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Handbook of Soils for Landscape Architects$
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Robert F. Keefer

Print publication date: 1999

Print ISBN-13: 9780195121025

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195121025.001.0001

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Macronutrients—Phosphorus and Potassium

Macronutrients—Phosphorus and Potassium

(p.131) 12 Macronutrients—Phosphorus and Potassium
Handbook of Soils for Landscape Architects

Robert F. Keefer

Oxford University Press

Plants have a P concentration between 0.03 and 0.70%, but the usual amount is between 0.1 and 0.4%. Phosphorus is found in every living cell of a plant and is involved in genetic transfer and energy relationships. The actively growing parts, that is, stem tips, new leaves, and new roots, need much P. Seeds, especially at maturity, also have a rich supply of P acting as reserve food. Phosphorus is used in plants for (a) root development—especially the lateral and fibrous roots; (b) cell division—energy for metabolism; (c) reproduction—flowering, fruiting, seed formation all controlled by nucleic acids; (d) maturation—counteracts the ill effects of excessive N fertilization; arid (e) disease resistance— especially important in root rots of seedlings. Plant P is a major constituent of chromosomes present as DNA (deoxyribonucleic acid) used in reproduction and RNA (ribonucleic acid) used in growth processes. Plant P is also a constituent of adenosine triphosphate (ATP) that stores energy for plant use, along with many other phosphate compounds, such as phytin (inositol hexaphosphate) stored in seeds, phospholipids in the chloroplasts, and complexes of sugars, sugar amines, aldehydes, amides, and acids—all involved in plant metabolism. Deficiency of P is not striking or characteristic and is difficult to diagnose. The older leaves may be dark bluish-green, bronze, or purple. The stalks are thin, leaves small, limited lateral growth, delayed maturity, and defoliate prematurely. Probably the most obvious symptom would be the purple coloration, but this is exhibited by only a limited number of plants. The best way to determine if a plant is deficient in P would be to conduct a plant tissue test. If the P level is lower than 0.2% P, then P probably is deficient and the soil in which the plant is growing would benefit from P fertilization. . . . Phosphorus Toxicity? . . . Phosphorus toxicity has not been observed in the field and has only been evident in greenhouse culture solutions when P was present at extremely high concentrations.

Keywords:   biotite, chlorophyll, feldspars, manures, peat, sawdust

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