Study On Temporal-spatial Variation Of Soil Salinization And Planting Risk Assessment In Cotton Field Of South Xinjiang

The information of soil profile salinization is of great significance to the prevention and control of soil salinization in cotton field of South Xinjiang,and it is also an important basis for precise irrigation of cotton field.How to obtain the salinization information of soil profile quickly and losslessly,and study the three-dimensional visualization and spatiotemporal variability of soil profile salinity based on this has become a difficult and hot topic in the research at domestic and overseas.This paper makes full use of the advantages of EM38-MK2 in quickly obtaining the salinization information of soil profile,takes the machine mining cotton field in southern Xinjiang as the experimental area,aiming at the influence of soil salt,water and other key factors on the apparent conductivity,based on the data of EM38-MK2 and the measured conductivity data of different depth stratified samples of soil profile collected synchronously,and makes use of multiple linearity Model,three-dimensional inverse distance interpolation method,indicator Kriging method and other methods were used to study soil sampling method,accurate interpretation of farmland soil conductivity,three-dimensional visualization of soil salt content,spatiotemporal variation of soil conductivity in cotton field and risk assessment of cotton growth.The main results are as follows:?1?Inversion Model for Soil Conductivity in Cotton Field in South Xinjiang Based on EM38-MK2DataIn this study,different soil sampling schemes were designed in line with the designing of the transmitting coil and receiving coil of the electromagnetic sensor?EM38-MK2?,and soil apparent electrical conductivities?ECa?and soil samples from corresponding soil profiles were collected in the same field in six different time periods for analysis of,effects of soil sampling scheme and soil moisture content on accuracy of the apparent EC model,and specification of factors for building apparent EC models for different soil layers.Moreover,comparison was done of the local model based on data of a single period with the model based on overall data of the six periods in inversion accuracy.Results show that the model based on single point sampling at the site of the transmitting coil of the EM38-MK2 was higher in sensoring accuracy and stability than the others and hence could effectively minimize the error caused by sampling.When soil moisture content was less than 10%,the correlation between apparent EC and measured EC was low,with determination coefficient being 0.58 and the inversion model could only roughly estimate EC;When it was more than 10%,apparent EC displayed a good relationship with measured EC,with determination coefficient being 0.80 and the inversion model could make an estimation of EC close to the measured one.The EMH+EMV model was built on the equation of EC_h0.375+(EC_h0.75+EC_v0.75)/2+EC_v1.51.5 defined as modeling factor and much higher than the EMH or EMV model in inversion accuracy with predicted apparent EC being very approximate to measured EC.The local models for predicting ECs in various soil layers different in depth were all higher than the overall one in inversion accuracy and their RPDs were more than 2.0,which indicate that they have high prediction ability.All the findings in the study demonstrate that sampling under the transmitting coil is conducive to stability of the sampling,which may guide future utilization of the equipment,and open up new ways of thinking and server as reference for monitoring soil salinization dynamically with the electromagnetic sensor technology on the field scale.?2?Study on two-dimensional spatiotemporal variability of soil salinity in cotton fieldsAiming at the repetition of soil salinization and the increasing scarcity of water resources in southern Xinjiang Tarim River Oasis Area,this paper takes the typical plot in this area as the research object,uses electromagnetic induction instrument to obtain soil salinization information technology quickly,and studies the soil salinity profile of Tarim River Oasis area in Xinjiang,combined with statistical interpolation,The classification of soil salinity profile and the spatial distribution of soil salinity profile in the study area were discussed with the ratio of apparent conductivity ECv_1.5.5 and ECv_0.75,and the results showed that the ECv_0.75.75 data in different periods were strong variation intensity,and the salt showed cumulative state throughout the growth period of cotton.The semi-variance functions of ECv_1.5.5 and ECv_0.75.75 ratios are in line with the exponential model in different periods,and the spatial autocorrelation between the data is composed of stochastic factors and structural factors.The spatial distribution of soil salt profile types in different periods shows that the type of soil salinity profile presents the distribution of bottom polymerization-table polymerization-bottom polymerization in the growth period.Soil texture,microtopography,temperature and groundwater burial depth are the most direct factors causing the distribution pattern of soil salt profile type.The results of this study have a certain guiding role in the scientific formulation of irrigation systems.?3?Study on 3D spatio-temporal variability of soil salinity in cotton fieldsBy collecting the apparent conductivity data of four different periods of soil and the indoor measured conductivity data of synchronously collected soil profile samples,the inversion model between the measured conductivity and apparent conductivity of different soil layers in the soil profile was constructed by using the multiple linear regression method,and the 3D-IDW method was used to realize