| Land use activities have risen due to population growth and its demand for food security and economic development,significantly impacting soil quality.Human interference on land has impaired the ability of soil to generate and return fertility for plant growth,hastening soil quality degradation.Soil nutrients and soil fertility are fundamental determinants of soil quality.Understanding the variations in soil nutrients and soil quality across different land use types is critical for agricultural sustainability,ecological preservation,and the efficient use of natural resources,including land use.The Benghe river basin,located in Yimeng rocky mountainous region in Shandong province,is densely populated with a variety of land use activities:the soil is loose,thin,and has a little surface cover:the terrain is fragmented,with a steep slope,a delicate ecosystem,and extreme soil erosion,all of which degrade the soil quality.Studying soil nutrients and soil quality under various land use types is significant for soil quality and ecological sustainability,comprehensive soil erosion management,and effective and efficient land use.Using the Benghe river basin,occupied by diverse land use types,as a research object,this study examined the variations in soil nutrients and soil quality under different land use types.The paper compared soil nutrient indicators:total nitrogen(TN),available nitrogen(AN),total phosphorus(TP),available phosphorus(AP),total potassium(TK),available potassium(AK),and soil organic matter(SOM)across four land use types(arable land,forestland,grassland,and garden land)to establish a relationship between land use types and soil nutrients.The study also analyzed soil physical properties(bulk density(BD),soil moisture content(SMC),soil texture(sand,silt,and clay)),and p H to evaluate soil quality in the Benghe river basin.The variabilities of soil quality under different land use types were determined to develop a connection between soil quality and land use types.The following are the major conclusions:(1)Soil nutrient contents in the watershed were uneven.In reference to soil nutrients classification standard of China,available nitrogen,total phosphorus,and available phosphorus belong to class I;total nitrogen class III;total potassium,available potassium,and soil organic matter belong to class IV.The soil nutrient contents generally decreased with soil depth.(2)Nutrient contents in soil varied according to the land use types.Generally,forest land and grassland contained more nutrients than arable land and garden land.Total nitrogen,available nitrogen,available potassium,and soil organic matter were abundant in forest land;total phosphorus and total potassium contents were abundant in grassland;available phosphorus was abundant in arable land.Soil nutrient contents varied under various land use types according to soil depth.At 0-10 cm soil depth,TN,AN,and SOM were abundant in forest land,followed by grassland,arable land,and garden land.TP:grassland>garden land>arable land>forest land.AP:arable land>garden land>forest land>grassland.TK:grassland>garden land>forest land>arable land.AK:forest land>arable land>garden land>grassland.At 10-20 cm soil depth,forest land contained the highest contents of TN,AN,and SOM,followed by grassland,arable land,and garden land.TP:garden land>arable land>grassland land>forest land.AP:arable land>garden land>forest land>grassland.TK:grassland>forest land>garden land>arable land.AK:forest land>arable land>garden land>grassland.At 20-30 cm soil depth,forest land had higher TN,AK,and SOM,followed by arable land and garden land.AN:forest land>garden land>arable land.TP and AP:garden land>arable land>forest land.TK:arable land>garden land>forest land.At 30-40 cm soil depth,TN and AK were predominantly in arable land than garden land.Garden land had higher TP,AP,TK,AN,and SOM than arable land.At soil depth of 0-20 cm,TN,AN,and SOM were higher in forest land,followed by grassland,arable land,and garden land.TP:grassland>garden land>arable land>forest land.AP:arable land>garden land>forest land>grassland.TK:grassland>forest land>garden land>arable land.AK:forest land>arable land>garden land>grassland.(3)Soil nutrient contents were unevenly distributed throughout the watershed;generally,soil nutrients were more concentrated in the east and central-west,moderate in the centre,and low in the north,southwest,and west of the watershed.The highest total nitrogen content was distributed in the east and central-west,the northwest and southwest had the lowest,and the moderate content was spread in the far east,the Lanshan district.Available nitrogen was highly concentrated in the east and central-west and intermediate in the central part of the watershed.The lowest available nitrogen content was distributed north,south,and west.Total phosphorus content was highest in the south,northwest,and east,and the lowest content was spread in the southeast and moderate in the north part of the basin.Available phosphorus was highly distributed in the east,especially in the Lanshan district.The north had moderate,while the southwest and the south of the watershed had low available phosphorous.The highest total potassium concentration