Soil Nutrients: Classification, Role, and More PDF

1. Plant Nutrients (including classification and sources; Essential and beneficial elements, criteria of essentiality, forms of nutrients in soil, mechanisms of nutrient transport to plants, factors affecting availability of major, secondary and micro-nutrie...

1. Plant Nutrients (including classification and sources; Essential and beneficial elements, criteria of essentiality, forms of nutrients in soil, mechanisms of nutrient transport to plants, factors affecting availability of major, secondary and micro-nutrients to plants, etc.) 2. Measures to Overcome Deficiency and Toxicity 3. Soil Fertility (including different approaches for soil fertility evaluation; Soil testing for available nutrients; Critical levels of different nutrients in soil, etc.) 4. Plant Analysis (including total and rapid tissue tests- critical levels of nutrients in plants; DRIS method; Deficiency symptoms-indicator plants, etc.) Plant nutrients - classification and sources; Essential and beneficial elements, criteria of essentiality, forms of nutrients in soil, mechanisms of nutrient transport to plants, factors affecting availability of major, secondary and micro-nutrients to plants. Measures to overcome deficiency and toxicities. Soil fertility- different approaches for soil fertility evaluation; Soil testing for available nutrients; Critical levels of different nutrients in soil. Plant analysis- total and rapid tissue tests critical levels of nutrients in plants; DRIS method; Deficiency symptoms- indicator plants. Ipsita’s part  Chapter 1 Plant Nutrients__________________________________________ 1.1 Introduction Nutrients are chemical elements that plants need for growth, development, and reproduction. These nutrients boost the plant enzyme function, improve biochemical processes, and help in plant cell growth. Soil is a major source of nutrients needed by plants for growth. Plants need nutrients for the same reasons that animals need them. They need them to germinate, grow, fight off diseases and pests and to reproduce. Like animals, nutrients are needed in larger, smaller or trace amounts for the plant to stay healthy. 1.2 Essential Nutrients and Their Classification An element is essential if a plant cannot complete its life cycle without it, if no other element can perform the same function, and if it is directly involved in nutrition. The nutrient available to the biological organisms are called as bioavailable nutrient. Beneficial elements are the mineral elements which stimulate plant growth but are not essential. Nicholas (1961) suggested the term functional or metabolism nutrients, which play a role in plant metabolism. Trace element is found in low concentrations, perhaps < 1 ppm. There are eighteen essential elements for plant nutrition, Macronutrients (C, H, O, N, P, K, Ca, Mg, S) and Micronutrients (Fe, B, Cu, Cl, Mn, Mo, Zn, Co, Ni). Non-mineral C,H,O Essential Based on N,P,K,Ca,Mg,S,Fe, essentiality Mineral Mn,Zn,Cu,Mo,Cl,Ni,B Beneficial Plant Basic structural C,H,O,Ca Nutrients Accessory structural N,P,S Based on function Regulatory and Carrier K,Ca,Mg Fe,Mn,Zn, catalyst and activator Cu,B, Mo, Cl Fig. 1 Classification of nutrients based on essentiality and function of nutrients 1. Macronutrients: used in large quantities by the plant  1. Structural/ framework nutrients: Carbon, Hydrogen, Oxygen 2. Primary nutrients: Nitrogen, Phosphorus, Potassium 3. Secondary nutrients: Calcium, Magnesium, Sulfur 2. Micronutrients: used in small quantities by the plant Iron, Boron, Copper, Chlorine, Manganese, Molybdenum, Zinc, Cobalt, Nickel Primary macronutrients are needed in relatively large quantities, often exceeding 100 pounds per acre per year for a vegetable crop. Secondary smaller nutrients are typically needed in moderate quantities. Micronutrients are just as important to total plant nutrition as the others, but a little bit goes a long way. 1.3 Source of Plant Nutrients Plant nutrients are all around us; in the air (N), water, and in the soil, as well as in many other natural materials. Due to specific soil properties and often its poor condition, the soil can’t always provide enough nutrients for plant growth. Because of this, farmers need to add additionally crop nutrients to the soil. There are various sources of plant nutrients. These can be natural, synthetic, recycled wastes or a range of biological products including microbial inoculants. They can be in the form of an organic source, such as plant debris, green manure, compost, waste, or manure or an artificial source, such as chemical fertilizers. Most organic nutrient sources, including waste materials, have widely varying composition and often only a low concentration of nutrients, which differ in their availability. Some of these, such as cereal straw, release nutrients only slowly (owing to a wide C:N ratio) while others such as the N-rich leguminous green manures or oilcakes decompose rapidly and release nutrients quickly. 