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Written by Miranda Prendergast-Miller, as based on information found on Agricology (www.agricology.co.uk)

Above: Grass-clover ley (Photo credit: M. Prendergast-Miller, SoilBioHedge)

Earthworms have been in the news recently, with new data confirming that earthworm numbers are low in UK arable soils due to intensive ploughing, repeated soil disturbance and low soil organic matter. Earthworms are important soil organisms: their burrowing and feeding activities allow water to percolate through soil; they breakdown organic matter, releasing nutrients for plants and other soil organisms like bacteria and beneficial soil fungi, but also stabilising the residual organic matter. Earthworms form characteristic soil casts – these small mounds of earthworm-processed soil form little hotspots of activity on the soil surface and support a myriad of other soil organisms.

The contribution of these humble organisms to ecosystems is considerable, and low numbers in arable soils are a concern. What are the knock-on effects on other soil organisms; the release of nutrients for crop growth; for water retention and possible flood control?

However, all is not lost. Earthworms can make a comeback, and in a relatively short period of time!

I have been working with colleagues at the Universities of York, Leeds and Sheffield (scan the QR code at the end of the article to read more) to assess the recovery of earthworms in newly established grass-clover leys. We set up the leys in arable fields which had been used for arable farming for many years, resulting in low soil organic matter and poor soil structure. These soils also contained very few earthworms compared to nearby long-term pasture soils.

Using simple equipment, sturdy boots and a shovel, my team and I – all converted earthworm-enthusiasts – counted the earthworms we collected from soil pits before the leys were sown, and then every 3-4 months over 2 years, as the leys developed. The leys were managed following standard practice and were regularly mown. Within a year, the grass-clover leys looked good. Even from space, using Google Earth, I could see our experiment as green stripes in fields of ready-to-harvest golden wheat. But what was happening in the soil itself?

All that new plant growth was pumping valuable carbon into the soil, through the grass and clover roots, stimulating the soil biology.

So what did we find?

The best time to find lots of earthworms is in cool, wet periods, and the best chance of finding lots of adults is in springtime. (Perfect timing for this year’s http://www.wormscience.org/ !). Adults are easier to name to a species level, and I’m indebted to David Jones at the Natural History Museum for his identifications. This meant I could build a profile of earthworm diversity, not just of their numbers.

Earthworm numbers are low in warm, dry summer months. They are sensitive to moisture, and when soils begin to dry out, they go into protective mode, coiling up into balls inside their ‘aestivation chambers’ or, for those species which can, burrowing deeper into the soil profile – which makes them harder to find.

Earthworms have lots of offspring. Indeed, over 50% of our pit counts were juveniles. While finding only small similarly-looking earthworms may not be as exciting as finding a big one like Lumbricus terrestris, these juveniles are crucial to the next generation of earthworms. Earthworms loved the grass-clover leys. Within one year, average earthworm numbers were higher in the leys (9 worms per pit) than in the arable soil (4 worms per pit). Within 2 years, the average ley earthworm population (25 worms per pit) was nearing that of the long-term pastures (32 worms per pit) we were also monitoring.

Importantly, we found 2 species we had not recorded in the arable soils and a higher number of adult earthworms in the leys (5 worms per pit) than in the arable soils (1 worm per pit). This told us that the populations in the leys were healthy. We also surveyed earthworms under hedgerows and within grassy margins along field edges. These had higher earthworm numbers than did arable soils. On average, we found 12 worms (per pit) in hedges and 19 (per pit) in margin soils.

Depending on the species, earthworms were selective and preferred different habitats. Small ‘epigeic’ earthworms that typically live on the soil surface amongst rotting leaves and other plant material, preferred the relatively drier litter-rich soils found under hedges; whereas the grassy margins were home to a wider range of earthworm types, especially the deep-burrowing ‘anecic’ species. Endogeic earthworms, like the surprisingly green or pink Allolobophora chlorotica, were found everywhere. These species tend to live within the soil, forming horizontal burrows.

Not all soil pits are the same: the number of earthworms we found in pits varied considerably. Sampling strategy is important and we had to take an average of numerous pits to get a reliable estimate of earthworm numbers.

