Climate Change and Mitigation REU - Summer 2014

Results

 

Analysis of TOC indicated higher OC concentrations in HM plots compared to HF and C plots. The TOC data was compared to the ICP-OES analysis of hydroxylamine extractants. This showed a statistically significant correlation at 0-5 cm depth between TOC and amorphous Mn, as well as between TOC and acid hydroxylamine extractable Fe and Al. For the deeper depth of 5-15 cm, there was no such significant correlation.

 

 

 

 

 

 

 

 

 

 

 

 

 

Fig. 1. Relationship between TOC and acid hydroxylamine extractable Mn, Fe, and Al at 0-5 cm depth.

 

The Al and Fe concentrations were compared to data that was previously attained with the acid ammonium oxalate method to test for accuracy. The results between the two methods significantly correlated (R-Squared= 0.8) for Fe but not for Al. This could be due to the extraction method used. Iron concentrations for both mehtods were similar and indicated evidence of possible C sequestration in the soil. Most likely via chemical stabilization and/or physical protection. The strongest correlation for amorphous Mn and acid hydroxylamine extractable Fe and Al was in NT-mesoaggregates (2000-250 µm), which may indicate dominating physical protection by the minerals.

 

Proof of higher Fe and Al concentrations in the high manure/compost plots was also presented, providing information on organic material and mineral deposition and on how the fertilizer treatment of soils in temperate agroecosystems may impact C sequestration. No such evidence was present for Mn concentrations but there were high Mn concentrations in macroaggregates for both depths, more specifically in the 2000-250 µm aggregate fraction. This could be an indication of amorphous Mn impacting soil aggregation and indirectly enhancing C sequestration, mainly via physical protection of the aggregates.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Similar results are seen with acid hydroxylamine extractable Fe and Al concentrations in soil, where NT plots have an overall greater concentration in comparison to the CT plots.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Analysis of DOC showed greater OC concentrations in the 250-53 µm aggregate size, especially in the NTHM plots, indicating possible enhancement of OC-mineral interactions in the NTHM plots.

 

Discussion

 

The binding of microaggregates into stable macroaggregates may be facilitated by the active minerals in the soil as well as the organic matter present and the biological activity around this organic matter (Huang et al. 2002). This fact accounts for why the highest concentrations for OC, amorphous Mn and acid hydroxylamine extractable Fe and Al were observed in the NTHM plots. Minimal disturbance management and continuous addition of organic materials are known to aid in building stable aggregates. The fact that we see significant positive correlations between TOC and the acid hydroxylamine extractable minerals means that there is possible chemcial stabilization and/or physical protection of SOC.