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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