🌱 Calculators

Seed Cultural Value

Computes the cultural value of a seed lot, CV = purity × germination ÷ 100, with both percentages taken from the laboratory analysis report. The result is the percentage of the lot's weight that is pure, live seed — what will actually become a plant: a lot with 98.5% purity and 92% germination delivers 90.6% useful seed, and the remaining 9.4% is inert matter and dead seed you are paying for. It is the basis for correcting the seeding rate (target kg/ha ÷ CV × 100) and for comparing prices between lots of different quality; the English equivalent is pure live seed (PLS). Enter the physical purity and the germination percentage.

Physical purity of the lot (%) Germination percentage (%)

Result

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Pure Live Seed: how much of the bag becomes a crop

When a seed order is about to close, price per bag lies. Two lots of the same cultivar can carry the same tag and put very different plant numbers in the ground, since part of the weight is inert matter, other species and dead seed. Planning a seeding rate without discounting that misses the target stand in both directions: a thin population when the lot was worse than it looked, wasted money when it was better. The laboratory analysis report holds the two figures that settle it.

CV = purity × germination ÷ 100, both percentages read straight off the report: physical purity is the weight percentage of pure seed of the declared species, and germination is the share of normal seedlings in the standard test. With the values on screen, 98.5 percent purity and 92 percent germination, cultural value works out to 90.62 percent — of every 100 kg in the lot, 90.6 kg is pure live seed and 9.4 kg is material you buy and never harvest. Trade standards usually sit between 70 and 85 percent germination, with purity above 98 percent.

Cultural value measures viable quantity, never vigour. Two lots at 92 percent germination can diverge sharply in cold or waterlogged soil, and only a tetrazolium or accelerated ageing test tells one from the other. The germination figure is a laboratory result under controlled conditions: field emergence usually runs below it, and fine-tuning a seeding rate calls for a regional field factor on top. Reports expire as well, since germination drops in storage, and treated or pelleted seed carries weight that is no seed at all.

Frequently asked questions

With a cultural value of 90.62 percent, how much more seed do I need?

Divide the target quantity by the cultural value and multiply by 100. If the plan calls for 60 kg/ha of pure viable seed, this lot demands 60 ÷ 90.62 × 100 = 66.2 kg/ha, nearly 6 kg extra per hectare. Seeding by population follows the same logic: 300,000 viable seeds per hectare means metering 331,000 seeds from this lot. Apply the correction before calibrating the drill rather than after the first pass, so the seeds-per-metre setting already carries it.

Can cultural value compare prices between lots?

That is where it earns its keep. Divide price per kilo by the cultural value as a decimal and you get the cost of a kilo of useful seed. A lot at 5.00 per kg with a 90.62 percent cultural value costs 5.52 per usable kilo; another offered at 4.80 per kg, but with 96 percent purity and 85 percent germination, has a cultural value of 81.6 percent and costs 5.88 — cheaper on the label, dearer in the field. Add freight too, charged on total weight, inert matter included.

Does a high cultural value guarantee a good stand?

No. It guarantees that most of the weight is pure seed able to sprout under ideal laboratory conditions, and nothing beyond that. Weak vigour, wrong seeding depth, compacted soil, heavy rain during emergence and pest attack all thin a stand carrying the same 90.62 percent. One practical note on the form: both fields accept percentages from 0 to 100 only, and typing 0.985 instead of 98.5 returns a cultural value of 0.91 percent, an error loud enough to catch itself.

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Net Assimilation Rate (Gregory Formula)

Computes the net assimilation rate of a plant by the classic Gregory formula, the core of plant growth analysis. The rate is the dry matter gain per day multiplied by the ratio between the difference of the natural logarithms of the two leaf areas and the difference of the areas themselves: NAR = [(W2 − W1) ÷ interval] × [ln(A2) − ln(A1)] ÷ (A2 − A1). The result measures net photosynthetic efficiency per unit of leaf area, with respiration already discounted — typical values for annual crops in full growth lie between 5 and 15 grams per square metre of leaf per day, and a decline along the cycle indicates canopy self-shading. Gregory's (1926) logarithmic form was adopted rather than the approximation NAR = mass gain ÷ (mean leaf area × interval), because the former is exact when leaf area grows linearly with dry mass over the interval, which is the standard assumption of classic growth analysis. Enter the initial and final dry masses, the initial and final leaf areas and the interval between the two samplings.

The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.