eChapters

3.1 Important Soil Physical Properties

3.1.1 Analysis of Soil Texture

Soil texture refers to the relative proportions of sand, silt, and clay on weight basis. Soil texture was recognized from very early times by experienced farmers from the feel of moist soil placed between the thumb and forefinger. The size groups arbitrarily classified by the International Society of Soil Science (ISSS) into clay (< 0.002 mm), silt (0.002 0.02 mm), fine sand (0.02-0.2 mm), and coarse sand (0.2 2.0 mm). Each soil textural name specifies the weight percent of each fraction falls within certain defined limits. The determination of the percentage of the soil separate present in a sample is called particle-size analysis.

Each type of particle present makes its contribution to the nature of the soil as a whole. Sandy soils are usually quite permeable to air, water, and roots, but they have two important limitations. One is their relatively low water-holding capacity; the second is that they are poor storehouses for plant nutrients. These limitations of sandy soils can, of course, be overcome if both fertilizer and irrigation water are available, but the costs are large.

Clay not only have a large surface area per gram, it also has electrically charged particles. These charges give clay the capacity to attract plant nutrient ions to its surface in forms available to plants, but sand lacks this capacity. Clay holds much more water than sands because they have a large surface area to be coated with water. One important problem with clay soils is their stickiness. When wet, they stick to ploughs, boots, or whatever they contact. Loam and silt loam soils are highly desirable for most uses. They have enough clay to store adequate amount of water and plant nutrients for optimum plant growth but not so much clay as to cause poor aeration or to make working with them difficult.

Soil sampling is the first step of soil analysis. As very small fraction of the huge soil mass is used for analysis, it becomes extremely important to get a true representative soil sample of the field.

SOIL MANAGEMENT PRACTICES

Good soil management is the basic for deriving greater benefits from the fertilizers used in crop production. Some of the good soil management practices are

Good tilth is the first feature of good soil management. It means a suitable physical condition of the soil and implies in addition a satisfactory regulation of soil moisture and air.

The maintenance of soil organic matter which encourages granulation is an important consideration of good tilth.

Tillage operations and timings should be adjusted as to cause the minimum destruction of soil aggregates. Good tilth minimizes erosion hazards.

The choice and sequence of adaptable crops or crop rotation are other very important considerations. These are related to climate, particularly rainfall and its pattern of distribution and the characteristics of the soil profile, including drainage and extent and duration of available soil moisture. A proper sequence of crop varieties greatly influences soil conditions. It is more realistic to evolve cropping patterns and land management practices according to land capability. Cropping patterns chosen and management practices adopted should aim at soil and moisture conservation for efficient nutrient and moisture utilization.

As compared to total N soil total P is present in much smaller amounts in soil; it is roughly about 10% of total N. Further, while N in soil is in the largest amount in surface 0 to 15 cm layer, soil P may be the same or in larger amounts in the sub-soil. Again, organic P constitutes only a small portion of total P. Thus, the Chemistry of soil P is generally centered on inorganic P. Total and organic P in some Indian soils is given in Table 8.1; hill soils had the highest and the desert soils the least total as well as organic P.

FRACTIONS OF INORGANIC P

All P in soils has originated from apatites [3 (Ca₃ (PO₄)₂.Ca×₂, where ×₂ could be F, Cl, (OH) or CO₃). Large deposits of apatites form phosphate rocks, which are the major materials for making phosphate fertilizers. As the soil weathering proceeds, P in apatite reacts with Al, Fe and other cations and forms compounds of different solubility. A knowledge of these can help in understanding the P-supplying capacity of soils. A number of chemical extractants and resins are used for determining different fractions. In general, 7 fractions of inorganic soil P are mentioned. These are: saloid-P (soluble and loosely bound P extractable by NH₄Cl), labile P (determined by using anion-exchange resins), Al-P (NH₄F extractable), Fe-P (NaOH extractable), Ca-P (H₂SO₄ or HCl extractable), reductant-soluble- P (CDB or sodium citrate-sodium dithionite-sodium bicarbonate extractable) and occluded P (CTB followed by NaOH extractable)

Out of the three primary plant nutrients (NPK), potassium (K) is taken up by crop plants in the largest amount, yet as compared to N and P, only a tiny fraction of it goes in the grain or seed. For example, Shivay et al. (2015) reported from a study on rice that about 20 kg N, 6 kg P (13.7 kg P2O5) and 46 kg K (55.2 kg K2O) was taken up by the crop to produce each Mg or tonne (1,000 kg) of rice kernel; however, only 4.3% of K taken up by the crop was found in the rice kernel as compared to 44% of N and 66% of P taken up by the crop. Some information on N, P and K removed per tonne of grain/ seed for some crops is given in Table 9.1.

