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Northwest A&F University (2017)

Cropland Soil Quality Assessment at A Regional Scale on the Loess Plateau

李彬彬;

Titre : Cropland Soil Quality Assessment at A Regional Scale on the Loess Plateau

Auteur : 李彬彬;

Grade : Master’s Theses 2017

Université : Northwest A&F University

Résumé
It’s of great importance to study the characteristics of cropland soil quality and its influencing factors on the Loess Plateau at a regional scale.We divided the Loess Plateau into five agricultural regions,named Guanzhong Plain,Weibei Upland region,Hilly and Gully region,Yinchuan Plain and Shallow Mountain and Hilly region,respectively,based on the ecology,agriculture,soil,cropping system and climate types.And Wugong,Ningxian,Zhuanglang,Pingluo and Ledu were selected as typical counties in each agricultural regions,respectively.We have conducted an in-depth study on the characteristics of soil quality at county scale,relationship between soil organic carbon and physicochemical properties,the scale effect of minimum data sets and regional evaluation of soil quality based on upscaling model.The main conclusions are as follows:1.The soil physical and chemical properties of typical counties in different agricultural regions were analyzed.Soil texture in the county of Wugong and Ningxian was primarily clay loam and loam,which was respectively uniform.And that in Zhuanglang and Ledu was primarily loam,sand clay loam and sandy loam,which was coarser than other counties.Higher variability of soil texture was observed in Pingluo due to irrigation with yellow river water.Subsurface soil compaction problem was most conspicuous in Wugong and Pingluo with an average value of 1.58g/cm3 and 1.46g/cm3,respectively.Soils in five typical counties were in a alkaline condition and pH value being more than 8.Soil total nutrients and available phosphorus in Wugong,Pingluo and Ledu were significantly higher than that in Ningxian and Zhuanglang.Besides that,there was no significant difference about the content of available potassium in different regions.In aspect of soil organic matter content,Ningxian was in a lower level and relatively abundant in Ledu.And that in Zhuanglang was in an upper level compared to other counties,however,the phosphorus and potassium was obviously low.2.The relationships between soil organic carbon(SOC)and soil properties in different typical counties were different,and the effect of climate and management practices on their relationships varied.On the whole,total nitrogen is the most important influencing factors of the SOC in the region of Loess Plateau.The correlation between SOC and soil chemical properties were stronger than soil physical properties.As a whole,SOC was correlated positively with silt content and soil nutrients and negatively correlated with pH,bulk density and clay content.Among them,climate and management practices had relatively little influence on the relationship between SOC and sand,silt,pH,total potassium,total nitrogen ;Nevertheless,the relationship between SOC and bulk density,clay,total phosphorus,available Phosphorus and Potassium can be affected greatly by climate and management practices.Total nitrogen,bulk density and total phosphorus were the main influencing factors of SOC at regional scale on the Loess Plateau,with total nitrogen being the main influencing factor in different typical counties.Thresholds for total nitrogen when SOC reaching the highest level in Wugong,Ningxian,Zhuanglang,Pingluo and Ledu were 1.39,0.95,1.33,1.38and 1.64 g/kg,respectively,and the values when SOC reaching the minimum level were 0.97,0.59,0.86,0.76 and 1.06 g/kg,respectively.3.The variability of soil quality indicators varied with scales and scale effect was observed among minimum data sets in different spaces.The variability of soil bulk density,pH,total potassium and carbon nitrogen ratio was relatively low at diverse spatial scales and other indicators,as a whole,showed an increasing trend with upscaling.This variability was more susceptible to the combinations of factors compared to the single.It indicates that synthetic factors caused the variability of soil quality indicators.As a result,it seemed that the indicator selection procedures must reference the synthetic factors not a single factor when assessing soil quality especially in multi-conditional region.Whether upscaling or downscaling,climate types,soil series,topography and cropland management practices would change and it led to the change of indicator variability or correlation.Eventually,scale effect was produced among minimum datasets at various spatial scales.So that’s important to consult the principles of pertinence and region when selecting indicators.Indicators selected were sure to reflect the regional problems so that it could improve the accuracy and application with a relatively low cost.4.Based on typical counties and“land use-topography-soil types" combinations,scaling-up model of soil quality was setup and explored cropland soil quality and its spatial characteristics on the Loess Plateau at a regional scale with this model.Seen from the regional scale,cropland on the Loess Plateau lacked soil organic matter and total nitrogen.However,total phosphorus,total potassium,available potassium and surface available phosphorus were relative abundance.The content of subsurface available phosphorus in Hilly and Gully region was utterly lacked.Cropland in Guanzhong Plain faced the serious problems of soil compaction in which more than 43%area in this region had surface bulk density value between 1.4~1.5g/cm3 and 97%area with a subsurface bulk density between 1.5~1.6g/cm3.In addition,there were more than 84%and 45%area with subsurface soil bulk density between 1.4~1.5g/cm3 in Yinchuan Plain and Weibei Upland region,respectively.Establishing a soil quality reference within Loess Plateau,surface soil quality was primarily five and six grade levels with the area 79%and 20%,respectively and was distributed mainly over Guanzhong Plain,Fenhe Vally,mountain field in west Shanxi and north Henan,Weibei Upland region,middle and southwest of Hilly and Gully region and the west Yinchuan Plain.Subsurface soil quality was primarily six and seven grade levels with the area ratio of 57%and 31%,respectively.Soil quality at six grade level was distributed in Weibei Upland and west Yinchuan Plain.Hilly and Gully region had area ratio of 55%and 45%with six and seven grade levels,respectively.Much more attention should be paid to Guanzhong Plain and east Yinchuan Plain where subsurface soil quality was primarily eight and nine grade levels

Mots clés : soil quality; loess plateau; scale effect; influencing factors;

Présentation (CNKI)

Page publiée le 7 février 2018