The over-supplementation of animal feeds with P within livestock-production systems leads to high rates of P excretion and thus to high P loads and losses, which negatively impact the natural environment. The addition of phytase to pig and poultry diets can contribute to reducing P excretion; however, cascading effects of phytase on plant–soil systems remain poorly understood.

Here, the authors addressed how three different diets containing various levels of exogenous phytase, i.e., (1) no-phytase, (2) phytase (250 FTU), and (3) superdose phytase (500 FTU) for pigs (Sus scrofa domesticus) and broilers (Gallus gallus domesticus) might affect P dynamics in two different plant–soil systems including comfrey (Symphytum × uplandicum) and ryegrass (Lolium perenne). They found that differences in phytase supplementation significantly influenced total P content (%) of broiler litter and also pig slurry (although not significantly) as a result of dietary P content.

P Use Efficiency (PUE) of comfrey and ryegrass plants was significantly higher under the intermediate “phytase” dose (i.e., commercial dose of 250 FTU) when compared to “no-phytase” and “superdose phytase” associated with pig slurry additions. Soil P availability (i.e., water soluble P, WSP) in both comfrey and ryegrass mesocosms significantly decreased under the intermediate “phytase” treatment following pig slurry additions. Dietary P content effects on P losses from soils (i.e., P leaching) were variable and driven by the type of organic amendment.