Boring Brits?

16 Feb 2012

We went out for lunch last Saturday. The weather was glorious and all the tables in the garden were occupied, so unfortunately we had to sit inside. The conversation soon got around to managing risk when growing wheat in low rainfall areas of Australia. I was talking to a consultant who has been a major driver in the development of risk management strategies in such situations; we were having lunch in Bendigo, Australia.

Obviously, much of the risk management strategy revolves around water availability. Last year soils were full of moisture at sowing in early May (our October equivalent), but this year they could be bone dry. So how do Victoria’s farmers cope with this extreme variation, when typically rainfall after sowing could be insufficient to meet the full needs of the crop?

When I was first in Australia, around ten years ago, this was done by estimating how much water there was in the soil at the start of the season. Either a steel rod was pushed into the soil or a calculation was made based on the amount of post-harvest rainfall, providing a crude measure of how many mm of water was available at the time of sowing.

The assumption was for 20 kg of grain for each mm of moisture, and as rain fell during the season this was measured and the estimated yield as adjusted accordingly, with nitrogen (N) applied based on yield potential.

The issue with N is that there should be sufficient to achieve the anticipated yield. However, too much will mean excessive green leaf and water loss and as a result, reduction in both yield and grain size.

Now, computerised systems are used that require information at the start of the season based on a soil core analysis. Available moisture and N are measured and where prospects are good for yield and some additional N is justified this is applied in the combine drill.

As the season progresses the computer programme predicts N uptake and, based on any rainfall after sowing, expected yield. Additional N is applied if a shortage is predicted.

Water availability, along with plagues of mice and locusts, are not the only risks to take into account.

Sow too early and the risk of frost damage increases. Crops are grown through the winter and harvested in November (equivalent to our April) with the threat of wipeout due to frost at flowering. Sow too late and there is an increased prospect of yield damage from high temperatures during flowering.

Variables impacting Australian wheat production (specific variety) These risks can also be assessed by a computer programme based on weather records over the last 100 years. The image shows a printout for a specific variety at a specific location:

  • potential yield according to sowing date is the thick line;
  • the falling lines on the left are the decreasing risk of frost damage as sowing is delayed; and
  • the increasing lines on the right are the increasing risk of heat damage as sowing is delayed. 

The optimum date for sowing, assuming sufficient moisture for germination, is early May.

Doesn’t this make British wheat production sound boring?

Jim is on a study trip to Australia so expect further Oz-blogs over the coming weeks