Agricultural management changes to best cope with projected climate change, in many respects, are similar to what is already considered good management.
Recently, I was part of a farmers and scientists consultative group, convened by Associate Professor Brendan Cullen, pasture and grazing systems, Melbourne University, at Cassilis, assessing management changes that may need to occur to cope with predicted climate change.
Our discussions were based on a property near Cassilis, in the Upper Hunter region, with an average annual rainfall of 625 millimetres. Monthly rainfall distribution currently favours summer over winter, but as for most of Australia, variation from year-to-year can be enormous, both monthly and annually.
Climate change predictions for the discussions were based on the NSW and ACT Regional Climate Modelling project. Mid-range Cassilis predictions for 2030 showed almost no change in total average annual rainfall by 2030 and even 2050.
However, the projected seasonal rainfall distribution change was more significant. Average autumn rainfall (all mid-range projections) was predicted to rise by 14 per cent by 2030 and 2050. Winter rainfall was predicted to fall slightly, by 4pc by 2030.
Spring rainfall projection was 7 to 8pc less by 2030 and 2050. Summer rainfall would be almost the same by 2030 and 5pc more by 2050.
Individual rainfall events were likely to be more significant, and dry spells likely longer. Note predictions vary for different parts of the state.
Mid-range predicted average temperature changes for Cassilis were around 1 to 2 degrees higher by 2050. for example, 1.1 degrees higher by summer 2030 and 1.8 degrees higher by 2050. Average winter temperatures are projected to be 0.4 degrees higher by 2030 and 1 degree higher by 2050.
Read more: Time for a re-think on pastures
Coping with these predicted changes emphasises management already adopted and promoted for many grazing and cropping businesses. For example, efficient soil storage of rainfall during the fallow period is even more important if dry spells are likely to be longer and more common.
Rainfall water capture is far more efficient if stubble from previous crops, especially cereals, is retained. Stubble retention from cereals two seasons out is especially important where crops like chickpeas are part of the rotation.
Soils less profitable for cropping are likely to increasingly suit grazing, for example, soils that store less soil water, especially lighter ones over relatively impervious clays, such as sodic ones. These already on many properties are converting to long-term pastures.
Pastures that can penetrate many of these so-called "hostile subsoils" can better exploit soil moisture at depth and improve their ability to capture rainfall and store more of it.
As was experienced after the 2017 to 2019 drought, retaining adequate ground cover is also vital to grazing for capturing rainfall when it eventually falls, especially in heavy rain events. Not only was that important to prevent wind and water erosion, but to ensure fast and substantial pasture recovery.
A classic 2020 NSW DPI Tamworth trial, for example, noted tropical grass with adequate ground cover quickly grew 4t/ha dry matter versus less than 1t/ha from lucerne with no ground cover.
Brendan Cullen reported pasture production modelling supported the view that well-managed pastures were likely to be not that much adversely affected by projected climate change. Much of the Cassilis project property example, owned by Henry and Christine White, was largely non-arable.
Professor Cullen's data noted that improved native pastures, like much of the White's property, are likely to be least adversely affected by climate change scenarios. On arable country, tropical grasses are likely to more commonly suit compared with temperate perennials.
Professor Cullen's modelling indicates profit projections, especially mid-range climate change projections, are positive, provided cropping and pastures are well managed. Research seeking more crop and pasture varieties able to cope with higher temperatures and dry periods are all part of the story of coping with climate change.
Next week: Manage to foster predators of crop and pasture pests.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.
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