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: nwabugwu2004@yahoo.com, degreatnwabugwu@gmail.com.

Received 1 December 2016; Accepted 6 January, 2017

Soil is a habitat of the most diverse assemblages of living

organisms. Living organisms in the soil environment

includes bacteria, fungi, protozoa and micro and macro

flora and fauna which contribute to the maintenance and

productivity of agro-ecosystems. These organisms are

involved in major soil process, such as nutrient cycling,

biological pest control, and stabilization of soil aggregates

and mixing of organic and mineral substance, formation

and maintenance of soil structure and degradation of

agrochemicals and pollutants. These activities positively

influence the physicochemical properties of soil and

consequently soil fertility and quality. But in the present

day high intensity agricultural production systems, more

emphasis is placed on application of fast reactive chemical

fertilizers, pesticides and herbicides leading to imbalance in

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)

in terms of the output on account of deterioration in soil

health is recognised as a major problem of recent times. So

interest in maintenance of soil ecosystems and monitoring

of soil health is growing. As the biological activities of the

soils are intimately linked with soil fertility maintenance

and productivity, sound understanding of various aspects

of these soils flora and fauna in the maintenance of soil

fertility in crop production systems and clean-up of

environment is vital. Effective ways of promoting this

microbial activity in agro-ecosystems include conservation

tillage, crop rotation, proper nutrient management and

application of organic manure. These processes should be

practiced to foster the development of healthy and diverse

communities of living organisms, improve soil health and

food/crop production. Therefore the paper reviews on

various living organisms and their effects on soil fertility

maintenance.

Key words: living organisms, soil fertility and maintenance,

flora, fauna.

INTRODUCTION Within the soil, is one of the most diverse assemblages of living organisms (Giller et al., 1997). The role of living organisms in soil fertility is known since 1881, when Darwin (1809–1882) published his last scientific book entitled “The formation of vegetable mould through the

action of worms with observations on their habits.” Since then, several studies have been undertaken to highlight the soil living organisms contribution to the sustainable function of all ecosystems (Bhadauria and Saxena, 2010).

Soil fertility changes and the nutrient balances are

taken as key indicators of soil quality (Jansen et al., 1995). Soil fertility is commonly defined as the inherent capacity of a soil to supply plant nutrients in adequate amounts, forms, and in suitable proportions required for maximum plant growth (Von Uexkuell, 1988). Soil quality has been defined as the capacity of the soil to function within ecosystem and land use boundaries, to sustain biological productivity, maintain environmental quality and promote plant, animal and human health (Doran et al., 1996). High quality soils not only produce better food and fibre, but also help establish natural ecosystems and enhance air and water quality (Griffiths et al., 2010). The fertility of soil is central to the sustainability of both natural and managed ecosystems (Sharmila et al., 2008). The natural ecosystems maintain their production through well balanced above and below ground biological processes which serve to conserve the nutrients, water and soil organic matters within the systems. Swift and Anderson (1993), stated that in natural ecosystems, the internal regulation of functions is largely a result of plant biodiversity that influence the magnitude of and temporal distribution of carbon and nutrient flows; however, this form of control is increasingly lost through agricultural intensification which undoubtedly has degraded soils. The major processes that contribute to soil fertility decline includes decline in soil organic matter and biological activities, degradation of soil structure and loss of other soil physical qualities, reduction in availability of major 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 play many important roles in the successful functioning of agricultural ecosystems. Therefore, this review is aimed to identify various living organisms and their effects on soil fertility maintenance. CLASSIFICATION OF ORGANISMS The modern studies have shown that living organisms can be broadly classified into two radically different kinds, prokaryotes (less complex cell structure) and eukaryotes (organisms with true nucleus), which further divided into many other forms. The free-living components of soil biota are bacteria, fungi, algae, actinomyotes and the fauna (Sharmilia et al., 2008) (Tables 1 and 2). According to Edmundo, (2007) soil organisms have been classified on the basis of body width into microflora (1-100µm, e.g bacteria, and fungi), micro fauna (3-120 µm, e.g protozoa, and nematodes), mesofauna (80 µm – 2 mm, e.g collembolan, acari) and macro fauna (500 µm-50 mm, e.g earthworms, termites) and vascular plants. Sharmilia et al. (2008) stated that organism may be grouped either on the basis of body width viz; micro, meso and macro organisms or on the basis of functional groups viz, mycophagous/herbivores, omnivores and predators,

Direct Res. J. Agric. Food Sci. 66 period of soil inhabitation habitat preference or biological activity.

