Law And Simulation Of Soil Water And Salt Movement In A Costal Saline-Sodic Cotton Field In Hebei Province

It is of great theoretical and practical significance to ensure the national grain and cotton production to clarify the law of soil water and salt transport and its effect on cotton growth and development.Based on the existing research,field experiment about cotton cultivation in Jidong coastal plain were conducted,soil salinity level(low and high salinity soil)and planting patterns(Conventional flat planting with film mulching,CF and Ridge-furrow planting with film mulching,RF)were considered.After measuring soil physical and chemical properties,soil water content(SWC),electrical conductivity(EC)of soil extract,electrical conductivity(ECsw)of soil solute,cotton growth characters,root growth distribution,cotton seed yield and cotton fibre quality,the law of soil water and salt transportation and cotton growth characters were analyzed,the mechanism of cotton growth and soil water and salt transportation were defined;a mathematic model which can simulate soil water and transportation under CF and RF conditions was created;combined with the typical hydraulic year and cotton water requirement,we simulated and summed the basic law of soil water and salt transportation under different salinity and cultivation conditions in Jidong coastal plain.The main results and conclusions are as follows:(1)Basic characters of soil water and salt transportation were clarified.Soil water and salt transportation in the 0 ~ 60 cm layer were influenced by precipitation and evapotranspiration as well as soil salinity level and cotton cultivation during the cotton growth period.Significant differences for soil water and salt transportation were found between the inside and outside the mulch under CF conditions.In 2014,SWC inside the mulch were 5.91% lower and EC were 19.56% lower than that outside the mulch during the boll setting stage;while in 2015,SWC and EC inside the mulch is 2.48% and 1.68% higher than that outside the mulch across the budding period.For RF planting,SWC inside the film mulch were always higher and EC was lower than that outside the film mulch,and in 2014 and 2015,SWC inside the film mulch is 22.33% and 9.87% higher than that outside the film mulch,and the correspond value for EC is 24.66% and 54.25% lower.SWC distribution in 0 ~ 60 cm layer for the four treatments increased from up to bottom and EC distribution showed the opposite during the dry period.SWC distribution were uniformly and EC distribution increased from up to bottom in 0 ~ 60 cm layer,no significant differences were found for SWC and EC distribution inside and outside the film mulch across the wet period.(2)The response mechanism of cotton growth and soil water and salt transport to soil salinity and cotton planting were revealed.Impact of soil salinity on cotton growth is significantly(p < 0.05)higher than planting pattern: seed emergency rate,aboveground dry biomass,root distribution,seed yield and some other growth characters for the high salinity treatments were significantly lower than that of the low salinity treatments.Compared to CF planting,RF can provide a more suitable environment for cotton growth.Soil salinity and planting pattern have no significant influence(p ? 0.05)on fibre quality.In conclusion,RF is suggested for high salinity soil to increase cotton production.(3)A mathematical model for water and salt transport simulation in the root zone for CF and RF conditions was built,and the correspond boundary conditions and model parameters were defined.With parameter sensitivity analysis,the most sensitivity parameters were selected out.RMSE for simulated and measured SWC values were 6.96% ~ 7.09%,and for ECsw were 12.98% ~ 19.50%.The water and salt simulation model in the present thesis got a high simulation accuracy.(4)The process of water and salt transportation under typical hydraulic year were also simulated with the new built mathematical model,relationship between precipitation and simulated salt leaching efficiency were statically analyzed.The simulation results showed that soil salinity decreased in wet and normal year and increase in dry year,moreover,salt leaching efficiency of RF is higher than that of CF.