Acidification Characteristics Of Red Soil Profiles Under Different Land Use Patterns And Parent Materials

Land use types and soil parent material are the two important factors that affect red soil acidification.Previous research was mainly focused on the effect implied by single land use or parent material on soil pH.However,for a variety of ways and a variety of organic combination of the study of the influence of red soil acidity characteristics are lack and insufficient system,especially researching on the acidity characteristics of profile is not comprehensive.This study comprised of four kinds of land use types?paddy field,dry land,orchard and forest land?under four kinds of parent materials?Red sandstone,River alluvial,Quaternary red earth and Plate shale?developed red soil,measuring different soil layers?0-20,20-40,40-60,60-80 and 80-100cm?pH,exchangeable acid(H⁺,Al³⁺),the total amount of exchangeable base(Ca²⁺,Mg²⁺),base saturation,total nitrogen,ammonium nitrogen and nitrate nitrogen content,to quantify the change of acidity index of each land use pattern and parent material at different soil layers and to understand red soil profile acidity characteristics and acidification degree under different land use types and parent material,The calculation of acidification rate of paddy soil derived from red sandstone and river alluvial parent material,to provide theoretical basis for the prevention of red soil acidification.The results showed that:?1?The size of red soil profile pH derived from red sandstone under different land use as follows:paddy field?5.69?>dry land?4.71?,orchard?4.74?>woodland?4.49?;Commutativity acid content size respectively:woodland(6.54 cmol·kg^-1)and the dry land(6.52 cmol·kg^-1)>orchard(3.51 cmol·kg^-1)>paddy field(0.79 cmol·kg^-1);Exchangeable base size respectively:paddy(4.47 cmol·kg^-1)>dry land(1.97 cmol·kg^-1)>orchard(1.26 cmol·kg^-1)>woodland(0.48 cmol·kg^-1);Size of base saturation respectively:paddy field?53.14%?>dry land?20.87%?>orchard?15.41%?>woodland?4.67%?.In different soil layer,with the increase of soil,red soil profile of red sandstone pH increased?80-100 cm?5.39?,60-80 cm?5.27?>40 to60 cm?5.11?>20-40 cm?4.81?>0-20 cm?4.68??;There was no significant difference commutativity acid content;Exchangeable base amount gradually increases,its size is respectively:60-100 cm(2.34 cmol·kg^-1)>40-60 cm(2.05 cmol·kg^-1)>0-40 cm(1.75cmol·kg^-1);Red sandstone red soil base saturation increased,its size:80-100 cm?33.95%?,60-80 cm?32.27%?,40-60 cm?31.31%?>20-40 cm?25.47%?>0-20 cm?21.08%?.?2?In the land uses of paddy field and orchards,exchangeable acids in red soils developed from red sandstone gradually decreased with the increase of pH at the profile level whereas total exchangeable salts and base saturation gradually increased with the increase in pH at the profile level.The total amount of exchangeable base increases gradually with increase in pH under dry land.Similarly,exchangeable acid gradually decreases as the pH increases under forest land use.A significant progression in pH and exchangeable Ca²⁺and Mg²⁺was observed at 20-60 cm depth for red-sand stone derived soils.While significantly decreasing trends in pH and exchangeable H⁺and Al³⁺at 20-40 cm depth for paddy land use.On the other hand,a considerable increasing tendency in pH and exchangeable Ca²⁺and Mg²⁺was examined at 0-40cm depth for paddy land use.However,quaternary red soils maintained increasing trends in pH at 0-40 cm depth while a decreasing trend in pH exchangeable H⁺and Al³⁺was observed at 0-40cm depth under paddy land use.?3?Compared with other soil layers,the pH and exchangeable Ca²⁺and Mg²⁺of paddy soils derived from red sandstone parent material increased significantly in 20-60 cm depth in comparison to other soil depths.Nevertheless,the exchangeable H⁺and Al³⁺and exchangeable Ca²⁺and Mg²⁺decreased significantly in 20-40 cm soil depth in paddy soil derived from alluvial parent material.Soil derived from Quaternary red soil parent material increased significantly in20-60 cm soil whereas the exchangeable H⁺and Al³⁺decreased significantly in the 0-60 cm soil.The pH of paddy soil is significantly higher in the 0-40 cm soil depth while the exchangeable H⁺and Al³⁺are significantly decreased in 0-40 cm soil.In the 0-20 cm soil depth,the exchangeable Ca²⁺contents of 4 parent materials in Paddy soil are as follows:Quaternary red earth(1.78cmol·kg^-1)>Plate shale(0.98 cmol·kg^-1);and exchangeable Mg²⁺content in the order:Quaternary red earth(0.84 cmol·kg^-1)>Red sandstone(0.63 cmol·kg^-1),Plate shale(0.60 cmol kg^-1),river alluvium(0.52 cmol·kg^-1).The order of content size of exchangeable Mg²⁺is as follows:Quaternary red soil(1.95 cmol·kg^-1),Red sandstone(1.76 cmol·kg^-1)>River alluvium(1.17 cmol·kg^-1).In 80-100 cm depth soil,the pH order of 4 parent material paddy soil is as follows:Quaternary red earth?6.37?,Red sandstone?6.27?,River alluvium?6.24?>Plate shale?5.73?.Quaternary red soil,red sandstone,river alluvial and shale,the change trend of exchangeable Al³⁺content is opposite to pH,and the change of exchangeable Ca²⁺content is same as pH.?4?There was a significant negative correlation between paddy soil pH and chemical N fertilizer application amount?p<0.05?,and also a significant negative correlation with soil total N and ammonium nitrogen content?p<0.05?.With the increase of soil total nitrogen and ammonium nitrogen content.There was a decreasing trend of different degrees.There was no significant correlation with NO^3--N content?p>0.05?.When the soil pH<4.9,the surface pH of paddy soil decreases significantly with the increase of straw returning;when the soil pH is higher than 4.9,the surface pH of paddy soil increases significantly with the increase of straw returning application.?5?The pH buffering capacity of the same parent material in different soil layers has difference,with the increment of soil layer.It is indicated that paddy soils derived from red sandstone and river alluvial parent material,is more sensitive to exogenous acid in 0-20 cm soil depth i.e.acidification is faster however sensitivity of paddy soils is significantly lower in the deep soil layer resultantly less acidification.Different buffering capacity was observed for different soils depths as mentioned below:0-20 cm(12.73 mmol·kg^-1·pH unit)>20-40 cm(11.82 mmol·kg^-1·pH unit)>40-60 cm(10.66 mmol·kg^-1·pH unit)>60-80 cm(9.42mmol·kg^-1·pH unit)>80-100 cm(8.85 mmol·kg^-1·pH unit).For alluvial soils,the sequence of buffering capacity is as follows:0-20 cm(18.42 mmol·kg^-1·pH unit)>20-40 cm(12.30mmol·kg^-1·pH unit)>40-60 cm(9.76 mmol·kg^-1·pH unit)>60-80 cm(9.39 mmol·kg^-1·pH unit)>80-100 cm(9.33 mmol·kg^-1·pH unit).The acidification rate for paddy soil comprising 2parent materials is as follows:Red sandstone(0.78 kmol·H⁺·hm^-2·a^-1)and River alluvial(0.36kmol·H⁺·hm^-2·a^-1).