HOW TO QUANTIFY CONTAMINATION OF ORGANIC LITTER BAG MATERIAL WITH SOIL

The litter bag method is often used to study different aspects of deco mposition of organic matter in soil or on the soil surface. Deposition of surrounding soil into the litter bags makes determination of decom position rates of organic matter and its nutrients particularly diffic ult. This contamination has to be removed or determined for subsequent correction of measured results. A common method to quantify soil cont amination of litter bag material is the determination of ash residues of organic matter, soil, and sample material. Later on, data like mass losses can be corrected for the contamination. For straw samples with predefined soil contaminations (10 % to 60 % soil in dry weight) we e valuated the effects of grinding and subsampling on the estimation of soil content, where ash residues are used as a marker to identify soil . The possibility of using element contents (SiO2, Al, Fe, and Pb) of litter bag material as internal standards to calculate soil contaminat ion was also tested. Calculation of soil contamination with internal s tandards from element analysis is generally possible. Results are comp arable to the ones using ash residues. The aluminium content was the m ost appropriate marker of soil in straw-soil samples. Subsampling caus es large errors in determination of soil content in litter bag samples . Errors can be reduced using subsamples from homogenized (ground) sam ples or using the whole litter bag sample to determine ash residues.