Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: 10/15/2003
Publication Date: 11/2/2003
Citation: Calderon, F.J., Reeves III, J.B., Mccarty, G.W. 2003. Nitrogen mineralization and changes in manure organic matter after soil application [abstract]. American Society of Agronomy. Agronomy Abstracts 2003 CDROM S05-calderon187520.
Interpretive Summary: The ability to predict the effects of manure application on soil nitrogen mineralization is essential for optimizing crop growth while avoiding groundwater and atmospheric contamination. However, estimating mineralizable manure N is problematic because of the wide variety of organic manure N forms as well as the lack of a rapid standardized method to measure this important nutrient pool. Infrared spectroscopy is a promising technology, since it can discern between different N functional groups in organic matter, in addition to being instantaneous and non-destructive. Our research allows us to estimate what forms or organic N change during the mineralization of organic N in manure. With this information, we can then select particular wavelengths which show sensitivity towards the components of organic N that determine the fertilizer value of the manure. The ultimate goal of this research is to produce a standardized instrument that can be used in the laboratory or the field to facilitate decisions about manure management. This will ultimately help farmers and monitoring agencies to prevent over-application of manure and that way avoid environmental degradation.
Technical Abstract: We carried out a laboratory incubation of manure-amended soil in order to monitor manure composition using infrared spectroscopy, as well as measuring manure N mineralization, gas fluxes, denitrification, and microbial N immobilization. The treatments consisted of four different dairy and beef manures and a non-manured control. The soils were amended with manure at a rate of 0.15 mg manure-N g-1 soil. The manure was enclosed in mesh bags in order to allow for the analysis of fresh as well as incubated manure. Microcosms consisting of 100 g of soil were placed in jars fitted for gas sampling. The microcosms were incubated aerobically, and subsets of jars were sampled at time zero, as well as weeks 1, 2, 4, 7, and 10. Our data shows that the timing and amounts of ammonium-N consumption and the net quantity of nitrified N varied markedly between soils and manures within the same microcosms. Manure addition resulted in initially high amounts of ammonium-N. The high mineral N was rapidly nitrified and denitrified, resulting in high N losses from the manured microcosms during the first two weeks of the incubation. All manured microcosms had net negative N mineralization. This deficit in mineral N is explained primarily by N loss through denitrification, and secondly, by increased net N immobilization by soil microbes in manured soils. Gas fluxes of N2O and CO2 increased in the manured soils, underscoring the potential impact of manure application on atmospheric contamination. Infrared spectroscopy of the fresh and incubated manures shows that this technique is sensitive to changes in manure organic N after soil application. This data shows that N containing functional groups, i.e., primary amines, amides, as well as bands associated with proteins decrease during the incubation. Bands associated with fatty acids such as C-H and carboxylic acids tend to decrease during the incubation, possibly due to utilization as C sources. The spectroscopic data also shows lignin-specific signals increase during manure decomposition, while cellulose-specific bands are not affected. In summary, this experiment shows that the use of manure bags is valuable in discerning between the N cycling dynamics of manure and soil, and that infrared spectroscopy shows potential as an analytical tool to ascertain the quality of manure as an N fertilizer.