The core tools of precision farming: GNSS/RTK, auto-steering, zone management and variable-rate application

Precision farming is a family of tools that brings the “right amount in the right place” principle to machinery. Most of these tools depend on position: as the JRC notes, satellite-based machine guidance is also an essential part of other precision farming technologies such as controlled traffic, variable-rate seeding and fertiliser application (JRC, 2019). This guide looks at the tools one by one and discusses which accuracy each job requires.

GNSS and corrections: accuracy classes

The receiver on the tractor computes its position from satellite systems (GNSS) such as GPS, Galileo and GLONASS; for farm-grade accuracy a correction signal is added. Accuracy is expressed in two ways. Pass-to-pass accuracy is the error between two adjacent passes made within a short time. Year-to-year (repeatable) accuracy is the ability to return to the same line months later. The University of Nebraska-Lincoln extension circular stresses that, except for RTK-level receivers, pass-to-pass error claims are significantly lower than year-to-year error estimates (UNL, 2008).

The values were compiled in 2008 from manufacturers' promotional literature (UNL, 2008); the JRC reports that systems range from ±40 cm at entry level to ±2 cm (JRC, 2019). When buying, always ask which test the stated figure comes from.

Where do corrections come from?

• Own base station: most manufacturers cannot guarantee correction quality more than 10 km from the base station; signal repeaters can help with obstacles such as hills and trees (UNL, 2008).
• Network RTK, Türkiye: TUSAGA-Aktif, run by the General Directorate of Land Registry and Cadastre and the General Directorate of Mapping, provides real-time positioning with centimetre accuracy from a network of 194 permanent stations. In the 2026 price list an RTK subscription costs TRY 1,000 per month or TRY 8,135 per year, and a DGPS subscription TRY 405 per month or TRY 2,985 per year, VAT included (TUSAGA-Aktif, 2026).
• Galileo HAS: since 2023 the EU's Galileo system has offered a free, global High Accuracy Service (HAS) at decimetre level (EUSPA). Its horizontal accuracy target is 20 cm, and corrections are received via the Galileo E6 signal or the internet. In a 3-hour field test with a tractor in Spain in May 2026, the 95% horizontal error was 5.9 cm; the receiver first needs a convergence time before reaching precise positioning (EUSPA, 2026).

Whatever the source, tree lines at the field edge can degrade satellite geometry; receivers that track several satellite systems are less affected (UNL, 2008).

Auto-steering

The Nebraska circular defines three levels of automation: lightbars that show drivers their position relative to previous passes, auto-guidance systems that steer the vehicle, and field robots. Steering is done either with a device on the steering column or with a valve connected to the tractor's electro-hydraulic steering circuit; column-mounted systems are easy to install but can respond less quickly than systems that turn the wheels directly (UNL, 2008). The STOA study lists a 10% reduction in fuel consumption in field operations among the expected gains of GPS-based automatic guidance, and automated headland turns can save 2-10% fuel (STOA, 2016). In the JRC survey, users reported an average fuel reduction of 5.4% (JRC, 2019). The 2026 Greek support call requires a documented pass-to-pass accuracy of ±3 cm or better for auto-steering retrofitted to an existing tractor; parallel guidance without automatic steering control does not qualify for the higher support rate (YPAAT, 2026).

Section control and ISOBUS

Section control automatically switches off the relevant part of a sprayer boom or spreader when it reaches an area already treated or the edge of the plot. According to a finding reported by STOA, map-based automatic boom section control reduced the area sprayed in each field by 15.2-17.5% compared with no section control (STOA, 2016). On more advanced sprayers each nozzle can be switched individually.

ISOBUS (ISO 11783) is the standard that lets tractor and implement “understand” each other. Under the technical definition in the Greek support call, a complete ISOBUS set-up includes the standard ISOBUS socket, a Universal Terminal (UT) and a Task Controller (TC) that supports section control (TC-SC) and/or position-based variable-rate application (TC-GEO) (YPAAT, 2026). When buying a terminal, check that the implement to be connected supports the same TC functions.

