Seed, Spacing and a Doubtful Bill
Your nursery must support a 12 ha block plantation at 3 m × 3 m spacing. The contractor's bill claims he has supplied 20,000 seedlings and asks for full payment. The sowing register of that nursery shows 22,000 seeds were sown. The tested seed lot has a germination of 68%, and nursery records show that 20% of germinated stock is lost to culling and transit. A field casualty of 15% is to be built into the planting target. Separately, a soil test of the plantation site shows pH 8.6, EC 0.9 dS/m and organic carbon 0.28%; a supplier is offering gypsum plus a microbial "growth booster" at ₹18,000 for the block. The Range Officer wants a written opinion on both.
1. Work out the seedlings required for the block and the seedlings that 22,000 seeds could actually yield. Does the bill stand?
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Step by step:
- Plants per hectare at 3 m × 3 m = 10,000 ÷ 9 = 1,111.
- For 12 ha: 1,111 × 12 = 13,333 plants.
- Add 15% field casualty: 13,333 × 1.15 = 15,333 seedlings needed at the field gate.
- Usable seedlings per seed = 0.68 × 0.80 = 0.544.
- From 22,000 seeds: 22,000 × 0.544 = 11,968 seedlings - short of the 15,333 required.
- Seeds that should have been sown for 15,333 seedlings: 15,333 ÷ 0.544 = 28,186.
The arithmetic does not close. The register supports at most about 12,000 usable seedlings, so a claim of 20,000 delivered from that bed cannot be true. Either the stock was bought in and mislabelled, or the register is false. The field requirement can be met by about 15,350 healthy seedlings, so quantity itself is not the issue - provenance and quality are. Recommend physical enumeration by bed, root-collar diameter and root-shoot ratio checks, and payment against verified count only.
2. Is the ₹18,000 gypsum-plus-booster offer worth accepting? Reason from pH, EC and organic carbon.
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pH 8.6 indicates alkalinity; EC 0.9 dS/m is below 1, so the soil is not saline and the salinity hazard is minor, but the combination points to a sodic or sodic-alkaline trend. Organic carbon at 0.28% is very low, and that, more than pH, will limit survival.
Gypsum is a legitimate amendment for sodic soils because calcium displaces sodium, but the dose must follow the exchangeable sodium percentage and gypsum requirement from a laboratory test, not a flat rate per hectare. A blanket purchase before that test is premature. The "microbial growth booster" has no labelled composition, no trial data on this soil and no basis for the price - reject it pending evidence.
Better use of the money: a proper soil test including ESP, farmyard manure or compost to lift organic carbon, and a species choice tolerant of alkalinity, such as Acacia nilotica, neem or arjun, rather than a sensitive species that will fail and be blamed on the guard. Spend on diagnosis before inputs.
3. Why should seed be treated before sowing, and what would you prescribe for a legume versus a hard-coated species?
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Seed treatment serves three purposes: breaking dormancy so germination is uniform, killing seed-borne and soil-borne pathogens before the seedling's own defences develop, and, in legumes, introducing the right rhizobia so nitrogen fixation begins early. Uniform germination also makes the arithmetic above predictable - a bed that germinates over six weeks cannot be counted or culled properly.
For a legume such as Acacia nilotica or Pongamia, prescribe hot-water treatment at around 80°C followed by soaking, then inoculation with the matching Rhizobium culture in a slurry with jaggery or gum arabic before sowing. Critically, do not mix a fungicide with the inoculant - it will kill the rhizobia.
For a hard-coated species, use hot-water or acid scarification, or mechanical nicking, depending on the thickness of the coat. Over-treatment is a real risk: too long in hot water kills the embryo, and excess fungicide damages the emerging radicle. Treat, then test germination on a sample before committing the whole lot to the bed.