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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.

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.

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.

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.

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.

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

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 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

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.

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 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