Characterization of soil organic matter from a sandy soil in relation to management practice using FT-IR spectroscopy

Previous results from differently fertilized long-term field experiments on a sandy soil suggested that the chemical composition of soil organic matte r (SOM) is affected by fertilization. The objective of this paper is to con firm this finding for a site with higher soil-clay contents. Four combinati ons of different fertilizer treatments at long-term field experiment locate d at a sandy loam were selected: liquid manure (LM), liquid manure+N (LM+N) , straw+N (S+N) and mineral nitrogen only (N). Soil organic matter was extr acted using sodium pyrophosphate solution at pH of 10 and hot water. The ex tracts were analyzed using Fourier-Transform infrared spectroscopy. The res ults indicate that the composition of SOM from the hot water extracts did n ot show significant differences while the sodium pyrophosphate extracted SO M is affected by the type of fertilization. Soil samples fertilized with LM +N and S+N show the highest intensity of the carboxyl band. This can be exp lained by the fact that the combination of S+N fertilization with green man ure leads to an enrichment of carboxyl groups in SOM. Differences between t he band intensities of the treatments for the SOM samples are, however, not as distinct as for the sandy soil samples. This is possibly a result of th e higher clay content and lower age of the long-term experiment at the sand y loam site. The intensity of the carboxyl band of the SOM is correlated wi th the cation exchange capacity of the soil samples. The composition of SOM may, in addition to the SOM content, be used for studying quantitative eff ects of different management practices or even land use changes on soil pro perties.