Soil Quality Assessment Of Cultivated Land In The Qaidam Basin Of The Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau was found to be sensitive to global climate change,whose soil changed its parameters,such as soil organic matter well,with anthropogenic activity,especially agricultural management.The sustainable development of soil may be under pressure due to human intervention in the soil,in which land use types took various impacts on soil quality.This study investigated cultivated lands under three types of land use（facility land,farmland,orchards）and the grassland for the control in the Qaidam Basin,analyzed their characteristics in soil physical,chemical,and microbiological properties,and assessed the impact of land use types on aggregate soil stability,soil organic carbon（SOC）fractions,and heavy metal concentrations.The effect of land use types on soil quality was finally evaluated.The main findings,together with the innovations,are as follows:（1）The cultivated lands in the Qaidam Basin are characterized by their difference in soil physicochemical properties and soil fertility status with land use types.Compared with the control grassland,the cultivated lands decreased their alkaline soil to the lowest p H of 7.97 for facility land and increased their soil bulk density to the most significant value of 1.39 g cm^-3 for the orchard.Among the four land use types investigated,the content of soil organic carbon（SOC）,total nitrogen（TN）,and total phosphorus（TP）all decreased with the increase of soil depth,except for total potassium（TK）content.The highest value of SOC was 17.75 g kg^-1（facility land）,and the lowest value was 10.95 g kg^-1（orchard）.The facility land had TN(1.58 g kg^-1)and the highest TP(1.16 g kg^-1),and the farmland had the highest TK(19.81 g kg^-1).The value of the soil integrated fertility index（IFI）is present as facility land（0.52）>grasslands（0.48）>farmland（0.32）>orchards（0.25）.Overall,the nutrient content of the soil in the Qaidam Basin is good,but attention should be paid to the use of organic fertilizers,and suitable compound fertilizer types should be selected to ensure good farming conditions and sustainable crop growth.（2）Overall,the proportion of micro-aggregates（<0.25mm）in the soil was relatively large,of which orchard soil micro-aggregates accounted for the most significant proportion,as high as 80.04%.Grassland had the most macro-aggregates（>5 mm）,up to 42.19%,while orchard soil had the least,only 2.26%.The average soil weight diameter（MWD）and geometric average diameter（GMD）under different land use types were expressed as facility land>grassland,farmland>orchard.The soil erodibility index（K value）of orchards is the largest,while the K value of facility land is the lowest.Therefore,the soil aggregates of facility land were the most stable,while the weakest was in orchard soil.（3）Grassland had the most significant value of particulate organic carbon（POC）at 0-10 cm(9.82 g kg^-1),while orchards had the lowest POC at 10-20 cm soil layer(4.11 g kg^-1).The mineral-associated organic carbon（MAOC）of soils for facility land was highest at 0-10 cm(9.49 g kg^-1),while orchard soil（10-20 cm）had the lowest value(4.41 g kg^-1).The POC/MAOC ratio was significantly lower in cultivated land than in grasslands.The soil carbon mineralization rates were performed as facility lands>farmlands>grasslands>orchards.The inert carbon of soils was observed with the highest value in grasslands and the lowest value in orchards.（4）Among the four land use types investigated,the microbial biomass carbon（MBC）of soil was significantly lower in orchards than others,and the microbial biomass nitrogen（MBN）of soil was significantly higher in farmland than others.The microbial diversity index（Shannon and Chao1）was significantly lower in grassland compared to other land use types.The annotation of microbial functional genes in the Qaidam Basin showed that most functional groups were associated with carbon cyclings,such as citric acid reduction cycle,quinone oxidoreductase,citric acid cycle,dicarboxylic acid hydroxybutyrate cycle,3-hydroxy propionic acid double cycle,and pentose phosphate reduction cycle（Calvin cycle）.The metabolic functional groups of grassland microbial communities are significantly higher than other land use types,with the most considerable value of Bray Curtis distance between samples.（5）The average content of heavy soil metals,i.e.,Сu(25.07 mg kg^-1),Сr(45.67mg kg^-1),N?(25.56 mg kg^-1),Zn(71.24 mg kg^-1),Рb(14.19 mg kg^-1),Сd(0.17 mg kg^-1),Аs(12.54 mg kg^-1),andНg(0.05 mg kg^-1)were lower than the environmental quality standards.However,theСu,Сr,N?,andАs were highest in farmland,and Zn andНg were highest in the facility land.TheРb content was highest in orchards,and theСd content was the same in facility land,orchard,and farmland.Among the four land use types investigated,the concentrations of heavy soil metal expressed as facility land>farmland>grassland>orchards.The evaluation of the soil comprehensive pollution index indicated that the soil was in a clean condition.The index of potential environmental risk indicated that heavy metals were slightly harmful to the soil.（6）The soil quality assessment values（SQAV）are expressed as facility lands>grasslands>farmland>orchards.The main soil properties that influenced SQAV under various types of land use were clay fractions,sulfur metabolism,total phosphorus,and organic carbon content.This result may provide a theoretical basis for sustainable and healthy agricultural land management,which suggests the need for appropriate land use strategies and sustainable soil management methods to improve soil conditions in the Qaidam Basin.