1.4 Role of Nutrients Plant nutrients improve plant cell growth, soil quality, increases crop yield, supports plant metabolism, activate enzymes, support protein synthesis. All the essential nutrients contribute towards the growth and development of crops. The role/function of nutrients is mentioned in table 1. 1.4.1 Role of essential nutrients Table 1 Role of essential nutrients Elements Form of Role of nutrients uptake Carbon (C) CO2 Major components of carbohydrates, protein and fats. They Hydrogen H2O provide energy required for growth and development of plants (H) by oxidative breakdown of carbohydrates, protein and fats Oxygen (O) O2 during cellular respiration. Nitrogen (N) NH4+, It is found in all plant cells, in plant proteins and hormones, and NO3- in chlorophyll, cytochromes. It promotes green, leafy growth. Inside the plant, nitrogen is converted into amino acids, the building blocks for proteins. Because all enzymes are proteins, It is necessary for enzymatic reactions in plants. As part of the chlorophyll molecule, nitrogen is directly involved in photosynthesis. It is a part of plant DNA. Helps in protein synthesis Phosphorus HPO42-, Helps transfer energy from sunlight to plants, stimulates early (P) H2PO4- root and plant growth, and hastens maturity Constituent of lipoprotein membranes, nucleic acids, CoA, nucleoproteins, ATP, NADP, etc. Potassium K+ Increases vigour and disease resistance of plants, helps form (K) and move starches, sugars and oils in plants, and can improve fruit quality. Essential for photosynthesis, as regulation of cell turgidity, respiration, and water movement in the plant. It also controls the opening and closing of the plant’s stomata. Adequate potassium fertilization helps plants cope with drought stress, improves winter hardiness, and improves crop quality. Calcium (Ca) Ca2+ Essential for root health, growth of new roots and root hairs, and the development of leaves. Stimulates root and leaf development. It forms compounds that are part of cell walls and strengthens plant structure. It indirectly promotes yield by reducing the toxicity of aluminum and manganese in the soil. Constituent of middle lamella of cell wall; Affects permeability of cell membrane; lipid metabolism activator of ATP-ase. Magnesium Mg2+ Key component of chlorophyll, the green colouring material of (Mg) plants, and is vital for photosynthesis. Essential constituent of chlorophyll; acts as catalyst; activator for enzymes; stabilization of ribosomal particle. Sulphur (S) SO42- Constituent of amino acids in plant proteins and is involved in energy-producing processes in plants. It is responsible for many flavour and odour compounds in plants such as the aroma of onions and cabbage. Iron (Fe) Fe2+ Necessary for the maintenance of chlorophyll in plants. Constituent of fd, cytochromes; chlorophyll synthesis. Manganese Mn2+ Activator of enzymes like decarboxyleses, reductases; (Mn) photolysis of water, formation of chloroplast. Perform some function in photosynthesis. Acta as regulator of the intake and state of oxidation of certain elements. Zinc (Zn) Zn2+ Helps in the production of a plant hormone responsible for stem elongation and leaf expansion Copper (Cu) Cu2+ Present in several enzymes and certain plant proteins A part of Plastocyanin; as a catalyst in nitrogen fixation;  constituent of acetic acid oxidase, Cytochrome oxidase, etc. Boron (B) H3BO3 Helps with the formation of cell walls in rapidly growing tissue. Translocation of sugar; metabolism of carbohydrate and fat; germination of pollen. Influences cell development by its influence on polysaccharide formation. Molybdenum MoO42- Helps bacteria and soil organisms convert nitrogen in the air to (Mo) soluble nitrogen compounds in the soil, so is particularly needed by legumes. Essential