Strawburn – environmental disaster or saviour?

I was recently involved in a fascinating discussion on Twitter reguarding that old   technique that was straw burning. For those that don’t remember this was the scorched earth policy of burning cereal straw residues be it straw chopped and spread, straw in the swath behind the combine or occasionally a long stubble. This practice has been employed ever since man first started growing crops on a wide scale, in fact it is fair to assume the practice has been employed by nature itself well before homa sapien got in on the act. Just think about the many programmes we have watched on the African savannah where the summer brings dry conditions and the grasses regenerate themselves by burning the old dead foliage.

But the burning of straw was not a natural thing, well not always, it was entirely intended to be man made and man controlled.  Fields were burnt iun sequence to rid of unwanted straw. INITIALLY it was fairly un-regulated then quite rightly some controls were put in place such as cultivate strips to protect field boundaries. The choices were 6m ploughed headlands or 24 metre cultivated boundaries, both of these were effective at controlling the spread of the fire. Well they were as long as the wind was in our favour. We also had to have a water supply at hand to put out any hedgerows etc that unwittingly caught fire.

The practice was very effective at removing surplus straw from the soil surface but there were other benefits such as the burning of weed seeds, the destroying of any green bridge, a reduction in mollusc populations. On the reverse of course there were negatives – nesting bird sites were undoubtedly destroyed, beneficial insects would also have destroyed. The wider environment was affected by thick smoke billowing upwards to the skies. During the 1980’s I was a student at that great old agricultural college at Caythorpe Court near Sleaford in Lincolnshire, and straw burning was a common site throughout the county. I can vividly recall a conversation with an RAF pilot from RAF Cranwell who was bemoaning the practice and said that throughout August the skies were thick like fog. I have to say that conversation, even back then, made me think that possibly this couldn’t be right.

Come 1993 and the practice was eventually banned. Straw was no longer allowed to be burned and many took the opportunity to bale and sell the straw. Many more especially in non-livestock areas such as Lincolnshire decided to chop and incorporate the straw – and why not incorporate the crop residues, increasing the organic matter content of the soil. Additionally you are of course incorporating potash and the OM will be broken down by soil microbes and converted into nitrate. More free plant food.

However what has happened over the last 20 years is the current block cropping type rotations such as wheat:rape:wheat:rape  came popular. To service this min-till came to the fore, then lost favour and has come back again in different guises. The plough is not the main primary cultivator on many farms. The top soil is not being turned quite as often, we are not ploughing weed seeds down as frequently as we once did. This was all ok, as we had herbicides to do the job for us.

Herbicide resistance blackgrass became real. In time we started to hear stories of IPU contaminating water courses, the Chewell Valley studies began to turn out worrying results. IPU and trifluralin were on borrowed time and eventually banned. Recently we have had other chemistry available to help the control of blackgrass however there are wider and wider areas of herbicide resistance. With the ever increasing list of herbicides being banned by the EU and no new chemicals on the horizon – what is the future going to bring?

Maybe the future is actually behind us. Maybe the old husbandry technique of burning straw could be a solution? What about restricted controlled burns in areas showing herbicide resistant blackgrass. Would this age old practice be a solution?  I have to admit I think its doubtful, very doubtful that any government would allow straw burning, but that does not mean we shouldn’t debate it. We could have ploughed or cultivated strips to  restrict the potential of fire risk. There could be licences or management plans in place that self police the situation, or there could be legislation in place. I know this is quite fanciful but in these times of reduced herbicide availability and indeed the consumer is showing they would prefer less pesticides applied to crops, would this not be another technique that can be used in the fight against blackgrass – and other weeds for that matter. Additionally there is the added bonus of removing the green bridge. As i say its another piece in the armory, but we shouldn’t forget the other techniques that should be employed in the fight – use of the age old technique of stale seedbeds, the use of spring cropping (free nitrogen from spring peas anyone?), not to mention the use of the plough when establishing crops at some point in the rotation. Lets consider a Michael J Fox and go Back To The Future to find solutions.

So will straw burning be allowed to be used on farm to help control resistant weeds populations? I doubt it very much, but lets keep debating it, who knows there may be a change of attitude?  The use of chemicals is not the only option. Both have their place.

So anyone for reducing the amount of herbicides applied by burning straw and stubbles in controlled burns in areas showing blackgrass resistance?Sounds good to me!

Thanks for reading.

 

AgronomyMan

1 thought on “Strawburn – environmental disaster or saviour?

  1. So to summarise from your blog the benefits are;
    Destroys the green bridge
    Kills the weed seeds
    Removes fungal disease & spores

    I have a couple more thoughts.

    Incorporated straw is a very poor food for bacteria (mainly lignin & cellulose) and they actually draw on nutrients in the soil to aid them in the slow process of breaking down the straw, thus reducing availability to the crop and using up oxygen in the root zone. This latter is of particular importance in heavier soils through a cold, wet winter.

    Burning straw releases trapped nutrients very rapidly back to the soil. Furthermore the previous crop roots provide a great source of extra organic matter and are more easily broken down by bacteria and soil fungi – so long as they are not exposed to the air! Sunlight kills huge quantities of soil bacteria.

    Burning straw is ecologically friendly, and carbon-neutral: after all, the carbon in the straw was fixed from the air in the first place.

    All this points directly to the advantages of zero-tillage regimes if combined with straw burning.

    Together these are environmentally and crop friendly because:
    It reduces need for insecticides (derived from fossil sources in the main)
    It reduces need for herbicides (derived from fossil sources in the main)
    It reduces need for some fertilisers
    Has positive crop growth effects
    Reduces tillage & tractor passes, so dramatically reduces use of diesel
    It conserves soil structure & moisture
    It helps to build organic matter
    It conserves and builds soil fauna & flora

    The problems in the 1970’s & 80’s was poor regulation and enforcement. Get these right and I see few issues with its reintroduction and great benefits to both farmer and environment.

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