Submitted to: Geoderma
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/5/2008
Publication Date: 9/8/2008
Citation: Mao, J., Olk, D.C., Fang, X., He, Z., Schmidt-Rohr, K. 2008. Influence of animal manure application on the chemical structures of soil organic matter as investigated by advanced solid-state NMR and FT-IR spectroscopy. Geoderma. 146(1-2)353-362. Interpretive Summary: Applying animal manure to agricultural soils is known to improve crop growth, but the reason for this benefit is more complicated than simply adding essential plant nutrients. It may be the form of these nutrients, the rate they are recycled within the soil, or their availability to the crop. Our study using a soil from Nebraska that had received manure for four years showed there were more nitrogen molecules in the soil (greater quantity of nitrogen), but there was no evidence that other easily degradable materials had been accumulated. These results will be used to improve our knowledge about how animal manures cycle nutrients within the soil. This will benefit scientists studying basic biochemical and nutrient cycling processes in the soil. The research will also benefit farmers by providing them a better understanding of how animal manures can affect crop production and their soils.
Technical Abstract: Annual application of cattle manure to a farmer's field in eastern Nebraska for 5 yr caused improved soil N and P supply and increased corn (Zea mays L.) yield in less productive portions of the field compared to another field treatment receiving the same amount of N as inorganic fertilizer. As a first step toward identifying the soil processes that led to these changes, the effects of manure addition on the chemical nature of soil organic matter were investigated by extracting two humic fractions-- mobile humic acid (MHA) and calcium humate (CaHA)--from the field soil for subsequent analysis by solid-state 13C nuclear magnetic resonance (NMR) spectroscopy and Fourier Transform-infrared (FT-IR) spectroscopy. Functional groups were selectively identified and quantified through NMR techniques that included quantitative direct polarization, cross polarization/total suppression of sidebands, 1H-13C heteronuclear correlation NMR, 13C chemical shift anisotropy filtering, CH-signal selection, and other spectral editing techniques. The NMR results showed that the CaHAs exhibited high aromaticity while the MHAs had lower aromaticity and greater contributions from lignin aromatic ethers. The chemical nature of each humic fraction did not differ significantly between an unfertilized control and the treatment receiving N as inorganic fertilizer. The FT-IR results were consistent with all these findings. The NMR results further showed that the CaHA fraction from the manure treatment was clearly depleted in aromatic rings and enriched in nonpolar alkyl compounds, most likely fatty acids, compared to the other two fertilizer treatments. Selective spectra further show strong indications of enhanced peptide contributions in the manure CaHA, consistent with the improved soil N supply associated with the manure treatment. The peptide enrichment was partially masked in unselective spectra by a simultaneous decrease in overlapping signals for OCH3 and COO groups that are associated with aromatic components, demonstrating the improved accuracy of the selective spectral-editing NMR techniques.