Plant-nutrition2.pdf

PLANT NUTRITION  BASIC PLANT NUTRITION 1.Factors affecting plant growth 2.Response of plants to nutrients 3.The essential elements 4.Function of nutrients and deficiency symptoms  GENETIC ENVIRONMENT SOIL TEMP....

PLANT NUTRITION  BASIC PLANT NUTRITION 1.Factors affecting plant growth 2.Response of plants to nutrients 3.The essential elements 4.Function of nutrients and deficiency symptoms  GENETIC ENVIRONMENT SOIL TEMP. PLANT GROWTH SOLAR WATER ENERGY BIOTIC CROP FACTORS CLIMATE FACTORS PLANT GROWTH FACTORS EFFECTS AND INTERACTION OF GROWTH FACTORS Temperature  temperature range for agricultural crops; 15ºC – 40ºC  temperature effects: photosynthesis, Temperature Effects: Photosynthesis Respiration Cell Wall Permeability Absorption of water and nutrients and Transpiration Enzyme Activity Protein Coagulation Moisture supply  water is needed to manufacture carbohydrates, maintain hydration of protoplasm, and for translocation of carbohydrates and nutrients.  low moisture level impairs nutrient absorption thru its effect on mass flow, diffusion and root interception.  excess water impairs nutrient absorption due to respiration caused by lack of O2 Solar Energy  most plants grow best in full sunlight. Some are shade tolerant (e.g. black pepper, cacao)  high density plant cause shading  less shading in plants with more erect leaves Soil properties  physical (texture, structure, bulk density, porosity, water holding capacity, hydraulic conductivity)  chemical (pH, CEC, base saturation, salinity, toxic elements)  biological (OM content and kind and amount of microbial population)  soil fertility or supply of nutrients  LIEBIG’S LAW OF MINIMUM “By the deficiency or absence of one necessary constituent all others being present, the soil is rendered barren for all those crops to the life of which that one constituent is indispensable.” Or: “Plant growth is limited by that nutrient present below the minimum requirement.” MITSCHERLICH’S LAW OF DEMINISHING RETURN In 1909, Mitscherlich developed an equation relating growth to the supply of plant nutrients. He observed that if plants were supplied with adequate amounts of all nutrients save one, their growth was proportional to the amount of this limiting element which was added to the soil.  dy dx = (A – y) c Where: dx = an increment of the growth factor; X1, X2, X3, or Xn dy = the increase in yield due to an increment of the growth factor dx A = the maximum yield possible obtained by supplying all growth factors in optimum amounts y = yield obtained after any given quantity of the factor x has been applied c = a proportionally constant which depends on the nature of the growth factor  DY = (A – Y) c 100 DX DY = increase in yield % of Y3 DX = increase in input maximum Y2 yield A = maximum possible yield Y1 Y = actual yield C = constant depending on nature of x (whether N, P, K etc.) 1 2 3 4 Units of input X MITSCHERLICH’S EQUATION  NUTRIENT ABSORPTION AND ASSIMILATION BY PLANTS  NUTRIENT ABSORPTION AND ASSIMILATION BY PLANTS 1. Mechanisms of nutrient movement to roots 2. Active and passive uptake 3. Nutrient mobility 4. Nutrient translocation and assimilation Cross section of the root showing primary tissues  Median longitudinal view of a root tip showing the primary meristem and primary tissues and regions that develop from them. B.Nutrient Absorption B.1. Mechanism Mass Flow – movement of nutrients to the roots due to uptake and transpiration of water. Diffusion – movement of nutrient ions from a zone of high concentration. Root interception (Contact exchange) – direct exchange between root surface and colloid surface. P and K absorption is mostly by diffusion. Table 1. Movement of nutrients from soil to roots of corn. Amount of % Supplies Nutrient nutrient needed Root Mass for 150 bu/a Diffusion interception flow N 170 1 99 0 P 35 3 6 94 K 175 2 20 78 Ca 35 171 429 0 Mg 40 38 250 0 S 20 5 95 0 Cu 0.1 10 400 0 Zn 0.3 33 33 33 B 0.2 10 350 0 Fe 1.9 11 53 37 Mn 0.3 33 133 0 Mo 0.01 10 200 0 P, K move from soil roots mostly by diffusion. All others mostly by mass flow. B.2. Active vs Passive Uptake Passive uptake – occurs in the outer or apparent free space (AFS) consisting of the walls of the epidermal and cortical cells of the roots. Uptake is by diffusion and ion exchange, hence controlled by concentration and electrical gradient. These processes are non-selective and do not require energy from metabolic reactions in the cell. Passive uptake occurs outside the casparian strip and plasmalemma as a barrier to diffusion and ion exchange.  