Abstract:
The present study investigated the application of three phosphate (P) fertilizer sources;
Imported Rock Phosphate (IRP), Eppawela Rock Phosphate (ERP) and Triple Super
Phosphate (TSP) on the short term availability of different P fractions in the lateritic
soils in the intermediate zone of Sri Lanka. The available different P fractions in pots
with and without Ruzi grass {Brachiaria ruziziensis L.) as an indicator plant was
determined after six months from the date of application of the fertilizers. Each P
fertilizer was applied in triplicate at three different levels, viz., 15, 30, 60 mg P20 5 /100
g soil, separately into pots with and without Ruzi grass. The control with and without
Ruzi grass was also carried out in triplicate without fertilizers. The soil moisture
content in all the pots was maintained at 60% field capacity. Phosphorus concentration
and total dry matter content of grass were determined bimonthly over a period of six
months. The soils were analyzed for the concentrations of different P fractions, viz.,
saloid bound P (Sa-P), aluminium bound P (Al-P), iron bound P (Fe- P), occluded P
(Occ-P) and calcium bound P (Ca-P). The results revealed that Ruzi grass utilized
more Sa-P and Al-P fractions than Occ-P, Fe-P and Ca-P fractions. The P uptake by
Ruzi grass was low for both IRP and ERP compared to TSP application. Both ERP and
IRP fertilizers did not show any significant P increase with increasing level of their
application. Unlike ERP and IRP, the TSP applications showed a linear increase of P
uptake by Ruzi grass with increasing the level of P treatment. The overall results
indicated that TSP is superior to IRP and ERP for short term application, though IRP
was found to be slightly better than ERP in providing available P
