This is an unedited chapter in my book. I would like it if you would have a skim through and give me some feedback. I am trying very hard not to make it sound like a textbook and failing completely, but it is the only way I know of getting information over quickly and concisely.
Although it is the journey to mineralisation that determines the crop producing power of organic matter, this should not be the only focus of its value to gardeners. Without organic matter, soil degrades noticeably even with massive applications of nutrient salts. The mineral particles of soil, while being very important, cannot be easily changed. What gardeners can change is the amount and quality of organic material entering the soil. All organic matter provides numerous vital services to the soil; however, the more intractable organic matter will do it for longer. So, what are the benefits of application of organic matter?
Organic matter provides three things for living organisms. It is made up of carbon chains and this carbon can be used to make energy. Carbon compounds can be broken down into small units and used to build parts of heterotroph bodies. Finally, organic matter will produce inorganic nutrients that drop out of organic matter due to decomposition.
1. Source of nutrients and energy
Organic matter provides the energy that drives soil processes, supplying carbon and ensuring that both energy and inorganic nutrients are released in a sustainable way. Organic matter allows captured solar energy to flow through various diverse routes powering interactions and enhancing beneficial biological integrations and synergies among allotment components resulting in maximising crop abundance. The more routes for energy to flow down the more robust and resilient the garden. Mineralisation of organic matter provides a direct source of nitrogen, phosphorus, sulphur and micro nutrients. Organic matter provides microbes with the energy and resources to produce rock dissolving compounds that provide plants with potassium and phosphorus. With the provision of widely sourced composted organic matter there is more likelihood that a broader range of inorganic nutrients will be available within the allotment soil. Widely sourced compost does not necessarily mean imported from outside the allotment. Using the full range of allotment woody and herbaceous debris provides a wide diversity of composted organic matter that can easily be built into the composting regime of the allotment.
2. Optimising nutrient flow through the top soil.
Organic matter regulates the relentless permeation of water through the soil volume optimising nutrient availability and balancing nutrient flow. A wave of dissolved nutrients will be taken through the allotment soil after major rain events. While this is a good thing, gardeners do not want this to occur too rapidly or confined to narrow paths through the soil. We want water to carry nutrients to all parts of the allotment evenly and slowly. Organic matter both in the top and subsoil will go a long way to give us this even slow spread of water and nutrients.
3. Composted organic matter releases nutrients slowly
Inorganic nutrients are not necessarily immediately available from organic matter. They are released from the substrate slowly, enabling plants and microbes to use them efficiently. Slow release of organic matter gives plants time to absorb nutrients before leaching events occur. Depending on mineralisation rate, organic fertilisers such as manures, composts and moulds applied as mulches release nutrients gradually allowing for them to be much better managed.
4. Cycles nutrients.
You do not want a lot of nutrient sloshing about in the ground water because the longer it is there the more likely it will be leached away and lost to the allotment. A tight cycle of immobilisation and mineralisation means that nutrients are used very efficiently, and few are lost. Using husbandry skills such as green manuring, cover crops, mulching, water calming, and composting we can lock nutrients into the allotment; the only loss being when crops are taken off. In this system of husbandry, increasing the application rates of organic matter does not necessarily increase leaching rates because of the slow nutrient release, organic matter’s ability to slow mass flow of water and its ability to store available nutrients. Sustainability includes using organic matter already on the allotment to concentrate and cycle nutrients. Identifying nutrient sources – such as hedge clippings, prunings, weeds from allotment fringes, pond weeds, sediment, leaf fall, litter fall from soft fruit, top fruit and hedge trees, crop litter, path sweepings together with windblown and rain moved debris; making sure they enter the composting process goes a long way to preventing valued resources from leaving the allotment. Weeds and green manures are particularly good at capturing poorly soluble inorganic nutrients and converting them into organic molecules, making them more available to crops through composting. Nutrients gleaned from the bed rock needs to be captured and integrated into the nutrient cycling of the allotment. This can be done by making sure there is a deep penetrable soil which allows the uptake of nutrients from low in the soil. Adding organic matter to the subsoil will encourage deep rooting and gleaning of nutrients, uplifting them to the surface as plant litter. Forest trees are continually cycling nutrients with leaves and litter from this source making a considerable contribution to the level of organic matter in the soil. Really you want the top of slope to be as leaky as possible both for water, nutrients and organic matter so that they are washed from other people’s allotment onto your soil. Hedge, tree and fence windbreaks will add their own nutrient and organic matter contribution. Once nutrients and organic matter are on the allotment every measure to prevent them from leaving quickly should be employed. A large bed of comfrey at the bottom of the allotment slope is one of the best ways of recycling nutrients leached from your soil. Crops of comfrey leaves can be transported to the top of slope where the compost heaps and comfrey bins are located. Any leachate that escapes from the bins and heaps will flow into the allotment and not be lost. If you let comfrey grow tall, it will provide an effective windbreak that collects windblown debris and prevent it from leaving the allotment.
