eBook Chapters

Genesis of Soil

World’s geography is very widely diversified in relief showing various features like mountains and hills covered with snow and trees, glaciers, higher altitudes to plain to lowest valleys, forests to barren lands, fertile fields to waste lands, plateaus, deltas, swamps, lowlands, deserts etc. Temperature varies from arctic cold to scorching hot of equator, Rainfall from aridity to per humidity. All these situations and conditions under different sets of combinations generate and develop numerous types of soil from a single type of parent material. Therefore, many types of soils may develop at a smaller area.

Physical, chemical and biological weathering processes disintegrate and decompose various rocks and minerals to make asymmetrical soil parent material. This parent material is converted in to the soil profile by soil forming processes in the presence of soil forming factors. Soil genesis is defined as mode of formation of the soil from the parent material due to the action of soil forming factors and processes. Parent material, Factors of soil formation and Processes of soil formation, are three main part of soil genesis. These are described here:

1. Parent Material,

2. Classification of parent material,

3. Factors of soil formation,

4. Processes of soil formation,

5. Types of soil forming processes.

Soil is a biologically active porous medium that has developed in the uppermost layer of the earth’s crust which serves as a natural medium for the growth of plants. It is one of the principal substrata of life on earth, serving as a reservoir of water and nutrients, and as a participant in the cycling of carbon and other elements through the global ecosystem.

Introduction

Soil management refers to a set of practices and strategies employed by farmers and land managers to maintain, improve, and sustain the health, fertility, and productivity of soil in agricultural systems. It encompasses a range of activities aimed at optimizing soil conditions for crop growth while minimizing environmental degradation. Soil management practices include soil testing to assess nutrient levels and pH, the application of fertilizers and soil amendments to correct deficiencies, erosion control measures to prevent soil loss, and conservation practices to enhance soil structure and health. Additionally, soil management involves the integration of organic matter, such as compost and crop residues, to enhance soil fertility and microbial activity. The overarching goal of soil management is to ensure the long-term sustainability of agricultural systems by preserving soil health, supporting crop productivity, and minimizing environmental impacts.

Method of Soil Management 1

. Soil Testing and Analysis: Soil testing and analysis play a pivotal role in soil management for agricultural crops, providing farmers with critical information about soil health, fertility, and nutrient status. By understanding the composition of their soil, farmers can make informed decisions about fertilization, soil amendments, and crop selection to optimize yields and minimize environmental impacts. For example, soil testing can reveal deficiencies or excesses of essential nutrients such as nitrogen, phosphorus, and potassium, enabling farmers to tailor their fertilizer applications accordingly. If a soil test indicates low levels of phosphorus, for instance, farmers can apply phosphorus-rich fertilizers to replenish the nutrient and support healthy crop growth. Conversely, if soil pH is too high or too low, amendments such as lime or sulphur can be applied to adjust pH levels and create optimal growing conditions for crops.

Introduction Soil management in horticultural crops refers to the deliberate and systematic approach of caring for soil to optimize its health, fertility, structure, and overall quality to support the growth and development of horticultural plants. It involves a range of practices aimed at preserving and enhancing soil resources, including soil testing, nutrient management, irrigation scheduling, erosion control, and organic matter addition. The goal of soil management in horticultural crops is to create and maintain an environment in which plants can thrive, maximizing crop yields, quality, and sustainability while minimizing environmental impacts such as soil erosion, nutrient runoff, and soil degradation. By implementing effective soil management strategies, horticultural growers can ensure the long-term productivity and viability of their farming operations, while also promoting soil health and resilience in agricultural ecosystems.

