Friday, March 29, 2024

Five by five best bet for beet

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“How much have you got?” is the perennial question when it comes to winter feed, and fodder beet hasn’t made the answer any easier.
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But a new protocol developed by a team of New Zealand beet agronomists led by Lincoln University fodder beet specialist Dr Jim Gibbs should add more accuracy to the process.

Instead of test-digging three four-metre lengths of row, or taking metre-square quadrats, Gibbs and the team advise digging 5m lengths of a pair of rows, and doing that at five random points across the paddock.

Testing this 5×5 approach and other methods in a 70ha paddock at Lincoln last autumn showed it was sufficiently rigorous to detect yield differences of 14% or more four out of five times, even in the multi-germ variety Brigadier.

Increasing the number of sites sampled to more than five, or increasing the length of row sampled, provided little increase in accuracy, but dropping below those standards rapidly increased variability in results, reducing the reliability of the sample technique as a tool to estimate field yields.

“Five by five does appear to be a very effective way to go,” Gibbs said.

He also stressed the importance of getting drymatter laboratory-analysed, warning against attempts at DIY drymatter analysis or relying on published figures for a particular variety.

“You can get it calamitously wrong if you take the book values.”

If actual drymatter is higher than estimated, cows will have access to more feed than planned and the risk of acidosis because of over-allocation increases.

“Too much too soon strips the wall off the rumen and it will take a very long period before they are back to normal, and that’s if they survive,” he warned.

On the other side of the scale, if drymatter was estimated higher than it actually was, cows would be undernourished all winter because of under-allocation, with increased risk of metabolic problems and a probable production impact in the following lactation.

Gibbs stressed the importance of randomising start points for samples in a paddock, suggesting the random function of a spreadsheet programme such as Excel being used to determine where each 5m measurement should be centred.

If the paddock was much bigger than five hectares, he suggested increasing the sample points to reflect the number of hectares, possibly dividing the paddock into blocks based on topography and soil type and deploying the randomised 5×5 approach to determine yield within each block.

Gibbs said there were still a lot of people going on to farms using yield assessment techniques, which it’s now known are not the best at dealing with the inherently variable spatial yield of the crop. Even apparently rigorous techniques, such as taking a 50m row sample, the same total row length as the 5×5 double-row approach, fall well short.

Suggestions that transition areas should be sampled more intensively, or that there should be any pre-selection of where to sample, for example making sure what appear to be high and low yielding areas are included when selecting sample sites, are ruled out in favour of random sample points.

Best practice for transition is to take a 5×5 yield estimate from the block and round the tonnage up to the nearest five tonnes to allow for the variation that’s still likely within the block.

“So if you get a yield of 21 or 22t drymatter (DM)/ha, calculate your transition break allocations on a 25t DM/ha crop.”

More: Journal of New Zealand Agronomy Society 2015. See www.agronomysociety.org.nz

Random plots from Excel

To generate random points using Excel, open a blank spreadsheet, click on the “Formulas” tab and then open the “Math & Trig” menu. Scroll down to the “Randbetween” function and enter one or two as the figure for the bottom of the random range, and the maximum length of one side of your paddock, less one or two metres, as the top figure.

The programme will give you a random number in that bottom to top range – effectively a co-ordinate along that axis of the paddock. To determine how far into the paddock to go from that point along one edge, click on a fresh cell on the spreadsheet – one adjacent to the previous cell makes sense – and use the Randbetween function as before to generate another random figure, only this time enter the length of the other side of the paddock as the range, less a metre or two at either end to take out any edge effect.

The two random figures generated give you your first point in the paddock to centre a 5m x 2-row test dig on.

To get more random points copy the two cells and paste them into the cells below. The more pastes you do, the more random points you generate. An irregular-shaped paddock can be dealt with by super-imposing a sufficiently big square or rectangle to cover the shape of the paddock, then using the dimensions of that square or rectangle to generate random co-ordinates until at least five fall within the actual shape of the paddock.

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