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  • 1
    Electronic Resource
    Electronic Resource
    Solubility and agronomic effectiveness of partially acidulated phosphate rocks as influenced by their iron and aluminium oxide content (1989)
    Springer
    Nutrient cycling in agroecosystems 19 (1989), S. 93-98 
    Details
    ISSN: 1573-0867
    Keywords: phosphate rock ; partially acidulated phosphate rock ; iron and aluminium oxide content ; water and citrate solubility ; phosphorus availability ; agronomic effetiveness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Partially acidulated phosphate rock (PAPR) has been shown to be an effective source of P for plants grown on acid soils. Less information in available, however, regarding the effect of the phosphate rock (PR) source on the solubility and agronomic effectiveness of PAPR. The effect of Fe2O3 + Al2O3 content in PR on the quality of PAPR produced was investigated in this study. Nine sources of PR from Africa, Latin America, and the United States, representing a range of Fe2O3 + Al2O3 from 0.7% to 12.4%, were used. In a single-step process, the finely ground PRs were partially acidulated with H2SO4 at the 30% or 50% acidulation level and granulated (−3.35 + 1.18 mm or −6 + 14 mesh). It was found that the water-soluble P content in PAPR decreased with increasing Fe2O3 + Al2O content in the PR used. Apparently, the presence of Fe2O3 + Al2O3 resulted in a reversion of some of the water-soluble P to citrate-soluble P and sometimes even to citrate-insoluble P. A short-term (6 weeks) greenhouse study was conducted to evaluate crop response to PAPRs and single superphosphate (SSP); maize, the test crop, was grown on an acid soil (pH 4.5)—Hartsells silt loam (Typic Hapludults). The agronomic effectiveness of PAPRs with respect to SSP (in terms of dry-matter yield of maize) decreased with increasing Fe2O3 + Al2O3 content in PRs. Phosphorus uptake by maize from PAPRs was found to correlate well with water solubility but not with citrate solubility. The results obtained in this study show that the detrimental effect of Fe2O3 + Al2O3 content on the solubility and P availability of PAPR should be considered when selecting a PR for PAPR production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01054680
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  • 2
    Electronic Resource
    Electronic Resource
    Comparison of Olsen and Pi soil tests for evaluating phosphorus bioavailability in a calcareous soil treated with single superphosphate and partially acidulated phosphate rock (1991)
    Springer
    Nutrient cycling in agroecosystems 29 (1991), S. 153-158 
    Details
    ISSN: 1573-0867
    Keywords: Pi soil test ; Olsen test ; calcareous soils ; partially acidulated phosphate rock ; soil test correlation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The Pi test for phosphorus (P) is a new method in which strips of iron oxide impregnated filter paper are used as a sink to sorb and extract P from a soil solution. In a greenhouse experiment, the Olsen and Pi tests were compared for their effectiveness in evaluating P availability to maize on calcareous soils. Phosphate rock from Togo, partially acidulated with H2SO4 at 50% acidulation level (PAPR 50% H2SO4) and single superphosphate (SSP) were applied at different rates to a calcareous soil (Vernon Clay, pH 8.2, CaCO3 18.9%) which was preincubated with KH2PO4 to raise plant-available P to different levels. In soils treated with SSP, dry-matter yield of maize correlated equally well with Pi-P and with Olsen-P (r = 0.96***). P uptake correlated significantly with Pi-P (r = 0.94***) as well as Olsen-P (r = 0.97***). Likewise, in soils fertilized with PAPR, significant correlations were found between dry-matter yield and Pi-P (r = 0.97***) and between dry-matter yield and Olsen-P (r = 0.94***). When all the data were pooled, Pi-P and Olsen-P correlated equally well with both dry-matter weight (r = 0.97***) and P uptake (r = 0.94***). Phosphorus extracted by the Pi test correlated significantly with P extracted by the Olsen test (r = 0.99***).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01048954
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  • 3
    Electronic Resource
    Electronic Resource
    Agronomic evaluation of modified phosphate rock products (1995)
    Springer
    Nutrient cycling in agroecosystems 41 (1995), S. 197-209 
    Details
    ISSN: 1573-0867
    Keywords: agronomic effectiveness ; compacted phosphate rock with superphosphate ; partially acidulated phosphate rock
