Fertilizer application. Is RTK necessary?

Fertilizer application and RTK: is it worth the investment

The short answer: for liquid fertilizers on fields of 1,000 ha and above — yes, it pays off. For solid fertilizers on smaller fields — no, autosteering on SBAS/EGNOS gets the job done at a lower cost. Between these two extremes, there are details that make a real difference to the bottom line.

Where fertilizer losses actually come from

The main source of waste is pass overlap. With a 24-metre working width and a pass-to-pass error of 0.5–1 metre, the overlap strip covers 2–4% of the field area. That strip gets a double dose while the rest of the field receives the planned rate.

On 1,000 ha applying UAN at 150 L/ha, that is 3,000–6,000 litres of product per season applied to areas that have already received their share. The second issue is skips. They happen less often, but their effect on yield is more damaging than the waste caused by overlap.

Solid fertilizers: navigation is not the main variable

When working with a centrifugal spreader at a 18–36 metre working width, navigation accuracy is not the primary quality factor. Spreading unevenness — wind effect, disc wear, granule inconsistency — already produces a rate variation of 8–15% even on perfectly straight passes.

Switching from SBAS-based autosteering to RTK reduces overlap from 1–3% to under 0.5%, but overall application uniformity barely changes as a result. Spending 5,000–15,000 dollars on RTK for that outcome is hard to justify.

The exception is liming and gypsum application from a soil map. Here, precise geographic registration matters directly to the outcome.

Liquid fertilizers and UAN: a different calculation

Boom sprayers with 24–36 metre widths combined with section control are where RTK genuinely earns its place. When sections overlap, the automatic shut-off fires — and navigation accuracy determines exactly how early and precisely that happens. Liquid fertilizers carry a higher cost per unit of nutrient than solids, so each extra percent of overapplication hits the budget harder.

With a 24 m boom and SBAS autosteering error of 10–30 cm, the overlap strip runs approximately 1–3%. RTK brings that below 0.5%.

Variable-rate application: RTK as a functional requirement

If you have soil sampling maps and plan variable-rate application, the question is not whether you need RTK — it is what accuracy your receiver delivers. A prescription map with 10×10 m resolution and a 20–30 cm navigation error is still a workable combination. But if the map was built on a dense 5×5 m sampling grid, a 30 cm error starts blurring zone boundaries and undermining the value of the sampling work.

In practice, most operations that have introduced VRA move to RTK after one or two seasons — when they see that the maps are there, the equipment is there, and the results are not what they expected.

Night shifts and extended working hours

SBAS/EGNOS correction accuracy varies throughout the day depending on satellite geometry. In the early morning and evening, accuracy can degrade noticeably, and the operator has no way of knowing until reviewing the tracks afterwards.

RTK holds a stable ±1–3 cm regardless of time of day. For operations running two shifts or with a seasonal application window compressed to 7–10 days, that consistency is not a minor detail.

Cost and payback period

A base RTK station or network subscription runs 800–2,000 dollars per year. Hardware costs 5,000–15,000 dollars depending on configuration.

A worked example for 1,500 ha with UAN (rate 150 L/ha, price 280 $/t, density 1.28–1.32 kg/L):

• Savings from reducing overlap by 5%: 11,250 L = approx. 14.4–14.9 t = approx. $4,032–4,172 per season
• Less RTK network subscription ($1,400/year): net gain ~$2,600–2,770/year
• Equipment payback (~$5,000): approximately 2 years

On 600 ha, the same math gives ~$1,590/season in fertilizer savings. After the subscription cost, roughly $190 remains — equipment will not pay back on fertilizer application alone. At these prices, the payback threshold sits around 1,000–1,200 ha. Below that area, RTK for fertilizer application only makes financial sense when spread across multiple field operations: planting, spraying, and tillage.

Practical decision table

RTK pays off where the cost of a positioning error is high: liquid fertilizers, precision agriculture, large areas, or situations where the equipment works across multiple operations. In other cases, SBAS-based autosteering handles the job without the premium.