An evaluation of the Olsen test as a measure of plant-available phosphorus in grassland soils derived from basalt parent material |
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| Authors: | AAW Bell JS Bailey RV Smith |
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| Institution: | The Queen's University of Belfast, Department of Agricultural and Environmental Science, Newforge Lane, Belfast BT9 5PX, UK.;Department of Agriculture and Rural Development for Northern Ireland, Agricultural, Food and Environmental Science Division, Newforge Lane, Belfast BT9 SPX, UK. |
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| Abstract: | Abstract. Anecdotal and circumstantial evidence have suggested that the Olsen test underestimates plant-available phosphorus (P) in basaltic soils in Northern Ireland. Therefore, the ability of this test to predict plant-available P in basaltic (and non-basaltic) soils was investigated by regressing Olsen-P data against herbage P indices calculated from plant tissue test data using the diagnosis and recommendation integrated system. The average Olsen-P concentration for a range of fields situated on basaltic soils was considerably lower than the average Olsen-P concentration for a range of fields situated on non-basaltic soils, and yet mean sward P status, as given by the herbage P indices, was similar for both groups of fields. Herbage P indices were also much better correlated with Olsen-P measurements in non-basaltic soils than in basaltic soils. Furthermore, at low Olsen-P values (?9mgPL?1) some swards on basaltic soils were genuinely deficient in P, while others were sufficient or even in surplus for this nutrient. The results confirm that Olsen-P is inadequate as a predictor of plant-available P in basaltic soils. It is concluded that an alternative soil test is needed to provide a reliable assessment of plant-available P in basaltic soils, to prevent overuse of fertilizer and manure P and to minimize the amounts of P entering local watercourses. |
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| Keywords: | Basaltic soils diagnosis and recommendation integrated system grassland Olsen-P test validation |
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