Quantity and intensity relationships in predicting P availability of soils in Sri Lanka

In a greenhouse experiment, P uptake by rye grass ( Lolium multiflorium L.), from four representative soils of Sri Lanka were found to be signifikantly correlated with P intensity (r = 0.65**) and quantity (r = 0.68**) measurements. The incorporation of maximum buffer capacity (MBC) values in multiple regression improved the relationship of P uptake with P quantity but not with P intensity. Multiple regression equation indicated that at equal quantity levels, increasing buffer capacity tends to increase P uptake, indicating that the quantity parameter was buffered by MBC. A seedling experiment of 14 days duration using mustard ( Brassica juncea L.) seedlings illustrated that P intensity had a more pronounced effect on P uptake (r = 0.80 ) than P quantity (r = 0.43*). The incorporation of MBC values improved the relationship between P quantity and P uptake, but unlike the previous experiment the multiple regression equation indicated a negative relationship between MBC and P uptake at equal quantity levels confirming the importance of P intensity when P uptake is considered for a shot period.