One month of incubation experiment was implemented to evaluate the changes of phosphorus fraction in inorganic P (Pi) and organic P (Po) induced by phosphorus fertilizer (KH2P04),cow manure ( manure) and CaC03 (lime). A 0.5 kg oven-dried weight of arable layers of Latosol from Darmaga, Bogor was used in this study. The rates of manure were 0, 12.5 and 25 ffha, lime were 0, 1, 3 times the CaC03 equivalent required to neutralize exchangeable aluminum amounting to 0, 3.01, 9.03 t/ha respectively and the rates of phosphorus fertilizer in KH2P04 were 0, 40 and 80 kg Plha. All treatments increased resin-Pi (biologically available P). Application of phosphorus fertilizer also increased NaHC03-Pi which is also included as biologically available PI whi!e manure and lime only tended to increase this fraction. Phosphorus fertilizer and manure application were able to enhance NaOH-Pi (moderately resistant P related to AI-P and Fe-P ) but lime did not affect it.Phosphorus fertilizer, manure and lime increased HCI-Pi (moderately resistant P related to Ca-P).The changes of NaHC03-Pi to resin-Pi and P immobilization by microorganism, which was indicated by the increase of NaHCOrPo (readily mineralizable), can be attributed to the decrease of NaHC03- Pi. The increase of NaOH-Pi by phosphorus fertilizer and manure indicated that the complexation of P fixation sites by PO6 and organic acids likely had occurred.

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The objectives of this experiment were: (I) to study the effect of K and Ca fertilization on the dynamic of K, (2) tostudy the relationship between the dynamic of K in the soils with corn growth, and (3) to determine the optimum K requirement on diflerent K/Ca ratio in the soil solution. Ultisol and Vertisol from upland area were used for the study. The determination of K and Ca dosage was based on the maximum soil sorption. The experiment was carried out in greenhouse using the factorial randomized complete design with three replications. Four levels K dosage and three levels Ca dosage were applied in the experiment. The C-7 hybrid of corn was selected as indicator plant. The result showed that adding of K and Ca increased the dry weight of plant in both Ultisol and Vertisol. In Ultisol, adding of K increased the amount of exchangeable Ca, Mg and K, and water-extracted K, whereas adding of Ca increased the exchangeable Ca and Mg and water-extracted K. The optimum K requirement for Ultisol was 58 mg kg-' for K/Ca ratio