the 3D visualization of soil salt The temporal and spatial changes of salt in soil profile of cotton field under mulch drip irrigation in arid area of Xinjiang were studied.The results show that there is a good correlation between the apparent conductivity and the measured conductivity,and the determination coefficient?R²?of the inversion model of the measured conductivity based on the apparent conductivity data is between 0.82 and 0.99;the 3D visualization technology based on 3d-idw can show the distribution position and content of salt in the soil profile with high precision,and the cross validation between the soil conductivity and interpolation in different periods The correlation coefficient?R?of soil conductivity is greater than 0.85.The three-dimensional statistical results of soil conductivity show that due to irrigation,mulching and uncovering activities and natural factors such as temperature,evaporation and groundwater level,the distribution characteristics and content of salt in soil profile are quite different in different periods.In March,the salt distribution type of soil profile in March was uniform,and the conductivity range of 0-100cm soil profile was 0.78-0.88dS/m.which is epimeric in June,July and October.The salinity in June and October is mainly distributed in 0-20cm,the conductivity in 0-20cm is 3.32 and 5.28 dS/m,the conductivity in 20-100cm is 0.99-1.36 and 0.95-1.70dS/m,respectively.The salinity in July is mainly concentrated in 0-40cm,the conductivity in 0-40cm is2.25-2.45 dS/m,and the conductivity in 40-100cm is 0.87-0.93 dS/m.The results can be used as a guide for the accurate irrigation time node and irrigation amount.?4?Risk assessment of cotton planting based on 3D visualizationThrough selecting the threshold value of salt tolerance in different growth periods of cotton,the conductivity of soil layers in different depths in different periods is transformed into the corresponding indicator value.According to the indicator value in different periods,the semi variance function is simulated and calculated by GMS software,and the theoretical model of semi variance function is used for fitting to get the best semi variance function model.When three-dimensional discrete data interpolation,according to the best semi variance function model,the three-dimensional ordinary Kriging interpolation method is used to calculate the corresponding indication value?i.e.conditional probability?of the value of the point to be measured under the given salt tolerance threshold in different periods.Finally,the three-dimensional probability spatial distribution map of the whole test area relative to the salt tolerance threshold in different periods is obtained.The results showed that the salt content of soil in different periods in the experimental area showed a left leaning distribution,and the data did not conform to the normal distribution,and had a specific value,which was consistent with the indicator Kriging method.By constructing the three-dimensional isotropic semi variance nested model of experimental semi variance function and model semi variance function model,the spatial correlation of indicator transformation values in three-dimensional space in different periods can be well described.The spatial pattern of soil salt is closely related to the extreme climate,soil type and river distribution in the arid area.With the development of soil,the proportion of high-risk area in surface soil gradually increased,and the proportion of low-risk area gradually decreased,while the proportion of low-risk area in other soil layers was dominant.The salt content of soil gradually accumulated to the surface,and the salt content of soil became one of the main obstacles to the normal growth and development of cotton.By considering the spatial-temporal heterogeneity of soil salt,the three-dimensional visualization method intuitively and clearly expressed the three-dimensional probability distribution of cotton salt tolerance threshold in different periods,which provided an important theoretical basis for precise irrigation of cotton fields.The innovations or new developments were made as follows:?1?In this study,a soil sample collection scheme with different sampling positions is designed for one transmitting circle and two receiving circles of EM38-MK2 earth conductivity meter.The optimal collection scheme is determined by analyzing the model inversion accuracy of different collection schemes:the apparent conductivity of soil sample directly below the transmitting circle of the earth conductivity meter has the highest fitting degree with the measured conductivity of soil sample.In this scheme,the inversion model with the highest accuracy can be obtained and the efficiency of soil sample collection can be greatly improved?2?In this study,EM38-MK2 was used to obtain the soil profile salinity information quickly and non destructively.Combined with 3D spatial visualization technology,the spatial-temporal variation characteristics of multistage cotton soil profile salinization were analyzed.The spatial-temporal variation of surface soil salinization was promoted to the spatial-temporal variation of soil profile salinization.?3?In view of the problem that the effectiveness of the assessment results of the surface soil salinization risk is poor due to the different distribution depth of cotton root system and the spatio-temporal variability of soil profile salinization in different periods,this study adopts the multi-stage and different depth soil profile salinization data,and combines the salt tolerance threshold of cotton in different periods to systematically and comprehensively carry out the Salinization Risk of cotton field in southern Xinjiang The effectiveness of the evaluation results is significantly improved.