5. Organic matter is a reservoir of carbon.
Plants assimilate carbon from the atmosphere into organic compounds via photosynthesis. These simple carbon compounds, such as glucose, are transformed into more complex molecules in cells. When the plant dies they enter the soil through litter, root exudates and root sheared cells. These carbon compounds provide energy for soil microbes, fungi and invertebrates producing a slow break down of organic matter and production of carbon dioxide by respiration. If production of organic matter exceeds that of soil organism respiration, then there will be an accumulation of carbon in the soil. The excess organic matter fulfils the roles listed here. Where a steady state occurs, the amount of soil organic matter in the soil reflects the balance between carbon produced, or added, in equilibrium with decomposition, leaching and erosion. The balance is maintained by the energy requirements of soil organisms and their needs are influenced by the temperature and moisture in the soil. Natural systems tend to self-regulate and to store more energy that can slowly be fed back enhancing the capture of additional carbon by photosynthesis through the vital services that microbe communities supply to the soil. The gardener needs to copy this natural system of carbon sequestration building a reservoir of organic matter to power the production of crops but also to maintain all the properties of the soil that enhance plant growth. Soil nutrients undergo continuous replenishment under long term compost and manure addition regimes and yield and health of crops slowly increase. A major service that organic matter supplies to the soil is to provide a long-term reservoir of metabolic energy that enables biological processes to be carried out. The importance of this store of carbon can be seen in the paucity of life below the top soil. Carbon is vital for heterotrophs and their populations diminish with the depth of the soil. Carbon is filtered out by the microbe community in the top soil leaving little to reach lower depths. The colour of the soil changes from dark brown to the colour of the underlying rocks because there is little organic matter to change its colour. This lack of organic matter will not necessarily affect plants because they obtain their carbon from the atmosphere by photosynthesis. However, it will affect the microbe community. Their populations will be minute compared with the top soil. To introduce some control over air and water percolation substantial amounts of organic matter can be added by the gardener using double and bastard digging techniques. The populations of microbes increased producing a friable textured soil due to the creation of different sized crumbs. Invertebrates process the soil to extract carbon and create fine earth that is mixed with organic matter in their guts to produce a valuable material that will enhance the fertility of the subsoil. There is an even range of different sized pores that allow water to flow through the soil while retaining some within micro pores. Organic matter mixed into the lower layers of the soil will allow root penetration to take place giving them access to water and nutrients even in the driest of seasons.
It is not the job of gardeners to mitigate climate change. That must be left to the individual conscience of others. However, if the principles of composting and hugelkultur are used in good husbandry, lots of organic matter will be buried in the soil taking a relatively long time to decompose.
6. Increases the cation exchange capacity.
Organic matter has a very high cation exchange capacity due to its large surface area covered with negative charged molecules produced by dissociation of hydrogen ions. Many nutrients fall out of organic matter as cations such as Ca2+, Mg2+, Na+, K+ and NH4+ forming electrostatic bonds with negative sites on organic matter surfaces. Acids secreted by plant roots, bacteria and the hyphae of fungi disrupt the electrostatic bonds by producing H+, releasing nutrients into the biofilm and making them available to plants. As nutrient ions are absorbed from the biofilm soil solution by soil organisms and roots they are replaced by those adhered to organic matter and there is competition for the negative sites between metal cations and H+. Cation exchange capacity is a measure of how well the soil can retain cations in plant available form and minimise leaching losses; it is a key factor in assessing productivity of the soil. The higher the cation exchange capacity of the soil components, the more nutrients can be stored and made slowly available to plants. The slow release of metal ions through cation exchange allows the biochemistry of the soil to proceed unhindered and organic complexes form that enhances the solubility of metal ions.
7. It moderates large changes in pH.
Soils rich in organic matter are resistant to pH change. Soil pH is a measure of the acidity or alkalinity of soil and is calculated as the negative log of the concentration of H+ or [H+] in the soil solution. Soil organic matter can take up or release H+ keeping its concentration relatively stable. Organic matter can neutralise both acids and alkalis, optimising soil solution pH levels around pH6.5 for maximum nutrient availability. Organic matter also moderates large changes in pH.
8. Micro nutrients are released and made available
An even distribution of micronutrients throughout the soil is essential for the healthy growth of crops. Although the base level of micronutrients depends on the breakdown of bedrock, micronutrients will also fall out of organic matter as it decomposes. Organic matter decomposes into numerous different compounds but there are some common functional groups like OH-, NH2, -NHR, CONH2, COOH and these are used to form complexes with ions. Chelating compounds with these functional groups surround inorganic ions with a coat of weak bonds increasing their solubility and availability to plant roots. Organic matter forms stable complexes with micronutrient metal ions and there is a very strong association between the soil organic content and the solubility of metal micronutrients.
9. High specific surface
Some organic matter, such as charcoal, has a high specific surface and can adsorb noxious gases produced by bacteria, which might reduce the growth of plants. Charcoal may also help prevent leaching because it has a strong adsorption affinity for nitrate, phosphate and other ions in the soil solution. The jury is certainly out about whether charcoal increases the fertility of the soil. I have been adding charcoal from my own charcoal burners since around 1997 with little noticeable difference in crop yields. However, my soil is particularly rich in organic matter and the difference that it makes is masked by the services other types of organic matter provide. It is certainly a type of organic matter that could be used to ameliorate degraded soils although I do not think it should be relied on exclusively. I would rather compost or bury woody material rather than char it to retain all its nutrients. All nutrients are lost from organic matter when it is burnt.
10. Organic matter delivers nutrients to plants within appropriate ranges
As organic matter is mostly derived from plants, by default the levels of nitrogen, phosphorus and potassium are in the right proportions and there is little danger of causing imbalances, excesses and flushes. The fear that composts build up an inappropriate level of phosphates in the soil is less likely in a system that tries to efficiently recycle nutrients already on the allotment. The slow release of phosphates together with the more efficient uptake by plants and the use of living mulches, cover crops and green manure will all help to manage the flow of phosphate through the growing beds. Soil organisms govern numerous nutrient recycling reactions in soil and nutrient flux through biomass is faster in organic soils. Nutrients are quickly passed from organism to organism in a very efficient way with less being dissolved in the ground water and more stored in microbial bodies. Rapid transformations of nutrients contribute to a sustained slow nutrient supply.