in the formation of proteins from soluble nitrogen compounds. Essential constituent of the enzyme nitrogenase and very important in nitrogen metabolism. Silicon (Si) Si4+ A component of cell walls. (Beneficial Plants with supplies of soluble silicon produce stronger, nutrient) tougher cell walls making them a mechanical barrier to piercing and sucking insects. This significantly enhances plant heat and drought tolerance. Improved leaf erectness, stem strength and prevention or depression of iron and manganese toxicity. Silicon has not been determined essential for all plants but may be beneficial for many. Sodium (Na) Na+ Involved in osmotic (water movement) and ionic balance in (Beneficial plants nutrient) Chlorine (Cl) Cl- Activator of enzyme for photolysis of water. Involved in osmosis, the ionic balance necessary for plants to take up mineral elements and in photosynthesis. Cobalt (Co) Co2+ Required for nitrogen fixation in legumes and in root nodules (Beneficial of nonlegumes. The demand for cobalt is much higher for nutrient) nitrogen fixation than for ammonium nutrition. Selenium Se2-, Se4+ Essential element for animals. (Se) (Beneficial nutrient) 1.4.2 Essential plant nutrients and their year of discovery Table 2 Essential plant nutrients and their year of discovery Elements Discovered by Year of discovery H, O Since time immemorial C Priestley et al. 1800 N Theodore DeSaussure 1804 P Ville 1860 P, K, Ca, Mg C. Sprengel 1839 S Von Sachs, Knop 1865 Fe E. Gris 1843  Mn McHargue 1922 Cu Lipman and MacKinney 1931 Zn Sommer and Lipman 1926 Mo Arnon and Stout 1939 B Warrington 1923 Cl Broyer et al. 1954 Ni Brown et al. 1987 Source: Tisdale et al., 1997 1.5 Terms Associated with Concentration of Nutrients Deficient: When the concentration of an essential element is low enough to limit yield severely and distinct deficiency symptoms are visible. Extreme deficiencies can result in plant death. With moderate or slight deficiencies, symptoms may not be visible, but yields will still be reduced. Critical range: The nutrient concentration in the plant below which a yield response to added nutrient occurs. Critical levels occur somewhere in the transition between nutrient deficiency and sufficiency. Sufficient: The nutrient concentration range in which added nutrient will not increase yield but can increase nutrient concentration. The term luxury consumption is often used to describe nutrient absorption by the plant that does not influence yield. Excessive or toxic: When the concentration of essential or other elements is high enough to reduce plant growth and yield. Excessive nutrient concentration can cause an imbalance in other essential nutrients, which also can reduce yield. Fig.2 The interrelationship Curve between plant growth and concentration of nutrients in plants Essential elements % Deficient % Sufficient % Excessive/Toxic N < 2.5 2.5-4.5 P 1.00 K 6.00 Ca 5.00 Mg 1.50 S 3.00  Micronutrients ppm ppm ppm B 5-30 10-200 50-200 Cl 100 Zn 10-20 27-100 100-400 Table 3. Concentration of nutrients for various plant species (Munson, 1998) 1.6 Criteria of Essentiality Criteria of essentiality was given by D.I. Arnon and P.R. Stout (1939), which is as follows- An element is not considered essential unless, a. A deficiency of it makes it impossible for the plant to complete the vegetative or reproductive stages of its life cycle. b. Such deficiency is specific to the element in question, and can be prevented or corrected only by supplying this element. c. And the element is directly involved in the nutrition of the plant quite apart from its possible effects in correcting some unfavorable microbiological or chemical condition of the soil or other culture medium. 1.7 Mobility of Nutrients Mobile N,S,B,Mn,Cl Mobility in soil Intermediate K,Ca,Mo,Ni Immobile P,Mg,Cu,Fe,Zn Plant nutrients Mobile N,K,Cl,Ni Mobility in plant Intermediate P,S,Mg Ca,B,Fe,Mn,Cu,Zn, Immobile Mo Fig.3 Classification of plant nutrients based on its mobility in soil and plant 1.7.1 Nutrient Mobility in Soil The movement of nutrients in soil varies greatly and largely influences their availability to the plants. On the basis of their mobility in soil, nutrients can be broadly categorized as: mobile, less mobile and immobile.  