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EFFECT OF HARVEST DATE ON QUALITY AND DRY MATTER OF CEREAL CULTIVARS

E. Cowlishaw and D. George

School of Land and Food, The University of Queensland, Gatton College, Gatton, QLD, 4343

Abstract

A field trial at the Gatton QDPI Research Station identified effects of harvest date on quality and dry matter production of selected oat, wheat and barley cultivars. Data for height, dry matter production, leaf stem ratios, protein content and digestibility were collected for five harvest dates at approximately monthly intervals until flowering. Results showed that stage of plant development strongly influences forage yield and quality. Highest quality occurred at harvest one (30-40% crude protein, 50% digestibility) but forage yield was lowest (200 kg/ha). Harvest delayed until flowering resulted in higher forage yields (2.4 t/ha) but lower quality (10% protein, 40% digestibility). Wheat and barley cultivars were earlier maturing, reducing the grazing period, but supplying higher quality and quantity of feed.

Key words: Oats, Wheat, Barley, Protein, Digestibility, Feeding habits

Oats is the main winter-spring forage crop grown in Queensland and northern New South Wales, with approximately 450,000 ha grown annually to provide quality forage for sheep, beef and dairy industries. Although there has been significant research on quality and yield of previously released cereal cultivars, the effect of harvest date on the forage performance of recent cultivars has not been studied. An irrigated experiment at the Gatton QDPI Research Station, identified the effects of harvest date on quality and quantity of oat (Algerian, Barcoo, Cleanleaf, Enterprise, Graza 70, Minhafer, Riel and Saia), wheat (Mawson) and barley (Malebo) cultivars recently released, or still in production.

Data (on height, dry matter production, leaf stem ratios, protein content, digestibility and nitrogen uptake) were collected at five harvest dates. Protein analysis was conducted at each harvest, while digestibility was analysed on harvest one, two, three and five. The trial concluded at flowering due to time restraints. Analysis was conducted on each character across harvest dates. Wheat and barley cultivars matured approximately three weeks before the oats.

To maximise grazing potential, a compromise between yield and quality must be made. By comparing recently released wheat cultivars with oats and barley, a feeding program to maximise livestock performance can be generated.

Results

This trial produced similar results to McDonald and Wilson (3) who showed that dry matter production by oats was greatest between August and December, reaching 15 t/ha at milky ripe stage. In this trial the highest yield occurred in mid-August at harvest five (flag leaf) for the oat cultivars (11.4 - 17.4 t/ha). At the corresponding growth stage, barley yielded 7.1 t/ha (Malebo) and wheat 5.7 t/ha (Mawson). However, wheat and barley showed increased yields at harvest five (flowering) reaching 20 t/ha. This result supports Hughes and Haslemore (2) who proposed that oats has a higher yield potential over a longer period of time than other winter cereals, thus increasing the available grazing time.

Early in the season at harvest one, barley showed the highest yield potential by reaching 1.7 t/ha compared to yields of 1.0 t/ha for wheat and approximately 1.3 t/ha for oats. This can be attributed to the high, early vigour and greater tiller production of barley compared to wheat and oats. Barley also had a high nitrogen uptake and a high nitrogen efficiency at harvest one, suggesting that if nutrients are limited, yield may decline. Wheat showed reduced vigour, lower nitrogen uptake, and a low efficiency rate, compared to oats and barley. This slow growth early in the growing season may inhibit early grazing compared to barley and oats. Oat cultivars, Cleanleaf and Riel, both showed high nitrogen efficiencies at harvest one, and also high yields. Thus there appears to be some correlation between nitrogen uptake efficiency and yield. However, later in the season, due to the high tiller production and poor lodging resistance much of the barley leaf matter was lost due to fungal growth. This reduced leaf matter, may have caused a decline in leaf-stem ratios, and a general loss in dry matter yield. This would limit the amount of available forage for grazing and cause higher trampling losses in the field.

As leaf stem ratios decreased from 7.7 at harvest one to 1.2 at harvest five, protein also decreased from 31.1 to 10.4%. A rapid decline occurred between harvest one and two for both leaf stem ratios and protein, suggesting that quality remains high when leaf stem ratios are high and immature stems are present. Barcoo tended to show a high leaf stem ratio throughout the season, but produced low protein and higher digestibility, especially later in the season. The low protein of Barcoo is unexpected, however the high digestibility would be expected due to the high leaf matter at harvest five. McDonald et al. (3) suggested that increasing leaf area increases photosynthesis, causing nonstructural carbohydrates (sugar and starch fructosan) to increase in plant tissue. Later, nonstructural carbohydrates decline because of high energy demands during stem production, thus causing a decline in protein and digestibility.

Cultivars in harvest one showed high leaf-stem ratios and high protein as expected. It appears that digestibility was not affected so much by the leaf-stem ratio, but rather by stem quality. Digestibilities showed similar results to McDonald et al. (3) with variation occurring after harvest four, from late tillering to flag leaf stage, suggesting that as the stems produced higher non structural carbohydrates near grain set, fibre increased causing a decline in the digestible fraction. Leaf stem ratios declined after harvest one, and remained at a low level until flowering. No significant decrease in digestibility occurred until harvest four or five, suggesting that decreasing leaf stem ratios had little effect.

Conclusion

The stage of growth and time of grazing have an important effect on the yield of all cereal crops examined and management should be controlled accordingly. Results from this trial show that total yield is greatest at harvest five (flag leaf) for oat cultivars and flowering for the wheat and barley, with oats producing higher yields, due to delayed maturity. However, late grazing would not utilise the high protein content which occurs at harvest one, when leaf stem ratios are highest. Fahey (1) concluded leaf intake was higher than stem intake, thus grazing when leaf matter is high will increase livestock performance.

References

1. Fahey, G.C., (Jnr.) 1994. Forage quality, evaluation, and utilisation, American Soc. of Agronomy, USA

2. Hughes, K.A., and Haslemore, R.M. 1984. NZ J. of Exp. Agric. 12, 1-5

3. McDonald, R.C., and Wilson, K.R. 1980. NZ J. of Exp. Agric. 8, 105-109

4. Minson, D.J., and McLeod, M. 1970. A rapid invitro system for measuring digestibility in pasture speies, CSIRO Division for Tropical Pastures

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