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Solubility and plant-availability of P in manure

Manure is a significant source of phosphorus (P), and its P content is nowadays more than what is sold as mineral fertilizer in Finland. Efficient utilization of manure based P, both from environmental and economical point of view requires knowledge of P solubility and availability. In this study we used Hedley fractionation to evaluate P solubility and pot experiment to estimate plant availability of P in different types of manures and feces. Barley (Hordeum vulgare var. Elmeri) was the test plant in the pot experiment.

The investigated manure types consisted of dairy cow, pig, poultry and fox manures. Samples of dairy cow and pig feces originated from feeding trials with different types of diets. Water-soluble P was the main P fraction in dairy cow, pig and poultry manures (55-91 %), but in fox manure only 19 %. Anaerobic digestion reduced the water-soluble P fraction in dairy cow slurry, but the labile P content (water + 0.5 M NaHCO3 –extractable P) was not affected. Use of phytase in the poultry diet increased labile P content in manure. Most of the P in fox manure was acid soluble (71 %). Poultry manure contained the highest share of organic P (45 %), while phytase in the diet reduced it down to 31 %.

This report was prepared as part of work package 4 on Standardisation of Manure Types with Focus on Phosphorus in the project Baltic Manure.


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