Tillage management: What factors affect seed rate?

Seeding rate is affected by many different factors. The thousand grain weight of the seed, the time of sowing, sowing conditions and the target plant population will all impact on the seed rate.

When calculating seed rate you will need the following three figures:
  • The target plant population (plants/m²);
  • The thousand grain weight (TGW) of the seed;
  • The estimated plant establishment percentage.

For example, the seed rate will be 183kg/ha (11.7st/ac) at a target plant population of 300 plants/m², a TGW of 51.9 and an estimated establishment of 85%.

Thousand grain weight

The TGW is provided on each individual bag of seed and will vary between different varieties, batches and seasons. Results from Department of Agriculture trials provide TGW figures for different varieties. A list of these TGWs is provided for spring barley, spring wheat and spring oats below.

Where seed is home saved the TGW must be calculated. This can be done by counting 1,000 grains and weighing the resulting sample. Growers may also count out 100 grains and multiply the weight by 10. This should be carried out a number of times in order to get a representative figure.

Spring barley:
  • Irina – 51.6;
  • Mickle – 50.3;
  • Propino – 52.6;
  • Gangway – 49.3;
  • Limona – 48;
  • Hacker – 48.7;
  • Paustian – 49.3;
  • Planet – 51.9.

Spring wheat:
  • Quintus – 46.8;
  • RGT Doubleshot – 42.5.

Spring oats:
  • Barra – 41.2;
  • Binary – 44.3;
  • Husky – 42;
  • Keely – 41.3.