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Phosphorous Deficiency

Symptoms (Biological Implications):

In plants, Phosphorous (P) is considered second to nitrogen as the most essential nutrient to ensure health and function. Phosphorous 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 photophosphoroylation for example the creation of stored energy in plants is a result of a chemical reaction including phosphorous. Phosphorous 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 phosphorous. The stunted growth induced by phosphorous 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 phosphorous deficient state. However phosphorous 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.

Detection:

Detecting phosphorous 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 phosphorous. 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, phosphorous 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 phosphorous levels before discoloration occurs. The most prominent method of checking phosphorous 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 phosphorous. Colorimetry is used to to determine this concentration. With the addition of the phosphorous extract into a colorimeter, there is visual color change of the solution and the degree to this color change is an indicator of phosphorous concentration. To apply this testing method on phosphorous deficiency, the measured phosphorous concentration must be compared to known values. Most plants have established and thoroughly tested optimal soil conditions. If the concentration of phosphorous 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 phosphorous 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..

Treatment:

Correction and prevention of phosphorous deficiency typically involves increasing the levels of available phosphorous into the soil. Planters introduce more phosphorous into the soil with bone meal, rock phosphate,manure, and phosphate-fertilizers. The introduction of these compounds into the soil however does not ensure the alleviation of phosphorous deficiency. There must be phosphorous in the soil, but the phosphorous must also be absorbed by the plant. The uptake of phosphorous is limited by the chemical form in which the phosphorous is available in the soil. A large percentage of phosphorous in soil is present in chemical compounds that plants are incapable of absorbing. Phosphorous must be present in soil in specific chemical arrangements to be usable as plant nutrients. Facilitation of usable phosphorous in soil can be optimized by maintaining soil within a specified pH range. Soil acidity, measured on the pH scale, partially dictates what chemical arrangements that phosphorous forms. Between 6 and 7 pH, phosphorous makes the least number of bonds which render the nutrient unusable to plants. At this range of acidity the likeliness of phosphorous uptake is increased and the likeliness of phosphorus deficiency is decreased. Another component in the prevention and treatment of phosphorus is the plant’s disposition to absorb nutrients. Plant species and different plants within in the same species react differently to low levels of phosphorus in soil. Greater expansion of root systems generally correlate to greater nutrient uptake. Plants within a species that have larger roots are genetically advantaged and less prone to phosphorous deficiency. These plants can be cultivated and bred as a long term phosphorous deficiency prevention method. In conjunction to root size, other genetic root adaptations to low phosphorus conditions such as mycorrhizal symbioses have been found to increase nutrient intake. These biological adaptations to roots work to maintain the levels of vital nutrients. In larger commercial agriculture settings, variation of plants to adopt these desirable phosphorous intake adaptations may be a long-term phosphorous deficiency correction method.