| The soil potassium is mainly derived from mineral weathering.Its content and effectiveness are not only affected by natural conditions such as soil parent material and soil type,but also strongly influenced by human activities such as land use mode and tillage fertilization intensity.The Chengdu Plain is a typical agricultural production base and an urbanized development area.In the past 35 years,the land use patterns and agricultural production levels in the Chengdu Plain have unde rgone major changed,exploring the evolution characteristics of soil fertility and its structural and artificial the driving factors have important practical significance for the sustainable use of local soil resources.Therefore,this paper takes the core area of Chengdu Plain as the research object,based on the 195 typical soil profile data of the second soil census and the 187 soil profile data collected and analyzed by the field survey in 2016-2017,based on geostatistical theory and GIS technology.The spatial and temporal evolution characteristics of soil potassium content(TK and AK)in 1980 s and 2010 s were compared and analyzed.The effects of soil parent material,soil type and fertilization,straw returning and land use on soil potassium spatial and temporal distribution were analyzed.The main findings are as follows:(1)From the perspective of time and space distribution,the content of total potassium and available potassium in the core area of Chengdu Plain has increased with time in the past 35 years.The average TK content of surface soil in 2010 s was 20.17g/kg,which was 6.89% higher than that of 1980s(18.87g/kg).The average content of AK in soils of 1980 s and 2010 s was 45.07mg/kg and 53.48mg/kg,respectively,an increase of 18.66%.The areas with more obvious increase are in the northern part of the study area,such as Pengzhou,Xindu,and Jixian.The 2010 s soil TK high value area(>25g/kg)is distributed at the junction of Jixian and Xindu,and the low value area(<5g/kg)is distributed in the westward area of Datun and other places.The high-potassium potassium high-value area(>80mg/kg)is mainly distributed in the northern and southern areas of the study area,and the low-value area(<30mg/kg)is mainly distributed in the northwest direction(partial areas of Dujiangyan,Wenjiang and Qixian).The nugget effect of TK and AK in the topsoil increased by 13.33% and 5.14%,respectively,indicating that the effects of human factors(such as land use,tillage and fertilization)on the surface potassium and AK were more obvious.(2)From the change of soil profile,compared with 1980 s,the TK content of 2010 s soil increased in different degrees in 0-60 cm soil layer,increasing by 6.04-10.43%.From the relative changes of the soil TK content profile in the 1980 s and 2010 s,the range of high value areas has expanded significantly,mainly in the eastern part of Pengzhou and Dujiangyan,and at the junction of Wenjiang,Handan-Dayu and Shuangliu.Then there is a decreasing trend.The spatial structure characteristic parameters changed significantly in 0-20 cm and 20-40 cm soil layers,and the nugget effect of soil TK content increased by 13.33% and 9.74%,respectively,compared with 1980 s,which indicates that the spatial variation of TK content in 0-40 cm soil layer is derived.The influence of anthropogenic factors is more obvious,while in the 40-100 cm soil layer,it is mainly affected by structural factors,and there is no change compared with 1980 s.The soil AK content in 2010 s showed a significant difference between the surface layer(0-20cm)and the soil layer below 20cm(P<0.05),and with the increase of soil depth,the area of soil AK content was gradually expanded and low.The value areas are mainly distributed in Dujiangyan,Wenjiang and Shuangliu.(3)According to the difference between different soil parent materials,the TK content of the soils of the gray-brown alluvial deposits and the Pleistocene sediments increased in different soil layers,and the sediments of the Pleistocene sedim ents increased the most(24.06%-51.50%).The TK content in the soil of purple alluvial deposits decreased greatly(7.54%-21.82%);the soil AK content of gray alluvial deposits and gray-brown alluvials increased,and the gray-brown alluvial increased the most.78.18%,while the content of AK in the soil of the Pleistocene sediment and the purple alluvial deposits showed a significant downward trend,with a decrease of 28.14% and 37.57%,respectively.The average content of soil SAK was the highest in gray alluvial(301.92-498.94 mg/kg),which was significantly higher than that in other soil-forming soils(P<0.05).From the perspective of different soil types,the contents of TK and AK in the soil were as follows: paddy soil > new soil,and SAK was new soil > paddy soil.Compared with 1980 s,the TK content of 2010 s soil showed a significant upward trend in the TK content of the submerged and de-embedded paddy soils.The soil AK content increased the most(24.52%)by the soil-seeding and de-emergence paddy soil.The type of paddy soil decreased the most(52.08%).From the perspective of the soil genus,compared with the 1980 s,the TK content of the irrigated gray tide field and the sorghum ash field decreased in different soil layers;the soil AK was the submerged tidal field,the infiltration type yellow mud field and the newly accumulated ash sand The decline is larger,while other soils show different degrees of increase.Land use patterns have a significant impact on soil potassium changes.From the surface soil,compared with the traditional rotation(rice buckwheat,rice bran oil),the rotation of rice,vegetable and vegetable increased the content of AK and SAK in the surface soil,and the garden land increased the consumption of soil AK and SAK.The content of AK in soil under the rotation of rice and vegetable was the most obvious with the deepening of soil layer.Farming and fertilization and straw returning are the main reasons for the spatial variation of soil potassium content.From the perspective of potassium sources,the total amount of potassium fertilizer in Pengzhou in 2010 s increased by 12.97 times compared with 1980 s,and the increase in potassium fertilizer input in Wenjiang District was smaller.At the same time,the total amount of straw returned to land in Pengzhou was also significantly higher than other regions,rice-vegetables.The fertilization level increased in the rotation system,and a large amount of straw returning to the field was the important reason for the significant increase of soil potassium content in the Pengzhou area in the northeast of the study area.The Wenjiang area in the southwest of the study area was mainly garden land,and the land use intensity was mainly used.Large,the level of fertilizer input is relatively low,and the overall performance of soil potassium is continuously decreasing,which is highly valued.In summary,we should combine the soil parent material,soil type and l and use pattern of each district and county in the study area,balance the application of chemical fertilizer according to the changes of potassium nutrient in different counties,change the concept of ―diazo,light,phosphorus and potassium‖ of farmers,and guide farmers.―Stabilizing nitrogen,controlling phosphorus and increasing potassium‖,at the same time,adjusting land use intensity,vigorously promoting straw returning,reducing agricultural production costs,and improving fertilizer utilization rate,thereby improving the current situation of sustained potassium deficiency in the core area of Chengdu Plain. |
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