Current Soil Conditions

A study conducted in 2016 over 75 fields revealed that soil compaction was present in 70% of annual crops and 60% of perennial crops. Most of the soils used for both annual and perennial cropping were in a moderate condition. However, the soil condition for established crops was improved by performing cultivations before planting. Nevertheless, some soil formations exhibited instability, especially on soils with a lighter texture and a low content of organic matter. The majority of soil cultivations successfully alleviated compaction, however some cultivations had little impact or even exacerbated compaction due to spreading, puddling, or compression when performed in damp or wet field conditions. Tillage pans may greatly diminish productivity and overall efficiency of production by impeding drainage and root development. Approximately 60% of fields cultivating annual crops and 50% of areas cultivating perennial crops had a well-established tillage pan. Approximately 10% of fields underwent deep cultivation without any evidence of soil compaction, indicating a lack of consideration for soil conditions and the need for subsoiling. The abundance of earthworms in the topsoil may serve as a valuable measure of soil health, and is primarily influenced by the intensity of farming practices and the presence, nutritional value, and consistency of earthworm food sources. Earthworm populations exhibited a general scarcity in both annual and perennial crops, while they were relatively more plentiful in areas with ample crop waste and apple orchards. The regular tilling of the soil is believed to be a significant contributing factor to the very low population of earthworms found in places where crops are grown every year. Fields that had a mustard cover crop reported the greatest populations of earthworms.

Carbon is found in all living organisms and is the major building block for life on earth. It exists in many forms, predominantly as plant biomass, soil organic matter, and as the gas CO₂ in the atmosphere and dissolved in sea water. Carbon cycles globally among five distinct pools among which the largest oceanic poolis estimated at 38000 Pg (Pg= petagram =1x10¹⁵g=billion tonnes) and is increasingat the rate of 2.3 Pg C yr^-1 (Fig. 1). The geological C pool, comprising fossil fuels, is estimated at 4130 Pg, pedologic, estimated at 2500 Pg to 1m depth, atmospheric pool comprising 760 Pg of C with nearly all of it as CO₂, and the smallest among theglobal C pools is the biotic pool estimated at 560 Pg. The pedologic and biotic C pools together are called the terrestrial C pool estimated at approximately 2860 Pg.

1. Introduction
As climate change advances, risk of managing soil and atmosphere with regard to emission and pollution is going out of hand. Many researches and reports say that currently the global warming is 1.1°C more than the pre-industrial levels, which is not far behind the target of 1.5°C which was agreed by nations under the Paris agreement in 2015 (Janki M, 2023). Achieving that will likely involve removing carbon dioxide from the atmosphere, according to the Intergovernmental Panel on Climate Change. But strategies like capturing and storing the carbon emissions from biofuel-burning power plants, or planting new forests to absorb carbon, can create their own problems. Recently UN security general said we are shifting to the “Era of global boiling” from global warming. Globally countries are witnessing unbearable heat waves, forest fires, irregular rainfall, flashfloods, coral bleaching and unpredictable weather patterns which often resulting in devastating effects on the coastal and hilly regions of the country. Around nine tipping points have been identified so far globally. Climate tipping points are threshold that when crossed leads to irreversible changes in the climate system and will have a severe impact on the living organisms on the earth. All these variations in climate are driving by increasing greenhouse gas (GHG) emissions and global warming. We cannot change the state of atmosphere to as existed thousands or millions of years ago. Only option left with us is to reduce emissions and prevention of further global warming and climate change. As we are already existing in some level of changed climate, responding to climate change involves a two-pronged approach, reducing emissions of and stabilizing the levels of heat-trapping greenhouse gases in the atmosphere through mitigation and secondly, adapting to the climate change. Because climate change is irreversible process.

Is it possible to feed a world population projected to reach 8.5 billion by 2030, 9.7 billion by 2050 and exceed 11 billion in 2100? India expected to surpass China as the most populous country in the world within seven years (UN report July 2015). Besides that there is an immense decline in yield and quality over the past three decades may be at the point of diminishing returns (Bouis 1993; Cassman et al. 1995; Flinn and De Datta 1984). Furthermore, the soil is partially under tremendous pressure to sustain yield and production. The excessive and exhaustive agriculture practices have not only declined the soil quality but it’s also reported for different human and animal health issues. Thus, keeping pace with population growth and health safety appropriate soil management practices must be addressed. Now burgeoning population load, declining yield, soil health diminution, and effect on human and animal health arises the opportunity for sustainable soil management to cater the problem at the right time. Figure 1 clearly indicates the tremendous load on soil and subsequent results. Burgeoning increase in population and a load of food production intensification, sustainable soil management will become increasingly important in future. Soil being the powerhouse of the mineral nutrients also retains most living organisms within it. The appropriate soil management practices ensure the critical level of mineral elements which finally come into the human body.

