Vol.5 (2), pp. 65-76, February 2017 ISSN 2354-4147 International Standard Journal Number (ISJN) e-ISJN: A4372-2604 Article Number: DRJA293117601 Copyright © 2017 Author(s) retain the copyright of this article Direct Research Journal of Agriculture and Food Science http://directresearchpublisher.org/aboutjournal/drjafs
Review
Evaluation on living organisms and their effects on soil fertility maintenance
Ibigweh, M. N*. and Asawalam, D. O.
Department of Soil Science and Meteorology, Michael Okpara University of Agriculture, Umudike. PMB 7267, Umuahia, Abia State, Nigeria. *Corresponding author E-mail: [email protected] , [email protected].
Received 1 December 2016; Accepted 6 January, 2017
Soil is a habitat of the most diverse assemblages of living interest in maintenance of soil ecosystems and monitoring organisms. Living organisms in the soil environment of soil health is growing. As the biological activities of the includes bacteria, fungi, protozoa and micro and macro soils are intimately linked with soil fertility maintenance flora and fauna which contribute to the maintenance and and productivity, sound understanding of various aspects productivity of agro-ecosystems. These organisms are of these soils flora and fauna in the maintenance of soil involved in major soil process, such as nutrient cycling, fertility in crop production systems and clean-up of biological pest control, and stabilization of soil aggregates environment is vital. Effective ways of promoting this and mixing of organic and mineral substance, formation microbial activity in agro-ecosystems include conservation and maintenance of soil structure and degradation of tillage, crop rotation, proper nutrient management and agrochemicals and pollutants. These activities positively application of organic manure. These processes should be influence the physicochemical properties of soil and practiced to foster the development of healthy and diverse consequently soil fertility and quality. But in the present communities of living organisms, improve soil health and day high intensity agricultural production systems, more food/crop production. Therefore the paper reviews on emphasis is placed on application of fast reactive chemical various living organisms and their effects on soil fertility fertilizers, pesticides and herbicides leading to imbalance in maintenance. the sensitive soil ecosystem, decline and deterioration in soil fertility and environment. This decline in soil fertility and inadequate response of chemical fertilizers (i.e. inputs) Key words: living organisms, soil fertility and maintenance, in terms of the output on account of deterioration in soil flora, fauna. health is recognised as a major problem of recent times. So
INTRODUCTION
Within the soil, is one of the most diverse assemblages of action of worms with observations on their habits.” Since living organisms (Giller et al., 1997). The role of living then, several studies have been undertaken to highlight organisms in soil fertility is known since 1881, when the soil living organisms contribution to the sustainable Darwin (1809–1882) published his last scientific book function of all ecosystems (Bhadauria and Saxena, entitled “The formation of vegetable mould through the 2010). Direct Res. J. Agric. Food Sci. 66
Soil fertility changes and the nutrient balances are period of soil inhabitation habitat preference or biological taken as key indicators of soil quality (Jansen et al., activity. 1995). Soil fertility is commonly defined as the inherent They state that feeding and locomotion are the other capacity of a soil to supply plant nutrients in adequate two main activities that divide the organism in the amounts, forms, and in suitable proportions required for different groups. Based on locomotion the soil animals maximum plant growth (Von Uexkuell, 1988). Soil quality can be distinguished as burrowing ones from the other has been defined as the capacity of the soil to function that move on the soil surface or through the pore spaces/ within ecosystem and land use boundaries, to sustain channels/cavities in the soil. In terms of feeding activity biological productivity, maintain environmental quality and the soil animals can be classified into five major groups. promote plant, animal and human health (Doran et al., They also classified living organisms on the basis of 1996). High quality soils not only produce better food and kingdom. All living things can be classified into one of the fibre, but also help establish natural ecosystems and five fundamental kingdoms of life namely; Moriera, enhance air and water quality (Griffiths et al., 