Soil is defined as a thin layer of earth’s crust which serves as a natural basic medium for the plant growth. Soil is a dynamic natural body composed of minerals, organic materials and living forms on which plants grow. Soil are formed by the weathering of rocks and minerals in presence of soil forming factors like climate, organisms, relief or topography, parent material and time (cl,o,r,p,t).The weathering of rocks and minerals are associated with physical and chemical phenomenon. The principal agents of physical weathering are temperature, water, wind, plant and animals. Chemical weathering is affected through the process of hydrolysis, hydration, carbonation, oxidation and reduction.

Each soil is characterized by a given sequence of horizons. Combining of this sequence is known as soil profile. Soil profile is a vertical section of the soil through its horizons. The layers or horizons in the soil profile vary in thickness and have different characteristics like colour, texture, structure etc. The horizons are designated by O, A, E, B, C and R.

Horizon: The layers seen in the vertical section of the soil profile are called horizons.

Soil is a living, dynamic ecosystem that nurtures plants. Soil is responsible for Sustaining plant and animal life below and above the surface, Regulation water and fertilizer/pesticide runoff, Storing and cycling nutrients. But, the natural soil balance was disturbed by man due to agricultural activities to get food. The intensification of agriculture leads to soil erosion, which leads to creation of unproductive soils.

In agriculture, soil erosion refers to the wearing away of a field’s topsoil by the natural physical forces of water and wind or through forces associated with farming activities such as tillage. As a result of improper cultivation practices, deforestation and overgrazing aggravates the problem of soil erosion.

Globally soil erosion has reached a level that endangers the sustainable supply of food for the growing global population. It already threatens food production and ecosystem service delivery and therefore, there is a pressing need to address this threat. This is especially true in India where, in a total area of 328 million hectares (m ha), 121 m ha is undergoing soil degradation, 68% of which is attributed to water erosion. Water erosion rates range from 5 t ha^–1 yr^–1 in dense forest regions to rates in excess of 80 t ha^–1 yr^–1 where erosion is most severe, such as in the Shiwalik mountainous region. India’s average soil loss has been estimated to be 15t ha^–1 yr^–1; however, given the limited coverage of measurements, this should be treated with caution. In the light of the serious threat that soil erosion poses in the country, there is a pressing need for a systematic nationwide assessment of land degradation due to erosion using appropriate techniques. The area under ravine soil erosion is highest in UP to a tune of 12.30 lakh hectares and lowest in Maharashtra to a tune of 0.20 lakh hectares

Soil is made up of minerals, organic matter, gases, liquids and micro-organisms in different proportions. It provides anchorage to plants. It is important for life as it provides the medium for the growth of a plant, habitat for several insects and other organisms. Soil is a store house of nutrients, micro-organisms, air and water. It is the source of four essential ‘living’ factors including food, clothes, shelter, and medicines.

SUMMARY

To meet the food requirement of spirally growing population we need to produce more crops per unit area of land. Soil is the raw material for land and is the outer covering of earth surface. It is a very important resource and gift of nature for the substrate where plant can grow. Agriculture is the backbone of our country, and agriculture mainly dependent on soil quality. The success management of soil quality depends on the mechanistic approach, how soil responds to agricultural use and practices over times. As soil degradation grows day by day there is a big challenge against agriculture to sustain. Now days the main cause for soil degradation is non-planed use of land resources. This is the time when we think about this big challenge and face it for the future generation which we need to manage the soil quality for self sustainability. Because adaptation of appropriate soil management scientific methodologies and land use planning could replenish the degraded soil properties for sustainable agriculture which is need of the hour.

Introduction

The natural resources of arid regions particularly soil and water are limited and is often in a delicate environmental balance. Desert encroachment due to lack of conservation planning, and the dangers of destroying or depleting beyond recovery these productive resources, are evident at present time and may be disastrous if development is based on short term expediency rather than long term stability.

