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  • 1
    Electronic Resource
    Electronic Resource
    Influence of pH, time and rate of application on phosphate rock dissolution and availability to pastures (1991)
    Springer
    Nutrient cycling in agroecosystems 28 (1991), S. 85-93 
    Details
    ISSN: 1573-0867
    Keywords: Phosphate rock ; soil pH ; andepts ; white clover ; ryegrass ; soil phosphorus ; monocalcium phosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The agronomic effectiveness of an unground reactive phosphate rock from Sechura, Peru, was compared with that of monocalcium phosphate in a severely P deficient and highly P retentive soil (vitrandept) over a period of three years. Soil pHs were adjusted to pH 5.1, 5.3, 5.6 and 6.4. The sward consisted mostly of ryegrass (Lolium perenne) and white clover (Trifolium repens). Fertilisers were applied at six rates at pH 5.3 and three rates at other pHs in the first year. For two of the rates fertilisers were reapplied in the second year. Dry matter yields, P uptake and ground cover of clover were determined during the experimental period. In phosphate rock treated plots a negative linear relationship was obtained between soil pH and the logarithm of yield. The agronomic effectiveness of phosphate rock relative to monocalcium phosphate increased with time at all pHs. Calculated at fertiliser rates which produced near maximum yields, relative agronomic effectiveness at soil pHs 5.1, 5.3, 5.6 and 6.4 were respectively 58, 60, 18, and 5 in year one; 118, 125, 77 and 38 in year three. At pH 5.3, as the rate of application increased the relative agronomic effectiveness of the phosphate rock generally decreased in year one but was enhanced in the intermediate rates in years two and three. The data for ground cover of clover gave a similar trend to that for herbage yield and P uptake.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01048859
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  • 2
    Electronic Resource
    Electronic Resource
    Extractable phosphorus to predict agronomic effectiveness of ground and unground phosphate rocks (1992)
    Springer
    Nutrient cycling in agroecosystems 32 (1992), S. 291-302 
    Details
    ISSN: 1573-0867
    Keywords: Phosphate rock ; phosphate rock reactivity ; chemical extractable P ; formic-P ; citric-P ; neutral ammonium citrate-P
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The reactivity of 11 phosphate rocks (PRs), both in their finely ground and unground forms, and containing up to 12% of CaCO3 were estimated from the P extracted with 2% citric acid, 2% formic acid and neutral ammonium citrate. With the neutral ammonium citrate, PRs were also extracted sequentially. To determine the relative agronomic effectiveness (RAE) of PRs a greenhouse experiment was conducted using three soils of different P retention, and growing ryegrass as the test plant. PRs were applied at three rates plus control. Ground Sechura PR was employed as the standard PR and single superphosphate was included to determine maximum dry matter production. Three cuts of ryegrass were taken over 4 months in 2 soils, and 8 cuts over 10 months in one soil. RAE of the PRs was calculated from dry matter yields obtained at a fertiliser P rate where superphosphate gave 90% of the maximum attainable yield, and also from the yield and P uptake values averaged over rates of application. Amount of P extracted by the different reagents correlated closely with each other (R2 0.82–0.99). Chemical extractable P integrated the effect of particle size as well as the inherent chemical reactivity of PRs. Formic P expanded the scale and thus was the most sensitive indicator to rank PRs. The ranking of PRs were similar between soils. RAEs between soils correlated significantly (R2 = 0.88–0.91). For predicting the agronomic potential of PRs, RAEs calculated from 4 cuts of ryegrass over 4 months appeared to be as good as those calculated from 8 cuts, over 10 months. The total P of PRs was smaller in the large and very small size fractions than in the intermediate ones. With unground rocks the extractable P decreased with increasing particle size mainly due to their decreasing specific surface area. Practical implications of these results are discussed. Extractable P did not decline with increasing total P in the different size fractions of PRs. End-over-end shakers, unlike wrist-action shakers, gave consistent extractable P values. Formic-P was the best predictor of the agronomic effectiveness of PRs even when the data from ground and unground PRs, and from 3 soils of differing P retention were treated as one population (R2 = 0.87–0.92).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01050366
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