الفهرس 
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Abstract
A series of laboratory experiments were carried out to study the effect of some integrated factors on solubility of phosphate rock(PR)P .To fulfill this aim three sparingly soluble sources were used namely: 1- PR from Abou Tartour, 2- PR from El-Sibaia Gharb, 3- Tricalcium phosphate (pure salt) Phosphate rocks were crushed to pass through a 1.18-mm sieve. One kg of each source was sieved to pass a set of sieves with the following diameters 500, 250, 212, 125, 75 and 45 µm (using Electric Sieve Shaker). Part of the PR from the >45-µm fraction was further ground manually for comparison with the other parts(ground) which contains granules of apatite-diameter 25nm identified samples were classified by the use of scanning electronic microscope as well as the diffraction of X-ray Total P content in the first source Abou Tartour ranged between 130.6 to 139.4 g / kg and second source El-Sibaia Gharb ranged between 72.40 to 88.80 g / kg and water Soluble between 0.2 to 0.6 g / kg, and extracted by Olsen between 10 to 17 g / kg. Those extracted by organic acids of the two sources of phosphate rock ranged between 39 to 44 citric acid; 0.25 to 41 for acetic acid; 0.27 to 49 of tartaric acid; 0.14 to 28 of oxalic acid and 0.32 to 52 for formic acid. Partial acidulation of the three sources was done at 0, 20,40, 60,80, 100%. There was an increase occurring in phosphorus with the smaller grain size and higher degree of acidulation in the three sources. Extraction by distilled water showed ranges from 1.10 to 38.90 for Abou Tartour and 1.10 to 25.70 for El-Sibaia Gharb and 4.40 to 78.50 g / kg for Tri calcium phosphate. Citric acid was higher with ranges of 41.30 to 49.60for Abou Tartour, 25.60 to 41.60 for El-Sibaia Gharb and 79.80 to 104.90 g P kg-1.It can be concluded that in practice the use of phosphate rock can be used directly in fertilization. Abbreviations and Expressions List of Abbreviations: 1-Ca : Calcium 2-CA: Citric acid 3-DAPR: Direct application of phosphate rock 4-FA: Formic acid 5-FAO/IAEA: FAO, Food and Agriculture Organization of the United Nations IAEA, International Atomic Agency 6-Fe: Iron 7-g: Gram 8-kg: Kilogram 9- IFDC: formerly International Fertilizer Development Center, now International Centre for Soil Fertility and Agricultural Development. 10- NAC: Neutral ammonium citrate 11- P: Phosphorus 12-P fertilizer: Phosphatic fertilizer 13-PR: Phosphate rock 14-PRs: Phosphate rocks, PR materials, PR products 15-PSM: Phosphate solubilizing micro-organisms 16-P2O 5: Phosphorus pentoxide 17-PAPR: Partially acidulated phosphate rock 18- RAE: Relative agronomic effectiveness 19-RPR: Reactive phosphate rock 20- SEM: Scanning electron microscopy 21-Si: Silicon 22-SSP: Single superphosphate 23- TSP: Triple superphosphate 24- WSP: Water-soluble phosphate 25-XRD: X-Ray diffraction Expressions used in PR solubility: a- Reactivity: Hatfield (1964) and IFDC (1986) indicated that reactivity of PR refers to the ease of converting P in PR to a form available to plants mainly due to chemical processes or reaction in soil. b- Absolute solubility index(ASI): Lehr and McClellan proposed in 1972 the absolute solubility index (ASI) as the proportion of soluble P to P in apatite. ASI = [(%soluble P) / (% P in apatite)] Χ 100 The percent-soluble P depends on the particular test selected . The major disadvantage of the ASI method is that the crystallographic studies are expensive, and they require skilled operations and specialized laboratories with sophisticated equipment for X-ray analysis. Therefore, they are used in basic studies to characterize main phosphate deposits. The expression of solubility can be an issue. In studies with several PR sources with large variations in total P content, Chien (1993) proposed that the solubility of the PRs is expressed more appropriately as a percentage of the rock rather than as a percentage of the total P. This was because unscrupulous practice, such as mixing sand with PR, can inflate the extractability, thus leading to incorrect conclusions of reactivity of PRs. c- Relative Agronomic Effectiveness(RAE): Hammond and Leon, (1983) determined RAE as a percentage of the ratio of the response to the tested fertilizer (Treatment – Control) to the response to the standard fertilizer, when both are applied at the same rate. This relation is expressed by the following equation: RAE = [(test P fertilizer - control)/ (standard P fertilizer - control)] × 100.