Mobile nutrients: These nutrients are highly soluble and their large fraction is found in soil solution. Because of their high mobility, they become readily available to plants and are very prone to leaching losses. Such nutrient ions are NO3−, SO42−, Cl− and H2BO3−. Less mobile/Intermediate nutrients: These are also soluble but are found in lower quantities in soil solution as they are adsorbed on clay complexes and easily get released into soil solution. Their availability to plants is moderate. These include NH 4+, K+, Ca2+, Mg2+ and MoO42− ions. Immobile nutrients: These nutrients are very tightly held by soil particles and are not easily released into the soil solution. Therefore, the availability to plants is low. They are Fe 2+, Mn2+, Zn2+, Cu2+, HPO42− and H2PO4− ions. 1.7.2 Nutrient Mobility in Plants The appearance of deficiency symptoms in plants chiefly depends upon the extent and the rate of re-translocation of nutrients from older to younger tissues within plants. Nutrients vary greatly in their mobility within plants. On the basis of their mobility, the nutrients are classified into two categories: mobile nutrients and immobile nutrients. Mobile nutrients: Mobile nutrients are those that are capable of being translocated from older to younger tissues within the plant. When the plant becomes deficient in these nutrients, as a consequence the deficiency symptoms are observed on the older leaves. These include nitrogen, phosphorus, potassium and magnesium. Immobile nutrients: Immobile nutrients are those that are not capable of being translocated from older to younger tissues within the plant. When the plant becomes deficient in these nutrients, the deficiency symptoms are thus evident on the younger tissues. These include calcium, sulphur, iron, manganese, zinc, copper, boron and molybdenum. 1.8 Mechanism of Nutrient Transport to Plants The process of nutrient movement may be broadly pictured by an equilibrium as follows- M (solid) ⇋ M (solution) ⇋ M (Plant root) ⇋ M (Plant top) The nutrient ions are continually removed from the system at one end (soil-the solid phase) and accumulated at the other end (the plant phase); M stands for any nutrient ion. Plants transport nutrients from the soil to their roots and throughout their bodies through a variety of mechanisms, including: Mass flow (Movement with water), Diffusion (Movement through water), and Root Interception. 1.8.1 Mass Flow Mass flow occurs when nutrients are transported to the surface of roots by the movement of water in the soil (i.e. percolation, transpiration, or evaporation). The rate of water flow governs the amount of nutrients that are transported to the root surface. Therefore, mass flow decreases are soil water decreases. Quantity of nutrients transported is proportional to: i. Rate of flow (volume of water transpired) ii. Solution concentration of nutrient. Most of the nitrogen, calcium, magnesium, sulfur, copper, boron, manganese and molybdenum move to the root by mass flow. 1.8.1.1 Factors affecting mass flow a. Soil water content: For dry soil, there is no nutrient movement b. Temperature: Low temperature reduces transpiration and evaporation c. Size of root system: i. Affects water uptake and therefore movement ii. Root density much less critical for nutrient supply by mass flow than for root interception and diffusion 1.8.2 Root interception Nutrients close to the root surface are directly absorbed. Root interception occurs when a nutrient comes into physical contact with the root surface. As a general rule, the occurrence of root interception increases as the root surface area and mass increases, thus enabling the plant to explore a greater amount of soil. The CEC of roots for monocots is 10 - 30 meq/100 g and takes up monovalent cations more readily and that of Dicots is 40 - 100 meq/100 g and takes up divalent cations more readily. The term root interception is coined by Stanley A. Barber, USA. 1.8.2.1 Factors affecting root interception A. Anything that restricts root growth i. Dry soil ii. Compaction iii. Low soil pH iv. Poor aeration v. Root disease, insects, nematodes vi. High or low soil temperature B. Root growth is necessary for all three mechanisms of nutrient supply, but absolutely essential for root interception to occur 1.8.3 Diffusion Diffusion is the movement of a particular nutrient along a concentration gradient. When there is a difference in concentration of a particular nutrient within the soil solution, the nutrient will move from an area of higher concentration to an area of lower