Water use efficiency guide
GroundCover™ Issue: 29
Water-USe efficiency guide to on-farm management
Getting the most out of every millimetre of rain that falls on your paddock is a good way to get the best yields you can.
It's called maximising your water-use efficiency (WUE), and a group of growers overseeing the Hart trial site at Brinkworth in the mid-north of South Australia have been working with Primary Industries and Resources South Australia (PIRSA) to do just that.
For wheat, it means aiming for a maximum possible yield of 20 kg grain for every mm of available water. According to Tom Yeatman, Senior Field Crop Consultant at PIRSA, it's not that difficult to achieve 75 per cent or even 80 per cent of the maximum yield. The challenge, he says, is to see whether that extra 20 per cent can be achieved cost-effectively.
What limits water-use efficiency?
Grower Allen Kelly of 'Glen Holme' at Manoora, part of the reference group for the Hart site, found that he could dramatically increase his crop yield and thus his WUE by identifying possible limitations to crop production. Important reasons were his soil types, problems with acid soils, crop nutrition and a diverse weed spectrum.
"The motivation for the change came from observing the ground cover at the Hart trials, and seeing how quickly the young crops grew to shade the soil, reducing evaporation and weed growth," said Mr Kelly.
Despite differences in rainfall (486 mm average at 'Glen Holme' compared to the Hart average of 425 mm per year) and more variable soils at 'Glen Holme', the Hart strategies were readily applied on Mr Kelly's property.
Mr Kelly decided that to achieve comparable results, he needed to radically increase seeding and establishment rates to bring the wheat up to 250-300 plants per square metre. (Wheat grown on 'Glen Holme' is predominantly Janz, with occasional diversions to Fame, Yallaroi and Tamaroi. However, the selection of variety did not affect WUE or seeding rates.)
He also found he needed to change his fertiliser regime to include 1 per cent zinc, and up to 250 kg/ha urea, but normally 150 kg/ha urea, in addition to the 100 kg/ha of DAP fertiliser he already applied. With all that, Mr Kelly still puts in a pulse crop before the wheat as part of his standard rotation for the best shot at a really good yield.
He discovered a bonus for zinc: "I really hit the nail on the head when I found Ascochyta was under control wherever I used zinc on the beans, and so now I use it routinely".
The increase in WUE from this fairly easy but serious change was from an average of 69 per cent (1988 to 1996) to 85 per cent (1997 and 1998) of the maximum possible yield of 20 kg/mm of wheat grain (see Table 1 for year-by-year whole-farm yields). It was achieved without modifying existing machinery, and without buying new machinery — a move that Mr Kelly had been considering to boost yields