Site elevation broadens the yield/frost equation
GroundCover™ Issue: 126 | Author: Bob Freebairn, agricultural consultant, Coonabarabran, NSW
- GRDC-funded research by Agricultural Marketing and Production Systems has highlighted large environment and production differences within paddocks that are related to elevation
- These differences can greatly affect crop yield
- Agronomic factors such as variety choice and sowing time can maximise yield in both high and low elevation zones
Site elevation broadens the yield/frost equation
Climatic differences, especially temperature, can be considerable over a given landscape or even one paddock. These differences, especially in temperature and seasonal frost number and severity, can undermine the best agronomy practices, especially sowing time and variety choice.
However, if agronomy practices are varied according to elevation parameters and to better suit the different environments within a paddock, profitability can be made more secure in many typical-sized paddocks.
Over the past two seasons, farmer-owned Agricultural Marketing and Production Systems (AMPS) has conducted research at north-west NSW locations with results highlighting big in-paddock elevation differences and different yield outcomes within a crop.
AMPS research agronomist Matt Gardner and colleagues from Agromax Consulting (Greg Giblett and Sam Simons) conducted the joint AMPS and GRDC-funded elevation by planting date research around Spring Ridge (Liverpool Plains) and Moree in north-west NSW.
Mr Gardner says their research highlights that of all the growing tools growers have for potentially increasing yield and profit, planting date can give the greatest yield increase. And while it does not come without risk, using temperature differences with elevation within a paddock or across a landscape may allow growers to plant earlier while minimising some of the frost risk associated with early planting.
An example of temperature variation over a paddock is illustrated in data collected from two research sites in one paddock at Spring Ridge. Elevation at the top of the slope site was 353 metres above sea level compared with 305m at the bottom of the slope, a difference of 48m.
Between 1 May and 12 October 2015 minimum temperature differences were 3.5ºC higher at the top site compared with the bottom site. Average maximum temperatures were 0.4ºC warmer at the top site. Also, the top site recorded 16 frosts (less than 0ºC) compared with 54 frosts at the lower site. Total frost hours were 31 hours at the top site and 243 hours at the lower site – clearly showing two very different frost risk profiles within the same paddock.
Impact on flowering date
Mr Gardner says these temperature and frost differences impacted on the flowering dates of a range of varieties (from slow-maturing to quick-maturing) sown at each site over three different sowing dates from late April to early June. Varieties assessed were (from slowest to fastest) EGA Eaglehawk, EGA Gregory, LongReach Lancer, Suntop, LongReach Spitfire and LongReach Dart.
Days to flowering from a 30 April sowing was, across all varieties, 132 at the top of the slope compared with 146 at the bottom, a difference of 14 days. From 19 May, sowing days to flowering were 123 versus 138 and with a 13 June sowing they were 118 versus 122.
Temperature and frost differences contributed to vastly different yield patterns for the various varieties and Mr Gardner says this largely reflected maturity differences.
LongReach Dart, a very quick-maturing variety, from the 30 April sowing yielded 6.2 tonnes per hectare from the elevated trial site but only 1.2t/ha from the bottom site. Early flowering resulted in major frost damage at the lower site but not at the elevated site.
Suntop, normally regarded as an early to mid-May sowing variety, showed its versatility yielding high in both the top and bottom of the slope in the late April sowings. Yields were respectively 7.3t/ha and 6.8t/ha.
LongReach Spitfire, a faster-maturing variety, yielded high in the late April sowing on the higher country (6.4t/ha) but relatively poorly on the lower site (2.6t/ha), again a reflection of flowering too early and being frosted.
Slower-maturing varieties such as LongReach Lancer and EGA Gregory yielded around the same at both top and low-elevation sites and with a hot, dry spring did not do as well as varieties with faster maturity.
Early sowing with appropriate varieties at both top and lower elevated sites tended to yield better than later sowings.
Mr Gardner feels that elevation differences offer an opportunity for some earlier planting while minimising the frost risk. He also points out that while elevation is responsible for variation in temperatures, other landscape aspects such as drainage points and tree lines can also combine to influence frost risk.
In summary, he suggests the question to ask is: ‘Are there opportunities within paddocks or farms where you can push planting dates forward and not increase the frost risk?’
Other AMPS research across northern NSW on the slopes and western plains has also shown that earlier sowing, with appropriate safeguards such as careful choice of variety, is a major factor in lifting yields and profitability.
For example, its 2015 time-of-sowing variety trial conducted in the north-western plains area near Gulargambone resulted in average yield from the 28 April sowing being 38 per cent higher than the 16 May sowing.
Suntop, a mid-season variety, for example, yielded almost 6t/ha from the earlier sowing. But while still in the leading yielding variety group, it only just topped 4t/ha from the 16 May sowing.
More information:Matt Gardner,
GRDC Project Code AMP00010