| Tobacco is one of the most important cash crops in China.Tobacco production is concentrated in southwest tobacco growing areas and Central South tobacco growing areas,and main tobacco producing provinces in China were Yunnan,Guizhou,Sichuan,Chongqing,Hunan and Henan become.The southern region has become the main force in the production of Chinese tobacco.Soil is the carrier to provide water and nutrients for tobacco growth,and it is an important role for storing,releasing,transforming and regulating the operation of nutrient elements.There is a close relationship between the nutrient status of soil and the production of high quality tobacco,and the level of nutrient content directly affects the growth and development of tobacco.Soil nutrient is affected by natural factors and human factors,and the spatial distribution is quite different.Soil acidity and alkalinity have a direct impact on the availability of nutrients and crop growth.By field investigation,laboratory analysis and data collection,analysis,this paper analyzed the difference of soil nutrient content,revealed the changes of soil nutrients in Chongqing southeast tobacco area;analyzed the correlation of topography,climate factors and soil nutrients,revealed the influence of environmental factors on soil nutrients;analyzed the distribution characteristics of different soil nutrient content of soil in different soil layer,reveal the soil effect on soil nutrient content;on the basis of the CART model,the soil nutrient content as the dependent variable,7 environmental variables as independent variables,established different soil nutrient structure of CART tree,obtained the importance of different environmental factors on soil nutrient content,analyzed the effect of environmental variables on soil the nutrient content of the size,further revealed the environmental control factors of tobacco soil nutrient content.The main conclusions are as follows:(1)The soil organic matter(SOM)content in different soil layers varies a lot and shows a decreasing trend with increasing soil depth.From the A layer to the C layer,the average SOM content decreased in turn,and the coefficient of variation(CV)increased sequentially,all of which were moderate intensity variations.The proportion of SOM in the suitable range of tobacco planting(15~30 g/kg)was 55.00%.The soil total nitrogen content,available nitrogen content and SOM content showed a significant parallel relationship,all decreased with the increase of soil depth,and all showed moderate intensity variation.The total phosphorus content in soil showed a decreasing trend with the increase of soil depth.The change trend of available phosphorus was A>C>B.With the exception of the A-layer,the total phosphorus and available phosphorus in the B and C layers showed strong variations.The total potassium content in the soil reached the maximum in layer C,followed by layer A,and the content in layer B was the lowest.A layer is a low-intensity variation,BC layer is a moderate intensity variation.Soil available potassium content showed a decreasing trend with the increase of soil depth,and all of them were moderate intensity variations.(2)The correlations between SOM content and environmental variables in different soil layers are quite different.The SOM content in A layer is significantly positively related to slope and topographic relief index(TRI).The correlation between SOM content in B layer and seven environmental variables is not significant.There was a significant negative correlation between the SOM content in the C layer and the annual average precipitation.In different slope directions,the content of SOM in the slopes of north,south,west and northeast are relatively high;the content of SOM in the same slope to different soil layers decreases with the increase of soil depth.In the soils developed from different parent materials,the SOM contents in the A,B,and C layers have the same tendency.They all show Cambrian limestone> Silurian marl> Permian limestone> Triassic limestone.> Ordovician limestone.In soils developed from the same soil parent material,the SOM content in different soil layers showed a decreasing trend with increasing soil depth.The content of soil total nitrogen and available nitrogen in different soil layers was significantly positively correlated with elevation,and negatively correlated with annual average temperature.The soil nitrogen content in different soil layers on the same slope varies greatly,and the soil total nitrogen and available nitrogen content decrease with increasing soil depth.In the soils developed from different parent materials,the total nitrogen content in layer A soil was significantly different,the difference in layer B was smaller,and there was almost no difference in layer C.Both were Permian limestone> Cambrian limestone> Triassic limestone> Silurian marl> Ordovician limestone.In soils developed from the same soil parent material,the total nitrogen and available nitrogen contents in different soil layers decreased with increasing soil depth.Environmental variables have a greater impact on soil total phosphorus content,but have less effect on soil available phosphorus.The total phosphorus content in different soil layers was significantly positively correlated with the elevation and annual average rainfall,and was significantly negatively correlated with the annual average temperature.On the same slope,the soil total phosphorus and available phosphorus content decreased first and then increased with the increase of soil depth.In soils derived from different parent materials,the total phosphorus content in the A and B layers was as follows: Triassic limestone> Ordovician limestone> Permian limestone> Silurian marl> Cambrian limestone.In soils derived from the same soil parent material,the total phosphorus content in Ordovician limestone and Triassic limestone soils decreased with the increase of soil depth,while the rest showed the first decrease and then increase trend;the soil available phosphorus content in layers B and C.Compared with the A layer,the trend showed that the available phosphorus content in the C layer of the soil developed from Permian limestone,Triassic limestone and Cambrian limestone was higher than that of the B layer.The total potassium content of the soil was significantly negatively correlated with the elevation and annual average rainfall,and was significantly positively correlated with the average annual temperature.The soil total potassium content first decreased and then increased with the increase of soil depth,while the soil available potassium content showed a decreasing trend with increasing soil depth.In the soils developed from different soil parent materials,the total potassium in the A and B layers is represented by the Silurian marl> Cambrian limestone> Ordovician limestone> Permian limestone> Triassic limestone,except In the Ordovician limestone,the soil total potassium content first decreased and then increased with the depth of soil layer in soils from other parent materials.The total potassium content in the C layer was higher than that in the A layer.In soils developed from the same soil parent material,the content of soil available potassium showed a decreasing trend with the increase of soil depth.(3)The topography has the greatest influence on the SOM content in the A layer.The main influence factors are TWI,TRI,and slope.The main influencing factors of SOM content in the B layer are altitude,TWI,and parent material.The climate has a great influence on the SOM content in the C-layer.The main influencing factors are the annual average rainfall,aspect,and average annual temperature.Overall,soil moisture-related factors play a major role in SOM content.From Layer A to Layer C,the main impact factors gradually change from topography to climate factors.The terrain,climate,and soil parent material affect the total nitrogen content of the ABC three-layer soil.The main controlling factors of the total nitrogen content in the A layer are elevation,annual average temperature,TRI,TWI,and the B layer is elevation,TRI,and year.Average rainfall,soil parent material and slope;C layer is elevation,parent material,and valley depth.The main controlling factors of soil available nitrogen content in A layer are elevation and annual average temperature,and the average temperature in B layer,annual average rainfall,altitude,TWI,and C layer in elevation,TWI,and aspect.The main controlling factors of total phosphorus content in the A layer are TWI,annual average rainfall,elevation,TRI,valley depth and slope,the average annual rainfall in layer B,TRI and parent material;the average annual rainfall in layer C,Mother Earth,slope and TRI.The main controlling factor of soil available phosphorus content in layer A is parent material and the layer B is TWI> average annual rainfall,slope,valley depth,TRI,parent material of soil,C layer is TWI,slope.The total potassium content in soil is mainly affected by the topography and climate.The main controlling factors for total potassium content in the A layer are the annual average annual rainfall and average annual temperature,the average annual average rainfall and annual average temperature in the B layer,and the C level is the annual average.Average rainfall,TWI,average annual temperature and elevation.The main controlling factors of soil available K content in the A layer are the annual average temperature,TRI,average annual rainfall,elevation and slope,the B layer is the elevation,annual average temperature and valley depth,and the C layer is the gully depth,parent material,TRI,and year.Average temperature and slope. |
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