Vertical Distribution Of The Observed And Simulated Soil Status In Fuping Ecological Station

The Shaanxi Central Plain is an important region for food production in Northwest China,obtaining its vertical distribution and process mechanism of soil water-heat-salt status in the typical field has important significance for the efficient use of water resources in this area and scientific management.The Shaanxi Central Plain typical winter wheat and summer maize rotation field as the research object,based on the soil observation data from Fuping ecological station ground part,carried out the temporal and spatial changes of soil water-heat-salt status for the experimental observation and numerical simulation.Firstly,using the classical statistical methods and drawing the space-time contour maps,the temporal and spatial variation characteristics of soil water-heat-salt status in the vertical direction are analyzed and imaged.After the detailed soil observation data for calibrating existing SWAP model and using the model of the study area during the observation period and historical period of each layer soil water movement,solute transport and heat transfer process are numerically simulated.The main results have been obtained as follows:(1)Studies on the descriptive statistics of each index of soil condition showed that:Since the establishment,the observation profile 0?250cm layer water content,conductivity and temperature range was 0.18?0.39cm3/cm3,0.06?4.67mS/cm and-1.90?35.06?.The coefficient variation of above three indicators with the increase of soil depth decreases gradually.0?80cm soil layer is water content and electrical conductivity is relatively active;the mean soil temperature at different depths basically stable at 15 ?.The value distribution of each index sequence is close to the normal distribution.(2)Studies on the temporal and spatial correlation characteristics of each index of soil difference;40cm to 80cm than 200cm to 250cm has the significant spatial correlation.During the period of April 2014 to September 2014,with the change of rainfall events in study area and field canopy increased environmental conditions,each layer of water content and temperature time sequence autocorrelation compared to the previous period has been significantly improved;80cm and above of the soil conductivity's time autocorrelation sequence change is not obvious.Most index series of the inter layer correlation represent the significant positive correlation.(3)Studies on temporal and spatial distribution characteristics of each index of soil condition showed that:The temporal and spatial distribution characteristics of 0~250cm each state index of intraday and intra year were investigated by drawing space-time contour maps.Soil water content and electrical conductivity in the range of 0?10cm than other layers basically have no obvious diurnal variation.By the diurnal variation of solar radiation and heat transfer in the process of decay and lag,diurnal variation in time and depth direction of the soil temperature are more significant.Maxima and minima of soil water content and electrical conductivity appeared in 0?10cm and 110cm below in different years.The middle layer of the annual variation is active.The temperature contours of the annual distribution have periodic variation characteristics.By the comprehensive comparison of three state index contour in the corresponding distribution of the year,soil water content compared to the soil temperature have larger extent affection to the soil electrical conductivity of temporal and spatial distribution in the study area during the observation period.(4)Studies on sensitivity analysis and calibration for SWAP model showed that:Environmental response parameters on the simulation results of each index is generally low sensitivity,while the soil hydraulic parameters and crop root uptake parameters on the soil salt content and soil water content simulated results is higher sensitivity.There are still more or less simulated deviations to upper layers of water content,salt content and temperature during the individual periods.But overall,the calibrated and verified SWAP model could well simulate dynamic variation laws of water-salt content and temperature of different soil layers in the study area.(5)Studies on simulating the dynamic variation of soil water-heat-salt status showed that:During the reconstruction period,0?80cm as soil water-salt dynamic range is more complex area,and the depth is greater than or equal to 100cm is stable area,and the middle layer is a continuous process of relatively stable.Consistent with the temperature change and soil temperature change profile in different seasons showed obvious periodical change characteristics.Inter-annual differences reconstruction period in each layer of soil water and salt fluxes varied from month to month is mainly reflected in the annual growth period of summer maize.The salt flux has the upward direction at greater than or equal to 80cm in individual date.But the water-salt flux direction in most cases is mainly down.Soil temperature gradient variation has small differences in inter-annual,but the heat transfer direction of soil profile will occur two times change in each year.Because of the vertical heat transfer process of the hysteresis and attenuation effect,the direction of the conversion time node will have slightly deviation.