不同年龄级别皂荚树土壤肥力的综合评价

Comprehensive Evaluation of Soil Fertility for Gleditsia sinensis at Different Ages

【目的】探明不同年龄级别皂荚树的土壤肥力状况,并对其土壤质量进行综合评价,为制定适宜的古树保护策略提供科学依据。【方法】以西安市鄠邑区不同年龄级别皂荚树树冠范围内0~40 cm土壤为研究对象,采用野外调查与室内分析相结合的方法,测定土壤pH、电导率(EC)、容重(BD)、有机质(OM)、全氮(TN)、全磷(TP)、全钾(TK)、碱解氮(AN)、有效磷(AP)和速效钾(AK)含量,并运用主成分分析法对不同年龄级别皂荚树土壤质量进行综合评价。【结果】鄠邑区皂荚树土壤pH为8.03~8.88,属碱性土壤;不同年龄级别皂荚树土壤的TK含量差异均不显著;土壤BD依次为二级古树>一级古树>非古树>三级古树;不同年龄级别皂荚树土壤的EC值、OM、TN、TP、AN、AP和AK含量表现出不同程度差异,其中,非古树土壤各肥力指标含量均最低,随着树龄增加,三级古树各指标含量增加至最大,除TP和AP外,其余指标含量均显著高于一级古树。以全国第二次土壤普查分类标准为依据,皂荚树土壤TK含量均为三级标准,属中上水平;AN含量均为四级及以下标准,属中低水平;古皂荚树土壤TP、AP、AK、OM和TN整体含量较高,均为三级及以上标准,属中高水平;非古皂荚树土壤各指标含量较低,均为四级及以下标准,属中低水平。皂荚树土壤综合肥力依次为三级古树(0.771)>二级古树(0.591)>一级古树(0.584)>非古树(0.281)。【结论】鄠邑区不同年龄古皂荚树的土壤肥力呈较大差异,其中,三级古皂荚树土壤肥力优于二级和一级,古皂荚树土壤肥力优于非古皂荚树,可实行分级养护,并通过增施有机质改良土壤,提高碱解氮含量。

【Objective】The soil fertility of Gleditsia sinensis at different ages was explored and its soil quality was evaluated comprehensively to provide the scientific basis for formulating appropriate protection strategy of ancient trees.【Method】Using the 0-40 cm depth of soil in the crown range of G.sinensis at different ages in Huyi District of Xi’an City as the test objects,the soil pH,electrical conductivity(EC),bulk density(BD),organic matter(OM),total nitrogen(TN),total phosphorus(TP),total potassium(TK),available nitrogen(AN),available phosphorus(AP)and available potassium(AK)content were measured by field investigation and laboratory analysis,and the soil quality of G.sinensis at different ages was evaluated comprehensively by principal component analysis.【Result】The soil pH of G.sinensis was 8.03-8.88,belonging to alkaline soil.There was no significant difference in TK content in soil of G.sinensis at different ages.The soil BD followed GradeⅡancient trees>Grade I ancient trees>non-ancient trees>Grade III ancient trees.The EC value,OM,TN,TP,AN,AP and AK contents in soil of G.sinensis at different ages presented different to a varying degree.Among them,the contents of soil fertility indexes were the lowest in non-ancient trees,while the indexes of Grade III ancient trees rose to the highest with the increase of tree age,except TP and AP,the contents of other indexes were significantly higher than those of Grade I ancient trees.Based on the classification standard of the second national soil survey,the content of soil TK was the third-level standard,belonging to the medium-upper level,while the content of AN was the fourth-level standard or below,belonging to the medium-lower level.The contents of TP,AP,AK,OM and TN in the soil of ancient G.sinensis were all high and above the third-level standard,belonging to the medium-higher level,while the contents of non-ancient trees were low and below the fourth-level standard,belonging to the medium-lower level.The soil comprehensive fertility of G.sinensis followed Grade III ancient trees(0.771)>GradeⅡancient trees(0.591)>Grade I ancient trees(0.584)>non-ancient trees(0.281).【Conclusion】The soil fertility of G.sinensis at different ages in Huyi District showed a great difference.The soil fertility of Grade III ancient trees was better than that of GradeⅡand Grade I ancient trees,and the soil fertility of ancient trees was better than that of non-ancient trees.Therefore,it is suggested that graded maintenance can be carried out,and available nitrogen content and soil can be improved by adding organic matter.