草场管理措施及退化程度对土壤养分含量变化的影响

Characteristics of soil nutrient distribution in high-altitude meadow ecosystems with different management and degradation scenarios

  • 摘要: 以不同管理措施和不同退化梯度的高寒草地土壤为研究对象,分析了两个序列的高寒草地不同土壤层次(0~20cm、20~40cm、40~60cm)中各种养分分布特征并探讨了管理措施和草场退化对高寒草地土壤的影响。结果表明:天然放牧草地经过围栏和翻耕措施后,土壤有机质、全N、全P含量明显升高,土壤速效氮、磷含量也得到明显上升。在20~40cm和40~60cm土层土壤存在类似的变化规律,但由于土层加深,受地表植被的影响减弱,变化规律不明显 。比较退化序列草地发现,在各层土壤中,有机质含量变化总趋势是:随草地退化程度的加重,有机质含量下降;同时,土壤有机质含量随深度增加而减少;在0~20cm土层,随着草地退化程度的加重,有机质含量依次下降32.6%和52.1%。土壤中全N、全P含量变化趋势与有机质变化基本一致,全K变化趋势不明显。中度、重度退化草地与轻度退化草地对比发现,速效氮含量分别下降15.1%和28.6%,速效磷含量分别下降25.4%和59.4%。利用围栏和翻耕措施可以恢复退化草地的植被,提高土壤养分含量。但翻耕后,土壤孔隙度和通透性增强,土壤的矿化作用和淋溶作用也增强,导致了有机质的矿化损失和NO3-N淋溶损失,减少了土壤中C的积累量。同时,翻耕会破坏高寒草地固有的生草层 ,使其下面的沙质基底成为草地沙化的主要物质来源。建议在川西北亚高山区的人工草地建设中慎重选择翻耕措施。

     

    Abstract: In two high frigid meadow soil series of northwest Sichuan with different management and degeneration gradients,distribution characteristics of different soil nutrients were analyzed for three soil layers (0~20cm,20~40cm,40~60cm). The influence of management type and degradation degree on high frigid meadow soils was then discussed. Results show that soil organic matter, total nitrogen and phosphorus in natural pastures increase significantly after fencing and tillage. At the same time, available nitrogen and phosphorus contents increase remarkably. But the tendencies in 20~40cm and 40 ~60cm soil depths show a lesser magnitude due to soil layer compaction. A steady decrease in organic content is observed with the increase of meadow degrading level. With increasing depths, soil organic matter content decreases. Within the 0~20cm soil depth at increasingly aggravated degradation, soil organic content decreases by 32.6% and 52.1%.Changes in total nitrogen and phosphorus follow the above trend of organic matter, while change in total potassium is largely insignificant. Comparison with lightly degraded meadow, moderately and heavily degraded meadows own 1 5.1% and 28.6% decreased available nitrogen, 25.4% and 59.4% decreased available phosphorus. After fencing, tillage, vegetation rehabilitation is improved, degraded land soil nutrient content increases. However, tillage enhances soil penetration, mineralization and eluviation, resulting in lose of soil organic matter and NO3-N, subsequently reducing soil carbon accumulation. Further more, plowing destroys inherent grass growing soil layer leading to sand-bed becoming dominant degenerated meadow features. Thus,tillage measures should be applied prudent ially in the sub-alpine rangelands of northwest Sichuan.

     

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