Farming for the Future
By Ronald G Doetch, Solutions in the Land
The hydrological cycle is one of the most important but poorly understood Earth System processes. It involves the journey of water from the Earth’s surface to the atmosphere, and back again. This gigantic system, which is responsible for the continuous exchange of moisture between our planet’s oceans, atmosphere, and land surfaces, is powered by the energy from the Sun. The bulk of the Earth’s water (about 96.5%) is stored in the global oceans, about 1.7% is stored in the polar ice caps, glaciers, and permanent snow fields, and another 1.7% is stored in groundwater, lakes, rivers, streams, and soil. Only one one-thousandth of our planet’s water is present in the atmosphere, but it is still the most important ‘greenhouse gas’ and therefore has a very strong influence on our weather and climate.
About 90% of this atmospheric water vapor is produced by evaporation from bodies of open water like oceans, lakes, and rivers. Plant transpiration and soil evaporation supply the remaining 10%. Plants take up water through their root systems to deliver nutrients to their leaves, and release it through small pores in their leaves, called ‘stomata’. While evaporation from the oceans is the primary driver of the surface-to-atmosphere portion of the hydrological cycle, plant transpiration and soil evaporation are also significant contributors. Soil moisture therefore plays a crucial role in our planet’s hydrological cycle. In most of the world, the water supply is the factor that most affects plant growth and crop yields, and hence food supplies. Although soil moisture is not a headline topic, this paper explores the reality that it is indeed our reckless abandonment of the soil that today affects our health, climate and economic concerns and only a refocusing and re-engagement with the soil will put us on the pathway to sustainability.
The focus of this paper is the thin layer between heaven and earth that we call soil. The Soil is a Living System Soil organisms are responsible, to a varying degree depending on the system, for performing vital functions in the soil. Soil organisms make up the diversity of life in the soil. This soil biodiversity is an important component of terrestrial ecosystems. Soil biodiversity is comprised of the organisms that spend all or a portion of their life cycles within the soil or on its immediate surface (including surface litter and decaying logs) Soil organisms represent a large fraction of global terrestrial biodiversity. They carry out a range of processes important for soil health and fertility in soils of both natural ecosystems and agricultural systems. This section provides brief descriptions of organisms that are commonly found in the soil and their main biological and ecological attributes. The community of organisms living all or part of their lives in the soil constitutes the soil food web. The activities of soil organisms interact in a complex food web with some subsisting on living plants and animals (herbivores and predators), others on dead plant debris (detritivores), on fungi or on bacteria, and others living off but not consuming their hosts (parasites).
Plants, mosses and some algae are autotrophs, they play the role of primary producers by using solar energy, water and carbon (C) from atmospheric carbon dioxide (CO2) to make organic compounds and living tissues. Other autotrophs obtain energy from the breakdown of soil minerals, through the oxidation of nitrogen (N), sulphur (S), iron (Fe) and C from carbonate minerals. Soil fauna and most fungi, bacteria and actinomycetes are heterotrophs, they rely on organic materials either directly (primary consumers) or through intermediaries (secondary or tertiary consumers) for C and energy needs. The Soil food-web diagram below shows a series of conversions of energy and nutrients as one organism eats another. The “structure” of the soil food web is the composition and relative numbers of organisms in each group within the soil. The living component of soil, the food web, is complex and has different compositions in different ecosystems. In a healthy soil, there are a large number of bacteria and bacterial feeding organisms. Where the soil has received heavy treatments of pesticides, chemical fertilizers, soil fungicides or fumigants that kill these organisms, the beneficial soil organisms may die (impeding the performance of their activities), or the balance between the pathogens and beneficial organisms may be upset, allowing those called opportunists (disease-causing organisms) to become problems.
The soil environment Source: S. Rose and E.T. Elliott MICRO-ORGANISMS These are the smallest organisms (<0.1 mm in diameter) and are extremely abundant and diverse. They include algae, bacteria, cyanobacteria, fungi, yeasts, myxomycetes and actinomycetes that are able to decompose almost any existing natural material. Micro-organisms transform organic matter into plant nutrients that are assimilated by plants. Two main groups are normally found in agricultural soils: bacteria and mycorrhizal fungi. Bacteria Bacteria are very small, one-celled organisms that can only be seen with a powerful light (1 000×) or electron microscope. They constitute the highest biomass of soil organisms. They are adjacent and more abundant near roots, one of their food resources. There are many types of bacteria but the focus here is on those that are important for agriculture, e.g. Rhizobium and actinomycetes.
