Characterization of cultivation effects on soil organic matter

Abstract

Abstract Humus properties in various Ap horizons from field plots, that have been cultivated in long‐term experiments under different management conditions, were investigated by pyrolysis‐field ionization mass spectrometry (Py‐FIMS) and 13 C‐NMR spectroscopy. The results of Py‐FIMS were evaluated by correlation and principal component analysis from reproducible data sets of bulk soil samples and extracted humic substances, and allowed a distinct discrimination on the basis of humus quality and composition. The chemical subunits suitable for discrimination are the major plant constituents carbohydrates, lignin, and proteinaceous materials as well as their humification products. The contribution of these compound classes to soil organic matter decreased with the intensity of management. CPMAS and solution 13 C NMR spectra of soils and humic substances demonstrated that with more intense management, both the intensities of the phenolic region (140–160 ppm) and the aromatic region (110–140 ppm) decreased. The combination of both independent methods MS and NMR, together with microbiological and biochemical data, yields the general result that intensive soil management leads to a less active humus.