INTRODUCTION 5011 organie matt，er(OM)pl盯5 a fundamental role in the maintenanee of the main 5011 properties and regimes related not just to the 5011 fertility.The whole funetioning ofsoilsisProfoundlyinflueneed勿5011 OM，its ability to provide eonditions for Plant growth，5011 biotafu工Ictioning，reduetion of greenhouse gases，modifieation of pollutants，and maintenanee of soilp饰sieal eondition(Eswaran et al.，1993: Shevtsova et aL，201〕3:Ni et al.，2004).Therefore，maintenanee of suffieiently high levels of organie matter has been noted as a prerequisite for stead叭high Produetion levels of eroPs and sustainable a罗ieultural develop〕二ent(Hassink et aL，1997;Sun et al·，2003;Williams et al.，2005). 5011 OM eontent was noted as fairly eonstant under eertain bioelimatie eonditions and eertain eroP- ping systems(Cai e.云al.，1989).A number of papers have also reported that for agrieultural 50115 with unaltered managem‘，nt praetiees 5011 OM eontent eould reaeh an equilibrium state over time(Liang et al.，2000;Peterson(;t al.，2002:Loveland and从7ebb，2003).To reach ane卿ilibrium state(or steady- state)，5011 OM eont.:nt Could inCrease or deerease，depending on whether the original eontent was below or above the steady一state level(丫石ng and Janssen，1997:Guo ot al.，2004).However，only model or long一term experimeilts eould attain the equilibrium Value of 5011 OM.Although models of 5011 OMd梦 namies，sueh as the‘gentury Model or the Rothamsted Model，Provide a useful tool to evaluate 5011 OM dynamies(Partone艺al.，1987;Coleman et al.，1997)，as”t little data exists to test these predietions.In addition，based on their relative turnover time in the models，3nalytieal methods have not been found to separate 5011 OM fraetions(Whalen et al.，2000).At present，withe劝sting analytieal methods there 178 Y .F，YIN and Z.C，CAI 15 limited information about the study of organie matter equilibrium for agrieultural 50115. Beeause of the possibility of separating newly ineorporated，partially deeomposed plant debris(light fraetion)from organie matter absorbed on inorganie surfaees or se四estered within 5011 aggregates (heavy fraetion)，based on turnover timep场sieal fraetionation of 50115 using density seParation eould distinguish 5011 OM dynamies(Sollins ot al.，1984:Christensen，2001).Although ma叮studies about the nature and turnover of 5011 OM in llght and heavy fraetions have been made(Dalal and Mayer，1986: Whalene艺al.，2000:Swanston et al.，2002)，not mueh work has been done regarding the relationship between light and heavy fraetions of organie matter.In a Previous stud孔for agrieultural 50115 with unaltered management Praetiees over a long time an inherent relationshiP was found between light and heavy fractions of organie oatter(Yin et al.，2005). The场pothesis here was that two equilibrium states of organie matter for agrieultural 50115 under eertain bioelimatie eonditions and for eertain eroPPing systems over a long period existed，namely equilibrium of light and heavy fraetions.Thee卿ilibrium valuesoftheselightandheavyfraetionsdiffered beeause of different dominant Physieal or ehemieal Proteetion faetors.Due to the limited eapaeity for 5011 minerals，whieh proteeted organie matter in the light fraetion，the heavy fraetion of organie matter needed a shorter time to reaeh an equilibrium level.Beeause an inherent relationshiP was found to exist between light and heavy fraetions of organie matter for agrieultural 50115 with unaltered management Praetiees over a long time and the Langmuir equation eould be used to exPress the relationshiP，the main objeetive of this study was to attain the OM equilibrium value in the heavy fraetion for seleeted agrieultural 50115 using a simple density fraetionation method with the Langmuir equation. MAI，ERIALS AND METHODS S乞tea几d 50乞1 sa阴尹l乞ng The first long一term experiment at the Fengqiu State Key Agro一Eeologieal Experimental Station(350 00‘N，1140 24‘E)in Henan provinee was established in the fall of 1989 on a Fluvo一叫uie 5011(Cambisols， World Referenee Base for 5
More abstracts about the Equilibrium of Organic Matter in Heavy Fraction for Three Long-term Experimental Field Soils in Chin