So what does this mean for soil health?

The key message from our data is that, although earthworm numbers were low in intensively managed arable soils, changing soil management by introducing a short-term grassclover ley can help boost earthworm numbers in a relatively short period of time. This is because the reduction in soil disturbance and the perennially green plant cover supplying nutrients increases the survival of juvenile earthworms, so more can grow and reproduce. And crucially, it’s not only the earthworms that benefit. The grassclover leys were a major boost to soil health all round by: improving soil structure; reducing bulk density; improving water retention; increasing resilience to flooding; increasing nutrient availability and plant growth; and increasing the number of beneficial soil fungi. Some of these improvements in soil quality are directly linked to recovery of earthworm populations.

Conventional inversion ploughing and power-harrowing does not support high earthworm populations. But shortterm changes in soil management can do a world of good to our soils – and help humble earthworms to thrive! So while you’re counting earthworms this week, think of ways to manage your soils to give you a beneficial effect in the future!

Miranda Prendergast-Miller says of herself:

“I am an environmental biologist, with a keen interest in soils, especially how soil-dwelling organisms, such as bacteria, fungi and earthworms interact, and how human activities impact them. In turn, I am interested in harnessing soil biology to reduce the impact of intensive agriculture and protect our precious soil resources. Currently, I am based at the University of York, working on a project with colleagues from the Universities of Sheffield and Leeds called ‘SoilBioHedge’. We are interested in understanding how farm management practices such as leys or reducing ploughing intensity affect soil organisms and the subsequent changes in soil productivity.”

SoilBioHedge:

This project was funded by the UK Natural Environment Research Council, under the Soil Security Program. The project is led by Prof. Jonathan Leake (University of Sheffield) and the earthworm study was led by Prof. Mark Hodson (University of York). Thank you to colleagues who joined in the earthworm sampling. Further project details can be found at:

Large parts of Germany have struggled for years with very erratic rainfall patterns. Some farmers are now tending to
question the usefulness of cover cropping in dry and even semiarid regions largely on the basis of their experience in
the dry summer and autumn of 2015. Does cover cropping conserve water or squander it?

Written by Markus Scheller ∙ Dettelbach-Euerfeld

The benefits of cover crops are undisputed: They help to increase biological activity in the soil and improve the soil structure. Cover crops also prevent soil erosion caused by wind or heavy rainfall and reduce nutrient leaching. Some species even have the ability to unlock nutrients bound in the soil, making them available to the crops. Despite this, cover crops are frequently accused of consuming water that is badly needed for the follow-on crop. Long term practical experience and scientific studies, especially in dry regions such as Austria‘s Burgenland, have clearly shown that this is not the case. Cover crops do not consume any more water than fallow land.

Water evaporation on uncultivated land is significant

The table below shows that water loss is large due to evaporation from the uncultivated soil surface. By contrast, the sum of transpiration for cover crop growth and evaporation from the cover crop canopy – evapotranspiration – in dry years is lower than that of evaporation from the bare soil. In winter in particular, the canopy cover reduces non-productive water evaporation from the soil.

Winter rainfall is normally sufficient to make up for the increased water consumption of cover crops in the autumn. Cover crops have not been shown to have any negative effects on the subsequent crop either. Quite the reverse, in fact; carefully chosen cover crop mixtures can prepare the soil specifically to meet the requirements of the follow-on crop. This has been demonstrated by comparison trials at Kraichgau in Baden-Württemberg (South-West of Germany) in which cover crop mixes were found to be superior to the standard single crop mustard both in terms of nutrient fixation and the productivity of the follow-on crop grain maize.

Moreover, the productivity of the follow-on crop depends far more on the rainfall pattern in the crop year than rainfall events during the cover crop growing season. Experiences on my own farm in Lower Franconia, Bavaria (Central-South Germany) with wheat/sugar beet rotations demonstrate the importance of establishing the cover crop. It is not always easy to use the residual moisture in the soil to germinate the cover crop seed, especially in the dry conditions typically found in Lower Franconia.

