Evaluation Of Soil Fertility For Typical Urban Forests And Green Spaces In Harbin And Changchun City

Changchun and Harbin are important center cities in northeast China.Urban soil fertility is an important factor for urban forests and green spaces.There has been no comprehensive evaluation of soil fertility at the city scale upon which to base greening practices in Changchun and Harbin City.These soil diagnosis-oriented measures could promote better development of urban forests and green spaces,and our study provided an example of urban soil fertility evaluation for improving soil-based urban vegetation ecological services for resident life.Glomalin related soil protein?GRSP?can improve soil quality and recover degenerated soil,fewer studies have focused on the urbanization induced variation of GRSP.It is beneficial to research GRSP's relationship with the soil fertility.Therefore,Changchun and Harbin cities were selected as research regions,and soil fertility of two cities were evaluated.Moreover,we analyzed the relationship between GRSP and soil fertility in Harbin city.This study reached the following results:With reference to the 6-grade criteria from the 2nd National Soil Survey,soil organic carbon?SOM?in Changchun was graded as no.2?high level?with an average of 34.51 g/kg and most regions had>30 g/kg.Total nitrogen?TN?,available nitrogen?AN?,and available phosphorus?AP?were graded no.3 or higher,with an average of 1.37 g/kg,133.04 mg/kg and38.47 mg/kg,respectively.The spatial map revealed that most urban regions had TN 1-1.5 g/kg,AN 90-150 mg/kg and AP 20-40 mg/kg.Total potassium?TK?and available potassium?AK?were graded the highest?grade no.1?averaging 58.7 g/kg and 255.85 mg/kg,respectively,and most regions had 50-60 g/kg and 200-300 mg/kg,respectively,based on the ArcGIS map analysis.TP reached the mid-low level?no.4 grade?,averaging 0.51 g/kg and most regions on the spatial map had 0.4-0.6 g/kg.The pH of the urban forest soil ranged from 5.43 to 8.89,and soil bulk density was in the range of 1.11-1.62 g/cm³.Spatial distribution of the Nemorow comprehensive soil fertility index?F?revealed that most urban regions were within the 1.5-1.8range,indicating medium soil fertility overall for Changchun City?grade no.3 in the 4-grade system?.In addition,forest type-related differences were mainly found in pH,TN,TP,and TK?P<0.05?,and ring road-related urban-rural gradient differences occurred in pH,SOM,and TP?P<0.05?,whereas administrative district-related differences were found in all studied parameters,except soil bulk density,TK,and AK?P<0.05?.F differences in different forest types followed the sequence Landscape forest?LF?>Affiliated forest?AF?=Ecological public welfare forest?EF?>Roadside forest?RF?.In different administrative districts,the sequence was Lvyuan>Chaoyang>Nanguan>Erdao>Kuancheng,whereas for ring road-related F differences it was 1-ring>3-ring=4-ring>2-ring>outside 4-ring.With reference to the 6-grade criteria from the 2nd National Soil Survey,SOM in Harbin was graded as no.2?high level?with an average of 34.26 g/kg and most regions had 30-40g/kg.TN,AN and AP were graded no.3,with an average of 1.22 g/kg,124.43 mg/kg and21.45 mg/kg,respectively.The spatial map revealed that most urban regions had TN 1-1.5 g/kg,AN 90-150 mg/kg and AP<20 mg/kg,respectively.TK and AK were graded as no.2 or higher,averaging 63.23 g/kg and 134.86 mg/kg,respectively,and most regions had 50-100 g/kg,150-200 mg/kg,respectively,based on the ArcGIS map analysis.TP reached the mid-low level?no.4 grade?,averaging 0.5 g/kg and most regions on the spatial map had 0.4-0.6 g/kg.The pH of the urban soil on the spatial map had 7.5-8.5,and soil bulk density was 1.3-1.4 g/cm³.Spatial distribution of the Nemorow comprehensive soil fertility index?F?revealed that most urban regions were within the 1.3-1.5 range,indicating medium soil fertility overall for Harbin City?grade no.3 in the 4-grade system?.In addition,green space type-related differences were mainly found in all studied parameters,except AK?P<0.05?.F differences in different types followed the sequence Farmland?FL?>LF>EF>RF>AF.Spatial structure of soil indexes reveled that C₀/C₀+C of TP,AN,AP,AK and F were 25%-75%,while SOM and soil bulk were?75%.Total GRSP?TG?and easily extracted GRSP?EG?averaged 7.91 g/kg and 0.71 g/kg,respectively in Harbin city.Farmland was higher than other 4 forest types,and it was higher in outside of 4th ring than the other 4 ring roads?P<0.05?.Spatial structure reveled that C₀/C₀+C of TG and EG were 50%.Spatial distribution map revealed that GRSP gradually decreased from west to east.Correlation analysis showed that GRSP was closely related to soil fertility.Soil fertility index were significantly correlated to TG content,except AK.pH,soil bulk density,SOM,TN,AN,AP,and F were significantly correlated to EG content.Stepwise regression analysis indicated that both TG and EG were affected by pH,TN,AN.GRSP can be used as the index to evaluate the soil fertility.Based on these results,some measures to improve the urban soil were proposed,such as loosening soil,reducing soil alkalinity,litter compost cycling on-site,inoculating with AM fungi,N-P fertilizer addition without the addition of K,and N-fixing using trees with low P demand to maintain suitable soil fertility.