The arid zone of India is spread over 38.7 million ha area, out of which 31.7 m ha in under hot arid region and 7 m ha under cold region. The hot arid region occupies major part of north-western India (28.57 m ha) and occurs in small pockets (3.13 m ha) in south India. The north-western arid region occurs between 22o30' and 32o05' N latitudes and from 68o05' to 75o45' E longitudes, covering western part of Rajasthan (19.6 m ha, 69%), north-western Gujarat (6.22 m ha, 21%) and 2.75 m ha (10%) in south-western part of Haryana and Punjab (Faroda et al. 1999). Rainfall distribution is highly uneven over space and time (CV>60%). The region receives low rainfall (<100 mm to 500 mm), has high evapotranspiration and high temperature regime (Rao and Singh 1998). Groundwater is deep and often brackish. The western-central area is devoid of drainage system and surface water resources are meager (Fig. 20.1). Due to low and erratic rainfall, replenishment of water resources is also very poor. The entire Rajasthan state is being categorized as the driest state and water scarce (having per capita water availability below 1000 m3 year-1) since 1991 in the country. Increasing pollution by industrial units, big and small, unregulated mining and even over-extraction of water from deep wells also add to the water quality problem in number of districts. Rapid urbanization and industrialization make such existing differences even more

Out of 329 m ha geographical area in the country, 187.8 m ha or 53% is affected by various forms of degradation process which include 148.9 m ha affected by water erosion, 13.5 m ha by wind erosion, 13.8 m ha by chemical deterioration and 11.6 m ha by physical deterioration. The annual loss of topsoil is nearly 16.0 t/ha/year resulted in to 8.4 m t/year total nutrient loss. 

Soil and water are the basic resources in drylands. Soil supports plant life by providing a medium for their growth and development. It is a non-renewable natural resource and susceptible to rapid degradation through various forms of erosion processes. Worldwide, around 52% of total productive land has been degraded by various kinds of degradation processes and almost 80% of the terrestrial land is affected by water erosion .Further, annually ~10 million hectares (Mha) of cropland becomes an unproductive at the global level due to soil erosion with an average rate of 30 t ha−1 year−1 soil erosion .In India, out of 328 million hectares of geographical area, 68 million hectares are critically degraded while 107 million hectares are severely eroded. Soil degradation in India is estimated to be occurring on 147 million hectares (Mha) of land, including 94 Mha from water erosion, 16 Mha from acidification, 14 Mha from flooding, 9 Mha from wind erosion, 6 Mha from salinity, and 7 Mha from a combination of factors (Battacharya et al., 2015).

Soil pollution is any physical or chemical change in soil that adversely affects the health of plants and other organisms living in and on it.

Soil pollution is important not only in its own right but because so many soil pollutants tend to move into surface water, groundwater, or air.

The chief soil pollutants are salts, petroleum products, heavy metals, and agricultural chemicals. Point source releases of industrial solvents (both LNAPLs and DNAPLs) and feedstock chemicals (e.g., for making plastics) often occur as the result of LUSTs (leaking underground storage tanks).

Salinization, a common problem in irrigated arid and semiarid regions, makes soil unfit for growing most crops. It is extremely difficult to remove excess salts from salinized soils.

A variety of techniques are used for soil remediation, which is cleaning up contaminated soil.

1. These include physical techniques such as
   1. Soil vapor extraction (SVE), moving air through the soil.
   2. Thermal conduction heating, heating the soil before SVE.
2. Bioremediation methods include
   1. Landfarming, fertilizing, liming, and repeatedly plowing contaminated soil to stimulate bacterial decomposition of high molecular weight hydrocarbons like those in diesel oil.
   2. Bioventing, pumping air at low rates through soil to provided O₂.
   3. Biosparging, pumping air into aquifers to provided O₂.
   4. Phytoremediation, particularly useful for removing heavy metals.

The term soil refers to the outer, loose material of the earth’s surface, a layer distinctly different from the underlying parent rock. A number of features characterize this region of the earth’s crust. It is the natural medium, which supports plant growth. It provides the physical support needed for the root system and also supplies nutrients needed for plant growth. It is a perennial source of organic matter. It supports a vast population of microorganisms.

This procedure uses Diethylene Tri-amine Penta Acetic acid (DTPA) as the chelating agent, which combines with free metal ions in soil solution and forms soluble complexes.

This is a distillation method proposed by Subbiah and Asija (1956), where the soil is distilled with alkaline KMnO solution. The ammonia liberated is trapped in boric acid and then determined by titration against a standard acid. This procedure estimates the easily mineralizable nitrogen in soil.

Estimation of plant available phosphorus content in soil has been attempted using several extractants. However, Bray’s reagent and Olsen’s reagent are the two common extractants used in India. Bray’s reagent (0.03 N NH₄F and N HCl) is used for acid soils, where, the fluoride ion complexes with Fe and Al in soil and thus releases the bound P. The Olsen’s reagent (0.5 M NaHCO₃) is used for neutral-alkaline soils.

In soil system, potassium (K) exists as water soluble, exchangeable, non- exchangeable and lattice K. The plant available K refers to the sum of water soluble and exchangeable K. Estimation of available K is usually done using neutral normal ammonium acetate as the extractant.