Active uptake – transport of ions into the inner cells require energy due to the higher concentration of ions beyond the plasmalemma and into the cytoplasm which is against an electrochemical gradient. Entry of ions into the impermeable membranes of the other organs within the complex derives energy from metabolism. The process is selective in that specific ions are transported by specific carriers. Plant cells are negatively charged, thus anions must move against an electrochemical gradient.  Summary of Nutrient Uptake and Mobility Nutrient Uptake Mobility N active mobile P active mobile K active mobile Ca passive immobile Mg passive mobile S active moderate (mainly upward) Fe active immobile Mn active immobile Zn active very low mobility Cu active moderately mobile Mo active moderately mobile B passive immobile Cl active moderately mobile  UPTAKE, TRANSLOCATION AND ASSIMILATION OF NUTRIENTS I. Nitrogen A. Uptake 1. Taken up as NO3- and /or NH4+ but the nitrate is often the predominant form (because NH4+ is easily oxidized by bacteria in aerobic soil to NO3- as soon as NH4+ appears). 2. NO3- uptake occurs against an electrochemical gradient or actively absorbed (energy requiring). 3. NO3- and NH4+ uptake differs with pH of medium. NH4+ uptake is optimum at neutral pH and decreases as pH decreases. NO3- uptake increases with decreasing pH and decreases with increasing pH probably due to competition with (hydroxide) OH. 4. Ammonia (NH3) is toxic to plant roots; it can penetrate cell membranes. 5. Urea which is converted to NH4+ by urease in soil can be taken directly by plants, though at slower rate than NO3 B.Translocation and Assimilation 1. Once N is converted to organic form it remains in this form in the plant. 2. Glutamic acid and glutamine are the two amino acids synthesized during reductive amination. 3. Total N in plants is in the form of: Content of plants : 2 – 4% Protein N : 80 – 85% Nucleic acid N : 10% Soluble amino N : 5% 4.N taken up by plant roots is translocated in the xylem to upper plant parts. Nearly all the NH4- N absorbed is assimilated in the root tissue and redistributed as amino acids, NO3- - N can be translocated unaltered to shoots and leaves. 5. Biological N fixation (BNF) 6 H+ N2 NH3 amino acid 6 e- - oxoglutarate II. Phosphorus A. Absorption and Translocation 1. Active uptake 2. Uptake is pH-dependent. Higher P uptake at low pH (4.0) than at high pH (8.7). 3. Readily translocated up and down plant and quickly assimilated into organic compounds such as hexose phosphate and uridine disphosphate. B.Assimilation 1. Orthophosphate (inorganic P) is esterified with OH groups of sugars and alcohols. Typical example of phosphorylated sugar: fructose-6-phosphate. 2. P can also be bound by a lipophilic compound (phospholipids), e.g. lecithin. 3. Another organic P compound is phytin (phytic acid) which occurs mainly in seeds. 4. The most important organic P compound is ATP. ATP is synthesized during respiration, in glycolytic pathway and photosynthesis. In roots, respiration provides the main source of ATP in green plant tissue, photophosphorylation in photosynthesis. III.Potassium 1. Taken up in high rate by plant tissues (to the point of luxury consumption). 2. K is taken up by active mechanism. Of all the essential nutrient cations K is the only one which can be transported against an electrochemical gradient into plant cell. K in plant is very mobile. The main transport direction is towards merismatic tissues. Thus when plant is sufficiently supplied with N and vigorously growing, K uptake is high. 3.The bulk of K mainly taken up during the vegetative stage (in cereals, from tillering to ear emergence) 4. K uptake and retention in plants are competitively affected by H+, Ca++, Mg++ and Na+. 5. K accumulation in xylem and mesophyll cells lowers the osmotic potential of cell sap and increases uptake and retention of water. Thus, plants well supplied with K require relatively lower amounts of water (more drought resistant).  Such plants also have lower transpiration rate. K in guard cells appear to regulate stomata opening and closing, hence regulating transpiration. 