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Plant Science Panel

Insecticides, biofuels, GMOs …

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'The Ugly Truth'

by Tracey Brown, director of Sense About Science

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Soil – A non-renewable resource that we’re throwing away?

A lot of people have an interest in soil, especially for growing crops, and in the microorganisms within it which take non-usable minerals and turn them into plant food. Decisions on how best to look after soil are provoking increasing debate. The EU Commission has withdrawn the Soil Framework Directive – which aimed to give soil the same protection as air and water. Farming bodies see this as a success against needless red tape and consider the current protection for soil to be sufficient. Others are more critical (see for example ”Farming lobby has wrecked efforts to defend our soil”).

What happens below the surface of a field has far reaching implications and alongside the soil protection debate the Plant Science Panel has also received questions on things like flood management strategies, improving crop yields and even microbes leading the next green revolution.

On Monday 28th July 2014 our panel of soil scientists, Dr Robin Sen, Prof. Karl Ritz, Prof. Phil Haygarth and Dr Arwyn Jones answered your questions.

If you have a question on a plant science related issue then get in contact with our plant science panel via Twitter, @senseaboutsci using #plantsci, or email us at [email protected].

19. "Annual crops which need to be planted every season, like oilseed, and some cereals and legumes, take a heavy toll on soil. Is there a way to breed, or genetically modify these crops to get perennial varieties?" (Chris Peters)

PH: "I am not a crop breeding expert, but I once was involved in researching the different rooting properties of different strains of grasses and how this affected soil water flow. I think in that case we demonstrated the principle that crop breeding could be of value to the soils and potentially the environment. However in reality, doing trials that actually link plant genetics to soil and environmental benefit are not easy and should not be underestimated. Moreover, in some cases solutions can also come from good old soil management as well as crop breeding and genetics."

KR: "This is an interesting question and may be better answered by one of our Sense about Science (sensible) plant scientists! However, from a soil perspective, perennial plants can be very effective at conditioning soils, since the persistence of their roots can provide a sustained delivery of organic materials belowground, and hold the soil fabric together. The major effect of annual cropping on soils you allude to relates to my answer to Question 1 (below), in that every gramme of plant (or animal) material removed from the soil in a field is by definition no longer in that soil to potentially sustain function. And this would also apply to perennial-based systems, it’s just that a bit more biomass tends to be left behind in the field each year. Perennial cereals exist, and are being grown in parts of the USA, but tend to provide lower grain yields, since more biomass is partitioned below ground. There is indeed much interest in these concepts, and the possibility of using genetic modification or other techniques is being investigated." 

18. "What are the knock-on effects of biodiversity if you have poor quality soil in a field? Aren't farms quite low biodiversity anyway?" (Helen Reegan)

RS: "There is a clear positive relationship between above and below ground biodiversity – more plant diversity is supported in soils with greater soil microbial diversity. Modern farming practices favour mono-cropping under intense management involving use of NPK (nitrogen, phosphorus and potassium) fertilizers and pesticides which have been shown to significantly reduce the soil biodiversity particularly in relation to soil fungi and invertebrates. This prevents soils from retaining nitrogen which is either lost into the atmosphere as a potent greenhouse gas, nitrous oxide, or into groundwater as nitrate which, along with phosphorus run-off, drives toxic eutrophication of our rivers and lakes. Soil structure and resilience is very much dependent on soil fungi that bind soil particles together which prevent loss of nutrients, air and water under waterlogging or drought conditions."

17. "As soil is a valuable resource should we not include it as a consideration in planning permission applications?" (@halpinrobbins)

PH: "I think that this is a great idea and is something I have written about in a paper with Karl Ritz as a result of the Land Use Foresight Report. Essentially we need to value soil and the services it provides us – and thus it would seem logical to have a check list of the service value of soil before it is sealed over and given to supporting buildings. Makes complete sense to me!"


16. "What is the effect on soil microorganisms, particularly invertebrates, of neonicotinamide pesticides (and their toxic breakdown products) as used on seeds. What is the long term effect on soil fertility?" (John Whetman)

KR: "There currently appear to be very few studies in the peer-reviewed scientific literature specifically investigating the effects of neonicotinamides on the living things in soil (soil biota). One would hypothesise that there are likely to be some impacts, given the potency of the material and the abundance of insects amongst the soil biota. In a recent review published in the Journal of Applied Ecology (2013, Volume 50, 977-987). Dave Goulson, now at the University of Sussex, concluded “Major knowledge gaps remain, but current use of neonicotinoids is likely to be impacting on a broad range of non-target taxa including pollinators and soil and aquatic invertebrates and hence threatens a range of ecosystem services”. Thus, more – and particularly scientifically robust – evidence is needed.

