Preface The book “A Textbook of Fertilizers” is the outcome of a perception by the author’s 28 years of experience as a teacher to have a textbook of fertilizers for the undergraduate and postgraduate students, researchers and teachers of State and Central Agricultural Universities (SAUs/CAUs), Indian Council of Agricultural Research (ICAR) and other Academic Institutions. The courses dealing with fertilizers already occupy an important position in the curricula of all the SAUs/ CAUs, ICAR Institutes and other agricultural colleges in the country. This publication endeavors to provide a comprehensive and authoritative treatise on fundamental and theoretical aspects of fertilizers in terms of their production technology, characterization, properties and uses under different soil-plant conditions. It emphasises the details of theories and principles and technology/ methodology for each fertilizer employed by the fertilizer industries. This book has eight major chapters. The first chapter “Introduction”, includes classification of essential nutrients and different fertilizers for crop production. Chapter 2 covers the details on nitrogenous fertilizers, their history of development of technology; different feedstock (hydrocarbon) and raw materials, commercial synthesis of ammonia, manufacturing process of different nitrogenous fertilizers and their chemical and physical properties, methods of application and fate to soils. Chapters 3 deals with the manufacturing process of different phosphatic fertilizers and their chemical and physical properties, methods of application and their fates in soils. Chapter 4 deals with the manufacturing process of different potassium fertilizers and their chemical and physical properties, methods of application and their fates in soils. Chapter 5 and 6 encompasses different fertilizers containing secondary nutrients and micronutrients, respectively. Chapter 7 deals with slow-release or controlled-release fertilizers and their importance and scope in the present context. While, specifications of different fertilizers as specified by the Fertiliser (Control) Order, 1985 (As amended up to February 2019) are given in Chapter 8. There are several important features of this book. The purpose of bringing out this textbook of fertilizers is to provide an up to date account of fertilizers in terms of their world production and consumption vis-à-vis in India. This is the first attempt by the author to provide the details of production technology, the chemistry, characteristics, properties and fate of each fertilizers upon application to different soils. In the recent years, understanding of many aspects of the commercial fertilizers as well as newly developed novel smart fertilizers including slow-release or controlled release fertilizers and nano-fertilizers have been greatly increased. In this book, the author has given systematic and in-depth coverage of the subject related to fertilizer technology and its systematic application to field crops. This book has been written to provide the fundamental aspects like basic principles and theories which are put into operation. References cited in the text are provided at the end of this book as separate chapter. I sincerely hope that teachers and students of Soil Science in various State/ Central Agricultural Universities, ICAR institutions and other private institutions/ organizations would find this book useful in handling for best management of fertilizers and improving nutrient use efficiency under different soil-plant conditions. I am sure that this publication will be of immense use to all concerned with fertilizers use and agricultural development such as agricultural administrators, researchers, teachers, students, soil chemists, extension workers, farmers, field advisor and marketing staff of the fertilizer industry, trading organization, training centres and international institutes. I am very much indebted to my Professors who have taught me the subject of soil science in general, and soil fertility and fertilizer technology in particular as well as other areas of soil science. Their stimulating comments and valuable suggestions are most appreciated. I would also like to acknowledge my friends and colleagues for their continuous advice and critical comments on the subject. Special appreciation is extended to my students Mr. Abhijit Sarkar, Mr. Kingshuk Modak and Mr. Khurshid Alam for rendering their necessary help for corrections of the manuscript as and when required. One of the most time-consuming tasks in the production of a book is that of the preparation of the manuscript. My sincere acknowledgements and appreciation for the services rendered by Mr. Vijay Kumar for his assistance in manuscript typing. I would also like to thank the Publishers for bringing out this book.

Plant absorbs large number of elements from the soil and other sources during their growth and development. But all these elements are not essential for plant growth. Seventeen mineral elements are known to be essential for the growth and development of all plants. A list of essential nutrients, their source and forms by which they are absorbed by plants are presented in Table 1.1. Except carbon (C), hydrogen (H) and oxygen (O), all the other nutrients are obtained by plants largely from soils, fertilizers or manures. It has been seen that the number of nutrients obtained from soil is about 5 times the number of nutrients obtained from air and water. However, most of the plant tissue, in general, from 74 to 99.5% is made up of C, H and O i.e. nutrients obtained from air and water and only 0.5 to 26% of the plant tissue is synthesized from soil constituents. In ordinary (normal) conditions of agriculture, except drought, C, O and H are not limited for plant growth. It is the remaining 14 elements from soil that are usually limiting plant development and hence considerable emphasis is placed on the improvement of soil in respect of greater availability of these 14 nutrients. It may be borne in mind that all nutrients are essential for all crops even though their requirements differ from crop to crop and even among varieties of a given crop. Secondly, all nutrients are equally essential regardless of amounts required. For example, to produce one tonne of grain, wheat may absorb 25, 9, 33, 3.7, 5.3 and 4.7 kg of nitrogen (N), phosphorus (P), potassium (K), sulphur (S), calcium (Ca) and magnesium (Mg), respectively and 56, 624, 70, 24, 48 and 2 g of zinc (Zn), iron (Fe), manganese (Mn), copper (Cu), boron (B) and molybdenum (Mo), respectively. If the crop (any crop) does not get the smallest amounts of micronutrients needed, it cannot make the best use of abundant NPK. According to Liebig’s Law of minimum which he enunciated in 1855, the growth of a plant is limited by that nutrient which is in shortest supply. This law in fact lays the ground rules for balanced crop nutrition.

