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  • 1
    Electronic Resource
    Electronic Resource
    Modified techniques for preparing paper strips for the new Pi soil test for phosphorus (1989)
    Springer
    Nutrient cycling in agroecosystems 19 (1989), S. 85-91 
    Details
    ISSN: 1573-0867
    Keywords: Pi soil test ; iron and aluminum oxides-impregnated paper ; vapor technique ; soil test correlation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The Pi soil test, a new approach to measure plant-available P, uses strips of filter paper impregnated with iron oxide as a collector for P in the soil suspension. A modified method for impregnating the paper strips with iron oxide was developed by exposing the FeCl3-treated paper to ammonia vapor instead of immersing it in NH4OH solution. The paper strips prepared by the vapor technique had a more uniform deposit of iron oxide, and the P extracted from four soils ranging in pH from 4.5 to 8.2 and fertilized with two P sources and three rates correlated significantly with dry-matter yield (r = 0.751) of maize. The vapor technique was effective in preparing strips impregnated with both Fe and Al oxides. The ratio of Fe and Al on the strips was about the same as that in the solutions in which the papers were immersed. Strips containing iron oxide alone extracted more P than did strips containing both Fe and Al oxides. The dry-matter yield and P uptake of maize correlated significantly with P extracted by the strips impregnated with Fe, Al, or (Fe + Al) oxides. Phosphorus extracted by the paper impregnated with Fe oxide, and a mixture of Fe and Al oxide in the ratio of 2:1 correlated best with dry-matter yield (r = 0.751 and r = 0.736) and P uptake (r = 0.776 and r = 0.777).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01054679
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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
    Soil testing for available phosphorus in soils where phosphate rock-based fertilizers are used (1995)
    Springer
    Nutrient cycling in agroecosystems 41 (1995), S. 179-187 
    Details
    ISSN: 1573-0867
    Keywords: P i test ; phosphate rock-based fertilizers ; soil P test
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Traditional soil tests for phosphorus (P) were developed to arrive at fertilizer recommendations when water-soluble P fertilizers have been used. When slowly water-soluble fertilizers such as phosphate rock (PR) have been used, soil tests using acidic extractants overestimate bioavailability of P, whereas alkaline extractants underestimate it. Therefore, separate calibration curves are needed for soluble and PR-based fertilizers. There are two soil tests that show promise as suitable tests in soils fertilized with soluble as well as PR-based fertilizers. These are the iron oxide impregnated paper (P i ) test and the ion exchange resin paper test. In both cases, the strips act as a sink for P mobilized in a soil solution, and P measured depends only on the concentration of P mobilized in the solution and not on the source of P or properties of the soil. Both tests somewhat simulate the sorption of P by plant roots without disturbing the chemical equilibrium, unlike other tests that extract P by the destructive dissolution of specific soil P compounds. In both cases, P measured from soils fertilized with PR-based fertilizers has shown very good correlation with plant response. Field calibration with crops under different pedological and agroecological regimes is needed for using these soil tests in developing fertilizer recommendations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00748307
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  • 4
    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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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    Effect of phosphate rock sources on biological nitrogen fixation by soybean (1993)
    Springer
    Nutrient cycling in agroecosystems 34 (1993), S. 153-159 
    Details
    ISSN: 1573-0867
    Keywords: Available phosphorus ; biological nitrogen fixation ; phosphate rock (PR) ; soybean
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Very little information is available concerning the effect of phosphate rock (PR) sources on biological nitrogen fixation (BNF) in legume crops. In a greenhouse study, the15N isotopic dilution technique was used to compare the effectiveness of three sources of PR (Hahotoe rock, Togo; Tilemsi rock, Mali; and Sechura rock, Peru) with that of triple superphosphate (TSP) in increasing soybean seed yield and the amounts of N fixed by the soybean crop. The acid Hartsells slit loam was limed to pH 5.2 and incubated with 8.5 mg N kg−1 as K15NO3 and sucrose for 2 months prior to planting. Then fertilizer P was incorporated into the soil at 12.5, 25, 50, and 100 mg P kg−1 rates. The relative agronomic effectiveness (RAE) of the three PRs with respect to TSP (RAE = 100%) in terms of increasing seed yield was Hahotoe rock = 6.0%, Tilemsi rock = 45.9%, and Sechura rock = 75.2%; this trend followed the same trend as PR reactivity, i.e., Sechura rock 〉 Tilemsi rock 〉 Hahotoe rock. BNF was affected significantly by all the P treatments. Of the total N derived from the three N sources (atmosphere, Ndfa; fertilizer K15NO3, Ndff; and soil, Ndfs), Ndfa was highest with TSP and lowest with Hahotoe rock, whereas the reverse was found with Ndfs. Among various plant parts, more Ndfa was translocated and stored in seeds than in stems + leaves and roots. The RAE values of the three PRs with respect to TSP (RAE = 100%) in terms of influencing the amount of BNF were Hahotoe rock = 3.0%, Tilemsi rock = 43.4%, and Sechura rock = 71.2%. A linear relationship was found between the amount of BNF by the whole soybean plant and the soybean seed yield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00750110
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  • 7
    Electronic Resource
    Electronic Resource
    Evaluation of soil phosphate status where phosphate rock based fertilizers have been used (1993)
    Springer
    Nutrient cycling in agroecosystems 35 (1993), S. 67-82 
    Details
    ISSN: 1573-0867
    Keywords: Phosphate rocks ; soil P tests ; soil test calibrations ; iron-oxide impregnated paper test ; mixed anion exchange/cation exchange membranes test
