This is a paper published in July 2018 by Mark Measures:
Further down this page is other, more recent work from India showing similar conclusion. But first, here is a direct copy, with acknowledgements, from Mark Measures’ website:
“Soil organic matter (SOM) is the focus of much attention in both organic farming and conventional circles; conventional arable farmers have finally woken up to the fact that SOM is important and that poor rotations and lack of organic matter inputs might be something to do with their poor soil structure and static or declining yields. Organic farmers have always believed that SOM is important, not just for soil structure but also for mineralisation, which results in nitrogen release, needed for crop growth and they have in the back of their minds the idea that SOM has something to do with pest and disease control. More recently it has been realised that SOM plays an important part in overall soil biological activity and nutrient release. The potential for carbon sequestration and for the soil to function as a carbon sink has led some to think that SOM can play an important and major role in reducing green house gases and addressing climate change.
Many organic farming practices will contribute organic matter to the soil; grass clover leys, use of farmyard manure, compost, green waste, cover crops and green manures will all contribute to SOM. The extent to which these inputs will result in a net sequestration of carbon is dependant on how they are processed in the soil, the level of nitrogen input and C:N ratio, on the initial SOM levels, on cultivations, soil type and climate. The evidence for long-term on-going carbon sequestration from organic farming is not clear-cut and categorical statements that organic farming will have a significant impact on green house gasses and climate change should be treated with caution.
The fate of organic matter, or carbon, added to the soil is particularly dependant on its form; fresh manure and slurry will contribute little to the build-up of SOM, but it will supply readily decomposable material that will provide nutrients to the plants. Compost, on the other hand will provide a more stable form of organic matter, which will contribute to SOM build up. Mineralisation is the oxidation of the chemical compounds in organic matter by the soil microorganisms, in the process releasing nutrients, particularly nitrogen, phosphorus and sulphur in a form available for plant uptake, together with the release of carbon dioxide. This process of mineralisation is brought about by cultivations and aeration and is absolutely central and fundamental to providing the nutrients for organic crop production.
Humus is an important component of SOM and of compost. Humus is relatively stable and is primarily the result of fungal decomposition of lignin and has many roles in the soil including water holding, soil structure and nutrient retention.
Farms that use well-made composted manure or green waste will tend to build SOM, while fresh or once turned FYM and green manures will not result in the same build up of SOM. They will of course be tremendously important for providing nutrients in a plant available form, either directly or indirectly as a result of biological breakdown. Multiple cultivations, whether that is ploughing or repeated use of cultivators will tend to deplete organic matter as it encourages mineralisation.
Soil type will have a major impact on SOM accumulation potential; dry, light sandy soils will tend to be difficult to build SOM and such soil in an arable rotation will often have naturally low levels of 1.5 – 2.5%, unless they have evolved under acidic conditions in which case levels of 6 – 10% may be found. Clay loam soils in the UK will typically have SOM in the range of 3 – 4.5%. Clay soils will tend to have higher SOM than other soil types.
Finally we need to recognise that the SOM accumulation reaches some equilibrium. Depending on the soil type, management practices, organic inputs, rotation and the cultivations used the accumulation of SOM will tail off at some point; it is not realistic to expect to be able to increase SOM from say 4% to 10% under normal farming practices, an equilibrium will be reached before that.
Does organic farming increase SOM?
The evidence from farm experience in the UK is limited because there has been very little thorough and reliable monitoring; inconsistent sampling methods and field locations, changes in analytical methods and infrequent sampling are all a problem. Experience from the arable organic farms that I have worked with is that sometimes, but not always, SOM levels initially increase following conversion to organic farming from continuous non-organic arable cropping; an example from Holme Lacy College shows an increase from 2.7 to 3.1% over 10 years, and average of 0.04% SOM per year. Experience elsewhere is that subsequently increases are small.
Replicated research over long periods of time is a more reliable indication. The 40-year-old DOK trial at FiBL (Switzerland) compares conventional, organic and biodynamic systems.
Table 1. DOK-trial soil carbon
The results after 35 years, Table 1. show that SOM levels have declined slightly in all four treatments. The conventional and the organic treatments are not significantly different, however it would be expected that if the conventional had followed a continuous cropping rotation that this would have resulted in a greater decline and that the difference between the organic and the conventional would be expected to be greater. The biodynamic treatment resulted in a small but significantly higher level of SOM than the conventional or the organic; this may be a result of the use of well-composted manure rather than the fresh manure in the organic.
