Rotavator: Buy, Hire, or Stay with Cultivator and Harrow
A farmer in Kota has 8 ha of sandy loam and a new 45 hp tractor. For wheat he currently hires a rotavator at Rs 2,200/ha for one pass. He is considering buying a 1.8 m rotavator for Rs 1.25 lakh, financed at 9% interest over 5 years. Field data: rotavator at 4.0 km/h with 75% field efficiency and 8 L diesel/h; his 2.1 m cultivator at 5.5 km/h with 80% efficiency and 5.5 L/h; a 2.4 m disc harrow at 6.0 km/h with 80% efficiency and 5 L/h. Diesel costs Rs 90/L and labour Rs 500 for an 8-hour day. A seedbed can be made either with two cultivator passes plus one harrow pass, or with one rotavator pass. The tractor is otherwise idle for 5 months. He can earn Rs 2,200/ha by hiring out the rotavator to neighbours, but only for about 10 ha a season because of local competition.
1. Using EFC (ha/h) = width (m) x speed (km/h) x field efficiency / 10, calculate the time, diesel and labour cost per hectare for each implement and for the two seedbed systems.
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Cultivator: EFC = 2.1 x 5.5 x 0.80/10 = 0.924 ha/h, so 1.08 h/ha. Diesel = 5.5 x 1.08 = 5.95 L = Rs 536. Labour = 1.08/8 x 500 = Rs 68. Total Rs 604/pass.
Disc harrow: EFC = 2.4 x 6.0 x 0.80/10 = 1.152 ha/h, so 0.87 h/ha. Diesel = 5 x 0.87 = 4.34 L = Rs 391. Labour = 0.87/8 x 500 = Rs 54. Total Rs 445/pass.
Rotavator: EFC = 1.8 x 4.0 x 0.75/10 = 0.54 ha/h, so 1.85 h/ha. Diesel = 8 x 1.85 = 14.8 L = Rs 1,333. Labour = 1.85/8 x 500 = Rs 116. Total Rs 1,449/pass.
Seedbed comparisons (variable cost only):
- Conventional: 2 x 604 + 445 = Rs 1,653/ha, time 3.03 h, diesel 16.1 L.
- Rotavator: Rs 1,449/ha, time 1.85 h, diesel 14.8 L.
The rotavator is Rs 204/ha cheaper in running cost and saves 1.18 h/ha, but it works the soil at one depth and the cultivator system leaves more surface tilth. If cotton residue is heavy, a second rotavator pass may be needed, which reverses the cost advantage.
2. Compare owning the rotavator with hiring it at Rs 2,200/ha. Assume a 10-year life, average interest on half the price, and repairs/insurance at 5% of price per year. Find the break-even area and decide, including the offer of 10 ha of custom work.
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Annual fixed cost of ownership: depreciation 1,25,000/10 = Rs 12,500; interest 0.09 x 62,500 = Rs 5,625; repairs and insurance 0.05 x 1,25,000 = Rs 6,250. Total Rs 24,375/year.
Own variable cost: 1,449/ha x 8 ha = Rs 11,592. Total for 8 ha = Rs 35,967, i.e. Rs 4,496/ha, against Rs 2,200/ha for hiring. Hiring wins clearly.
Break-even area: 24,375/A + 1,449 = 2,200, so A = 24,375/751 = 32.4 ha/year. He has only 8 ha and can get 10 ha of custom work, total 18 ha. At 18 ha: 24,375/18 + 1,449 = Rs 2,803/ha, still above Rs 2,200. He would need about 24 ha of custom work to reach break-even, which the local competition will not allow.
Decision: Hire the rotavator for wheat, and use the cultivator and harrow for normal seedbeds. Buying is justified only if his area expands to roughly 32 ha or a reliable custom-hiring contract for 25 ha or more appears. The 45 hp tractor can handle a 1.8 m rotavator comfortably, so power is not the constraint; utilisation is.
3. Beyond the economics, what agronomic and engineering risks arise if he uses a rotavator at the same depth every season? Suggest a rotation of tillage operations.
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Risks:
- A rotavator works to a fixed depth, so repeated use creates a compacted layer just below the tilled zone (plough pan), restricting wheat root depth and water infiltration.
- The blades pulverise soil structure and leave a fine, powdery surface that crusts after irrigation and is prone to wind erosion on sandy loam.
- Crop residue is chopped and mixed shallowly, which can cause poor seed placement and uneven emergence if the field is not levelled.
- Rotavating wet soil smears the sides of the tilled strip and makes the compaction worse.
- Fuel and time per hectare are high; a second pass is often needed, which erodes the cost advantage.
Tillage rotation:
- Year 1: two cultivator passes + harrow for wheat; retain residue.
- Year 2: one rotavator pass only if the seedbed is rough or cotton stalks are heavy.
- Every third year: chisel plough or subsoiler to 25-30 cm to break the pan, followed by levelling.
- Operate only at friable moisture, vary the working depth slightly, keep blades sharp, and check the tractor's draft and wheel slip. Use the rotavator as a rescue tool for late, cloddy fields, not as the default every season.