Analysis On The Spatial And Temporal Variations Of Soil PH And Its Influencing Factors In The Core Area Of Chengdu Plain

Soil acid-alkalinity is a comprehensive reflection of many chemical properties of soil.Its dynamic changes not only reflect soil fertility,but also play a key role in affecting plant growth,soil microbial activity and soil nutrient availability.Therefore,to understand the temporal and spatial variation characteristics of regional soil pH and its influencing factors,is not only the need to understand the status of regional soil pH,but also the premise of regional soil pH regulation,Chengdu Plain is an important production base for grain,cotton and oil in Sichuan Province.With the adjustment of agricultural economic structure,soil pH has changed greatly.Based on 151 typical soil profiles from the second soil census in 1980 and 187 soil profiles from 2016-2017,variance analysis,regression analysis and geostatistics were used.The variation pattern of soil pH in the core area of Chengdu Plain and its influencing factors were studied in the past 35 years.These results suggested that:(1)During the 35 years,the soil layers in the study area have been acidified obviously.Among them,the surface soil acidification(0～20cm)is the most significant,the pH value of the soil decreased by 1.20 units;the pH value of 20～100cm soil layer decreased by 0.74 ～ 0.68 and 0.68 units,respectively.Soil pH value varies under different environmental factors.Among the four kinds of soil parent material,the pH value of each soil layer developed by grey alluvium decreased the most,by 0.94-1.41 units;Secondly,the soil developed by gray-brown alluvium decreased by 0.61-1.26 units;Purple alluvial soil decreased by 0.41-1.01 units;Only the surface layer of the Pleistocene sediments was acidified,but the pH value of the deep soil was not changed significantly.In terms of soil subtypes,the pH value of surface soil in percolated paddy soil,latent paddy soil and desubmersed paddy soil decreased by 1.34 units,which was higher than that in stored paddy soil(-0.96).In the 20～40cm soil layer,the pH value of percolation paddy soil decreased the most;In 40～100cm soil layer,the acidification of latent paddy soil is the most serious.In terms of soil,the pH value of the topsoil in the reclaimed ash field was the fastest and decreased by 1.46 units.In the 20～40cm soil layer,the water storage ash tide field decreased the fastest;In the 40～100cm soil layer,the submergence tide field,the infiltration ash tide field and the water storage ash tide field decreased the fastest,and decreased 0.77-0.96 units.There is no obvious acidification in each soil layer of the newly accumulated soil.(2)In the two periods,the pH value of each soil layer has a moderate spatial autocorrelation,which is influenced by both structural factors and random factors.Compared with the 1980 s,the random factors of 2016-2017 had a stronger effect on the spatial variation of soil pH in the study area.The regression analysis further showed that the soil-forming parent material and the soil genus had a significant effect on the spatial variation of soil pH in the 1980 s study area;Among the random factors,rotation further improved the interpretation ability of soil pH spatial variation in 2016-2017,increased 4.9-10.4,significantly affected the spatial variation of soil pH in each soil layer,but had no significant effect on the soil parent material.It shows that in 35 years,the role of randomness is further strengthened and structural factors are weakened.According to the spatial distribution of pH,the soil pH values of each profile in 1980 and 2016-2017 showed the spatial distribution pattern of south high and north low;The relatively low value areas are mainly concentrated in Dujiangyan,Pengzhou and other areas in the north of Qingbai River,and the high value area is mainly distributed in Chongzhou area west of the Jinma River.And,it was found that the whole soil layer in 1980 was weak alkaline and the whole soil layer in 2016-2017 was acidic and weak acidic.(3)It can be seen from the temporal and spatial variation map of soil pH in the study area that all soil layers(0～100cm)show an acidizing trend,and the spatial variation of acidification degree is obvious.Among them,the high acidification degree of topsoil was mainly distributed in the counties of Chongzhou and Wenjiang,and the pH value of soil decreased by more than 2 units in some regions.From the soil factors affecting the soil acidification in the study area,the parent material(15.3%-30.1%)became the main factor affecting the acidification degree of each soil layer during the 35 years.In addition,there was a certain correlation between nitrogen application and soil acidification.Soil acidification increased with the increase of nitrogen application years and the accumulation of nitrogen application rate.However,the external acidification factors caused by nitrogen fertilizer application have to play a role through the properties of the soil itself.Different soil types have different acid buffering properties,resulting in different acidification degree.