Interestingly there is a significant difference in the soil microbial biomass between some treatments, Table 2., Showing that Organic (O2) and Biodynamic (D2) has greater biomass than Conventional both with manure (M) and without manure (N).
Table 2. FiBL DOK-trial Microbial Biomass
The Aarhus University (Denmark) farming systems trial was set up in 1997 on 3 sites, the one at Foulum continues to run. A replicated trial compares organic using both green manure and manure with a continuous cropping non-organic rotation. While there are significantly higher levels of carbon inputs to the soil under organic management and there is indication that a one-year green manure with residues returned does increase SOM, overall the conclusion is “not able to detect consistent differences in measured Soil Organic Carbon between systems”.
The Rodale Farming Systems Trial (USA) has been running since 1981, it is a replicated trial comparing an organic manure system with an organic legume system with a conventional continuous arable cropping system. Table 3. The SOM levels in both the organic systems increased from 3.5% to approximately 4.25% in the first 20 years (0.37%/year) thereafter stabilising or in the case of the organic legume system subsequently declining to approximately 3.9%. The conventional has shown some recent decline to approximately 3.3%. In the absence of trial data and peer-reviewed papers it is not possible to know the statistical significance of these results.
Table 3. Rodale SOM levels
The Scotland Rural College (SRUC) organic systems trial was set up in 1991 following a period of conventional ley arable farming. The results, Table 4. show over a period of 20 years that organic ley-arable under a rotation of 50% ley, 50% arable maintains SOM, but that under the prevailing conditions SOM did not increase, even during the conversion period. This reflects the previous cropping regime and the fact that these are inherently high SOM soils, in the order of 8%. The stockless organic rotation introduced 8 years ago indicates a slight decline in SOM, but which may not be significant.
Table 4-.Tulloch rotational train, SRUC Aberdeen Soil Organic Matter
The conclusion of the review of available evidence undertaken by Organic Research Centre in 2011 is that:
Organic cropping systems have considerable potential for increasing soil carbon, through the incorporation of fertility building grass-clover leys and use of livestock manures within diverse crop rotations, when compared with specialist (e.g.: monoculture) cropping systems;
The exact amount of carbon that can be sequestered through organic management of cropping systems is still uncertain, due to the disparity in assessment methods, and farming/land-use systems;
The difference between the wide range of organic and conventional farm types is not yet clear, partly because of the current difficulty in defining these systems and their individual characteristics;
Organic management of grassland is unlikely to increase soil carbon levels over those from conventional management, but the reliance on legumes and biological instead of industrial nitrogen fixation will still have a positive impact on climate change mitigation through reduced fossil energy use and related carbon dioxide and nitrous oxide emissions
The ratio of Clay to SOM is considered important by some of authorities (Agroscope and Aarhus University) and it may be a more important measure of the need and potential to increase SOM levels than SOM% per se.
Claims that the practice of Mob Grazing results in substantial increase in organic in the order of a change from 3 to 5% over 3 or 4 years have not been substantiated under UK conditions.
The use of very high levels e.g. 50 tonnes/ha/year of imported manure, compost or green waste will undoubtedly result in SOM increase over time, up to a point, but that is not typical of organic farming.
The studies that I have seen have focused on arable systems, the situation with permanent pastures is very different, and soils under permanent pasture generally have higher SOM and will have developed an equilibrium. This higher level may be due to both the lack of cultivations and the use of manures and fertilisers as well as forage residues. In my experience there is very little difference in SOM levels between conventional and organic management of permanent pastures.
Based on the evidence of the three farming systems trials visited under the Winston Churchill Fellowship in 2017/18, the results of the SRUC trials, my personal experience and the review of research by Organic Research Centre I draw the following conclusions.
SOM is important for soil physical, biological and nutrient reasons and mineralisation of SOM is particularly important in organic farming.
The following practises will all tend to increase SOM: Grass clover leys, farmyard manure, compost rather than fresh manure, green waste, over-winter cover crops and annual green manures.
The following will tend to decrease SOM: cultivations, continuous cropping, nitrogen supply.