7.1 Introduction

Soil is an essential component of ecosystem sustaining all living vegetation, microorganisms, herbivores and carnivores. It is the outermost layer of the earth. It varies greatly in its physical and chemical properties which depend on its age and on the conditions (parent material, climate, topography and vegetation) under which it was formed. Processes such as leaching, weathering and microbial activity combine to make a whole range of different soil types, each of which has particular strengths and weaknesses for agricultural/ horticultural production.

The materials present in the soil are mostly in three states, i.e., solid, liquid and gaseous. They differ in their percentage from soil to soil. A good soil should have 5% organic matter, 45% mineral matter, 25% air and 25% water. So, while establishing an orchard, whole soil profile should be taken into consideration. Digging a pit shows the different layers of soil profile. Usually these are same and not distinct in many areas. Inorganic materials are the major component of most soils. They consist largely of mineral particles with specific physical and chemical properties which vary depending on the parent material and conditions under which the soil was formed. It is the inorganic fraction of soils which determines soil physical properties such as texture and has a large effect on structure, density, water retention and aeration. Air and water percentage in soil vary significantly with soil texture and weather conditions. The soil texture is a property which is determined largely by the relative proportions of sand, silt and clay particles content in it. The classification of soil based on particle size is termed as textural classification of soil. As per USDA classifications, clay particle size is less than 0.002 mm, silt size varies in between 0.002 to 0.05 mm and sand size in between 0.05 to 2.0 mm. On the basis of percentage of these particles present in a soil, the type of soil can be easily determined.

Soil mechanics as a distinct branch of soil science is comparatively of recent growth. Its need arose from the fact that the requirements of the engineer are very often quite different from those of the agriculturist. Whereas the former would as a rule require hard, compact, impervious soil, the latter would have no use for it for the growth of his plants which require soft, friable and porous soil. The agriculturist generally has to look up to nature to help him out of his difficulties, the engineer has to depend on his scientific skill to modify the soil to suit his requirements. In this chapter an attempt will be made to explain in a simple language the requirements of the building, road, and irrigation engineer for particular types of soils and how they are met by modifying the soil if the required properties already do not exist.

Q. 1 Hygrophilic soils are those
(A) Which attract water       (B) Which do not attract water
(C) Which transmit water    (D) Which produce water

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:

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

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.

Introduction

Nitrogen constitutes 78% of the atmospheric gases and there is about 75,000 Mg N on each hectare of land. However, 99% of the atmospheric N is as N₂ and is inert and non-reactive, while the rest 1% or even less is the reactive-N. Reactive-N is linked with H, O and C and is responsible for the creation and sustenance of all life on the planet Earth. Nitrogen is the key nutrient that separates proteins from carbohydrates and fats, the three major macronutrients for humans. As a component of proteins, N is present in DNA and RNA, which carry the hereditary characters and then as the major constitute of the body muscles of humans (and animals). Plant growth and crop production are also very much dependent on the adequate availability of N in soil.

Spatial variability in soil parameters including nutrients has been attributed to the parent material, topography, landforms, cropping pattern, fertilization and manuring practices.. Blanket nutrient recommendations further widen the variability and enhance the risk of soil degradation in terms of soil organic carbon and nutrient mining, acidity, green house gas emission, water and environmental pollution. Unfavorable economics on account of blanket recommendation, adversely influence farmers to increase investments in new crop management technologies. This results in low farm productivity and poor soil health, that jeopardize food security and agricultural sustainability.

