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6. (a) Describe how the dry matter digestibility (DMD) of a grass plant alters during its various stages of growth - Leaving Cert Agricultural Science - Question 6 - 2017
Question 6
6. (a) Describe how the dry matter digestibility (DMD) of a grass plant alters during its various stages of growth. (b) Describe four measures that can be used to m... show full transcript
Worked Solution & Example Answer:6. (a) Describe how the dry matter digestibility (DMD) of a grass plant alters during its various stages of growth - Leaving Cert Agricultural Science - Question 6 - 2017
Step 1
Describe how the dry matter digestibility (DMD) of a grass plant alters during its various stages of growth.
Answer
The dry matter digestibility (DMD) of a grass plant changes significantly as it progresses through its growth stages.
During the leafy stage, grass has a high DMD due to its rich content of sugars and soluble carbohydrates. As the plant matures, these soluble carbohydrates begin to convert into cellulose, which is less digestible. This conversion leads to a reduction in DMD as the plant grows.
Near the heading date, the DMD tends to drop even further, often experiencing a decline of approximately 0.5% per day after this date. This drop is attributed to the increased fibrous content and the maturation of the grass. Once the plant heads, the stems become more prominent, contributing to a reduced digestibility as well. Overall, the trend is clear: DMD is highest in young, leafy grass and diminishes as the plant matures into a more fibrous state.
Step 2
Describe four measures that can be used to maintain a high grass DMD for longer during the grazing season.
Answer
To maintain a high grass DMD for a longer duration during the grazing season, several effective strategies can be employed:
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Rotational Grazing: Implementing rotational grazing techniques allows for optimal recovery time for the grass. By giving the pasture time to regrow, new foliage emerges, which is typically higher in DMD.
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Topping: Topping (cutting back the plant) can encourage new growth, which tends to have higher DMD than older, mature grass.
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Fertilization: Applying nitrogen (N) fertilizer or slurry can enhance grass growth by promoting the development of new foliage, thus sustaining higher DMD levels.
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Choosing Varieties: Selecting late-flowering grasses can delay the drop in DMD related to heading dates. By mixing different varieties with different maturity rates, you can extend the period of high DMD throughout the grazing season.