A COMPARISON OF OLSEN AND MORGAN SOIL-PHOSPHORUS TEST-RESULTS FROM THE CROSS-BORDER REGION OF IRELAND

A comparison of the Olsen and Morgan soil phosphorus (P) tests using 1 99 soils from the cross-border region of Northern Ireland and the Repu blic of Ireland gave a non-linear relationship (Olsen = 5.96 Morgan(0. 773), R-2 0.74), Differences in the intercepts of log Olsen v. log Mor gan equations were observed when either county or underlying solid geo logy were included as factors in the regression analysis but regressio n slopes did not vary significantly. For a given Morgan-P concentratio n, predicted Olsen-P was highest in County Down and least in County Fe rmanagh but there were no significant differences between five other c ounties (Louth, Cavan, Donegal, Monaghan and Armagh), Soils sampled ov er Carboniferous geology tended to give the lowest predicted Olsen-P c oncentrations, Soil pH was shown to influence the log Olsen v. log Mor gan relationship, with increasing soil pH lowering the predicted Olsen -P for a given Morgan-P concentration. Although significant (P < 0.001 ), the impact of including either county or geology as factors or pH a s a variable in the regression model was slight and the inclusion of e ach only increased the regression R-2 to a maximum value of 0.77.