Nutrients & Supplements Topics
In , Underwood and Marston independently discovered the necessity of cobalt. Required for production of many enzymes, supports the immune system, improves antibody response, regulates white blood cells, aids protein digestion, is important for skin and coat health, protects the liver from heavy metal and copper damage. Evidence from the Framingham Offspring Study suggests that the prevalence of vitamin B12 deficiency in young adults might be greater than previously assumed [ 15 ]. In the s, William Cumming Rose identified essential amino acids , necessary protein components that the body cannot synthesize. However, the FDA does not require food labels to list magnesium content unless a food has been fortified with this nutrient.
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Hence, casts are large in size, towerlike, and made of superposed layers of different ages, the older i. Casts produced by anecic earthworms have a higher proportion of organic matter, especially large particles of plant material, and a larger proportion of small mineral components than in the surrounding soil.
Earthworms construct burrows or galleries Plate A1. The type and size of the galleries depends on the ecological category of earthworm that is producing it. Anecic earthworms create semi-permanent subvertical galleries, while endogeic worms dig rather horizontal burrows. These galleries may be filled with casts, which can be split into smaller aggregates by other smaller earthworms or soil organisms.
Galleries are cylindrical and their wall area coated with cutaneous mucus each time the worm passes through. Soil micro-organisms bacteria are markedly concentrated at the surface of the gallery walls and within the adjacent 2 mm of the surrounding soil.
This microenvironment comprises less that 3 percent of the total soil volume but contains percent of the whole soil microflora and is where some functional groups of bacteria predominate Lavelle and Spain, Root hairs are attached to the cast where higher availability of nutrients C, N and P exists compared with the surrounding soil. Termite mounds are among the most conspicuous structures in savannah landscapes. Termite mounds are of diverse types and are the epigeal part of a termite nest that originates from subterranean beginnings.
In Africa, termites build up half of the biomass of the plains. Termites process high quantities of material in their building activities, thus influencing the soil properties as compared with surrounding soils Lee and Wood, Soil texture and structure are modified strongly in termite mounds. In general, the soil of the termite mounds exhibits a higher proportion of fine particles clay , which termites transport from the deeper to upper soil horizons.
Although not generally considered soil organisms, roots grow mostly within the soil and have wide-ranging, long-lasting effects on both plant and animal populations aboveground and belowground, and thus they are included among soil biota.
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 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. Earthworm galleries burrows provide an easy pathway for roots to take as they grow through the soil Plate A1. 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 that may be affected include:.
However, other soil organisms are detrimental or harmful to plant production. For example ants, aphids and phytophagous nematodes can be serious pests, and some micro-organisms, bacteria and actinomycetes cause also plant diseases. However, most damage is caused by fungi, which account for most soil-borne crop diseases. Humans generally begin their influence on soil biodiversity with naturallypresent communities at a particular site resulting essentially from ecological and evolutionary forces.
However, they also have the ability to introduce new organisms and, through imposition of different management practices, put selective pressures on the naturally present or introduced soil biota. This provides the opportunity to manage soil organisms and their activities in order to enhance soil fertility and crop growth.
Although probably enough is known in theory to manage these communities, considerable basic and applied research is required in order to achieve appropriate levels of biological husbandry and optimal management of these biological resources. Effects of earthworms on plant production. Earthworm management in tropical agroecosystems, pp.
Soil nutrient transformations in the rhizosphere via animal-microbial interactions. Guidelines and reference material on integrated soil and nutrient management and conservation for farmer field schools.
Interactions of bacteria, fungi and their nematode grazers: Strategies de reproduction chez les vers de terre. Dordrecht, Netherlands, Kluwer Academic Publishers. Food resources and diets of soil animals in a small area of Scots Pine litter.
Les bases de la production vegetale. Tome 1, Le Sol. Collection sciences et techniques agricoles. Decomposition in terrestrial ecosystems. The soil coleoptera community of a ropical grassland from Laguna Verde, Veracruz Mexico.
The agricultural importance of termites in the tropics. Role of nematodes in decomposition. Nematodes in soil ecosystems, pp. Organic matter affects both the chemical and physical properties of the soil and its overall health. Properties influenced by organic matter include: 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, 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.
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. In one year experiment in Brazil, such practices resulted in a percent increase in microbial carbon biomass and a percent increase in microbial N biomass Figure A2.
The roots of most plants are infected with mycorrhizae, fungi that form a network of mycelia or threads on the roots and extend the surface area of the roots. In undisturbed soil ecosystems, e. 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.
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: 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 Figures A2.
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. 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. 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 Figure A2.
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 acidsensitive 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.
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 Figure A2. 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 rootdwelling bacteria. After nine years, no tillage in combination with the intensive cropping system had resulted in a 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, Calegari and Alexander noted that the P content both inorganic P and total P of the surface layer 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 Figure A2.
Three to five years after initiating an intensified production system, both P and potassium K can be accumulated in the topsoil. On the other hand, where direct seeding is practised and the crop residues are left on the surface, 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.
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:. The effects of the management practices depend largely on the agroclimatic situation as temperature and moisture influence speed of decomposition and general cycling of organic matter and nutrients.
Improved yield and crop quality: Improved soil and crop health reduce impacts of disease-causing organisms pathogens and viruses and harmful bacteria.
Soil organic matter is an important means of C sequestration, and organic matter management practices contribute to C storage up to 0. 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.
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. 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, 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 percent of the total carbon dioxide CO 2 respired and, consequentl,y of the organic C respired Satchell, ; Lamotte, Therefore, decomposition is a process determined by the interactions of three factors: These factors operate at different spatial and temporal scales Lavelle et al.
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 take several years to decompose, e. Breakdown of compounds that can take up to ten years to decompose, e. 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. Food Sources of Vitamin E ranked by milligrams of vitamin E per standard amount; also calories in the standard amount. Food Sources of Iron ranked by milligrams of iron per standard amount; also calories in the standard amount. Iron mg Calories Clams, canned, drained, 3 oz Non-Dairy Food Sources of Calcium ranked by milligrams of calcium per standard amount; also calories in the standard amount.
The bioavailability may vary. Some plant foods have calcium that is well absorbed, but the large quantity of plant foods that would be needed to provide as much calcium as in a glass of milk may be unachievable for many.
Many other calcium-fortified foods are available, but the percentage of calcium that can be absorbed is unavailable for many of them.
Food Sources of Calcium ranked by milligrams of calcium per standard amount; also calories in the standard amount. Food Sources of Magnesium ranked by milligrams of magnesium per standard amount; also calories in the standard amount.
Food Sources of Dietary Fiber ranked by grams of dietary fiber per standard amount; also calories in the standard amount. Foods are from single nutrient reports, which are sorted either by food description or in descending order by nutrient content in terms of common household measures.