“Green is the most important factor for soil health” Christine Jones 2017
Kenneth Williams’ (AKA Arthur Fallowfield) reply to any question began: "the answer lies in the soil!"
Restoring biodiversity to agricultural soils. Christine Jones
This is a radical view of farming and soil management, which exposes the failings of conventional food production, challenges some organic farming practices and places photosynthesis and carbon at the centre of future food production and land management. The following summarises some key messages from a one-day workshop, including a few of my own comments.
The problems of conventional farming are well known, but Christine reminds us of some:
In her home country of Australia soil organic matter (SOM) has dropped from between 4 and 25% in 1840 to typically less than 1% in farmed land.
Food quality is now 2 to 5 times less nutritious than 60 years ago 1 and 2 ; declines of Cu 24%, Ca 41%, Fe 54%, Mg 10%, K 16%
Nutrient decline is coupled with chemical residues which are toxins reducing nutrient availability and the first line of defence against pests and diseases at root level.
Declining health of plants, animals and people
Reduction in availability of soil nutrients
Climate change aggravated by GHG from fertiliser manufacture and SOM loss
Nitrate and phosphate pollution of water courses and sea
Her view is that these are easily reversible and that the fundamental mechanism is photosynthesis, capturing carbon and feeding the soil life and increasing its fertility: photosynthesis is the basis of the pyramid of life, not soil. Published papers are available on www.amazingcarbon.com
Instead of putting all the emphasis on legumes, as we tend to do in organic farming in the UK and using high levels of soil fertilisers, foliar feeds and inoculants as is common practice in organic farming in the USA, Christine provides guiding principles to inform local practices which will drive a change in agriculture.
Maintenance of year-round living cover
Provide support for soil microbial activity
Promote plant and microbial diversity.
Land responds positively to the presence of animals provided management is appropriate.
Ralf Waldo Emerson “as to methods there may be a million and then some but principles are few. Those who grasp principles can successfully select their own methods”
What does this mean in practice?
1. Green crop cover
Ensuring that the soil is always covered by green plants, and lots of them, actively growing if possible, is the most important factor for soil health. Maximising photosynthesis will produce sugars, which will promote root growth and most importantly produce root exudates, which will stimulate soil microbiology to improve soil nutrient availability, either directly or indirectly via mycorrhiza and build SOM.
Crop cover can be maximised by growing permanent pastures, leys and cover crops; bare soil is unacceptable at any time of year and pastures should not be over grazed, increasing sward height will increase rooting depth.
This will increase diversity of microbes, hold soil, reduce temperature and improve water relationships and root depth and increase plant exudates.
Carbon is the key driver for soil microbes, preventing erosion, keeping lower temperatures in hot weather and improving water holding capacity, nutrient supply and content and crop yield. It is much more important than conventional nitrogen fertilisers, which damage microbiological activity e.g. super phosphate shuts down mycorrhizal activity, and she proposes more important than leguminous N fixation.
There are thousands of free living and associative N fixing bacteria in soil, so it is not just legumes that are the major means of fixing N and they are not always essential.!
2. Support microbial activity
Creating the right environment is more important than bacterial inoculation.
Christine’s view is that it is very rarely worth inoculating with either bacteria or fungi, the only exception being potatoes with mycorrhiza and legumes with rhizobial bacteria. Provide the right conditions instead i.e. cover crops, wide diversity of crops, green manures, manures, rotation, and structure.
Mycorrhiza; it is in their interest to keep plants alive, which they do by supplying them with water and nutrients in return for energy in the form of carbon.
Annuals produce more sugars than perennials, important for root and soil relationships.
Crop diversity is essential, a familiar argument of Martin Wolfe, diversity of species and types. Multiple mixes, do better than simple mixtures and over a certain number of species underground networks behave differently. Diversity seems to supply more N and become more drought resistant. This might mean planting 20 plant species in a cover crop – and we thought we were doing well with 3 or 4! The Jena trials 3 in Germany and of course ORC’s work on Multispecies Leys support the importance of crop diversity.
The role of animals is challenged by some, but they are of course part of the natural ecosystem so not surprisingly we find that they have an impact on soil functioning. The work of J. R. Leake in the UK has shown how mycorrhizal activity and nutrient supply is increased by the use of manure, the very long-term effect of farm-yard manure on soil organic matter has been demonstrated at Rothamsted and Kris Nichols at Rodale observed that the pulling effect of cows grazing grass has a beneficial effect on root senescence and soil fertility, compared with cutting. Christine encourages us to include animals, provided of course they are fed and managed properly but recognises that there other ways of achieving the same results in stockless systems.
Some other lessons
Christine challenges the use of aerated compost, which will be bacteria dominated and produce humic acids; she argues that even with CMC type composting methods they will not be stable and that anaerobic, plastic covered, fungal dominated static piles of compost is preferable.
The process at root hair level is the one that really builds humus. Humus is not organic matter. Adding clay to compost could build humus, not otherwise.
SOM is made of recently died or decayed material of vegetable or animal origin, which is active, unstable and part is rapidly processed in the soil and in the process of mineralisation; an essential stage in making nitrogen and other nutrients available to plants in an organic system. We can’t test for humus, but we can do a potassium permanganate test for labile carbon, deducting this from organic matter gives the humus level.
They are involved through some unknown mechanisms in moving water, sugars and other nutrients to the plant, which can signal its needs to the fungi. Plants can communicate with each other by sending chemical signals down roots and through fungal hyphae, e.g. stimulate pest response in neighbouring plants.
Ploughing and subsoiling damage mycorrhiza as well as earthworms; they may both take many months or years to recover. Cultivations should be avoided or minimised, e.g. by shallow ploughing. Ideally tillage should be limited to 5 cms.
The emphasis of the approach is almost entirely on providing the optimum conditions for supplying carbon to the soil in order to maximise biological activity and enhancing nutrient mobilisation and transfer; the soil has more than sufficient nutrients for crop needs in the long term and application of fertilisers is almost entirely unnecessary. Even phosphate is not needed for the old soils of Australia. If there is one thing that might need adding it is Sulphur.
Christine provided a number of practical examples of the results of applying these management principles, particularly the Hagarty 4 study comparing a split treatment field, which found a 30 – 50 % increase in SOM compared with conventional over 5 years, greater at depth, improved nutrient cycling, soil structure, biological activity and water holding capacity and increased stocking rates through the following practices:
1. Keeping soil covered
2. Stopping the using N and P fertiliser and herbicides
3. Using vermi-liquid and diluted compost extract
4. Rotational grazing of a tall sward with longer intervals.
“ In the same way as it is important to ‘feed the rumen not the cow’ it is also important to ‘feed the soil microbiome not the plant’” Christine Jones.
1 Thomas D. A study on the mineral depletion of foods available to us as a nation over the period 1940 -1991 Nutrition and health 2003
2 Davis D R., et al. Changes in USDA Food composition data for 43 garden crops. 2004
Changes in USDA food composition data for 43 garden crops ... - NCBI
3 Jena expt Germany: Wagg C. et al. Soil carbon and forage yield increased with plant diversity 2017
4 Ampt P and Doornbos S. Communities in Landscapes project: Benchmark study of innovators. University of Sydney 2010 http://www.amazingcarbon.com/PDF/CiL%20project%20SEIS.pdf