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Phosphorus (P) is critically needed to improve the soil fertility for crop production in large areas of developing countries. The high cost of conventional, water-soluble P fertilizers constrains their use by resource-poor farmers. Finely ground phosphate rock (PR) has been tested and used as a direct application fertilizer on tropical acid soils as a low-cost alternative where indigenous deposits of PR are located. However, direct application of PR with low reactivity or with inappropriate soil/crop combinations does not always give satisfactory results. Partial acidulation of PR (PAPR) or compaction with triple superphosphate (PR + TSP) or single superphosphate (PR + SSP) represent technologies that can be used to produce highly effective P fertilizers from those indigenous deposits. Numerous field trials conducted by IFDC in Asia, sub-Saharan Africa, and Latin America have demonstrated that PAPR at 40-50% acidulation with H2SO4 or at 20% with H3PO4 approaches the effectiveness of SSP or TSP in certain tropical soils and crops. This paper discusses how the agronomic effectiveness of PAPR is affected by mineralogical composition and reactivity of PR used and by soil properties and soil reactions. The paper also indicates that if a PR has high Fe2O3 + Al2O3 content, it may not be suitable for PAPR processing because of the reversion of water-soluble P to water-insoluble P during the PAPR manufacturing process. Under these conditions, compaction of PR with water-soluble P fertilizers (e.g. SSP, TSP) at P ratio of approximately 50:50 can be agronomically and economically attractive for utilizing the indigenous PRs in developing countries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00748309
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  • 4
    Electronic Resource
    Electronic Resource
    Agronomic evaluation of fertilizer products derived from Sukulu Hills phosphate rock (1995)
    Springer
    Nutrient cycling in agroecosystems 44 (1995), S. 113-122 
    Details
    ISSN: 1573-0867
    Keywords: Compacted phosphate rock ; partially acidulated phosphate rock ; phosphate rock ; relative effectiveness ; TSP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Partial acidulation of phosphate rock (PR) or compaction of PR with soluble P fertilizers can improve the usefulness of unreactive PR for use as P fertilizer. A greenhouse study was conducted to evaluate nonconventional phosphate fertilizers derived from a low reactive Sukulu Hills PR from Uganda. Raw PR (which contained 341.0 g kg−1 Fe2O3), beneficiated or concentrate PR, partially acidulated PR (PAPR) and PR compacted with triple superphosphate (TSP) were evaluated. Compacted materials had a P ratio of PR:TSP = 50:50. PAPR materials were made by 50% acidulation with H2SO4. TSP was used as a reference fertilizer. Fertilizers were applied to an acidic (pH = 5.4) Hiwassee loam (clayey, kaolinitic, thermic Rhodic Kanhapludults) at rates of 0, 50, 100, 200, 300 and 400 mg P kg−1 soil. Two successive corn (Zea mays L.) crops were grown for 6 weeks. Compacted concentrate PR + TSP and raw PR + TSP were 94.4 and 89.7% as effective as TSP, respectively, in increasing dry-matter yields for the first corn crop. PAPR from the concentrate was 54.8% as effective as TSP. Raw PR, concentrate PR and the PAPR from the raw PR were ineffective in increasing dry-matter yields. The same trends were obtained when P uptake was used to compare effectiveness. Ineffectiveness of the raw PR and its corresponding PAPR was attributed to a high Fe2O3 content in the raw PR. Bray I and Pi paper were found to be nearly equally suitable at estimating available P in the soils treated with responsive fertilizer materials. Mehlich 1 overestimated available P in soil treated with raw PR, concentrate PR or the PAPR from the raw PR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00750800
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  • 5
    Electronic Resource
    Electronic Resource
    Induced phosphorus fixation and the effectiveness of phosphate fertilizers derived from Sukulu Hills phosphate rock (1995)
    Springer
    Nutrient cycling in agroecosystems 44 (1995), S. 231-240 
    Details
    ISSN: 1573-0867
