b'2Harmonising soil phosphorus index systems:A cross-border challengeVero SE1, Doody D1, Campbell JM2, Mellander P-E3,4, Burgess E4 and Higgins S11Agri-Food and Biosciences Institute, Newforge Lane, Belfast BT9 5PX, UK2School of Geography and Environmental Science, University of Ulster, Coleraine, BT52 1SA, UK3Crops, Environment and Land Use Programme, Teagasc, Johnstown Castle EnvironmentResearch Centre, Wexford, Co. Wexford, Ireland4Agricultural Catchments Programme, Teagasc, Johnstown Castle Environment ResearchCentre, Wexford, Co. Wexford, IrelandCurrently two soil phosphorus (P) index systems are operated within Ireland. In the Republic of Ireland (ROI) Morgans extract is the statutory method (10% sodium acetate, pH 4.8). This test is considered optimal for brown earth soils. The ROI system uses four indices (1 to 4), with Index 3 considered optimum for grassland soils. Northern Ireland (NI) uses the Olsen P test (0.5 M sodium bicarbonate, pH 8.5) which more strongly extracts sorbed P and is intended for neutral to calcareous soils. The NI system consists of five indices (0-4), with Index 2+ indicating optimum availability for intensive grassland systems. In both cases, P values above the agronomicoptimum are expected to pose the greatest risk to water quality. The management of cross-border waterbodies requires a harmonised approach and a clear understanding of the P contributions from different soil types. This is masked by inconsistent approaches to soil testing which reflect political jurisdictions rather than soil type. The objective of this study is to quantify the relationship between both index systems. Soil samples (c.1,000) taken from catchments in the border region were assessed using Morgans and Olsen soil tests. For 33% of samples the NI system assigned a higher index than the ROI system, i.e. assumed a greater agronomic availability of P. Of these samples, 57% indicated a high/excessive index using the NI system, versus an optimal index using the ROI system. The implications are that thefarmers using the NI system may attribute greater risk of P loss to watercourses than thoseusing the ROI system for a given soil. Furthermore, 33% of samples indicated optimal P using the NI system but low P content using the ROI system. This may result in over- or under-application of P from an agronomic perspective, depending on soil type.These are preliminary results and research is ongoing.46'