Introduction

Soil, a dynamic living matrix, is an essential part of the terrestrial ecosystem. It is a critical resource not only to agricultural production and food security but also to the maintenance of most life processes. Soils contain enormous numbers of diverse living organisms assembled in complex and varied communities ranging from the myriad of invisible microbes, bacteria and fungi to the more familiar macro-fauna such as earthworms and termites. The diversity in soils is several times higher than that above ground. Each hectare top soil contains approximately 1,000 kg of different fungi, 500 kg of bacteria, 750 kg actinomycetes and 150 kg of algae and many protozoa (Table 1). These diverse micro-organisms interact with one another and with the plants and animals in the ecosystem forming a complex system of biological activity. Environmental factors, such as temperature, moisture and acidity, as well as anthropogenic actions, in particular, agricultural practices affect soil biological communities and their functions to different extents. Diversity of soil micro-organisms has emerged in the past decade as a key area of concern for sustainable soil health and crop production. Besides, the well-being and prosperity of earth’s ecological balance, the sustainability of agricultural production systems directly depends on the extent and status of microbial diversity of soil.

1. Introduction
Soil is an extremely complex ecosystem and performs many functions, i. e, biomass production; food contingency, fuel and fibre; buffering and transforming actions; breakdown of organic matter; nutrients recycling; carbon sequestration; providing a biological habitat; source of raw materials; and regulation of water quality and supply (Weil and Brady, 2017; Telo da Gama, 2023). However, because of natural as well as anthropogenic reasons, there is a widespread degradation of soils. Soil degradation means deterioration in overall soil functioning which leads to slowdown of distribution of ecosystem services because of the impairment of soil health through anthropogenic perturbations. Therefore, farmers and researchers are very much concerned about soil health and crop productivity. Soil health status and its quality are often used interchangeably and have been defined by research community differently but recently the word soil health is acquiring popularity due to its flexibility in allowing diverse stakeholders, including policymakers to use the term in their own way. Recently, soil health is a topic of much discussion and research (Bünemann et al., 2018). Soil health is described as “the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans” (USDA-NRCS, 2019). A broader, ecologically based approach is “the capacity of soil to function as a vital living system, within ecosystem and land-use boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and promote plant and animal health” (Doran et al., 2000). Soil health refers to the actual capacity of a soil to function, contributing to ecosystem services. Many have defined it as “fitness for use” while the rest regard as “capacity of the soil to function”. Lehmann et al. (2020) stated that the concept of soil health “connects agricultural and soil science to policy, stakeholder needs and sustainable supply-chain management” and compared the soil health concept to soil fertility, soil quality and soil security. Furthermore, they came to a conclusion that soil health is narrower concept than soil security, but more comprehensive than soil quality and even broader than soil fertility, in relation to the current sustainable development goals (SDGs) as proposed by United Nations. From an overall perspective. Soil health comprises of refinement and unification of the chemical, physical, physico-chemical, biophysical, biochemical indicators of soil that supports productivity and environmental quality (Figure 1). Soil can be classified as healthy or unhealthy based on its ability to sustain plant and animal productivity while maintaining air and water quality.

9.1. Introduction

Soil biology is a branch of science that studies the soil inhabiting organisms in relation to their ecology, functions, behaviour and impact on various soil processes and plant growth. Soil fertility is directly dependant on humus content as well as the presence of microorganisms in soil, although surface soil does not contain more than 0.5% by weight of living organisms. However, such a small portion of soil constituent as compared to other organic and inorganic constituents plays a significant and major role in transformation of plant nutrients from their unavailable to available form from organic wastes, soils and fertilizers. They have a direct role in improving soil tilth, providing an appropriate environment for root growth, decomposing organic residues to form humus and in turn releasing nutrients for plants use, releasing many plant growth promoters, fixing inert atmospheric nitrogen in plant usable forms and they promote many other important processes without which plants cannot survive. Absence of living organisms in soil leads to its infertility. An understanding of microbial processes in soil environment, keeping in view of soil nutrient status, carbon sequestration, soil health and quality, overall sustainability in agriculture and also global warming in respect of greenhouse gas emissions (nitrous oxide and methane) through agricultural practices, is very important in regulating nutrient release at different plant growth stages. If we are in a state to understand how various biological processes influence various changes in soil environment or in the opposite way that how different soil conditions alter the soil biota in number as well as in their functions and diversity, it is easier to implement soil management practices that promote to gain more benefits.

Microorganisms are ubiquitous in nature. Possessing a diverse habitat, they are found everywhere in soil, air and water at a varied temperature and pH. One may find the highest genetic diversity of life within the domain of microorganisms. But unfortunately very few are known to us, so far only 1% of the microbial species on the earth are culturable. However, it is believed that soil of one gram may contain hundreds of millions to billions of microbes which may represent several thousand microbial species. In respect of the population, bacteria top the list followed by actinomycetes, fungi, algae and protozoa in accordance with a decreasing numerical order. Out of three important soil fertility components viz. physical, chemical and biological; the biological component is least understood due to its wide complexity.

