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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
    Factors affecting the agronomic effectiveness of phosphate rock for direct application (1995)
    Springer
    Nutrient cycling in agroecosystems 41 (1995), S. 227-234 
    Details
    ISSN: 1573-0867
    Keywords: acid soils ; agronomic effectiveness ; 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 soil fertility for sustainable crop production in large areas of developing countries. In recent years, phosphate rock (PR) for direct application has been tested in tropical acid soils as a potential alternative to conventional water-soluble P fertilizers like single superphosphate (SSP) and triple superphosphate (TSP). Some developing countries have PR deposits which, if used to supplement other imported P fertilizers, would allow a saving of much needed foreign exchange. Solubility of P fertilizers is not the only criterion in selection of the most suitable P fertilizer. This paper discusses the results of experiments to compare the relative agronomic effectiveness (RAE) of various PR sources with respect to SSP or TSP as influenced by four important factors: PR sources, soil properties, management practices, and crop species. Under certain conditions, PRs can be agronomically effective.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00748312
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  • 3
    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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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Phosphorus availability from partial acidulation of two phosphate rocks (1980)
    Springer
    Nutrient cycling in agroecosystems 1 (1980), S. 37-49 
    Details
    ISSN: 1573-0867
    Keywords: phosphate rock ; degrees of acidulation ; phosphorus availability ; granule size ; water-soluble P ; citrate-soluble P ; agronomic effectiveness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Two phosphate rocks, one from Pesca (Colombia) and the other from Togo, were acidulated to various degrees with H2SO4 and H3PO4 for evaluation in varying granule size ranges. Products acidulated with H2SO4 were also prepared using different drying temperatures. Phosphorus availability was measured by dry-matter yield and P uptake in greenhouse experiments with maize. It was observed that partial acidulation with H2SO4 was effective in increasing the water-soluble P level of phosphate rock when the drying temperature of the product was not excessive. Crop response and P uptake were both highly correlated to the water solubility of the product. The relative agronomic effectiveness (RAE) of Togo rock increased from 3% when unacidulated to 33%, 47%, and 52% when 20%, 30%, and 40%, respectively, of the H2SO4 required to make SSP was added. Similar results were obtained with Pesca rock. No consistent effect due to granule size was observed. Twenty percent acidulation of Pesca rock with H3PO4 was 53–76% as effective as TSP with a single crop and 79–90% as effective over three cropping periods, showing a potential for high residual value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01073563
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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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