Introduction

Soil test-based fertility management is an effective tool for increasing productivity of agricultural soils that have a high degree of spatial variability. However, major constraints impede wide scale adoption of soil testing in most developing countries. In India, these include the prevalence of small holding systems of farming as well as lack of infrastructural facilities for extensive soil testing (Sen et al., 2008). Under this context, GIS-based soil fertility mapping has appeared as a promising alternative.

Introduction

Organic matter in soil is the key to soil health. SOM improves many physical, chemical, and biological characteristics of the soil, including water holding capacity, cation exchange capacity, pH, buffering capacity, and chelating of micronutrients. Furthermore, well decomposed SOM improves soil structure by increasing aggregation, enhances biological activities in the soil, slowly releases nutrients, and suppresses some diseases. A loss of SOM can lead to soil erosion, loss of fertility, compaction, and general land degradation.

Introduction

The soil is the largest terrestrial pool of organic carbon, about 1150 Pg (1Pg = 10¹⁵ g) compared with about 700 Pg in the atmosphere and 600 Pg in land biota (Lal and Kimble,1997). Organic carbon level of soils reaches a fixed equilibrium that is determined by a number of interacting factors such as precipitation, temperature, soil type, tillage, cropping systems, fertilizers, the type and quantity of crop residues returned to soil, and the method of residues management. In the temperate climate, it may take about 50 years for the organic carbon of soils to reach a new equilibrium level following a change in management. However, this period is much shorter in a semiarid and arid climate and also in tropical climate like India.

5.1. What is soil organic matter?

Plant and animal residues which are not yet added to the soil are considered as organic materials. However, once they are added to soil, they become soil organic matter. Therefore, organic materials contributing to the soil matrix are referred as Soil Organic Matter (SOM). Sometimes SOM is also used to highlight only the non-living organic materials produced by living organisms. But SOM should be regarded as a broad term that includes biomass, partially decayed residue, and highly decomposed and transformed organic substances, humus. Agricultural soil contains nearly 1-5% of SOM, which is regarded as least amount in soil as compared to other three soil components, minerals (45%), air (25%) and water (25%). However, it contributes enormously to soil productivity. Soil productivity and fertility exhibit direct positive relationship with SOM content in soil. Plants and animals are considered as primary and secondary sources of soil organic matter, respectively. Plant residues and application of organic manures e.g., farmyard manure, compost or green manuring help to build up organic matter in soil and thus, enrich the soil with organic carbon and other plant nutrients. Under natural conditions, roots of grasses in grasslands, the leaves including shoot portion of the large trees in forest lands and after harvesting the crop remnants in agricultural field provide enough incorporation of organic materials in soil. SOM plays a vital role to maintain sustainability in agricultural production through producing healthy soils and thus, healthy crops.

Soil organic matter makes up only a few per cent of most soils, but it has a great deal of influence on soil properties and on agricultural productivity.

2.1. Quantity of Organic Matter

Based on the content of organic matter, soils are identified as mineral or organic. Mineral soils dominate most of the world’s cultivated land and may contain anything from a trace to 30 per cent of organic matter. Organic soils are naturally rich in organic matter, chiefly due to climatic reasons. Although they contain more than 30 per cent organic matter, it is precisely for this reason that they are not vital cropping soils.

Plants are the generators or the primary source of organic matter while animals are the transformers- secondary source of organic matter. In agriculture, plants add 10–30 percent of organic matter through their roots stubbles and leaf fall and exudations. The excreta of livestock, the organic wastes of urban and rural residential areas include the garbage and sewage and sludge. The by products of agro based industries viz. bagasse, vinasse, pressmud from sugar industries, the coir dust from the coir industries, dust of cotton from ginning industries, the fruit and food processing industries wastes.

