Within the Central Western area sowing early has become an essential component of maximising wheat yields on long fallows (18months). The practices of long fallowing and early sowing are quite often complimentary to one another as the fallow reduces the pressure of weeds and diseases that can quite often be difficult to control within early sown crops. Another core benefit is early sown crops sown to slow developing cultivars are more effective in utilising the additional stored water that has accumulated over the fallow period.
Taking aim at the flowing window
Within environments that are subject to cool winters and hot summers (Western NSW) one of the main drivers for yield quality is flowering time. When selecting a sowing time and cultivar combination the main goal is to get the crop to flower during the optimal window for yield. Within Southern NSW the optimal flowering window can vary from late August (in the west) to early October (in the east).
This window is the trade off point between increasing drought and head, and the declining risk of frost. There is no perfect time to flower, only a period of time where the level of yield exposure to the elements is minimised.
To best aim for this window within South Western NSW the optimal sowing times are listed below for the various varieties.
In systems with stored soil water such as a long summer fallow, winter and slow developing spring varieties sown early yield quicker than cultivars sown later. This is due to a longer growing season being available to early sown crops. This allows the crops to establish a deeper root system, extract more water, reduce evaporation and produce more biomass. In conditions where there is no stored soil water for growth around anthesis and grain filling, early sown crops are susceptible to haying off and will yield the same or in some cases less than faster developing cultivars sown later.
Grain yield for a range of cultivars for different development rates sown on two dates on long fallow at Rankins Springs in 2015.
- Growers with long fallows should have either a winter or slow spring cultivar in order to maximise yields under seasons with an April sowing opportunity.
- A mid-fast or fast cultivar should be used in non-fallow paddocks and in seasons where there is no establishment opportunity until May.
- Winter-slow and mid developing cultivars should not be sown dry, even on long fallows. If these cultivars are not established at their optimal times they will flower to late and suffer yield loss due to drought and heat stress.
- In seasons with a late break where an establishment opportunity hasn’t arrived by the start of May, yield will be maximised by dry sowing as much wheat area as possible to a mid-fast or fast developing cultivar.
- Keeping a winter cultivar (eg Wedgetail) gives the greatest range of potential establishment dates although majority of the value is limited to mixed farmers who can graze the crop within its vegetative stages.
- Winter cultivars take longer to reach stem elongation and are less susceptible to stem frost when compared to spring cultivars.
- There is unlikely to be a yield advantage of sowing winter cultivars intended only for grain production before early April as the extra accumulated biomass will not contribute to grain yield.
- Winter cultivars will be much more attractive once cultivars better adapted to Western NSW become available in 2018.