人为干扰对黄土高原子午岭油松人工林土壤物理性质的影响

Effect of Human-induced disturbance on physical properties of soil in artificial Pinus tabulaeformis Carr.forests of the Loess Plateau

研究了放牧、收集枯落物及清灌等人为干扰活动对黄土高原于午岭油松林土壤结构及抗蚀性的影响。结果表明，随人为干扰强度的增加，0～50cm土壤中砂粒含量比无干扰时分别增加了11.83％、37．80％和51．60％；粉粒下降了8．16％、11．83％和15．55％；粘粒下降了8．10％、20．84％和30．72％，土壤表现出粗骨化趋势；〉0.25mm水稳性团聚体含量比无干扰林地分别下降了16．59％、43.12％和61．13％。〉1．0mm的团聚体含量仅为无干扰林地土壤的27．78％和24．34％，1．0—0．25mmm的团聚体下降幅度较小；〉0．05mm微团聚体的比例分别下降了19．39％、32．62％和33．47％。而〈0．05mm微团聚体所占比例随干扰程度的增加而大幅度上升。土壤容重增加了0．11-0．41g／cm^3。土壤总孔隙度分别降低了13．64％、25．47％和39．14％，毛管孔隙下降了7．79％、11．54％和29．32％，非毛管孔隙下降了28．47％、60．79％和64．08％。说明表层土壤非毛管孔隙对人为干扰更为敏感。最大持水量分别下降23．42％、37．15％和52．92％；毛管持水量下降33．79％、43．01％和52．22％；自然含水量下降31．03％、39．34％和46．28％。饱和持水量下降16．14％、28．80％和49．68％；田间持水量下降了12．39％、33．92％和47．47％；土壤有效水含量下降了9．55％、20．55％和58．91％。土壤前3min初渗率下降了38．74％、51．45％和63．23％；稳渗速率下降了54．06％、71．63％和84．10％，相应地受人为干扰林地前30min累计人渗量也较未受人为干扰林地土壤分别低48．15％、65．93％和73．35％。饱和导水率较对照下降了8．73％、33．33％和51．00％。土壤的结构系数。由79．12％下降到27．32％。团聚度由59．48％下降到11．11％，分散率上升了l倍多，分散系数上升了4倍多。土壤枯落物层及有机质的减少是引起土壤物理性质恶化的主要原因，其次是放牧和踏实等活动。

The effects of grazing, litter collection and shrub clearance on soil structure and ant-erodiblity were investigated in artificial Pinus tabulaeformis Carr. forests of the Loess Plateau. Results showed that compared with those in undisturbed soil, the sand grain contents in 0 - 50 cm soil with the human disturbances of increasing intensities increased separately by 11.83%,37.80% and 51.60%, the contents of silt reduced separately by 8.16 %, 11.83 % and 15.55 %, the contents of clay decreased separately by 8.10%, 20.84% and 30.72%, which illustrated that the soil tended to become coarsen; compared with the content of water stable aggregates in undisturbed forestland, the contents of water stable aggregates of 〉 0.25 mm decreased separately by 16.59%, 43.12% and 61.13%, the contents of water stable aggregates of 〉 1.0 mm are separately 27.78% and 24.34% that of in undisturbed forest land ; the contents of water stable aggregates of 1.0 - 0.25 mm declined to an smaller extent and the proportions of micro-aggregates decreased separately by 19.39%, 32.62% and 33.47%, while the proportions of microaggregates of 〈 0.05 mm greatly increased with increasing disturbance intensity. The bulk weights of soil increased by 0.11 - 0.41g/cm^3. The total porosity decreased separately by 13.64%, 25.47% and 39.14% and the capillary spaces decreased separately by 7.79%, 11.54% and 29.32%, and the non-capillary spaces decreased separately by 28.47%, 60.79% and 64.08 %. It was shown that the non-capillary space of topsoil is more sensitive to human disturbance. The highest soil water holding capacities decreased separately by 23.42%, 37.15% and 52.92% and the water-holding capacities by soil capillary reduced by 33.79%, 43.01% and 52.22% ; the natural water contents dropped drown separately by 31.03%, 39.34% and 46.28% and the saturation moisture capacities reduced separately by 16.14%, 28.80% and 49.68% ; the field water holding capacities decreased separately by 12.39%, 33.92% and 47.47%, and the content of available soil water reduced separately by 9.55%, 20.55% and 58.91%. The initial infiltration rates in the first three minutes decreased separately by 38.74%, 51.45%, and 63.23% and the stabilized infiltration rates dropped separately by 54.06%, 71.63% and 84.10%, so that the accumulative infiltration in the initial three minutes were 48.15%, 65.93% and 73.35% separately lower than in undisturbed forestlands. The saturated hydraulic conductivities decreased separately by 8.73 %, 33.33 % and 51.00% compared with that in the control. The structure coefficient of soil declined from 79.12 % to 27.32 %, the aggregations fell from 59.48 % to 11.11%, the dispersion rations were more than one times higher and the dispersion coefficients were more than four times higher. Decrease in litter amount and organic matter in soil were the major reason resulting in deterioration in soil physical properties and the grazing and trampling followed.