Full-scale slurry tank sampling: Effects of sampling strategy and sample storage on measured physical and chemical...

Accurate analyses of liquid animal manure (slurry) from full-scale slurry storage tanks are essential for effective nutrient management in agriculture. Inadequate or inconsistent sampling methods and improper storage conditions can lead to significant inaccuracies in nutrient analysis of slurry. This study evaluates the impact of different slurry sampling methods, storage types, and durations on the physical and chemical properties of slurry. Slurry was sampled using three different sampling methods in the same full-scale tank both before and after mixing. Samples were stored at 5°C and -18°C for different durations (1-24 weeks) to assess changes in physical and chemical properties of the slurry. The analyzed parameters were ammonium, total nitrogen, total phosphorus, sodium, dry matter, volatile solids, and pH. The results show that the measured parameters varied considerably with sampling methods, in some cases by up to 80%-100%. The largest differences were observed for dry matter and total phosphorus between top and bottom samples in the unmixed tank, reflecting sedimentation effects. Profile sampling gave similar results as mixing prior to sampling. Storage at 5°C maintained sample integrity over 4 weeks, while storage at -18°C led to substantial changes in pH. Our findings indicate that proper sampling is crucial for representative analysis and that storage conditions can influence pH over extended periods.