Nitrogen (N) is an essential element for all forms of life because it is a major component of amino acids, which are the building blocks of proteins, nucleic acids such as deoxyribonucleic acid (DNA) and other cellular constituents. It is a structural component of chlorophyll in plants, which is used in photosynthesis to make their food. Nitrogen ranks first among the essential nutrient elements required for plants. Its careful management is very important for crop production. Nitrogen exists as two main stable isotopes (isotopes of a given element have the same number of protons but different numbers of neutrons in each atom) namely, 147N (abundance 99.63%) and 157N (abundance 0.37%). These can be separated by chemical exchange or by thermal diffusion. Both 147N and 157N isotopes of N are stable isotope which do not disintegrate as in case of other radioactive isotope like 32 15P. There are four other isotopes of N viz. 127N, 137N, 167N and 177N, mostly are radioactive having very short half-life and not used in agriculture. The 137N has a half-life of about 10 min, while other three have half-life of only few sec. The 157N (tracer) isotope is used as a tool for determination of pathways of transformation of N in soil or plant or animal. The major part of N comes from atmosphere (air). On the basis of volume by volume (v/v), air contains about 78-79% N2, 20-21% oxygen (O2) and 0.03% carbon dioxide (CO2). Most living organisms cannot utilize N2 gas present in the atmosphere directly because it is present as di-nitrogen form or di-atomic form (N≡N). It is called as an inert gas. Therefore, to break this triple bond, huge amount of energy is required. After breaking of triple bond of N2 molecules, it combines with other element particularly with O2 or hydrogen (H) to form oxides of N (NO, NO2, NO3 and N2O) or ammonia (NH3). Thus, breaking of triple bond is must for forming NH3 which further can be used as the key material for almost all fertilizers. Therefore, the fixation of N2 is vital for production of all nitrogenous and complex fertilizers like NP/NPK and nitrophosphates.

Phosphorus (P) is the second most important essential nutrient limiting crop/ plant growth, next only to nitrogen (N). Phosphorus is an important component of nucleic acid like deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). It is needed for energy storage and transfer, which is the single most important essential function of P. Phosphate compounds act as “energy currency” within plants. The most important common P energy currency is adenosine diphosphate (ADP) and adenosine triphosphate (ATP). The ATP transfers energy for synthesis of ADP. Life is not possible without P. It is the source of energy that powers practically all energy-requiring biological processes in plants. Phosphorus is present in plant as phospholipid such as lecithin and cephalin which appears to be involved in the structural framework of protoplasm. Phosphorus is involved in many important processes such as photosynthesis, cell division, tissue development, and growth in plant. Requirement of P by the crops is less, compared to N and potassium (K). It is present in plant tissues. It is reported that for 5-6 t ha-1 of wheat grain yield, it removes about 100-120 kg N, 20-30 kg P2O5 and 150-180 kg K2O from soil. Phosphorus is 11th most abundant element on the earth crust. However, it is the least mobile element among the major plant nutrients. Its complex chemistry in soil makes it highly deficient nutrient element in most of the arable soils across the globe. Only 0.1% of the total P in the soil is available for uptake by plants because of its fixation as various insoluble compounds depending upon the soil pH. About 43% of the world’s arable soil is P deficient which limits crop growth and production (Roy et al., 2018). In the Indian context, about 80% of the soils are reported to have low to medium available P content (Muralidharudu et al., 2011). Thus, application of P-fertilizers to maintain the soil fertility and sustain crop productivity becomes imperative in today’s input intensive agriculture.

