NRES 201 Lecture 38 Fall 2014 Phosphorus NRES 201 Phosphorus 1 Phosphorus Today s lecture topics Phosphorus in plants Phosphorus in soils The phosphorus cycle Factors affecting phosphorus availability Phosphorus fertilizer sources 2 1 NRES 201 Lecture 38 Fall 2014 Phosphorus Functions of P in plants Energy storage and transfer Mechanism ATP and ADP as energy carriers Energy release through hydrolysis 12 kcal mol Source http scienceaid co uk 3 Role in metabolism Making the impossible happen Exemplary processes Photosynthesis Respiration Active ion uptake 4 2 NRES 201 Lecture 38 Fall 2014 Phosphorus Inheritance Constituent of DNA and RNA Required for Cell division Development of meristematic tissue Critical early in the life of the plant Source http science howstuffworks com 5 Plant nutrient concentrations Source Havlin et al 1999 6 3 NRES 201 Lecture 38 Fall 2014 Phosphorus Phosphorus in soils Total content Surface soil P N or K Buildup due to Long term fertilizer use Manure Fundamental aspects of P fertility Most soil P is not plant available Solubility is crucial So is root growth 7 The phosphorus cycle Source Havlin et al 2005 8 4 NRES 201 Lecture 38 Fall 2014 Phosphorus P is taken up from the soil solution As H2PO4 As HPO42 Soluble P is in equilibrium with insoluble P 9 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 S 10 5 NRES 201 Lecture 38 Fall 2014 Phosphorus 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 soils 11 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 N 12 6 NRES 201 Lecture 38 Fall 2014 Phosphorus Soil solution P Typical concentrations Very low except in fertilizer bands Usually 0 05 mg P L Chemical forms Mainly H2PO4 and HPO42 A function of pH Source Brady and Weil 2008 13 Organic soil P Soil 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 surface Source Tisdale et al 1993 14 7 NRES 201 Lecture 38 Fall 2014 Phosphorus Chemical forms Esters of orthophosphoric acid H3PO4 Derived from plants and microorganisms 15 Organic P turnover in soils Mineralization immobilization turnover MIT Mineralization is due to Microbial activity A soil enzyme phosphatase 16 8 NRES 201 Lecture 38 Fall 2014 Phosphorus Effect 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 mineralization 17 Factors 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 to a flush in mineralization of P Cultivation Stimulates mineralization because of Improved aeration Exposure of fresh organic matter to microbial attack Causes a decline in soil organic P 18 9 NRES 201 Lecture 38 Fall 2014 Phosphorus Inorganic P Primary minerals Fe Al phosphates Occur in acid soils Common examples Variscite Al Strengite Fe Dragline in Florida Ca phosphates Occur in neutral and Source http www florallakes org calcareous soils Apatites or phosphorites rock phosphate Like the silicate minerals Lots of isomorphous substitution Mined to make P fertilizers 19 pH and the solubility of P minerals Solubility trends 20 10 NRES 201 Lecture 38 Fall 2014 Phosphorus Inorganic P Secondary precipitates Derived from Primary minerals Formed through weathering P fertilizers Formed as fertilizer soil reaction products Ca precipitates Dicalcium phosphate DCP Dicalcium phosphate dihydrate DCPD Tricalcium phosphate TCP Octacalcium phosphate OCP Fe and Al precipitates Strengite like variscite like etc 21 P held on solid surfaces Anion exchangeable P Substituted for an external OH group Favored by acidity Si OH H2PO4 Si H2PO4 OH H2O Electrostatically attracted Favored by acidity H Si Si OH2 OH Si OH2 H H2PO4 Si OH2H2PO4 22 11 NRES 201 Lecture 38 Fall 2014 Phosphorus Binuclear bridging Favored by acidity O labile Fe OH Fe O P OH OH OH OHO O P O O H OH Fe OH Fe OH H2O H2O Fe nonlabile O O Fe O P O OH 23 P held on solid surfaces Precipitated P Ca phosphates precipitated on CaCO3 AlPO4 precipitated on Al OH 3 FePO4 precipitated on Fe oxides 24 12 NRES 201 Lecture 38 Fall 2014 Phosphorus Factors affecting phosphorus availability Clay content and composition Clay adsorbs P Greater P adsorption with 1 1 minerals than with 2 1 minerals due to A larger number of exposed OH groups Greater potential for positive charge Presence of Fe and Al oxides 25 This figure shows the effect of soluble P on P adsorption by four different soil orders Within an order P adsorption was increased by higher clay content Adsorption was far higher with 1 1 clays in Andisols or Oxisols than with 2 1 clays in Mollisols Andisols Source Tisdale et al 1993 26 13 NRES 201 Lecture 38 Fall 2014 Phosphorus Soil 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 decreases 27 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 0 28 14 NRES 201 Lecture 38 Fall 2014 Phosphorus Root growth Uptake of an immobile nutrient is reduced by Poor drainage A dense compact layer Shallowness to bedrock sand or gravel Strong subsoil structure Droughtiness strong acidity etc Cool wet weather Source http centralvalleycoop com 29 Phosphorus fertilizer sources Triple superphosphate TSP Essentially monocalcium phosphate P2O5 by weight Ca H2PO4 2 P P2O5 62 142 Fertilizer grade 0 46 0 Contains 20 P Made by heating rock phosphate with H3PO4 Ca10 PO4 6F2 12 H3PO4 9 Ca H2PO4 2 CaF2 The leading P fertilizer in the 1950s and 60s Still widely available Source http www google com 30 15 NRES 201 Lecture 38 Fall 2014 Phosphorus Diammonium phosphate DAP Chemical formula NH4 2HPO4 Fertilizer grade 18