They state that feeding and locomotion are the other two main activities that divide the organism in the different groups. Based on locomotion the soil animals can be distinguished as burrowing ones from the other that move on the soil surface or through the pore spaces/ channels/cavities in the soil. In terms of feeding activity the soil animals can be classified into five major groups. They also classified living organisms on the basis of kingdom. All living things can be classified into one of the five fundamental kingdoms of life namely; Moriera, Protista, Fungi, Plantae, Animalia and are well represented in soil ecosystem, (i) Kingdom Moriera: includes prokaryotes-single cell organisms that do not possess nucleus e.g bacteria, actinomycetes and blue green algae. (ii) Kingdom Protista: include single cell organisms that do possess nucleus e.g nucleated algae and slime modules. (iii) Kingdom fungi: These non-motile eukaryotes lack fragella and developed spores like yeast, moulds, and mushrooms. (iv) Kingdom Plantae: these eukaryotes develop from embryos and use chlorophyll like mosses and vascular plants. (v) Kingdom Animalia: the multicellular eukaryotes develop from a blastula (a halo ball of cells). ACTION OF DIFFERENT ORGANISMS Soil organisms are very important in agriculture because they mediate many beneficial processes that include recycling of plant nutrients: nutrients like nitrogen, phosphorus and sulphur which occur mostly as organic compounds (in manures, compost, crop residues, soil organic matter e.t.c) that are not available for plant uptake. During decomposition, soil organisms break these compounds and convert the nutrients into inorganic forms that plant can uptake through their root systems. Meeting some crop nutrients requirements through recycling reduces the need for fertilizers (Newton and Chantal, 2010). According to Adekunle and Dafiwhare (2011), microbes (bacteria, Achaea, fungi and protozoa) are very important in all processes related to soil function. The microbial constituents of soil are entirely responsible for breakdown of organic matter and degradation of toxic molecules. Microorganisms are also responsible for the mineralization process in the forest ecosystem. They act on the humus to release carbon dioxide (CO2), water and nutrients which could be absorbed directly by plants. The actions of microbes were summarized by Hoff et al. (2004) to include degradation of complex nutrient sources extra-cellular, transportation of simple nutrients across 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 growth. According to Rigobelis and Nahas, (2004) the most important soil nutrient supply to the forest soil environment is the one derived from litter decomposition by action of organism under condition of high air temperature and soil moisture content. These organisms mobilized the chemical elements in the litter and make them re-absorbable by plant roots. They are able to perform these because of their ability to obtain nutrients through absorption.

Larger soil organisms consume organic residue. They break it down into smaller pieces which allow bacterial and fungi to work more efficiently. Bacteria, fungi and other microscopic organisms decompose the dead plant residue and increase the organic matter contained in the soil (ALBA, 2012).

The mineralizers split complex and large plant molecules (e.g cellulose, hemicellulose, lignin) into smaller molecules (e.g sugars, amino acids, aromatics, aliphatics), simpler mineral forms (e.g ammonium and nitrate) and nitrate, nitrogen, carbon dioxide, water, sulphate) (Killham, 1994), important groups include the nitrifying bacteria (Nitrosolobus, Nitrobacter, Nitrosomonas) that are involved in the conversion of ammonium to nitrate. Another group of organisms is most active under poorly aerated conditions, such as when soils are flooded or poorly drained or when the demand for oxygen is greater than what can be supplied by diffusion through air-filled pores. Denitrifying bacteria converts nitrates to forms of nitrogen that are lost to the atmosphere as nitrogen gas or nitrous oxide. Fermenters such as yeast and certain bacteria decompose organic materials under anaerobic conditions, often forming foul-smelling substances. Other groups of organisms such as mycorrhizal fungi make phosphorus more accessible to plants either by dissolving complex phosphorus-bearing

substance or by effectively expanding the surface area of plants roots.

Pioneer organisms such as lichens, mosses and liverworts, subsequently colonizes the substrate, further breaking down the rock and incorporating detritus and organic compounds formed through photosynthesis and nitrogen fixation (Thomas, 2013). In the process, they stabilize and moderate the micro-environment, creating conditions favourable for later colonizers, eventually resulting in the establishment of higher plants and invertebrate animals.

Plants usually absorb nutrients from the soil during growth and return them through their litter (leaf-fall), which decomposes to release the nutrients, rendering them available for reabsorption by the plants (Ojo et al., 2011). Plant roots exude compounds such as amino acids, simple sugar and organic acids. These compounds provide a continuous energy to microorganisms living in the root zone (the rhizosphere) (McBrayer, 1973).

The animals which have had a considerable effect on soil development are macro invertebrates (macro fauna). They influence soil processes, which may affect both physical and chemical fertility of soils and contribute to the maintenance and productivity of ecosystems (Lavelle and Pashanasi, 1989). Soil macro invertebrate (macro fauna) maintain soil physical, chemical and biological soil fertility by immobilization, humification, biocontrol processes and serve as decomposers as well as soil engineer to encourage crop production (Sugiyarto, 2009), examples include ants, termites, millipedes, centipedes beetles, spiders, earthworms e.t.c (Jeff and Shannon, 2002) and they break up organic matter increasing it surface area and thereby enhancing microbial activity and nutrients cycling. Soil macro fauna mix and redistribute mineral and organic material and microorganisms within the profile. According to Werner,

Direct Res. J. Agric. Food Sci. 68

Fungi Molds

actinomycetes

Protista

Protozoa

Yeast

diatoms

Ancestral

prokaryotes

Animalia

Archaeobacteria

Monera

Bacteria

Plantea

Producers

Decomposers

Consumers

Figure 1. Five living organisms and their mode of action. Source: Sharmilia, et al., 2008.