As is often the case with systems as complex as soil, there is in general evidence for long-term effects of biocides on soil fertility being negative, neutral and on occasion positive, depending on the chemical involved, the soil type, the context of the system under study, and even the weather!"

15. "Sand inundated the area where I live in the 14th Century. It does not grow or drain well here. Is sandy 'soil' different?" #soil,#senseaboutsci (@FancyAster)

KR: "‘Sand’ is considered as one of the three ‘fundamental particles’ of which mineral soils are constituted, the other two being silt and clay. There is a decreasing size relationship across these three, sand being largest at 2 down to 0.1 mm diameter. Most soils are comprised of a mixture of these three particle types, and are basically classified according to these proportions. Thus a ‘sandy soil’ is predominantly made of sand. If you Google ‘soil texture’ you may spend many hours getting into the gritty detail, but here’s a really quick introduction. Soils are tremendously diverse in the way they are constituted, so in a sense, all soils are ‘different’, including your particular sandy soil.

Sandy soils typically drain quickly since the pores between the large particles are also large, and they may be less ‘fertile’ since if they tend not to retain moisture and nutrients, especially if also low in organic matter. If a sandy soil ‘does not drain well’, there may be a reason deeper down there such as a sealed later layer or pan."


14. "Could #rhizomorphs be manipulated to release fertilizers/biomolecules for soil restoration?" (Arnaud Queyrel, @AQueyrel)

RS: "Rhizomorphs are produced in many mushroom forming fungi and are major long distance channels for water and nutrient transfer within growing fungal networks. They help bind and stabilise soils. Rhizomorphic fungi secrete enzymes, nutrients and water involved in decomposition of wood and litter to release essential locked up nutrients for fungal and plant growth. Therefore, soil restoration through manipulation of soil organic matter by, for example, manuring or composting, supports growth of these fungi and other beneficial microbial communities."


13. "What is currently being done to protect the soil in UK farms?" (Carl Borthwick)

PH: "The Natural England website sums it up quite well saying "Little statutory protection exists specifically for England's soil, although they are indirectly protected by other legislation such as that covering the prevention of pollution and contamination, and for land use planning.”. Defra published a soil protection review in 2010 that also provides some guidelines. In my personal opinion though, I fear that soil is all too often being missed, as the focus is often pulled away from soil per se, in favour of the wider strategic benefits such as food and water. I think that we need a more soil-centric way of viewing our priorities. I must say that the British Society of Soil Science is a great place to start doing this!"

12. "Is there anything we - as individuals - can do to help protect our soil?" (@MimiTanimoto)

RS: "As individuals we may have ownership or use of soils in our gardens, allotments or, as farmers or landowners, our fields and landscapes. These people intuitively know the importance of protecting their soils to maintain soil fertility for sustainable food production but also conservation of, for example, woodland, grassland or moorland habitats. Many are already involved in outreach and educational activities on soils, often harnessing the power of the internet and particularly social media. We all should push for more soils education starting in our primary schools when children are all so very inquisitive about the natural world. Biology and Environmental Science curricula in secondary and higher education should pay much more attention to soils particularly with recent suggestions that Earth’s soils will be irrevocably damaged in the next 60 years- the lifetimes of our children."

AJ: "As most people live in urban environments, their practical options to protect soils may be limited. However, they can put pressure on politicians and local decision makers to be aware of the need to preserve and enhance soil functions. As mentioned by Robin, education and communication are paramount. Society as a whole needs to be aware of the role that soil plays in their lives and well-being and for this to happen there has to be a sea-change in the intensity of communication and underpinning investment."

11. "Can green manures [rapidly growing plants that are ploughed into the soil to add nutrients] fully replace livestock manure to improve soil structure, or can they only do this in certain conditions?" (@tracydwjones)

PH: "In terms of soil structure, then any return of organic matter, whether from a plant or animal faeces, is a good thing. But I don’t think that it is a case of one replacing another. Instead it depends on local availability. If your farm is sited adjacent to a supply of animal manure – then that is best. And I suspect that in some cases animal manure may have more nutrient value than green manure."

