14th February 2017
Combating Black Grass with Anaerobic Digestion
As many farmers will be aware, black grass is becoming an increasing issue across the UK. Especially in the East of England, arable farmers are having to combat the prolific weed, which is causing wide spread issues when growing cereals. This problematic grass has spread across the UK for a number of reasons but the main focus now is how to fight the weed and prevent further contamination.
Control can be achieved by the use of herbicides although resistance is relatively common and increasing. Changes in farming practice such as ploughing, changing seeding time and crop rotations are all successful in reducing the grip of black grass but cannot guarantee full success. The most effective control being seen as the strategic use of herbicides and modification of farming practices.
Concerns have been raised regarding the use of digestate from anaerobic digestion plants, that it might be contaminated with black grass seeds from crop feedstock. The subsequent spreading as a fertiliser would simply spread the black grass over the whole land area.
In order to understand whether this was a real issue, AD4Energy, the British firm that specialises in the design, build, commissioning and maintenance of anaerobic digestion plants, have been running trials on black grass to find out what effect anaerobic digestion has on the weed.
Through a 60 day trial the company set out to find out whether anaerobic digestion could prevent the growth and spread of black grass. The black grass seed sample was spread across 6 digesters, each containing digestate from a functioning digester. Each digester represented a timescale, from 10 to 60 days. Once the allotted time was complete, the digested sample was removed from the digester, the seeds harvested, washed and incorporated with sterilised top soil in a seed tray. This was watered daily and monitored over an extended period. A control sample at day zero was also set up, where the seeds were mixed with water and incorporated into the soil.
The trial showed that after only 10 days in the digester, the germination of the black grass seeds was prevented. In contrast the control sample had vigorously grown, producing a healthy crop of black grass. This was encouraging, as it indicated that the anaerobic digestion process was effective at stopping the spread of the weed.
To take the trial further, the experiment was amended so that the seed and digestate mix was digested between 2 and 8 days, with a control sample set up alongside. The results of this test showed a retention of only 2 days was sufficient to render the black grass unable to germinate.
In both trials the only trays of soil that showed signs of black grass growth were the control samples.
These conclusions were encouraging as the normal retention time for a digester is in excess of 10 days. Even after an extended period of stability and watering, there was still no sign of growth from the digested seeds and the trays of soil remained barren.
This is positive news for farmers with anaerobic digestion plants, as the digestion process helps prevent the spread of black grass.
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