The Nitrogen Budget Under Scrutiny
A 1,800-hectare cropping property in the Wheatbelt grows wheat-on-wheat with a canola break every third year. The owner, Dan, applies 180 kg/ha of urea (46% nitrogen) to wheat. A catchment group has flagged rising nitrate levels in the local drain, and Dan's fertiliser supplier now offers a slow-release product at $1,150/t versus $780/t for standard urea. Dan's agronomist estimates that 30% of applied nitrogen is currently lost to leaching and volatilisation, and that slow-release would cut losses to 12%. Wheat yields 3.2 t/ha at $310/t. Dan's bank has also tightened lending against input costs.
1. Calculate the nitrogen applied per hectare and the cost of nitrogen lost under each product, then assess whether the slow-release product is justified on yield grounds alone.
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Nitrogen applied: 180 kg/ha urea × 0.46 = 82.8 kg N/ha.
Standard urea cost: 0.180 t/ha × $780/t = $140.40/ha. N lost = 30% of 82.8 = 24.84 kg N/ha. Cost of lost N = 0.30 × $140.40 = $42.12/ha.
Slow-release cost: 0.180 t/ha × $1,150/t = $207/ha. N lost = 12% of 82.8 = 9.94 kg N/ha. Cost of lost N = 0.12 × $207 = $24.84/ha.
Extra product cost = $207 − $140.40 = $66.60/ha. Saved N cost = $42.12 − $24.84 = $17.28/ha. Net cost of switching = $66.60 − $17.28 = $49.32/ha.
On yield grounds alone, there is no evidence in the figures that slow-release lifts yield - it only reduces loss. Unless the retained nitrogen converts to yield, the switch costs $49.32/ha with no return. Across 1,800 ha that is $88,776 per year. So the product is not justified on yield grounds alone; it would need either a documented yield response or an off-farm benefit (catchment compliance, market access) to stack up.
2. The catchment group proposes a nutrient-management plan that would let Dan access a $60/ha stewardship payment if he cuts nitrogen losses by at least half. Evaluate this against the slow-release option.
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Cutting losses by half means going from 30% loss to 15% - close to the 12% the slow-release product achieves. The slow-release product at 12% loss qualifies, so Dan would receive $60/ha.
Net position with slow-release plus payment: extra cost $66.60/ha, saved N $17.28/ha, plus $60/ha payment = $66.60 − $17.28 − $60 = −$10.68/ha, i.e. a small net gain of $10.68/ha. Across 1,800 ha that is about $19,224 per year.
But there are other routes to a 15% loss target: split applications, timing urea before forecast rain, or using a urease inhibitor. If split application achieves 15% loss at, say, $20/ha extra cost, the net position is $60 − $20 = +$40/ha, far better than slow-release.
The judgement call is that the stewardship payment changes the economics but does not automatically make the most expensive product the right one. Dan should compare all loss-reduction pathways against the $60/ha threshold, and confirm the payment's conditions (measurement, audit, duration) before committing. The payment also carries risk: if the scheme is reviewed or the measurement method changes, the $88,776 annual outlay remains while the offset may not.