2010). Protista, Fungi, Plantae, Animalia and are well The fertility of soil is central to the sustainability of both represented in soil ecosystem, natural and managed ecosystems (Sharmila et al., 2008). The natural ecosystems maintain their production through (i) Kingdom Moriera: includes prokaryotes-single cell well balanced above and below ground biological organisms that do not possess nucleus e.g bacteria, processes which serve to conserve the nutrients, water actinomycetes and blue green algae. and soil organic matters within the systems. Swift and (ii) Kingdom Protista: include single cell organisms that Anderson (1993), stated that in natural ecosystems, the do possess nucleus e.g nucleated algae and slime internal regulation of functions is largely a result of plant modules. biodiversity that influence the magnitude of and temporal (iii) Kingdom fungi: These non-motile eukaryotes lack distribution of carbon and nutrient flows; however, this fragella and developed spores like yeast, moulds, and form of control is increasingly lost through agricultural mushrooms. intensification which undoubtedly has degraded soils. (iv) Kingdom Plantae: these eukaryotes develop from The major processes that contribute to soil fertility decline embryos and use chlorophyll like mosses and vascular includes decline in soil organic matter and biological plants. activities, degradation of soil structure and loss of other (v) Kingdom Animalia: the multicellular eukaryotes soil physical qualities, reduction in availability of major develop from a blastula (a halo ball of cells). nutrients (N.P.K) and micronutrients and increase in toxicity due to acidification and pollution (FAO, 2001). The community of living organisms that lives in soil will ACTION OF DIFFERENT ORGANISMS play many important roles in the successful functioning of agricultural ecosystems. Therefore, this review is aimed Soil organisms are very important in agriculture because to identify various living organisms and their effects on they mediate many beneficial processes that include soil fertility maintenance. recycling of plant nutrients: nutrients like nitrogen, phosphorus and sulphur which occur mostly as organic compounds (in manures, compost, crop residues, soil CLASSIFICATION OF ORGANISMS organic matter e.t.c) that are not available for plant uptake. During decomposition, soil organisms break The modern studies have shown that living organisms these compounds and convert the nutrients into inorganic can be broadly classified into two radically different kinds, forms that plant can uptake through their root systems. prokaryotes (less complex cell structure) and eukaryotes Meeting some crop nutrients requirements through (organisms with true nucleus), which further divided into recycling reduces the need for fertilizers (Newton and many other forms. The free-living components of soil Chantal, 2010). According to Adekunle and Dafiwhare biota are bacteria, fungi, algae, actinomyotes and the (2011), microbes (bacteria, Achaea, fungi and protozoa) fauna (Sharmilia et al., 2008) (Tables 1 and 2). According are very important in all processes related to soil function. to Edmundo, (2007) soil organisms have been classified The microbial constituents of soil are entirely responsible on the basis of body width into microflora (1-100µm, e.g for breakdown of organic matter and degradation of toxic bacteria, and fungi), micro fauna (3-120 µm, e.g molecules. Microorganisms are also responsible for the protozoa, and nematodes), mesofauna (80 µm – 2 mm, mineralization process in the forest ecosystem. They act e.g collembolan, acari) and macro fauna (500 µm-50 mm, on the humus to release carbon dioxide (CO 2), water and e.g earthworms, termites) and vascular plants. Sharmilia nutrients which could be absorbed directly by plants. The et al. ( 2008) stated that organism may be grouped either actions of microbes were summarized by Hoff et al. on the basis of body width viz; micro, meso and macro (2004) to include degradation of complex nutrient sources organisms or on the basis of functional groups viz, extra-cellular, transportation of simple nutrients across mycophagous/herbivores, omnivores and predators, cell membranes for metabolic processes and tolerating or Ibigweh and Asawalam 67
Table 1. Classification of soil biota based on body size.
Organism Size (mm) Examples Micro flora <1 Bacteria, Algae, Fungi, Actinomycetes Micro fauna <2 Protozoa, Nematodes Meso fauna 2-10 Collembolan, acarine Macro fauna >10 Earthworms, termites, snails, arachimds
Source: Sharmilia et al., 2008.
Table 2. Classification of soil fauna based on their activity.
