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Transcript
Micronutrient elements Boron & molybdenum 1 Total boron in the soil The content of B in the soil ranges between 20-200 mg/kg dry weight. Most of which is inaccessible to plants. 2 Boron in the soil solution 1. Between pH 5 and 9, H3BO3 is the dominant form of B in the soil solution. 2. The pH of the soil solution and the amount of clay, oxides, and organic matter are important factors that affect B availability. 3 B containing Minerals Tourmaline (30-40 mg B/kg) and hydrated minerals Adsorbed B AI and Fe oxides, clay minerals, calcium carbonate, and organic matter Ligand exchange: kaolinite>montmorillonite>illite 4 Organic matter bound B the sorption capacity for B in composed organic matter is about 4 times greater than for soil or clay. It is believed to be thru ligand exchange. Hot water soluble B (0.5-2.0 mg B/L) Soluble B consists mainly of boric acid which under most soil pH conditions (pH 4-8) B(OH)3 + H2O B(OH)4-; pK4=9.2 5 Factors affecting boron availability 1. pH Absorption of B is closely dependent on soil pH, adsorption increase the pH range 5-9 2. B leaching In acid, sandy soil or podzolic soil, B is easily leached from soil; but in arid and semiarid regions, B may accumulate to toxic concentration. 3. Organic matter Native B and hot water soluble B in soil are significantly correlated with organic C content. 6 Healthy Percentage of sugar beet Infected dead pH Carbonate, % 6.7 7.0 0.1 0.1 100 99 0 1.0 0 0 7.5 8.1 0.3 14.4 46 0 40 25 14 75 7 Soils developed from sandstones and acid igneous rocks Spodosol and podzols Sometimes Andosols, Lithosols and Luvisols Sandy soil Liming acids with marginal B concentrations Hot water soluble B <0.5 mg/L 8 Boron in plant Uptake B uptake is a possible combination of active transport as esters with cis diols and passive diffusion as undissociated boric acid. But the exact nature of boric acid transport across cell membrane is still not totally resolved. 9 Translocation To most of plant species, B is translocated through the xylems, and limited phloem. It is controlled by the transpiration flow. B is not readily transported in the plant. Deficiencies occur first in the growing points and young leaves. But in some species, such as celery, carrot, bean, and cauliflowers, apple, pear, and aprico, B is mobile and is transported as a complex with polyols . 10 Cell walls B is now believed to play a key role in the structure and integrity of cell walls. The chemical composition and ultrastructure of cell walls are quickly affected by a lack of B. The role of B in cell walls is cross linking of pectic polymers (B-RG). It is important to cell wall structure. 11 Membrane function 1.The effects of B are thus mediated either directly or indirectly by the plasmamembrane bound H+ pumping ATPase. 2.The effects of B are primarily on plasmmembrane itself (Cakmak and RÖmheld 1997). B stabilizes the structure of plasma membrane by complexing membrane compounds containing cisdiol groups such as glycoproteins and glycolipids to keep channels and enzymes at optimum conforation within the membrane. 3.B exerts its most important influence at the cell/plasma interphase. 12 Function of B in the plant Other functions Pollination B was associated with the higher growth rate of pollen tubes. Root elongation IAA levels is regulated by the B via IAA oxidase activity • Meristematic activity • synthesis of N-bases such as uracil 13 Deficiency symptoms 1. Abnormal or retarded growth of apical growing points, in advantage stage, death of the terminal growing points 2. Stems have an unusual shape. They may become thick and crack. 3. Youngest leaves are misshapen, wrinkled and are often thicker and of a darkish bluegreen color. Irregular chlorosis between the intercostal veins occur. 