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  • 1
    Electronic Resource
    Electronic Resource
    Isotope methods for assessing plant available phosphorus in acid tropical soils (2003)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 54 (2003), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Use of isotope methods to measure the availability of phosphorus (P) in soils that are well supplied with P is well established. We have evaluated such methods for acid tropical soils with very small P contents, which are less well studied. The isotopically exchangeable P in soil suspensions (E value) and that in plant growth experiments (L value) were measured in soils that had received varying amounts of P fertilizer in two field experiments in Colombia. We determined the E values over 4–5 weeks of equilibration allowing for the kinetics of isotope exchange. The decrease in radioactivity in the soil solution at a particular time, t, divided by that at the start (rt/R) was described by three parameters (r1/R, r∞/R, and a coefficient n) derived from the time course of isotopic exchange over 100 minutes. Values of Et were calculated either from measured values of rt/R or those extrapolated until 12 weeks. Agrostis capillaris was grown on the same soils labelled with carrier-free 33P-orthophosphate ions to obtain L values. Agreement between E values derived from measured and extrapolated values of rt/R was satisfactory, but errors in n and r∞/R limited the precision with which we could estimate E values. For most soils, the P concentrations in the soil solution were greater than the detection limit of the malachite green method (0.9 µg l−1) but smaller than its quantification limit (3.6 µg l−1). In the soils with the least available P, the P content of the seed limited the determination of the L value. The E values were strongly correlated, but not identical, with the L values measured for the same time of isotopic exchange. We conclude that these approaches are not precise enough to detect in these soils the ability of a plant to access slowly exchangeable forms of P or to quantify the mineralization of organic P. However, these isotope techniques can be used to estimate the total fraction of added fertilizer P that remains available to the plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.2003.00542.x
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  • 2
    Electronic Resource
    Electronic Resource
    Nitrogen-15 and sulfur-35 balances for fertilizers applied to transplanted rainfed lowland rice (1991)
    Springer
    Nutrient cycling in agroecosystems 28 (1991), S. 55-65 
    Details
    ISSN: 1573-0867
    Keywords: Nitrogen balance ; sulfur balance ; Oryza sativa L. ; urea ; elemental S ; runoff ; leaching ; Thailand
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A field experiment was conducted on a poorly-drained Aeric Paleaquult in northeastern Thailand to determine the effect of N and S fertilizers on yield of rainfed lowland rice (Oryza sativa L.) and to determine the fate of applied15N- and35S-labeled fertilizers. Rice yield and N uptake increased with applied N but not with applied S in either sulfate or elemental S (ES) form. Rice yield was statistically greater for deep placement of urea as urea supergranules (USG) than for all other N fertilizer treatments that included prilled urea (PU), urea amended with a urease inhibitor (phenyl phosphorodiamidate), and ammonium phosphate sulfate (16% N, 8.6% P). The applied15N-labeled urea (37 kg N ha−1) not recovered in the soil/plant system at crop maturity was 85% for basal incorporation, 53% for broadcast at 12 days after transplanting (DT), 27% for broadcast at 5–7 days before panicle initiation (DBPI), and 49% for broadcast at panicle initiation (PI). The basal incorporated S (30 kg ha−1) not recovered in the soil/plant system at crop maturity was 37% for sulfate applied as single superphosphate (SSP) and 34% for ES applied as granulated triple superphosphate fortified with S (S/GTSP). Some basal incorporated15N and35S and some broadcast15N at PI was lost by runoff. Heavy rainfall at 3–4 days after basal N incorporation and at 1 day after PI resulted in water flow from rice fields at higher elevation and total inundation of the 0.15-m-high15N and35S microplot borders. Unrecovered15N was only 14% for 75 kg urea-N ha−1 deep placed as USG at transplanting. This low N loss from USG indicated that leaching was not a major N loss mechanism and that deep placement was relatively effective in preventing runoff loss. In order to assess the susceptibility of fertilizer-S to runoff loss, a subsequent field experiment was conducted to monitor35S activity in floodwater for 42 days after basal incorporation of SSP and S/GTSP. Maximum35S recoveries in the floodwater were 19% for SSP after 7 days and 7% for S/GTSP after 1 day. Recovery of35S in floodwater after 14 days was 12% for SSP and 3% for S/GTSP. This research suggests that on poorly drained soils with a low sorption capacity, a sizeable fraction of the fertilizer S and N remains in the floodwater following application. Runoff could then be an important mechanism of nutrient loss in areas with high probability for inundation following intense rainfall.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01048856
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  • 3
    Electronic Resource
    Electronic Resource
    Long-term greenhouse evaluation of partially acidulated phosphate rock fertilizers (1987)
    Springer
    Nutrient cycling in agroecosystems 13 (1987), S. 31-44 
    Details
    ISSN: 1573-0867