(1993) when organisms are present in the soil, they stimulate the decomposition of cover crops residues. Their feeding and burrowing activities incorporate residues and other amendments into the soil, enhancing organic matter decomposition, humus formation, nutrients cycling and development of soil structure. Earthworm burrows can persist, even after the worms responsible for building them are gone, providing pathways for rapid root 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 that they keep the soil surface almost bare of litter and decomposing organic matter. At this process, they transport considerable quantities of material from one place to another. The fungus growing termites build their mound using soil and clay cemented by salivary secretions which make the moulds enriched with clay particles but impoverished in carbon (Muwawa et al., 2014). They efficiently biodegrade plant biomass and other lignocellulosic materials thereby contributing to the global carbon and nitrogen cycles (DeSouza et al., 2009). Also, their tunnelling activity improves gas exchange, water infiltration and root proliferation (Newton and Chantal, 2010). ORGANISMS AND THEIR ROLES IN SOIL FERTILITY MAINTENANCE Although some soil organisms cause plant diseases, most soil habitants are beneficial to crop production and the environment through processes like the fixing and cycling of nitrogen, biological pest control, formation and maintenance of soil structure and degradation of agrochemicals and pollutants (Newton and Chantal, 2010), and they are particularly important for agriculture (Figure 1). According to Forsyth, (2009) these microbes

include bacteria, archaea, fungi and protozoa which are very important in all process related to soil function. Some of these processes include soil formation, soil structure, cycling of nitrogen, carbon, phosphorus and sulphur. Maha, (2013) illustrated that decomposers animals include protozoa, earthworms, micro arthropods such as mites and collembolan and macro arthropods such as insects, arachnids, millipedes, centipedes. Bacteria Bacteria are the smallest and most abundant organisms in soil. They are free-living and the most interesting marvellous component of the soil microbial population. Bacteria have been intensively studied and have added significance because of their involvement in the nitrogen and carbon cycles and also in other cyclical transformations in soil, it is clear that bacteria are essential for soil fertility. The major contribution of bacteria is to decompose organic nitrogenous compounds in plant and animal residues, with the ultimate liberation of ammonium and litter can be oxidized to nitrate only by nitrifying bacteria. Chemoautotrophic bacteria are mainly responsible for such transformations (Mishra, 2010).

Another important contribution of bacteria is the nitrogen cycle. Certain bacterial species are unique in fixing atmospheric nitrogen in the form of ammonium nitrogen. Nitrogen can be fixed by bacteria either symbiotically, in which case they grow in the roots of the host plants and form nodules or by free living bacteria. Azotobacter (aerobic) and clostridium (anaerobic) are the best known nitrogen fixers. Azotobacter is very common in rhizophere region of plants and they maintain themselves on the root exudates. The plants rich in 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 useful to the host plant through the production of gibberelins and possibly other growth hormones, which results in an increase crop yield due to bacterization, (Mishra, 2010) (Plate 1). Denitrification and sulphate reduction involve a variety of facultative and obligate anaerobic bacteria (Rittman and McCarty, 2001). Nitrification and sulphur oxidation, on the other hand, are the result of the activity of a limited number of genera of aerobic autotrophic bacteria (Oren, 2009).

Bacteria also play a significant role in destroying hazardous contaminants or transform them to less harmful form, in the soil and this process in known as bioremediation (Bioremediation Discussion Group, 2006). Bacterial inoculations (Straube et al., 2003) are sometimes added to speed the remediation process. As indicated many hydrocarbons degrading bacteria can be found in soils and the common ones are Achromobacter, Acinetobacter, Actinomyces, Bacillus, Burkholderia, Extiguobacterium, Klebsiella, Microbacteruim, Nocardia, Pseudomonas, Spirillum, Streptomyces and Vibro. However, at petroleum hydrocarbon polluted sites, these populations may grow and increase because they use petroleum hydrocarbons as a carbon source (Mohanty and Mukherjee, 2008). Bioremediation of petroleum hydrocarbon-polluted soil relies on the petroleum degradation ability of the microbial consortium resident in the soil (Franzmann et al., 2002). Although petroleum degradation microorganisms are widely distributed in both soil and water, they may not be present in sufficient numbers at a given polluted site. In such cases, it may be useful to inoculate the polluted area with highly

effective petroleum-degradation microbial strains in a process called bioagumentation (Supaphol et al., 2006). Fungi Fungi in the soil are associated with various types of activities. They play a major role in the processes of humus formation and aggregate stabilization. They usually dominate in the upper horizons of the forested soils as well as in acid or sandy soils. They carry out the largest share of decomposition in many cultivated soils as well (Brady and Weil, 2008). According to Steffen and Tuomela (2010), the natural environment for litter –decomposing fungi is the top soil layer where they degrade plant and animal litter material (debris).

Soil fertility depends in no small degree on nutrients cycling by fungi, since they continue to decompose complex organic materials after bacteria and actinomycetes have essentially ceased to function. Soil tilth also benefits from fungi as their hyphae stabilize soil structure. In addition to the breakdown organic residues and formation of humus, numerous other fungal activities have significant impact on soil ecology. Some fungi are predators of animals. For example, certain species even trap nematodes (Brady and Weil, 2008).

The important part of the role of fungi in ecosystem is the capture of mineral nutrients. The growth of most plants is enhancing by the presence of mycorrihizal fungi. Mycorrihizal fungi take up nutrients used by the plants, such as phosphorus (P) and Nitrogen (N) compounds (Carlile et al., 2004). According to Phil et al. (2012), mycorrihizal fungi form mutualistic associations with

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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.

Species P concentration in shoot P concentration in root Total P uptake -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 host plant and forms extensive mycelia net-works through soil absorbs P and transfer directly to the plant (Figure 2). They are also able to explore and exploit considerably larger volume of soil per unit C than plant root. They also contribute humification and detoxification process in soil (Singh, 2006). Keston, (2013) also found positive mycorrihizal effects on shoot P concentrations and shoot biomass of grasses such as Bromus spp. and Festuca spp.

