Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 9, 2002
Publication Date: January 5, 2003
Interpretive Summary: Animal production in the U.S. increasingly occurs in concentrated animal feeding operations. Large numbers of animals are gathered in a relatively small land area. It has been estimated that over 55 billion Mg of animal manure are produced each year across the U.S. Large-scale CAFO faced with increasing regulations are managing manure as a waste product. Manure contains large quantities of plant nutrients in both inorganic and organic forms in partial state of decomposition. The understanding of nutrient release, in particular P release from animal manure and compost must be improved because the imbalance in N and P contents and inconsistent crop responses to the organic nutrients have resulted in manure becoming a less desirable by-product of the livestock feeding industry. We measured the production of carbon dioxide from the decomposition of manure organic matter and the release of soluble P extracted by water in raw and composted cattle manure. Over a period of 46 weeks, the breakdown of manure and release of carbon dioxide can account up to 17% of the carbon content in manure alone. The gaseous release was even greater in soils amended with the raw manure compared to soils alone and soils amended with composted manure. Although enzymes regulated the release of soluble P from organic P forms, the P release in manure and manure-amended soils was found to be fast and independent of manure organic matter breakdown. It was more vital than ever that alternative measures be developed to render manure P less reactive. Manure readily released large amounts of reactive P that when applied on or in the soil near-surface zone would be subject to loss in runoff and would degrade water quality.
Information is needed regarding water-extractable nutrient release during animal manure decomposition because dissolved N and P transfer to runoff water may increase with surface applications and shallow soil incorporation in permanent pastures and conservation tillage systems. Flushes of CO2-C were large, exceeding 100 mg kg-1 d-1 and increased in amplitude as a function of substrate decomposability and ambient temperature. Inorganic N and DRP were released rapidly from both stockpiles and composted manures when incubated alone or as soil amendments. Dissolved P release varied inversely with soil sorption capacity and degree of P saturation in Amarillo fine sandy loam (Aridic Paleustalf) and Pullman clay loam (Torrertic Paleustoll). Net mineralizable C, MIN_N, and DRP flux densities were log-normally distributed during the 322-d incubation period. Results from the log-normal distribution modeling approach suggest that the incubations needed to be carried out only for as long as needed to attain the 50% maximal flux density (½flux densitymax) beyond the maximum to predict MIN_C, MIN_N, and DRP release flux density distributions. There were strong correlations between the loge of the cumulative CO2-C and inorganic N fluxes and between the loge of cumulative CO2-C and DRP released, and these correlations had an inflexion point occurring between 14 and 20 d. The non-linearity of the C-to-N and C-to-DRP relationships indicates the presence of multiple substrate pools and supports the use of log-normal distributions to describe MIN_C, MIN_N, and DRP release from manures and manure-amended soils and to shorten laborious incubations.