11. Replaces lost nutrients
Losses of nutrients from the allotment are because of erosion, leaching, conversion to gaseous oxides or immobilisation in crops. The skill for the gardener is to replace the nutrient and carbon loss by increasing the amount of soil organic matter in the soil. If organic matter is continuously added over the years, both immediately accessible nutrient and the residual from the decomposition of previously applied compost and manures will build the fertility of the soil. Only with an input of nutrients in the form of manures, homemade composts, and moulds can the soil can maintain intensive crop growth.
12. Organic matter is a nitrogen source
Organic matter in the soil will provide nitrogen through mineralisation but this must be planned for during the year. Mineralisation release will increase with temperature so if organic matter is dug in during the winter it will start to mineralise intensively in spring when the temperatures begin to rise, and this is when quickly growing seedlings need the nutrients. Mineralisation is very slow below 10oC. So, in early spring you will need to apply more readily available nitrogen in the form of dried blood, chicken manure, comfrey liquid and nettle tea, which will release nitrogen more rapidly than compost or farmyard manures.
13. Organic matter provides the energy source for nitrogen fixation
Nitrogen capture and fixation by bacteria and archaea is very energy intensive using organic matter carbon to power the process. Most nitrogen fixing bacteria and archaea are free living saprophytic heterotrophs, however a significant number are facultative symbionts which can either live within the root nodules of specific host plants or freely in the soil. However, when symbiotic bacteria like Rhizobia are free living they do not fix nitrogen. Rhizobia and Frankia can use organic matter generated by photosynthesis and transported from the leaves to bacterial nodules without leaving the plant. Free living nitrogen fixers must glean their organic matter from the soil or from exudates from plant roots or fungal hyphae. Increasing the proportion of organic matter in the soil will enable nitrogen fixing bacteria to flourish and add this vital nutrient to the soil. The cyanobacteria produce their own organic matter by photosynthesis and then use some of this to power nitrogen fixation. If they are growing in allotment ponds they are a source of fixed nitrogen and make very good additions to the compost heap. You don’t really want cyanobacteria covering the soil surface because it indicates that the soil contains a little too much water. Covering the soil with mulches, cover crops and crops makes their presence unlikely.
14. Organic matter buffers periodic flushes of ammonium
When applications of manures and composts produce bursts of organic matter mineralisation during favourable seasonal conditions, an excess of ammonium can build up. The excess of ammonium draws water out of sensitive, small roots by osmosis. The adsorption of ammonium ions on organic matter is a relatively loose electrostatic association that does not prevent plant acquisition yet greatly mitigates the potential for leaching loss and root scorching.
15. Organic matter makes phosphorus available
The increase in phosphorus availability to plants following applications of organic matter is not only due to mineralisation release of inorganic phosphorous, it also involves the blockage of adsorption sites by organic acids. As organic molecules become adsorbed onto oxide surfaces of mineral soil particles, they compete with phosphorus adsorption. Organic acids cause the surface charge of mineral soil particles to become more negative, which results in decreased phosphorus (as phosphate (PO4)3- ) adsorption. More phosphate is released into the ground water raising the level available to plants. Organic matter is not the only source of organic acids. They are also produced by phosphate dissolving bacteria and fungi having the same effect on mineral particles as acids from organic matter. The rise in the soil pH during organic matter decomposition and the formation of complexes with soluble aluminium and iron by organic compounds also increases the amount of phosphate available in the ground water.
16. Organic matter can regulate the Al3+ availability
Organic matter added to the soil reduces aluminium toxicity. In the soil solution, Al3+ is toxic to most plants but it only becomes a problem in very acidic soils. Addition of organic matter retains cations such as Ca2+, Mg2+and K+ increasing the pH and reducing the solubility and availability of aluminium compounds. Aluminium ions will also be attracted to negatively charged sites on organic matter where they can be stored safely for long periods. However, if you want blue hydrangeas, maybe you need to review the addition of organic matter to the top soil and just use it to mulch around the plants. While decomposition will produce organic acids initially lowering the pH, mineralisation release of cations will eventually raise the pH. The blue colour of hydrangeas is enhanced by low pH and high availability of Al3+.
17. Increasing the depth and volume of top soil.
Adding organic matter will automatically increase the depth and the volume of the soil. Increasing the volume means that there are just more resources for crops to exploit. More water, more nutrients, more air, more microbes, more invertebrates, more roots - and with the extra resources comes healthier and more resilient crops. Increasing the volume of the soil with organic matter will increases the resources that can be stored and released slowly throughout the volume of the soil.
While there is a lot of controversy about digging, increasing the depth of the top soil by introducing compost, manure and mould into the subsoil allows deep penetration of plant roots while improving drainage. In drought when the top soil solution has evaporated leaving solid nutrients that plants cannot absorb, plants need to extend roots into subsoil to find water. If mass flow of water is tamed by organic matter providing a much more tortuous route for it to follow, nutrients are much less likely to be rapidly washed away. More organic matter in subsoil will capture nutrients on active surfaces producing a much higher cation exchange capacity. In other words, organic matter increases the nutrient and water storage capacity of the soil. Nutrients captured by organic matter in the subsoil will be transported through the plant and recycled to the surface of the soil via litter drop of leaves, twigs and branches.