Carbon may be present in soil in four different forms:

1. Carbonates: Mainly as CaCO₃ and MgCO₃, active CO₃ ^2- and HCO₃ ^- ions and gaseous CO₂.
2. Highly condensed elemental organic form: Charcoal, graphite.
3. Completely decomposed resistant organic residues: Humus.
4. Undecomposed and partially decomposed organic residues.

The latter three fractions constitute the total organic carbon of which last two are chemically active form.

Carbon may present in soil in four different forms:

1. Carbonates: Mainly as CaCO₃ and MgCO₃, active CO₃^2- and HCO₃^- ions and gaseous CO₂.
2. Highly condensed elemental organic form: Charcoal, graphite.
3. Completely decomposed resistant organic residues: Humus.
4. Undecomposed and partially decomposed organic residues.

Soil organic matter (SOM) is one of the most complex materials existing in nature. Besides the organic constituents in undecayed plant and animal tissues, SOM contains both living and dead microbial cells, microbially synthesized compounds and an unending array of derivatives of these materials produced as the result of microbial activity. Soil organic matter contains most of the naturally occurring organic compounds. Some components of SOM are undoubtedly unique to the soil environment, particularly those involving inorganic-organic complexes.

Soil organic matter is any material produced originally by living organisms (plant or animal) that is returned to the soil and goes through the decomposition process. At any given time, it consists of a range of materials from the intact original tissues of plants and animals to the substantially decomposed mixture of materials known as humus. Soil organic matter (SOM) is the organic component of soil, consisting of three primary parts including plant residues and living soil organisms, decomposing (active) organic matter, and stable organic matter (humus). Most soil organic matter originates from plant tissue.

4.0 Soil organic Matter

The soil organic matter (SOM) is a storehouse of multi-nutrient elements, composed mainly of carbon, hydrogen and oxygen and small amounts of other elements like nitrogen, phosphorous, sulphur, potassium, calcium , magnesium and organic residues coming out from the decomposed plant or animal products (Figure 4.1). The SOM may have the recently incorporated materials or age-old decomposed materials or with living flora or fauna in the organic matrix. Soil organic matter is one of the important components determining soil quality indices and also for enriching the fertility status of soil for production maximization. The nutrient retention capacity , water holding capacity, degradation of pollutant elements, carbon sequestration, soil structure and aggregate stability are affected by the presence of SOM.

ABSTRACT

Microorganisms play a key role for the proper running of the ecosystem. They help in nitrogen fixation, which is unique and most necessary property found only in this group. They help in decompositions, mineralization, nutrient cycling, phosphate solubilization, soil aggregate formation, symbioses, parasitism and many other important works. A great emphasis has been given by many scientists to conserve the microbial diversity. Developing human civilization has a great negative impact not only on the above ground biodiversity but also on the belowground biodiversity. This article is an overview, what important and crucial role nitrogen fixers play for maintaining soil and plant health. Nitrogen fixer not only fixes atmospheric nitrogen but also produces growth promoting hormones which are very important for plant growth. 

To millions of different organisms around the world, soil is the habitat. A handful of soil can contain billions of soil micro-organisms. One gram of a fertile soil can harbour up to one billion bacteria. Only 5% of what is produced by green plants is consumed by animals, but 95% is consumed by microorganisms. Soil organisms are generally grouped into microfauna/microorganisms and macrofauna. The main soil microorganisms are bacteria, fungi, and protozoa. The macro-fauna includes oligochaeta, arthropods, mollusks and nematodes. These organisms play an essential role in soil formation and soil environment.

