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Transcript
Phosphorus & Potassium Roles of Phosphorus: • 1. Essential for plant growth • 2. Plays a role in photosynthesis, respiration, energy storage and transfer, cell division and other processes. • 3. Promotes early root formation and growth • 4. Vital in seed formation • 5. Strengthens structural tissue – prevents lodging • 6. Improves winter hardiness • 7. Improves forage crop quality • 8. Increases water use efficiency- reduces water stress • 9. Can boost yield levels and reduce grain moisture levels • 10. Increases uptake of Mg – prevents grass tetany Plant Utilization: • • • • • • Crop Alfalfa Bermuda Corn Cotton Wheat Soybean Yield P2O5 taken up 8 ton 120 lb 8 ton 96 lb 160 bu 91 lb 1000 lb 51 lb 60 bu 41 lb 60 bu 58 lb Phosphorus Deficiency: • Symptoms: – Overall stunted appearance – Leaf shape is distorted – Dead areas arise on leaves – Purple or reddish color on leaves • A grower can expect to get 20-30% efficiency from water soluble Phosphorus fertilizer the first year after application. Fertilizer Sources of P Available P Unavailable P Plant Absorption of Phosphorus: • Plants absorb most of their P in the orthophosphate ion (H2PO4) dissolved in soil water. • It may also be absorbed in the HPO4- ion but in smaller quantities. Plants Take Up P As: Solution P Primary orthophosphate ion: H2PO4- (pH < 7.0) Secondary orthophosphate ion: HPO4= (pH > 7.0) The form most common is a function of soil pH – both equally present at neutral pH Where does P come from: • P comes from the chemical weathering of apatite rock. • The higher the ph of the soil the more Hydrogen ions are given up to form the 2 orthophosphate ions. • Decomposing organic matter, humus and microbes. – 20-50% of soil P is in O.M. How Does P Move In The Soil? • There is no gas form of P • P does not leach (unless it is in extremely high amounts) • It is not subject to oxidation-reduction • It does not move- except through diffusion P Movement: • It has been estimated that P greater than ¼ in away from a plant root will never move close enough to be taken up by the root. Phosphorus mobility in plants: • P is mobile in plants and moves readily from older tissue to newer tissue. Other forms of P: • Soluble forms of P will form compounds with: – Calcium in alkaline soils – Iron in acid soils – These forms are not available to plants Factors Affecting Soil P Availability: • 1. Amount of clay – clays fix P • 2. Type of clay – Kaolinitic clays fix more P than other clays • 3. Time of application – The longer the soil and added P are in contact the greater the chances for fixation. • 4. Aeration – for microbial breakdown and plant growth. • 5. Compaction – influences aeration Factors Affecting Soil P Availability: • 6. Moisture – inc. soil moisture to optimum levels make P more available • 7. Temperature – influence plant growth and O.M. decomposition. • 8. Other nutrients – Calcium increases P uptake • 9. Soil pH • 10. Crop root type Higher P concentration Plant root Lower P concentration Key to P Fertility: • • • • P does not move in the soil P does not change forms So Soil: • • • • • • pH Microbial activity Weathering Having crop residues Using Manures Commercial fertilizers Soil pH effect on P • optimum P availability – pH 6.0 to 7.5 • acid soil (pH < 6.0) – lime to bring pH up • alkaline soils (pH >7.5) – too costly to acidify • S can be used Ammonium phosphates most commonly used P-fertilizers –ammonium orthophosphates nearly 100% water soluble Other sources of P monoammonium phosphate (MAP) –NH4H2PO4 –10-52-0 diammonium phosphate (DAP) –(NH4)2HPO4 –18-46-0 Other sources of P ammonium polyphosphate (APP) –(NH4)3HP2O7 + NH4H2PO4 • orthophosphate • polyphosphate –10-34-0 –mainly used in fluid fertilizers Calcium phosphates triple superphosphate (TSP) –monocalcium phosphate • Ca(H2PO4)2 –40-46% P2O5 –water soluble ordinary superphosphate (OSP) –monocalcium phosphate and gypsum • Ca(H2PO4)2 + CaSO4 • 2H2O –18-20% P2O5 –10% S –high water solubility phosphate