10. "Why do we need to regulate and legislate for proper soil management? Surely the farmer's own profits are hurt if they don't take care of their farms - just like any business not looking after itself." (Andy Gifford)

KR: "Soils are fundamental to civilisation, as well as being a primary business asset for most farmers (and other land users besides). Thus it is in everyone’s absolute interests that soils – an essentially non-renewable resource in the timescale of human civilisations – are well managed and indeed protected. Most agree that regulation and legislation for environmental protection is in principle an appropriate device to underpin this. It’s a question of scale and degree, and balancing the various interests of all involved. Soil science can inform policy by providing evidence-based means for assessing soil health and sustainability; and assist (all manner of) land users in devising appropriate and effective management techniques and systems, so that they can take due care of their soils."


9. "Which insects and other invertebrates are necessary for soil fertility?" (@RebeccaNesbit)

RS: "In addition to bacteria and fungi, many invertebrates (including insects) are crucially important to soil fertility. We all know from school about the soil improving activities of earthworms, that were studied by Darwin, but other important examples of invertebrates such as springtails and oribatid mites do very much the same job of consuming bacteria, fungi and/or breaking down dead plant and animal detritus. These microscopic invertebrate groups can each number hundreds of thousands of individuals in a cubic meter of soil. They are part of the soil food web that defines healthy living soils but are also sensitive to pesticides or more correctly, insecticides, and thus need to be studied in much more detail befitting their importance in maintaining and improving soil fertility."

8. "Is it true that I should always wipe or wash my mushrooms as the bugs (bacteria) in the soil they're grown in will make you sick?" (Victoria Murphy)

RS: "It is always good to pick young wild edible mushrooms if you do not want to eat insect protein. You could brush off any soil and insects but there is no real need to wash or wipe your mushrooms. The inner flesh of mushrooms will contain soil bacteria as the mushroom forming fungus associates with bacteria in the soil. Cooking kills these bacteria but even eating mushrooms raw should not make healthy people sick and could even boost your immunity to those bacteria."


7. "Should greedy people who've ruined their soil structure have their land confiscated? In 'west' intensive agriculture, deep ploughing and excessive pesticide use has killed living soil for greed." (@HamblettMike)

AJ: "This is a difficult question as land degradation isn’t always about ‘greed’ but often reflects a lack of education on sustainable soil management or viable alternatives for earning a living. I think it’s important that land owners and managers are made aware of the impact of specific management practices on soil characteristics and the ecological services that they perform. If the soil is already showing signs of poor management, then users could be obligated to carry out remediation or conservation measures."


6. "Is anybody monitoring what happened to the soil fauna (not just the worms..but all the springtails and oribatid mites) following the recent winter floods? What are the predictions as to what may have occurred with (heavy) water standing for months on top of the soil?" (Charlie Clutterbuck)

PH: "Yes, Professor Davey Jones at Bangor University is monitoring earthworms and bugs. Early data are focused on earthworms which show population decline after 3 month flooding. Some seem to survive in air pockets, whilst cocoons hatch and new earthworms appear shortly after the flood disappears. It does depend to a large extent on how the floodwater is deposited on the soil (top down or bottom up) and on the species. There are some worm species in the Somerset Levels that are far more waterlogging tolerant than others."


5. "I am currently in Northern Ghana doing fieldwork for my research on agricultural development interventions in dryland areas. I am working with two case studies, one of which is a local NGO. They are working with farmers to minimise soil erosion (using stone bunds, grass strips, tree planting) and increase soil fertility (organically). They want to practice conservation agriculture to minimise soil erosion but in a climate where there is a long dry season (about 6 months without rain), it is not possible to have permanent plant cover on the fields because they die during the dry season. This means that in the dry season when there are also strong winds, much soil is eroded. Furthermore, heavy rains in the wet season also erode the poor soils, characteristic of this area.

Do the panel have any suggestions of how to grow a cover crop year-round in a dryland environment? What low cost methods could be applied in this environment to effectively minimise soil erosion?" (Rachael Taylor)

AJ: "Plants need some water to survive a long dry season so some sort of irrigation-based system would be needed. Traditional soil management practices in the Sahel look to conserve or focus water. Zai pits have been used to restore degraded lands and increase soil fertility by concentrating organic matter and allowing precious irrigation water to be used efficiently. A solution would be to use these techniques to develop a tree cover that, eventually, could provide protection to permanent soil cover. For example, see this website"

4. "Soil, and the good management of soil, can play an important part in creating carbon sinks [i.e. soil can take in carbon dioxide from the air]. Should we be including this in efforts to meet UK and EU carbon emission reduction targets?" (Adrian Morton)

PH: "There is a great paper from Professor Pete Smith at Aberdeen University that sums up this debate. Pete concludes that the idea of using soil to absorb carbon dioxide has huge global potential and could be very cost effective. There are also many other benefits in terms of soil fertility, workability, waterholding capacity, nutrient cycling, reduced emission risk and a range of other good things. However, there are also limitations in the ways soils perform. For example, Pete writes that the soil may not store the carbon permanently, and that it is hard to measure how much the soil is actually absorbing."


