Soil Structure And Erodibility Of Soil And Water Conservation Forests In Typical Black Soil Region

In order to explain the effect of different water and soil conservation forest types and the dynamic change of the same one in different forest restoration on character of soil structure and soil erodibility. Soil structural characters of different types of forests in black soil area were studied by measuring and analyzing the soil bulk density, NCP/CP, GSSI. We also investigated the effects of different stands on soil structure characters of soil water-stable aggregates, capacity of soil collapse, and organic matter content in this study were studied by measuring and analyzing. Base on this experiment, a study on 8,21,30,37 and 52-year-old larch plantations in typical black soil region was undertaken to examine soil structural characteristics and dynamic changes of plantations. The characters of soil structural and dynamic change of organic carbon in Larch Plantations were studied by measuring and analyzing the structural indicators and organic carbon content in different size aggregates.Results showed that, in 0-30cm soil, the bulk densities of Manchurian ash and Dahurian larch plantations were lower than that of Mongolian Scots pine and Korean spruce stands, Average NCP/CP of different plantations was all higher than that of abandoned land (P<0.05) increased from 59.75% to 128.82% relatively, Soil aeration and permeability were enhanced, especially in Dahurian larch plantation. Average GSSI of different plantations was higher than abandoned land too(P<0.05), with the increased range of 2.98%-4.36%. So soil and water conservation plantations can promote soil approaching ideal soil structure, Manchurian ash and Korean spruce stands performed better than the others. However they have different ways of changing three phases to be close to ideal soil three phase, or ideal soil structure, the percentage of larger size aggregates of the four stands all get increased, PA0.25 and PAD0.25 was significantly increased and decreased separately(P<0.05).Soil water stability index in stands was significantly enhanced, with 4.46-7.92 times more than that in tillage(P<0.05).Organic matter content of top soil in forest land was relatively increased from 32.6% to 62.7% compared with tillage significantly(P<0.05).Thus we conclude that soil and water conservation forests can reduce soil erodibility, especially for the Manchurian Ash plantation.During soil depth of 0-30cm in different forest age larch plantations in typical black soil region, bulk density variation among different plantations was 1.06-1.19 g·cm-3, and it could decrease obviously with plantation age increasing(P<0.05).Ratio of NCP/CP were observed between 0.03 and 0.11, only which in 37-year-old larch plantations improved significantly (P＜0.05). Values of GSSI changed from 73.19 to 95.82 with the maximum belonging to natural secondary forest. There was no significant difference of GSSI between natural secondary forest and 37-yare-old plantation, and neither was between natural secondary forest and 52-yare-old plantation. However there would be dramatically variation between natural secondary forest and the plantation with age of 8a,21a,and 30a (P＜0.05). We confirm that larch plantation can improve soil structure, but this kind of amelioration could not lastingly increase with plantation aging.37 years old larch plantation was indicated as the critical age in this study.A study was undertaken to examine soil organic carbon distribution characteristics of aggregates and dynamic changes of plantations by measuring and analyzing composition of dry aggregates, organic carbon content and organic carbon storage of different aggregate size fraction. Results showed that during soil depth of 0-30cm, the composition proportion of aggregates was distribution in shape of "∧"with decreasing size fraction. The percentage of 2-5mm size fraction accounted the largest proportion and existed significant difference from those of other size fractions (P<0.05). The organic carbon contents of all different size aggregates in topsoil, range of 32.17-48.75g/kg, were higher than those in subsoil, range of 28.82-33.53g/kg. Lowest organic carbon content was found in 2-5mm aggregate and which was significant different from those of other size fraction aggregates (P<0.05). The changing trend of organic carbon storage during soil profile was very similar to that of dry aggregate distribution among larch plantations with different ages. The soil organic carbon storage in topsoil was higher than that in subsoil. Organic carbon storage in 2-5mm aggregate was also the highest in all size fractions. we concluded that changes of organic carbon storage in soil aggregates were mainly determined by the composition of soil aggregates, but for the organic carbon contents. It presents a theoretical basis for further researches and assessments on SOC of larch plantation.