Rainfall and soil moisture update, September 2024

Key messages

• Soil moisture is declining across much of the Riverine Plains as water use increases in line with dry matter production
• Given a decile 5 finish to the season, projected wheat yields currently range from 3.4 – 5.2 t/ha, across several locations in the Riverine Plains
• A decile 1 finish could see wheat yields reduce to between 2.5 t/ha to 3.7t/ha at these locations

Good growing conditions to date have helped many crops across the Riverine Plains region achieve quite high levels of dry matter production. However, with the low rainfall and warmer weather currently being experienced, some farmers are concerned about whether there is enough moisture to fill these high dry matter crops, and how this might affect grain yield.

Riverine Plains has compiled the following article, presenting rainfall, soil moisture and projected yields for a range of locations and using different rainfall outcomes for the end of the season, with the aim of assisting farmers with the decision to cut hay or take crops through to grain. 

Rainfall - how much have we actually received?

January’s rainfall was in the range of decile eight to ten at most sites, which is in the highest 20 percent of years on record, while February and March rainfall totals were average or below. The wet start to the year resulted in some good starting soil moisture at sowing; we’ve estimated most areas would have retained around 50mm of summer rainfall through to sowing, though the actual figure will depend on your individual location and soil type, as well as the effectiveness of your summer weed control.  

April-May rainfall was also around average for most of the region, before falling away during June and then recovering to about average during July. August rainfall totals were low, falling into deciles one to four at all locations except Henty, which had a decile five month.  

Rainfall totals and deciles for a number of locations across the Riverine Plains are shown in Table 1.

Table 1  Monthly rainfall and deciles (dec) for various locations across the Riverine Plains, 2024 

Rainfall totals sourced from Bureau of Meteorology, ClimateARM Riverine Plains and Dookie Land Management Group on-farm weather stations. 

Soil moisture 

As of 12 September 2024, Dookie Land Management Group probes show 90, 85, 80, 60 and 20 percent full at depths 30-140cm, and are showing quite good soil moisture reserves at the majority of sites. The Riverine Plains LLS Rand probe shows that the profile is around 45 percent full from 30-120cm.

The trend across the Riverine Plains soil moisture probes during August was for drier soil profiles across  most locations, which was expected given the drier conditions and increased crop water use. During August, soil water content decreased by 18-23 mm at the Riverine Plains Rutherglen and Murchison sites, while there was a 5 mm decrease at the Rand site. 

Yield potentials for a decile 8, 5 and 1 finish

Growing season rainfall (GSR) to end of August ranged from 144 mm at Yarrawonga to 197 mm at Euroa.  Using GSR figures, assumed stored soil moisture of 50mm, and expected minimum rainfall for September and October (Table 2), we have come up with some projected yields for wheat and canola at various locations across the Riverine Plains given a decile 1, 5 or 8 finish to the season (Table 3).  

For decile 5 September and October rainfall, projected wheat yields range from 3.4 and 3.5 t/ha at Yarrawonga and Lockhart, to 5.0 t/ha and 5.2 t/ha at Euroa and Albury (Table 3).  Canola yields are predicted to be around half those of wheat at all sites, based on a canola water use efficiency of 10kg/ha/mm rainfall. 

Yield scenarios for wheat and canola, for decile 1 September and October and decile 8 September and October are also presented in Table 3. In the event of a decile 1 finish, projected wheat yields will likely range from 2.5 t/ha at Yarrawonga and Lockhart to 3.7t/ha at Euroa and Albury, with canola yields again predicted to around half those of wheat. 

Table 2. Minimum expected rainfall totals for September and October at decile 8,5 and 1at locations across the Riverine Plains

For more information, please contact the Riverine Plains office on 03 5744 1713 or email Peter Chen at peter@riverineplains.org.au