Labile fractions of soil organic matter, their quantity and quality

Abstract

The objective of the present paper is to contribute to the evaluation of quantity and quality of non-humified part of soil organic matter (SoM). in samples of soil organic matter from the humus profile of Šumava forest soils and forest meadows, taxonomically designated as mor and moder forms, the fractions of labile soil carbon C cws , C hws , C PM and fraction of stable carbon represented by carbon of humus acids C Ha and C Fa were determined. organic matter of samples was fractionated according to the degrees of hydrolyzability by two different methods in particle-size fractions of 2.00-0.25 mm and < 0.25 mm. The quality of labile fraction C hws was expressed on the basis of reaction kinetics as the rate constant of biochemical oxidation K bio and rate constant of chemical oxidation K chem of the first order reaction from a reduction in the concentration of C-compounds. The highest values of labile forms of carbon were determined in samples with the least favorable conditions for transformation processes of SoM, and these samples also had the highest content of labile forms in hydrolyses by both methods and the most labile fractions at the same time. The degree of SoM humification was strictly indirectly proportional to the lability of SoM and its hydrolyzability. The quality of labile fraction C hws can be expressed by both K bio and K chem while the sensitivity of K bio is higher but the reproducibility of K chem is better. K bio corresponds with the degree of SoM transformation, K chem with the proportion of C PM in total C ox .

Anaerobic degradability of organic matter of cattle faeces and a possibility of its utilization

“…Any organic matter of natural origin has its labile and stable fractions (Kolář et al, 2009a). In both these groups of fractions there are anaerobically degradable fractions to which all labile fractions also belong (Kolář et al, 2010).…”

Relationships between quality and quantity of soil labile fraction of the soil carbon in Cambisols after liming during a 5-year period

“…The quality of C hws fraction was determined by the rate constant of its biochemical oxidation k bio (Kolář et al 2009). …”

“…TirolPadre and Ladha (2004) attempted to determine the real quality of labile SOC by measuring the kinetics of SOC oxidation with 33 mmol neutral KMnO 4 at room temperature. We found out that the determination of the rate constant k chem of this oxidation showed excellent reproducibility but it corresponded to the proportion of C PM in total C ox rather than to the degree of SOC lability (Kolář et al 2009). This is the reason why we prefer to express the quality of SOC labile fraction by the rate constant of biochemical oxidation k bio of C hws fraction derived from the kinetic study of several determinations of biochemical oxygen demand during 20 days (Kolář et al 2006(Kolář et al , 2009.…”

“…We found out that the determination of the rate constant k chem of this oxidation showed excellent reproducibility but it corresponded to the proportion of C PM in total C ox rather than to the degree of SOC lability (Kolář et al 2009). This is the reason why we prefer to express the quality of SOC labile fraction by the rate constant of biochemical oxidation k bio of C hws fraction derived from the kinetic study of several determinations of biochemical oxygen demand during 20 days (Kolář et al 2006(Kolář et al , 2009. k bio is more sensitive to the degree of SOC lability but because it is determined from biochemical oxidation its reproducibility is worse than in k chem .…”

“…The ratio of microbial biomass carbon to total organic carbon C MIC :C org is considered as an important indicator of soil microbial activity. The labile fraction of SOM is described in a very different way (Kolář et al 2009). …”