Semi-dwarf wheat plants
Semi-dwarf wheat plants
Depth of sowing
Deep sowing may delay or stifle emergence, while shallow sowing risks seed damage from herbicide uptake. The length of the first shoot (coleoptile) has a bearing on depth of sowing. If a variety is sown deeper than the natural growth extension of the coleoptile then the seedling may not emerge. Most current varieties are derived from so
called semi-dwarf lines which have shorter stems and shorter coleoptiles than older varieties.
Seasonal differences in depth and availability of moisture influence decisions about depth of sowing. A sowing depth between 25mm and 50mm, depending on soil type and available moisture, is a useful guide to sensible seed placement. In moist conditions shallower may encourage faster emergence and crop establishment.
Seeding rate
To achieve total ground cover and establish the foundation for maximum yield, a crop density of 150-200 plants per square metre is needed. This equates to a seeding rate of about 60kg/ha in lower rainfall zones (up to 400mm annual rainfall) and about 80-90kg/ha in the higher rainfall zones.
Sowing rate can be calculated by knowing the seed weight, germination percentage and the required plant density.
For example: wheat seed with a seed weight of 4.5gm/100seeds, germination percentage of 95 per cent and a required plant density of 170 plants/m² = 4.5 x (10/95) x 170 = 80.5 kg/ha.
The source of seed is very important. Most farmers grow and store their own seed for use in the following year.
However, when introducing a new variety or extra seed, it is sensible to source the best quality seed. If certified seed is not available, a thorough inspection for insects, weed seeds or mixed grains prior to purchase is the obvious precaution.
Seed dressings
Seed dressings for the control of smuts and bunts should be applied to all wheat seed prior to sowing. Although major losses from these diseases are now rare, this is due to the routine use of seed treatments. Seed not treated prior to sowing may result in yield losses as high as 85 per cent.
Seed dressing
Some seed dressings can also suppress a selection of wind or stubble borne diseases, however some chemicals can reduce coleoptile length. Advice on products and application rates is also available from cropping advisors or chemical resellers.
Crop nutrition
Soil tests are available to assist in the assessment of paddock nutrient status.
Adequate phosphorus is essential for the early growth of wheat. Most Victorian soils are low in available phosphorus, and much of the crop requirement will need to be supplied through the application of fertilisers at sowing time. Paddock history of phosphorus application and crop yields, in conjunction with soil test results and economics of application will determine the rates required.
The rule of thumb is a requirement for 3kg/ha of available phosphorus for each tonne of wheat anticipated. The application is then adjusted in the light of soil test results.
Table 3. Adequate soil phosphorous ranges (Colwell) for different soil types.
Nitrogen availability is equally important. Besides its role in plant growth, the availability of soil nitrogen at grain fill, along with soil moisture, is the key determinant of grain protein. The farmer has a high degree of control over nitrogen build up and availability through the choice of crop sequences, use of long fallow and tillage methods. The availability of nitrogen in the soil will be affected by many factors: soil organic matter, paddock history including fallowing, soil type, moisture content, time of year and tillage methods. High yields are a drain on soil nitrogen.
Conversely, low yield and summer rain to mineralise nitrogen can mobilise soil nitrogen for the next crop. Soil tests for N assessment should be done as close as possible to sowing time and at the same time each year.
Cropping advisors are a good source of support in determining fertiliser application strategies.
