| Eucalyptus urophylla×Eucalyptus grandis(E.urophylla ×E.grandis)plant species are strong adaptability,rapid growth and barren tolerance.Age groups of E.urophylla ×E.grandis are imperative on physicochemical properties and soil quality index,which are mainly formed due to decomposition rate and other factors that create heterogeneity of the soil environment and help to maintain the physical and chemical properties of soil.However,the long-term and large-scale pure forest management of E.urophylla ×E.grandis planation leads to soil quality index decline effectively when E.urophylla×E.grandis grows up.In recent years,a series of studies has focused on the effects of age groups of E.urophylla×E.grandis on various soil properties across different soil depths and topographical factors.However,the results are controversial and don’t provide complete insights into the effects of E.urophylla ×E.grandis on soil physicochemical properties and soil quality index.Therefore,based on the preliminary investigated work from 2018 to 2020,soil selected(0-40 and 40-100 cm)E.urophylla×E.grandis plantations of varying ages were selected as research objects to better understand the effects of E.urophylla×E.grandis on soil physicochemical properties and soil quality index across different soil depths and topographical factors.For the convenience of the study,the plantation was divided into 5different age,namely Young forest stand age(Ag1),immature forest stand age(Ag2),near mature forest stand age(Ag3),mature forest stand age(Ag4)and over mature forest stand age(Ag5).The physicochemical properties and soil quality index under different age groups of E.urophylla×E.grandis were studied.The results are displayed as followed:(1)Soil physical properties including soil bulk density,total porosity,capillary porosity,saturated and capillary water holding capacity and field capacity were significantly different among various age groups of E.urophylla×E.grandis(P < 0.05)except soil non-capillary porosity(P < 0.05).The soil bulk density of Ag3(7%)was significantly lower than other age groups of forestlands under soil layer(0-40 cm).The total porosity of the soil,capillary porosity,saturated and water holding capacity of soil and field capacity were significantly affected by the age groups of E.urophylla×E.grandis and were significantly higher at Ag3.(2)Soil chemical properties such as soil organic matter(SOM),Soil Available nitrogen(SAN),Soil Available Phosphorous(SAP),Soil Available potassium(SAK),Soil Available Boron(SAB)significantly affected by age groups of E.urophylla×E.grandis and showed different trends across studied age groups in bulk soil layer(0-40 and 40-100 cm).The SOM was significantly higher at Ag3 than all other age groups.The soil available nitrogen contents of Ag2 were significantly higher in 0-100 cm soil than other forestland,however,the differences were not significant among Ag2,Ag3,and Ag4.Soil available Phosphorus was significantly higher at Ag5 than all other age groups of E.urophylla×E.grandis forestland.The trend of available phosphorous in 0-100 cm soil represented as Ag5 >Ag1 > Ag3 > Ag2 > Ag4.The soil available potassium of young forestland(Ag1)was significantly higher than other age groups.However,the soil available potassium decreased along increasing age group up to Ag3 and then increased in Ag4 and Ag5.The soil available boron was significantly higher at Ag3 in a unimodal pattern,increasing from young age to Ag3 and then decreasing with age.(3)PCA analysis showed that physical properties are correlated to each other,the bulk density was significantly positively correlated with p H and CC and negatively correlated to TP and CP.(4)Soil quality index was significantly affected by the different age groups of E.urophylla×E.grandis.The soil quality in 0-40 cm layer of soil across various age groups of E.urophylla×E.grandis was affected.The SQI of Ag2 was significantly higher as compared to other ages.The soil quality index of over mature forestland Ag5 age groups was significantly lower than other age groups.Similarly,the SQI under 40-100 cm of soil layer showed similar results,except near mature forestland(Ag4)soil quality index,which was significantly lower than the Ag2.The relation between the soil quality index and aspect of slope showed significant correlation.The SQI of south aspect was significantly lower as compared to other aspects and the SQI of flat aspect of slope was significantly high under both layers of soil.We concluded that different age groups of E.urophylla×E.grandis across different soil depths(0-40 cm,40-100 cm and 0-100 cm)significantly affected the soil physicochemical properties and soil quality index,which indicates an influence of the age groups of E.urophylla × E.grandis under different layers of soil.In addition,the SOM,soil p H and different topographical aspects seem to influence soil available nutrients,saturated and capillary water holding capacity of soil and soil quality index in accordance to the E.urophylla×E.grandis age groups and soil layers.The changes of soil quality of E.urophylla×E.grandis plantations were compared between different growth ages.It provided data support and theoretical basis for the rotation logging cycle and soil quality improvement of E.urophylla×E.grandis. |
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