Start with the soil
Undertake a full assessment of the soil and its nutrient levels through visual examination, looking into paddock history and soil testing. Soils which are acid, sodic, saline, nitrate deficient or too high in aluminium will limit the productivity of new and improved pastures. Applications of lime are beneficial if soils have a pHCa below 4.6.
Nutrients essential for pasture growth include:
- Nitrogen – available from urea and ammonium fertilisers or via legume-based species.
- Phosphorus – a frequently limited nutrient in Australian soils, applied as superphosphate and can be broadcast on existing pastures and placed in the soil during the sowing of new pastures.
- Potassium – a common deficiency in soils with a history of cropping or hay removal, and is available as murate of potash.
- Sulfur – can be applied in single superphosphate and gypsum, and supplies sulfur and calcium.
- Calcium – important to soil structure and is a component of lime, dolomite and gypsum.
- Magnesium – deficiency is seen in acid sandy soils and impacts animal health; can be rectified with dolomite or dolomite/lime mixtures.
What is inoculation and is it necessary?
Rhizobium is a soil bacterium which fixes nitrogen inside the root nodules of legumes and, in turn, supports the plant to produce nitrogen which is returned to the soil.
Unless the roots are nodulated by effective strains of rhizobia, the plant will source its nitrogen from the soil and deplete soil reserves. When rhizobia are not present in high numbers in the soil, they must be introduced via a process called seed inoculation.
Inoculated seed can also be pelleted to provide a protective layer of fine lime to improve rhizobia survival.
Nitrogen increases via legume pastures have benefits for companion grasses as the nitrogen cycles over time, and grain yield and quality is improved in cereal crops.
Inoculation of seed is considered cheap insurance.
When deciding on inoculation, producers need to consider the following:
- The paddock history – have well-nodulated plants of the same species or those which require the same inoculant group been present, or is the legume new to the paddock?
- What is the length of the previous pasture rotation?
- Can an ideal environment for optimum rhizobia survival be guaranteed (soil moisture, temperature and pH)?
Sowing and seeding
Producers have three choices when planting a new pasture:
- Conventional sowing: This technique involves preparation of the soil using cultivation and harrows and, provided weed control and nutrition is well managed, can deliver optimal establishment due to improved seed-to-soil contact and germination.
- Minimum and no-till: A higher degree of management is needed to ensure successful soil‑to‑seed contact but, by using well setup equipment and press wheels, the benefits are minimal soil disruption and reduced weed germination.
- Broadcasting: This is an option in challenging or timbered terrain or across vast landscapes, and can be carried out by air or from a vehicle. Germination can be limited due to poor soil-to-seed contact and fertiliser placement.
Regardless of the sowing method, to ensure establishment success producers need to:
- source the freshest seed available
- sow in the optimum seeding window – autumn is considered ideal in southern systems for reducing the risk of failure from heat and moisture stress
- follow seed company and agronomic advice on seed inoculation and pest control
- ensure seeding equipment is correctly calibrated to meet the spacing and seed rates recommended for the species.