concentration. Nutrients with a positive electrical charge, such as potassium, calcium, and magnesium, move from areas of high concentration to low concentration. Diffusion is a relatively slow process compared to the mass flow of nutrients with water movement toward the root. Nutrients supplied primarily by diffusion are considered immobile nutrients e.g. P, K 1.8.3.1 Factors affecting diffusion a. Diffusion coefficient in water (Dw)  b. Soil water content i. Drier soil = slower diffusion ii. Less water = less area to diffuse through c. Tortuosity i. Pathways through soil are not direct ii. Around soil particles, through thin water films iii. Affected by texture and water content 1. More clay = longer diffusion pathway 2. Thinner water films = longer path d. Buffering capacity e. Nutrients can be removed by adsorption as they move through soil, reducing diffusion rate Fig. 4 Diagrammatic representation of mechanism of flow of nutrients 1.8.4 Other forms of uptake of nutrients Active uptake Energy-driven carriers and ion channels transport nutrients across the plasmalemma and tonoplast of root cells. Apoplastic, symplastic, and transcellular pathways Nutrients are transported from the soil to the root vasculature through these pathways. 1.9 Factors Affecting Nutrient Availability to Plants Agricultural production and productivity are directly linked with nutrient availability in soil. Soil productivity and nutrient availability are interrelated. Soil productivity is the capacity of a soil to produce a certain yield of crops or other plants with a specified system of management. Soil fertility is an index of available nutrients to plants. It represents the nutrient status of soil. All fertile soils are not productive. All productive soils are certainly fertile. The factors which affect the nutrient availability in soil is as follows- 1.9.1 Interaction of ions The availability of an ion is influenced by the presence of other ions in soil solution. Two types of interactions occur between ions. a. Promotive: Ion uptake may be enhanced by the presence of certain ions particularly Ca, a phenomenon termed “Viets effect”-Viets 1944. The uptake of K, Rb, Br, Cl, sulphates and phosphates is accelerated by Ca. b. Antagonistic: The presence of certain ions is antagonistic to the absorption of others. Na decreases the uptake of K, Similarly NH4 decreases K uptake. Ca and Mg percentages decrease concomitantly with increased K uptake. P can greatly interfere with Zn and Fe uptake. High N and P in soil reduce K uptake. 1.9. 2. Soil reaction Soil reaction is the status of pH of soil. Soil reaction is an indication of the acidity or basicity of soil and is measured as pH unit. The pH of a soil is a measure of the hydrogen ion concentration in the soil solution. Soil pH is defined as the negative logarithm of the hydrogen ion concentration. pH = - log [H+] Most plant nutrients are optimally available to plants within this 6.5 to 7.5 pH range, plus this range of pH is generally very compatible to plant root growth. Acidic soils have pH < 7. It is injurious to plants due to high toxicity of Fe and Al. At very low pH availability of many nutrients like N,P,K,Ca,Mg, S, Mo is negligible. Saline soils have pH between 7 - 8.5. It contains large amounts of soluble salts like chlorides and sulphates. Above pH 8, the availability of N decreases. In the saline range, phosphate ions tend to react quickly with calcium (Ca) and magnesium (Mg) to form less soluble compounds. The availability of K, S, Ca and Mg is not affected by saline soil. In the saline range the availability of micronutrients except Mo is also affected. 1.9.3. CEC (Cation Exchange Capacity) CEC is defined by measurement of the amount of positively-charged ions (cations) which can be bound by a given weight of soil. Cations bound on the soil surface can exchange places with cations in the soil solution, making them available to the plants and protecting them from loss by leaching. A larger CEC implies a greater capacity to retain K +, Ca2+, Mg2+, and NH4+. Soils with large CEC are typically high in 2:1 clay minerals and soil organic matter (OM), which have a lot of negative charges. High CEC means that soil is more fertile. Low CEC means that fewer nutrients can be held by the soil, implying a need for more frequent nutrient additions. Soils with low CEC become acidic very quickly (for example sandy soils) and