农牧交错带开垦年限对土壤理化特性的影响

Effects of a conversion from grassland to cropland on soil physical-chemical properties in the agro-pastoral ecotone of Inner Mongolia:analysis of a 50-year chronosequence

为研究农牧交错带天然草地转变为农田后,开垦年限对土壤理化特性的影响,按照邻近样地的取样原则,于2007年10月选择位于内蒙古东部农牧交错带太仆寺旗的天然草地和邻近的6个不同开垦年限的农田样地(垦殖年限为5、10、15、20、35、50a)作为研究对象分析其土壤理化性状。结果表明:在0～30cm土层中,天然草地转变为农田后,开垦年限对土壤养分含量和物理性状均有显著影响。土壤的有机碳含量、全氮含量、速效钾含量均随农田开垦年限的延长而降低,草地土壤的养分含量最高。与天然草地相比,0～10cm土层,有机碳含量分别下降36%、47%、43%、57%、68%、68%;速效钾含量分别下降33%、55%、39%、65%、60%、40%。开垦年限对土壤物理性状也有明显影响,草地土壤的粘粒含量最高,砂粒含量最低;开垦年限越长的农田,土壤砂粒含量越高,粘粒含量越低;农田土壤的容重显著高于草地,随农田开垦年限的延长,土壤容重增加;而土壤pH值显示降低趋势。研究表明在研究区域天然草地具有较好的土壤养分保持能力,开垦年限越长越易导致土壤养分的缺乏和土壤的酸化和沙化,影响整个农牧交错带生态系统的稳定性和持续性。

The study investigated the long time effect of a conversation from grasslands to croplands on soil physical-chemical properties in the farming-pastoral ecotone of Inner Mongolia using direct field samplings. We determined a land use history for the 1955—2002 from field survery. This land use history was used to build a chronosequence of cropland sites with a different age since the conversation from grassland. Results showed that 50 years of reclamation induced a reduction of soil organic carbon （SOC） content,total nitrogen （TN） content,soil available kalium content,pH levels,clay content and soil bulk density. It was founded that there was clear dependency of soil properties （dissolved organic carbon content; soil available kalium content; pH levels; clay content and soil bulk density） on cropland age. It was expected that this research would provide information for suitably using land and avoiding environmental degradation.