From dry to damp: getting your pastures ready
New Zealand farmers know that pastoral fortunes can shift rapidly once summer’s extreme dryness gives way to cooler, wetter autumn conditions.
First principles would say the relationship is partial and highly variable, at which point a question might be asked about the use of taxpayer money through the SFF. The answer might be that ‘rapid measurement’ will give an advantage, but the scientist would then point out that being able to make an unreliable measurement rapidly doesn’t improve its reliability.
In addition, the aim of the SFF project is to “create awareness of opportunities to use the brix and pasture energy scale technology to improve the professionalism of farming by lifting the value of produce leaving the farm and reducing costs”. This is quite a jump when the actual relationship of Brix to ME is variable and no relationship to product quality has been shown for milk, meat or fibre.
Brix has been used in the wine and fruit industries to estimate sucrose as an indication of potential fermentation or sweetness (and hence quality). It doesn’t measure exact amounts, however, and nor does it measure all components that contribute to ME.
Dr Doug Edmeades, winner of the Hamilton City Council Agricultural Science Prize at the Waikato Kudos Awards 2014, points out that the amount of soluble sugar in a pasture doesn’t indicate anything about the feed value of that pasture to a ruminant animal: ruminants can use all the parts of the plant carbohydrate, from the readily digested simple sugars through to the complex celluloses.
The refractometers used for measuring Brix are calibrated for sucrose, but other dissolved sugars affect the readings, reducing accuracy as the SFF has already found. In addition, water availability affects the moisture in which the sugars dissolve. Brix in forage crops is influenced by many management and environmental factors such as ambient temperature, soil moisture content, fertilisation, time of the day samples are collected, as well as the maturity and part of the plant sampled. In drought, for instance, plants tend to concentrate water soluble carbohydrates in the roots and tissues to survive. In contrast, nitrogen applications can result in a decrease in dissolved sugars since they are likely to be redirected to growth. This means that a low Brix pasture could be growing rapidly, whereas a high Brix pasture hasn’t been converting the sugars created from photosynthesis into ‘growth’.
In research with high sugar grasses, Brix has been implicated in increased milk production because of increased dry matter intake. The research also indicated that Brix changed according to the preparation method of the grass samples, and within 120 seconds of being taken.
DairyNZ has many tables of ME for different forages for different times of the year, collated from research and actual measurements of ME, not proxy measurements. Looking them up will take less time (depending on broadband functioning, admittedly) than preparing a Brix sample, and give a far better indication of likely energy availability than the proxy Brix assessment.
To ignore the research that has been funded by New Zealand taxpayers and farmers (through levy payments as well as taxes) is illogical. To fund research that has been shown by the scientific process not to have positive results is a waste of time and money.
It is acknowledged there have been mistakes in the past, and reinvestigation has resulted in different results, but in the particular case of Brix a simple examination of first principles reveals the fallacies.
Science advisors are needed on all research-funding bodies in order to select projects appropriately. Science knowledge in conjunction with farmer practicality and policy overview gives the best chance of successful outcomes – which is what we all want for the sector.
• Jacqueline Rowarth is professor of agribusiness, The University of Waikato.
