Korean highland farmers evaluating the THOR 2.4 + CT-2100 system investment face a single visible number — the purchase price — against multiple distributed, future benefits that are harder to quantify but collectively far larger. This quantification gap is the primary reason farmers delay or decline the stone clearing investment: the cost is immediate, certain, and visible; the benefit is deferred, distributed across multiple seasons, and expressed in the absence of problems rather than the presence of a new revenue line.
This guide builds the 5-year ROI model for a representative Korean highland potato farm, showing each benefit category in quantitative terms — not as approximate percentages but as a structured economic framework that can be applied to any specific farm’s acreage, crop mix, and market channel. The model includes the subsidy impact, which typically changes the breakeven timeline from 3–5 years to 1.5–3 years. And it includes a section on when the investment does not make sense — because the honest analysis sometimes points against purchase.
The Five Return Categories — Where the Value Actually Comes From
Category 1
Yield Improvement — More Tubers Survive to Harvest
On un-cleared fields, EP-AWB-1600 digger share deflections around embedded stones leave tubers in the ground, cut tubers from share contact, and create uneven harvest depth that produces incomplete extraction. Measured loss from stone-related harvest inefficiency on un-cleared Korean highland potato fields: 3–8% of total tuber count per season. On 10 ha at 30 t/ha yield, 5% loss is 15 tonnes/year. At the wholesale price of highland fresh market potato, this yield recovery alone represents significant annual revenue improvement. Stone clearing eliminates this ongoing loss across every harvest season for the life of the investment.
Category 2
Grade Uplift — More Grade 1 Proportion at Market
Stone-related tuber damage (bruising from stone-to-tuber contact in the digger share zone, skin abrasion from stone fragments in the web separator) produces Grade 2 and Grade 3 downgrade tubers. Measured Grade 1 improvement from stone clearing in Korean highland potato: 10–20 percentage point increase in Grade 1 proportion. At a 30–50% price premium for Grade 1 over Grade 2/3, this grade uplift represents the single largest annual return category for fresh market potato operations. On 300 tonnes harvested from 10 ha, a 15 percentage point Grade 1 improvement (45 additional tonnes reaching Grade 1 price vs Grade 2 price) at a 40% price differential produces an annual revenue improvement in the hundreds of thousands of won per hectare.
Category 3
Machine Damage Avoidance — Eliminating the Ongoing Repair Cost
Un-cleared highland fields cause measurable annual damage to machinery: digger share replacement (2–4 times per season on heavy-stone fields vs once per 2 seasons on cleared fields), PSW-3200 blade wear acceleration from residual stone contact, EP-PAI-2100 planter share damage from surface stone impact, drip irrigation tape punctures from surface stones, and tractor tyre damage from access track stones. Korean highland farmers who track machinery repair costs before and after stone clearing consistently report 40–70% reductions in annual maintenance and repair expenditure — a cash flow improvement that recurs every season.
Category 4
Labour Savings — Eliminating Manual Stone Collection
Korean highland farms that manage stones manually — picking and moving stones by hand during the spring preparation period — spend 2–5 person-days per hectare on stone management annually. At prevailing Korean agricultural labour rates (seasonal workers in highland areas command premium rates due to limited availability), this manual labour cost per hectare per year represents a significant ongoing expense. Mechanical stone clearing (THOR 2.4 + CT-2100) achieves the same or better clearance quality in 0.2–0.5 operator-days per hectare — an 80–90% labour time reduction. The labour saving recurs every year for the life of the investment.
Category 5
Subsidy Impact — Reducing Year 0 Investment Cost by 30–50%
The Korean agricultural machinery subsidy (30–50% of eligible purchase price) reduces the gross investment cost in Year 0 — directly shortening the breakeven period. A 40% subsidy applied to the THOR 2.4 + CT-2100 system purchase price changes the farmer’s net investment from 100% of list price to 60%. The same annual return (Categories 1–4) now recovers a smaller initial investment — reducing the typical breakeven timeline from 3–5 years to 1.8–3 years depending on farm scale and market.