Bacteria are important in agricultural soils because they contribute to the carbon cycle by fixation (photosynthesis) and decomposition. Some bacteria are important decomposers and others such as actinomycetes are particularly effective at breaking down tough substances such as cellulose (which makes up the cell walls of plants) and chitin (which makes up the cell walls of fungi). Land management has an influence on the structure of bacterial communities as it affects nutrient levels and hence can shift the dominance of decomposers from bacterial to fungal. One group of bacteria is particularly important in nitrogen cycling. Free-living bacteria fix atmospheric N, adding it to the soil nitrogen pool; this is called biological nitrogen fixation and it is a natural process highly beneficial in agriculture. Other N-fixing bacteria form associations (in the form of nodules) with the roots of leguminous plants.
The nodule is the place where the atmospheric N is fixed by bacteria and converted into ammonium that can be readily assimilated by the plant. The process is rather complicated but, in general, the bacteria multiply near the root and then adhere to it. Next, small hairs on the root surface curl around the bacteria and they enter the root. Alternatively, the bacteria may enter directly through points on the root surface. Once inside the root, the bacteria multiply within thin threads. Signals stimulate cell multiplication of both the plant cells and the bacteria. This repeated division results in a mass of root cells containing many bacterial cells. Some of these bacteria then change into a form that is able to convert gaseous N into ammonium nitrogen (they can “fix” N). These bacteria are then called bacteroids and present different properties from those of free cells. Most plants need very specific kinds of rhizobia to form nodules.
A specific Rhizobium species will form a nodule on a specific plant root, and not on others. The shapes that the nodules form are controlled by the plant and nodules can vary considerably in size and shape. Actinomycetes are a broad group of bacteria that form thread-like filaments in the soil. The distinctive scent of freshly exposed, moist soil is attributed to these organisms, especially to the nutrients they release as a result of their metabolic processes. Actinomycetes form associations with some non-leguminous plants and fix N, which is then available to both the host and other plants in the near vicinity. Bacteria produce (exude) a sticky substance in the form of polysaccharides (a type of sugar) that helps bind soil particles into small aggregates, conferring structural stability to soils. Thus, bacteria are important as they help improve soil aggregate stability, water infiltration, and water holding capacity.
Nematodes Nematodes are tiny filiform roundworms that are common in soils everywhere. Free-living nematodes graze on bacteria and fungi, thus they control the populations of harmful micro-organisms. These nematodes are 0.15-5 mm long and 2-100 ìm wide; an exception are Mermithidae nematodes, which may be 20 cm long and are very common in tropical soils, being parasites of some arthropods such as locusts. Nematodes can only move through the soil where a film of moisture surrounds the soil particles. They live in the water (they are hydrobionts) that Farming for the Future 5 4.28.14 fills spaces between soil particles and covers roots. In hot and dry conditions, they enter into a dormant stage, and as soon as water becomes available, they spring back to activity. Nematodes are recognized as a major consumer group in soils, generally grouped into four to five trophic categories based on the nature of their food, the structure of the stoma (mouth) and oesophagus, and the method of feeding (Yeates and Coleman, 1982): bacterial feeders, fungal feeders, predatory feeders, omnivores, and plant feeders.
