No doubt you’ve heard something like it. “A good drought ruined by rain”. “Beautiful day. Just watch someone come along and mess it up.” Good examples of Australian humour.

Within the GRDC-supported Central Queensland Sustainable Farming Systems project (CQSFSP) the sorghum team is feeling a bit the same way. A good dry weather experiment ruined by rain.

After years of drought in Central Queensland, consultant Graham Spackman and Maurie Conway and David Reid from QDPI&F wanted to know how much rainfall was captured in the following fallow when sorghum is planted on wide rows.

According to Mr Spackman, the continued dry seasons meant some Central Queensland farmers hadn’t grown crops, had little or no stubble and the soil surface in  paddocks with those problems had become flat and fine.

Growers and the scientists working with them on the CQSFSP might have increased their knowledge about grain yield response to changing row configurations, but they don’t know yet what impact stubble distribution after wide row sorghum is likely to have on capture of rainfall and runoff.

Which is why the CQSFS team decided to set up the infiltration trial on the Pukullas family’s property, Wyntoon, in a paddock that had grown a light crop of chickpeas in 2004, leaving minimum stubble, prior to the sorghum crop, which went in on row spacings of 0.5m, 1metre, 1.5 and 2metres on December 31, 2004.

After spray out and harvest – 1.6 t/ha across all four treatments – Mr Spackman says the CQSFSP team inserted 88 PVC access tubes across the paddock, at 0.5 metre intervals across all four row treatments.

The idea was to allow soil moisture levels to be monitored in the post-sorghum fallow. The different levels of stubble cover provided by the different row spacings were expected to have an impact on runoff and infiltration in future rainfall events.

“Unfortunately”, the trial site received about 100 mm of rain in May, followed by two subsequent falls of around 30mm.

Virtually all of the rain was captured in the soil because of its low intensity, fully re-wetting the soil profile, obliterating the stubble cover and the effects of row width treatments on soil moisture accumulation. 

Mr Spackman says while rain is always a great relief after drought, the “fantastic but unexpected” rain means this trial might not prove useful in determining sorghum row width impact on capture of rainfall in the soil.

And he says this is a bit ironic, because in most circumstances it is dry conditions that limit research outcomes – not wet ones.