Eldor A Paul, Sherri J Morris and Michelle L Haddix
Colorado State University, Bradley University
Presented at the All Scientist Meeting (2015-04-15 to 2015-04-16 )
The soil at KBS is its most important, natural recourse. Its soil organic matter and biota reflect its climate, pedological controls , vegetation, soil biota and management. In this presentation, we focus on the organic matter characteristics that must be understood to understand and model the treatments and interactions on this site. The KBS soil shows a 4 fold increase in 14C age with depth with the non –acid-hydrolysable C, representative of the even older old C, accounting for 23 to 56% of the SOC. The C:N ratio decreases from LF (intra aggregate- light fraction) through inter aggregate(>53µmPOM) to the silt (2-53µm) and clay (<2 µm) as decomposition proceeds and clays interact with amino compounds. All SOC fractions, of the cultivated soils, contain both new (corn) and old (forest) SOC with less corn C in finer fractions but least in silt, which in this soil is also the oldest fraction. The relationship between 13C MRTs and those from 14C carbon date, developed for corn belt soils including KBS, is: 14C MRT= 176 (13CMRT)0.54. Pyrogenic C (charcoal), considered to be resistant to decomposition, exists in all fractions especially the silt and clay and can account for some of the high ages associated with these fractions. Grain crops produce more belowground C, per unit basis, than the poplars but the poplars have higher overall SOC and more mycorrhyzal fungi. MiDIR spectra of KBS-cultivated soil gives an estimate of the functional groups of the soil organic matter as well as the mineral matrix. The OH, NH, and aliphatic-absorbance bands in the LF fraction are indicative of carbohydrates and amino compounds in plant residues. Fatty acids and phenolics accumulate in the silt although the method of their protection is not known. Clays which contain the most SOC per unit basis have low C:N and show a high peak in the protein -amide absorbance range. Pyrolysis, molecular beam -mass spectrometry, which shows differrence in % of total ion intensity for each of the mw/mz peaks, produced on pyrolysis and separated on a mass spectrometer, shows a large number of statistically, different peaks between the native and cultivated soil. Cultivation, which removed 38% of the C, reduced peaks associated with lignin, cellulose and plant pectins, but increased peaks associated with glycine, alanine and lipids, especially ergosterol a fungal sterol. Pyrolysis of the incubated, native soil, where incubation had resulted in a 17% loss of the original SOC showed a fairly uniform attack on all the SOC contituents. Decreases were noted in peaks representing carbohydrates and lignin-phenols while N coumpounds increased during incubation . The undestanding of the chemistry and dynamic of the KBS soil under different management practices is helping us interpret the effects of mangement and the reponses to global change.
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