The Influence of Different, Long-Term Fertilizations on the Chemical and Spectroscopic Properties of Soil Organic Matter

Abstract

Currently, revealing soil management strategies that store the maximum atmospheric CO2 in the soil is a major issue. This is best explored by investigating long-term experiments, like the Skierniewice (Poland) field trial, established in 1921 on sandy loam Luvisol. In this trial, the variants analyzed included control (CON), manure (MAN), legumes (LEG), and manure + legumes (MAN + LEG). Soil samples from the A horizon were analyzed for total organic carbon (TOC), carbon content of humic acids (HA), fulvic acids (FA), and humin (HUM), as well as for spectroscopic properties of bulk soil and isolated HUM. Compared to the control, all other treatments caused an increase in TOC, while the application of manure resulted in an increase in the amount of HUM. Legume application caused an increase in UV-Vis absorbance and fluorescence emission. Thermochemolysis and gas chromatography/mass spectrometry showed that HUM was enriched in carbohydrates in almost all pairs of soil and HUM. Compared to the CON, the largest proportion of carbohydrate in HUM was found in MAN + LEG. Different long-term soil management strategies not only altered TOC, but also, surprisingly, the chemical composition of HUM, which is considered to be particularly stable and a long-term sink of atmospheric carbon.