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Low efficiency of wheat production in the Victorian Wimmera in above average seasons

J.M. Carter, M. Drum, T. Young, R. Flood, W.K. Gardner, M. Jasper and C. Young

Department of Agriculture, Victorian Institute for Dryland Agriculture,
Wimmera Research Station, Private Bag 260, Horsham VIC 3401

The water use efficiency of crops in the Wimmera is high in dry seasons, however, when above average rainfall occurs water is not used efficiently and crops yield below their potential. This study attempts to identify the major limiting factors in this system and how production improvements can be made through better use of the water in above average seasons.


Data were collected from wheat, Triticum aestivum, receival points from 1951 to 1985 throughout the west, central and eastern Wimmera. Trends in yield and grain protein levels were examined in relation to the growing season rainfall (May to October). Yields of wheat in experiments at the Wimmera Research Station grown on high fertility (fallow-wheat-medic- medic, 1946-66) and low fertility (fallow-wheat, 1946-66) land were also collated and compared.

Results and discussion

The analysis of wheat production in the Wimmera showed that yields increase sharply with May to October rainfall from 50-200 mm, remain static from 200-350 mm and tend to decline above this. Wheat yield per mm of May to October rainfall declines rapidly the more the May to October rainfall exceeds 200 mm. This strongly suggests that factors other than moisture limit yields in average and above average seasons. Similarly, when the average grain protein content was examined for the same period, a marked decline was clear with increasing rainfall. This trend was greater than could be explained by a 'dilution effect' due to increasing yield and strongly suggests that nitrogen supply is somehow reduced in wetter years and may in fact be limiting yields.

The potential to increase yields in above average years is consistent with data collected in the 1960s (Table 1). A comparison of the yields of crops grown on high fertility and low fertility land showed that although a small yield penalty occurred in dry to average seasons on high fertility land, this was more than offset by the gains in above average seasons. This indication that higher yields can be achieved in wetter seasons in a farming system which maintains high levels of fertility is being explored further in a more detailed analysis of historical research data.

Table 1. Wheat yield comparisons on low and high fertility soils.

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