Organism Activity Carnivores Predators, animal parasites Phytophagus Above ground green plant material, root systems and wood material Sarcophagus Caprophagus, xylophagus, Necrophagus and detrivores. Symbionts VAM and Endophytes Microphytic feeder Fungal hyphae, spores, algae, lichens, bacteria feeder. Miscellaneous feeders Omnivores (food varies from site to site)
Source: Sharmila et al., 2008.
deactivation of compounds that could inhibit fungal substance or by effectively expanding the surface area of growth. According to Rigobelis and Nahas, (2004) the plants roots. most important soil nutrient supply to the forest soil Pioneer organisms such as lichens, mosses and environment is the one derived from litter decomposition liverworts, subsequently colonizes the substrate, further by action of organism under condition of high air breaking down the rock and incorporating detritus and temperature and soil moisture content. These organisms organic compounds formed through photosynthesis and mobilized the chemical elements in the litter and make nitrogen fixation (Thomas, 2013). In the process, they them re-absorbable by plant roots. They are able to stabilize and moderate the micro-environment, creating perform these because of their ability to obtain nutrients conditions favourable for later colonizers, eventually through absorption. resulting in the establishment of higher plants and Larger soil organisms consume organic residue. They invertebrate animals. break it down into smaller pieces which allow bacterial Plants usually absorb nutrients from the soil during and fungi to work more efficiently. Bacteria, fungi and growth and return them through their litter (leaf-fall), other microscopic organisms decompose the dead plant which decomposes to release the nutrients, rendering residue and increase the organic matter contained in the them available for reabsorption by the plants (Ojo et al., soil (ALBA, 2012). 2011). Plant roots exude compounds such as amino The mineralizers split complex and large plant acids, simple sugar and organic acids. These compounds molecules (e.g cellulose, hemicellulose, lignin) into provide a continuous energy to microorganisms living in smaller molecules (e.g sugars, amino acids, aromatics, the root zone (the rhizosphere) (McBrayer, 1973). aliphatics), simpler mineral forms (e.g ammonium and The animals which have had a considerable effect on nitrate) and nitrate, nitrogen, carbon dioxide, water, soil development are macro invertebrates (macro fauna). sulphate) (Killham, 1994), important groups include the They influence soil processes, which may affect both nitrifying bacteria (Nitrosolobus, Nitrobacter, physical and chemical fertility of soils and contribute to Nitrosomonas) that are involved in the conversion of the maintenance and productivity of ecosystems (Lavelle ammonium to nitrate. Another group of organisms is most and Pashanasi, 1989). Soil macro invertebrate (macro active under poorly aerated conditions, such as when fauna) maintain soil physical, chemical and biological soil soils are flooded or poorly drained or when the demand fertility by immobilization, humification, biocontrol for oxygen is greater than what can be supplied by processes and serve as decomposers as well as soil diffusion through air-filled pores. Denitrifying bacteria engineer to encourage crop production (Sugiyarto, 2009), converts nitrates to forms of nitrogen that are lost to the examples include ants, termites, millipedes, centipedes atmosphere as nitrogen gas or nitrous oxide. Fermenters beetles, spiders, earthworms e.t.c (Jeff and Shannon, such as yeast and certain bacteria decompose organic 2002) and they break up organic matter increasing it materials under anaerobic conditions, often forming foul- surface area and thereby enhancing microbial activity smelling substances. Other groups of organisms such as and nutrients cycling. Soil macro fauna mix and mycorrhizal fungi make phosphorus more accessible to redistribute mineral and organic material and plants either by dissolving complex phosphorus-bearing microorganisms within the profile. According to Werner, Direct Res. J. Agric. Food Sci. 68
Decomposers
Fungi Molds Producers Consumers actinomycetes
Plantea Animalia
Protista Protozoa Monera Yeast Archaeobacteria Bacteria diatoms
Ancestral prokaryotes
Figure 1. Five living organisms and their mode of action. Source: Sharmilia, et al ., 2008.
