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MANAGEMENT OF WINTER WHEAT FOR HIGH FORAGE AND GRAIN YIELDS

S.M. Goss and N.J. Mendham

University of Tasmania, Hobart, 7001, Tasmania.

Abstract

The new CSIRO bred winter wheats, Lawson and Paterson, are being compared with other Australian and European wheats in their response to management factors. These include grazing or cutting frequency and timing, and nitrogen application. Canopy characteristics such as leaf area, number of tillers, and radiation interception are being monitored in relation to forage production and the pattern of crop development, including recovery of inflorescence initials for grain production. Nitrogen nutrition is being monitored using sap nitrate levels with a view to using just sufficient amounts to optimise leaf area for radiation interception while minimising disease and losses of N from the system.

Key words: Winter wheat, cultivars, grazing management, grain yield

The wheat cultivars generally used in the temperate wheat growing regions of Australia tend to be early maturing spring cultivars, which can be grown through the winter months due to the mild winters experienced in Australia (1). Spring wheats are usually planted in late autumn to delay ear emergence until spring in order to avoid frost damage.

Winter wheats, however, require a period of vernalisation in order to initiate flowering. This may be combined with a response to short days for inflorescence initiation, followed by a response to long days during stem extension. The extended vegetative growth stage in unvernalised winter wheat allows a greater flexibility in planting time, so those crops planted in early winter will still set seed at a similar time to crops planted in early autumn. Early sowing also allows the grazing of the crop while still vegetative, possibly without detrimentally effecting the final grain yield (1).

Very little research has been undertaken into the potential use of winter wheat as a dual-purpose crop in Tasmania. Recent work by the CSIRO in crossbreeding of wheat has resulted in the commercial release of a number of winter wheat cultivars, several of which may be suitable to grow in Tasmanian conditions. This research project is comparing two of these cultivars (Lawson and Paterson), and a cultivar currently under evaluation (Declic) with two early maturing cultivars (Rosella and Kellalac) and the cultivar currently grown in Tasmania for grazing (Isis).

The new cultivars are being tested for grain yield and dry matter production under three different grazing regimes. Over the whole experimental period, trials will be undertaken to examine the effects of other management practices, including nitrogen application, irrigation (waterlogging and drought tolerance) and weed control.

Materials and methods

The selection of wheat cultivars used has a range of vernalisation requirements to allow a comparison of the new winter wheat cultivars currently used in Tasmania or on the mainland. Cultivars were planted in plots 1.2 m wide by 16 m long, with six plots in each block, and a total of four blocks. Each plot was split into three treatments, which were randomly assigned. These treatments consist of a control level (no cutting), early cutting (late vegetative stage), and late cutting (floret primordium stage). Cutting was done using a mower to simulate grazing. In a complementary experiment, two different levels of nitrogen application (50 and 150 kg/ha) were used in a set up identical to the grazing only experiment. In this experiment, only Isis, Lawson and Rosella were used.

Samples were taken at regular intervals to ascertain developmental stage, apex height and tiller number, and dry matter calculated when plots were cut for treatments. Dry matter was also calculated at harvest time. Readings such as leaf area (to determine leaf area index), and sap nitrate levels in response to cutting and nitrogen fertilisation were also taken.

Results

Few conclusive results are available at the time of writing, but at this stage some interesting trends can be seen. Developmental stage results show a rapid increase in the early maturing cultivars consistent across all cutting treatments, with the winter wheat cultivars showing a slower, more drawn out development curve. Paterson showed more rapid early progress than Lawson, but as development progressed, the two cultivars showed similar development curves. Early cutting results showed no set back in developmental stage, but resulted in a stasis in the development curve. All cultivars seemed to be equally affected by the early cutting.

In the late cut treatments, however, early maturing cultivars like Kellalac and Rosella show a marked decrease in developmental stage with cutting, with a slow recovery rate. The winter wheat cultivars however showed little or no difference in developmental stage, showing that they are better able to cope with late grazing than earlier maturing cultivars.

Tiller numbers varied little between cultivars in the uncut treatment, but in the cut treatment, recovery of growth in respect to tiller number varied greatly. In the early cut treatment, Kellalac and Rosella showed a decreased number of tillers after cutting, while the remaining cultivars showed no change or a slight increase in tiller number. The late cut treatment showed similar results, with the earlier maturing cultivars showing a decrease in tiller number, and the late maturing cultivars showing no change. Earlier maturing cultivars however showed a more rapid recovery from late cutting than did the late maturing cultivars.

Apex height was much greater, and increased at a more rapid rate in the early maturing cultivars than in the late maturing cultivars, and the greatest apex height was recorded at each stage by the cultivar Rosella. Early cutting did little to decrease the average apex height, as cutting in all cultivars was carried out during the late vegetative stage, when the growing point of the wheat was still below cutting height. The late cut treatment did however remove growing points in some of the cultivars, thus causing a reduction in the average apex height. Both Kellalac and Rosella showed a large reduction in apex height with cutting, while Lawson and Isis showed only a small reduction. No decrease in average apex height was seen in Paterson or Declic.

Full dry matter results for the whole growth period are unavailable at present, but currently show that early cut dry matter is similar across all cultivars used (1.5 kg), while late cut dry matter is similar in Lawson, Paterson and Declic (3. 5 kg). These cultivars have a higher late cut dry matter than Isis (2. 5 kg), which in turn has a higher dry matter yield than both Rosella and Kellalac (2 kg).

Conclusion

At this stage of experimentation, only trends in the data can be seen, showing that Paterson, Lawson and Declic show good canopy recovery after both early and late cutting in comparison with the other cultivars used. It can also be seen that late cutting has a greater effect on dry matter production, tiller number and developmental stage than does early cutting, with a more marked effect seen in the early maturing cultivars.

References

1. Simmonds, D.H. 1989. In: Wheat and wheat quality in Australia. (William Brooks: Queensland)

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