Sowing Rate Calculators

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Sowing rate is the quantity of seed sown per unit area, expressed as seeds/m² or kg/ha. The correct rate ensures the target plant population for maximum yield. The formula is: sowing rate (kg/ha) = (target plants/m² × TSW × 100) / (germination% × establishment%). TSW (thousand seed weight in grams), germination percentage from the seed certificate, and expected field establishment are the key inputs. Target populations vary by crop: wheat 200–350 plants/m²; maize 6–9 plants/m²; canola 30–60 plants/m².

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Sowing Rate Formula

kg/ha = (target plants/m² × TSW × 100) / (germination% × establishment%)

Example: wheat target 300 plants/m²; TSW = 45 g; germination 92%; establishment 90%: Rate = (300 × 45 × 100)/(92 × 90) = 1,350,000/8,280 = 163 kg/ha.

Target Plant Populations

  • Winter wheat: 200–350 plants/m²
  • Maize: 6–9 plants/m² (65,000–90,000/ha)
  • Soybean: 30–50 plants/m²
  • Canola: 30–60 plants/m²
  • Sunflower: 5–7 plants/m²

Seeds/m² Calculation

Seeds/m² = target plants/m² / (germination% × establishment%) × 100. Example: maize, target 8 plants/m², germination 95%, establishment 92%: Seeds/m² = 8/(0.95 × 0.92) = 9.2 seeds/m².

Calibration

Use actual TSW from the seed bag label — different seed lots vary ±20–30%. Calibrate seeding equipment against calculated kg/ha before planting.

Glossary

Sowing Rate (kg/ha)
(Target plants/m² × TSW × 100) / (germination% × establishment%); adjusted for thousand seed weight and seed quality; always use actual TSW from the seed certificate.
Thousand Seed Weight (TSW)
Weight of 1,000 seeds in grams; determines seeds/kg (= 1,000,000/TSW); printed on seed certificate; varies ±20–30% between lots; essential for accurate sowing rate calculation.
Field Establishment Rate
Proportion of germinated seeds that become established plants in field conditions; typically 85–95%; lower in difficult seedbeds; multiplied by germination% to get total seed-to-plant conversion.

Frequently Asked Questions

kg/ha = (target plants/m² × TSW × 100) / (germination% × establishment%). TSW = thousand seed weight from seed bag. Germination% from seed certificate. Establishment% = expected proportion of germinated seeds that emerge as established plants (typically 85–95% in good conditions). Example: canola, target 50 plants/m², TSW = 4.5 g, germination 96%, establishment 90%: Rate = (50 × 4.5 × 100)/(96 × 90) = 22,500/8,640 = 2.6 kg/ha.

TSW = weight of exactly 1,000 seeds in grams; seeds/kg = 1,000,000/TSW. A wheat lot with TSW = 45 g has 22,222 seeds/kg; TSW = 55 g has 18,182 seeds/kg — the same 160 kg/ha gives very different seeding rates. Always use the actual TSW from the seed certificate for the specific lot being planted. Never use a fixed kg/ha without checking TSW, as variety and season differences cause 20–30% variation.

Germination% indicates what proportion of seeds will germinate under ideal lab conditions. Field establishment% is lower because some germinated seeds fail to emerge. Effective establishment = germination% × establishment%. To achieve 8 plants/m² with 88% germination and 90% establishment: effective rate = 0.88 × 0.90 = 0.79 → must sow 8/0.79 = 10.1 seeds/m². Lower germination% means you must increase sowing rate proportionally to still achieve the target plant population.

Too low: fewer plants per area → weed competition increases; individual plants compensate with more tillers/branches but total yield potential is reduced. Too high: excessive competition → smaller individuals; in cereals → weak stems prone to lodging (falling over before harvest); unnecessary seed cost. Optimal: flat yield curve around the optimum means ±20% from target doesn't dramatically affect yield; precise calibration matters most for expensive seed (hybrids, treated varieties) or challenging conditions.