| The soil in the typical black soil area of Northeast China is rich in organic matter and has a good structure,and is the main source of food in China.In recent decades,soil erosion has occurred and degradation is more serious due to unreasonable farming.In order to clarify the soil quality of farmland in the black soil area,this study selected sloping farmland in Jiusan,Keshan,Hailun and Bin County of Heilongjiang Province,a typical black soil area in northeast China,as the research object.Through a combination of field survey,soil sample collection and experimental analysis,physical,chemical and biological indicators were measured,an index system for soil quality evaluation was constructed,and the spatial differentiation pattern of the main quality indicators of soil quality was analyzed.The minimum data set of the main indicators of soil quality in the black soil area was constructed by using principal component analysis and correlation analysis combined with Norm values,and the soil quality index(SQI)calculated based on the full data set(TDS)and minimum data set(MDS)indicators was analyzed.SQI-TDS was used to verify the scientificity and practicality of SQI-MDS and to explore the spatial distribution pattern of soil quality in the black soil area,which provides a scientific basis for soil quality evaluation work and scientific management of farmland in the black soil area.The main findings are as follows:(1)The soils in the study area are compact and clayey,with an overall weak acidity,and the soil texture is powder loam-powder clay loam,with increasing trends in bulk weight(BD),sand content(Sand),shear strength(SS),and penetration resistance(PR)from north to south(p < 0.05),and BD,SS,and PR of the 0-20 cm soil are significantly less than those of the 20-40 cm soil layer,while other indicators show opposite trends.Other indicators showed opposite trends.The mean organic carbon content(SOC)was 21.13 g/kg,which was high.SOC,total nitrogen(TN)and total phosphorus(TP)showed significant differences(p < 0.05)among the four regions,with a decreasing trend from north to south,while the effective phosphorus(AK)and fast-acting potassium(AP)contents were more influenced by anthropogenic fertilization and showed no significant pattern among regions.The content of each nutrient was higher in 0 cm-20 cm than in 20 cm-40 cm among different levels of soil.The distribution patterns of microbial and organic carbon contents were similar,and there were significant differences in sucrase(SUC),urease(URE)and phosphatase activities(PHO)among different areas,but there was no significant pattern.(2)BD,Sand,SS and PR show the following trend among different slopes:lower slope(LS)> middle slope(MS)> up slope(US)> top slope(TS)and sedimentation area(SA),and the other indicators have the opposite trend with the distribution of BD,and the smallest in LS.There were significant differences in bulk weight,SOC,TN and TP among different slopes,which were significantly lower at the LS than at TS and SA(p < 0.05),and the trend of change in soil fast-acting nutrient content and SOC was the same among different slopes,but the AP content was higher in the slope than at TS instead.MBC in MS and LS was significantly smaller than that in TS and SA,and the trends of enzyme activity and MBC were similar among different slope positions.There were significant or highly significant correlations among most soil quality indicators.There were positive correlations between soil BD,Sand,SS,PR and p H,and negative correlations with other soil quality indicators,and highly significant linear correlations between soil TN,TP,MBC and SOC(p < 0.01).(3)Principal component analysis and correlation analysis were used and combined with Norm values to construct MDS indicators for quality evaluation of black soil areas including: MWD,p H,SOC,TN,AK and AP.SQI-TDS and SQI-MDS showed a highly significant positive correlation,and both SQI-TDS and SQI-MDS results indicated a high number of relatively low and lower level sample points and few relatively high level sample points.There were significant effects of level,area,and slope position on soil quality.Between different areas,the overall trend of soil quality decreases from north to south,with non-significant differences between Jiu San and Keshan;between different slope positions,soil quality on,in and below the slope is significantly less affected by erosion than TS and SA(p <0.05),showing that:SA >TS > US > MS > LS;soil quality decreases significantly with increasing soil depth(p < 0.05)... |
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