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Case study One: The Speights Stubby Grassometer


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Last updated 26 October 2012 15:29 by NZTecAdmin

Ken explained, ‘You need to carry out 15 to 20 measurements over a paddock.”

Immediately I recognised that Ken was familiar with the “Teaching Adults to Reason Statistically Progressions.” The more random measurements you try the greater is your confidence in the results of the survey (see page 27)."

“If the grass reaches the top of the label you can say for certain that the dry matter yield will be 2500 kilograms per hectare,” added Ken. For townies, dry matter is the food component of grass with the water removed. A hectare (ha) is an area of 100 metres x 100 metres (10 000 metres squared).

Providing proper grazing is essential to the profitability of farms and the welfare of animals. Normally a cow eats about 17.5 kg of dry matter per day. Stocking rates of about three cows per hectare are usual in New Zealand. An optimal residue of dry matter that leaves the pasture healthy after grazing is 1500 kg/ha (kilograms per hectare).This gives the simple formula:

(3 cows/ha x 17.5 kg/cow x number of days) + 1500kg/ha = pre-grazing cover.

So if Ken knows the pre-grazing cover is 2500kg of dry matter/ha he can work out the number of days that his cows can feed on that pasture.

3 cows/ha x 17.5 kg/cow x d (days) + 1500kg/ha = 2500kg/ha

So the pasture will last 1000/3 x 17.5 ≈ 19 days

Simple – Yeah Right! (getting our beers mixed up)

It’s just as well that Ken and his fellow farming tutors at Telford Polytechnic recognise the numeracy required to work this out. Rates like kg/ha are found at steps 5 and 6 of the numeracy progressions. There is more to farming than milking cows.

Thank goodness for the Speights Stubby test. It’s all tax deductable as well and the resource is definitely renewable.

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