NRES 201 Lecture 38 (Fall 2014): Phosphorus1NRES 201Phosphorus12Today’s lecture topics- Phosphorus in plants- Phosphorus in soils- The phosphorus cycle- Factors affecting phosphorus availability- Phosphorus fertilizer sourcesPhosphorusNRES 201 Lecture 38 (Fall 2014): Phosphorus2Functions of P in plantsEnergy storage and transfer- Mechanism- ATP and ADP as energy carriers• Energy release through hydrolysis(12 kcal/mol)3Source: http://scienceaid.co.uk- Role in metabolism• Making the impossible happen- Exemplary processes- Photosynthesis- Respiration- Active ion uptake4NRES 201 Lecture 38 (Fall 2014): Phosphorus3Inheritance- Constituent of DNA and RNA- Required for:- Cell division- Development of meristematic tissue- Critical early in the life of the plant 5Source: http://science.howstuffworks.com6Source: Havlin et al. (1999)Plant nutrient concentrationsNRES 201 Lecture 38 (Fall 2014): Phosphorus4Phosphorus in soilsTotal content- Surface soil: P < N or K- Buildup due to:- Long-term fertilizer use- ManureFundamental aspects of P fertility- Most soil P is not plant-available- Solubility is crucial- So is root growth7The phosphorus cycleSource: Havlin et al. (2005)8NRES 201 Lecture 38 (Fall 2014): Phosphorus5- P is taken up from the soil solution-As H2PO4--As HPO42-- Soluble P is in equilibrium with insoluble P9- Soil P occurs in organic and inorganic forms- Most organic P in microbial biomass- Most inorganic P in minerals- Labile P is organic or inorganic- P turnover by mineralization and immobilization- No loss of soil P by volatilization- A major difference between P and N or S10NRES 201 Lecture 38 (Fall 2014): Phosphorus6- Loss of P occurs by -Erosion• The major loss process for agricultural soils- Runoff• From animal confinement facilities• From recently fertilized or manured soils• From decomposing plant litter (no-till)- Leaching• From sandy soils• From organic soils• From forest soils• From manured soils11- P losses much lower than N losses- Fertilizer P is soluble- Much more soluble than soil P- But only for a while- Fertilizer P can be fixed or immobilized- Both processes reduce plant availability- P is less dynamic than N12NRES 201 Lecture 38 (Fall 2014): Phosphorus7Soil solution PTypical concentrations- Very low, except in fertilizer bands- Usually  0.05 mg P/LChemical forms- Mainly H2PO4-and HPO42-- A function of pHSource: Brady and Weil (2008)13Organic soil PSoil content- Ranges widely- Total range: 3-90% of total soil P- Typical: 10-40% (600-2400 lb organic P/A-6”)- Highest at the soil surfaceSource: Tisdale et al. (1993)14NRES 201 Lecture 38 (Fall 2014): Phosphorus8Chemical forms- Esters of orthophosphoric acid (H3PO4)- Derived from plants and microorganisms15Organic P turnover in soilsMineralization-immobilization turnover (MIT)Mineralization is due to- Microbial activity- A soil enzyme (phosphatase)16NRES 201 Lecture 38 (Fall 2014): Phosphorus9Effect of the C/P ratio of organic amendments- Analogous to C/N and C/S ratios- Originates from microbial uptake of P- Can cause immobilization or mineralization17Factors promoting mineralization of organic P- Adequate soil moisture- Warm temperatures- Good aeration- Wetting and drying cycles- Same effect as for N and S- Microbial utilization of dead biomass leads toa flush in mineralization of P- Cultivation- Stimulates mineralization because of:• Improved aeration• Exposure of fresh organic matter tomicrobial attack- Causes a decline in soil organic P 18NRES 201 Lecture 38 (Fall 2014): Phosphorus10Inorganic P: Primary mineralsFe-Al phosphates- Occur in acid soils- Common examples- Variscite (Al)- Strengite (Fe)Ca phosphates- Occur in neutral andcalcareous soils- Apatites or phosphorites (rock phosphate)- Like the silicate minerals- Lots of isomorphous substitution- Mined to make P fertilizersSource: http://www.florallakes.org19Dragline in FloridaSolubility trendspH and the solubility of P minerals20NRES 201 Lecture 38 (Fall 2014): Phosphorus11Inorganic P: Secondary precipitatesDerived from- Primary minerals- Formed through weathering- P fertilizers- Formed as fertilizer-soil reaction productsCa precipitates- Dicalcium phosphate (DCP)- Dicalcium phosphate dihydrate (DCPD)- Tricalcium phosphate (TCP)- Octacalcium phosphate (OCP)Fe and Al precipitates- Strengite-like, variscite-like, etc.21P held on solid surfaces:Anion exchangeable PSubstituted for an external OH group- Favored by aciditySi + H2PO4- Si + OH-Electrostatically attracted- Favored by aciditySi + H+ Si Si + H2PO4- Si OH H2PO4H+H2OOH OH2+OH2+OH2H2PO422NRES 201 Lecture 38 (Fall 2014): Phosphorus12Binuclear bridging- Favored by acidityFe-OHO +Fe-OHOHO-P=OOH-Fe-O Fe-OHOO-P-OHOH+ OH-H+H2OH2OFeO P FeOOOOH(labile)(nonlabile)23P held on solid surfaces:Precipitated P- Ca phosphates precipitated on CaCO3- AlPO4precipitated on Al(OH)3- FePO4precipitated on Fe oxides24NRES 201 Lecture 38 (Fall 2014): Phosphorus13Factors affecting phosphorus availabilityClay content and composition- Clay adsorbs P- Greater P adsorption with 1:1 minerals than with2:1 minerals due to:- A larger number of exposed OH groups- Greater potential for positive charge- Presence of Fe and Al oxides25Source: Tisdale et al. (1993)26- This figure showsthe effect of solubleP on P adsorptionby four differentsoil orders- Within an order,P adsorption wasincreased byhigher clay content- Adsorption wasfar higher with 1:1clays in Andisols orOxisols than with2:1 clays inMollisolsAndisolsNRES 201 Lecture 38 (Fall 2014): Phosphorus14Soil pH- Solubility of Fe and Al phosphates- Increases as pH rises- Precipitation of Fe and Al hydroxides- Liming acid soils increases P availability- Solubility of Ca phosphates- Increases as pH decreases27- Mineralization of organic P- Tends to increase as pH rises- Form of orthophosphate-H2PO4-taken up 10 faster than HPO42-- Net effect- P most available at pH 6.0-7.028NRES 201 Lecture 38 (Fall 2014): Phosphorus15Root growth- Uptake of an immobilenutrient is reduced by:- Poor drainage- A dense, compact layer- Shallowness to bedrock,sand, or gravel- Strong subsoil structure- Droughtiness, strongacidity, etc.- Cool, wet weather29Source: http://centralvalleycoop.comPhosphorus fertilizer sourcesTriple superphosphate (TSP)- Essentially monocalcium phosphate[Ca(H2PO4)2]- Fertilizer grade: 0-46-0- Contains 20% P- Made by heating rock phosphate with