M. Duffera et Wp. Robarge, CHARACTERIZATION OF ORGANIC AND INORGANIC PHOSPHORUS IN THE HIGHLAND PLATEAU SOILS OF ETHIOPIA, Communications in soil science and plant analysis, 27(15-17), 1996, pp. 2799-2814
Surface horizon samples from two Vertisols, an Andisol, and an Alfisol
were collected from farmers' fields, research station farms, and from
uncultivated/nonfertilized areas to characterize the organic and inor
ganic forms of phosphorus (P) in the highland plateau soils of Ethiopi
a using the Hedley soil P fractionation scheme. The total P values ran
ged from 226 mg . kg(-1) in the Akaki Vertisol samples developed on al
luvial deposits to 1570 mg . kg(-1) in the Andisol samples, where the
HCl fraction dominates the inorganic soil P pool. The Alfisol samples
contained 400 mg . kg(-1) of total P, with the NaOH and residual P bei
ng the dominant P fractions. The resin inorganic phosphorus (Pi) acid
bicarbonate Pi fractions generally accounted for less than 15% of the
total P in all soils, and were positively correlated with organic C. T
he NaOH P fraction, which was most prominent in the surface horizon sa
mples of the Alfisols, accounted for 4-15% of total P. The HCl P fract
ion, ranged from 1% in the Alfisols to 46% in the Andisols, and positi
vely correlated with pH, All of the P fractions were negatively correl
ated with clay and extractable Al contents. The organic P (Po) fractio
ns were positively related to organic carbon (C) and dithionate extrac
table iron (Fe). All samples collected from farmers' fields showed a l
oss of P from the residual, and HCI fractions as compared to the uncul
tivated/nonfertilized samples. There is also a decrease in the labile
P (resin Pi, bicarbonate Pi, and Po) fractions, except for the Akaki V
ertisol samples. However, under research station management, the amoun
t of labile P fractions either increased or remained at the same level
as the uncultivated/nonfertilized samples, except for the Andisol. Ad
dition of P fertilizer at the recommended rates to the Debre Zeit rese
arch station Vertisol appears to have resulted in a slight increase in
the labile P and prevented loss of P from the HCl P and residual P fr
actions.