The bacterial feeders prey on bacteria (bacterivores) and may ingest up to 5 000 cells/minute, or 6.5 times their own weight daily. This helps disperse both the organic matter and the decomposers in the soil. Bacterial- and fungal-feeding nematodes release a large percent of N when feeding on their prey groups and are thus responsible for much of the plant available N in the majority of soils (Ingham et al., 1985). The annual overall consumption may be as much as 800 kg of bacteria per hectare and the amount of N turned over in the range of 20-130 kg (Coleman et al., 1984). Fungi These organisms are responsible for the important process of decomposition in terrestrial ecosystems as they degrade and assimilate cellulose, the component of plant cell walls. Fungi are constituted by microscopic cells that usually grow as long threads or strands called hyphae of only a few micrometres in diameter but with the ability to span a length from a few cells to many metres. Soil fungi can be grouped into three general functional groups based on how they source their energy: Decomposers – saprophytic fungi – convert dead organic material into fungal biomass, CO2, and small molecules, such as organic acids. These fungi generally use complex substrates, such as the cellulose and lignin, in wood. They are essential for decomposing the carbon ring structures in some pollutants. Like bacteria, fungi are important for immobilizing or retaining nutrients in the soil. Mutualists – mycorrhizal fungi – colonize plant roots through a symbiotic relationship. The definition of symbiosis is a close, prolonged association between two or more different organisms of different species that may benefit each member.
Mycorrhizae increase the surface area associated with the plant root, which allows the plant to reach nutrients and water that otherwise might not be available. Mycorrhizae essentially extend plant reach to water and nutrients, allowing plants to utilize more of the resources available in the soil. Mycorrhizae source their carbohydrates (energy) from the plant root they are living in/on and they usually help the plants by transferring phosphorus (P) from the soil into the root. Two major groups are identified: (i) ectomycorrhizae, that grow on the surface layers of the roots and are commonly associated with trees; and (ii) endomycorrhizae, such as arbuscular mycorrhizal fungi and vesicular mycorrhizal fungi, that grow within the root cells and are commonly associated with grasses, row crops, vegetables and shrubs.
Arbuscular mycorrhizal fungi can also benefit the physical characteristics of the soil because their hyphae form a mesh to help stabilize soil aggregates. Vesicular-arbuscular mycorrhizae are the most widespread mycorrhizal fungi. Mycorrhizae are particularly important for phosphate uptake because P does not move towards plant roots easily. These organisms do not harm the plant, and in return, the plant provides Farming for the Future 6 4.28.14 energy to the fungus in the form of sugars. The fungus is actually a network of filaments that grows in and around the plant root cells, forming a mass that extends considerably beyond the root system of the plant. Pathogens – or parasites cause reduced production or death when they colonize roots and other organisms.
Root-pathogenic fungi, such as Verticillium, Pythium andRhizoctonia, cause major economic losses in agriculture each year. Many fungi help control diseases, e.g. nematode-trapping fungi that parasitize disease-causing nematodes, and fungi that feed on insects may be useful as biocontrol agents. Rhizosphere The rhizosphere is the region of soil immediately adjacent to and affected by plant roots. It is a very dynamic environment where plants, soil, micro-organisms, nutrients and water meet and interact. The rhizosphere differs from the bulk soil because of the activities of plant roots and their effect on soil organisms. The root exudates can be used to increase the availability of nutrients and they provide a food source for micro-organisms. This causes the number of microorganisms to be greater in the rhizosphere than in the bulk soil. Their presence attracts larger soil organisms that feed on micro-organisms and the concentration of organisms in the rhizosphere can be up to 500 times higher than in the bulk soil. An important feature of the rhizosphere is the uptake of water and nutrients by plants. Plants take up water and nutrients into their roots. This draws water from the surrounding soil towards the roots and rhizosphere. The soil organisms near the rhizosphere influence plant roots because they translocate nutrient compounds increasing the available nutrients for plants.