(1993) when organisms are present in the soil, they include bacteria, archaea, fungi and protozoa which are stimulate the decomposition of cover crops residues. very important in all process related to soil function. Their feeding and burrowing activities incorporate Some of these processes include soil formation, soil residues and other amendments into the soil, enhancing structure, cycling of nitrogen, carbon, phosphorus and organic matter decomposition, humus formation, nutrients sulphur. Maha, (2013) illustrated that decomposers cycling and development of soil structure. Earthworm animals include protozoa, earthworms, micro arthropods burrows can persist, even after the worms responsible for such as mites and collembolan and macro arthropods building them are gone, providing pathways for rapid root such as insects, arachnids, millipedes, centipedes. growth, water infiltration and gas exchange. Ojo et al. (2011) ant and termites consumes and digest vast quantities of dead organic matter, with such efficiency Bacteria that they keep the soil surface almost bare of litter and decomposing organic matter. At this process, they Bacteria are the smallest and most abundant organisms transport considerable quantities of material from one in soil. They are free-living and the most interesting place to another. The fungus growing termites build their marvellous component of the soil microbial population. mound using soil and clay cemented by salivary Bacteria have been intensively studied and have added secretions which make the moulds enriched with clay significance because of their involvement in the nitrogen particles but impoverished in carbon (Muwawa et al., and carbon cycles and also in other cyclical 2014). They efficiently biodegrade plant biomass and transformations in soil, it is clear that bacteria are other lignocellulosic materials thereby contributing to the essential for soil fertility. The major contribution of global carbon and nitrogen cycles (DeSouza et al., 2009). bacteria is to decompose organic nitrogenous Also, their tunnelling activity improves gas exchange, compounds in plant and animal residues, with the water infiltration and root proliferation (Newton and ultimate liberation of ammonium and litter can be oxidized Chantal, 2010). to nitrate only by nitrifying bacteria. Chemoautotrophic bacteria are mainly responsible for such transformations (Mishra, 2010). ORGANISMS AND THEIR ROLES IN SOIL FERTILITY Another important contribution of bacteria is the MAINTENANCE nitrogen cycle. Certain bacterial species are unique in fixing atmospheric nitrogen in the form of ammonium Although some soil organisms cause plant diseases, nitrogen. Nitrogen can be fixed by bacteria either most soil habitants are beneficial to crop production and symbiotically, in which case they grow in the roots of the the environment through processes like the fixing and host plants and form nodules or by free living bacteria. cycling of nitrogen, biological pest control, formation and Azotobacter (aerobic) and clostridium (anaerobic) are the maintenance of soil structure and degradation of best known nitrogen fixers. Azotobacter is very common agrochemicals and pollutants (Newton and Chantal, in rhizophere region of plants and they maintain 2010), and they are particularly important for agriculture themselves on the root exudates. The plants rich in (Figure 1). According to Forsyth, (2009) these microbes Azotobacter population have been observed to grow Ibigweh and Asawalam 69
Plate 1. Nitrogen Cycle showing N-transformation by Living Organisms.
better. Besides nitrogen fixation, Azotobacter is also effective petroleum-degradation microbial strains in a useful to the host plant through the production of process called bioagumentation (Supaphol et al., 2006). gibberelins and possibly other growth hormones, which results in an increase crop yield due to bacterization, (Mishra, 2010) Fungi (Plate 1). Denitrification and sulphate reduction involve a variety of facultative and obligate anaerobic bacteria Fungi in the soil are associated with various types of (Rittman and McCarty, 2001). Nitrification and sulphur activities. They play a major role in the processes of oxidation, on the other hand, are the result of the activity humus formation and aggregate stabilization. They of a limited number of genera of aerobic autotrophic usually dominate in the upper horizons of the forested bacteria (Oren, 2009). soils as well as in acid or sandy soils. They carry out the Bacteria also play a significant role in destroying largest share of decomposition in many cultivated soils as hazardous contaminants or transform them to less well (Brady and Weil, 2008). According to Steffen and harmful form, in the soil and this process in known as Tuomela (2010), the natural environment for litter – bioremediation (Bioremediation Discussion Group, 2006). decomposing fungi is the top soil layer where they Bacterial inoculations (Straube et al., 2003) are degrade plant and animal litter material (debris). sometimes added to speed the remediation process. As Soil fertility depends in no small degree on nutrients indicated many hydrocarbons degrading bacteria can be cycling by fungi, since they continue to decompose found in soils and the common ones are Achromobacter, complex organic materials after bacteria and Acinetobacter, Actinomyces, Bacillus, Burkholderia, actinomycetes have essentially ceased to function. Soil Extiguobacterium, Klebsiella, Microbacteruim, Nocardia, tilth also benefits from fungi as their hyphae stabilize soil Pseudomonas, Spirillum, Streptomyces and Vibro. structure. In addition to the breakdown organic residues However, at petroleum hydrocarbon polluted sites, these and formation of humus, numerous other fungal activities populations may grow and increase because they use have significant impact on soil ecology. Some fungi are petroleum hydrocarbons as a carbon source (Mohanty predators of animals. For example, certain species even and Mukherjee, 2008). Bioremediation of petroleum trap nematodes (Brady and Weil, 2008). hydrocarbon-polluted soil relies on the petroleum The important part of the role of fungi in ecosystem is degradation ability of the microbial consortium resident in the capture of mineral nutrients. The growth of most the soil (Franzmann et al., 2002). Although petroleum plants is enhancing by the presence of mycorrihizal fungi. degradation microorganisms are widely distributed in Mycorrihizal fungi take up nutrients used by the plants, both soil and water, they may not be present in sufficient such as phosphorus (P) and Nitrogen (N) compounds numbers at a given polluted site. In such cases, it may be (Carlile et al., 2004). According to Phil et al. (2012), useful to inoculate the polluted area with highly mycorrihizal fungi form mutualistic associations with Direct Res. J. Agric. Food Sci. 70
Figure 2. Phosphorus Cycle showing P-transformation.
