The Characteristics Of Aggregates Structure In Black Soils Of Northeast China

Soil aggregate could physically protect soil organic carbon(SOC), and it is the most important mechanism of soil C sequestration.Aggregate structure is the product of the soil repeated reunion, and itsstructural feature decides the capacity of soil C sequestration in a longterm. It has been documented that conservation tillage assists inenhancing soil aggregate stability and C sequestration. For black soils ofNortheast China, what’s the internal structure of soil aggregate? Howdoes conservation tillage affect the structure of soil aggregate, andthereby affect C sequestration? Above questions are unclear. Hence,based on the long-term trial of conservation tillage established in Blacksoils of Dehui, Jilin provice in2001, and native and cultivated soils fromthe Black Soil Zone, using a variety of research methods to analyze themicrostructure characteristics of0-30cm undisturbed soil column and1-2mm soil aggregates under conservation tillage practices, and thereby toevaluate the effects of the conservation tillage practices on soil structurewith different pore structure parameters and morphological characteristics.The main results of the research were as follows:(1) The inter-annual responses of SOC contents in the plow layer fordifferent tillage practices were different. The SOC contents of ridgetillage and mouldboard plough were higher than no-tillage in the tenyears time, especially ridge tillage. But the SOC contents for ridge tillage and no-tillage were significantly higher than for mouldboard plough at0-5cm depth. The proportion of>0.25mm aggregates in0-5cm and20-30cm layers were the highest under ridge tillage. Compared withmouldboard plough, the proportion of>0.25mm aggregates wassignificantly higher in0-5cm layer under no-tillage, but in the20-30cmlayer it was lower under no-tillage than under mouldboard plough.(2) The total porosity and macroporsity of0-30cm undisturbed soilcolumn had the same change trend, that is, soil porosity decreased withsoil depth increasing, and below20cm layer, the change approached auniform trend. For the microstructural morphology of the undisturbed soilcolumn, no-tillage practice had the least number of pores, but the poreswere mostly macropores formed by soil fauna (especially earthworms)and crop residues; Mouldboard plough had the largest number of pores,and the mesopore was the most. Ridge tillage, the pores were mainly theconnectivity tubular pores formed by the crop roots.(3) The surface micromorphology qualitative aspect of1-2mm soilaggregates: The native soil aggregates presented closely flaky aggregatedstructure, slightly more clay minerals, loose structure, and the poremainly lies in the interior of aggregate. Soils under mouldboard ploughpresented a transition of aggregated structure and skeleton structure, morecoarse particles, less debris particles, loose structure. Soils under ridgetillage presented closely aggregated structure, aggregated particles uniformly distributed, and dense structure. Soils showed closelyaggregated structure, more fine particles, less debris particles, and densestructure under no tillage. Consequently, conservation tillage significantlyimproved the structure of soil aggregates, increased aggregation andimproves the potential of C sequestration, especially ridge tillage.(4) The internal microstructure quantitative aspect of1-2mm soilaggregates: The porosity, the number of pores, the number of pore throatswithin aggregates of native soils were higher than under ridge tillage,no-tillage and conventional tillage. Compared with conventional tillage,conservation tillage increased the number of pores, the specific area andthe number of pore throats. The internal micro-morphology aspect of soilaggregates: In native soils, aggregates had a large number of pores whichcontain the connectivity large pores formed by the plant roots, andpresented a complex porous structure. The structure of soil aggregatesunder conventional tillage had less number of pores. Compared withconventional tillage, conservation tillage increased aggregation within thesoil aggregates and the number of pores, and thereby improved theaggregate structure.