BENEFICIAL ORGANISMS IN AGRICULTURAL SOILS;
Agricultural practices can have either positive or negative impacts on soil organisms. Land management and agricultural practices alter the composition of soil biota communities at all levels, with important consequences in terms of soil fertility and plant productivity. The different agricultural practices used by farmers also exert an important influence on soil biota, their activities and diversity. Clearing forested or grassland for cultivation has a drastic effect on the soil environment and, hence, on the numbers and kinds of soil organisms. In general, such activity reduces the quantity and quality of plant residues and the number of plant species considerably. Thus, the range of habitats and foods for soil organisms is reduced significantly. Through changing the physical and chemical environment, agricultural practices alter the ratio of different organisms and their interactions significantly, for example, through adding lime, fertilizers and manures, or through tillage practices and pesticide use. The beneficial effects of soil organisms on agricultural productivity include organic matter decomposition and soil aggregation; breakdown of toxic compounds, both metabolic by- products of organisms and agrochemicals; inorganic transformations that make available nitrates, sulphates and phosphates as well as essential elements such as Fe and Mn; and N- fixation into forms usable by higher plants. “In 1937, President Franklin D Roosevelt wrote… ’The Nation that destroys its soil, destroys itself.’ ”
Organic matter affects both the chemical and physical properties of the soil and its overall health. Properties influenced by organic matter include: soil structure; moisture holding capacity; diversity and activity of soil organisms, both those that are beneficial and harmful to crop production; and nutrient availability. It also influences the effects of chemical amendments, fertilizers, pesticides and herbicides. Soil organic matter consists of a continuum of components ranging from labile compounds that mineralize rapidly during the first stage of decomposition to more recalcitrant residues (difficult to degrade) that accumulate as they are deposited during advanced stages of decomposition as microbial by-products (Duxbury, Smith and Doran, 1989). Freshly added or partially decomposed plant residues and their non-humic decomposition products constitute the labile organic matter pool. The more stable humic substances tend to be more resistant to further decomposition. The labile soil organic matter pool regulates the nutrient supplying power of the soil, particularly of nitrogen (N), whereas both the labile and stable pools affect soil physical properties, such as aggregate formation and structural stability. When crops are harvested or residues burned, organic matter is removed from the system. However, the loss can be minimized by retaining plant roots in the soil and leaving crop residues on the surface. Organic matter can also be restored to the soil through growing green manures, cuttings from agroforestry species and the addition of manures and compost. Soil organic matter is the key to soil life and the diverse functions provided by the range of soil organisms.
Soil micro-organisms are of great importance for plant nutrition as they interact directly in the biogeochemical cycles of the nutrients. Farming for the Future 8 4.28.14 Increased production of green manure or crop biomass aboveground and belowground increases the food source for the microbial population in the soil. Agricultural production systems in which residues are left on the soil surface and roots left in the soil, e.g. through direct seeding and the use of cover crops, therefore stimulate the development and activity of soil micro-organisms. In one 19-year experiment in Brazil, such practices resulted in a 129- percent increase in microbial carbon biomass and a 48-percent increase in microbial N biomass under conventional tillage and conservation agriculture Source: Balota, Andrade and Colozzi Filho, 1996. In undisturbed soil ecosystems, e.g. in conservation agriculture, colonization with mycorrhizal fungi increases strongly with time compared with colonization under natural vegetation. Fine roots are the primary sites of mycorrhizal development as they are the most active site for nutrient uptake. This partly explains the increase in mycorrhizal colonization under undisturbed situations as rooting conditions are far better than under conventional tillage. Other factors that might stimulate mycorrhizal development are the increase in organic carbon (C) and the rotation of crops with cover crop/green manure species. Relationship between bulk density and macroporosity of a soil under different types of management Source: Gassen and Gassen, 1996. Another consequence of increased organic matter content is an increase in the earthworm population.
Earthworms rarely come to the soil surface because of their characteristics: photophobia, lack of pigmentation and tolerance to periods of submergence and anaerobic conditions during rainfall. Soil moisture is one of the most important factors that determine the presence of earthworms in the soil. Through cover crops and crop residues, evaporation is reduced and organic matter in the soil is increased, which in turn can hold more water. Residues on the soil surface induce earthworms to come to the surface in order to incorporate the residues in the soil. The burrowing activity of earthworms creates channels for air and water; this has an important effect on oxygen diffusion in the rootzone, and the drainage of water from it. Furthermore, nutrients and amendments can be distributed easily and the root system can develop, especially in acid subsoil in the existing casts. The shallow-dwelling earthworms create numerous channels throughout the topsoil, which increases overall porosity, and thus bulk density. The large vertical channels created by deep-burrowing earthworms increase water infiltration under very intense rainfall conditions.
