Functional analysis of soil organic matter as affected by long-term manurial treatment

The composition of soil organic matter (SOM) is influenced by land use and fertilization. We studied changes in the SOM in a long-term field experimen t on a sandy Podzoluvisol. The control plot and four combinations of manuri al treatments of the experiment were selected: one with mineral fertilizer only and three combinations of organic manure with mineral fertilizer: catt le manure +NPK, cattle manure +PK and straw + NPK. The SOM was extracted by sodium pyrophosphate solution (pH = 10) and hot water (100 degrees C). The extracts were analysed by Fourier-Transform Infrared (FT-IR) spectroscopy and gel permeation chromatography (GPC). The FT-IR spectra from sodium pyro phosphate extracts indicate that composition of SOM is indeed influenced by different fertilization. The C=O band at 1710 cm(-1) in the samples of the plots fertilized with cattle manure has the highest absorption intensity, whereas the material from the plot fertilized with straw + NPK has the leas t intense. The GPC analyses of the extracts showed that adding cattle manur e +NPK increased the molecular size of SOM in comparison with the control p lot. The analysis of hot-water extracts with FT-IR showed no significant di fferences in functional groups, but GPC chromatograms distinguished feature s in molecular size distribution. Fertilization with cattle manure increase d the molecular size of the SOM in comparison with the control, but the dif ferences in content of carboxylic groups and molecular weight were detected in sodium pyrophosphate extracts only.