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Soil phosphorus (P) tests have usually been calibrated using regression relationships between test values and crop yields for soils with a history of soluble P fertilizer use. However, the regression relationships have frequently been found to be different where phosphate rock (PR) based fertilizers have been used. Consequently, the traditional soil P tests often give incorrect estimates of soil P status of PR fertilized soils where calibrations were derived using soils treated with soluble P fertilizers. Alkaline soil tests (e.g., Olsen, Colwell) usually underestimate, while acid tests (e.g., Truog, Bray 2) usually overestimate, the soil P status of PR fertilized soils where normal calibrations are used. Several ways of overcoming this problem are discussed. Separate calibrations can be used for soluble and PR based fertilizers. In practice, this could involve mathematical modification of test values obtained with PR fertilized soils to enable use of the normal calibrations. Soil and fertilizer P models are available which use fertilizer history to derive current fertilizer recommendations and/or predict consequences of different fertilizer strategies. These could be extended to include functions describing the dissolution of PR in soil. This requires more detailed information on PR dissolution rates in different soils. Two soil tests for use with both soluble P and PR fertilized soils have recently been developed. They are the iron-oxide impregnated paper and the mixed anion exchange membrane/cation exchange membrane tests. While more evaluation is required in field situations, evidence to date indicates that both tests show promise.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00750221
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  • 8
    Electronic Resource
    Electronic Resource
    Iron oxide-impregnated filter paper (Pi test): II. A review of its application (1996)
    Springer
    Nutrient cycling in agroecosystems 47 (1996), S. 7-18 
    Details
    ISSN: 1573-0867
    Keywords: FeO paper ; iron oxide impregnated filter paper (Pi test) ; laboratory evaluation ; P in aquatic environment ; phosphate rock based fertilizers ; soil test correlation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The iron oxide impregnated filter paper test (Pi test) is a recently developed soil test for phosphorus (P) in which the FeO paper acts as an infinite sink for P mobilized in a soil solution. Several papers have been published evaluating the effectiveness of the test for predicting plant availability of P under different soil conditions. The use of FeO paper to predict algal availability of P in water bodies and runoffs has also been studied. The purpose of this paper is to review studies on the use of the Pi test to evaluate plant availability of P in soils, and predict availability of P to algae in an aquatic environment. Phosphorus extracted by the FeO paper is primarily physically bound extractable (resin P) and correlates significantly with Bray I and Mehlich P in acid soils and Olsen P in calcareous soils. Dry-matter yield and P uptake by maize (Zea mays L), kidney beans (Phaseolus vulgaris L), and upland rice (Oryza sativa L) grown in acidic soils correlated well with Pi-P. Likewise, in calcareous soils, Pi-P was as good as Olsen-P in predicting crop response. Field trials have shown that the Pi test is a good predictor of plant yield in soils with wide ranging properties. Compared to the standard method to measure bioavailable P to algae in waters and agricultural runoffs involving lengthy algal essays culturing selenastrum capricornutum with sediment samples, the Pi method is a faster and easier method to estimate P that may be potentially available for uptake by algae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01985714
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  • 9
    Electronic Resource
    Electronic Resource
    Sorption of phosphorus by the iron oxide-impregnated filter paper (Pi soil test) embedded in soils (1990)
    Springer
    Plant and soil 126 (1990), S. 287-294 
    Details
    ISSN: 1573-5036
    Keywords: extraction by embedding strips ; in situ evaluation ; iron oxide paper (Pi) strips ; moisture effect on P extracted ; Pi soil P test
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Incubation experiments were carried out to evaluate the feasibility of extracting phosphorus from soil by embedding iron oxide-impregnanted filter paper strips (Pi strips) in soils having a wide range in pH, texture, and extractable-P contents. Under flooded conditions, the amount of P extracted by the Pi strips increased with the period of submergence and embedding time of the Pi strips. Under unsaturated conditions, the Pi strips were found to extract P from soils over a wide range in moisture conditions; however, keeping the soil at moisture level between saturation and field capacity was found to result in maximal sorption of P by the strips. An embedding time of 16 h was found to be adequate. Phosphorus extracted by embedding Pi strips in soil columns for 16 h at field capacity moisture level correlated significantly with P extracted by shaking the soil with 0.01 M CaCl2 solution and a Pi strip for 16 h in the laboratory (r=0.94**). The P extracted by embedding Pi strips correlated best with Bray 1 P in acid soils (r=0.97**) and with Olsen P in alkaline and calcareous soils (r=0.96**). The results of the studies demonstrate the feasibility of developing a nondestructive method of monitoring changes in plant-available P in situ under field conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00012831
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  • 10
    Electronic Resource
    Electronic Resource
    Phosphorus availability to maize from partially acidulated phosphate rocks and phosphate rocks compacted with triple superphosphate (1990)
    Springer
    Plant and soil 127 (1990), S. 123-128 
    Details
    ISSN: 1573-5036
    Keywords: agronomic effectiveness ; compaction ; iron and aluminum oxide content ; partially acidulated phosphate rocks ; phosphate rocks
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Two phosphate rocks (PR), moderately reactive Hila PR from Colombia and slightly reactive Capinota PR from Bolivia, were compacted with triple superphosphate (TSP) such that 50% of total P in the mixture was in water-soluble form. The effectiveness of these materials as phosphorus sources was compared with that of partially acidulated phosphate rocks (PAPR) at 50% acidulation with sulfuric acid and TSP in Hartsells silt loam (pH 4.5) with maize as the test crop. Huila PAPR and Huila PR compacted with TSP were as effective as TSP as phosphorus sources. Huila PR was only half as effective. The slightly reactive Capinota PR with 8.8% Al2O3 + Fe2O3 content was not suited for direct application, and Capinota PAPR was only half as effective as TSP. Capinota PR compacted with TSP, however, was as effective as TSP. PR compacted with TSP, urea, and KCl was no more effective as phosphorus source than PR compacted with TSP alone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00010844
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