rock –fluoroapatite • [Ca3(PO4)2]3 • CaF2 –25-40% P2O5 –insoluble • more soluble in acid soils Other P sources nitric phosphate phosphoric acid potassium phosphate basic slag farmyard manure –esp. chicken Fertilizer Production strip mining of P-rock –deposits • N. Africa • N. America –Florida, N. Carolina, Idaho, Utah • Russia Methods of Applying P Fertilizer: • 1. Banding – applying P in the row with the seed. – Plants utilize the P more – Co-banding with N increases uptake of both nutrients • 2. Broadcast- applying to soil surface, – Less efficient more becomes fixed • 3. Plow down – mixed deeper into soil – Good for deep rooted plants Potassium Roles of Potassium: • Essential in photosynthesis, respiration and protein synthesis. • Important in translocation of heavy metals (Fe) • Helps plant overcome effects of disease • Important in fruit formation • Improves winter hardiness • Important in osmotic regulation in plants • Important in carbohydrate breakdown • Important in ionic balance Helps Plant Fight Disease: • Trials have shown: – Leaf blight and stalk rot in corn – Wilt and damping off in cotton – Mold and mildew in soybeans – Black spot and stem end rot in potatoes – Leaf spot and dollar spot in turf K • Strengthens stems • Thickens cuticle • Reduces the number of shrunken moldy discolored soybeans or seed. N to K balance in Forages Nutrients Yield lb/a 2nd cutting • 500-0-0 2,693 • 500-70-0 2,887 • 500-0-60 4,509 • 500-0-120 4,679 • 500-70-60 4,267 • 500-140-140 4,999 – Bermuda grass in Texas Plant Deficiency Symptoms: • Increased drought stress • Burned or scorched appearance on leaf margins. Older leaves show deficiency symptoms first in grasses – Newer leaves on cotton • Plants grow slowly and have poor root development • Weak stems • Plants are more subject to diseases Forms of Potassium in Soil: • 1. Unavailable K – found in rock minerals – Released as rock weathers – takes hundreds of years • 2. Slowly available K – fixed or trapped between layers of certain soil clays – Available as clays swell and shrink. • 3. Available soil K – K found in soil solution plus K held in exchangeable form by soil organic matter and clays. About 2% or less of total K in soils How K moves in the soil: • K does not move readily in soils except sandy or organic soils. • When it does move it does so by diffusion How do plants take up K? • Plants can take up K in two ways: – 1. Soil solution – 2. Exchangeable K – loosely held by soil clays and organic matter. Factors Affecting Plant Uptake of K: • • • • • • 1. Any factor affecting/limiting root growth 2. Soil aeration 3. Level of K in soil 4. Fixation of K 5. CEC level 6. Soil temperature – low temps reduce K availability • 7. Soil moisture – drought reduces K uptake Methods of Applying K Fertilizer: • • • • • 1. 2. 3. 4. 5. Broadcast Broadcast, plow down Direct seed placement Fertigation Deep placement or knifed Sources of K Fertilizer: • K deposits occur as beds of solid salts beneath the earths surface, and brines in dying lakes and seas • Mined in 4 ways: • 1. Conventional underground coal mining method • 2. Continuous mining method • 3. Solution mining – sodium chloride brine dissolves KCl pumps to surface for refining • 4. Surface Brine Recovery- K and other minerals harvested with solar evaporation from natural brines – Great Salt Lake, Dead Sea Minerals K is Mined From: • 1. Sylvinite – KCl and NaCl (20-30% K2O) • North American KCl (0-0-60) 90% of K sold in U.S. and Canada • 2. Sylvite – KCl (63% K2O) • 3. Langbeinite – K2SO4 and MgSO4 (23% K2O) Fertilizer Grade Particle Size: • • • • • 1. 2. 3. 4. 5. White Soluble – ideal for liquids Special Standard Standard Coarse Granular – suitable for bulk blending Other Sources: • K2SO4 – Sulfate of potash (SOP) 50% K2O and 18% S – Used in Cl- sensitive crops or where Cl buildup is a problem • K2SO4-2MgSO4 – Potassium-magnesium sulfate “KMag” or “Sul-Po-Mag” (22% K2O, 11% Mg, 22% S) – Good source of water soluble K and Mg • KNO3 – Potassium nitrate (13-0-44) – Little or no Cl or S