Table 3. Effects of mycorrhizal inoculation on P concentration in shoot and root, and total P uptake of different forage grass species.
P concentration in shoot P concentration in root Total P uptake Species -AM1 +AM1 (g/kg) -AM(g/kg) +AM (g/kg) -AM (mg/pot) +AM (mg/pot) BB2 0.37 1.27 0.44 0.88 0.86 3.60 BD 0.48 1.05 0.48 0.86 0.91 2.91 BH 0.47 1.20 0.44 0.92 1.53 3.24 PM 0.41 0.89 0.38 0.73 1.29 3.34
Treatment: -AM = no mycorrhiza applied, +AM = mycorrhiza applied. BB = B. Brazantha; BD = B. decumbens; BH = B. humidicola; PM = P. maximum. Sources: Keston, (2013).
plants roots, where the fungus derives carbon from the extensive and diverse group of Gram-positive, aerobic, host plant and forms extensive mycelia net-works through mycelial bacteria that play important ecological roles in soil absorbs P and transfer directly to the plant (Figure 2). soil nutrient cycling. In addition, they are known for their They are also able to explore and exploit considerably economic importance as producers of biologically active larger volume of soil per unit C than plant root. They also substances, such as antibiotics, vitamins and enzymes contribute humification and detoxification process in soil (de Boer et al ., 2005). Actinomycetes are also an (Singh, 2006). Keston, (2013) also found positive important source of diverse antimicrobial metabolites mycorrihizal effects on shoot P concentrations and shoot (Terkina et al ., 2006). Soil actinomycetes particularly biomass of Streptomyces sp. enhance soil fertility and have grasses such as Bromus spp. and Festuca spp. antagonistc activity against wide range of soil borne plant Water uptake may also be improved by mycorrihizae pathogens (Aghighi et al ., 2004). They are one of the making plants more resistant to draught. According to major components of the microbial populations present in Valentin et al. (2009), fungi might be more suitable for soil (Tables 4 and 5). bioremediation applications because of their better ability In forest ecosystem, much of the nitrogen supplied to grown in the soil. Oil degrading fungi and yeast depends on certain actinomycetes that are capable of include; Alluescheria, Aspergillus, Candid, Debayomyces, fixing atmospheric nitrogen gas into ammonium nitrogen Mucor, Penicillium, Saccharommyces and Trichoderma that is then available to higher plants (Brady and Weil, (Table 3). 2008). They are undoubtedly of great importance in the decomposition of soil organic matter and liberation of its nutrients. They reduce even the more resistant Actinomycetes compounds, such as cellulose, chitin and phospholipids, to simpler forms and play a role in the final stage of Actinomycetes are one of the major components of the composting. They are much diffused in the soil and microbial populations present in soil. They belong to an synthesize vitamins, siderophores, amino acids and Ibigweh and Asawalam 71
Table 4. Dry Matter yield, P Concentration and P Uptake of Jatropha Grown in Libertad and Luisiana Clay as affected by AM Inoculation and P Application.
