy that protects your position. If 200 kg per hectare of super is not achievable, applying 100 kg still delivers phosphorus and sulphur, slows the decline in Olsen P, supports clover and keeps the recovery path manageable when conditions improve.
Long term work out of Ballantrae shows how quickly things slide when fertiliser is removed completely, with production losses compounding year on year, while a reduced rate slows that decline and keeps the system more stable. It is the same thinking you apply elsewhere on farm, you would not stop maintaining fences completely because timber prices lifted, you would prioritise and keep things functional, and fertiliser deserves the same approach.
Key takeaways
- Know your Olsen P before making any decision, because soil test results set the direction and without them you are guessing
- Nitrogen still stacks up, and at current prices it remains the cheapest feed on farm with the numbers continuing to support it
- If you reduce phosphate, reduce it rather than stopping completely, as a half rate protects soil capital and keeps recovery manageable
- Sulphur still matters, as it is a low cost input that supports clover and pasture quality
- Protect your winter crop programme, because underperforming crops create a feed deficit that costs more than the fertiliser saving
- Spend where it matters most by prioritising your highest producing paddocks where the revenue risk sits
- Every farm is different, with soil type, system, history and payout all influencing the right decision
- Cheaper now can become more expensive later, as fertiliser is an investment in production that shows up in future performance
- Get advice before making big changes, because the cost of getting this wrong is far higher than the cost of getting it right