Muga and eri side by side, one acre in Assam at 2025-26 prices. The headline benefit–cost ratios favour muga — but the two statements are not built on the same accounting basis, and the difference matters more than the gap between the ratios.
Comparative financial metrics
| Metric (one acre, Assam, 2025-26) | Muga (som) | Eri (castor) |
|---|---|---|
| Plantation establishment cost (₹) | 45,522 | 38,222 |
| Cost charged to the year (₹) | 2,276 (5 % apportioned) | 38,222 (full cost) |
| Silkworm seed brushed | 800 dfls, 2 crops | 400 dfls, 4 crops |
| Labour engaged (MD per year) | 160 | 148 |
| Total cost (₹ per acre per year) | 98,233 | 1,06,722 |
| Gross return (₹ per acre per year) | 1,98,720 | 2,04,000 |
| Net return (₹ per acre per year) | 1,00,487 | 97,278 |
| Benefit–cost ratio | 2.02 | 1.91 |
| Principal revenue head | Reeling cocoons (97 % of return) | Pupae (82 % of return) |
The two models are not costed on an identical basis. Muga charges only the
apportioned 5 % share of plantation establishment to the year, while eri charges the full
establishment cost of the castor plantation. On a comparable apportioned basis the eri
benefit–cost ratio would be appreciably higher. Both models exclude the imputed value
of family labour and land rent.
- Concentration risk runs the other way from the ratio. Muga’s return rests on reeling cocoons and eri’s on pupae — but the pupae market is thinner and more local than the cocoon market, so eri’s 1.91 carries more downside than muga’s 2.02.
- Eri is the more labour-efficient of the two at 148 man-days against 160, while turning four crops a year instead of two — which matters where household labour is the binding constraint rather than land.
- Castor is an annual and som is a perennial. That is the real reason the accounting differs, and it is also why eri can be started and stopped in a season whereas muga is a four-year commitment before the first full crop.