Investigation On Chemical Nature Of Physically-seperated Labile Organic Matter Pools Of Farmland Soils

Labile organic matter pools are the fine indicators of soil quality, and are more sensitive than soil organic matter (SOM) by changes in short-term management practices.Light fraction organic matter (LFOM) and macro organic matter (MOM) are both labile organic matter pools.This study aimed at investigating chemical difference between LFOM and MOM.In this study,we selected four types of soils:Irrigated desert soil, Loessial soil, Dark loessial soil and Cinnamon soil.The sites of the four types of soils are different ecological environments. Bulk soil was separated into LFOM (<1.8g ml-1);MOM (>0.05mm) was obtained from bulk soil by wet sieving and separated into LMOM (<1.8g ml-1) and HMOM (>1.8gml-1).The concertrations of neutral sugars and amino sugars of LFOM,LMOM and HMOM were determined by gas chromatography as aldononitrile acetates derivatives.Some main results were obtained.1.Light fraction organic carbon (LFOM-C) and nitrogen (LFOM-N), light macro organic carbon(LMOM-C) and nitrogen (LFOM-N) and heavy macro organic carbon (HMOM-C) and nitrogen (HMOM-N) concentrations of Irrigated desert soil were significantly higher than other three kinds of soils, respectively. Compared to Irrigated desert soil, Dark loessial soil and Cinnamon soil, LMOM-C and LMOM-N concentrations of Loessial were significantly lower, respectively. LFOM-C and LFOM-N concentrations of Irrigated desert soil, Dark loessial soil and Cinnamon soil were all lower than LMOM-C and LMOM-N, but it was adverse in Loessial soil. The C-to-N ratio of LFOM was higher than MOM (LMOM+HMOM) in all kinds of soils.2.The concertration of total neutral sugars in LFOM, LMOM and HMOM of Dark loessial soil was significantly higher than Irrigated desert soil, Loessial soil and Cinnamon soil, respectively. Compared to other types of soil,the concertration of total neutral sugars in HMOM of Irrigated desert soil was significantly lower. Neutral sugars concentration of LFOM was higher than LMOM and HMOM, respectively.(G+M)/(A+X) of HMOM was about1.5-4times than (G+M)/(A+X) of LFOM and LMOM. In HMOM,(G+M)/(A+X) of Irrigated desert soil and Loessial soil was about2-3times than Dark loessial soil and Cinnamon soil.(G+M)/(A+X) of LFOM was similar with LMOM.3.In Irrigated desert soil, Loessial soil and Cinnamon soil, the concentration of total amino sugars in LFOM was all lower, respectively, compared to Dark loessail soil.The amino sugars concentrations of LMOM in Dark loessial soil were significantly higher than other three types of soils, respectively.In Irrigated desert soil, Dark loessial soil and Cinnamon soil, the concentrations of total amino sugars of LFOM were higher than LMOM, and which was adverse in Loessial soil. GulM/GalM of LFOM was lower than LMOM in all kinds of soils.In general,LFOM and MOM are important labile OM pools, but their chemical natures are different. In LFOM, the C/N is wider, and the decomposition level of LFOM is lower than MOM.Compared to MOM, LFOM is consist of more plant-derived and bacteria-derived organic matter.