Water uptake may also be improved by mycorrihizae making plants more resistant to draught. According to Valentin et al. (2009), fungi might be more suitable for bioremediation applications because of their better ability to grown in the soil. Oil degrading fungi and yeast include; Alluescheria, Aspergillus, Candid, Debayomyces, Mucor, Penicillium, Saccharommyces and Trichoderma (Table 3). Actinomycetes Actinomycetes are one of the major components of the microbial populations present in soil. They belong to an

extensive and diverse group of Gram-positive, aerobic, mycelial bacteria that play important ecological roles in soil nutrient cycling. In addition, they are known for their economic importance as producers of biologically active substances, such as antibiotics, vitamins and enzymes (de Boer et al., 2005). Actinomycetes are also an important source of diverse antimicrobial metabolites (Terkina et al., 2006). Soil actinomycetes particularly Streptomyces sp. enhance soil fertility and have antagonistc activity against wide range of soil borne plant pathogens (Aghighi et al., 2004). They are one of the major components of the microbial populations present in soil (Tables 4 and 5).

In forest ecosystem, much of the nitrogen supplied depends on certain actinomycetes that are capable of fixing atmospheric nitrogen gas into ammonium nitrogen that is then available to higher plants (Brady and Weil, 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 compounds, such as cellulose, chitin and phospholipids, to simpler forms and play a role in the final stage of composting. They are much diffused in the soil and 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.

Shoot biomass production (mg[dry wt]) Root biomass production

(mg[dry wt]) Mycorrhizal root length (%)

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, such as streptomycin and chloramphenicol, against some soil-borne root pathogens. According to Franco-Correa et al. (2010), inoculation of clover plants with either of the selected actinomycetes enhanced plant growth and N acquisition. Co-inoculation of actinomycetes and Glomus mosseae produced synergic benefits on plant growth. They also state that actinomycete strains have the ability of solubilizing sparingly available inorganic P sources or mineralizing some P from the organic P sources in soil. The secretion of acid phosphatase indicated that some actinomycete strains would be able to mineralize organic P sources (Richardson et al., 2009). Actinomycete also can improve both shoots and roots biomass accumulation.

These actinomycetes can be considered as Mycorrhiza Helper Bacteria because they may promote the mycorrhizal colonization rate at different stages of bacterium–fungus–plant interactions, including spore germination (Tarkka and Frey-Klett, 2008), and particularly by Streptomyces species (Schrey et al., 2005). Soil actinomycetes particularly Streptomyces species enhance soil fertility and have antagonistic activity against wide range of soil borne plant pathogens (Aghighi et al., 2004). Moreover, fungi and actinomycetes are able to colonize rhizosphere and use root exudates

as carbon source, supply roots with easily assimilable nitrates and play a key role in the biological control of root pathogens and in the maintenance of soil health (Govaerts et al., 2007). Macro and micro flora These are large (high) and microscopic (small) plants which include algae (cyanobacteria), mosses, fern, liverwort, lichen, grasses, vascular plants e.t.c. Blue-Green Algae (Cyanobacteria) are one of the major components of the nitrogen fixing biomass in paddy fields and dominant nitrogen-fixer blue-green algae are Anabaena, Nostoc, Aulosira, Calothrix, Plectonema etc. The blue green algae (cyanobacteria) are capable of fixing the atmospheric nitrogen and convert it into an available form of ammonium required for plant growth and other positive effects for plants and soil (Sahu et al., 2012). They are well adapted to a wide range of environmental conditions and have been widely employed as inoculants for enhancing soil fertility and improving soil structure, besides enhancing crop yields, especially in rice (Dhar et al., 2007). Cyanobacteria also add organic matter, synthesize and liberate amino acids, vitamins and auxins, reduce oxidizable matter content of

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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, ameliorate salinity, buffer the pH, solubilize phosphates and increase the efficiency of fertilizer use in crop plants (Kaushik 2004), increase in water holding capacity through their jelly structure (Roger and Reynaud, 1982), increase in soil biomass after their death and decomposition, decrease in soil salinity, preventing weeds growth (Saadatnia and Riahi, 2009), increase in soil phosphate by excretion of organic acids (Wilson, 2006).

Azolla (fresh water fern), a free floating aquatic fern found in ponds, flooded rice fields and other still fresh waters is used as an N-biofertilizer for wetland rice because of its ability to fix atmospheric N in symbiosis with N2-fixing blue-green algae (Table 6). Other role of azolla as a biofertilizer includes reduction in NH4-N loss by volatalization (Chu and Bo-qi, 1988). Anabaena in association with water fern Azolla contributes nitrogen up to 60 kg/ha/season and also enriches soils with organic matter (Sahu et al., 2012). Anabaena and Nostoc are found to fix large amount of atmospheric nitrogen (up to 20 - 25 kg/ha). Blue green algae belonging to genera Nostoc, Anabaena, Tolypothrix and Aulosira fix atmospheric nitrogen and are used as inoculants for paddy crop grown both under upland and low land conditions.

Pioneer organisms such as lichens, mosses and liverworts, subsequently colonizes the substrate, further breaking down the rock and incorporating detritus and organic compounds formed through photosynthesis and nitrogen fixation (Thomas, 2013). In this process, they stabilize and moderate the micro-environment, creating conditions favourable for later colonizers, eventually resulting in the establishment of higher plants and invertebrate animals.