5-Year ROI Model — Representative 10 Ha Highland Potato Farm
The following model uses representative Korean highland potato parameters — not actual prices (which vary seasonally) but relative value relationships that hold across market cycles. All currency amounts are expressed in relative units (RU) to maintain applicability across price cycles:
| Year | Activity | Cost (RU) | Annual benefit (RU) | Cumulative net (RU) |
|---|---|---|---|---|
| Year 0 | THOR 2.4 + CT-2100 purchase (post-40% subsidy) | −60 RU | — | −60 RU |
| Year 1 | First cleared harvest season. Annual operating cost (fuel, teeth, CT-2100 wear). Grade 1 +15pp, yield +5%, machine damage −60%, labour −80%. | −5 RU | +25 RU | −40 RU |
| Year 2 | Established clearance. Benefits sustained. Annual operating cost. | −5 RU | +25 RU | −20 RU |
| Year 3 | Breakeven point. All five benefit categories fully operational. | −5 RU | +25 RU | +0 RU (breakeven) |
| Year 4 | Positive territory. Investment fully recovered, surplus accumulating. | −5 RU | +25 RU | +20 RU |
| Year 5 | 5-year total: full investment recovery + 40 RU surplus. | −5 RU | +25 RU | +40 RU surplus |
Key model assumptions (10 ha highland potato, 30 t/ha yield)
- →Year 0 investment = 100 RU list price; subsidy = 40 RU; net = 60 RU
- →Annual operating cost (teeth, fuel, wear) = 5 RU/year
- →Annual benefit = 25 RU (sum of Categories 1–4; conservative estimate)
- →Breakeven at Year 3; 5-year cumulative surplus = 40 RU on 60 RU net investment = 67% 5-year ROI
- →Machine service life extends well beyond 5 years — subsequent years continue generating 20 RU annual surplus with only operating costs
Scale Sensitivity — How Farm Size Changes the ROI Timeline
The ROI model above is based on 10 ha. The economics change materially at different farm scales because the THOR 2.4 + CT-2100 system cost is largely fixed (the machine cost is the same regardless of farm area) while the annual benefit scales with farm area:
| Farm area | Net investment (post-40% subsidy) | Annual benefit | Breakeven |
|---|---|---|---|
| 5 ha | 60 RU (same machine cost) | ~12 RU/yr | ~5 years |
| 10 ha | 60 RU | ~25 RU/yr | ~3 years |
| 20 ha | 60 RU | ~50 RU/yr | ~1.5 years |
| 40 ha | 60 RU | ~100 RU/yr | <1 year |
When the Investment Does NOT Make Sense
Honest investment analysis requires identifying the conditions under which the stone clearing system purchase is not cost-effective, not just the conditions where it is. Four scenarios where the THOR 2.4 + CT-2100 individual purchase is not the right answer:
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Below 5 ha with low crop value. On very small farms growing lower-value crops (bulk grain, low-grade vegetable commodity), the annual benefit per hectare may not reach the level needed to recover the fixed THOR + CT-2100 system cost within a reasonable period. For these situations: contracting the stone clearing service from a THOR-equipped contractor (paying per-hectare service fee) captures the benefit without the capital investment, and the per-hectare service fee is typically lower than the annual ownership cost at small scale.
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Land with very low stone density (alluvial plains). Fields in Korean agricultural plain zones (lowland rice, lowland vegetable) with naturally low or zero stone density do not need stone clearing. Purchasing stone clearing equipment for land that does not have a stone problem produces no benefit return. The correct stone management assessment includes confirming that the farm actually has a stone problem before committing to the investment.
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Short-term farm tenure (less than 3 years remaining). If the farmer plans to retire, sell, or discontinue farming within 2–3 years, the 3-year breakeven timeline means the investment may not be fully recovered before the farm operation ends. For short-tenure situations, contracting the clearing service or purchasing only the EP-EW-4000 (lower capital cost, faster payback on smaller farms) are more appropriate than the full THOR + CT-2100 system investment.
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Tractor not available or below 180 HP minimum. Purchasing the THOR 2.4 without confirming a compatible 180 HP minimum tractor is available produces no return — the machine cannot operate below its rated HP minimum. The tractor specification confirmation is a necessary pre-purchase step, not an afterthought. If no compatible tractor is available, either upgrade the tractor (a larger total investment that must be included in the ROI calculation) or contract the clearing service from an operator who has the correct tractor.
Annual Operating Cost Breakdown — What Goes Into the “5 RU per Year” Estimate
The 5 RU annual operating cost in the model represents the real recurring costs of running the THOR 2.4 + CT-2100 system after the initial purchase. Understanding what this covers helps Korean highland farmers build accurate annual budgets for their stone management programme:
THOR 2.4 teeth
The largest single annual operating cost item. Korean granite conditions require partial or full tooth set replacement every 1–3 seasons. Amortised annually, this is typically the dominant cost in the 5 RU estimate.
Fuel cost
THOR 2.4 at 180 HP under load consumes approximately 15–20 L/hour of diesel. CT-2100 at 110 HP adds 8–12 L/hour. For 25–40 operating hours/season combined, annual fuel cost is a predictable, budgetable item.
CT-2100 tines + chain
CT-2100 pick-up tine wear and chain replacement — lower cost than THOR teeth, replaced every 2–3 seasons on typical Korean highland operation.
Lubricants + minor parts
Gearbox oil (annual change on both machines), bearing grease (seasonal consumption), PTO shaft universal joint replacement (every 3–5 years amortised).