Many important chemical properties of soil organic matter result from the weak acid nature of humus. The ability of organic matter to retain cations for plant use while protecting them from leaching, i.e. the cation exchange capacity (CEC) of the organic matter, is due to the negative charges created as hydrogen (H) is removed from weak acids during neutralization. Many acid-forming reactions occur continually in soils. Some of these acids are produced as a result of organic matter decomposition by microorganisms, secretion by roots, or oxidation of inorganic substances. Commonly used N fertilizers through microbial conversion of NH4+ to NO3-. In particular, ammonium fertilizers, such as urea, and ammonium phosphates, such as monoammonium and diammonium phosphate, are converted rapidly into nitrate through a nitrification process, releasing acids in the process and thus increasing the acidity of the topsoil.
When acids or bases are added to the soil, organic matter reduces or buffers the change in pH. This is why it takes tonnes of limestone to increase the pH of a soil significantly compared with what would be needed to simply neutralize the free H present in the soil solution. All of the free hydrogen ions in the water in a very strongly acid soil (pH 4) could be neutralized with less than 6 kg of limestone per hectare. However, from 5 to more than 24 tonnes of limestone per hectare would be needed to neutralize enough acidity in that soil to enable acid sensitive crops to grow. Almost all of the acid that must be neutralized to increase soil pH is in organic acids, or associated with aluminium (Al) where the pH is very low. However, with large values of soil organic matter, the pH will decrease less rapidly and the field will have to be limed less frequently. A lime application of 1-2 tonnes/ha every 2-3 years might be sufficient to regulate the acidity. Organic matter may provide nearly all of the CEC and pH buffering in soils low in clay or containing clays with low CEC. In comparing conventional and conservation tillage in Brazil, the highest values of soil CEC and exchangeable calcium (Ca) and magnesium (Mg) were found in legume-based rotation systems with the highest organic matter content).
In particular, systems with pigeon peas and lupine resulted in a 70-percent increase in CEC compared with a fallow/maize system. Organic matter releases many plant nutrients as it is broken down in the soil, including N, phosphorus (P) and sulphur (S). Leguminous species are very important as part of a cereal crop rotation in view of their capacity to fix N from the atmosphere through symbiotic associations with root dwelling bacteria. Again in Brazil, five years after starting an intensive system in which oats and clover were rotated with maize and cowpea, there was 490 kg/ha more total soil N in the 0-17.5-cm soil layer than under the traditional oats/maize system with conventional tillage. After nine years, no tillage in combination with the intensive cropping system had resulted in a 24-percent increase in soil N compared with conventional tillage. Although N uptake by plants was less in no-tillage systems, probably because of N immobilization and organic matter building, the maize yields under the different tillage systems did not differ. As the no-tillage system was more efficient in storing soil N from legume cover crops in the topsoil, in the long term this system can increase soil N available for maize production (Amado, Fernandez and Mielniczuk, 1998). Calegari and Alexander (1998) noted that the P content (both inorganic P and total P) of the surface layer (0-5 cm) was higher in the plots with cover crops after nine years. Cover crops were shown to have an important P-recycling capacity, especially when the residues were left on the surface. This was especially clear in the fallow plots, where the conventional tillage plots had a P content 25 percent lower than the no-tillage plots.
Depending on the cover crop, the increase was between 2 and almost 30 percent. Even more important is the effect of land preparation on the increase of P availability in the soil Nitrification process and acid formation in the topsoil Source: Mielniczuk, 1996. Phosphorus content of soil after 9 years of conservation agriculture, compared with conventional tillage Note: P content of the soil (0-10 cm) was 9 mg/kg in 1985. On the other hand, where direct seeding is practiced and the crop residues are left on the surface, 50-75 percent of the nutrients were concentrated in the top layer of the soil.
Organic matter influences the physical conditions of a soil in several ways. Plant residues that cover the soil surface protect the soil from sealing and crusting by raindrop impact, thereby enhancing rainwater infiltration and reducing runoff. Increased organic matter also contributes indirectly to soil porosity (via increased soil faunal activity). Fresh organic matter stimulates the activity of macrofauna such as earthworms, which create burrows lined with the glue-like secretion from their bodies and intermittently filled with worm cast material. Surface infiltration depends on a number of factors including aggregation and stability, pore continuity and stability, the existence of cracks, and the soil surface condition. Organic matter also contributes to the stability of soil aggregates and pores through the bonding or adhesion properties of organic materials, such as bacterial waste products, organic gels, fungal hyphae and worm secretions and casts. Moreover, organic matter intimately mixed with mineral soil materials has a considerable influence in increasing moisture holding capacity. The quality of the crop residues, in particular its chemical composition, determines the effect on soil structure and aggregation.