Dry weight (gm) P Concentration (g/100g) P Uptake (mg/plant) TREATMENT shoots roots shoots roots shoots roots Libertad clay +AM+P 5.77 2.33 0.56 0.34 32.5 7.9 +AM -P 4.69 1.85 0.41 0.24 19.1 4.5 -AM+P 3.77 1.50 0.41 0.28 15.4 4.2 -AM -P 2.40 0.87 0.07 0.05 1.7 0.4 Luisiana clay +AM+P 7.72 3.13 0.63 0.36 48.64 11.27 +AM -P 6.29 2.21 0.48 0.22 30.19 4.86 +AM -P 5.73 1.98 0.52 0.28 29.8 5.54 -AM -P 3.60 1.12 0.09 0.06 3.24 0.67
Source: Ultra, Jr. (2010).
Table 5. Effects of Actinomycete strains on Mycorrhiza Formation and Biomass Production by Trifolium repens L. Plants Growing during 6 month under Greenhouse Conditions.
Root biomass production Shoot biomass production (mg[dry wt]) Mycorrhizal root length (%) (mg[dry wt]) Control (none) 96 22 15 Glomus sp. 185 36 58 Streptomyces MCR9 189 46 10 MCR9+ Glomus sp. 605 47 69 Thermobifida MCR24 252 35 4 MCR24+ Glomus sp. 584 54 73 Streptomyces MCR26 210 41 3 MCR26+ Glomus sp. 506 68 68
Source: Franco-Correaa et al., 2010
organic acids, useful for plant growth, and antibiotics, as carbon source, supply roots with easily assimilable such as streptomycin and chloramphenicol, against some nitrates and play a key role in the biological control of root soil-borne root pathogens. According to Franco-Correa pathogens and in the maintenance of soil health et al . (2010), inoculation of clover plants with either of the (Govaerts et al. , 2007). selected actinomycetes enhanced plant growth and N acquisition. Co-inoculation of actinomycetes and Glomus mosseae produced synergic benefits on plant growth. Macro and micro flora They also state that actinomycete strains have the ability of solubilizing sparingly available inorganic P sources or These are large (high) and microscopic (small) plants mineralizing some P from the organic P sources in soil. which include algae (cyanobacteria), mosses, fern, The secretion of acid phosphatase indicated that some liverwort, lichen, grasses, vascular plants e.t.c. Blue- actinomycete strains would be able to mineralize organic Green Algae (Cyanobacteria) are one of the major P sources (Richardson et al ., 2009). Actinomycete also components of the nitrogen fixing biomass in paddy fields can improve both shoots and roots biomass and dominant nitrogen-fixer blue-green algae are accumulation. Anabaena, Nostoc, Aulosira, Calothrix, Plectonema etc. These actinomycetes can be considered as Mycorrhiza The blue green algae (cyanobacteria) are capable of Helper Bacteria because they may promote the fixing the atmospheric nitrogen and convert it into an mycorrhizal colonization rate at different stages of available form of ammonium required for plant growth bacterium–fungus–plant interactions, including spore and other positive effects for plants and soil ( Sahu et al., germination (Tarkka and Frey-Klett, 2008), and 2012 ). They are well adapted to a wide range of particularly by Streptomyces species (Schrey et al ., environmental conditions and have been widely 2005). Soil actinomycetes particularly Streptomyces employed as inoculants for enhancing soil fertility and species enhance soil fertility and have antagonistic improving soil structure, besides enhancing crop yields, activity against wide range of soil borne plant pathogens especially in rice (Dhar et al ., 2007). Cyanobacteria also (Aghighi et al ., 2004). Moreover, fungi and actinomycetes add organic matter, synthesize and liberate amino acids, are able to colonize rhizosphere and use root exudates vitamins and auxins, reduce oxidizable matter content of Direct Res. J. Agric. Food Sci. 72
Table 6 . Effects of algae on plant and some soil physical properties.