Grass production is the ultimate ecosystem service, in which the maintenance of soil structure, water regulation, and particularly nutrient supply play prominent role (Hoogerkamp et al., 1983). Fin grass roots and consequently the rhizosphere around them, have an important positive effect on soil structure, latter also improve water infiltration. The introduction of legume

appears to play a more important role in how soil biota function, and does promote other ecosystem service including soil structure, water retention, biodiversity, and carbon and nitrogen storage (Phil et al., 2012).

High plants usually absorb nutrients from the soil during growth and return them through their litter (leaf-fall), which decomposes to release the nutrients, rendering them available for reabsorption by the plants (Ojo et al., 2011). Plants directly influence the soil community by their root growth and plant cover (Figure 3). The majority of microorganisms found in the soil are associated with plants roots that provide them with carbon and other nutrients such as nitrogen fixing trees and shrubs known as “fertilizer tree systems” (Table 7). The “fertilizer tree” system is an agroforestry technology in which leguminous trees or woody shrubs are grown and the biomass used to replenish the fertility of soils. The planted leguminous species replenish soil fertility by transforming atmospheric nitrogen and making it available in the soil. The cycle begins by planting tree species as a pure stand (fallow) or intercropped with food crops in the first year. The trees are allowed to grow for about two years after which they are cut and the biomass incorporated into the soil during land preparation. The trees’ leaf and root biomass decomposes and releases nutrients for crops planted in the plot over the next two to three years. The most common species used in “fertilizer tree systems” are Sesbania sesban, Gliricidia sepium, Tephrosia vogelli, Tephrosia candida and pigeon pea (Akinnifesi et al., 2007, 2009). Macro and micro fauna Soil fauna come in a variety of shapes and sizes and play a variety of role in soil development and the maintenance of soil fertility (Jeff and Shannon, 2002). Fauna in soil include hair like worms called nematodes, snails, slugs, insect larva, beetles, ants, termites, spiders, earthworms, protozoans, micro anthropods such as mites and collemblolan and macro anthropods such as insects, 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

Groundnuts (Arachis hypogea) 152 – 189 118 - 137 India

101 - Ghana

Pigeon pea (Cajanus cajan) 150 – 166 - India 13 – 163 120 Malawi

Chickpea (Cicer arietinum) 67 – 85 170 Australia 35 – 80 - Nepal

Soybean (Glycine max) 85 – 154 110 Brazil 15 – 170 - Nepal

Common bean (Phaseolus vulgaris) 25 – 65 60 - 90 Brazi 8 – 26 75 Tanzania

Cowpea (Vigna unguiculata) 9 – 51 110 Brazil

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). They are illustrated as decomposers animals. They influence soil processes, which may affect both physical and chemical fertility of soils and contribute to the maintenance and productivity of ecosystems (Sugiyarto, 2009). Soil macro invertebrate (macro fauna) maintain soil physical, chemical and biological soil fertility by immobilization, humification, biocontrol processes and serve as decomposers as well as soil engineer to encourage crop production (Larvelle et al., 1994), and they break up organic matter increasing its surface area and thereby enhancing microbial activity and nutrients cycling. Soil macro fauna mix and redistribute mineral and organic material and microorganisms within the profile (Jeff and Shannon, 2002).

Large amounts of organic matter from plant and animal (prey, carrion) sources accumulate in refuse dumps within nests. This material, combined with metabolic wastes and secretions from the ants themselves, which

may become incorporated into nest soil, undergoes decomposition and mineralization by the microflora, leading to an accumulation and local concentration of nutrients (Pętal, 1978).

The burrowing by arthropods, particularly the subterranean network of tunnels and galleries that comprise termite and ant nests, improves soil porosity to provide adequate aeration and water-holding capacity below ground, facilitate root penetration, and prevent surface crusting and erosion of topsoil. Also the movement of particles from lower horizons to the surface by ants and termites aids in mixing the organic and mineral fractions of the soil. The faeces of arthropods are the basis for the formation of soil aggregates and humus, which physically stabilize the soil and increase its capacity to store nutrients (Thomas, 2013).

Earthworms are recognized as a key factor in the way many terrestrial ecosystems work (Bartlett et al., 2010). 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 create their own living conditions near their preferred food sources.

Plate3. Common garden earthworm performing its role and a root following the pathway opened by the earthworm.

communities in most ecosystems and comprise a large proportion of macrofauna biomass. Their activity is beneficial because it can enhance soil nutrient cycling through the rapid incorporation of detritus into mineral soils. In addition to this mixing effect, mucus production associated with water excretion in earthworm guts also 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 effect is the concentration of large quantities of nutrients (N, P, K, and Ca) that are easily assimilable by plants in fresh cast depositions. In addition, earthworms seem to accelerate the mineralization as well as the turnover of soil organic matter. Earthworms are known also to increase nitrogen mineralization, through direct and indirect effects on the microbial community. The increased transfer of organic C and N into soil aggregates indicates the potential for earthworms to facilitate soil organic matter stabilization and accumulation in agricultural systems, and that their influence depends greatly on differences in land

management practices (Bhadauria and Saxena, 2010). Earthworm burrows can persist even after the worms responsible for building them are gone, providing pathways for rapid root growth, water infiltration, and gas exchange. Deep-burrowing species can burrow through compacted soil and penetrate plow pans. OPTIMIZING THE USE OF LIVING ORGANISMS IN THE MAINTENANCE OF SOIL FERTILITY For optimum plant growth and microbial health, nutrients must be available in sufficient and balanced quantities. The most important constraint limiting crop yield in developing nations worldwide, and especially among resource-poor farmers, is soil infertility (Mohammadi and Sohrabi, 2012).