18. Deeper penetration of roots.
If less energy is expended to push roots through the soil, there is more for growth and production of flowers and fruit. We will get larger and more vegetables. Organic matter increases the soil depth giving plant roots more volume to forage for nutrients. There is an overall improvement of soil quality and decreased root resistance. Even when compost is added to the top of the soil it allows unrestricted root growth and better soil penetration optimising fine root, fungal hyphae, bacteria and invertebrate penetration. If a deep soil has been prepared, containing copious amounts of compost and manure, then perennial, annual vegetable and fruit plants will easily be able to penetrate their roots deep into the soil. Encouraging deep rooting means that plants have access to water and nutrients deep in the soil that might help them to survive drought events. The skill involves infusing organic matter relatively evenly throughout the volume of the soil as deeply as possible so that each plant receives adequate water and nutrients.
19. Organic matter improves soil conditions and increases soil resilience.
If compost, manure and mould contributions are continuously applied, the whole environment of the soil improves regardless of the soil’s mineral constituents. Organic matter makes cultivation so much easier by giving the soil friability and a rich body. Weeds can be taken out with ease and added to the compost heap. The spade and hoe pass through the top soil with little effort particularly if the soil has not been walked on and compaction relaxed. Well-rotted and sieved compost spread over the surface of the soil increases the ease with which seed beds can be prepared. In friable soils, plant roots, saprophytic and mycorrhizal fungal hyphae, bacteria, soil invertebrates, air and water can penetrate the soil with more ease. If compost mulches are used, they cover the surface of the soil and prevent the germination of weed seeds between the crop plants.
Organic matter increases friability. Both clay and sandy soils are changed into much easier soils to work and the improvement increases over time. Due to the small size of clay particles it tends to become very sticky when wet and rock hard when very dry. Pores are very small and easily distorted or destroyed. Introducing well decomposed compost and mixing it throughout the volume of the soil means that individual particles are more likely to be coated with organic matter and bacteria. Both large and small crumbs are formed increasing the number of pores that air and water can flow through easily. The more compost added the more the soil becomes a friable, easily worked medium for cultivation. Organic matter increases the water storage capacity of sandy soils. Sandy soils have large particles with large pores and are subject to drought due to loss of water through evaporation and excessive drainage. Introducing large amounts of organic matter into sandy soils will help them to retain water by introducing a wider range of pores. Organic matter is a spongy material that adsorbs and retains water producing more tortuous route for the water to follow as it flows downhill through the top soil.
Changing the proportions of clay, silt and sand is not an option for the average allotment holder. Garden management influence soil organic matter and soil friability and the soil structure is strongly influenced by nature and content of the soil organic matter. The presence of well-rotted organic matter will aid seed emergence and emergence of aerial structures of herbaceous plants by reducing bulk density and compaction. Mature composts are better than fresh because they have a much greater friability than immature composts. Organic matter improves the friability of the soil by improving particle structure. It cements clay and sand particles producing larger crumbs. If the carbon compounds stay a long time it means that they are providing vital services for longer. The natural system is continuously adding vast amounts of plant and animal litter – with no let up. In a cropping system where there is little organic matter being dropped onto the surface by trees and bushes. Where ground is left bare, with little or no organic matter reaching the surface and ground is left uncovered and exposed to elements, where leaching and erosion further reduces soil organic matter and soil depth, you need to add copious amounts of good organic matter in the form of rich composts and manure.
Organic matter makes soil more friable and easier to work enabling gardeners to get a fine tilth. Fine tilths are not necessary for seed germination, but it does look better and the seedlings can be seen growing through the soil much earlier. Getting a fine tilth will look good and make other gardeners admire your seed beds but there will be little else that recommends fine tilth. Organic matter plays a vital part in determining soil structure. Soil structure is the arrangement of these soil particles into crumbs. It can be altered by gardeners adding organic matter. The soil crumbs are held together by the glue of organic matter. When fresh organic matter is added to the soil microbes release long chain sugars or polysaccharides quickly. Polysaccharides promote the formation of crumbs that are water stable. As organic matter decomposes over longer term different sizes of aggregates are formed that are resistant to physical disruption. Soil organic matter helps form and maintain air passages and channels protecting the soil from compaction. When the soil is like this it is friable and will give a fine tilth. The life in the soil changes the characteristics of the soil. It transformation of carbon by plant and micro and macro biological processes that provides energy and results in the establishment of a cycle that connects above and below ground energy transformations.
20. Organic matter increases chlorophyll, nitrogen and phosphorus within plants.
Organic matter additions to soil significantly increase leaf chlorophyll, nitrogen and phosphorus content of crops. You can see the dark greenness of the foliage over the allotment when you have got the organic matter content of the soil right. While this does not necessarily change the taste of these crops, it does increase the nutritional benefit, particularly if a diverse source of organic matter containing a range of micronutrients is used to fertilise the soil. Flavour has more to do with freshness than the amount and type of organic matter in the soil. The taste of vegetable and fruit crops relies on the time it takes for them to reach the table to be eaten. The shorter the time the better the vegetables and fruit taste. Really, vegetable gardeners are just producing flavoured water; however, the “flavour” is nutritionally essential to healthy life. The “flavour” gives us access to micronutrients and vitamins that we cannot get otherwise.
