Effect of Pelleting, Temperature, and Soil Type on Mineral Nitrogen Release from Poultry and Dairy Manures

Abstract

AbstractPellets are produced from manures for more convenient and economical use. The rate of N mineralization of manures under different conditions is of agronomic importance, since it allows estimation of mineral N supply to plants as a function of time. Pelleted manure may have mineralization characteristics differing from those of its raw components due to the high temperatures and pressure involved in the pelleting process. The rate of N mineralization of raw manures and pelleted manure was studied in water and in soil incubation experiments. About 10% of total N in the manures was initially KCl‐extractable NH4. Within 1 d, 30 to 35% of total N in poultry manure and 18% in mixed 75% dairy and 25% poultry manure were mineralized in water. Mineralization kinetics of manures in soil showed an initial rapid process followed by a slow release of mineral N and could be described as two simultaneous first‐order reactions. During the first week, 34 to 44% of total N in poultry manure and 14 to 23% in 75% dairy + 25% poultry manure were mineralized in soil pellets releasing more N than ground manures. After 2 to 3 months, mineral N in soil was 34 to 50 and 27 to 44% of total N in poultry and 75% dairy manures, respectively, the pellets contributing equal or less mineral N to soil than the ground manures. Pelleting increased the relative amount of rapidly mineralizable N in the manures and created higher NH4‐N concentrations in soil, which under less favorable conditions for nitrification increased the susceptibility to loss of NH3‐N. Temperatures in the range of 14 to 35°C had little effect on the rate of mineralization but affected N loss from poultry manure pellets by delaying nitrification at 14 and 35°C compared with 25°C.