Sample Control Treatment Control/Treatment (%) Plant height (cm) 13 20 65 Roots length (cm) 3 5 60 Weight of fresh leaf and stem (g) 0.17 0.27 62 Weight of fresh root (g) 0.26 0.47 55 Weight of dry leaf and stem (g) 0.04 0.09 44 Weight of dry root (g) 0.06 0.15 40 Moisture (%) 25 30 83 Bulk density (g/ml) 1.68 1.53 109 Particle density (g/ml) 1.95 1.86 104 Porosity (%) 14 18 77
Source: Saadatnia and Riahi, (2009).
the soil, provide oxygen to the submerged rhizosphere, appears to play a more important role in how soil biota ameliorate salinity, buffer the pH, solubilize phosphates function, and does promote other ecosystem service and increase the efficiency of fertilizer use in crop plants including soil structure, water retention, biodiversity, and (Kaushik 2004), increase in water holding capacity carbon and nitrogen storage (Phil et al ., 2012). through their jelly structure (Roger and Reynaud, 1982), High plants usually absorb nutrients from the soil during increase in soil biomass after their death and growth and return them through their litter (leaf-fall), decomposition, decrease in soil salinity, preventing which decomposes to release the nutrients, rendering weeds growth (Saadatnia and Riahi, 2009), increase in them available for reabsorption by the plants (Ojo et al., soil phosphate by excretion of organic acids (Wilson, 2011). Plants directly influence the soil community by 2006). their root growth and plant cover (Figure 3). The majority Azolla (fresh water fern), a free floating aquatic fern of microorganisms found in the soil are associated with found in ponds, flooded rice fields and other still fresh plants roots that provide them with carbon and other waters is used as an N-biofertilizer for wetland rice nutrients such as nitrogen fixing trees and shrubs known because of its ability to fix atmospheric N in symbiosis as “fertilizer tree systems” (Table 7). The “fertilizer tree” with N 2-fixing blue-green algae (Table 6). Other role of system is an agroforestry technology in which azolla as a biofertilizer includes reduction in NH 4-N loss leguminous trees or woody shrubs are grown and the by volatalization (Chu and Bo-qi, 1988). Anabaena in biomass used to replenish the fertility of soils. The association with water fern Azolla contributes nitrogen up planted leguminous species replenish soil fertility by to 60 kg/ha/season and also enriches soils with organic transforming atmospheric nitrogen and making it matter (Sahu et al., 2012). Anabaena and Nostoc are available in the soil. The cycle begins by planting tree found to fix large amount of atmospheric nitrogen (up to species as a pure stand (fallow) or intercropped with food 20 - 25 kg/ha). Blue green algae belonging to genera crops in the first year. The trees are allowed to grow for Nostoc, Anabaena, Tolypothrix and Aulosira fix about two years after which they are cut and the biomass atmospheric nitrogen and are used as inoculants for incorporated into the soil during land preparation. The paddy crop grown both under upland and low land trees’ leaf and root biomass decomposes and releases conditions. nutrients for crops planted in the plot over the next two to Pioneer organisms such as lichens, mosses and three years. The most common species used in “fertilizer liverworts, subsequently colonizes the substrate, further tree systems” are Sesbania sesban , Gliricidia sepium, breaking down the rock and incorporating detritus and Tephrosia vogelli , Tephrosia candida and pigeon pea organic compounds formed through photosynthesis and (Akinnifesi et al. , 2007, 2009). nitrogen fixation (Thomas, 2013). In this process, they stabilize and moderate the micro-environment, creating conditions favourable for later colonizers, eventually Macro and micro fauna resulting in the establishment of higher plants and invertebrate animals. Soil fauna come in a variety of shapes and sizes and play Grass production is the ultimate ecosystem service, in a variety of role in soil development and the maintenance which the maintenance of soil structure, water regulation, of soil fertility (Jeff and Shannon, 2002). Fauna in soil and particularly nutrient supply play prominent role include hair like worms called nematodes, snails, slugs, (Hoogerkamp et al., 1983). Fin grass roots and insect larva, beetles, ants, termites, spiders, earthworms, consequently the rhizosphere around them, have an protozoans, micro anthropods such as mites and important positive effect on soil structure, latter also collemblolan and macro anthropods such as insects, improve water infiltration. The introduction of legume arachnids millipedes and centipedes (Newton and Ibigweh and Asawalam 73
Table 7. Estimates of the amount of Nitrogen Biologically Fixed by some grain Legume.