BENEFITS OF SOIL ORGANIC MATTER;
As noted above, the benefits of a soil that is rich in organic matter and hence rich in living organisms are many. Direct organic matter amendments include: 1. inoculants and compost; 2. animal manure; 3. use of vermicompost; 4. use of waste sludge. 6. improved cropping systems and rotations; 7. planting cover crops; 8. maximizing crop residues and their management; 9. improved rooting systems.
The effects of the management practices depend largely on the agro-climatic situation as temperature and moisture influence speed of decomposition and general cycling of organic matter and nutrients.
SOIL ORGANIC MATTER AND DECOMPOSITION;
Soil organic matter consists of living parts of plants (principally roots), dead forms of organic material (principally dead plant parts), and soil organisms (micro-organisms and soil animals) in various stages of decomposition. It has great impact upon the chemical, physical and biological properties of the soil. Organic matter in the soil gives the soil good structure, and enables the soil to absorb water and retain nutrients. It also facilitates the growth and life of the soil biota by providing energy from carbon compounds, N for protein formation, and other nutrients. Some of the nutrients in the soil are held in the organic matter, comprising almost all the N, a large amount of P and some S. When organic matter decomposes, the nutrients are released into the soil for plant use. Therefore, the amount and type of organic matter in the soil determines the quantity and availability of these nutrients in the soil. It also affects the colour of the soil. Dead matter constitutes about 85 percent of all organic matter in soils. Living roots make up about another 10 percent, and microbes and soil animals make up the remainder. Organic matter that has fully undergone decomposition is called humus. The origins of the materials after formation of humus cannot be recognized. Humus is dark in colour and very rich in plant nutrients. It is usually found in the top layers of a soil profile. The dark colour of humus absorbs heat from the sun, thereby improving soil temperature for plant growth and microbial activity under cooler climatic conditions. Some of the most important functions of organic matter in the soil are:
- It increases soil fertility as it retains cations and conserves nutrients in organic forms and slowly releases required nutrients for plant uptake and growth.
- It binds soil particles together; the cementing and aggregation functions improving soil structure and aeration.
- It acts as a sponge in the soil, retaining soil moisture. Soils with high organic matter content can hold more water than those low in organic matter.
- It provides food for micro-organisms living in the soil. Decomposition is the general process whereby dead organic materials are transformed into simpler states with the concurrent release of energy and their contained biological nutrient and other elements in inorganic forms.
Such forms are directly assimilable by micro-organisms and plants, and the remaining soil organic matter may be stabilized through physical and chemical processes or further decomposed (Lavelle and Spain, 2001). These transformations of dead organic materials into assimilable forms involve the simultaneous and complementary processes of mineralization and humification:
- Mineralization is the process through which the elements contained in organic form within biological tissues are converted to inorganic forms such as nitrate, phosphate and sulphate ions.
- Humification is an anabolic process where organic molecules are condensed into degradation-resistant organic polymers, which may persist almost unaltered for decades or even centuries.
Decomposition is essentially a biological process. Nutrients taken up by plants are derived largely from the decomposition process. Micro-organisms are by far the major contributors to soil respiration and are responsible for 80-95 percent of the total carbon dioxide (CO2) respired and, consequently of the organic C respired (Satchell, 1971; Lamotte, 1989). Therefore, decomposition is a process determined by the interactions of three factors: organisms, environmental conditions (climate and minerals present in the soil); and the quality of the decomposing resources (Swift, Heal and Anderson, 1979; Anderson and Flanagan, 1989).
These factors operate at different spatial and temporal scales (Lavelle et al., 1993). Living organisms are made up of thousands of different compounds. Thus, when organisms die, there are thousands of compounds in the soil to be decomposed. As these compounds are decomposed, the organic matter in soil is gradually transformed until it is no longer recognizable as part of the original plant. The stages in this process are:
- Breakdown of compounds that are easy to decompose, e.g. sugars, starches and proteins.