Frequently Asked Questions
How do I build a specific ROI model for my farm — what data do I need?
Building a farm-specific ROI model requires four data categories: (1) Current performance baseline: current Grade 1 proportion at market, current annual machinery repair cost attributable to stone damage, current manual stone management labour hours and cost, and current harvest loss percentage (tubers left in ground or damaged on un-cleared sections). (2) Farm parameters: total hectares, crop yield per hectare, market channel (fresh market, processing, seed), and crop price per grade. (3) Investment parameters: THOR 2.4 + CT-2100 current price quote from Korea Watanabe, expected subsidy rate at your county, and expected annual operating cost (fuel, teeth, CT-2100 wear). (4) Expected benefit parameters: estimate from the five categories above — using the ranges published in this guide (5% yield improvement, 10–20 percentage point Grade 1 uplift, 40–70% machine damage reduction, 80% labour saving). Korea Watanabe can assist in structuring the farm-specific model using your baseline data at no charge as part of the pre-purchase consultation.
Does the ROI model change if I grow radish or cabbage instead of potato?
Yes — the ROI model varies significantly by crop. Radish produces the highest Category 2 (grade uplift) return because the Grade 1 premium on straight, undamaged radish over forked radish can exceed 200–300% — the highest grade differential of any Korean highland crop. The yield improvement (Category 1) is similar to potato. Machine damage (Category 3) is slightly lower for radish because the harvesting machinery is less mechanically demanding than the EP-AWB-1600 potato digger. Cabbage produces the lowest stone clearing ROI of the three main highland crops — its stone sensitivity is operational (machinery protection) rather than grade-determining (root quality), so the Category 2 grade uplift is absent. The primary ROI driver for cabbage is Category 3 (machinery damage avoidance) and Category 4 (labour). The ROI calculation for a cabbage-dominated farm typically shows longer breakeven than for potato or radish — confirming the 4-crop rotation’s value in improving the stone clearing ROI across the full farm portfolio.
Should I buy the THOR 2.4 or hire a contractor for the first few years while building the ROI case?
The buy vs hire decision for the initial period depends on contractor availability in your area and the per-hectare service fee compared to ownership cost. In some Korean highland counties, THOR-equipped contractors are not available or are fully booked by February — making machine ownership the only practical option for guaranteed spring preparation timing. Where contractors are available, hiring for Years 1–2 while observing the benefit improvement on your fields builds the empirical ROI data that makes the purchase decision for Year 3 based on actual rather than modelled benefit values. If the contractor’s per-hectare fee is below the per-hectare ownership cost at your farm scale, continuing to contract rather than own remains the economically correct choice. Korea Watanabe can provide a per-hectare ownership cost estimate for your farm area — compare this to the local contractor fee to determine the most economical long-term arrangement.
Does the potato machinery system investment also benefit from stone clearing, or only the stone clearing machines?
Every machine in the potato system performs better on stone-cleared fields — and their maintenance cost is lower. The PSW-3200 rotavator uses fewer blades per hectare on cleared fields. The EP-PAI-2100 planter shares last longer without stone impact damage. The EP-AWB-1600 digger shares require replacement less frequently, and its web separator operates at full efficiency rather than being impeded by stone fragments. The combined effect is that the complete 7-step Watanabe potato system achieves its rated performance on stone-cleared fields and sub-optimal performance on un-cleared fields — making the stone clearing investment the prerequisite that unlocks the full value of the entire system investment. Farmers who invest in the 7-step potato machinery system without the stone clearing foundation consistently report that the system performs below its capability — the missing element is always the stone clearing that the THOR 2.4 and CT-2100 provide at the foundation of the system.
What is the residual value of the THOR 2.4 and CT-2100 after 5 years — does this affect the ROI calculation?
Well-maintained THOR 2.4 and CT-2100 machines retain meaningful residual value after 5 years of Korean highland operation — the machines are built for 15–20 year service lives, and a 5-year-old machine with full maintenance history retains 40–60% of its new purchase price in the Korean second-hand agricultural machinery market. Including this residual value in the 5-year ROI calculation improves the ROI figure: the net investment is not just recovered through operational benefits but partially through the asset’s retained value at Year 5. A 50% residual value on the net investment (60 RU after subsidy) represents 30 RU of additional value above the operational benefits calculated in the model — further shortening the effective breakeven and improving the total 5-year return. Korea Watanabe advises buyers to maintain their machines to the published maintenance schedule specifically to preserve residual value as well as operational performance.
Build Your Farm-Specific ROI Model — Korea Watanabe Consultation
Farm area (ha) + crop mix + current Grade 1 % + annual machinery repair estimate → personalised 5-year ROI model with subsidy-adjusted breakeven timeline. No charge. Korea Watanabe, Ansan-si, Gyeonggi-do.
Editor: Cxm
