sources, N for crop improvement and increase metabolism.pptx

Study of nitrogen content in crop

1. Sources, forms, mobility, transformation, fixation, losses and availability of Nitrogen in Soil

2. Nitrogen Nitrogen is the first element of the macronutrients usually applied in commercial fertilizers. Nitrogen is of special importance in the formation of protein in plants . It forms a constituent of every living cell in the plants. It is also present in chlorophyll , the green pigments that are receptors of light energy in photosynthesis through which plants assimilate carbon from atmospheric carbon dioxide and entrap solar energy.

3. Sources of N Primary sources Atmosphere : The atmospheric N is fixed by lightning and carried to the soil in rain water. Few microorganisms are also able to fix atmospheric N. Total amount of N contributed through rainfall is 1-50 lb/ac/year. (1lb=0.45 kg) Secondary source Igneous rocks contain very low concentration of N, while the sedimentary rocks contain more N, which is inherited from earlier soil, or some living things.

4. Forms of N

5. Organic form Organic N occurs as protein, amino acids, amino sugars and other complex N compounds. Bound amino acid 2 0-40% Amino sugars (Hexosamine) 5-10% Purine, pyrimidine 1% or less

6. Nitrogen is also present as amine group (-NH2) which has covalent bonds to a C and to two H atoms. Six of the 8 electrons in the outer shell are involved in these 3 bonds, 2 electrons remain which can accept another H ion and bond to it. A positively charged site is thus formed.

7. Resistant to decomposition These positive sites can bond to negatively charged clay surface and help to stabilize soil structure. Such bonding stabilizes the organic compound and make it more resistant to decomposition . Positively charged sites that are not bonded to clay particles can serve as sites for anion exchange . Proteins are commonly found in combination with clay, lignin and other materials resistant to decomposition

8. Inorganic forms N 1 . Ammonium NH 4 2. Nitrite NO 2 3. Nitrate NO 3 4. Elemental N(No) Plant absorbs N as both - NH 4 - , NO 3 - .

9. Mobility of nitrogen In soil: Nitrogen is highly mobile in the form of Nitrate NO 3 . Immobile in the form of Ammonium NH 4 . In plants: Both the available form of Ammonium NH 4 and Nitrate NO 3 are mobile in the plants.

10. N transformations in soils Nitrogen cycle N - mineralisation Aminisation N immobilization N factor Ammonification Nitrification Denitrification Elemental N loss

11. Nitrogen mineralization Mineralization is the conversation of organic N to inorganic N as a result of microbial decomposition. Mineralization increases with a rise in temperature and is enhanced by adequate soil moisture and a good supply of O 2 . Mineralization of organic N involves in two reactions. i.e 1) Aminization 2) Ammonification. AMINISATION Aminisation is the decomposition of proteins and the release of amines, amino acids and urea is called aminisation . Proteins → R – C – COOH + R NH 2 + C = O + CO2 + Energy

12. Ammonification “ Amines and aminoacids produced during aminisation of organic N are decomposed by other heterotrophs (Nitrosomonas & Nitrobacter) with release of NH 4 + is termed ammonifcation . Nitrobacter R – NH 2 + H 2 O NH 3 + R – OH + energy ↘ H 2 O NH 4 + + OH –

13. NITRIFICATION Nitrification is the process of biological oxidation by which the NH 4 + form of N converts to nitrate form of N . There are two steps. NH 4 is converted first to NO 2 - and then to NO 3 - . Nitrosomonas 2NH 4 + 3O 2 2 NO 2 - + 2H 2 O + 4H + Nitrobacter 2NO 2 + O 2 2NO 3 - + Energy Conversion of NO 2 - to NO 3 - is faster than that of NH 4 to NO 2 . accumulation of NO 2 - would be toxic to plants.

14. Gaseous losses of N Volatilization : Gaseous loss of N in which inorganic N ions can be converted to gas and lost to the atmosphere. NH 4+ NH 3 + H + It dependent on pH When pH exceeds 7.5 volatilization occurs, Denitrification : Nitrates are subjected to reduction in soils especially in those that are poorly drained and low in aeration. This process is known as denitrification 2NO 3 2NO 2 2NO N 2 O N 2

15. Ammonium fixation Organic and inorganic soil fractions have the ability to fix NH 4 + in forms relatively unavailable to higher plants. 2 types of fixation 1. Fixation by clay minerals - 2:1 type structure have the capacity to fix NH4 + and K+ ions (Vermiculite) 2. Fixation by organic matter - Immobilization

16. NITROGEN IMMOBILIZATION “Immobilisation is the process of conversion of inorganic N (NH 4 + or NO 3 - ) to organic N and it is basically the reverse of N mineralization”. The microorganisms accumulate NH 4 + N and NO 3 – N in the form of protein, nucleic acid and Other complexes. If C:N ratio is greater than 30, it favours immobilization and lesser C:N ratio encourage mineralization. N factor is the no of units of inorganic nitrogen immobilized for each 100 units of materials under going decomposition. The average values for the nitrogen factor vary from 0.1 to 1.3 . N FACTOR

17. Biological N fixation (BNF) Biological N fixation (BNF) is the biochemical process by which elemental N is combined into organic forms. It is carried out by bacteria, actinomycetes, blue green algae (cyanobacteria). Quantity of N fixed is 175 million metric tonnes . Symbiotic N fixation Non Symbiotic N fixation

18. Symbiotic N fixation Rhizobium – Legumes (Nodule forming) The host plant supplies the bacteria carbohydrate for energy and the bacteria fix atomospheric N, thus an association mutually benefitted is called symbiosis Azolla - Anabaena ( Non nodule forming) The Anabaena blue green algae inhabit cavities in the leaves of the floating fern, azolla and fix quantities of N comparable to those that of better Rhizobium-legume complex

19. Non symbiotic N fixation Free living microorganisms in soils and water are able to fix N, since these organisms are not directly associated with higher plants, the transformation is referred to as non symbiotic or free living.