| With the rapid increase of population and the expansion of industrial land,the the quantity and quality of cultivated land are decreased continuously,and the contradiction between human and land is extremely prominent in the coastal zone.Land resources have become an important obstacle to the economic development and the food security of the coastal zone,and the challenges facing the food security and the sustainable use of land are becoming more and more serious.Coastal tidal flat wetland is an important reserve land resource,and the soil salinization is a key factor restricted its development and utilization.It is of great significance for the prevention and utilization of salinized soil to explore the soil water and salt movement rules,its influencing factors,and forcast of soil sanilization under different amelioration modes.In this paper,a typical coastal tidalflat reclamation area(reclaimed in 1951,1974,1982 and 2007)with different years in Rudong County,Jiangsu Province,and the typical new tidal flat reclamation area(reclaimed in 2008)in adjacent Tongzhou Bay Coastal Zone are selected as study area.The spatial and temporal distribution characteristics and the main controlling factors of soil salinization in the traditional farming mode,the dynamic characteristics of soil moisture,soil salt content(SSC),salt ions,pH,sodium adsorption ratio(SAR)and exchange sodium percentage(ESP)and its main controlling factors under different amelioration modes,and the response of oat growth and yield and their relationship with soil salinity were analyzed by statistical analysis(descriptive statistical analysis,correlation analysis,one-way ANOVA),spatial interpolation analysis,redundancy analysis and Monte-Carlo test.Then the dynamic of soil water content,SSC,soil pH,SAR and ESP under the amelioration modes were predicted based on the BP neural network model,the random forest model and the multiple linear regression model.The main conclusions are as follows:(1)The differences of soil salt ions and other salinization indicators in the study areas is huge,and the main ions are Na+ and Cl-,which also a high degree of soil salinization and belongs to the chloride type under the traditional agricultural reclamation mode.Soil salinity also showed an obvious temporal and spatial variation characteristic.According to the spatial characteristics,the soil K+,Na+,Mg2+,SO42-,Cl-,SSC,pH,SAR and ESP are gradually decreasing from sea to inland,while the concentration of Ca2+ shows a spatial distribution pattern with higher content in the southeast and northwest and lower content in the middle area of study area,and the spatial distribution of HCO3-is just the opposite of Ca2+.According to the temporal characteristics,SSC,pH,SAR and ESP first increased slowly and then continued to decrease with the increase time of reclamation years,and decreased to mild salinization level after 30 years'reclamation,and basically to non salinization level after 61 years'reclamation.Correlation analysis,redundancy analysis and Monte Carlo test showed that soil properties,such as soil particle size,soil nutrients and soil bulk density,were the main controlling factors affecting the degree of soil salinization in the study area.(2)The experiment showed different amendment methods have significant influence on soil moisture,SSC,salt ions,pH,SAR,ESP and other physico-chemical properties under the rapid ameliorate mode.The surface soil water content decreased gradually while the soil salinity gradually increased during the growing period of oats,and showed an obvious temporal variability.Compared with the CK treatment,the amendment treatments continuously increased the surface soil moisture except in the later growing stage of SM+OM treatment,and significantly reduced the content of soil salt,Na+and Cl-ions in the depth of 0?40 cm during the oat growth period.In the growth period of oat,the surface soil pH decreased gradually while SAR and ESP showed a slow rising trend with increasing time,and the value of surface soil pH,SAR and ESP were also different in the growing season,and the amendment treatments could effectively reduce the SAR and ESP in the whole growing season,especially under BM+OM treatment.The redundancy analysis showed that soil salinity was mainly controlled by Na+and Cl-,and the soil pH was mainly influenced by the content of HCO3-and Ca2+,while SAR and ESP were mainly influenced by Na+,Cl-,HCO3-and Ca2+,and the Monte Carlo test also showed Na+,Cl-,HCO3-and Ca2+ are the key ions that influencing soil salinization.The redundancy analysis of soil salinization degree and environmental factors and Monte Carlo test showed that the effects of soil bulk density,soil moisture content,evaporation and amendment treatment on the salinization characteristics of surface soil under different ameliorate modes were extremely significant,and the influence of wind speed and precipitation also reached a significant level.(3)In this experiment,different amendment treatments had significant effects on oat growth(stem diameter and plant height),aboveground biomass and yield under the rapid ameliorate mode.The oat stem diameter and plant height of PAM+OM,SM+OM,BS+OM and BM+OM treatments were consistently higher than that of OM treatment during the growing season,while the stem diameter and plant height were not observed under CK treatment,and the aboveground biomass and yield showed a similar trend.Correlation analysis and redundancy analysis showed that oat growth was significantly affected by soil salinization.The degree of soil SAR and ESP are the key factors affecting oat growth during the whole growth period.Suface soil salinity had a significant restriction on the growth of oat at the seedling stage,filling stage and maturity stage,but not at the jointing stage and heading stage.Similarly,soil pH reached a very significant level at the seedling stage,jointing stage,heading stage and maturity stage whereas the filling stage were not.From the view of oat growth and yield,BM+OM treatment can significantly reduce the level of soil alkalinity(pH,SAR and ESP),and significantly increase the growth and yield of oats,thus it is an ideal ameliorate method.(4)According to the simulation results of soil water and salinization characteristics,the BP neural network(BP-ANN)model and random forest(RF)model can be well applied to the prediction of soil moisture,SSC,pH,SAR and ESP under ameliorate mode,while the predictive effect of multiple linear regression(MLR)model is poor.Under the ameliorate mode,the characteristics of soil moisture and soil salinization are influenced by various environmental factors,such as climatic factors,soil structural factors and soil fertility,and the spatial variability of soil water and soil salinization is larger.The error of BP-ANN model,RF model and MLR model is larger when predicting the high value and low value,whereas the effect is ideal when the intermediate value is simulated. |
PDF Full Text Request