14 Deficiency symptoms 4. The roots may grow in a very unusual way. In turnips and swedes, B deficiency result in glassy like root which are hollow and cracked 5. Flower and fruit formation is restricted or inhibited. The tissue of the fruit may have some soft, brown spots. Sometimes it results parthenogenesis. Drop of buds, flowers and fruits Fruits developed remain very small and are of poor quality. 15 Growth stunted; growing point killed; leaves dull grayish green, changing to yellow before dying off. Boron toxicity shown by narrow brown rims on leaflets; magnesium deficiency by intervenal necrosis and withering 16 B deficiency of cucumber. older leave developed yellow; new leave are distorted and appear mottled;Aborted fruit (top); twisting and scarring; • • • • 17 B deficiency: Stems stiff; terminal buds die and growths die back (up is capsicum;bottom is cucumber and tomato) 18 • Fruits pitted and corky areas in skin; ripening uneven 19 • • • Cauliflower Head Boron deficiency Browning of curd Longitudinal section. Browning of curd and lesions in•pith. (Not specific for boron; may be due to other causes in the field) Secondary infection of Bacillus Carotovorus. Corky condition of epidermis (bottom) 20 • • • Young Sugar Beet Plant Boron deficiency • Early stage of boron deficiency. Young leaves distorted and fail to expand.(left) “Crown Rot“ and death and distortion of young leaves; older leaves cracking and distortion of laminae, yellow pigment formation and severe marginal scorch. (right) 21 • • • Table Beet Plants Boron deficiency • Collapse of foliage, beginning with young leaves; rotting of outer tissues of the roots. ("Canker") ; Transverse section. "Canker" lesions, mainly in outer tissues. Rough skin condition which may accompany "Brown Heart" condition. 22 • Swede Plant Boron deficiency • Mottling and tinting of foliage and death of growing point. (right) • Rough skin condition which may accompany "Brown Heart" condition. (middle and right) 23 • • Runner Bean Stem and Leaves Boron deficiency • Stem thickened and stiff; growing points die; leaves slight chlorotic mottling. Carrot Plants Boron deficiency Growth of young leaves restricted giving a rosette effect, older leaves orange tints; growing point may die. 24 Crops differ in their sensitivity to B deficiency. Most sensitive crops: Cruciferae such as cabbage, turnips, brussels, sprouts, cauliflower and Chenopodiaceae such as sugar beet and swede. Others crops sensitive to B deficiency: celery, groundnut, coffee, oil palm, cotton, sunflower, olive, and pines. Legumes and fruit trees have a high B requirement Graminaceous monocots have a low B requirement. 25 The symptoms of B toxic often occurs on the older leaves. Begins with chlorosis on the tips and margins and finally spreads between the lateral vein, followed by progressive necrosis in the advanced stage. The leaves take on a scorch appearance and drop prematurely. 26 B toxicity of Mellon(left of up) and sweet potato (bottom0 27 B toxicity:rice(up) • 28 +B Symptoms of B toxicity are first seen in older leaves. They include yellowing between the veins,followed by necrosis. Note small brown necrotic spots ,and large areas of dead tissue 29 Arid and semi-arid soils with high B level B concentration in the irrigation water >0.3-1mg/L for sensitive crops; 1-2mg/L for semi tolerant plants and 2.1-4 mg/L for tolerant plants Industrial pollution 30 Sensitive crops: peach, grapes, kidney beans and figs Semi-tolerant crops: barley, peas, maize, potato, lucerne, tobacco, and tomato Most tolerant crops: turnips, sugarbeet and cotton. 31 boric acid (H3BO3 boron frits (Na2B4.XH2O) Sodium tetraborate (Na2B4O7.5H2O) borate-65 (Na2B4O7.XH2O) sodium pentaborate (Na2B10O16.10H2O) solubor (Na2B4O7.10H2O + Na2B10O16.10H2O) borated superphosphate ***Most compound fertilizers in Zim supply trace amounts of boron 32 Application of boron fertilizer 1. Soil application 2.Foliage spray early autumn or anthering 3. Application as starter or pop-up 33 34 Content of Mo in soil 0.8-3.3 mg/kg in agriculture soil Soil derived from granitic rocks , shells, slates or argillaceous schist are often high in Mo Highly weathered acids soils tends to be deficient Soils formed from igneous rocks and shale and poorly drained neutral or alkaline organic soils have high level Mo 35 Fraction of soil Mo Dissolved Mo Mo occluded with oxides Mo solids phases: including molybdenit (MoS2), powellite (CaMoO4), ferrimolybdite (Fe2(MoO4)3 and PbMoO4. Mo associated with organic compounds. 