would need liming more frequently than soils with high CEC. 1.9.4. AEC (Anion Exchange Capacity) Anions in soil are adsorbed to positive charges of clay minerals and organic matter. Important anions in soil are (H2PO4– , HPO4=, CI–, SO4=, NO3–, MoO4=). Anion exchange is much greater in soils high in 1: 1 type clay minerals and those containing hydrous oxides of iron and aluminium then that of soils containing high amounts of 2: 1 type of clay minerals. Clay minerals in the montmorillonite group of expansible layer silicates usually have anion exchange capacities of the less than 5 me/100 g. On the other hand, kaolinites can have an anion exchange capacity as high as 43 me/100 g at an acidic equilibrium pH of 4.7. High anion exchange capacity in soil ensures more availability of anions to plants. 1.9.5. Soil Texture Soil texture can determine probability of soil nutrient of the soil. (i) Fine texture, such as clay and silt, ensures the availability of nutrients in the soil. (ii) But coarse texture like sand prevents the availability of nutrients in the soil as coarse texture encourages the leaching of nutrients from the soil. 1.9.6 Erosion Heavy rainfall causes the washing or carrying away of top soil which is rich in plant nutrients. Top soil can also be blown away by winds, resulting in nutrient reduction in the soil. Annual loss of NPK in India due to soil erosion is estimated at 8.4 mt. 1.9.7. Soil Moisture Content The ideal soil moisture content for crop growth exists when approximately at 50% of the entire pore space is occupied by water. Moderate moisture in the soil ensures adequate availability of nutrients in the soil. At optimum moisture content, nutrient supply to plant roots by diffusion and mass flow is enhanced. Leaching results in the loss of nutrients such as calcium, magnesium, potassium and NO 3- from the top soil in solution. It also results in the accumulation of aluminum and hydrogen ions which become acidic and toxic to plants. 1.9.8. Level of organic matter in the soil High level of organic matter leads to adequate availability of nutrients in the soil through gradual mineralization. High level of organic matter ensures availability of water in the soil and vice versa. High level of organic matter in the soil helps to prevent soil erosion. Adequate level of organic matter improves the activities of micro-organisms in the soil Which ensures more availability of nutrients by decomposition of organic matter and N fixation. Organic manure also helps to improve the structure of the soil. It also reduces rapid soil temperature fluctuations. 1.9.9. Soil Air In nutrient management, soil aeration influences the availability of many nutrients. Particularly, soil air is needed by many of the microorganisms that release plant nutrients to the soil. Microorganisms involved in mineralization of organic matter and N fixation are typically aerobic in nature. 1.9.10. Soil temperature: Soil temperature is an important regulator for nutrient transformation and uptake by roots of crops. Below 9 0C and above 400C, nutrient transformations in soil is affected. 1.9. 11. Application of manures and fertilizers Their rate, placement in soil and time and number of applications affect the availability of nutrients to plants. Split application, placement in the root zone and balanced nutrition ensures more availability to the plants 1.10. Factors Affecting the Availability of Micronutrients Poor Drainage: Highly leached acidic sandy soils; resulting in leaching of micronutrients, thus deficiency of micronutrients occur. Soil Temperature and moisture: Cool, wet soils reduce the rate and amount of micronutrients that may be taken up by crops. Cropping Intensity and Systems: Intensification of agriculture, characterized by raising of more crops per unit time and involving heavy dependence on high analysis fertilizers has progressively depleted the soils of their available micronutrient reserves. Management and cultivation Practices: Large scale deforestation is responsible for progressive decline in organic matter and depletion of micronutrient cations in tarai soils of Uttaranchal, Uttar Pradesh and soils of Andaman and Nicobar Islands. Emergence of Khaira disease of rice due to zinc deficiency is an example of deforestation. Doses and nature of fertilizers: Intensively cropped soil with high doses of commercial fertilizers and long term application