Bob Freebairn
9 Aug 2021, 5:30 a.m.
Purlewaugh long term rainfall trend. Similar to many central northern NSW areas, trending slightly upwards, contrary to many beliefs on climate change effects.
In many years involved in agriculture, from a child raised on a farm in the Greenethorpe district, to an agronomist and now running a farm, enormous climate fluctuation has been, well, a constant. A study of 120 years of rainfall records, at most Australian centres, documents variability has always been the case.
Every farm business can benefit by assessing what climate conditions have gone on in the past to guard against future variability with events such as droughts, floods, hot and dry spells.
CliMate app (https://climateapp.net.au) is a good starting point to assess climate trends. Perhaps surprisingly for many centres including our own at Purlewaugh, east of Coonabarabran, CliMate indicates a slight increase in total annual rainfall over the past 120 years. This is based on a “moving” analysis of data. Average rainfall per month also appears not to have changed much, despite predictions winter rainfall is getting less and summer rainfall higher.
Sometimes research compares say the last 10 years to a past 20 – 30 year period, suggesting climate conditions, and therefore likely crop and pasture production, have deteriorated. However an examination of past rainfall records can generally find extended periods of way below rainfall average as well as way above averages. It is worth noting many prominent scientists have a different view re climate change (see Jennifer Marohasy’s edited book “Climate Change. The Facts 2020”).
Temperature records are far sparser and for many areas don’t go back that many years (hence the reason for some recent record highs). Sometimes, like in our closest town, recording centres have changed several times over the last 50 years, often with a big difference in temperature. Both for temperature and rainfall it seems a fair assumption that enormous variability has always been the story. To me, advice about crop, pasture and soil management issues will be much the same regardless of whether we are experiencing climate change or variability.
A good example is the need to efficiently store soil water over the fallow in a cropping business, even in southern NSW environments as well as central and northern regions. Even high rainfall areas regularly have dry spells at critical periods of crop growth and stored sub soil moisture becomes critical for reliable yields. This is backed by CSIRO and others research that indicates efficient storage of fallow moisture per annum is worth an extra 1.0 t/ha or more for cereal croppers.
Zero till farming combined with stubble retention, has almost been universally adopted over the last 40 years and is an example of better managing climate variability. Retaining stubble and replacing cultivation with timely herbicide applications to control weeds, commonly conserves 25 – 50 mm more moisture for a winter crop compared with a cultivated fallow. In addition soil is better protected from rain and wind erosion. Earlier crop sowing, with appropriate maturing varieties, is also important if sowing opportunities occur to maximise sowing success.
Perennial pastures, especially the swing to long term persistent perennial grasses, is changing rapidly in many areas and I feel reflects a better appreciation of what suits our climate. Tropical species have a greater ability to respond to rain between mid-spring (early spring in warmer areas) through summer to late autumn. In many areas these provide more total annual feed, as well as last longer, than temperate perennials. They also can combine well with winter legumes to fill the winter feed gap.
Lucerne also has an increasing role in variable rainfall environments and except for the cold areas responds to rain whenever it falls. While lucerne has its issues, such as requiring periodic replanting, bloat and low ground cover in dry times, it does build soil nitrogen, and can be productive and fits in with cropping rotations. Several newer legumes like serradella and biserrula can cope with dry spells and more reliably set seed and provide late growth in response to a late seasonal break. While sub clover remains a valuable and almost universal winter legume, the addition of these species can add to length of green feed as well as total productivity.
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