21. Prevents and lessens compaction
Regularly adding organic matter in the form of manures, composts and mould resists compaction and increases the resilience of the soil. The structure of organic matter, where there are multiple air spaces and voids giving the material a relatively springy, spongy nature will enable some organic matter to resist distortion of pores and voids. Woody composted material will have the strength to prevent some of the xylem and phloem structures within the plant body from distorting keeping these tiny pores open even in relatively extreme compaction episodes. Organic matter makes crumbs more resilient by binding particles together tightly and the matrix of the crumb structure is maintained with more robustness against break down by the stress of digging, trampling and watering. The interaction between organic matter, mineral soil particles, pores, air and water are very important in maintaining a friable, crumbly fertile soil.
22. Organic matter increases the number of pores in the soil
Organic matter will lighten the soil because of the mixing of low density compost heightens the porosity and interaction between organic and mineral parts, increasing the friability and crumb structure. The volume of solid particles and pore space influences the air balance and root penetration capacity of the soil. Porosity is a measure of the holes or voids between both organic and mineral solid soil particles. Organic matter increases pore space routes for that air, water and nutrients use to move through the soil. The more tortuous the maze of pores the more time water and nutrients will spend percolating through the soil. A healthy soil will have pores and channels of many sizes that will improve water soakage and air infiltration of the topsoil. A friable soil is one with a relaxed, open, lose structure with as much pore space as possible will increase the ease with which pores are accessed and utilised by organisms. The pores provide habitats for both microbes and invertebrates. It gives space for the growth of microbes and a reservoir for moisture to sustain microbe communities. Pores improve the soils ability to store and transmits air and water by improved penetration and water holding capacity allowing plants to resist drought conditions. Infiltration of water will force stale, carbon dioxide rich air to bubble out of pores and into the atmosphere. As water drains through the soil it will drag fresh, air behind it allowing oxygen to reach the roots of crop plants. Oxygen will also be transported through pores by molecular diffusion and free convection of air movement due to temperature gradients. Increasing the size and number of pores will enhance gas exchange and increase aerobic conditions.
23. Reduces surface crusting.
A hard surface crust should always be avoided and rarely forms if the soil is protected with a mulch and organic matter is regularly added to the top soil. Crusting is where a hard surface of up to 5mm. is formed establishing a capillary connection with moist soil beneath and increasing evaporation. Water is quickly drawn up to the surface where it evaporates noticeably reducing the amount of water in the top soil. Crusting will also increase surface run off and prevent infiltration of rain water. 1. Organic matter will prevent soil cracking.
Soils containing a large proportion of clay shrink when they are dry and swell when they are wet. Cracking should really be avoided because it increases the area of soil exposed to the air producing greater evaporation and water loss. Organic matter will reduce this and go some way to prevent cracking.
24. Organic matter will prevent soil cracking.
Soils containing a large proportion of clay shrink when they are dry and swell when they are wet. Cracking should really be avoided because it increases the area of soil exposed to the air producing greater evaporation and water loss. Organic matter will reduce this and go some way to prevent cracking.
25. Prevents loss of surface particles
Top soil particles will leave the allotment garden via physical export by wind, rain and the boots of gardeners. As small particles of organic carbon and clay are relatively light, they will be one of the first parts of the soil to be lost due to wind or water erosion. Measures to combat this are important in maintaining high organic content of the soil. On dry windy days, it is obvious that a considerable amount of top soil leaves the garden through windblown dust and grit. Organic matter together secretions of thick mucilaginous glue-like compounds produced by soil organisms are major binding agents and these sticky films help bind soil particles together to make crumbs. The production of crumbs by microorganisms may well be an active behaviour evolved as a method of protection. The organisms collecting particles and sticking them around themselves like caddis fly larva do. Stable crumbs resist being moved by wind as they are larger and heavier than clay or small organic particles. The production of good crumb structure by addition of organic matter is one of the husbandry techniques that gardeners can use to improve the resilience of soil. Addition of woody organic matter encourages a fungal soil that supports the growth of mycorrhizal fungi and their helper bacteria. These fungal communities are particularly important in producing good water stable soil crumbs. Fungal hyphae envelope soil particles making large crumbs which resistant to wind erosion.
Organic mulches reduce surface water runoff and erosion it causes. Stabilising the soil surface by both organic mulching and mixing organic matter with the top soil reduces the surface runoff. There is no doubt that organic matter has a direct effect on the production of stable crumb structures that will resist erosion.
Both organic mulches and the organic matter mixed into the top soil will resist surface runoff and the erosion that it causes. The open nature of the soil produced by organic matter additions increasing the number of pores, encourages surface water to soak into the soil rather than run off in eroding rivulets. Organic matter mulches make surface water flow in more tortuous routes and this will slow it down and reduce the energy available to move large amounts of soil. Slowing down the flow of surface water allows time for lighter eroded elements of the soil to settle out in voids and pores or be captured by the net like structures of fungal hyphae. Plant roots are less exposed to direct damage due to exposure and they can make their own contribution to binding and stabilising the soil surface.
26. Enhances the breakdown of base rocks.
Adding composts, manures and moulds will power the production of organic acids by soil organisms and the erosion of base rocks, soil rock and stone by bacteria and fungi. Some soils may be inherently fertile, but this does not mean that they cannot be further improved by organic matter additions. This basic soil fertility may be reliant on the relatively speedy erosion and break up of nutrient rich ground rock. Microbes and addition of organic matter will improve this break down of rock and the incorporation of minerals within the bodies of microbes will reduce the concentration of ions in the soil solution and reduce saturation. A constant slow process of dissolving away soluble substances is much less likely to produce an excess of nutrients, and a soil containing organic matter will prevent salts building up to a plant toxic level by buffering. Increases top down erosion of bed rock and other rocky material by production of acids from increased population of microbes. This will release nutrients from the rock and make them available to plants. Increases the erosion and weathering of bed rock and rocky material by production of acids produced by the community of microbes. Gardeners want to prevent soil erosion but increase rock and rocky material weathering.
