NRES 201 Lecture 36 Outline of Last Lecture I Comparison of nitrogen and sulfur II Sulfur in plants III Sulfur in soils IV The sulfur cycle V Sulfur fertilizer sources Outline of Current Lecture VI Phosphorus in plants VII Phosphorus in soils VIII The phosphorus cycle IX Factors Affecting Phosphorus Availability X Phosphorus fertilizer sources Current Lecture Functions of P in plants Energy storage and transfer Mechanism o ATP and ADP as energy carriers Energy release through hydrolysis o Role in metabolism o Exemplary processes photosynthesis respiration active ion uptake Inheritance o Constituent of DNA and RNA o Required for cell division and development of meristematic tissue o Critical early in the life of the plant Phosphorus in Soils Total Content Surface Soil P N or K o Buildup due to long term fertilizer use and manure Fundamental aspects of P fertility o Most soil P is not plant available o Solubility if crucial as well as root growth o P is taken up from the soil solution o Soluble P is in equilibrium with insoluble P o Soil P occurs in organic and inorganic forms These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Most organic P in microbial biomass Most inorganic P in minerals Labile P is organic or inorganic Loss of P occurs by Erosion The major loss process for agricultural soils Runoff Leaching from sandy organic forest and manure soils P losses much lower than N losses Fertilizer P is soluble much more soluble than soil P Soil Solution P Typical Concentrations are very low except in fertilizer bands It is a function of pH 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 Inorganic P Primary minerals Fe Al phosphates o Occur in acid soils Ca phosphates o Occur in neutral and calcareous soils o Apatites of phosphorites rock phosphates Like the silicate minerals Lots of isomorphous substitution Mined to make P fertilizers Soil pH Solubility of Fe and Al phosphates o Increases as pH rises o Liming acid soils increases P availability Solubility of Ca phosphates increases as pH decreases Mineralization of organic P tends to increase as pH rises Net effect P is most available at pH 6 0 7 0 Root Growth Uptake of an immobile nutrient is reduced by o Poor drainage o A dense compact layer o o o o Shallowness to bedrock sand or gravel Strong subsoil structure Doughtiness strong acidity Cool wet weather Phosphorus Fertilizer Sources Triple Superphosphate TSP o Contains 20 P o The leading P fertilizer in the 50s and 60s and still widely available Diammonium Phosphate DAP o Contains 20 P o Leading P fertilizer in US o Can be solid or liquid
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