Study of living organisms in soil is referred to as soil biology (Greek word bios= life, logos = study). The soil is teeming with millions of living organisms which make it a living and a dynamic system.

ABIOTIC FACTORS: Environmental influences produced other than by living organisms for example, temperature, humidity, pH and other physical and chemical influences. Contrast it with ‘biotic factors’ - meaning effects due to biological components.

The plant roots, soil animals and microorganisms make up soil biological communities, accelerate biochemical activities through intra- and extra-cellular enzymes and interact in such a manner that biogeochemical cycling on this earth continues uninterrupted. Without intermeshing vital processes of soil microflora, microfauna and associated mesofauna, the soil would have become a repository of plant residues and animal remains with no facility for recycling the vital nutrients for plant growth, thus halting the whole process of geo-chemical recycling in nature. Though living component rarely makes up more than 4% of the total soil organic carbon, it plays vital role in geochemical recycling, soil development and ecosystem stability.

Biotechnological research started in early seventies with some impressive discoveries in the field of genetics, microbiology, biochemistry, biology and chemical bioengineering. The amalgamation of these sciences particularly integration of their basic principles and applied aspects gave rise to a new field, completely diverse and versatile in nature, what we call today ‘biotechnology’. Originating from research laboratories in universities, biotechnology rapidly captured the attention of industries as the number of its potential products increased. This newly developed frontier science later found broad application in medical science, pharmaceutical industry, agriculture, veterinary sciences and chemical industry for the welfare of mankind. Biotechnology by definition means ‘any technique that uses living organism or a part thereof to make or modify a product, to improve plant or animal or to develop microorganisms for specific purposes’.

Soil bulk density (BD) or apparent density is determined in -situ by core method. Stainless steel or metallic cores of cylindrical shape with known height and diameter are inserted into the soil till the rim of the core. The soil core is then excavated and the soil sample is oven dried to get the dry weight. The ratio of the oven dry weight to the total volume of the core gives the bulk density of the soil.

Carbon is the cornerstone of all life on Earth. Plant tissues and microbial cells contain approximately 40 to 50% of carbon on dry weight basis. Yet, the ultimate source is the CO₂ of the atmosphere. The CO₂ is converted into organic carbon by the action of photoautotrophic organisms (higher plants and green algae). It has been estimated that the vegetation on earth’s surface consume some 1.3 x 10¹⁴ kg of CO₂ per annum which is about V₂₀ of the total CO₂ supply of the atmosphere or ¹/₁₀₀₀ of that in the ocean.

Organic C in agricultural soils contributes positively to soil fertility, soil tilth, crop production, and overall soil sustainability. Changes in agricultural management can potentially increase the accumulation rate of soil organic Cd (SOC), thereby sequesteringCO₂fromtheatmosphere.Optimizingagricultural management for accumulation of SOC can result in the sequestration of atmospheric CO₂, thereby partially mitigating the current increase in atmospheric Carbon dioxide. In addition to the environmental benefits of soil C sequestration, Carbon dioxide consideration has also been given to the implementation of a C credit trading system which may provide economic incentives for C sequestration initiatives.

Changes in agricultural practices for the purpose of increasing SOC must either increase organic matter inputs to the soil, decrease’decomposition of soil organic matter (SOM) and oxidation of SOC, or a combination thereof. These practices include, but are not limited to, reducing tillage intensity, decreasing or ceasing the fallow period, using a winter cover crop, changing from monoculture to rotation cropping, or altering soil inputs to increase primary production (e.g., fertilizers, pesticides, and irrigation). Implementing practices that sequester C can reverse the loss of SOC that may have occurred under intensive cultivation thereby increasing SOC to a new equilibrium

