Tillage - Is it killing our Earthworms?


A recent study found that tillage methods are having a real impact on earthworm numbers in soil. I caught up with team member Olaf Schmidt, Associate professor UCD, to find out the results of the study and what the potential implications could be.

Tillage - Is it killing our Earthworms?

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  • 3 years ago

A recent study found that tillage methods are having a real impact on earthworm numbers in soil. I caught up with team member Olaf Schmidt, Associate professor UCD, to find out the results of the study and what the potential implications could be.

Recently a research study was published in the scientific journal Global Change Biology, to show a systematic decline in earthworm populations in soils that are ploughed every year. The disruption caused to soil by digging, overturning and stirring by conventional tillage methods in Ireland, is having a serious effect on earthworm populations worldwide.

Scientists from two Universities, UCD and the University of Vigo, worked in conjunction with each other on the study. They examined in total 215 different field studies carried out in over forty different nations. Some of said field studies dating back as far as the year 1950. Each of the studies mentioned studied the effect of different tillage methods on earthworm populations.

I caught up with one of the chief scientists/researchers of the study, Associate professor of UCD, Olaf Schmidt to find out a little more to help us understand the importance of the study and its results.

When asked about the mentioned decline of earthworm populations, Schmidt informed me that the study did not look at how quickly populations decline due to tillage methods but “how fast do populations recover when tillage is switched from conventional ploughing to some form of reduced tillage” he also added that “results show that the maximum increase is reached after experiments are run for ten years”, meaning it takes quite a while for populations to recover.

When asked about the potential knock on Implications from the above mentioned reduced earth worm populations Olaf stated, “The low numbers of conventionally ploughed land means that we get few of the functions or ecosystem services we can expect from earthworms.”. These functions he said include the production of soil aggregates and maintenance of soil structure, digging of channels that act as large pores for water and air transport within the soil and nitrogen excretions by the worms. He also mentioned that “. Earthworms are also food for many wildlife species (badgers, hedgehogs, many bird species) so there's less food for these in a landscape.”

This proves that there would be many knock-on effects, maybe not in the short term, definitely in the long run.

I questioned Olaf about actions being taken to help prevent this decrease in population numbers. He informed me that their results convincingly proved that “any form of reduced tillage will increase earthworm numbers.”. The team of scientists he said “analysed five forms of reduced tillage separately and the most positive effects are seen in no tillage and superficial tillage/soil loosening”. He added that there are other forms of tillage methods known as Conservation Agriculture which proves successful. This method he said, “usually involves retention of organic residues or mulching”. He said there is also another successful practice to help boost numbers. This involves the addition of organic matter. The reduced tillage and organic matter he said he said leads to an increase in soil organic carbon. He added that “by protecting earthworm’s farmers are likely (to) also protect soil” generally.

I asked Olaf about the non-inversion tillage, no tillage and the conservation agriculture mentioned in his article and whether Ireland has started to adopt them. He informed me that he wasn’t sure of numbers in Irelands industry but said that “there certainly is a major trend internationally for the adoption of these techniques”, particularly in Australia and North and South America.

When questioned about the cost effectiveness and practicality of these methods Mr Schmidt stated, “They are economically attractive because not having to plough is a big saver of costs, labour and fuel” he also added that “internationally these methods are introduced mainly for soil protection, especially from erosion” saying the methods are used efficiently in many countries.

Minimum tillage according to Olaf, is “an action that farmers can implement for an incentive payment”.

Knowing of most farmer’s resistance to change, with the phrase “if it’s not broke don’t fix it” coming to mind, I questioned Mr Schmidt about opposition from farmers with regards these methods. He said he has heard through people of the farmer’s reluctance as “traditionally a ploughed, clean, tidy field is seen as the standard”. He added that there are also issues for farmers surrounding “weed control, fear of lower germination and the need for other drilling machines”.

To find out the real importance of the study and its importance among its ecosystem I questioned Olaf on the benefits of higher populations to farmers. “Earthworms are useful for two reasons. They are beneficial organisms to have in your soil” they have important functions such as soil structure maintenance and the building of pores for water and air transportation. Olaf said “The larger the populations, the more of these functions you will get - for free…they are also good indicators of soil quality and soil health, it is easy to check for a farmer of his/her soil is in good status by just digging up a bit of soil and checking worm numbers. We know of course that there is much more life in the soil…but to study them is difficult. Earthworms are so nice because everybody can look for them very easily.”

He also said guides were made available for farmers to check its earth worm population numbers.

Mr Schmidt said that as soil is “essential for the survival of humankind” that this made earthworms “essential for soil formation and maintenance” adding “their importance is hard to overestimate”.

The great evolutionary biologist, Charles Darwin called earthworms “nature’s plough” because they continually consume and defecate soil enhancing its fertility in the process.

In his experiments in England in the late 1800s, Darwin found about 54,000 earthworms inhabited each acre of land and that each of these populations turn over tens of tons of topsoil every year.

When asked if he agreed with Darwin’s declaration as to the earthworm’s importance Olaf stated, “I would not say earthworms ‘were’ important (to humankind), they still are and will always be as long as we produce most of our food from land”.

He finished up by saying in order to protect these numbers that we, as the human race, need to find more “sustainable tillage practices and ecological processes” and then the beneficial organisms that drive them processes will become more important.

This study to me points to the clear need to upgrade our tillage industry and practices it employs. The earthworm to most might seem useful only as fishing bait, but if this study tells us anything it shows us that drastic implications are ahead if we proceed in the damaging of population numbers of our soil shuffling friends. The earthworm offers numerous benefits to our soils, act as food to our wildlife, and are vital to the tillage sector worldwide. Therefore the protection of the earthworm should be a top priority.

The published paper entitled “Conventional Tillage decreases the abundance and biomass of earthworms and alters their community structure in a global meta-analysis” is published in the journal Global Change Biology, with an online version available at http://dx.doi.org/10.1111/gcb.13744

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