"Overall we are pretty happy with the results. In 1998 we got a WUE of 117 per cent on the best paddock, which is almost as good as the 124 per cent they got at Hart in their best small trial plot," says Mr Kelly.
WUE is calculated using a model taking into account growing-season rainfall (April to October). Both Mr Yeatman and Mr Kelly point out that it is possible to get WUE rates of more than 100 per cent when the crop is able to use water stored in the soil from rainfall that arrives outside the official April to October growing season.
Growers should also see higher WUE rates in very dry years, when crops are searching for every last drop of water (the reason for the high WUE rate in 1994 on 'Glen Holme'), and very low WUE rates in wet years, when there is more water than any crop could use. These are important limitations of the model.
The Hart trials showed growers should consider:
- management of rotation, weeds and disease in previous years
- paddock selection and preparation — with as few cultivations as possible
- sowing to maximise weed control, availability of nutrients, seed contact with the soil and establishment of the target population of plants
- post-emergent weed and leaf disease control, nutrient monitoring and application
- harvesting, storage and transport of the grain to maximise yield and grain qualitymarketing to maximise returns.
Mr Kelly said monitoring his crop water-use efficiency "is the only way of comparing yields across years and across paddocks".
Table 1: Wheat grain yields and corresponding water-useefficiency (WUE) as a proportion of the maximum possible yield for 'Glen Holme' (as an average for the whole farm's wheat crop). The long-term average effective rainfall is 371.5 mm.
|Year||Wheat grain yield (t/ha)||Water-use efficiency (% of maximum potential)||Effective rainfall (mm in Apr. - Oct. minus 110)|
Table 2: Treatments and wheat grain yields with corresponding protein content and water-use efficiency (WUE) as a proportion of the maximum possible yield for dedicated small plots at the Hart site. Effective rainfall (mm in Apr.-Oct. minus 110) was 124 mm.
|Sowing rate (plants/m2)||kg N/ha||Impact-in-Furrow*||Hifel**||Yield(t/ha)||Water-use efficiency (% of maximum potential)||Protein (%)||Screenings (%)|
|Coefficient of variation||5%||3%||14%|
* Impact-in-Furrow is a fungicide applied in-furrow on fertiliser
**Hifol is a foliar fertiliser
Research at the Hart Site is supported by growers through the GRDC, and by Primary Industries and Resources South Australia, Australian Barley Board, Australian Wheat Board Ltd, and South Australian Cooperative Bulk Handling.
Contact: Mr Tom Yeatman 08 8842 3900, Mr Allen Kelly 08 8848 4328