Learning how to manage soil biological processes may be a key step towards developing sustainable agricultural systems and soil fertility (Plates 2 and 3). Many techniques are available which includes producing green

Ibigweh and Asawalam 75

manures or cover crops, applying supplemental animal manures or composted materials, mulching, maintenance of biodiversity, increased input of carbon, reduced pesticide applications, poly-cultures, crop rotations, hedgerows and buffer strips or utilizing reduced tillage, aimed at optimizing production while maintaining a rich biological diversity of the soil (Dharmendra et al., 2013). Agricultural practices that promote the activities of wide varieties of living organisms are viable biological strategies to promote soil fertility. CONCLUSION One of the main gaps in agricultural management systems is the lack of awareness and understanding and hence inadequate management of soil biological processes to maintain and improve soil productivity. Soil living organisms are important in soil fertility maintenance, ecological functions and ecosystem services, because they mediate useful biological processes like nutrient cycling and nitrogen fixation, biological pest and diseases control, organic matter decomposition and carbon sequestration, maintenance of a good soil structure for plant growth and rainwater infiltration and detoxification of contaminants. Therefore, processes that support soil fertility maintenance, ecological functions and ecosystem services should be encouraged by adopting soil and crop management practices that foster the development of healthy, diverse communities of living organisms. Such practices include no-till, diversified crop rotations, proper fertility management and the application of organic manures. Authors’ declaration

We declare that this study is an original research by our research team and we agree to publish it in the journal. REFERENCES Adekunle VAJ, Dafiwhare HB (2011). Diversity and abundance of

microbes, pH and organic matter in soils of different forest types in tropical humid lowland forest ecosystem, Nigeria. Journal of Biodiversity and Ecological Sciences JBES, Vol.1: 333-342.

Aghighi S, Bonjar GHS, Rawashdeh R, Batayneh S, Saadoun I (2004). First report of antifungal spectra of activity of Iranian actinomycetes strains against Alternariasolani, Alternaria alternate, Fusariumsolani, Pytophthora megasperma, Verticillum dahlia and Saccharomyces cerevisiae. Asian Journal of Plant Science. 3(4):463-471.

Agriculture and Land-Based Training Association (ALBA) (2012). Soil fertility and Irrigation Management. Farmer Education Program (PEPA) Resource Guide. Pp 1-50.

Akinnifesi FK, Mhango J, Sileshi G, Chilanga T (2007). Early growth and survival of three miombo indigenous fruit tree species under fertilizer, manure and dry-season irrigation in southern Malawi. Forest Ecology and Management (in press).

Akinnifesi FK, Sileshi G, Franzel S, Ajayi OC, Harawa R, Makumba W, Chakeredza S, Mngomba S, de Wolf JJ, Jonas N, Chianu, JN (2009).

On-Farm Assessment of Legume Fallows and Other Soil Fertility Management Options Used by Smallholder Farmers in Southern Malawi. Agricultural Journal 4 (6): 260-271, 2009.

Bartlett M, Briones M, Neilson R, Schmidt O, Spurgeon D, Creamer R (2010). A critical review of current methods in earthworm ecology: From individuals to populations. European Journal of Soil Biology., 16(2):67-73.

Bhadauria T, Saxena KG (2010). Role of Earthworms in Soil Fertility Maintenance through the Production of Biogenic Structures. Applied and Environmental Soil Science. Hindawi Publishing Corporation Volume 2010, Article ID 816073, Pp 1-7.

Bioremediation Discussion Group. Bio Group. 1Oct.(2006) <http://www.bioremediationgroup.org/BioTerms/Home.htm#B>.

Brady NC, Weil RR (2008). The Nature and Properties of Soils. Revised 14th ed. Pearson Prentice Hall. New Jersey, USA; 2008.

Carlile MJ, Watkinson SC, Gooday GW (2004). The Fungi (2nd ed.), Elsevier academic press, London. p.588

Chu LU, Bo-qi, W (1988). The function and potential of boifertilizer and organic manure in Agricultural production – the new models and research in Fujan, China. In Rape Report 1994/7. FAO, Bangkok, Thailand. Pp. 111-126.

de Boer W, Folman LB, Summerbell RC, Boddy L (2005). Living in a fungal world: impact of fungi on soil bacterial niche development. FEMS Microbiology Rev. 29, 795–811.

DeSouza O, Araújo APA, Reis-Jr R (2009). Trophic controls delaying foraging by termites: reasons for the ground being brown? Bulleting in Entomological Response 99:603-609.

Dhar DW, Prasanna R, Singh BV (2007). Comparative performance of three carrier-based blue-green alga biofertilizer for sustainable rice cultivation. Journal of Sustainable Agriculture. 30:41-50

Dharmendra S, Parul J, Abhishek G, Rajeev N (2013). Soil Diversity: A Key for Natural Management of Biological and Chemical Constitute to Maintain Soil Health & Fertility. International Journal of Bio-Science and Bio-Technology Vol. 5, No. 1, 41-50.

Doran JW, Sarrantonio M, Liebig MA (1996). Soil health and sustainability. Adv. Agron., 56: 1-54.

Edmundo B (2007). Soil biota, ecosystem services and land productivity. Ecological Economics, 6 4:269 – 285.