Strategies for preserving soil moisture are the key

This begins right from the point of harvesting the previous crop. It is important to pay careful attention to your combining operation. For example, check the settings on the combine harvester (low losses), make sure the knives on the straw chopper are sharp, select a short chop length and uniform straw distribution. The timely use of a mulcher to shred the straw may even be worthwhile to reduce the ‘chimney effect’ of the stubble, i.e. loss of water via the hollow stalk, especially with large quantities of straw. Control of volunteer cereals is also critical for the successful establishment of the cover crop.

If the straw is harvested, pay particular attention to the area underneath the swath as the proportion of shed seed, chaff and weed seeds will be particularly high here. The main thing is to prevent the volunteer cereals swelling or germinating ahead of the cover crops seeds. If volunteers from cereals that are harvested early in the season, such as winter barley, are encouraged to germinate, it is very important to shallow till immediately after the cereal harvest to break the capillary action. In later crops such as winter wheat, farmers are often left with no choice but to till at the same time as sowing the cover crop, as sowing ought to take place by the end of August at the atest to ensure reliable establishment of the cover crop. Plan to sow as early as possible to prevent non-productive evaporation from bare soil during summer when temperatures are high.

The aim is to make productive use of the residual moisture to form biomass and absorb nutrients. By cultivating a mixture of crops it is possible to exploit the benefits of cover crops even under unfavourable climate conditions and to minimise risks. Cover crop mixes containing a variety of components promote diversity and provide herbage growth even when individual species fail – often ensuring that adequate soil functioning can still be achieved.  

Sowing methods that conserve water

Direct seeding and shallow mulch seeding are effective means of conserving moisture. Since good reconsolidation is important with these techniques, it can be helpful to make an additional pass with a roller.

The right tillage for the followon crop

The way in which soil is prepared for the follow-on crop and therefore how the cover crop is managed also has an important impact on the soil water balance. Leaving the cover crop in situ until just before the following crop is sown maximises water conservation. A rolling pass in autumn or winter when the soil is trafficable can encourage the cover crop to die off over winter, if this is the intention. This has proved particularly helpful in the mild winters of recent years. For early sown summer crops, e.g. oats, spring barley and sugar beet, a shallow cultivation pass in winter when there is a ground frost is a good idea, depending on the location, to speed up the drying of the soil prior to sowing.

If the cover crop is followed by maize, the cultivation pass may either be carried out to incorporate manure or immediately before drilling. Even cover crop plantings that are not needed to satisfy greening requirements should under no circumstances be ploughed up in autumn or early spring. Such action would have a negative impact on the water balance and reduce the performance potential of the cover crop.

Conclusion

Cover crops are an important part of the crop rotation system, even under difficult conditions. They benefit the soil in many ways, often giving more back to it than they took from it in the first place in the form of water or nutrients. The positive effects of growing cover crop mixes are numerous; they support soil organisms, increase aggregate stability, reduce the risk of nitrate leaching and erosion etc. The key to success, however, is to pay as much attention to the cover crop as to the main crop. The farmer‘s job is to find the right timing, prepare the seedbed optimally, and select a cover crop mix that is appropriate for the region and the crop rotation system.

Cover crops for nitrogen fixation

After the cereal harvest there is an opportunity to produce and fix nitrogen for follow-on crops. Special cover crop mixes with good nitrogen fixing capabilities are available for this purpose. N-Fixx is a good choice for winter cereal crop rotations. It comprises nine different components, including 80 % legumes. According to Deutsche Saatveredelung AG (DSV), this mix is not only good at fixing nitrogen, it also enriches the soil humus and promotes soil health to boost the performance of subsequent food and forage crops.

Think “soil quality” rather than “new drill” when planning your change to zero-tilling.

Min till and no till are quickly becoming part of everyday agriculture. Whether used to increase soil health and the productivity of soils, or as part of a Black Grass strategy, or both, we are seeing this type of tillage being accepted as a bona fide method of farming. And, where it is done correctly the rewards can be a healthier soil and a lower input growing system. However, a word of caution needs to be put into the tillage conversation as many farmers are rushing to the machinery depot to pick up the new drill.

