Sustainable phosphorus for soilless greenhouse horticulture: An exploration of potential routes

The move from a ‘linear’ supply of nutrients based on finite resources to a ‘circular’ one involves many unanswered questions. Where should these nutrients come from? How can they be recovered? How applicable are circular fertilisers? How can the risk of contaminants be mitigated? In this report, we examine such questions for soilless greenhouse horticulture, which has unique properties and requirements compared to soil-based systems. Specifically, phosphorus (P) is examined, since the Netherlands has a P surplus and yet it comes from finite natural reserves. We make an inventory of the most important P side-streams in the Netherlands and compare the different available P-recovery technologies. Moreover, recovered P fertiliser products are evaluated using a new methodology specific to greenhouse horticulture’s unique requirements: solubility and purity. Insoluble products such as struvite can be applied if dissolved on-site in a separate tank, and we quantify the effect of this on the nutrient recipe. We also conclude that soilless systems are often far more sensitive to contaminants than is currently reflected in the EU Fertilising Products Regulation (FPR) 2019/1009. With these results, we aim to inform and improve confidence and understanding between parties in the transition to circular nutrients for soilless systems.