<P> Phosphorus deficiency is a plant disorder associated with insufficient supply of phosphorus . Phosphorus refers here to salts of phosphates (PO), monohydrogen phosphate (HPO), and dihydrogen phosphate (H PO). These anions readily interconvert, and the predominant species is determined by the pH of the solution or soil . Phosphates are required for the biosynthesis of genetic material as well as ATP, essential for life . Phosphorus deficiency can be controlled by applying sources of phosphorus such as bone meal, rock phosphate, manure, and phosphate - fertilizers . </P> <P> In plants, Phosphorus (P) is considered second to nitrogen as the most essential nutrient to ensure health and function . Phosphorus is used by plants in numerous processes such as photophosphorylation, genetic transfer, the transportation of nutrients, and phospholipid cell membranes . Within a plant cell these functions are imperative for function, in photophosphorylation for example the creation of stored energy in plants is a result of a chemical reaction including phosphorus . Phosphorus is a key molecular component of genetic reproduction . When phosphorus is present in inadequate levels, genetic processes such as cell division and plant growth are impaired . Hence, phosphorus deficient plants may mature at a slower rate than plants with adequate amounts of phosphorus . The stunted growth induced by phosphorus deficiency has been correlated with smaller leaf sizes and a lessened number of leaves . Phosphorus deficiency may also create an imbalance in the storage of carbohydrates . Photosynthesis, the main function of plant cells that produces energy from sunlight and water, usually remains at a normal rate under a phosphorus - deficient state . However phosphorus usage in functions within the cell usually slow . This imbalance of rates in phosphorus deficient plants leads to the buildup of excess carbohydrate within the plant . This carbohydrate buildup often can be observed by the darkening of leaves . In some plants the leaf pigment change as a result of this process can turn leaves a dark purplish color . </P> <P> Detecting phosphorus deficiency can take multiple forms . A preliminary detection method is a visual inspection of plants . Darker green leaves and purplish or red pigment can indicate a deficiency in phosphorus . This method however can be an unclear diagnosis because other plant environment factors can result in similar discoloration symptoms . In commercial or well monitored settings for plants, phosphorus deficiency is diagnosed by scientific testing . Additionally, discoloration in plant leaves only occurs under fairly severe phosphorus deficiency so it is beneficial to planters and farmers to scientifically check phosphorus levels before discoloration occurs . The most prominent method of checking phosphorus levels is by soil testing . The major soil testing methods are Bray 1 - P, Mehlich 3, and Olsen methods . Each of these methods are viable but each method has tendencies to be more accurate in known geographical areas . These tests use chemical solutions to extract phosphorus from the soil . The extract must then be analyzed to determine the concentration of the phosphorus . Colorimetry is used to determine this concentration . With the addition of the phosphorus extract into a colorimeter, there is visual color change of the solution and the degree to this color change is an indicator of phosphorus concentration . To apply this testing method on phosphorus deficiency, the measured phosphorus concentration must be compared to known values . Most plants have established and thoroughly tested optimal soil conditions . If the concentration of phosphorus measured from the colorimeter test is significantly lower than the plant's optimal soil levels, then it is likely the plant is phosphorus deficient . The soil testing with colorimetric analysis, while widely used, can be subject to diagnostic problems as a result of interference from other present compounds and elements . Additional phosphorus detection methods such as spectral radiance and inductively coupled plasma spectrometry (ICP) are also implemented with the goal of improving reading accuracy . According to the World Congress of Soil Scientists, the advantages of these light - based measurement methods are their quickness of evaluation, simultaneous measurements of plant nutrients, and their non-destructive testing nature . Although these methods have experimental based evidence, unanimous approval of the methods has not yet been achieved . </P>

What are the general symptoms of phosphorus deficiency
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