Food and Agricultural Organization of the United Nations (FAO) (2001). Soil fertility management in support of food security in Sub-Saharan Africa. FAO, Rome; 2001.

Forsyth MH (2009). Microbial Diversity in Virginia Old Hardwood Forest Soil Week #1 Bio 203 laboratory module. Virginia State University, USA, p. 14.

Franco-Correaa M, Quintanaa A, Duquea C, Suareza C, Rodriguez MX, Bareab J (2010). Evaluation of actinomycete strains for key traits related with plant growth promotion and mycorrhiza helping activities. Applied Soil Ecology: 45: 209–217.

Franzmann PD, Robertson WJ, Zappia LR, Davis GB (2002). The role of microbial populations in the containment of aromatic hydrocarbons in the subsurface. Biodegradation 13, 65–78.

Giller KE, Beare MH, Lavelle P, Izac AM, Swift MJ (1997). Agricultural intensification, soil biodiversity and agroecosystem function. Applied Soil Ecology 6 (1):3–16.

Govaerts B, Mezzalama M, Unno Y, Sayre KD, Luna-Guido, M, Vanherck K, Griffiths BS (2007). Microbial-feeding nematodes and protozoa in soil: Their effects on microbial activity and nitrogen mineralization in decomposition hotspots and the rhizosphere. Plant and Soil 164:25-33.

Griffiths BS, Ball BC, Daniel TJ, Hallett PD, Neilson R,Wheatley RE, Osler G, Bohanec M (2010). Integrating soil quality changes to arable agricultural systems following organic matter addition, or adoption of a ley-arable rotation. Appl. Soil Ecol., 46(1): 43-53.

Hoff JA, Klopfenstein NB, Ton JR, McDonald GI, Zambino PJ, Rogers JD, Peever TL Carris LM (2004). Roles of woody root associated fungi in forest ecosystem processes: recent advances in fungal identification. Research Paper, RMRS-RP-47, Fort Collins, CO: US Depart. Agric., Forest. Service, pp:6. http://www.els.net.

Hoogerkamp, M., Rogaar, H. and Eijsackers, H.J.P. (1983). Effect of earthworms on grassland on recently reclaimed polder soils in the Netherlands. In: Earthworm Ecology: froin Darwin to vermiculture(Ed. by J.E. Satchell), pp.85-105. Chapman and Hall, London, New

York. Jansen DM, Stoorvogel JJ, Shipper RA (1995). Using sustainability

indicators in agricultural land use analysis: An example from Costa Rica. Neth. J. Agr. Sci., 43(1):61-82.

Jeff B, Shannon B (2002). Soil Fauna in the Sub-Boreal Spruce (SBS) Installations of the Long-Term Soil Productivity (LTSP) Study of Central British Columbia: One-Year Results for Soil Mesofauna and Macrofauna. LTSPS Research Note. Ministry of Forests, Research Branch Laboratory, Victoria, BC Canada.

Kaushik BD (2004). Use of blue-green algae and Azolla biofertilizers in rice cultivation and their influence on soil properties. pp 166-184. In. PC Jain (ed.), Microbiology and Biotechnology for sustainable development. CBS Publishers & Distributors, New Delhi, India.

Keston, O.W.N (2013). Microbial Contributions in Alleviating Decline in Soil Fertility. British Microbiology Research Journal, 3(4): 724-742.

Killham K (1994). Soil ecology. Cambridge: Cambridge University Press.

Lavelle P, Dangefield C, Fragoso C, Eschenbrenner D, Lopez HD, Pashanasi B, Brussard L (1994). The relationship between soil macro fauna and tropical soil fertility. In: Woomer PL, Swift MJ, ed. The biological management of tropical soil fertility. UK: John Wiley and sons. Pp137-169.

Lavelle, P. and Pashanasi, B. (1989). Soil macro fauna and land management in. Peruvian Amazonia (Yurimaguas, Loreto). Pedobiologia, 33:283-291.

Maha AAL (2013). Ecological Role of Animal Diversity in Soil System (A Case Study at El- Rawakeeb Dry Land Research Station, Sudan) 1st Annual International Interdisciplinary Conference, AIIC 2013, 24-26 April, Azores, Portugal - Proceedings-Pp.345-350.

McBrayer JF (1973). Exploitation of deciduous leaf litter by Apheloria montana. Pedobiologia 13:90–93.

Mishra RR (2010). Soil microorganisms and organic matter decomposition. In. Soil Microbiology. 4th ed. Published by Satish Kumar Jain., 2010; 83-104.

Mohammadi, K. and Y. Sohrabi, (2012). ARPN Journal of Agricultural and Biological Science, vol. 7, no. 5, (2012).

Mohanty G, Mukherji S (2008). Biodegradation rate of diesel range n-alkanes by bacterial cultures Exiguobacterium aurantiacum and Burkholderia cepacia. Int. Biodeterior. Biodegrad. 61:240–250.

Muwawa EM, Makonde HM, Budambula NLM, Osiemo ZL, Boga HI (2014). Chemical properties associated with guts, soil and nest materials of Odontotermes and Macrotermes species from Kenya. J. Bio. & Env. Sci., 4(2):253-263.

Newton L, Chantal H (2010). Soil Biology of the Canadian Prairies. Agricultural Soils of the Prairies. PS&C., Prairie Soils and Crops Journal., Vol. 3: 16-24.

Ojo JOA, Ogunwale JA, Oluwatosin GA (2011). Fundamental of tropical soil science. Evans. Pp. 15-18.

