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Soil is the largest terrestrial ecosystem where a wide variety of relationships exists between different types of soil organisms. The associations existing between different soil microorganisms, whether of a symbiotic or antagonistic nature, influence the activities of microorganisms in the soil. Microflora composition of any habitat is governed by the biological equilibrium created by the associations and interactions of all individuals found in the community. In soil, many microorganisms live in close proximity and interact among them-selves in a different ways. Some of the interactions or associations are mutually beneficial, or mutually detrimental or neutral.

Introduction

Soil is a complex system consisting of physical, chemical and biological components. These components dynamically interact making it functional to sustain life. All life forms rely on soil microbial processes for their survival. Microbial diversity in the soil is greater than the diversity of any other group of organisms existing in the earth. Microbes as inhabitant of soil are responsible for diverse metabolic functions that affect soil and plant health (Table 1).

Abstract

The traditional forage production systems and grazing lands are under extreme pressure due to the population growth of both human and livestock, decreasing area and inputs. In the central India, especially the Bundelkhand region, the soil is highly weathered, degraded and have low inherent nutrient, which was further worsened due to use of chemical fertilizers and pesticides, for enhancing crop production to meet the escalating demand of the population.

Introduction

Microorganisms generally present in all the environments are the most abundant and diverse living organisms present on earth. Microorganisms have great impact on the biosphere due to their inbuilt ability to transform the key elements of life into forms usable by other organisms and plants. Because of heterogeneity in nature of soils from variations in physical, chemical and biological properties the various natural habitat are microbially most diverse environments on the earth maintaining the stability between complex microbial communities and their function (Daniel 2005). One gram of soil contains about 10 billion microorganisms of possibly thousands of different species but microbial diversity in general, and particularly in extreme environments, and its role in ecology is poorly understood (Rossello-Mora and Amann 2001).

Deserts present a unique environment with very little precipitation and large variations in day and night temperatures, making it inhospitable environment for living organisms. Still a number of microbial species do survive in those harsh environments. The populations of aerobic bacteria in deserts across the world are reported to vary from < 10 in Atacama desert to 1.6 × 10⁷ cfu g^–1 in soils of Nevada (Skujnis 1984), and India is not exception to that with the bacterial population in the range of 1.0 × 10³ to 8.35 × 10⁶ cfu g^–1 sediment or ml^–1 water in the samples collected from cold deserts of north western Himalayas (Yadav et al. 2015).

Soil is a living entity having dynamic physico-chemical and biological properties. Besides supporting the growth of various biological communities, it also serves as a medium on which the organic residues, in the form of dead plant and animal or their excretions, are degraded and decomposed. The biological properties to soil are endowed through the interactive activities of plant root, soil microbes and soil animals. The soil organisms live in a constant state of competition and have to struggle hard for their survival. In this struggle some species become dominant and some remain sub-dominant and others perish or remain in very low profile. So a sort of dynamic equilibrium is the net result of wide range of interactions occurring both at organism and population levels amongst different components of soil biota. Many interactions are short-lived and sporadic and others are more stable.

Soil is inhabited by incredibly diverse living microorganisms that are significant to plant growth and development. Soil microorganisms produce a variety of metabolites, probably several thousands, which influence the plant growth either positively or negatively. Therefore, in such a complex situation, identification of any one metabolite or a compound as active phytohormone or phytotoxin is really an uphill task. Appropriate extraction procedure, knowledge about the proper site for its action, appropriate conducive physiological environment and the effective intensity or concentration is of prime importance. Compounds, in general, are inhibitory to growth at higher concentrations but usually stimulatory at lower concentrations. All growth regulators, irrespective of their provenance or structure, may be divided into two groups.

