Phosphorus Status of Major Coconut Growing Soils of Sri Lanka on the performance of Pueraria phaseoloides

Phosphorus status of major coconut growing soils in the Intermediate Zone of Sri Lanka on the growth parameters and root nodulation of Pueraria phascoloides was studied in plant house and field experiments. In the plant house experiment, Pueraria phaseoloides was planted in Non Calcic Brown, Red Yellow Podzolic, Sandy Regosols, Yellow Latosols and Alluvial soils treated with phosphorus at the rate of 1g of Triple Super Phosphate (TSP) per pot (T1) along with a control (T0-no TSP) treatment. In the field experiment, Pueraria phascoloides was grown on above soils with application of Eppawela Rock Phosphate (ERP) at the rate of 912 kg ha-1 (T1) along with a control (T0) treatment. The relationships between the relative increase of each crop parameter (X) due to phosphate treatment, which is defined by [T1 (X) – T0(X)] / T0 (X) and the initial available soil phosphorus determined by the 2.5 % Acetic acid and Olsen’s bicarbonate were studied. The critical level for available soil phosphorus was determined by fitting the data in above relationships to the Cate and Nelson model. The results of the pot experiment showed that Pueraria phaseoloides significantly responded to P fertilizer application on soils containing available phosphorus less than 5 mg kg-1 in both extraction methods. In the field experiment, the limiting value of soil phosphorus was 10 mg/kg-1 as determined by 2.5 % acetic acid and 9 mg kg-1 as determined by Olsen’s method. Results revealed that the inherent phosphorus levels of most of the coconut growing soils in the Intermediate zone were below the limiting values and phosphate fertilizer application to Pueraria phascoloides is essential to enhance its growth and root nodulation. DOI: http://dx.doi.org/10.4038/cocos.v19i1.474