Potassium is the third important essential nutrient element after nitrogen (N) and phosphorus (P) required by all living organisms, including plants and animals. Potassium is essential for many metabolic activities like carbohydrate metabolism, nitrogen metabolism. It is required for the activation of over 60 enzymes in plants. It controls/regulates the activities of various essential nutrients. It is vital to photosynthesis, and synthesis of carbohydrates, starch and proteins in plants. It plays vital role in controlling the opening and closing of stomata in photosynthesis. It also helps in controlling water use by plants by regulating the osmotic pressure of guard cells during transpiration. It plays a major role in transport of water and nutrients throughout the plant in xylem. Potassium improves crop yield and quality of flowers, fruits, vegetables and other field crops in terms of size, shape, colour, taste, shelf-life, and fibre quality. Potassium stimulates the growth of strong stems and provides strength to the plant against some disease by promoting thickness of the outer cell walls. It is required for translocation of assimilates. Under reduced K supply, translocation of NO3-, PO43-, Ca2+, Mg2+ and amino acids is hampered. It also imparts resistance against environmental stresses such as drought, cold and frost. Adequate K can reduce moisture loss from growing plants, thereby giving some drought resistance. It reduces lodging of crops and enhances their winter-hardiness. It is taken up by the plants as K+. Being a basic element, it takes part in neutralization of the acidity in plants caused by several organic acids produced. It does not form organic compounds in the plant system. It is the most mobile element in the plant. Thus, it can move through all the plant system due to osmotic pressure. When any plant sample is dipped into water, some K comes out. This shows that it is highly mobile. Potassium is also required for animal nutrition and human beings. Potassium is essential for many metabolic functions. It maintains salt balance between cells and body fluids. Adequate K is essential for nerve function and preventing muscle cramps. It is routinely added to many animal feeds. Since K+ is not stored in the human body, dietary replacement is required on a regular basis. Government agencies state that diets containing foods that are good sources of K and low in Na may reduce the risk of high blood pressure and stroke.

5.1. Importance of Secondary Nutrients in Agriculture Secondary nutrients such as sulphur (S), calcium (Ca) and magnesium (Mg) are the macronutrients that are required in relatively large amounts for crop growth. Among the secondary nutrients, Ca is the 5th most abundant element in the earth’s crust while, Mg and S are ranked 8th and 13th, respectively. The average S content of the earth’s crust ranges from 0.06 to 0.10%; whereas, Ca in soil solution of temperate region soils is 30 to 300 ppm and soils of tropical areas is 8 to 45 ppm (Tisdale et al., 1997). In case of Mg, its’ concentration ranges from 5-50 in temperate region and 120-2400 ppm in tropical region. The Ca and Mg are the most abundant cations occupying the exchange sites of the soil colloids. Thus, most soils with the possible exception of highly weathered, leached acid soils, contain enough Ca and Mg for crop growth. In soils, occurrence and reactions of S are different from those of Ca and Mg. The plant available S is SO42- ion which is relatively mobile in soil solution. Like nitrogen (N), S is also subjected to chemical and biological oxidation-reduction reactions. On the other hand, Ca and Mg are much more stable and they exist in soil as Ca2+ and Mg2+ cations and present in association with soil colloidal fraction similar to that of K. In general, Ca and Mg are the most abundant cations occupying in the exchange site. Secondary nutrients in soils may be lost due to several reasons such as (i) crop removal, (ii) leaching, (iii) erosion, and (iv) volatilization. The amount of Ca and Mg attain importance in areas where soils are either strongly alkaline or acidic. These soils are often deficient in Ca and Mg. The Ca deficiency is most widespread in acidic soils. The alluvial soils of the Indo-Gangetic Plains (IGP), being neutral to moderately alkaline in reaction, have sufficient bases on their exchange complex and Ca deficiency is, therefore, rarely found in these soils. However, alkali soils may contain inadequate quantities of Ca due to dominance of Na+ on the exchange complex. Magnesium deficiency is found in sandy soils with low exchangeable Mg2+, acid soils and those with high in native or applied K. Alkali soils have high exchangeable Na+. The Ca2+ is a suitable ion to replace this Na+ from the exchange complex when Ca2+ is supplied through gypsum (CaSO4.2H2O). The replaced Na+ forms Na2SO4 which is then leached down to remove the salt away from the root zone of the crops. Gypsum also reacts with Na2CO3 to form CaCO3 and Na2SO4 which is leached down the profile. A thorough leaching of the soil with irrigation water should be done after application of gypsum to free it from Na2SO4.

Iron (Fe), zinc (Zn), copper (Cu), manganese (Mn), nickel (Ni), boron (B), molybdenum (Mo) and chloride (Cl) elements are known as micronutrients. The micronutrients are also called as trace elements or minor elements as they are required very small quantities by plants. The elements Fe, Zn, Cu, Mn and Ni are known as micronutrient cations and B, Mo and Cl are known as micronutrient anions and they behave accordingly in soils. Among these elements, Fe content in soil as well as plant is the highest and sometimes higher than phosphorus (P) and sulphur (S). In plant, the concentration of micronutrients often found up to 100 mg kg-1, except that of Fe and Mn which may go up to 500 mg kg-1 (dry weight basis). Another element, cobalt (Co) is also regarded to be essential for the growth of certain higher plants and animals, and likely to be included in the list of micronutrients. The importance of micronutrients has been realized during the past four decades when micronutrient deficiencies were observed in most of the soils in our country, where intensive agriculture is practiced.