That word of caution should be ‘air’. A soil without air is a soil that will not sustain a healthy growing crop to a profitable yield. The air allows moisture to percolate into the root zone. It allows roots to grow in-between soil particles and allows gaseous exchange. We need air to supply the Nitrogen that is available from the atmosphere, and we need air spaces to allow CO2 to escape from the soil so that it may enter the stoma on the leaves.

Why do you think most stoma are on the bottom of the leaf? If a farmer on a heavier soil starts reduced tillage with no soil life, including bacteria, fungi, algae together with earthworms, who are the main workers of the soil, there is a good chance that growth and yields will drop, sometimes significantly. At a farmer meeting recently when no-till farmers were asked ‘how many farmers saw a yield drop’ after starting no-till, around half of them raised their hand. This wouldn’t happen if the health of the soil was examined and worked on before the new drill arrived.

Compost application, cover crops (with the right species), fertiliser and chemical control are all contributing factors to soil health and need close examination before setting out on this journey. I often hear the phrase, ‘Cover crops are a waste of time’ but then on farms that use them, I hear, ‘We saw a difference after the first crop’. When on farm the first question I am asked is ‘Where do I start?’ The answer will never be ‘Buy a new drill’. We need to look at soil type and then decide what can be done to make it suitable to use a no-till farming system. If you are lucky enough to have an open, aerated soil with a good structure then off you can go.

If, on the other hand, you have a heavier soil that is more clay, then we really have to work out how we can increase the Organic Matter content so that the soil can breathe, and breathe is the correct word, as the soil is a living entity that requires air (oxygen) to operate at peak efficiency. A soil that is lacking air will rely on high inputs of fertilisers and agrochemicals. By far the best way to achieve this goal would be to obtain hundreds of tonnes of organic matter, compost them correctly and then apply to the soil. Anybody who has listened to Simon Cowell will know that this works, and perhaps it may be the start of a journey for you to be a future soil farmer of the year. Unfortunately, this system is not available to many so other ways of farming must be found.

Cover crops are undoubtably a great idea to everyone who has the interest to try them. They will not increase organic matter levels in the soil anywhere near as quickly as applying compost, but it is a fantastic second place. We have seen heavy soils lifted and aerated after only one or two sowings and you can really feel the spring in the soil as you walk the fields. The roots grow large and deep in comparison to stunted and on the surface. To start to accomplish this, work has to be done on the best potential seed mix for your soil. You need to also consider the best way to get rid of them, which is generally by sheep or crimping, but herbicides are also needed (we are able to limit herbicide impact and help to repair the bacterial damage the herbicide does to soil life).

A good cover crop can give you a huge boost in plant available nutrients plus the rooting will open the soil and allow new roots to penetrate deep into the ground. Another part of getting a soil ready for a new tillage system is to increase microbiology and the rest of the soil food web. This can be achieved by reducing the amount of nitrogen applied by using a Humate to sequester the nitrogen making its uptake far more efficient. The Humate will also complex phosphorous which stops it locking onto the Cations in the soil.

This means you can put on considerably less and still get more into the plant. Remember, that for every kilogramme of nitrogen that is applied to the soil and is not utilised by the plant you could stand to lose 100kg of organic carbon, which slumps the soil. This explains why so many fields are lower than their surrounding roads. A soil that slumps, put simply, contains no air, which leads to poor rooting, which in turn leads to higher fertiliser and agrochemical use as the plant’s resistance to pest and disease drops.

We have seen that, by supplying a large amount of the required nutrients to the plant as a foliar programme, we can further lighten the load on the soil leading to even better rooting. A reduction in fertiliser and especially agrochemicals will lead to increased yields, so there is no need to accept the drop that we are told to expect. No one system will suit everyone but by having an open mind, looking at the tools at your disposal, and taking well worked out steps you will get a superb soil that works away below your feet providing the nutrients that your plant needs to produce the crop/yield that you want.

Interested in hearing a little more? Visit us online on www.aivafertiliser.co.uk, call us via 01235 834 997 or email office@aivafertiliser.co.uk.