- Breakdown of compounds that take several years to decompose, e.g. cellulose (an insoluble carbohydrate found in plants) and lignin (a very complicated structure that is part of wood).
- Breakdown of compounds that can take up to ten years to decompose, e.g. some waxes and the phenols. This stage also includes compounds that have formed stable combinations and are located deep inside soil aggregates and are therefore not accessible to soil organisms.
- Breakdown of compounds that take tens, hundreds or thousands of years to decompose.
These include humus-like substances that are the result of integration of compounds from breakdown products of plants and those generated by microorganisms. The easily decomposable sugars, starches and proteins are quick and easy for fungi and bacteria to decompose, hence the C and energy they provide is readily available. Most of the microbes living in the soil can secrete the enzymes needed to break up these simple chemical compounds.
The larger mites and small soil animals often help in this first stage of degradation by breaking up the organic matter into smaller pieces, thereby exposing more of the material to colonization by bacteria and fungi. Some of the energy or nutrients released by the breakdown of molecules by enzymes can be used by the bacteria and fungi for their own growth. For example, when an enzyme stimulates the breakdown of a protein, a microbe may be able to use the C, N and S for its own physiological processes and cell structure. If there are nutrients that the microbes do not use, they will be available for other soil organisms or plants to take up and use. When microbes die, their cells are degraded and the nutrients contained within them become available to plants and other soil organisms. The second stage of decomposition involves the breakdown of more complicated compounds by many fungal and bacteria species. These compounds take longer to decompose because they are larger and are made up of more complicated units. Specific enzymes, not commonly produced by most micro-organisms, are required to break down these compounds. Decomposition only takes place where conditions are suitable. Abiotic conditions have a considerable effect on the rate of breakdown. There must be some moisture available, soil temperatures must be suitable (usually between 10 and 35 °C) and the soil must not be too acidic or alkaline. Decomposition also occurs at higher temperatures, as in composts, or under waterlogged conditions through anaerobic processes. Thus, the types of organisms involved in breaking down the organic matter also depend on the conditions.
The type of organic matter, the way it is applied or incorporated into soil and the way it is decomposed influence the physical, chemical and biological balances in the soil and determine the various impacts. It can change: A. amount of N available to plants; B. amount of other nutrients available; C. how the soil binds together (soil aggregation); D. number and type of organisms present in the soil. Micro-organisms can access N in the soil more easily than plants. This means that where there is not enough N for all the soil organisms, the plants will probably be N deficient. When soils are low in organic matter content, application of organic matter will increase the amount of N (and other nutrients) available to plants through enhanced microbial activity. The number of microbes in the soil will also multiply, as they can use the organic matter as a source of energy. Where the number of fungi and bacteria associated with the breakdown of organic matter increases, there may be some improvements to the soil structure. Adding organic matter can also increase the activity of earthworms, which in turn can also improve soil aggregation.
In Summary, using biological approaches to agriculture production and protection restores the land and ecosystem while providing for societal needs. Water is the life blood of all living things and systems. Everything is connected to our hydrological system. These benefits improve bottom-line profitability for the current farmer and provides for generation to come: Reduced input costs: reduced fertilizer needs owing to improved nutrient cycling and reduced leaching from the root zone; reduced pesticide needs owing to pest-predator interactions among organisms and natural biocontrol; reduced tillage costs owing to reliance on biotillage by macrofauna under conservation agriculture approaches. Improved yield and crop quality: soil organic matter and soil biodiversity contribute to improved soil structure, root growth and mycorrhizal development, access to water and nutrients and hence improved root and tuber development and aboveground plant production. Improved soil and crop health reduce impacts of disease-causing organisms (pathogens and viruses and harmful bacteria). Pollution prevention: soil organic matter enhances biological activity of soil organisms that detoxify and absorb excess nutrients that would otherwise become pollutants to groundwater and surface water supplies. Soil organic matter is an important means of C sequestration, and organic matter management practices contribute to C storage (up to 0.5 tonnes/ha/year) and reduced greenhouse gas emissions. The living, breathing, ever-changing soil is a complex system that we have interrupted, stifled, and damaged while increasing demands for food, fiber and fuel for societal needs. We must begin to repair and replace what we have taken and allow that healing to begin.