Forms and profiles distribution of phosphorus soils along a toposequence of Amaoba- Ime, Ikwuano Lga, Abia State, Nigeria
The forms and distribution of phosphorus (P) in profile of soils along a toposequence at Amaoba Ime in Ikwuano LGA of Abia State of Nigeria were investigated in 2015. Five pedons representing crest, upper slope, middle slope, lower slope and valley bottom were assessed. A total 25 augur soil samples were collected from 0-20, 20-40, 40-60, 60-80 and 80-100cm depth in the five sampling units along the toposequence. The samples were analyzed for various forms of P and other physical and chemical properties. Soil P varied widely, the distribution of forms of P with depth along the toposequence was not uniform in the soils studied. The site has a very low (< 9%) organic P (PO) contribution to the total P (TP). The occluded P constituted 75 to 79% to TP and total inorganic P (TPI) forms in the soils, respectively. The occluded P and Fe-P occupied more than 90 % of the TPI. Active PI constitutes 22 % TP. Ca-P and Al-P were lower (< 8 %) than other forms of P in the soils, while Al-P was low in lower horizonsof the soil. The relative abundance of various forms of PI were in the sequence of Ca-P < Al-P < Fe-P < Occluded P. The correlation coefficient indicates that the P forms are closely related. The multiple correlation analysis revealed TP correlated positively P (< 0.05) with Al-P, FeP and Occluded P. PO had a significant negative correlation with sand (r = -0.56*), PE (-0.41*) and positive relationship (P < 0.05) (r = 0.62*) with silt.Occluded P correlated negatively with Mg (r = -0.40*) and positively with Al-P, Fe-P, Ca-P, and total P. Al-P correlated positively with Fe-P, Ca-P, Occluded P and total P. Fe-P correlated positively with Al-P, Ca-P, Occluded P and total P. In general, soil PE is above the critical level of 15mg/kg. In conclusion, status of the TP and their various forms in the Amaeke Ibeku soils do not depend upon their topography.
Keywords: Phosphorus, Status, Toposequence, Soils and Amaoba-Ime