Agriculture in India is one of the most important sectors of its economy. It provides livelihood to almost two thirds of the work force in the country and accounts for 18% of India’s GDP. About 43 % of India’s geographical area is used for agricultural activity and large number of production systems are in practice in different parts ofthe country. In pre-independence era (before the 1950s), agriculture in India was a system of harnessing nature for the sustenance of human beings, similar to the presently defined organic farming. Some countries have moved away from inorganic to organic farming yet it is not possible for India to depend entirely upon this system of farming due to large population. Total availability of plant nutrients from organic sources is projected to be 7.75 million tonnes by 2025 (Tandon, 1997) against the total requirement of37.50 million tonnes (Katyal, 2001) for 1504 million population (Sekhon, 1997). Thus nutrients supply through organic sources alone would result in deficiency of about 30 million tonnes of nutrients. Hence, it is imperative to use both organic and inorganic sources of plant nutrients enhance food production for the increasing population (Mahajan et al., 2007). In India the contribution of organic sources was 80-100 per cent in 1949-50 and reduced to about 32 per cent in 1993-94 and 20-25 per cent in 2004-05. So, it is imperative to enhance organic sources to meet total nutrient consumption. Following independence, rapid population growth in India placed great pressure on land and on these traditional farming systems; huge demands for food grains led to increased use of fertilizers and pesticides to boost production. Still a negative balance of about 8 million tones of NPK is foreseen in 2020, even if we continue to use chemical fertilizers, maintaining present growth rates of production and consumption. The most optimistic estimates at present, show that only about 25-30 per cent nutrient needs of Indian agriculture can be met by utilizing various organic sources. Many of the gains in production during the last 4-5 decades resulted from the “Green Revolution,” a campaign of technological interventions in agriculture widely adopted by farmers in developing countries. Expansion of irrigation to cover rain fed areas, popularization of hybrids/ transgenic varieties of crops, and use ofsynthetic chemical fertilizers and pesticides were the maj or technologies promoted. This paid rich dividends in India, quadrupling food grain production from 50 million metric tons in 1950-51 to 211 million metric tons in 2001-02, and enabling India to become self-sufficient in food grain. Now a second green revolution is also in the offing, to boost agricultural production and meet the estimated requirement of 337 million metric tons.

1. Introduction
Sustainable crop production describes farming practices that do not negatively impact the environment, biodiversity, natural agroecosystem, or the quality of the crops produced. Growing crops sustainably improves the system’s capacity to sustain long-term, steady, and uniform levels of food production and quality without raising the need for or increasing the demand for agricultural inputs necessary for effective management. Sustainable crop production deals with keeping the soil healthy with the integrated approach of maintaining organic matter, protecting biodiversity while reducing use of pesticides, ensuring food safety and food quality. It is an approach to grow food to feed our population without adversely affecting the natural ecosystem, soil and biodiversity, natural resources, environment etc. Since the soil is one of the key natural resources for food production, establishing and preserving soil health is crucial for agricultural sustainability and ecosystem function. The distinction between soil quality and health is quite narrow, and the phrases are sometimes used interchangeably. The “fitness for use,” “capacity of a soil to function,” or “the ability of the soil to serve as a natural medium for the growth of plants that sustain human and animal life” are some basic definitions of soil quality (Karlen et al., 1992; Pierce & Larson, 1993; Doran & Parkin, 1994; Acton and Gregorich, 1995; Karlen et al., 1997). Assessment of soil health by analyzing different associated attributes is necessary to monitor its status. However, soil health or quality evaluation focuses on the physical, chemical, and biological parameters which are highly interlinked to one another. All the parameters have their significant effect in governing overall soil health. This chapter will discuss the chemical parameters only which are very much important for the sustainable crop production and have very crucial role in determining the soil health. It will cover important chemical parameters, essential plant and soil nutrients, heavy metals, agrochemicals etc. which having significant effect on soil health determination

3.1. Soil colloids

Clay fraction of the soil contains particles less than 0.002 mm in size.

Particles less than 0.001 mm size possess colloidal properties and are known as soil colloids.

Soil Chemistry is the study of chemical composition of soil in relation to crop needs. It deals with the chemical constitution of the soil, the chemical properties and the chemical reactions in soils. Traditional soil chemistry focuses on chemical and biochemical reactions in soils that influence nutrient availability for plant growth, and potential environmental consequences associated with inorganic and organic fertilization. Soil chemistry has increasingly focused on soil genesis and the environment over the past few decades.

1. Central Fertilizer Quality Control & Training Institute (CFQC&TI) is situated at

a. Mysore           b. Karnal

c. Faridabad        d. Coimbatore

ACTIVATION ENERGY: The energy required before the reaction of concern will proceed. Often, heating will supply the needed energy. Enzymes or other catalysts lower the activation energy of a reaction.

Soil Classification

Soil classification deals with the systematic categorization of soils based on distinguishing characteristics as well as criteria that dictate choices in use.

Soil classification is grouping of objects in orderly and logical manner into classes based on the properties of soils (differentiating characters) for the purpose of studying and identifying them. The soil individuals are grouped into classes of the lower category (soil series) which are grouped into classes of higher categories (soil orders). The lower categories are defined by large number of differentiating characters and higher category by a few differentiating characteristics.

