Effect of the organic amendments on the phosphorus dynamic in an oxisol

The incorporation of vegetable residues and animal manures to the soil has shown reduction of phosphorous (P) fixation and increment of the available P content in this system. With the purpose of studying the effects of organic materials application on the dynamic of P in an oxisol from the eastern plains of Colombia (pH: 4,3 and exchangeable aluminum 3,20 c mol/kg), cowpea and crotalaria residues at a level of 3% each, chicken manure at three levels (1,87, 3,73 and 5,60%), lime at the levels of 1,5 and 17,6 ton/ha and inorganic phosphorus (100 kg/ha of P205) as calcium monophosphate were applied to the soil in a completely randomized factorial incubation experiment, at the green house. Soil samples were taken after 30, 60 and 105 days of incubation; pH, soil available P, and exchangeable Al were analyzed. P fractionation was carried out through a sequential extraction technique described by Hedley (1982). The treatment with chicken manure showed the highest values of soil available P (45 mg/kg) when compared to the other amendments (whose phosphorous soil values were between lo and 14 mg/kg) and the check treatment (9 mg/kg). The soil available P also increased as chicken manure levels increased. The P soil fractions showed the highest values when chicken manure was used as treatment, with significant difference in relation to the rest of the treatments. The previous was related to the high phosphorous content (2%) of this material which s contributed also to the residual P fraction that may be a P reserve for crops. the treatments with cowpea and crotalaria which had low P content (0.2%) did not show significant difference among the P fractions, although they decreased the phosphorous fixed by Fe and Al. On the other hand, through al the application of calcium monophosphate, it was confirmed that when soluble inorganic P is added to an Oxisol it is a principally held by Fe and Al hydrous oxides