Definition : Soil microbiology is the study of microorganisms living in soil which complete whole or some part of their life cycle in soil. They include both beneficial as well as deleterious microorganisms but as a specialized branch main thrust is laid on their metabolic activities and the role they play in energy flow, cycling of nutrients associated with the primary productivity and soil ecosystem development. Besides, it focuses on environmental impact, whether favourable or unfavourable, on soil microorganisms and the various soil biochemical processes mediated by various microbes. A clear understanding of the interactions between soil microbial communities and elemental soil components is imperative to comprehend total ecosystem function. Atlas and Bartha have defined the soil microbiology as ‘the study of organisms that live in soil; their metabolic activity; their roles in energy flow; their roles in nutrient cycling’. As per Tate soil microbiology involves ‘the study of soil ecosystem which is the product of intricate interactions between physical and chemical matrix of highly variable composition and living communities of all form’.

1. Amoeba are unicellular organisms that feed on

a. Bacteria and algae     b. Bacteria and fungi

c. Fungi and algae        d. Nematode and fungi

Microorganisms being minute and microscopic are ubiquitous. Besides supporting the growth of various biological systems, soil and soil microbes serve as a best medium for plant growth. Soil fauna & flora convert complex organic nutrients into simpler inorganic forms which are readily absorbed by plants.

Soil microbes as nitogen fixers-Symbiotic (Associative): The organisms involved are Rhizobium, Bradyrhizobium in legumes(aerobic): Azospirillum, Azotobacter (grasses), Actinonycetes- Frantkia (with Casuarinas, Alder).

Soil microbes as biocontrol agents: Several ecofriendly bioformulations of microbial origin are used in agriculture for the effective management of plant diseases, insect pests, weeds etc. eg: Trichoderma sp and Gleocladium sp are used for biological control of seed and soil borne diseases. Fungal genera Entomophthora, Beauveria, Metarrhizium and protozoa- Maltesia grandis. Malameba locustiae etc.- are used in the management of insect pests. Nuclear polyhydrosis virus (NPV) is used for the control of Heliothis/American boll worm. Bacteria like Bacillus thuringiensis, Pseudomonas are used in cotton against Angular leaf spot and bollworms.

Degradation of pesticides in soil: Soil receives different toxic chemicals in various forms and causes adverse effects on beneficial soil micro flora / micro fauna, plants, animals and human beings. Various microbes present in soil act as the scavengers of these harmful chemicals in soil. The pesticides/chemicals reaching the soil are acted upon by several physical, chemical and biological forces exerted by microbes in the soil and they are degraded into non-toxic substances and thereby minimize the damage caused by the pesticides to the ecosystem. For example, bacterial genera like Pseudomonas, Clostridium, Bacillus, Thiobacillus, Achromobacter etc. and fungal genera like Trichoderma, Penicillium, Aspergillus, Rhizopus, and Fusarium play important role in the degradation of the toxic chemicals / pesticides in soil.

Biodegradation of hydrocarbons: Natural hydrocarbons in soil like waxes, paraffins, oils etc are degraded by fungi, bacteria and actinomycetes. E.g. ethane (C2 H6) is metabolized and degraded by Mycobacteria, Nocardia, Streptomyces Pseudomonas, Flavobacterium and several fungi.

4.1. Role of soil microorganisms

Soil N utilization by plants.

Dead organic matters decomposed.

Nutrient transformation.

Physical and chemical properties of soil.

CO₂ content.

Soil formation.

Soil minerals are naturally formed inorganic compounds with definite chemical composition and characteristic geometric (crystalline) form. They are classified as primary and secondary minerals, silicates and non-silicates minerals, and crystalline and non-crystalline minerals. Primary minerals have not been significantly altered chemically since deposition or crystallization from molten magma and are usually found in the sand and coarse silt fractions. Secondary minerals form as a result of the alteration of primary minerals by weathering and are found in the clay and fine silt fractions.

ALLIC: soil family class term used in Oxisols as a calcareous and reaction class category. Soils placed in the allic class are acid and have low CEC with high amounts of KCl-extractable aluminum in a layer at least 30 cm thick within the control section. If used for agriculture, these Oxisols require large inputs of lime to displace the aluminum and raise pH.

