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Long-term study of fallow practices and nitrogen fertilisation on soil water conservation and yield of wheat in the Victorian wimmera

C. Cantero-Martinez, O'Leary and D.J. Connor

University of Melbourne, Parkville VIC 3052 Victorian Institute for Dryland Agriculture P.B. 260 Horsham VIC 3400

Long-bare fallow over a 10- to 12-month period is a common practice for dryland wheat production in the Victorian Wimmera. There are, however, alternative fallow methods such as minimum tillage with retained stubble residues which offer yield increases due to improved water supply. This paper summarises the results from 10 years of reduced tillage experimentation examining the yield response and water use of wheat in a fallow-wheat rotation.


An experiment was maintained from 1980 to 1990 at the Wimmera Research Station, Dooen. In each year, the water use, growth, and yield of wheat was measured following three methods of long fallow viz., chemical (no cultivation), blade-plough (sub-surface cultivation) and scarifier following burning (common local practice). From 1984, the comparison was extended to include two levels of nitrogen (N). These were a control (no N fertiliser) and 20-60 kg N/ha applied between sowing and tillering.

Results and discussion

Over the decade of the experiment, annual rainfall varied from 190 to 585 mm and yield from 1.0 to 5.7 t/ha. There were small but significant differences in water conservation and resultant wheat yield by the three fallow methods. The differences were not consistent from year to year but a pattern was evident. In the driest year (1982), there was no advantage in any method. In years of low yield (<3.7 t/ha, 5 years in 10), chemical fallow had a yield advantage over both tillage methods, scarifier (up to 0.8 t/ha) and blade plough (up to 0.6 t/ha). In seasons with yield greater than 3.7 t/ha (4 years in 10), yield following the scarifier fallow exceeded that of the alternative methods. In the 7-year sequence when nitrogen was applied and when the yield of the unfertilised control exceeded 3.5 Oa (5 years in 7) the addition of nitrogen increased yield by a maximum of 0.6 t/ha.

These data demonstrate the complexity of fallow management for maximum crop yield in a variable, rainfed environment and the value of long-term experimentation. Despite the complexity, the pattern of response is explicable. The advantage of chemical fallow in years of low rainfall and yield potential was shown to result from greater water conservation. It is proposed that the advantage of the scarified fallow in years of greater yield potential can be attributed to better N supply. The results of this experiment can form the basis of improved advice to farmers on fallowing and crop management with the aid of seasonal weather outlooks.

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