Composition and properties of leachates from farmyard manure heaps

Besides some rheological characteristics, the N-total, NH4+-N, NO3--N, P K+, dry matter and ash content, as well as chemical oxygen demand and conductivity of farmyard manure leachates were examined. The K+ concentration was highest with an average of 5921 mg l(-1), followed by N-total (1139 mg l(-1), 66% of it as NH4+-N and 4% NO3--N) and P (334 mg l(-1)). All parameters were highest in leachates of fresh manure and lowest at the end of a 6 months storage period. During the storage, the P concentration in leachates showed a decrease of 67.7%, followed by a decrease in N-t (-57.3%) and K+ (-24.0%). In leachates from a manure with an relatively high initial N-t content of 0.51% and a low C:N ratio of 16.8 the N-t concentration was 0.5-1 times higher than that of a manure with 0.44% N-t and a C:N ratio of 19.9. The viscosity and the thixotropy of leachates were both relatively high at the beginning of the manure's storage period, which led to a strongly developed blocking of porous systems. These properties that contribute to explain the high retention rate of nutrients in the top soil layer at manure storage sites, decreased with an increase in storage time.