    Keywords: Partially acidulated phosphate rock ; P uptake ; lucerne ; phosphoric acid ; sulfuric acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Twelve granular partially acidulated phosphate rock (PAPR) fertilizers were compared with unacidulated phosphate rocks (PR) and superphosphate at five rates of total P in the presence and absence of supplementary sulfate and plant residue recycling treatments in a long-term green-house experiment with lucerne (Medicago sativa L., cv. CUF101). The PAPRs were prepared from two PRs (Christmas Is. A grade and Duchess, Queensland) and acidulated at two rates (25% and 50% on an H2SO4 to single superphosphate basis) with either H2SO4 or H3PO4. Six harvests (each bulked from three cuttings) were collected over a 2-year period. It was generally found that lucerne response to PAPRs depended closely on their water-soluble plus citrate-soluble P contents which increased with increased degree of acidulation. The H3PO4 tended to yield more soluble P on acidulation of PR than H2SO4 and acidulation of Christmas Is. PR yielded more soluble P than did acidulation of Duchess PR. There was little evidence for enhanced availability of P due to action of the triple point solution in hydrolyzing granules on residual PR in those granules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01049800
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  • 4
    Electronic Resource
    Electronic Resource
    Long-term greenhouse evaluation of partially acidulated phosphate rock fertilizers (1987)
    Springer
    Nutrient cycling in agroecosystems 13 (1987), S. 45-54 
    Details
    ISSN: 1573-0867
    Keywords: Biosuper ; elemental sulfur ; Lucerne ; partially acidulated phosphate rock ; P uptake ; S uptake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The effect of cogranulation with elemental sulfur (S) on the availability of phosphorus (P) from partially acidulated phosphate rock (PAPR) prepared from Christmas Island or Duchess phosphate rock (PR) was studied as part of a larger experiment examining factors affecting the agronomic effectiveness of PAPR sources. PAPRs cogranulated with (10% w/w) or without elemental S were compared at four rates of P (excluding controls) in the presence and absence of supplementary sulfate (SO4) from gypsum on a P-deficient pasture soil with no previous history of elemental S applications. Lucerne (Medicago sativa L., cv. CUF101) yields and P and S uptake were determined in six bulked harvests collected over a 2-year period. Large responses to P rates were recorded but only minor and inconsistent responses to SO4-S occurred during the experiment. In contrast, elemental S in PAPR granules resulted in greater lucerne yields and P and S uptake by lucerne tops; these effects, which did not appear until 6 months after application, were attributed to the acidulation of residual PR in PAPR granules by action of H2SO4 produced by the oxidation of elemental S. These effects increased with increasing rates of PAPR applied and were greater for the Christmas Island PAPRs and at the 50% acidulation rate. This was attributed to the development of a more prolific root system at the higher P rates and the higher levels of soluble P provided by 50% PAPRs which enabled plants to more fully exploit P solubilized from S-granulated PAPR products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01049801
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  • 5
    Electronic Resource
    Electronic Resource
    Phosphorus acquisition and cycling in crop and pasture systems in low fertility tropical soils (1997)
    Springer
    Plant and soil 196 (1997), S. 289-294 
    Details
    ISSN: 1573-5036
    Keywords: litter decomposition ; Oxisols ; phosphorus fractionation ; root distribution ; root length ; savannas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Soil-plant processes which enhance P acquisition and cycling in low-P Oxisols were investigated in a crop rotations and ley pasture systems experiment on the Colombian eastern plains. Comparison of rooting patterns indicated that, despite low available P at depth, there are important differences in root size and distribution among native savanna, introduced forage and crop species which affect their ability to acquire P from these soils. Differences in crop/forage residue decomposition and P release rates suggest that managing the interaction of residue with soil may help slow P fixation reactions. Despite these differences, soil P fractionation measurements indicate that applied P moves preferentially into labile inorganic P pools, and then only slowly via biomass production and microbes into organic P pools under both pastures and crop rotations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004226708485
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  • 6
    Electronic Resource
    Electronic Resource
    Fate and efficiency of sulfur fertilizer applied to food crops in West Africa (1991)
    Springer
    Nutrient cycling in agroecosystems 29 (1991), S. 35-44 
    Details
    ISSN: 1573-0867
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Increased food production in West Africa must be linked to increased fertilizer use. However, the increased use of the high analysis sulfur-free materials currently available in the region will lead to increased incidence of sulfur (S) deficiency. In order to determine the S fertilizer requirements of major cereal crops, and compare the fate and efficiency of alternative S sources, experiments were conducted at six sites in semiarid and subhumid West Africa from 1985–1988. Sulfur fertilizers increased grain yields from 10% to 65% (200 to 2000 kg/ha) in 14 out of 20 site-years (at 5 out of 6 sites). Maximum response was generally obtained with only 5–10 kg S/ha. Both powdered (−60 mesh S0) and granular (S0-fortified TSP) elemental S sources were usually as effective as sulfate sources (gypsum or SSP). The residual effectiveness of S0, however, was superior to that of sulfate at most sites. Sulfur-35 balances demonstrated substantial leaching and low crop recovery (5%–10% of S applied) of fertilizer S. Up to 50% of the applied S was lost from sulfate sources, whereas 〈20% was lost from S0 sources. Although S0 sources were at least as effective as sulfate sources, the low S rates required suggest that S deficiencies in the region can be corrected at relatively low cost with sulfate-containing fertilizers, provided they can be supplied at more appropriate nutrient ratios.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01048987