27.1. Bacteria

Bacteria are the major single-celled microorganisms in the soil ecosystem that are responsible for many important processes. There are many different types of bacteria and most of them are aerobic, requiring oxygen from the soil atmosphere. However, there are bacteria that live without oxygen and other types can live both with and without oxygen. The growth of these bacteria is limited by the food that is available in the soil. They decompose plant materials as well as other organisms’ wastes that contain plant nutrients in an unusable form and convert them into a form that can be used by plants. One such essential nutrient that is converted by bacteria is nitrogen. Nitrogen-fixing bacteria are able to use the nitrogen (N₂) that exists in the atmosphere and convert it through cellular processes into ammonia (NH₃). Nitrifying bacteria mix ammonia with water to create ammonium ion (NH₄+) and nitrate (NO₃^-), which can be used by other organisms.

ntroduction

Millions of living organisms present in soil make it a living and a dynamic system. Under a microscope, it reveals a complex array of soil particles and pore spaces filled with air and water. In these pore spaces that plant roots and millions of organisms develop, which are ranging from sub-microscopic to macroscopic in size. The physical and chemical characteristics of soil determine the nature of the environment in which vast number of soil microorganisms especially soil microorganisms are found. Living organisms in soils include both macro (earthworms, rodents, termites etc.) and microorganisms (bacteria, fungi, actinomycetes, algae and protozoa). These organisms not only help in the development of soils but also carry out a number of transformations, facilitating the availability of nutrients to the plants.

Pasteurization: The heat treatment given to soil to free it of harmful microorganisms or pathogens and pests is called pasteurization. It kills weed seeds also.

Pasteurization of greenhouse plant growing media

Greenhouse growing medium may contain harmful pests such as disease causing organisms, nematodes, insects and weed seeds. It is advisable to decontaminate it by heat treatment or by treating with volatile permissible chemicals.

11.1 Determination of Penetrability of Soil

Penetrability of a soil is usually assessed by the penetration resistance, which a measure of soil strength and thereby the soil compaction. Penetration resistance is the capacity of the soil in its confined state to resist penetration by a rigid object. Besides soil strength, the penetration resistance also depends on the size, shape and orientation of the axis of the penetrating probe. The penetrating probe may be a finger, pencil, stick, root or any specially designed object having a specified geometric shape and a device to measure the resistance as it is pushed into the soil.

Soil penetrability is intimately related to agriculture because of its adverse impact on draught requirement during ploughing, root development and crop yield, to civil engineering due to its relation to settlement, stability and ground water flow.

Soil penetrability is a measure of the ease with which an object can be pushed or driven into the soil. Any device designed to measure the resistance to penetration may be called penetrometer. There are several types of penetrometers: (i) pocket penetrometer, (ii) proctor penetrometer, (iii) cone penetrometer, and (iv) split-spoon penetrometer. Here, we will discuss about two most commonly used penetrometers viz. pocket penetrometer and cone penetrometer used for agricultural purposes.

Crusting soils

What is soil crusting?

Soil crusting refers to formation of a compact thin layer having high bulk density and high penetration resistance at the soil surface when dries after dispersion of fine particles and clogging of pores due to beating action of rain drop and slaking of irrigation water.

In arid and semiarid regions, crust formation occurs due to the destruction of soil aggregates. Crust formation occurs in all types of soils except sand. It is characterized by high bulk density, low non capillary pores, low hydraulic conductivity and aeration and high penetration resistance.

Introduction

Soil aeration status involves the rate of such ventilation, as well as the proportion of pore space filled with air, The composition of that soil air and the resulting chemical oxidation or reduction potential in the soil environment. Water provides the base for food, nutritional and environmental security. Soil water plays a significant role in controlling the energy balance of the soil and its overlying micro-environment by modifying its radiation exchanges and thermal properties. Soil temperatures affect plant and microorganism growth and also influence soil drying by evaporation. It is a central maximum of ecology that “everything is connected to everything else.” This interconnectedness is one reason why soils are such fascinating and challenging objects of study. In this chapter we shall explore three aspects of the soil air, water and temperature.

Soil physics is the study of soil’s physical properties and processes. Soil physics deals with the dynamics of physical soil components and their phases as solid, liquids, and gases. Physical properties of soil include texture, structure, density, porosity, consistency, temperature, colour and water content. The physical properties depend on the amount, size, shape and arrangement and mineral composition of its particles , kind and amount of organic matter and the volume and form of its pores and the way they are occupied by water, air at a particular time.