3a. "Are there data to confirm that mulches - both organic and inorganic - are beneficial to soils (in terms of moisture conservation, insects, soil structure etc.) especially with reference to climate change and warming soils?" (David Bracey)

3b. "I am fascinated by the clear and almost instant impact adding an organic mulch such as Strulch (commercial processed straw) to my veg plants has on them. They almost sigh with relief and put on a growth spurt that can't just be due to moisture retention? Has any controlled research been done on the impact of mulching on plant-soil microenvironments?" (Francesca Sherwood)

3a KR: "Yes! Mulches, where the surface of the soil is covered with some form of material, can certainly reduce water loss by evaporation. Organic mulches (depending on thickness) can also insulate the surface zone. Such mulches may also encourage greater biodiversity within them, by providing a habitat rich in organic matter, a fundamental source of energy for soil life. And they may have beneficial effects in terms of eventually adding organic matter and any associated mineral nutrients to the soil below. Earthworms can contribute substantially to such incorporation, which will then also improve soil structure. Inorganic mulches (such as plastic sheeting) also certainly prevent evaporative loss, but can result in very high temperatures developing in the soil surface zones, especially where solar radiation is high. This approach can be used for weed and pest control."

3b Prof. Phil Haygarth: "There has been lots of research on mulching, a quick look on google scholar reveals lots of papers . I am sure if you looked carefully there would be some specific papers to answer your question. If it helps think of it in terms of basic soil principles: The mulch will firstly retain moisture. This is going to be a good thing as it will help nutrients move around the soils. A mulch will also help insulate the soil and raise the temperature, which will in turn allow biological activity (bacteria, fungi and others) to thrive – thereby accelerating nutrient cycles, and be of positive benefit to the plant. An often forgotten benefit, mulch of course can help prevent soils erosion. Oh – and some people think they look nice too!"


2. "If the soil is a living entity, when did it evolve?" (Charlie Clutterbuck)

RS: "Soil is by definition very much a “living entity” mostly made up of microscopic life, air, water and rock-derived minerals. Microscopic life evolved on Earth around 3.8 billion years ago but the evolution of photosynthesising and nitrogen gas consuming bacteria (called cyanobacteria) about 300 million years later was crucial for carbon and nitrogen rich soil development. Coincidentally, putting oxygen into the atmosphere and taking carbon dioxide out of it were and still are significant functions of living soil. We know there is water on Mars, but NASA's Curiosity rover has not found microscopic life in the rocks so no real evidence of soils. We will need to make soil immediately when we start colonising Mars..."


1. "There is huge disagreement over different farming methods and their effects on the environment. Pesticide and fertiliser use, monocultures, tillage, organics etc are all variously debated. What is the single most beneficial change to soil management  each panellist would like to see widely adopted in large scale agriculture?" (Tom Sheldon)

Prof. Karl Ritz: "I’d propose a change based on a single beneficial principle: ensure no more is taken out of the soil than is returned to it (the fundamental rule of sustainability!) This relates for example to organic matter, mineral nutrients, water, structural condition, and so on. And preferably on an annual basis. It’s like your bank account – short term overdrafts can assist, but long-term deficit will inevitably lead to problems."

Dr Arwyn Jones: "Increasing the organic matter (decomposed plants and animals) in the soil. This not only helps soil fertility and productivity but also provides a wealth of secondary benefits such as improved soil structure and increased water retention. It also absorbs carbon and improves biodiversity. This is achievable by changes in land management practices such as how the soil is tilled, and the addition of composts and manure. 'Green fertilizer' can also be used – this is when rapidly growing plants  are planted between main cropping periods and then ploughed into the soil."

Dr Robin Sen: "The urgent need to move away from a near total reliance on chemical agriculture, to farming that takes advantage of soil microbes as natural bio-fertilizers and bio-pesticides. For example, we will exhaust mined phosphate rock supplies (used in many fertilisers) in the next 50 years, but there are actually fungi and bacterica that can provide plants with plentiful phosphorus even in highly infertile soils such as those in the tropics. Soil microbial technologies have exciting potential to kickstart a green agro-industrial sector and provide the sustainable intensification of farming that the Earth's growing population needs."



Our Q&As answer the questions people put, which may mean that some parts of a subject are covered well and others not. If there is an issue that you think is not tackled, you are welcome to send a follow up question to our plant science panel


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