6. K enhances translocation of assimilates through stimulation of ATP production which is needed in the loading of photosynthates in sieve tubes (phloem). IV.Calcium 1. Content in plants: 0.5-0.8% 2. Ca absorption and translocation is mainly a passive process (mass flow in transpiration stream). The preferential direction is the shoot apex (actively growing parts). 3. Ca is largely immobile. Once deposited, it is not moved from older to younger leaves. 4.Ca is largely in plant occurs as free Ca++ and as Ca oxalates, carbonates and phosphates usually as deposits in cell vacuoles. In seeds Ca occurs as a salt of inositol hexaphosphoric acid (phytic acid). In cell wall it is bound as pectate (phytic acid is an organic P compound). Ca often occurs as chelated compound which is highly soluble in water but stable to changes in pH (Ca = EDTA). 5. Ca content of legumes is higher in dicotyledons than in monocotyledons and also higher in legumes than in other species. V. Magnesium 1. Taken up in lower amount than Ca. 2. Plant tissue content about 0.50%, DM. 3. Competitive relationships: NH4, K, Ca, Mn 4. Mg moves similarly as Ca in plant, except that Mg (unlike Ca) is mobile in the phloem passive uptake, transpiration stream. 5. Like Ca, Mg is present in cereal grains as salt of inositol hexaphosphoric acid (phytin or phytic acid). 6. Mg is the center of the chlorophyll molecule (30% component). VI.Sulfur 1. Absorbed as SO42- and translocated against an electrochemical gradient (active uptake). 2. Translocation is mainly upward (acropetal). 3. Plant use atmospheric S as S2 (sulfide) by absorption through the stomata. 4.S is assimilated into amino acids cyteine, cystine, and methionine. The first step is reduction of SO42-. Cystein is the first stable product in which S is present in reduced organically bound form. 5.S is also a constituent of biotin (associated with CO2 fixation and decarboxylation reactions) and thiamine (Vitamin B1). 6.In some plant species S occurs as sulphoxides which is responsible for the lachrymatory factor in onions and odor of garlic. 7. S is also an important component of mustard oil. Amino acid oxine mustard oil 8. Total S content of plant = 0.2 – 0.5% VII. Iron 1. Fe is taken up as Fe3+ or as Fe- chelate. However, Fe3+ is reduced before it is absorbed at the other plasmalemma by a source of electron from within the cell via a cytochrome or flavin compound. Also, there is a separation of Fe and the chelate prior to absorption (active uptake). 2. Ions that compete with Fe absorption: Mn++, Cu++, Mg++, K+ and Zn 3. Fe uptake is depressed by high pH, high phosphate and calcium concentrations in nutrient medium.  Good aeration also depresses Fe uptake due to oxidation to Fe3+ NO3 also depresses Fe uptake 4. Fe is immobile in plant, hence chlorosis appears first in young cells. 5. The major form translocated in xylem is ferric citrate. 6.Another form of Fe in chloroplast is ferredoxin. It is a non-haem iron protein which participates in oxidation- reduction processes by transferring electrons. 7.Ferredoxin is important as a redox system in photosynthesis, in nitrite reduction, sulfate reduction and nitrogen assimilation (ferredoxin is stable Fe-S protein). VIII. Manganese 1. Uptake is metabolically medicated (active uptake). 2. Mg depresses Mn uptake. 3. Liming reduces uptake due to Ca and high pH. 4. Competition is with Ca, Mg, Fe, Zn. 5. Mn is relatively immobile in the plant. 6. Mn is preferentially translocated to merismatic tissues. IX. Zinc 1. Zn content of plants: 10-100 ppm 2. Active uptake 3. Ion competition: Cu, Fe, Mn, Mg, Ca 4. Very low mobility 5. High P levels induce Zn deficiency 6. Other Zn metallo-enzymes: glutamic acid dehydrogenase, lactic acid dehydrogenase, alcohol dehydrogenase and peptidases. X. Copper 1. Active uptake 2. Ca strongly inhibits Cu uptake 3. Not readily mobile but can be translocated from older to younger leaves. 4. Cu is a constituent of the chloroplast protein phytocyanin which is part of the electron transport chain linking the two photochemical systems of photosynthesis. 5. Cu-containing enzymes which reduce both atoms of molecular oxygen: cytochrome oxidase, ascorbic acid oxidase, polyphenol oxidase and laccase. XI.Molybdenum 1. Form absorbed: molybdate, MoO4- 2. Active uptake 3. Mobility in plant: moderate 4. Plant content: