Crop establishment
Factors affecting crop establishment
Poor seedling establishment occurs because of:
- inaccurate or variable seed depth
- poor seed-soil contact
- poor quality seed
- unsuitable soil temperatures
- soil insects and soil disease
- herbicide residues.
The impact of poor establishment and seedling vigour will be reduced if seedbed requirements are matched to machinery capabilities and seed quality.
Surface sealing may be a problem if heavy rains fall immediately after sowing and prior to emergence. The emerging shoot is often unable to penetrate the hard surface crust that forms as the soil dries. The problem is more prevalent on soils with declining organic matter, especially red-brown earths and grey clays. Harrowing as soon as practical after sealing has occurred will break the soil crust and allow leaf development to proceed. In many instances this has doubled the initial emergence. Gypsum application may help alleviate this problem on hard setting clays.
Weeds
Weed control is essential if wheat is to make full use of stored summer rainfall, and to prevent weed seeds from contaminating the grain sample at harvest. Plan weed management well before planting and consider options such as chemical as well as non-chemical control.
Non-chemical weed control
Crop rotation, especially with summer crops, can be an effective means of managing a spectrum of weeds that will result from continuous wheat cropping. Barley is a more vigorous competitor with weeds than wheat and may be a suitable option for weed suppression. Increased planting rates and narrow rows may also help where the weed load has not developed to a serious level.
Chemical weed control
When selecting a herbicide it is important to know your crop growth stage, weeds present and plant back period. For best results, spray weeds while they are small and actively growing. Herbicides must be applied at the correct stage of crop growth, or significant yield losses may occur. Check product labels for up to date registrations and application methods.
Winter cereal growth stages (L=leaf, T=tiller)
1. Three leaf stage
Three leaves have unfolded (L), the fourth leaf is present, yet to fully expand. A leaf is not fully emerged until the point of leaf base attachment with the leaf sheath (ligule and auricles) is clearly visible.
2. Start of tillering
Tillers come from buds at the base of the lower leaves, where the leaf sheath joins a node on the true stem in the base of the young plant at, or just below ground level. The first tiller (T) appears between a lower leaf and the main shoot. Usually 3-4 leaves are present.
3. Early tillering
Tillers continue to appear between the lower leaves and the main shoot, that now has 4-5 fully emerged leaves, plus one or more tillers.
4. Mid tillering
The main shoot has 5-6 fully emerged leaves plus one or more tillers. New leaves continue to be produced and the main stem and tillers increase in size as the leaf blades and sheaths expand and elongate.
5. Late tillering - start of jointing
When the main tiller is mature, the growing point on the true stem deep in the base of the plant stops producing leaves and develops the young seed head at its apex. Under normal growing conditions, this occurs when the main shoot has between 5-7 developed leaves.
6. Jointing
When the reproductive (noding or jointing) stage has begun, small hard swellings (nodes) develop on the stem at the point of leaf sheath attachment. Its start may be first detected by the appearance or feel of a node in the stem slightly above the ground level. At this early stage the first joint can be more easily seen if the stem is dissected along its length.
The stem between the nodes elongates rapidly, starting from the bottom node, pushing the seed head upwards. The developing head may be seen by dissecting a stem.
7. Early boot stage
A visible swelling of the head within the sheath of the flag leaf can be seen at the top of the main stem.
Irrigation
Wheat responds well to irrigation. Critical periods for water are at tillering and flowering. Water requirements (in-crop) after starting with a full profile will be approximately 3 ML/ha. Water use efficiency (WUE) for wheat ranges between 10 and 20 kg/mm soil water/ha. As an example, if the expected yield output is 15 kg/mm and the yield target is 4.5 tonnes/ha, the water required would be approximately 300 mm or 3 ML of irrigation water/ha (assuming no in-crop rainfall and full moisture profile).
Irrigated wheat crops will normally require additional nitrogen fertiliser:
- wheat or barley double-cropped after cotton or grain sorghum - 140 kg N/ha
- wheat or barley double-cropped after maize - 120 kg N/ha
- wheat or barley double-cropped after soybean or fallow - 100 kg N/ha.
Note: For protein levels of 11.5 % or higher in fully irrigated crops, a late application of nitrogen at booting would be necessary.
Consider near-infrared light plant tissue testing in-crop to determine side dressing rates of nitrogen to obtain optimum yield and protein levels.
