AS MUCH of eastern Australia luxuriates in the novelty of good late summer rainfall croppers are now assessing how they can get maximum value from the falls.
There will be a myriad of competing factors that dictate how much stored moisture will be available to the crop at critical times during the spring, ranging from obvious ones such as soil type and time of rain through to variables such as paddock cover and extent of weed control.
Cameron Taylor, Birchip Cropping Group (BCG) commercial services manager said his Victorian Mallee-based organisation conducted some research over a wet summer in 2010.
"On our soil types on the good clays with no soil constraints if you get a heavy rain event of more than 40mm you can store up to 40 per cent of that if the rain is late enough in the summer," Mr Taylor said.
"That figure, however, drops to around 33pc on the sandier soil types."
Further to the north, Condobolin farmer Graham McDonald, who has received a season-altering 70mm in the past week, said he would hope to potentially have a retention rate a little better than that.
"Being this late into the summer, we're only a fortnight away from the days getting noticeably shorter and the mornings a bit cooler so we'd really hope that we might be able to store a little bit more."
Both men said the key thing would be to control weeds in a timely fashion.
"That 40pc plant available water can drop to 20pc when weeds are not controlled while on the sand it drops to 16pc or so," Mr Taylor said.
He said in the Victorian environment spraying generally helped store added moisture from falls in excess of 25mm but said farmers generally sprayed when they received smaller amounts to ensure the weeds did not grow too big in case of a follow up rain and also to ensure they did not suck up valuable soil fertility.
"Some of the weeds can be really hungry in terms of nutrients so with the broadleaf weeds people are really looking to get onto them before the leaves are the size of a 50c piece."
"You risk big losses in nutrients if they are not controlled, primarily nitrogen."
Mr Taylor said one of the major problems with storing plant available water in many Australian environments was constraints in the subsoil.
"We often see the case where there is water at depth but the plants can't necessarily access it because of some form of constraint that means the roots don't push down into the moisture."
Mr Taylor said the summer moisture would generally be utilised by the plant in the spring.
"The top 10cm will dry out and from the germination rain you just want to get the two bands to join up.
"The moisture usage is fairly low in winter so it is nearly always the case that the stored moisture is accessed in spring when the plant is transpiring more."
The other major unknown in terms of the amount of accessible soil moisture is the condition of the soil and the rate of the rainfall.
"We haven't had a crop in two years so the soil was pretty bare and it has run off fairly quickly," Mr McDonald said.
Mr Taylor said retaining stubble and improved soil types as a result of no-till cropping reducing compaction had helped water permeation.
It has proved difficult, however, for those enduring long droughts to retain the cover meaning infiltration rates have not been as good as they would normally.
Brendan Taylor, AgForce grains section president said initially in Queensland some of the rain in his state had come down heavily and had run off paddocks before it had a chance to soak in, but added many places had now received enough to get the soil moisture profile filling nicely.
In northern NSW Rebecca Reardon, NSW Farmers' treasurer, said water was pooling after a rain in January, but it was due to soil structure issues.
"After all that dry the dust had got so fine that when it rained it did not soak in to maximum effect, hopefully any rain we get from now on will be more effective in filling the profile."
The story Farmers seeking to set winter crop up on stored moisture first appeared on Farm Online.