The pressures on our nutrient resources from intensive agricultural practices are increasing the need for optimised fertiliser use. Alternative nutrient sources derived from industrial waste products can recycle nutrients back into the food system, promoting a circular approach to nutrient management and reducing fertiliser inputs. By products from cement manufacturing such as cement by-pass dust (CBD) and cement kiln dust (CKD) contain considerable amounts of K and are highly alkaline, making them a suitable fertiliser and alkalising agent. Analysis of existing soil pH and K indices found the CBD/CKD produced by four plants supplies enough K to meet the demands of 7% of grassland or 5% of arable land across England and Wales. However, the practice of treating CBD and CKD as liming agents
was significantly oversupplying K. A field trial found that CBD and CKD applied at liming rates (5 t ha-1) to a ryegrass (Lolium perenne L.) pasture, were as effective as lime and K fertiliser at increasing biomass production, K availability and uptake and soil pH. However, a Partial Nutrient Balance assessment revealed that these rates would lead to build up of soil K and
risk leaching. A mesocosm experiment with ryegrass and white clover (Trifolium repens L.) demonstrated that intercropping the two species enhances growth and P uptake in limed pastures and improve the efficiency of applied P. Finally, a pot barrier experiment discovered that the facilitative and competitive effects of intercropping ryegrass and clover required direct root interaction. This research identified aspects of current regulatory practice in Great Britain that are leading to inefficiencies in CBD and CKD application and demonstrated that the use of intercropping can increase P efficiency in limed soils. It has also contributed to the understanding of the level of interaction between white clover and perennial ryegrass in intercropped systems.