Given that organic arable farming involves many of the beneficial practises identified above, there is likely to be some advantage to organic farming during conversion from conventional, continuous cropping conventional farming, particularly where longer leys are involved.
There is no evidence that organic arable farming offers potential for on-going, long term sequestration of carbon in the soil. The indications are that increased SOM levels of between 0 and 0.4% per year may be possible during the first 10 – 20 years of organic conversion, but that this depends on the initial SOM levels, soil type and management practices. Thereafter increases are unlikely.
SOM is likely to be higher under some established organic arable rotations than under conventional rotations, but this is not necessarily so and will depend on various management practices, particularly the length of the ley and use of compost.
65% of organic farms in the UK are permanent pasture, not in an arable rotation. These farms are unlikely to show a significant difference between conventional farms.
Organic arable farming has higher levels of soil microbial biomass compared to conventional. Organic farmers wanting to improve crop productivity should focus on improving the quality and biological activity of their soils rather than merely focusing on total SOM.
Given the wide range of results from arable system comparisons and the fact that the majority of organic farming in the UK is permanent grassland claims that organic farming will contribute significantly to climate change mitigation through carbon sinks should be avoided.
Climate change mitigation is one the principle challenges of our time and needs to be addressed by a radical change in the food and farming system as a whole, including food distribution and with a particular focus on drastic reduction in use of fossil fuels. Organic food and farming systems offer the best agricultural system to do that. Soil carbon sinks play a supporting role.”
Mark Measures July 2018
FiBL Dossier No 1. August 2000 Organic Farming enhances soil fertility and biodiversity (online) https://shop.fibl.org/CHde/1090-doc.html?ref=1
Fliessbach A. 2017 Okologi-Kongres Denmark Comparison of organic and no-organic farming systems in the DOK trial (online) https://okologi-kongres.dk/wp-content/uploads/2017/12/G2-Fliessbach_DOK_Kolding2017.pdf
Hu T., Sorensen P., Olesen J E. Soil 2018 Carbon varies between different organic and conventional management schemes in arable agriculture. European Journal of Agronomy 94 (2018) 79-88 (online) http://orgprints.org/32999/7/1-s2.0-S1161030118300108-main.pdf
Moyer J. 2008 Farming System Trial A 34 Year Old Living Laboratory https://ostafjells.nlr.no/media/ring/1209/Jordkarbon/Norway%2035%20years%20of%20FST.PDF
Smith L., Padel S., Pearce B. 2011 Organic Centre Wales Soil Carbon Sequestration and Organic Farming: an overview of current evidence. http://www.organicresearchcentre.com/manage/authincludes/article_uploads/Organic%20farming%20soil%20carbon_6.0.pdf
B.R. Taylor, D. Younie, S. Matheson, M. Coutts, C. Mayer, C. A. Watson and R. L. Walker 2006 Output and sustainability of organic ley/arable crop rotations at two sites in northern Scotland
C. A. Watson & J. A. Baddeley & A. C. Edwards & R. M. Rees & R. L. Walker & C. F. E. Topp 2011 Influence of ley duration on the yield and quality of the subsequent cereal crop (spring oats) in an organically managed long-term crop rotation experiment
Towards a Global Organic Future
A few months earlier – to set the scene – Kiran Pandey and Rajit Sengupta had recorded that India is home to 30% of the total organic producers in the world, according to the World of Organic Agriculture 2018 report, but most are struggling due to poor policy measures, rising input costs and limited market (a study by ASSOCHAM and Ernst & Young).
Sharma points out that, at a time when global temperatures are soaring, the latest study by a French think tank – Sustainable Development and International Relations (IDDRI) – has shown that agro-ecological farming alone has the potential to reduce greenhouse gas emissions in Europe by 47% and thereby keep global temperature rise below 2degrees.
80% of the world’s food is produced by small farmers – the rest comes from industrial farms
Her answer: “No. There are more than 570m farms worldwide; more than 90% are run by an individual or family and rely primarily on family labour. They produce about 80% of the world’s food”. (Below, small farmers in America.)
Please also see the website on vermecology by Rob B. which looks at the role of earthworms for organic farming:
Rob has also commented on this website, as follows:
Hello Christine, Appreciate the work you are doing and the word you are spreading. My take, as one of a dying breed of soil ecologists, is to promote organic farming/permaculture and to focus on earthworms as monitors/mediators. We have know that these problems would bite for over a century (Sir Albert Howard/Lady Eve Balfour). Personally I started research in 1980 and for the longest time thought I was talking to myself. My latest paper had 3,000 hits in a month, so there is now some interest in the critical loss of earthworms and the need for healthy soil restoration.