For soil resources, experience has shown that a natural system approach to classification, i.e. grouping soils by their intrinsic property (soil morphology), behaviour, or genesis, results in classes that can be interpreted for many diverse uses. Differing concepts of pedogenesis and differences in the significance of morphological features to various land uses can affect the classification approach. Despite these differences, in a well-constructed system, classification criteria group similar concepts so that interpretations do not vary widely. This is in contrast to a technical system approach to soil classification, where soils are grouped according to their fitness for a specific use and their edaphic characteristics.

Classification means the process of ordering or grouping of objects having large number of population and wide variations into shorter one in a systematic manner with selected characteristics. Soils being the natural objects have no exception with other objects to classify them in a best possible way. Thus, soil classification refers to the systematic categorization of soils into various groups, classes or any simpler form based on the similar properties and other distinguishing characteristics. The main purposes of soil classification are to organize knowledge, easy remembering of the soil properties for each group and better understanding about the components and the relationships among individuals and various groups of soils. Various soil classification systems have been evolved during the past for categorizing the soils into various groups but the Soil Taxonomy has been now accepted as most scientific system of classification.

Soil Colloids A colloid, also known as colloidal solution or colloidal system, is a mixture in which finely divided particles (less than 1µm in size) known as dispersed phase are suspended in a medium, called dispersion medium. The particles must be dispersed in a medium and both the dispersed phase and dispersion medium may be solid, liquid or gaseous which leads to numbers of possible colloidal systems. In soil, the clay fraction (< 2µm in size) together with finer fractions of some organic matter forms the composition in a state of colloidal nature, known as soil colloids. The soil solids as dispersed phase predominates in the dispersion medium (soil solution). As such, colloids in a soil are referred to as ‘sol’. Clay colloids display the most reactive fractions of soil governing their distinct properties such as adsorption and exchange of ions, zeta potential, flocculation and other electrokinetic phenomenon.

6.1. What is colloid and colloidal system?

A colloidal particle may be defined as a substance which is microscopically dispersed evenly throughout another phase and is possessing a size of 10^-7 to 10^-3 mm and representing a larger surface area per unit mass. Thus, a colloidal system refers to a two-phase system in which small particles of one phase which might be of solid, liquid or gas is suspended evenly in the second phase of solid, liquid or gaseous material. These colloidal systems may be of solid in liquid or solid in gas or liquid in liquid or liquid in gas. Unique examples of liquid in liquid colloidal system includes the fat droplets dispersed in water of milk. When you put floor disinfectant liquid in water, it forms a white emulsion. Thus, emulsion becomes a colloidal system of liquid in liquid. Likewise, in fog, water droplets are suspended in gaseous air. So, fog is an example of a colloidal system, constituting of liquid dispersed in gas. When we refer smoke, it contains carbon particles (solid) suspended in air (colloidal system of solid and gas). However, smog is composed of smoke and fog. In case of soil colloidal system, soil colloids, which are of tiny particles (<0.001 mm size) and may be of organic and inorganic nature, are suspended in soil solution (water) and referred to as sol. Colloidal chemistry, which involves in the surface reactivity and charge characteristics of colloids, plays a pivotal role in total soil chemistry.

Soil Colloids

A colloidal system is a two-phase heterogenous system in which one material in a very finely divided state is dispersed through the second phase. Solid in liquid (dispersion of clay in water) and liquid in gas (fog or clouds in atmosphere) are examples. The clay fraction of the soil contains particles less than 0.002 mm in size. Particles less than 0.001 mm size possess colloidal properties and are known as soil colloids.

Soil colloidal substances are composed of very fine particles (< 0.002 mm diameter) that undergoes two phase system in a heterogenous manner, where, one phase (disperse phase) is disperse in a fine state of subdivision in another medium called dispersion medium. The soil colloidal properties are affected by the physico-chemical and biological parameters of soils. The availability of plant nutrients are governed mostly by the surface charge characteristics of clay colloids.

5.0 Soil Colloids

Soil colloids being one of the active constituents determine the physical and chemical properties of the soil with the diameter ranging from 1 μm to 2 μm. The origin of the particles may be organic and inorganic constituents.

Soil colour is the most obvious characteristic of soil. It has no direct effect on plant growth; however, it has indirect effect through temperature, moisture. Soil colour can indicate the climatic conditions under which it has developed and can be related to its parent material. It can also reflect upon its age, and the temperature and moisture characteristics of the climate. Thus, cooler regions tend to have grayish to black topsoils, due to the accumulation of humus. In moist warm regions, soils tend to be more yellowish-brown to red. Arid soils tend to be light in color (due to low organic content) and primarily express the color of their mineral content. Practically all colours occur in soils - white, red, brown, gray, yellow, black, etc. Predominantly soil colours are not pure, but mixtures. Frequently two or three colours occur, called as “mottling”.