27. Organic matter sustains productivity.
I have been producing vegetables from my allotment for over forty years without a noticeable decline in the yield and quality. I have only used organic matter as fertiliser. Soil organic matter has played a major role in sustaining the allotment’s productivity because it is the dominant source of plant nutrients. The thing about organic matter is that there are few limits to the amount that can be produced by the garden. If the garden is layered with herbs, bushes and trees exploiting the full volume of space above the soil, copious amounts of carbon will be captured and fixed into organic molecules within the plants. Making sure that as much of the fixed carbon as possible is locked into the allotment soil is a major skill in the panoply of management techniques that is gardening husbandry. It is only the organic matter that sustains productivity by providing us with so many different services. The ability of the experienced gardener to achieve abundance with little additions of imported organic matter is one of the joys of allotment gardening. Composting easily achieves this locking in and recycling of nutrients. I have no hesitation in saying that compost making is one of the most important skills that a gardener can develop. However, management of water movement through the soil is the second most important factor in producing sustainable crop yields and this too can be greatly influenced by organic matter additions.
28. Increases the soils water holding capacity.
Organic matter has sponge like characteristics. Due to the structure of xylem and phloem tubes within plants, organic matter is a very porous material that adheres considerable amounts of water and retains it even in drought conditions. The filling of these tiny pores, which present such small surface areas to the outside environment, means that water within them is not so subject to evaporation. If water is stored in organic matter so too are dissolved nutrients. The interchange between nutrients electrostatically adhered to the organic matter surfaces and those dissolved in the soil solution within the decomposing pores of plant organic matter promotes the slow diffusion of nutrients throughout the soil volume. The increased ability of soil enriched by organic matter to enhance water retention enables plants to survive drought conditions. It reduces surface water runoff by increasing the soil’s surface permeability and preventing crusting. It improves water soakage, preventing waterlogging and dry volumes of soil. Some soil organic matter has deliquescent like properties attracting ground water to itself helping to retain and store soil solution and reducing evaporation. Both the mineral and organic components contribute to the water holding capacity of the soil, but it is only the organic component that can be actively managed by the allotmenteer.
29. Reducing the preferential flow of water through the top and subsoil.
When you dig deeply in the soil, as I do, it is obvious that there are damp and dry volumes scattered through the soil. In other words, there are streams of water travelling through the soil where cracks and voids allow it to flow downhill in preference to other more compacted areas. For a garden to work at its maximum potential water should flow through the whole volume of the garden soil as evenly and slowly as possible. By digging trenches on contour and adding copious amounts of organic matter both to the subsoil as hugelkultur and to the top soil as composted organic matter, the route of water through the soil becomes more tortuous; more of a random walk. Surface water captured by organic mulches will slowly percolate through this organically rich soil helping to ensure that all the allotment is supplied with water. This spreading out of ground water throughout the width of the garden due to the porous nature of organic matter and the use of level trenches in parallel contours across the allotment garden allows volumes of soil that were previously relatively dry become moister and volumes that were liable to waterlogging become drier.
30. Prevention of water loss by evaporation
The amount of water within soil can be noticeably increased by protecting its surface with an organic mulch. Organic matter throughout the volume of the soil leads to prevention of water loss by evaporation because it reduces the capillary effect and wicking at the surface. Organic matter has a sponge like nature which tends to retain water within its structure allowing to escape slowly. In perennial crop growing, the ground can be covered by living mulches which will drop litter onto the soil and form a mulch without too much intervention from the gardener. The idea is to produce a self-mulching soil – one which will not need imports from outside the allotment.
31. Organic matter improves drainage
If you excessively drain away water, you excessively drain away nutrients. Slowing the percolation of water through the soil while not allowing build up of excessively wet volumes is a husbandry skill that is important in developing fertile allotments. Adding organic matter improves the porosity of the soil allowing water to flow through the allotment without being impeded. Water will flow according to the gradient and gravity and both can be used by the gardener to enhance irrigation and nutrient distribution. I may advocate the slowing of mass flow and the storage of water in organic matter but stopping water flow needs much more thought and larger areas of land than allotments. However, if you have a large enough area of garden you might consider storage of water in ponds and lakes using dams and swales. However, if the ground water is spread evenly throughout the soil volume, much more can be stored and made available to plant roots.
32. Crumb Structure
Both living and dead organic matter stick mineral and organic particles together to form clumps or crumbs. producing a porous crumb structure. This material is sticky and can coat soil particles, regardless of whether they are sand or clay, sticking them together making crumbs of soil and changing air and water pores.
