Assessing the effectiveness of manure export plus intensive silage cropping for lowering the O lsen‐ P status of P ‐enriched grassland

A substantial proportion of farmed grassland soils in N orthern I reland ( NI ) are overly enriched with P and pose a risk to water quality. To address this problem, manure could be exported rather than recycled to P ‐enriched land and the latter intensively cropped with grass silage to deplete soil P . To assess the efficacy of such a strategy, a P ‐ and K ‐enriched grassland site was intensively cropped over a 6‐yr period with fertilizer N alone supplied to support silage growth. By year 6, soil P had declined from index 5 to index 3, and it was estimated that two more years of this management may bring it into the target index 2 range. Soil K , however, declined rapidly from index 4 to index 1 in just 4 yr, with the result that grass production became limited by K deficiency. It was concluded that nonrecycling of manure to P ‐enriched grassland under silage management is probably the most effective strategy for lowering soil P status, but care must be taken to prevent K deficiency occurring.