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While early crops of malting barley have been harvested over the past 10 days, many more will be ready for harvesting in the next week or two. Growers won’t need to be reminded of the consequences of the difficult year on their spring crops. As a result however, the spring barley harvest will present a challenge to growers in the form of attaining a clean sample as poorly filled grains will increase screenings within the sample.
This will be a particular issue for malting crops as high screenings will incur penalties and may lead to rejections. Early barley crops have proven difficult to fully de-awn although recent rainfall is likely to have helped this.
Efficient malting requires plump, even sized grains to ensure uniform water uptake into the grain. This helps to ensure that germination takes place at the same time and uniformly across all grains. Small or under-sized grains will perform differently to well-filled grains and so malting standards are set based on the percentage of grains retained over a specific size of screen.
Boortmalt, for example, currently reject any loads with screenings over 8% as specified in growers’ contracts. The determination of screenings is based on a 2.25mm slotted sieve screen and payments are adjusted according to percentage screenings, see Table 1. Small grains, awns, loose husks and trash will all contribute to increasing screenings so it is essential that your combine harvester is producing as clean a sample as possible.
There are a number of adjustments an operator can make to the combine in order to produce a clean sample. Fine tuning combine settings is a balancing act and only small adjustments should be made at a time. Adjust settings one at a time when the combine is working in the field.
De-awning
Where de-awning is proving difficult on crops which aren’t yet fully mature, this is a thrashing issue. On walker combines adjust the threshing drum speed and, if possible, adjust the gap between the rasp bars and the concave. Adjust concaves and rotor speed accordingly on rotary machines. Caution is advised however as if thrashing become too aggressive, particularly within drums, this may lead to increased broken or skinned grains and damaged straw. Some machines have de-awning plates fitted as extras which will also help with this problem.
Sieve adjustment
Sieve adjustments can make a significant difference to grain samples. The top sieve handles the bulk of the trash and screens out the majority of the material. If the sample is dirty, try closing this sieve slightly. Again, keep a close eye on what’s coming out the back of the combine.
The bottom sieve can be thought of as a regulator to determine how much needs to be returned and re-thrashed and will always be open less than the top sieve. If too much grain is allowed to be returned for re-thrashing this may put more strain on the combine.
Fan speed
Fan speed can be tricky but it will have a significant effect on the grain sample. Too much air will blow clean grain into the return and blow free grains out the back, whereas too little air will leave more trash in the sample. Increase fan speed accordingly but monitor losses out the back of the combine.
Forward speed
If forward speeds are excessive, this can lead to increased grain loss as well as a poorer quality sample. If all of the above adjustments are failing to provide a clean sample, reduce forward speed.
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