Submitted to: Bioresource Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/15/2009
Publication Date: 1/18/2010
Publication URL: DOI:10.1016/j.biortech.2009.12.070
Citation: Dao, T.H., Schwartz, R.C. 2010. Mineralizable phosphorus, nitrogen, and carbon relationships in dairy manure at various carbon-to-phosphorus ratios. Bioresource Technology. 101(10):3567-3574. Interpretive Summary: Manure has been used as a source of a particular nutrient in crop production, but it contains all major elements required for crop growth. Determining the optimal amount of manure to apply requires accurate knowledge of manure composition and nutrient release rates under the environmental conditions existing at the site of storage prior to field application. Animal manure has a large organic P fraction that is converted to phosphate by phytase enzymes. The production of these enzymes by manure microbes is carried out in responses to the organisms’ needs for inorganic phosphorus. Amino acids and nucleic acids are also needed for protein synthesis and the production of other enzymes involved in the transformations of C and P-containing substrates. Such linkages between nutrient transformations are vital to the survival of the organisms. Little is known about the effect of manure composition on the concurrent transformations of nutrients during storage. Manure nutrients can either be solubilized, rendered insoluble, broken down to simple products such as ammonia, or lost as gaseous carbon or nitrogen compounds to the atmosphere. These transformations determine the final composition and the value of manure to crop growth, organic matter for improving soil quality, or the risk of nutrient discharges when land applied. The experimental results pointed to a threshold range of phosphorus and nitrogen in the mineralization of manure carbon. Nutrient composition, therefore, had a profound effect on rates of release and accumulation of active phosphorus forms in dairy manure. The improved understanding of linkages between phosphorus, and carbon transformations will assist us in developing practices to maximize nutrient conservation in manure for recycling them in crop production.
Technical Abstract: Animal manure contains all major elements required for plant and microorganisms’ uptake and assimilation for growth, namely, phosphorus (P), nitrogen, and carbon. Information about interactions between transformations of nutrients and the turnover of P forms in dairy manure, is essential to accurately determine the environmental fate of manure organic P as these forms add to the bioactive environmental P pool upon mineralization. An aerobic fermentation study was conducted to determine the kinetics of mineralization of dairy manure and evaluate the effects of manure carbon (C) to P ratios on P and C transformations. As the ratio of manure C:P widened, from 70:1 to 130 to:1, the rate of P mineralization increased and inorganic phosphate accumulated according to first-order reaction kinetics. Dissolved C concentrations declined rapidly during the first three weeks of fermentation, with rates of disappearance following a double exponential kinetic model. Carbon concentrations were positively correlated with N:P at the narrow C:P ratio, and the correlation disappeared at the wide C:P treatments exceeding 70 to 100:1. Therefore, all observations pointed toward a threshold range of P and N in the mineralization of manure C, with an increased need for soluble bioactive P for the transformation of manure solid C in wide C:P manures. The management of nutrient composition of dairy manure, therefore, can have a profound effect on the rates of release and accumulation of bioactive P forms. The carbon load of dairy manure suspensions may be manageable, to alter the rate of mineralization of organic P and manure C, thus the risks of elevated soluble P and the loss of C under non-limiting nitrogen conditions.