Stickiness of organic molecules can be demonstrated by food on a plate, babies and cereal, hankies and grass under rotary mowers. Soil organic matter, poly cations, clay minerals and soil organisms all have key roles in cementing soil particles together. The formation of crumbs by polysaccharides is due to the presence of functional groups that can lose a proton (H+) and become negatively charged. These molecules will then interact with positively charged mineral oxides producing a stable organic-inorganic crumb microstructure. These crumbs are resistant to disintegration by water and, if soil particles stick together robustly, they will not be susceptible to runoff, water and wind erosion. Crumb formation usually begins with organic matter accumulating mineral particles which are further cemented into bigger crumbs by microbes. As organic residues decompose gels and other viscous microbial by products are passed into the soil and encourage larger crumb formation. Particles of organic matter in the biofilm are the substrate for microbe bonding materials that produce micro crumbs and encrust mineral particles stably with organic matter films. Soil invertebrates like earthworms secrete sticky mucus and this further helps to glue small soil particles together to form larger crumbs. Calcium and certain types of organic matter become preferentially absorbed by soil crumbs further stabilising them. Soil made up of a range of different sized crumbs will give the soil an open, friable and porous structure that is characteristic of rich, productive soil. Crumb structure controls the fluctuations of water, nutrients and gases in the soil. The structure of the crumbs also helps to determine the amount of residual organic matter it can store. Gardeners can improve soil crumb structure by increasing soil organic matter and stimulating biological activity. Crumbs are temporary and as they produce a structure that allows plants to thrive they need to be constantly replaced as they disintegrate. Even the most resilient of organic matter will turn over every ten to one hundred years. In my experience the soil becomes very friable and particularly well structured throughout its volume after 30 years of continual cultivation and additions of organic matter. A good crumb structure improves friability, tilth, and capillary action, water rising in small apertures, conducting water upward due to evaporation like the wick of an oil lamp. This capillary water will bring nutrients from lower in the soil.
The friability of the soil is how it crumbles in your hands.
33. Organic matter produces a fine friable tilth.
All soil properties can be improved by adding organic matter in the form of compost, manure and mould to make a fine, friable tilth. To enhance organic matter in the soil, maximise green manure and crop residue incorporation and add manure and composts from a variety of sources in rotation; cover as much of the soil as possible either with mulches or crops. If the soil is rich in decomposed organic matter with a range of different sized crumbs and crumbles easily indicating that air, water and plant roots will be able to penetrate it effortlessly then it is what we call friable. All but the tiniest amount of organic matter turns over every ten to 100 years. In my experience the soil becomes very friable and particularly well structured throughout its volume after 30 years of continual additions of organic matter.
34. Organic matter increases the population and diversity of soil life
Why on earth do we spend money of methods of garden management that nature is much better at than gardeners with all their xenobiotic powders and potions could ever be? Organic matter provides easily accessible food for soil organisms. Allotments that only use organic matter have much greater biological activity than plots that use other methods. Soil continuously supplied with different kinds of organic matter, increases the population and diversity of soil organisms that continually release nutrients making them available to plants. Wood processors like woodlice and wasps are increased when woody mulches are used to cover the soil. When crop plants have become established they should be heavily mulched with woody shreddings. The larger animals like black bird Turdus merula, badger Meles meles, shrews Sorex araneus and fox Vulpes vulpes all help to process woody shreddings mulches by digging them up and mixing them with the top soil in search of invertebrate prey. One of the main complaints on the allotment sites is that paths and mulched beds have been attacked by badgers. I would rather have the wildlife; it certainly does all the digging that is necessary. Organic matter mulches particularly of woody shreddings mimic the forest floor where numerous invertebrates have evolved to thrive. The number of predators that exploit this habitat is considerably more than those that exploit bare soil or even crop covered soil. Tapping into this “forest floor” ecosystem enables the gardener to introduce a whole panoply of new invertebrates into the allotment garden. More permanent thickly mulched paths made along swales and around perennial fruit plants, increases the diversity of microbes and invertebrates, providing a habitat for aggressive “forest floor” predators. More reticent organic residues at various stages of decomposition builds up in the soil and contributes to numerous different habitats for both microbes and invertebrates.
Organic matter applications lead to production of a soil community populated by a widely diverse group of microbes which will be less likely to allow an uncontrolled increase in the population of disease microbes. Organic matter increases the diversity of microbes in the soil which raises the likelihood of microbes with the ability to break down unusual organic compounds and mineralise them. Organic matter intensifies interaction between microbes, root hairs and soil animals because of its large active surface area. There is a noticeable increase in the populations soil life when a biodynamic or bioorganic system is used. Organic matter provides a source of carbon for soil microorganisms which cycle nutrients and compete with pests and diseases.
35. Organic matter stimulates colonisation of crops by mycorrhizal fungi.
Fungal hyphae are microscopic and can grow into very small pores and voids accessing volumes of the soil that relatively large plant roots cannot because of size. Mycorrhiza secrete acids and enzymes that break down both organic matter and mineral particles releasing nutrients. They actively transport these nutrients to the plant roots where they share them with their host plants. There is evidence that mycorrhiza transfer nutrients, photosynthates and communication compounds between plants thereby strengthening the resilience and robustness of plant growing systems. Producing an allotment garden that has more habitats and niches in which fungi can flourish enables plants to access nutrients from a much wider range of organic materials and micronutrients. Organic matter additions increase the depth of the soil and thereby the length of plant roots as they grow into new volumes of soil exposing more root area to infection by mycorrhizal fungi. These fungi noticeably improve the health and resilience of crops by transferring nutrients to the roots of plants. Mycorrhizal fungi can easily extend their hyphae into buried organic matter and sporulate in pores and voids. These spores will germinate on the surfaces of roots when they grow into the organic matter. Organic matter provides fungi helper bacteria with substrate to make their bodies and energy. Compounds secreted by these bacteria help to promote the fungi and plant symbiosis.