36 Mo availability in soil Molybdate is the most prominent form in soil solution above a pH about 4. Molybdate is absorbed by sequioxides and clay minerals via ligand exchange similar to phosphates. The Mo concentration in soil solution is usually determined predominantly by soil pH and total Mo content of the soil. As the pH falls the Mo soil solution concentration decrease. 37 Soils derived from quartzic material, sandy pebbly alluviums, and sandy loam and soils with high anion exchange capacity are often Mo deficiet. Peat soils Calcareous soil derived from loess and alluvium 38 Content of Mo in plant The Mo concentration of plant materials is usually low and plants are adequately supplied with less than 1 mg/kg dry matter. Deficiency is usually under 0.2 mg/kg dry matter. 39 Lucerne leaves 0.34 Sugar beet tops 0.72 Phaseolus bean tops 0.40 Tomato leaves, healthy 0.68 Spinach leaves 1.60 Tomato leaves, deficiency 0.13 40 Mo uptake and translocation Mo is absorbed by plants as molybdate. The uptake is depressed by the SO4- and phosphate. Mo may possibly move in xylem as MoO42-, as Mo-S amino acid complex or as a molybdate complex with sugar or polyhydroxy compounds. Mo is moderately mobile in plant. 41 Mo is an essential component of nitrate reductase and nitrogenase Mo plays another essential role in the N metabolism in legumes such as soybean and cowpea.—xanthine dehydrogenase Other functions Synthesis of vitamins IAA oxidase activity Phosphatase activity Chlorophyll structure stability 42 43 Mo deficiency frequently begins in the middle and older leaves. Interveinal mottling, marginal chlorosis of the older leaves and upward curling of the leaf margins are all typical. As the deficiency progress necrotic spots appear at leaf tips and margins. 44 In the cruciferae the lamella is not properly formed and in the extreme case only the leaf rib is present, like a whip, so the deficiency is called “whiptail” Curd formation is also distorted In Mo deficiency maize the tasseling stage is delayed; flower fail to open and grain size and viability is greatly reduced; premature sprouting of grains. 45 Mo deficiency of cauliflower: interveinal mottling, marginal chlorosis of the older leaves and upward curling of leaf margins and tip necrosis in early stage;in the serious deficiency, leaf lamella is not properly formed and in extreme case only the leaf rib is present. it is called whiptail);curd formation is also distorted. • 46 TOMATO PLANTS Molybdenum deficiency Leaflets somewhat chlorotic, strongly incurled and die back from tips. Left: healthy leaf receiving molybdenum. Right: Molybdenum deficient leaf; leaflets, incurled margins, • intervenal chlorotic motting and death of tips. 47 • • Young Cabbage Plants (Savoy) Molybdenum deficiency • Leaves cupped and show chlorotic mottling, especially around margins; tips and margins develop dead patches; plants fail to heart. (Similar to manganese toxicity; 48 High Mo levels in fodder and a Mo concentration of 5 to 10 mg Mo/kg in the dry matter is dangerous to ruminants such as cattle. Molybdenosis : diarrhoea, depigmentation ) of hair or wool, bone formation and reduction in growth. Poorly drained soils derived from granitic alluvium and black shales ash on highly organic soils. 49 Molybdenum trioxide MoO3 Mo 60% Ammonium molybdate(NH4)6Mo7O24.4H2O Mo 54% Na molybdate Na2MoO4.2H2O Mo 38-46% Molybdenized superphosphate 50 Seed treat 7g/ ha Soil application 0.01-0.5kg/ha Foliar spray 85g/ha 51