Unfortunately it does not yet translate into proper funding nor policy change. Cheers, Rob B
And today (8th Aug 19), I received a forwarded email from Devinder Sharma, from India, entitled:
“Protect the soil the way we protect tigers”
Here is the rest of his posting:
“The alarm bells have been ringing for quite some time now. Reports after reports warning of a continuing degradation of India’s soils – the foundation of assiduously built food security and more importantly the healthy well-being of the country — have been conveniently swept under the carpet.
Added to this monumental blunder of allowing the wilful devastation of land resources in the name of economic growth lies the threat awaiting in the form of climate change. The Consultative Group on International Agricultural Research (CGIAR) — the global body which governs the international agricultural research centres — has conclusively established that agriculture, livestock and deforestation together account for 41% of the greenhouse gas emissions (GHGs).
Intensive cropping patterns, unbalanced nutrient application, injudicious use of pesticides and mining of groundwater has turned the soils sick. What is not being understood is that a sick soil cannot produce a healthy generation.
In August 2016, a report of the Indian Space Research Organization (ISRO), estimated that nearly 30% of the country’s land – more than 4 times the size of UK – is faced with desertification. That desertification continues to prevail in semi-arid regions of Rajasthan and in some parts of Haryana was quite well-known but the fact that desertification had encroached on more than 50% of the land in states like Jharkhand, Gujarat, Goa, Delhi and Rajasthan is more worrying. Even the hilly states of Jammu & Kashmir, Arunachal Pradesh and other states of northeast India as well as Orissa are now fast getting into a desertification spiral.
This report comes two years after the 5th National Report on Desertification, Land Degradation and Drought in 2014 had warned of nearly 45% of country’s total land, 146.82 million hectares of the total 329 million hectares, suffering from various degrees of land degradation, including water erosion (93.68 million hectares), wind erosion (9.48 million hectares), waterlogging (14.30 million hectares), salinity or alkalinity (5.94 million hectares), soil acidity and other complex reasons . . .
Studies point to some 5.3 billion tonnes of soil getting eroded every year, much of it from water and wind erosion. Of this, 29% was permanently lost to the sea, 10% was deposited in reservoirs, reducing their storage capacity and 61% got shifted from one place to another. While this results in tremendous loss in productive capacity of soil, it also helps in expanding the area under deserts. The more the green cover is lost to deforestation and urbanisation, the more is the barren land exposed to soil erosion. In Haryana, for instance, accompanied by strong winds shifting of sand dunes have often resulted in cultivated lands being encroached upon.
The priorities of successive governments have been in complete contrast to what has been spelled out in the numerous environment documents since the 1st Plan
Beginning with the 1st Five Year Plan, the thrust has been on ‘land rehabilitation’ thereby showing that the planners were seized of the crisis that was expected to build up in the years to come. Numerous Ministries and departments, including the Department of Land Resources, Ministry of Environment, Forests and Climate Change; Ministry of Agriculture; Ministry of Water Resources; Ministry of Rural Development had framed a number of policies wherein the effort was to contain soil degradation . . . (but) over the years the Ministry for Environment, Forests and Climate Change has been on the forefront of bringing in policy directives that actually have undermined the protection, conservation and rehabilitation of land resources. Recent changes introduced silently by the environment ministry, tribal affairs ministry and the mines ministry to redefine forests in a bid to bypass the forest and environment clearances required for mining companies, needing several thousand hectares of mineable area, is one such example . . .
If the soil is unhealthy, you may be sure your food is also unhealthy
It has often been said that you are what you eat. And what you eat depends on how healthy and nutritious the soil is. After all the plants derive their nutrition from the soil, and if the soils are unhealthy be sure your food too is unhealthy. Ask any farmer the difference between an organically-rich healthy soil and a chemically farmed soil, and he will tell you how enriching it is to work with nature. Healthy soil not only supports biodiversity – more bees, more earthworms, more birds – restricts run-off and erosion, and is also is also a storehouse for soil nutrients and carbon.
Soils are predominantly rich in three major nutrients – nitrogen, phosphorous and potash. In addition, it also provides 16 micro-nutrients, including iron, molybedenum, calcium and zinc. But because of intensive farming practices, like having a continuous cropping pattern of wheat and rice, interspersed with potato and vegetables, like we see in Punjab, the organic content in the soils have been exhausted. In Punjab and for that matter in other Green Revolution areas, the organic matter in the soil has almost come down to 0.1 %. This means farmers are left with no option but to apply more of chemical fertilizers to produce the same harvest they used to produce five years back.
Excessive use of chemical fertilizers, especially nitrogen in the form of urea fertilizer has led to nutrient imbalance in the soils
Moreover, the effective uptake of nitrogen by plants from the urea that is applied does not exceed 30%. Rest of the chemically applied nitrogen seeps underground causing contamination of groundwater. The problem got compounded with agricultural universities recommending more application of chemical fertilizers as the way forward to meet the nutrient deficiency arising from intensive farming. At no stage did the universities and the extension officials of the State Department of Agriculture advise farmers to take up integrated farming practices that include the application of organic manures and green compost in adequate proportions.
Continuous application of chemical fertilizers along with mechanized farming has compacted the soils. In many places, a solid layer has been formed almost a foot below the surface thereby restricting the spread of plant roots. Organic cultivation practices on the other hand turn the soil porous, which allows for an enabling environment for soil microbes. One indicator of a healthy soil is the percentage of earthworms visible in the soil. The more the number of earthworms, the healthier is the soil.
A soil health card for every farmer
The thrust on making available a soil health card for every farmer suffers from the same deficiency in approach. It is designed primarily to ensure that farmers apply balanced doses of chemical fertilizers. I would have preferred a soil health card that measures the organic content in the soils and accordingly makes suggestion on how to improve the strength and structure of soils. At a time when chemical fertilizers, especially nitrogen fertilizers, have been found to be acerbating greenhouse gas emissions leading to climate changes, the emphasis should be on reducing its application.
I have always advocated subsidizing organic manure, bio-pesticides and working out a separate price policy for organic produce which incentivizes organic farming
It is important to understand the political economy that promotes chemical fertilizers and pesticides. It has been generally accepted that fertiliser subsidy is fertilizers and pesticides. It has been generally accepted that fertiliser subsidy is the major determinant of land degradation. Although there have been efforts to reduce subsidies on chemical fertilizers, especially phosphorous and potash, but still due to political reasons and lobbying by farmers groups, it has not been possible to cut down subsidies on fertilizers in a desirable manner. This makes organic farming systems unattractive to farmers. Numerous studies, both nationally and at the international levels, have conclusively shown that business as usual is not the right approach. To provide healthy food, protect environment and ensure proper soil management, the time is ripe to radically overhaul the crop cultivation practices. An international study – backed by World Bank and United Nations and involving more than 400 scientists globally – called IAASTD in short – has shown that crop production by non-chemical practices goes up steadily and is the only sustainable path ahead.
Studies have shown that 1% reduction in fertilizer subsidy reduces land degradation by 3%.
This is a startling analysis and should be driving the national agricultural policies, including the research priorities. While population density and poverty ratio, the coefficients of both are statistically significant, are normally also thought to be responsible for land degradation, a study done by Mythili Gurumurthy (2015) show that these two variables cannot be held as reasons for land degradation. The results of poverty ratio-land degradation link also corroborate the results of other studies that poor are victims rather than cause of land degradation.
Feeding the soils with organic manure, and laying out a well-working drainage system, which increases water use efficiency are required to protect soil erosion as well as to maintain soil fertility. But more importantly, policy makers have to understand that rebuilding the soil health is a precursor to meeting the food requirements for a growing population in the future, and at the same time a healthy soil is a determinant for a healthy population.
Take the case of China. Hit by a significant drop in food production this year in the wake of rapid urbanization, it has now vowed to protect arable lands. China aims to retain at least 124.33 million hectares of arable land in 2020, with no less than 53.3 million hectares of high-quality farmlands, news agency Reuters reported. In India, nearly 45 % of the cultivable land is faced with degradation and the country has still to wake up to the looming threat.
“Farmland should be protected the way we protect pandas,” stated a spokesperson for the Chinese government. India too should launch a nation-wide programme to save and protect soils the way it protects tigers.”