How is grass turned into silage, how is its quality judged, and how are grass yields and dry matter measured?
The process of silage-making on Northern Ireland farms, assessing silage quality using colour, smell and moisture, using oven drying to find percentage dry matter, and estimating grass yields with a rising plate meter or herbage samples.
A focused CCEA GCSE Agriculture and Land Use answer on silage and grassland management, covering the silage-making process, assessing silage quality by colour, smell and moisture, oven drying to find percentage dry matter, and estimating grass yields with a rising plate meter or herbage samples.
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What this dot point is asking
CCEA wants you to describe how silage is made on Northern Ireland farms, judge silage quality from its colour, smell and moisture, calculate percentage dry matter from an oven-drying experiment, and explain how grass yields are estimated using a rising plate meter or by harvesting herbage samples.
Making silage
The main steps in silage-making are:
- Cut the grass, ideally when young and leafy for good quality.
- Wilt it for a short time to lose some water (so it does not ferment too wet).
- Gather it and pack it tightly into a clamp, or bale and wrap it in plastic.
- Exclude the air by compacting and sealing, so the grass ferments without oxygen, which preserves it and stops it rotting.
Excluding air is the key idea: with no oxygen the right fermentation happens and the silage keeps; if air gets in, the silage spoils and goes mouldy.
Judging silage quality
Percentage dry matter
The dry matter is the part of a feed left after all the water is removed, and it is where the nutrients are. To find it, oven dry a weighed sample until its mass stops changing, then:
Dry matter lets a farmer compare feeds fairly: fresh grass and silage are mostly water (low dry matter), while hay and meal are mostly dry matter, so comparing by dry matter shows the true feed value.
Estimating grass yield
Farmers estimate how much grass is in a field so they can plan grazing and silage.
- Rising plate meter - a plate is dropped onto the grass and its height is read; taller, denser grass gives a higher reading, which is converted to an estimate of grass available.
- Harvesting herbage samples - a measured area is cut, the grass is weighed (fresh, and sometimes dried for dry matter), and this is scaled up to estimate the yield per field.
Examples in context
Example 1. Baled silage on a small farm. A small beef farmer makes baled silage: the grass is cut, wilted, baled and wrapped in plastic to seal out air. The wrapped bales ferment and keep through winter, giving a flexible store of feed that is easy to handle without needing a large clamp.
Example 2. Checking feed value before winter. Before winter, a dairy farmer oven dries silage samples to find the dry matter and sends samples for analysis. Knowing the dry matter and quality lets the farmer work out how much silage the cows need and whether extra meal is required to balance the ration.
Try this
Q1. Name the three indicators used to judge silage quality. [3 marks]
- Cue. Colour, smell and moisture.
Q2. A 100 g grass sample dries to 20 g. Calculate the percentage dry matter. [2 marks]
- Cue. (20 divided by 100) times 100 = 20%.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA Unit 1 style4 marksDescribe the main steps in making silage and explain how a farmer can judge whether the silage is good quality.Show worked answer →
Two marks for the process and two for judging quality.
Silage-making: the grass is cut, usually wilted for a short time to lose some water, then gathered and packed tightly into a clamp or baled and wrapped. Packing it tightly and sealing it removes the air, so that fermentation can take place without oxygen, which preserves the grass.
Judging quality: good silage is a pleasant greenish or olive colour, has a sweet or slightly acidic (pleasant) smell, and has the right moisture level (not too wet and slimy or too dry). Bad silage is dark or mouldy, smells unpleasant or rotten, and is too wet.
Markers reward the key steps (cut, pack tightly, exclude air, ferment/seal) plus the three quality indicators: colour, smell and moisture.
CCEA Unit 1 style4 marksA 200 g sample of fresh grass is oven dried and the dry sample weighs 50 g. Calculate the percentage dry matter, and explain why dry matter is useful to a farmer.Show worked answer →
Two marks for the calculation and two for the use.
Percentage dry matter = (dry mass divided by fresh mass) times 100 = (50 divided by 200) times 100 = 25%.
Dry matter is the part of the feed left after all the water is removed, which is the part that actually contains the nutrients. It is useful because feeds vary a lot in water content, so comparing them by dry matter lets the farmer judge the true feed value and work out how much an animal needs to eat. Wet feeds like fresh grass or silage have a low dry matter, while hay and meal have a high dry matter.
Markers reward the correct working and answer (25%) plus the idea that dry matter shows the nutritious part and allows fair comparison of feeds.
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