Fertilizers have played a pivotal role in enhancing food grain production in India especially after the introduction of high yielding and fertilizer responsive crop varieties during the green revolution era. However, there are certain problems associated with fertilizers because of their relatively low nutrient use efficiency (NUE) or nutrient uptake by crops. The fertilizer use efficiency is 30-50% for N, 15-20% for P, 70-80% for K and 8-10% for S. In case of micronutrients, the use efficiency is only 1-2%. The low NUE is typically the result of higher release rate of fertilizers than the absorption rate by plants, and/or transformation of fertilizers/ nutrients to forms that are not bioavailable to crops. Application of N and P fertilizers at levels exceeding plant requirements due to low acquisition efficiency leads to significant environmental consequences in many parts of the world due to losses, such as nitrate (NO3-) leaching, NH3 volatilization, and nitrous oxide (N2O) emission. Excessive use of fertilizer N affects the groundwater. Similarly, excessive use of N and P fertilizers leads to surface runoff which in turn causes eutrophication in aquatic ecosystems. These negative environmental consequences associated with fertilizer inputs further emphasize the need of technological approaches to improve nutrient management in modern agriculture. As such, there is great need in developing innovative fertilizers to minimize the losses of nutrients and increase their efficiencies. In addition, current agricultural activities contribute up to 20-30% to the annual atmospheric emissions of greenhouse gases (GHGs), such as methane (CH4) and carbon dioxide (CO2). Even higher contribution is being noted for N2O (about 60%), which is a potent GHG and catalyst for stratospheric ozone depletion, with more than 300 times the global warming potential than CO2. Its emission is closely related to mineral fertilizer input. High fertilization rates lead to N and P losses with negative impacts on atmospheric GHGs concentrations and water quality. There is an urgent need to improve NUE in agricultural systems, and to manage biogeochemical cycles in a sustainable way. This includes the development and application of modern technology as alternatives to conventional fertilization. There is a need to reduce the use of fertilizers/nutrients in agricultural systems by increasing NUE. The recent development in smart fertilizer delivery systems including nanofertilizers or the new generation fertilizers is a good alternative to commercially available fertilizers to improve the NUE and enhance resource utilization. Smart fertilizers may be a solution to enhance food production and environmental quality.

The Fertilizer (Control) Order The Fertilizer (Control) Order (FCO) is a set of legally enforceable executive orders issued by the Govt. of India under the Essential Commodities Act, 1955 passed by the Parliament. This order came into force in 1957, essentially to regulate the sale, price and quality of fertilizers in India. Amendments are made from time to time as per the exigencies and need of the hour and therefore a large number of amendments were made over a period of time. Consequently, after an overall review of the various provisions of the order, a revised Fertilizer (Control) Order 1985, was issued, which came into effect on September 25, 1985. The FCO consists of five Schedules comprising of different activities as mentioned in Figure 8.1, besides forms of registrations and appendices. Schedule I comprises Part A and B. While Part A contains the specifications of different fertilizers (e.g. minimum nutrient content, maximum moisture content, range of physical parameters, maximum levels of impurities/ contaminants, etc.), that can be marketed in India (no material not performs the specifications as in the FCO cannot be sold as fertilizer), Part B lists the tolerance limits in plant nutrients and physical parameters for various fertilizers. Schedule II encompasses again two parts, with Part A describing the procedures for drawal of samples of fertilizers, and Part B describing detailed methods of analysis of fertilizers. Schedule III encompasses four parts namely, Part-A, Part-B, Part-C and Part-D. While Part-A contains specifications of different biofertilizers, Part-B contains tolerance limits of biofertilizers, Part-C describes the procedures for drawal of sample of biofertilizers, Part-D describes the methods of analysis of biofertilizers. Schedule IV also encompasses four parts. Part-A contains specifications of organic fertilizers, Part-B contains tolerance limits of organic fertilizers, Part-C describes the procedures for drawal of sample of organic fertilizers, and Part-D describes the methods of analysis of organic fertilizers. Schedule V also contains of four parts. Part-A contains specifications of non-edible de-oiled cake fertilizers, Part-B contains tolerance limits of non-edible de-oiled cake fertilizers, Part-C describes the procedures for drawal of sample of non-edible de-oiled cake fertilizers, and Part-D describes the methods of analysis of non-edible de-oiled cake fertilizers.

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