    Keywords: compacted phosphate rock ; partially acidulated phosphate rock ; P availability ; phosphate rock ; P fixation capacity ; relative effectiveness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A greenhouse study was conducted with two surface, acidic soils (a Hiwassee loam and a Marvyn loamy sand) to measure the effect of increasing P-fixation capacity, on the relative agronomic effectiveness (RAE) of phosphate fertilizers derived from Sukulu Hills phosphate rock (PR) from Uganda. Prior to fertilizer application, Fe-gel was added to increase P-fixation capacity from 4.4 to 14.3% for the Marvyn soil and from 37.0 to 61.5% for the Hiwassee soil. Phosphate materials included compacted Sukulu Hills concentrate PR + Triple superphosphate (CTSP) at a total P ratio of PR:TSP = 50:50; 50% partially acidulated PR (CPAPR) from Sukulu Hills concentrate PR made with H2SO4; and Sukulu Hills concentrate PR (PRC) made by magnetically removing iron oxide from raw PR ore. Triple superphosphate (TSP) was used as a reference fertilizer. After adjusting soil pH to approximately 6, P sources were applied at rates of 0, 50, 150, and 300 mg total P kg−1 soil. Two successive crops of 5 week old corn seedlings (Zea mays L.) were grown. The results show that the RAE of the phosphate materials measured using dry-matter yield or P uptake generally decreased as P-fixation capacity was increased for both soils. CTSP was more effective in increasing dry-matter yield and P uptake than CPAPR. PRC alone was an ineffective P source. Soil chemical analysis showed that Bray 1 and Mehlich 1 extractants were ineffective on the high P-fixation capacity Fe-gel amended Hiwassee soil. Mehlich 1 was unsuitable for soils treated with PRC since it apparently solubilizes unreactive PR. When all of the soils and P sources were considered together, Pi paper was the most reliable test for estimating plant available P.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00750930
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  • 6
    Electronic Resource
    Electronic Resource
    Comparison of Bray I and Pi tests for evaluating plant-available phosphorus from soils treated with different partially acidulated phosphate rocks (1989)
    Springer
    Plant and soil 114 (1989), S. 211-216 
    Details
    ISSN: 1573-5036
    Keywords: Bray I soil P test ; partially acidulated phosphate rock ; phosphate rock ; Pi soil P test
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Phosphate rocks from seven locations in Africa and Latin America were partially acidulated with H2SO4 at 30% or 50% acidulation level and were applied to an acid silt loam. Dry-matter yield of and P uptake by maize grown on the soil were correlated with P measured by Bray I soil test and Pi soil test in which P is extracted by shaking a soil sample with 0.01M CaCl2 solution and a strip of iron hydroxide impregnated filter paper. There was a highly significant correlation between water-soluble P in the partially acidulated phosphate rocks (PAPR) and P measured by the Pi test (r=0.92**). The dry-matter yield correlated significantly with P measured by the Pi test (r=0.91**) as well as by the Bray test (r=0.73**). Phosphorus uptake correlated highly significantly with Pi−P (r=0.94**); correlation with Bray I−P was less significant (r=0.67*). Bray I solution extracted more P than Pi did, which resulted in an overestimation of plant-available P. Bray I therefore was less effective than the Pi soil test in evaluating P availability from different PAPRs applied to the soil.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02220800
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  • 7
    Electronic Resource
    Electronic Resource
    A discussion of the methods for comparing the relative effectiveness of phosphate fertilizers varying in solubility (1990)
    Springer
    Nutrient cycling in agroecosystems 24 (1990), S. 149-157 
    Details
    ISSN: 1573-0867
    Keywords: Phosphate rock ; SSP ; TSP ; partially acidulated phosphate rock ; relative effectiveness (RE) index ; substitution rate (SR)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Because various phosphate (P) fertilizers differ widely in their solubility, it is commonly observed that crop response to P fertilizers varies under the same soil and crop conditions. Furthermore, a major problem encountered in the methods for determining the relative effectiveness (RE) of water-insoluble P fertilizer (e.g., phosphate rock) with respect to water-soluble P fertilizers, e.g., single superphosphate (SSP) and triple superphosphate (TSP), is that their growth response curves are usually nonlinear and often do not share a common maximum yield. In this paper, we review and discuss the advantages and disadvantages of the three most commonly used methods for calculating the RE of phosphate rock with respect to TSP (or SSP). The three methods are vertical comparison, horizontal (substitution rate) comparison, and linear-response comparison.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01073583
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