Oren A (2009). Chemolithotrophy. In: eLS. John Wiley & Sons Ltd, Chichester.

Pętal, J. (1978). The Role of Ants in Ecosystems. In Production Ecology of Ants and Termites; Brian, M.V., Ed.; Cambridge University Press: Cambridge, UK, 1978; pp. 293–325.

Phil M, Felicity CN, van Eekeren (2012). Management of grassland systems, soil and ecosystem services. In. Soil Ecology and Ecosystem services. First ed. Diana H, Wall et al., Oxford University Press., 2012; 282-293.

Richardson A.E, and Simpson R.J (2011). Soil Microorganisms Mediating Phosphorus Availability Update on Microbial Phosphorus. Plant physiology Volume 156(3):989-996.

Rigobelis EC, Nahas E (2004). Seasonal fluctuations of bacterial population and microbial activity in Soils calibrated with Eucalyptus and Pinus. Sci. Agric., 6:88-93.

Rittman BE, McCarty PL (2001). Environmental Biotechnology: Principles and Applications, McGraw Hill Publishers, New York. 754 p.

Roger PA, Reynaud PA (1982). Free-living Blue-green Algae in Tropical Soils. Martinus Nijh off Publisher, La Hague.

Saadatnia H, Riahi H (2009). Cyanobacteria from paddy fields in Iran as a Biofertilizer in rice plants. Plant Soil Environ, 55, 2009 (5): 207–212.

Direct Res. J. Agric. Food Sci. 76 Sahu D, Priyadarshani I, Rath B (2012). Cyanobacteria - as Potential

Biofertilizer. CIBTech Journal of Microbiology, Vol. 1 (2-3): 20-26. Review Article 20.

Schrey SD, Schellhammer M, Ecke M, Hampp R, Tarkka MT (2005). Mycorrhiza helper bacterium Streptomyces AcH 505 induces differential gene expression in the ectomycorrhizal fungus Amanita muscaria. New Phytol. 168, 205–216.

Sharmila R, Pradeep S, Roy MM (2008). Soil Biodiversity under Forage Production Systems. IGFRI, Jhansi (India), Pp.1-25.

Singh H (2006). Mycorrhizal fungi in rhizosphere remediation, In: Singh, H., (Ed.), Mycoremediation – Fungal bioremediation, John Wiley & Sons Inc., New Jersey (USA) 2006, pp. 533–572.

Steffen KT, Tuomela M (2010). Fungal soil bioremediation: development for large scale applications, In: Esser, K., Hofrichter, M., (Eds.), Mycota X (2nd ed.), Springer, Berlin, Heidelberg 2010, pp. 451-467.

Straube WL, Nestler CC, Hanson LD, Ringleberg D, Prichards PH, Jones-Meehan J (2003). Remediation of polyaromatic hydrocarbons (PAHs) through landfarming with biostimulation and bioaugmentation. Acta Biotechnologica 23, 179–196.

Sugiyarto (2009). The Effect of Mulching Technology to Enhance the Diversity of Soil Macroinvertebrates in Sengon-based Agroforestry Systems. BIODIVERSITAS (Journal of Biological Diversity) Vol. 10, No. 3, pp. 129-133.

Supaphol S, Panichsakpatana S, Trakulnaleamsai S, Tungkananuruk N, Roughjanajirapa P, Gerard O’Donnell A (2006). The selection of mixed microbial inocula in environmental biotechnology: example using petroleum contaminated tropical soils. J. Microbiol. Method 65, 432–441.

Swift MJ, Anderson JM (1993). Biodiversity and ecosystem function in agricultural systems. In: Schulze, E.D., Mooney, H.A. (Eds.), Biodiversity and ecosystem function. Ecological Studies, vol. 99. Springer-Verlag, Berlin, pp. 14–41.

Tarkka MT, Frey-Klett P (2008). Mycorrhiza helper bacteria. In: VArma, A. (Ed.), Mycorrhiza, Springer-Verlag, Berlin Heidelberg. pp. 113–132.

Terkina IA, Parfenova VV, Ahn TS (2006). Antagonistic activity of actinomycetes of Lake Baikal. Applied Biochemical Microbiology. 42 (2), 173–176.

Thomas WC (2013). Role of Arthropods in Maintaining Soil Fertility. Agriculture.3 :629-659. www.mdpi.com/journal/agriculture.

Ultar Jr. VU (2010). Contribution of arbuscular mycorrhiza inoculation on the growth and phosphorus nutrition of jatropha (Jatropha curcas) in degraded upland soils of Samar, Philippines. 19

th World Congress

of Soil Science, Soil Solutions for a Changing World. Brisbane, Australia. Pp 67-70.

Valentín L, Kluczek-Turpeinen B, Oivanen P, Hatakka A, Steffen K, Tuomela M (2009). Evaluation of basiomycetous fungi for pretreatment of contaminated soil, J. Chem. Technol. Biotechnol. 84; 851-858.

Von Uexkuell HR (1988). Nutrient cycling in soil management and smallholder development in the Pacific Islands.In: IBSRAM (International Board for Soil Research and Management) Proceedings. Bangkok, p. 21.

Werner MR (1993). Earthworms in California agroecosystems. Proceedings, Sustainable Soil Management Symposium. Pp 53–63.University of California, Davis.

Wilson LT (2006). Cyanobacteria: A Potential Nitrogen Source in Rice Fields. Texas Rice 6:9–10.