| With the continuous development of the sub-center(Tongzhou district)of Beijing,the limited soil resources have changed from the original agricultural needs to mainly meet the needs of residents for sightseeing,leisure and living.Because of the different types of cultivated land in the past,the soil properties vary greatly.It is the key to manage the limited soil resources in Tongzhou district to grasp the soil fertility characteristics and influencing factors of different greening sites in the region and evaluate the soil fertility.For this purpose,we selected the soil types of centralized landscaping,such as orchards,nurseries,urban green spaces and afforestation projects,respectively,with 30,38,21 and 20 sample points.Soil was collected at depths of 0-20cm,20-40cm and 40-60cm,and its physicochemical properties were determined.Single factor index and Nemero comprehensive index were used to evaluate soil fertility.The correlation and principal component analysis were carried out for each fertility index,and the contribution of different indexes to soil fertility was evaluated by principal component analysis.The following conclusions are drawn:(1)In different greening sites,the mean value of soil p H was 8.09,the bulk density was 0.54 g·cm-3-1.81 g·cm-3,0.76 g·cm-3-1.81 g·cm-3,1.25 g·cm-3-1.93 g·cm-3,0.74 g·cm-3-1.90 g·cm-3,the organic matter was 1.70 g·kg-1-46.68 g·kg-1,1.03 g·kg-1-31.30 g·kg-1,5.44 g·kg-1-46.59 g·kg-1,2.03 g·kg-1-54.56g·kg-1,and the total nitrogen was 0.19 g·kg-1-3.11 g·kg-1,0.13 g·kg-1-1.25 g·kg-1,0.27 g·kg-1-1.10 g·kg-1,0.10 g·kg-1-1.27 g·kg-1.The mean minimum contents of alkali-hydrolyzed nitrogen,available phosphorus and potassium were 16.70 mg·kg-1,13.21 mg·kg-1 and 107.51 mg·kg-1,respectively.The cation exchange capacity was more than 10 cmol·kg-1,which was at a medium high level.In different soil layers,the available potassium and alkaline nitrogen in orchards and urban green spaces were larger and the p H was lower.However,the content of available potassium and available nitrogen was lower and the p H was higher in nursery and afforestation projects.The content of total nitrogen and available nitrogen decreased with the increase of soil depth,and the content of available potassium decreased first and then increased.With the increase of soil depth,the organic matter of orchards,nurseries and afforestation projects decreased,the cation exchange capacity first decreased and then increased.While the organic matter content of urban green space first decreased and then increased,and the cation exchange quantity decreased.The bulk density of orchards,urban green spaces and afforestation projects increased,and the available phosphorus content decreased.(2)The soil organic matter and total nitrogen of the four types of landscaping land were at a low level.The available nitrogen at more than 75%of the monitoring sites is at level 4 or below,and the content is low.The contents of available phosphorus and available potassium are mostly in grade 4 and above,and the contents are all high.The comprehensive soil fertility indexes of orchards,nurseries,urban green spaces and afforestation sites were 0.61-0.96,0.59-0.71,0.61-0.99 and 0.53-0.79,respectively,and the comprehensive index of soil fertility 0-60cm in orchards and urban green Spaces was larger.The composite index of each forest land decreased with the increase of soil depth.In orchard,the comprehensive soil fertility index of 0-20cm was 0.92,which means the soil fertility was at a medium level.The comprehensive fertility index of the remaining soil layers of each forest land is less than 0.9,it indicates that the comprehensive fertility of soil is at the barren level.(3)Through correlation analysis,it was found that organic matter in 0-20cm soil had a strong positive correlation with alkali-hydrolyzed nitrogen,and in 20-40 cm and 40-60cm soil,organic matter,total nitrogen,available nutrients and cation exchange capacity had a strong correlation,with a maximum correlation coefficient of 0.86.The three layers of soil organic matter,total nitrogen,available nutrients and cation exchange capacity were positively correlated.Principal component analysis results showed that the main influencing factors of topsoil in orchards and urban green spaces were:organic matter and total nitrogen,and 20-40 and 40-60cm soils were total nitrogen and organic matter.In nursery,soil fertility of 0-20,40-60cm was mainly affected by available potassium,and organic matter had the greatest impact on 20-40cm soil.The main factors affecting soil fertility of afforestation projects were alkaline nitrogen,cation exchange capacity and organic matter.The factors that had the least effect on soil fertility of the four forest lands were soil p H and bulk density.(4)It is suggested that in the management process of the following four greening lands,it is necessary to make full use of the accumulated phosphorus and potassium in the soil,while paying attention to the application of organic fertilizer.Urban green space,afforestation projects need more loose soil to reduce soil bulk density,improve soil physicochemical properties,increase soil fertility and provide a good growing environment for vegetation. |
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