Fertilizer effectiveness of three carbonate apatites on an acid ultisol

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Abstract
Two properties that are detrimental to agronomic production with acid tropical soils are elevated aluminum concentrations and low phosphate availability. Direct application of carbonate apatites to acid tropical soils possessing low buffering capacity could possibly resolve this problem. The property that determines the effectiveness of directly‐applied carbonate apatites is the CO3/PO4ratio, which indicates the degree of anionic isomorphic substitution occurring within the mineral crystal lattice. Increasing ratios denote greater mineral solubility under acid‐soil conditions. Research was conducted to determine: a) fertilizer efficiency of three carbonate apatites (from North Carolina (NCPR), Central Florida (CFPR), and Kodjari, Upper Volta (KPR)), varying in CO3/PO4ratios, to that of triple superphosphate (TSP), and b) liming effects induced by the liberation of carbonates from each source, compared to CaCO3. Maize (Zea mays L.) was grown in pots containing 3 kg of a Dothan fine sandy loam (fine, loamy siliceous, thermic, Typic Paleudult). Yield was lower from carbonate apatite sources than from TSP during the first cropping period, but was equal to TSP treatments for the second cropping period with rocks possessing a CO3/PO4ratio greater than 0.14. The liming effect induced by liberation of carbonates and phosphates from NCPR (400 mg P kg‐1or 306 mg CO3kg‐1) equaled that from CaCO3(600 mg CO3kg‐1) during the first cropping period. Over experimental duration, the soil pH was increased by 0.60, 1.26, and 1.10 pH units with a resulting decrease of 0.13, 0.17, and 0.14 cmol(+) extractable Al kg‐1by CaCO3(600 mg CO3kg‐1), NCPR (306 mg CO3kg‐1), and CFPR (171 mg CO3kg‐1), respectively
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