Soil conservation: it is using and managing land based on the capabilities of land itself, involving the application of the best practices to result in greatest profitable production without damaging the land Principles of soil conservation The aim of soil conservation is to obtain the maximum sustainable level of production from a given area of land whilst maintaining soil loss below a threshold level which theoretically, permits the natural rate of soil formation to keep pace with the rate of soil erosion. In addition, there may be a need to reduce erosion to control the loss of nutrients from agricultural land to prevent pollution of water bodies; to decrease rates of sedimentation in reservoirs, rivers, canals and ditches In the longer term, erosion has to be controlled to prevent land deteriorating in quality until it has to be abandoned and cannot be reclaimed, thereby limiting options for future landuse.

AGRICULTURAL WASTE: The characteristics of the agricultural waste materials make them important in respect of their use and economic value. Agricultural wastes can he put to use because (1) Farm development (improvement of soil health, soil fertility, soil physical conditions and plant protection), it is the source of energy and power, (3) it acts as animal feed and fodder, (4) it is the human food

Soil Consistence Defined

Soil consistence is the strength with which soil materials are held together or the resistance of soils to deformation and rupture. Soil consistence is measured for wet, moist and dry soil samples. For wet soils, it is expressed in terms of both stickiness and plasticity. Stickiness is the ability of soil materials to adhere to other objects. Plasticity is the ability of the soil materials to change shape continuously under a constant pressure and to retain the impressed shape when the pressure is removed. Soil consistence may be estimated in the field using simple tests or may be measured more accurately in the laboratory.

Soil consistency is a term used to designate the manifestation of different physical forces acting within the soil at various moisture levels. The consistency limits, also known as ‘Atterberg Limits’ (Atterberg, 1911; 12) are defined by the water content of the soil to create specified degree of consistency. These limits are – (i) Liquid limit or upper plastic limit, (ii) Plastic limit or lower plastic limit and (iii) Sticky limit.

8.1 Determination of Liquid Limit or Upper Plastic Limit

Equipments and Materials

Liquid limit device (Casagrande, 1932) and accessories, spatula, dish, oven, moisture box, balance, desiccator

Soil consistency is a term used to designate the manifestation of different physical forces acting within the soil at various moisture levels. The consistency limits, also known as ‘Atterberg Limits’ (Atterberg, 1911; 12) are defined by the water content of the soil to create specified degree of consistency. These limits are – (i) Liquid limit or upper plastic limit, (ii) Plastic limit or lower plastic limit and (iii) Sticky limit.

7.1. Determination of Liquid Limit or Upper Plastic Limit

Equipments and Materials

Liquid limit device (Casagrande, 1932) and accessories, spatula, dish, oven, moisture box, balance, desiccator

Introduction
Soil crusts are surface alterations in the topsoil resulting from natural processes, such as the impact of raindrops followed by drying. These crusts manifest as thin, hardened layers on the soil surface, particularly common in arid and semi-arid regions. Their thickness typically varies from less than 1 mm to 5 cm (Evans and Boul, 1968). Once dry, these layers become denser, harder, and more brittle than the underlying soil, reducing both the number and size of pores and reorganizing the soil’s pore structure. In temperate regions, surface crusts primarily form on unstable loamy soils, particularly in areas under cultivation. In tropical regions, soil crusting affects a broader range of soils and poses a significant problem not only in arid zones but across various climatic conditions. In humid areas, intensive farming exposes the soil surface to high-energy rainfall for extended periods, accelerating the degradation of soil organic matter. As a result, bare soil areas expand, and biomass production declines. From an agronomic perspective, the most critical drawbacks of soil crusting are its negative effects on seedling emergence and water infiltration. Seedling emergence is particularly affected for crops with small seeds or when the timing of emergence is crucial due to climate or market demands. In some instances, costly replanting becomes necessary. The reduction in water infiltration caused by crusted soils creates significant challenges for irrigation, especially in areas where water scarcity limits large-scale use, forcing farmers to adopt more efficient water management strategies. Reduced water infiltration also leads to increased surface runoff, contributing to soil erosion and environmental risks, such as the pollution of surface waters due to nutrient loss. Additionally, restricted gas exchange between the soil and atmosphere further contributes to lower crop yields. Epstein and Grant (1973) observed that soil erodibility is closely linked to the rate and extent of crust formation, with soil loss peaking within the first 10 minutes of rainfall before stabilizing. It is well established that during crustforming rain events, water infiltration declines over time, leading to an increase in runoff volume. This increase in runoff, combined with the intensified energy