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OSR Crop monitoring in store

Date Added: 20/09/2012

High Value of Oilseed Rape Warrants Careful on-farm Crop Monitoring

By Richard Elsdon, Technical Manager, United Oilseeds

Whilst it‘s too early to comment about harvest yields of oilseed rape, there's no doubt that the present crop in the field is the most valuable we've seen for many years.

We're currently seeing ex-farm values of £380 per tonne for harvest and after adding the appropriate premiums, a price in excess of £400 per tonne is quite achievable. Clearly, OSR is now the most valuable crop on most arable farms and consequently deserves careful storage with great attention to detail.

As a result of the poor weather, it's likely the current crop will come off the combine well above 9% moisture and consequently require drying. It‘s at this critical stage that the care and attention must start.

What should you look for? If the crop is very wet, say anything above 15%, it's capable of heating up overnight to the point where it's very uncomfortable to put your arm in the next morning.

This heat is generated by micro-organisms using the oil as an energy source and it will reduce or "steal" the overall oil content of the crop and reduce its value. In addition, if left at a high temperature, the oilseed will become rancid - which is an expensive problem to resolve.

Both these scenarios can be avoided by drying and then cooling the crop immediately it's combined.

It's also important to remember that the higher the moisture content of the incoming crop, the lower the drier temperature should be. This may lead to reduced output from the drier, but will help avoid problems later in the season.

But guard against complacency. There's often a temptation to assume that once the dry crop comes off the drier, it's now safe. After all, it's been dried and then cooled by the drier. But there may still be an issue.

Even the most effective drier cannot lower the temperature of the outgoing crop below about two or three degrees centigrade above the ambient temperature of the day on which it's dried. For example, if the temperature during the day is 23 degrees centigrade, the crop temperature is likely to register 25-26 degrees centigrade once dried.

The next consideration is the long term cooling of the crop. Some growers assume that hot August temperatures make cooling the crop effectively impossible. Not so.

Even in August, the overnight temperature will drop to 14-16 centigrade, enabling some cooling to take place. Admittedly, the temperatures soon rise again during the day and this is when a Differential Thermostat should be deployed. This piece of technology is not new and I remember using one in an onion store in 1977 to great effect.

A differential thermostat simply compares the temperature 30cm below the surface of the heap of crop with the ambient air temperature outside the store and controls the cooling fan as appropriate.

When the outside temperature is below that inside the crop (often three centigrade) the cooling fan automatically switches on. When the relative outside temperature increases and is no longer three centigrade cooler, the fan is switched off. As the differential thermometer measures the temperature difference at very short intervals, it can grab cool air whenever it's available throughout the night.

Automatic technology is effective and helpful, but a little manual temperature checking is also called for to ensure the system is working and that air is passing evenly throughout the entire crop.

So the second part of managing a stored crop of oilseed rape on-farm effectively is to walk the heap every week and record the temperatures across the bin. This can be done with high tech probes wired back to a central recording computer or by inserting a 15mm copper pipe, with the lower end crimped over, into which a thermometer (like the ones we used in the science labs at school) is inserted.

For ease of extraction, tie some string to the end of the thermometer long enough to lie on the surface outside the pipe. Pull out the thermometer and record the temperature at this location on a clip board. Then lower the thermometer back to the bottom of the pipe and leave it there for one week before checking again.

You'll need several thermometers to gauge temperature across the heap accurately, but they should last several seasons and will provide you with an essential indication of what's happening inside your stored crop. If you have a probe that measures temperature, by all means use that instead, but always record the temperature in the same area each time.

I meet growers who are reluctant to blow the crop if rain or fog is forecast, in case it pushes moisture back into the heap. In my experience, this won't actually occur, because the cooling fan moves such a small amount of air its churning action actually has a warming effect and reduces the relative humidity. Also, the air is always cooler than the crop and though it's subsequently warmed by it, the relative humidity is reduced.

Walking the crop has one more advantage. We all know that dry oilseed rape is difficult to walk over as your feet tend to sink in to it - usually by up to 15cms. Should you discover an area of the crop where you feet don't sink in or penetrate, then you have a problem that requires urgent investigation. Yet another example of the old adage the best fertilizer is the farmer's foot step!

By adopting these simple techniques and applying them regularly, it is quite possible to store oilseed rape in a previously cleaned and disinfected store until mid-summer the following year in perfect condition.

Surely thorough on-farm monitoring is worthwhile for such a valuable crop?



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