36. Increasing the habitat potential of the allotment.
Organic matter increases the habitats within the soil producing niches for organisms that may not survive for long periods in degraded soils. The increased population of animal life in the soil is a visible consequence of adding organic matter to the soil and increasing its fertility.
37. Organic matter contributes to pest and disease suppression
Organic matter, particularly when used as a mulch, helps to produce a pest resistant and disease suppressive soil by increasing the populations of predators. By injecting large doses of diverse compost, new communities of microbe communities compete with resident pathogens Soil populated by a diverse microbial population is much less likely to see uncontrolled increases in pests and diseases. The more diverse habitats enable invertebrate predators like spiders and wasps to establish a permanent home especially if digging and soil disturbance is avoided. Plants supplied with organic matter are healthier, yield more and have a greater resistance to drought, pests and diseases. The reaction of plant crops to organic matter soil additions will depend on plant species, variety and cultivar; the architecture of their roots; local climate; soil type; and other soil additions. However, the provision of widely sourced composted organic matter is directly related to better plant nutrition and health. Healthier plants can resist the attacks of pathogens and have enough resources to maintain protective symbiosis with endophyte, mycorrhizal fungi and nitrogen fixing bacteria.
38. The living part of organic matter
It really makes sense when thinking about how organic matter improves the soil for sustainable crop production to include the organisms that make their homes there. Live organisms themselves are organic matter that will have similar characteristics to dead organic matter and will provide similar services just because of their presence in the soil. For example, they will contribute to water retention, crumb formation, pore formation, bioturbation, and the countless other vital roles that maintain the soil’s fertility. Living things are the soil, together with dead organic matter and mineral particles. To what extent weed seed and invertebrate surfaces contribute to the fertility of the soil through ion exchange or water retention is unclear but I would be very surprised if they had no effect at all. There are countless numbers of weed seeds, spores, cysts, and eggs in the top soil and they can live for hundreds if not thousands of years without germinating adding to a background of live organic matter that interacts with other soil elements. Organic matter increases invertebrate activity and bioturbation and fine earth production – it is not just worms.
39. Production of carbon dioxide.
Actively decaying organic matter produces carbon dioxide near the surface of the soil and this can stimulate plant growth. The carbon dioxide is being produced where it is going to be used. With the open, friable crumb structure that organic matter produces this carbon dioxide can be exchanged with atmospheric oxygen very easily.
40. Increases the temperature
Temperature increases were exploited by the Victorian gardeners when they used manures to produce hot beds. They also used tan – the oak bark waste from the tanning industry to produce hotbeds. Their skill and the success of these hot beds allowed them to grow exotic fruit like peaches, nectarines and pineapples under glass.
The increase in temperature caused by organic matter used as mulches and dug into the soil makes it possible to work on the allotment earlier in the spring. Compost improves soil heat balance and the equilibration of temperature throughout the soil. Soil temperature influences the rate of biological growth – things grow better when the temperature is between a certain range. The soil temperature plays an important role in controlling growth and activity of microorganisms, volumes of gases, redox potentials and diffusion of solutes and gases. While temperature fluctuations mainly depend on climate, radiation, heat and light, temperature can also be influenced by the colour of the soil. Composts are usually dark brown or dark greyish and result in a higher light and heat absorption that warm soils supplied with compost faster than light coloured soils. Soil will be warmed earlier in the spring because of the openness of rich organic soil.
41. Organic matter has an equalising effect
Organic matter evens out annual and seasonal fluctuations of water, air, heat and availability of nutrients. This will help to match them with the changes of requirements during the life cycles of crop plants.
42. The many different compounds
The soil contains numerous active independent organic compounds secreted by plant, animals and microbes; the majority of which have not been identified or isolated. Organic matter provides the energy and materials to produce the many different compound secreted by soil organisms. These compounds have the potential to supply the same services as other organic matter in the soil. Secretions will add to the tortuous matrix of particles that air and water must negotiate when they pass through the soil. Active surface sites on these compounds interact with organisms to filter and concentrate soil nutrients and carbon so that little organic matter reaches the subsoil.
43. Reduces the effects of xenobiotic, industrial contaminants
It is not the job of the gardener to deal with xenobiotic industrial chemicals but if this happens as a side effect of good husbandry and advanced skills then I see no reason for claiming some credit. Woody shreddings will provide a habitat for white rot fungi like oyster fungus, Pleurotus ostreatus which produces laccases and lignin peroxidases that break down the most pernicious and complex of the organic xenobiotic industrial contaminants. These fungi break down antibiotics in farm manures and prevent build-up of resistant bacteria in soil. There is no doubt that antibiotic compounds are made by many soil organisms and there must have been an adaptation to counter their effects. The over use of powerful antibiotics like those produced by penicillin Penicillium chrysogenum especially in farm animals has produced excessive numbers of resistant bacteria. The resistance is usually carried on plasmids which can be replicated and passed to other bacteria relatively easily. Some antibiotics are passed out of the farm animals in their faeces and broken down by bacteria, archaea and fungi, however if massive doses of antibiotic manures are added to the soil, bacteria adapted to coping with it will increase their populations while bacteria susceptible to antibiotic will decrease until the antibiotics are dealt with.
44. Organic matter prevents soils from becoming degraded
It is obvious that the resilience of soils and their ability to sustain intensive cropping of vegetables and fruit relies on the addition of copious amounts of organic matter. The inevitable loss of organic matter must be continuously replaced to make sure that all the many services that organic matter provides will continue to be supplied. This is the fertility of the soil, its friability, its sustainability.