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  • 7
    Electronic Resource
    Electronic Resource
    Long-term greenhouse evaluation of partially acidulated phosphate rock fertilizers (1991)
    Springer
    Nutrient cycling in agroecosystems 29 (1991), S. 295-307 
    Details
    ISSN: 1573-0867
    Keywords: Partially acidulated phosphate rock ; P uptake ; relative agronomic effectiveness ; substitution value ; superphosphate ; yield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The agronomic effectiveness (yield and P uptake) of twelve granular, partially acidulated phosphate rock fertilizers (PAPR) and two finely ground, unacidulated phosphate rocks (PR) were compared to that of a single superphosphate in a long-term greenhouse experiment with lucerne (Medicago sativa L., cv. CUF101), grown in a low P sorbing, moderately acid, sandy loam soil of moderate P status (Paleustaf). The PAPRs were prepared from two unreactive PRs (Christmas Is. ‘A’ grade and Duchess rock from Queensland) and acidulated at two rates (25% and 50% on a H2SO4 to single superphosphate basis) with either H2SO4 or H3PO4. Additional products included H2SO4 PAPRs cogranulated with elemental S (10% w/w). Superphosphate was consistently superior to all PRs and PAPRs in agronomic effectiveness throughout this two-year study. The most effective of the PAPRs were those that were 50% acidulated with H2SO4 and cogranulated with elemental S; this type of fertilizer from both rocks was approximately 2/3 as effective as superphosphate when relative agronomic effectiveness indices (RAE) were calculated from cumulative yields. The increase in agronomic effectiveness relative to superphosphate (RAE value) by the partial acidulation of the PR could be attributed to its effect of increasing the P solubility in the PAPR. A curvilinear relationship existed between the RAE values of PRs and PAPRs, measured from cumulative yield or P uptake data, and the percentage of the total P in each fertilizer that was in a soluble (water + citrate soluble) form. Cogranulation with elemental S (10% w/w) significantly displaced this relationship upwards by increasing the RAE of H2SO4 PAPRs by more than 50%. The maximum cumulative recovery of applied P by lucerne tops after five bulked harvests (fifteen consecutive harvests) was 61.5%, which occurred at the low application rate of superphosphate. The decline in the substitution value of PRs for superphosphate, that occurred with increasing P rates tended to be offset both by increasing the level of acidulation and by cogranulating the PAPR with elemental S.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01052399
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  • 8
    Electronic Resource
    Electronic Resource
    Elemental sulfur fertilizers and their use on crops and pastures (1993)
    Springer
    Nutrient cycling in agroecosystems 35 (1993), S. 127-149 
    Details
    ISSN: 1573-0867
    Keywords: Bentonite ; cube root model ; elemental sulphur fertilizers ; rate of oxidation ; sulphur coated urea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract This paper reviews the use of elemental sulfur (S°) as a fertiliser and its efficacy in different pastoral and cropping situations. The effect of S° particle size on rate of oxidation is critical to the effectiveness of S° fertilisers. Emphasis is therefore centred on the issue of how particle size of S° affects the rate of oxidation in different environments and cropping systems, and the size of S° in different S° fertiliser products. Rate constants of S° oxidation offer the opportunity to generalise particle size relationships needed in S° fertilisers for different crops in different environments, or alternatively, to calculate the agronomic effectiveness of different S° fertilisers available on the market. Conversely they offer a technique to set specifications as to S° particle size requirements, which together with dispersion rate specifications provide the basis for the design of S° fertilisers for specified crops and environments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00750226
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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    A combinatorial algorithm for calculating ligand binding (1984)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 5 (1984), S. 24-34 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We consider the problem of predicting the mode of binding of a small molecule to a receptor site on a protein. One plausible approach, given a rigid molecule and its geometry, is to search directly for the orientation in space that maximizes the degree of contact. The computation time required for such a naive procedure is proportional to n3m3, where n is the number of points in the site where binding can occur, and m is the number of atoms in the ligand. We give an alternative, combinatorial approach, in which only “contact-no-contact” criteria are considered. We relate this problem to the well-known combinatorial problem of finding cliques in a graph and show that we can use a solution to the clique problem not only to solve our original problem, but also the problem of avoiding energetically unfavorable matches. Our experience with this method indicates that the computation time required is proportional to nm2.8, with a lower constant of proportionality than that of the naive procedure.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540050105
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