Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 2, 1999
Publication Date: N/A
Interpretive Summary: Manure disposal is an important issue for farmers. Manure nutrients (nitrogen (N), phosphorus (P), and potassium (K)) can be used as a fertilizer, but manure can also pollute air and water if it is applied in excess of crop requirements. Manure contains both inorganic and organic N. Plants can use inorganic N (ammonium) immediately, but organic N (protein) must be converted to inorganic N (mineralized) before it is plant available. In order for farmers to apply manure at suitable rates, they must be able to estimate how much of the manure nutrients will be available to the crop. There are no fast methods for measuring organic N mineralization, and laboratory assays take months. Therefore, manure samples are often stored prior to analysis. The objectives of this experiment were to determine if storage methods (refrigeration, freezing, oven and freeze drying) alter manure N mineralization characteristics, and to determine which storage method(s) is most appropriate. Two manure slurries from a dairy heifer lot were collected and 7 treatments (fresh, frozen (4 wk), refrigerated (1 d, 1 wk, 4 or 5 wk), freeze-dried or oven- dried) were compared for effects on mineralization by incubation of slurry and soil mixtures. Freeze- and oven-drying resulted in N losses of 30% or more. Approximately 18 to 25% of the organic matter in the slurry was degraded, but conversion of organic N to inorganic N was minimal. In the oven- and freeze-dried slurries, there was greater immobilization (conversion of inorganic N to organic N) when compared with fresh manure. Results indicate that oven- and freeze-drying are unsuitable methods of storage, but the mineralization characteristics of manure are not affected by refrigeration or freezing.
Technical Abstract: In vitro incubations of manure-amended soil are often used to evaluate manure N and C availability. It is typically necessary to store samples prior to analysis and manures are dried, refrigerated, or frozen. Storage may alter the composition or structure of the manures and alter mineralization characteristics. An experiment was designed to evaluate the effects of manure storage on C and N mineralization characteristics. Two dairy slurries were collected and 7 treatments (fresh, frozen (4 wk), refrigerated (1 d, 1 wk, 4 or 5 wk), freeze-dried or oven-dried) were compared for effects on C and N mineralization. Rates and extents of N and C mineralization were determined by incubation of slurry-amended soil at 25oC. Slurry was added at a rate approximately equivalent to 250 kg of N per ha incorporated into the upper 15 cm of soil. The appearance of NH4+ and NO3- and the production of CO2 were monitored over 112 d. Freezing or refrigeration had no effect on slurry N content, however freeze- and oven-drying resulted in N losses of 30% or more. Carbon dioxide-C production followed first-order kinetics over 9 wk for all treatments with approximately 18 to 25 % of the slurry C mineralized. Net mineralization of organic N was minimal in all treatments and soil N mineralization- immobilization turnover was not affected by freezing or refrigerating the slurries. However, with oven- and freeze-dried slurries, there was a greater immobilization of N when compared with fresh manure. Nitrification was delayed in all treatments, but all NH4+ was converted to NO3- by 112 d. Results indicate that oven- and freeze-drying are unsuitable methods of storage, but the mineralization characteristics of manure are not affected by refrigeration or freezing.