Zone management

Zone management means managing a field as sub-areas with similar characteristics instead of as a single unit. An extension note from South Dakota State University describes mapping soil apparent electrical conductivity (ECa) as one practical way to create zones: sandy soils with low organic matter have low EC, silts medium and clays higher EC, and areas with consistent ECa readings have similar soil properties and may be grouped for sampling and management. Contact systems using coulters give readings for about 30 and 90 cm depth, non-contact electromagnetic systems for about 30-36 and 100 cm, with 6-18 m between measurement passes (SDSU, 2021). Building zones from multi-year yield maps and satellite imagery is covered in the relevant guides on the platform.

Variable-rate application (VRA): at the level of the machine

There are two routes to variable-rate application. In map-based application, a prescription map loaded on the terminal sends the rate for the zone the machine is in to the controller, so position data is essential. In sensor-based application, sensors on the machine, such as optical sensors measuring a vegetation index, read the crop in real time and the rate is adjusted on the spot (STOA, 2016). Under the Greek call's definition, a variable-rate spreader must have electronic application control, the ability to change the rate automatically according to forward speed, position, a prescription map or sensor data, and the ability to shut off application automatically on parts of the area; manual rate adjustment alone is not sufficient. The sprayer equivalent is automatic rate control according to forward speed, automatic switching of boom sections and a positioning system (YPAAT, 2026).

In orchards a different tool stands out: sprayers that detect the size and architecture of the tree and adjust spraying accordingly. According to findings compiled by STOA, such precision spraying in orchards and vineyards can reduce pesticide use by up to 20-30% and the sprayed area by 50-80% (STOA, 2016). For citrus orchards in Kozan, this can be seen as the orchard counterpart of variable-rate application in field crops. Building a fertiliser prescription from combine data is covered in detail in the platform's yield map guide.

Which tool for which job?

• Jobs that return to previous tracks (controlled traffic, strip tillage): RTK, with centimetre-level year-to-year accuracy as well (UNL, 2008).
• Jobs where each pass relies only on the previous one (tillage, seeding, spraying, harvesting): some long-term drift can be tolerated, so these jobs can accept less accurate and therefore less expensive options (UNL, 2008).
• Inter-row mechanical hoeing (row crops such as cotton and maize): active guidance by camera, optical sensors or high-accuracy GNSS, plus an automatic side-shift correction system (YPAAT, 2026).
• Work inside orchards: tree rows can limit satellite visibility; the Nebraska circular notes growing interest in guidance with range-measuring sensors in orchards for this reason (UNL, 2008).

Sources

1. UNL, 2008. Adamchuk, V.I. Satellite-Based Auto-Guidance. University of Nebraska-Lincoln Extension, EC706 (accessed 29 September 2026)
2. JRC, 2019. Soto, I. et al. The contribution of precision agriculture technologies to farm productivity and the mitigation of greenhouse gas emissions in the EU (JRC112505, doi:10.2760/016263) (accessed 29 September 2026)
3. EUSPA. Galileo High Accuracy Service (HAS) (accessed 29 September 2026)
4. EUSPA, 2026. Galileo HAS ready to increase efficiency of farming tasks: latest tests prove suitability for precision agriculture (21 May 2026) (accessed 29 September 2026)
5. TUSAGA-Aktif, 2026. Türkiye Ulusal Sabit GNSS Ağı-Aktif (CORS-TR): istasyonlar, ürünler ve 2026 bedelleri (TKGM, HGM) (accessed 29 September 2026)
6. European Parliament STOA, 2016. Precision agriculture and the future of farming in Europe: Scientific Foresight Study (PE 581.892, doi:10.2861/020809) (accessed 29 September 2026)
7. SDSU Extension, 2021. Mirzakhani Nafchi, A. Creating Management Zones Using Electrical Conductivity (accessed 29 September 2026)
8. ΥΠΑΑΤ, 2026. Πρόσκληση εκδήλωσης ενδιαφέροντος για τις Παρεμβάσεις Π3-73-2.1, Π3-73-2.2 και Π3-73-2.6 του ΣΣ ΚΑΠ 2023-2027 (ΑΔΑ: ΡΘΗΟ4653ΠΓ-ΧΙ7), Παραρτήματα 3 και 4, Περιφέρεια Θεσσαλίας (accessed 29 September 2026)