of nitrogenous fertilizers plays a major role in removal and consequential depletion of the micronutrients in soil. Parent Material and Climate: Soils developed on flood plain alluvium largely from siliceous sandstone exhibited strikingly lower concentrations of Zn, Cu, Mn and Fe than the soils developed on basaltic alluvium. Soil Texture: Soil texture affects how well nutrients and water are retained in the soil. Clays and organic soils hold nutrients and water much better than sandy soils. As water drains from sandy soils, it often carries nutrients along with it. This condition is called leaching. When nutrients leach into the soil, they are not available for plants to use. Soils with higher amounts of clay (fine texture) are less likely to be low in plant  available micronutrients. Sandy soils (course texture) are more likely to be low in micronutrients. Organic Matter in Soils: Soils low in organic matter (less than 2.0%) may have lower micronutrient availability. Soils that have very high levels of organic matter (greater than 30% organic matter to a depth of 30 cm) often have low micronutrient availability. Chelating compounds: To increase the availability of micronutrients and make them slowly available over a longer period, chelated compounds are formed. For this Chelating agent e.g. EDTA is commonly used. This agent combines with iron, copper, calcium or magnesium to form chelated compounds that supply secondary nutrients of micronutrients. The use of also some synthetic Chelating agents are also used e.g. HEDTA, DTPA, EDDHA, NTA. The use of chelated compounds of micronutrients has become very important for correcting micronutrient deficiencies particularly in horticultural crops. References Arnon, D.I. and Stout, P.R. (1939) The Essentiality of Certain Elements in Minute Quantity for Plants with Special Reference to Copper. Plant Physiology, 14, 371-375 Munson, R.D. 1998. Principles of plant analysis. p. 1-24. In Y.P. Kalra (ed.) Reference methods for plant analysis. CRC Press, Boca Raton, FL. Tisdale, S.L., Nelson, W.L., Beaton, J.D. and Havlin, J.L. (1997) Soil Fertility and Fertilizers (Fifth edition), Second Indian Reprint, Prentice Hall of India Ltd, New Delhi Outcomes Assessment Part A Answer the following questions. True or False [1x5=5 1. Nitrogen is primary nutrient. [T] 2. Active uptake of nutrients is energy-driven mechanism. [T] 3. At low pH, the availability of Fe and Al is low. [F] 4. C, H and O are beneficial nutrients. [F] 5. In diffusion, nutrients are transported from higher to lower concentration. [T] Part B Answer the following questions. [2x5=10 1. What is mass flow mechanism? Write down the factors affecting this process. 2. Write a note on “Criteria of Essentiality”. 3. Classification of essential nutrients 4. What is mobility of nutrients ? 5. Role of macronutrients Part C Write a brief note on each of the following [5x5=25 1. Role of micronutrients in plants 2. Factors affecting the nutrient availability in soil 3. Mechanism of nutrient transport in soil 4. Factors affecting the availability of micronutrients in soil 5. What is the difference between mass flow and diffusion ? Part D Select the correct answer from the four choices given under each question. [1x10=10] 1. Molybdenum was discovered by a. Arnon and Stout  b. Miller c. Dokuchaev d. Sachs and Knop 2. Which of the following are secondary nutrients? a. N, P, K b. Ca, Mg, S c. Fe, Mn, Zn, Cu d. C, H, O 3. Which nutrient improves winter hardiness ? a. N b. P c. K d. Ca 4. EDTA is commonly used in a. Micronutrients b. Secondary nutrients c. Macronutrients d. None of the above 5. P and Zn have which of the following relationship ? a. Synergistic b. Antagonistic c. Promotive d. Both a and c 6. Nutrient transport with the movement of water is called as a. Mass flow b. Diffusion c. Root interception d. All of the above 7. With increasing CEC, the availability of nutrient a. Increases b. Decreases c. No effect d. Decreases multiple times 8. The capacity of a soil to produce a certain yield of crops is called as a. Soil fertility b. Soil texture c. Soil productivity d. Soil aeration 9. Criteria of essentiality was given by Arnon and Stout in the year a. 1939 b. 1954 c. 1929 d. 1945 10. The nutrient concentration in the plant below which a yield response to added nutrient occurs is called as a. Deficient b. Luxury consumption c. Sufficient d. Critical range