Grain legum N fixed Kg ha -1 Time period (days) Country 152 – 189 118 - 137 India Groundnuts ( Arachis hypogea ) 101 - Ghana 150 – 166 - India Pigeon pea ( Cajanus cajan ) 13 – 163 120 Malawi 67 – 85 170 Australia Chickpea ( Cicer arietinum ) 35 – 80 - Nepal 85 – 154 110 Brazil Soybean ( Glycine max ) 15 – 170 - Nepal 25 – 65 60 - 90 Brazi Common bean ( Phaseolus vulgaris ) 8 – 26 75 Tanzania 9 – 51 110 Brazil Cowpea ( Vigna unguiculata ) 47 – 105 66 Nigeria
Sources: Keston, (2013).
Figure 3. Cyclic interactions between plant/roots, soil biota (root biota, decomposers and ecosystem engineers) and soil properties (chemical and physical). Source: Phil et al., (2012).
Chantal, 2010; Maha, 2013; Jeff and Shannon, 2002). may become incorporated into nest soil, undergoes They are illustrated as decomposers animals. They decomposition and mineralization by the microflora, influence soil processes, which may affect both physical leading to an accumulation and local concentration of and chemical fertility of soils and contribute to the nutrients (P ętal, 1978). maintenance and productivity of ecosystems (Sugiyarto, The burrowing by arthropods, particularly the 2009). Soil macro invertebrate (macro fauna) maintain subterranean network of tunnels and galleries that soil physical, chemical and biological soil fertility by comprise termite and ant nests, improves soil porosity to immobilization, humification, biocontrol processes and provide adequate aeration and water-holding capacity serve as decomposers as well as soil engineer to below ground, facilitate root penetration, and prevent encourage crop production (Larvelle et al., 1994), and surface crusting and erosion of topsoil. Also the they break up organic matter increasing its surface area movement of particles from lower horizons to the surface and thereby enhancing microbial activity and nutrients by ants and termites aids in mixing the organic and cycling. Soil macro fauna mix and redistribute mineral mineral fractions of the soil. The faeces of arthropods are and organic material and microorganisms within the the basis for the formation of soil aggregates and humus, profile (Jeff and Shannon, 2002). which physically stabilize the soil and increase its Large amounts of organic matter from plant and animal capacity to store nutrients (Thomas, 2013). (prey, carrion) sources accumulate in refuse dumps Earthworms are recognized as a key factor in the way within nests. This material, combined with metabolic many terrestrial ecosystems work (Bartlett et al., 2010). wastes and secretions from the ants themselves, which Earthworms are a major component of soil fauna Direct Res. J. Agric. Food Sci. 74
Plate.2. Anthill of termite with termites mixing the soil with organic matter and creat e their own living conditions near their preferred food sources.
Plate3. Common garden earthworm performing its role and a root following the pa thway opened by the earthworm.
communities in most ecosystems and comprise a large management practices (Bhadauria and Saxena, 2010). proportion of macrofauna biomass. Their activity is Earthworm burrows can persist even after the worms beneficial because it can enhance soil nutrient cycling responsible for building them are gone, providing through the rapid incorporation of detritus into mineral pathways for rapid root growth, water infiltration, and gas soils. In addition to this mixing effect, mucus production exchange. Deep-burrowing species can burrow associated with water excretion in earthworm guts also through compacted soil and penetrate plow pans. enhances the activity of other beneficial soil microorganisms. This is followed by the production of organic matter. So, in the short term, a more significant OPTIMIZING THE USE OF LIVING ORGANISMS IN effect is the concentration of large quantities of nutrients THE MAINTENANCE OF SOIL FERTILITY (N, P, K, and Ca) that are easily assimilable by plants in fresh cast depositions. In addition, earthworms seem to For optimum plant growth and microbial health, nutrients accelerate the mineralization as well as the turnover of must be available in sufficient and balanced quantities. soil organic matter. Earthworms are known also to The most important constraint limiting crop yield in increase nitrogen mineralization, through direct and developing nations worldwide, and especially among indirect effects on the microbial community. The resource-poor farmers, is soil infertility (Mohammadi and increased transfer of organic C and N into soil Sohrabi, 2012). aggregates indicates the potential for earthworms to Learning how to manage soil biological processes may facilitate soil organic matter stabilization and be a key step towards developing sustainable agricultural accumulation in agricultural systems, and that their systems and soil fertility (Plates 2 and 3). Many influence depends greatly on differences in land techniques are available which includes producing green Ibigweh and Asawalam 75
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