Tropical pasture grasses produce small, light seeds that germinate best when pressed against moist, firm soil. Loose, cloddy, or trash-covered seedbeds increase the risk of seed dying before roots can access subsurface moisture.
Controlling existing vegetation
Before cultivation, address existing grass and weed competition. Options include:
- Knockdown herbicide (e.g. glyphosate) 4–6 weeks before sowing
- Heavy grazing to reduce biomass, followed by herbicide
- Cultivation to bury vegetation and allow decomposition
For scrub country being developed, ensure all timber is pushed and burnt well before sowing so ash residue does not suppress germination.
Cultivation and seedbed preparation
Where cultivation is used (light to medium soils), aim for a fine, firm seedbed without deep furrows. One to two passes with a disc or offset disc followed by a roller or cultipacker is usually sufficient. Avoid over-cultivation on heavy cracking clays — this creates a hard crust when wet and crumbles into large clods when dry.
On no-till systems, ensure adequate herbicide knockdown and consider using a narrow-tine pasture seeder that places seed directly into the soil with good press-wheel contact.
Sowing depth
- Most tropical grasses: 5–15 mm
- Buffel grass: 10–15 mm
- Signal/humidicola: 5–10 mm (very small seed — shallower is better)
- Legume seed: 10–20 mm depending on species
For aerial or broadcast sowing (used in inaccessible or rough country), higher sowing rates compensate for variable depth and contact. Aerial sowing works best when followed immediately by stock trampling or a light rainfall event to press seed into the soil surface.
Seed rates and rhizobium inoculation
Use certified seed where possible and check germination percentage. Adjust sowing rate for actual viable seed. Legume seed must be inoculated with the correct rhizobium strain immediately before sowing — pre-inoculated coated seed is available and more practical for large areas. Do not co-apply insecticide and rhizobium — chemicals kill the bacteria.