Depth control
The addition of an airseeder unit will not necessarily convert an acceptable tillage implement into an acceptable planting implement. Positive depth control of planting machines in the form of mechanical depth stops or a hydraulic stop is essential to avoid hydraulic creep.
Some other compromises to minimise depth variation:
- Frame length and width affects seed depth. Flexible frames with sectional widths <3m will assist, as will large diameter tandem walking wheels.
- Planter units fitted behind tillage implements give good depth control. Depth control wheels should be as close as possible to the line of planting tines. Select planting tines on bars towards the centre of the planter rather than on the front or rear bar.
- To overcome the problem of high breakout tines driving too deep into small hills in the seedbed, some form of scraper on the tine may be useful. Flat chisel tines have some advantage in displacing surplus soil.
- In melon-hole country or in controlled traffic situations where crossing contour banks is necessary, ground following tools such as pivoting tines or parallelograms will give much better depth control and may justify the additional cost over fixed tines.
- Press wheels will often compensate for poor depth control.
Deep moisture
If planting moisture is deeper than normal, deep furrow planting techniques (using adapted scarifier or chisel ploughs or press wheel planters) will allow seed placement in the moisture zone. Wider row spacings to avoid soil coverage of adjacent rows. and avoid excessive planting speeds or excess soil will be thrown into the corresponding row. Common features of deep furrow techniques include narrow tines with high breakout pressures, narrow points to minimise soil disturbance and moisture loss and high pressure narrow press wheels (slot into the seed trench and help stabilise it) which reduce the seed-surface distance and help seed/soil contact.
Plant spacing
Wheat is normally planted in 15-30 cm rows. Row spacings out to about 36 cm have little effect on yield in most seasons, although some yield reduction may be expected in very good seasons in wide rows. With zero tillage and moisture-seeking machinery there has been a trend to plant in rows as wide as 45 or 50 cm. When planting in wider rows the normal plant population should be maintained. After assessing the planting rate of seed, ensure the planter is spacing seed at the right distance apart. Using data from the following tables, calculate the right seed placing distance to give the required established plant spacing and achieve a desired plant population density per hectare.
Note: 1 000 000 plants/ha is equivalent to 100 plants/m2. 50 000 plants/ha is equivalent to 5 plants/m2.
Example: In 25 cm rows 20 plants/m of row is the equivalent of about 800,000/ha.