was generally distributed in the west and east,moderate in the central,and deficient in the north of the watershed.Available potassium was highly distributed in the east,intermediate in the north,and lower in the southwest part of the watershed.Soil organic matter was generally uniform throughout the watershed.The highest was distributed in the central-west,and the lowest was in the east,especially in the Lanshan district.Human activities significantly contributed to the uneven distribution of soil nutrients in the watershed.According to the geostatistical analysis,the soil nutrients in the Benghe river basin exhibited a weak autocorrelation,with the majority of nutrient indicators having a nugget to sill ratio greater than 0.75.The weak autocorrelation suggests that soil nutrient contents distribution was determined primarily by random factors such as fertilization and soil management,among other human activities.(4)The distribution of soil physical properties and p H varied according to soil type and land use type.Under soil types,brown soil had higher bulk density,followed by skeleton soil and cinnamon soil type.Soil moisture content:cinnamon>brown>skeleton soil type.The proportion of sand particles:skeleton>brown>cinnamon soil type.The proportion of silt:brown>cinnamon>skeleton soil type.Clay and p H:cinnamon>skeleton>brown soil type.The soil textural class of the Benghe river basin is silt loam soil.The cinnamon soil type had more clay particles,higher p H values and soil moisture content,and lower bulk density than other soil types.The brown soil type had more silt particles and moderate bulk density,p H,and soil moisture content.Skeleton soil had more sand particles,high bulk density,relatively low p H values,and soil moisture content.Across land use types,garden land had higher bulk density,followed by arable land,grassland,and forest land.Arable land had higher soil moisture content,followed by forest land,grassland,and garden land.Garden land had a higher proportion of sand particles,followed by grassland,arable land,and forest land.The silt percentage was higher in forest land,followed by arable land,garden land,and grassland.Forest land had a higher proportion of clay,followed by grassland,arable land,and garden land.Grassland had a higher p H than forest land,arable land,and garden land.Soil p H ranged from weak acid to neutral in the Benghe river basin.(5)The spatial distribution of soil physical properties and p H was influenced by human activities associated with distinct land use types.The external factors,such as irrigation technology,fertilization,farming systems,soil management practices,and other human operations,affected p H,bulk density,soil moisture,and clay distribution,evidenced by a nugget:sill ratio greater than0.75.Physical soil properties and p H were unevenly distributed across the Benghe river basin.The watershed had a high bulk density in the north and south,ranging from 1.42 g/cm~3 to 1.57 g/cm~3,a low bulk density in the centre and southeast,and a moderate bulk density in the western and eastern parts of the watershed.Soil moisture content was generally higher in the north and the northwest,ranging from 18.51 to 32.84%,encompassing the entirety of Pingyi county.The central and southeast regions,including the Lanshan district,had a moderate moisture content.Low soil moisture content was spread in the southwest and east parts of the watershed.The east and southwest had fewer clay particles,the northwest had more clay particles,ranging from 29.97 to45.61%,and the central part of the watershed had intermediate clay.Sand and silt particles were spread relatively uniform throughout the basin.A lower percentage was distributed in the west and a higher proportion in the far east,the Lanshan district.Soil p H was generally high in the northwest ranging from 6.01～7.62,moderate in the centre of the watershed,and low in the south and the east,encompassing Fei county and the Lanshan district.(6)On the basis of the principal component analysis,norm value calculation,and Pearson correlation analysis,four soil indicators(total nitrogen,soil moisture content,p H,and sand)were retained for the minimum data set(MDS)to evaluate the soil quality.At 0-20 cm soil depth,the soil quality in the Benghe river basin was generally low,ranging from very low to very high,with an average soil quality index of 0.38.The soil quality indices ranged between 0.7 and 0.12.Soil quality varied according to land use types:forest land had an average SQI of 0.52,grassland 0.40,arable land 0.39,and garden land 0.29.The soil quality in forest land was high,grassland was medium,arable land was low,and garden land was very low.(7)Similar to soil nutrient distribution,soil quality varied significantly over the Benghe river basin.The southeast and central-west parts of the watershed had high soil quality,while the east,northwest,west,and central parts had moderate soil quality.The northeast and southwest of the watershed were generally deficient in soil quality.The nugget to sill ratio in the geostatistics was above 0.75,signifying random factors such as human activities are accountable for the variations of soil quality across the Benghe river basin. |
