While research across much of the Australian grain belt supports earlier sowing as a way to improve winter crop yields, many challenges exist for sowing earlier than currently considered “normal”.
Unreliable rain in early sowing windows (April/May), stresses the need to assess technology to allow for more reliable early sowing.
Ongoing research suggests earlier sowing of appropriate slower maturing or/and winter habit varieties of both cereals and canola develop deeper roots due to a longer vegetative phase. Deeper roots better utilise soil water and nutrients, with the end result of higher yield potential, often combined with valuable grazing opportunities.
For example, research led by Dr John Kirkegaard, CSIRO, in a long-term study at Harden, noted early sowing of an appropriate maturity wheat variety (April verses May) may result in yield improving from 4.7 to 5.5 t/ha. Combined with appropriate agronomy, like adding 50 kg/ha extra nitrogen to satisfy higher yield potential, yield can increase to 6.0 t/ha. Potential yield gains for canola are even higher.
Based on long term rainfall data at a typical NSW central west area, Purlewaugh, the “CliMate” App (www.climateapp.net.au) predicts there is a 44 percent probability of receiving 25mm or more rain over a five-day period in April and a 41 percent probability in May. Combining April and May, the probability goes to 67 percent.
Clearly if one requires 25mm or more rain event for early sowing there is less than a 50 percent chance of sowing in April and a one third chance of not being able to sow in the April/May window. A lot of years early sowing may not be possible.
However, if one could establish wheat or other crops like canola or pulses on a 10mm rain event probability of successfully sowing early increase dramatically. In the Purlewaugh example, CliMate indicates the probability increases to 70 percent for April, 71 percent for May and 90 percent for combined April/May.
“CliMate” is useful and easy to use when exploring any sowing window and designated rainfall event for most locations in the grain belt.
Reliable early sowing, especially on heavy soils and in drier areas (provided there is good sub soil moisture) need to occur in many years on little or no sowing rain. Moisture seeking with narrow points, with modified delvers plus press wheels allows seed to be placed in moisture at depth, but not with too much soil cover over the seed.
A risk with moisture seeking is if heavy rains fall between sowing and emergence. One can check this risk with “CliMate”. There will always be risk with unexpected heavy rain events (that melt delved soil into the sowing row placing soil too thick over seed). However medium-term rainfall forecasts may help minimise this risk.
In non-moisture seeking sowing where variable soil types exist across a property, lighter soils van be preferred for early sowing. Generally, it is possible to establish crops on smaller rain events on lighter textured soils, compared to heavier textured clays, thereby increasing the probability of early sowing success.
Stubble retention, early and timely control of fallow weeds helps maximise sub soil moisture levels for all soils and helps ensure fallow moisture is relatively close to the soil surface. The closer moisture is to the surface the less rain is needed for sowing at normal depth. Stubble retention is also important for efficient capture of fallow rain.
Capitalising on the potential for higher yield from early sowing requires greater attention to soil fertility, especially nitrogen. Disease and pest management can also be different for early sown crops. For example, in wheat it is important to guard against increased barley yellow dwarf virus risk.