The water contents expressed under certain standard conditions are commonly referred to as soil moisture constants. They are used as reference points for practical irrigation water management. The usage of these constants together with the energy status of soil water gives useful knowledge. These constants are briefly explained below:

6.1 Saturation Capacity

Saturation capacity refers to the condition of soil at which all the macro and micro pores are filled with water and the soil is at maximum water retention capacity”. The matric suction at this condition is essentially zero as the water is in equilibrium with free water. Excess water above saturation capacity of soil is lost from root zone as gravitational water.

The soil water plays an important role in the physical, chemical and biological activities taken place in the soil which directly or indirectly affects the crop growth. The water content of the soil can be measured by different methods. These methods are gravimetric method, neutron scattering method and electrical resistance method.

Soil moisture stress in relation to crop and development of crop
Agronomic methods are supported with mechanical measures where land slope exceeds permissible limits and runoff gains erosive velocities. The following boxes explain the nature of agronomic measures which are essential in inter-bunded or terraced areas. These practices enhance the utility value of all kinds of mechanical structures.
1. Contour Tillage: All agricultural operations such as ridging, ploughing, harrowing, sowing, trenching, etc., are recommended to be done on the contour wherever possible or at least generally across the direction of the slope where holdings are very small. Even though the operation is very simple, it plays a major role in retarding the process of soil erosion through runoff. It also conserves soil, and due to increased time of concentration, more rainwater seeps through the soil profile to recharge ground water. Summer ploughing leaves the soil highly absorbent of initial rains.
2. Dead furrows: When all tillage operations are complete, it is advisable to leave a deep dead furrow at every 10 m interval. This should remain in position until the crop is harvested. Dead furrows aid in reducing the runoff velocity and they also conserve water.
3. Organic Matter: Indian soils are very poor in organic matter, especially in drought-prone areas: This can be improved by leaving the crop residue in situ (on the fields). Adding organic manures such as farmyard manure and compost every year as basal application to the soil improves the physical condition of the soil considerably.
Soil-Air, Soil-Temperature, and Soil-Moisture relationships are well balanced with the presence of organic matter. Organic matter improves the activities of soil microorganisms and also provides the much needed micro plant nutrients of all kinds, besides nitrogen, phosphorus and potash. Addition of large amounts of chemical fertilizers to dryland crops should be discouraged as it damages the soil due to:

5.1. Determination of Soil Moisture

5.1.1. Determination of Soil Moisture Content by Gravimetric Method (Direct method)

Traditionally water content in soil is expressed as the ratio of the weight of water present in the soil to the weight of dry soil. When this ratio is multiplied by 100, it becomes the percentage of water in the soil sample on dry weight basis.

6.1 Determination of Soil Moisture

6.1.1 Determination of Soil Moisture Content by Gravimetric Method (Direct method)

Traditionally, water content in soil is expressed as the ratio of the weight of water present in the soil to the weight of dry soil. When this ratio is multiplied by 100, it becomes the percentage of water in the soil sample on dry weight basis.

Equipments and Materials

Soil auger, aluminium moisture box with air tight lid, balance, oven and desiccator

Soil moisture is the water retained within soil pores and represents a critical link between precipitation, evapotranspiration, runoff, infiltration and groundwater recharge. It provides the principal water supply for plant growth and strongly influences crop establishment, nutrient availability and yield. This chapter discusses soil-moisture storage, field capacity, permanent wilting point, available water, infiltration, percolation and root-zone dynamics. It examines methods of measurement, estimation and monitoring and explains how soil texture, structure, organic matter, vegetation and weather influence moisture conditions. Effective soil-moisture management supports irrigation scheduling, drought mitigation, water-use efficiency and prevention of waterlogging, thereby strengthening agricultural productivity and environmental sustainability.