Abstract
The over-supplementation of animal feeds with phosphorus (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, we 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). We 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. Our study shows how commercial phytase levels together with higher dietary P contents in pig diets contributed to increase PUE and decrease WSP thus making the plant–soil system more P conservative (i.e., lower risks of P losses). Our evidence is that dietary effects on plant–soil P dynamics are driven by the availability of P forms (for plant uptake) in animal excretes and the type of organic amendment (pig vs. broiler) rather than plant species identity (comfrey vs. ryegrass).
Highlights
Agricultural grasslands and croplands play a key role as livestock support systems and often receive large amounts of phosphorus (P) from animal excreta [1,2]
To contribute to reducing this knowledge gap we addressed how the supplement of three different exogenous phytase levels to the diet of two animal species, pig (Sus scrofa domesticus) and broiler (Gallus gallus domesticus) might potentially affect total P (%) content in slurries and litter, and how this in turn might be related to changes in P dynamics in two different plant–soil systems, including comfrey (Symphytum × uplandicum) and ryegrass (Lolium perenne)
Pig diet treatments were defined as: (1) ‘no-phytase’ = maize distiller dried grain solubles (DDGS) and rapeseed extract diet with no phytase formulated to contain 1.5% less energy, reduced amino acid content and P (i.e., 37% and 19% less P in grower and finisher formulations compared to treatment 2), (2) ‘phytase’ = a by-product based diet containing maize (DDGS) and rapeseed extract with commercial levels of phytase (250 FTU, 0.01%, Quantum® Blue, AB Vista, Marlborough, UK), formulated to contain recommended levels of energy, amino acids and P, and (3) ‘superdose phytase’ = the same formulation as the ‘no-phytase’ diet but including a phytase super dose (1000 FTU, 0.02%, Quantum® Blue, AB Vista, Marlborough, UK)
Summary
Agricultural grasslands and croplands play a key role as livestock support systems and often receive large amounts of phosphorus (P) from animal excreta [1,2]. Within intensive animal production systems, which include monogastric animals such as pigs and poultry, optimal P efficiencies require a combination of high P absorption, a sufficient animal skeletal storage, and a low P excretion [14] Achieving this P balance in animal husbandry settings is challenging because most of the plant-derived P in cereal diets is bound up in the form of phytate P, which is associated with low digestibility [14]. Previous experimental studies show that additions of phytase to animal diets contributed to reduce total P in animal wastes when compared to control diets without phytase [20,21] It remains unclear, whether and how phytaseassociated diets affect P dynamics in soils or have any effect on PUE of cultivated plant species. These predictions were tested by measuring (1) total P (%) of animal wastes, (2) P Use Efficiency (PUE) of ryegrass and comfrey plants, (3) soil P availability (WSP), and (4) soil P losses (i.e., P in leachates) in a mesocosm experiment under controlled greenhouse conditions
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