Soil Water And Heat Dynamics In Orchard Under Water Storage Pit Irrigation In Winter

The planting area of apple trees in China and the annual output of apple are in the first place in the world.In order to solve the problems of water resources shortage,drought and soil erosion in the main apple producing areas,Professor Sun Xihuan put forward the method of water storage pit irrigation in 1998.Winter irrigation is an important measure for water storage and soil moisture conservation.The water storage pit irrigation has increased the contact area between the soil and the atmosphere,and changed the dynamic change law of the water heat in the soil.Therefore,it is of great significance to study the water and heat dynamics of the soil in the orchard under the condition of water storage pit irrigation,which is of great significance to the safe overwintering and water efficient utilization of the storage pit irrigation orchard.In this paper,the field experiment and theoretical analysis were combined to set the ground irrigation as the control.The different winter irrigation water(no irrigation,60L/ plant,180L/ strain and 300L/ strain)and the cover(cover and no cover)were set up,and the freezing thawing process,soil moisture content and temperature of the soil under different treatment in the orchard with the time space The dynamic change law is studied.The main research results are as follows:(1)The freezing and thawing process of orchard soil can be divided into 3 stages: unstable freezing,stable freezing and thawing and thawing.With the increase of water content,the initial freezing time and the stable freezing delay,the stable freezing depth decrease,the stable freezing time shortens,the pit cover can postpone the freezing time of the soil,reduce the freezing depth and shorten the stable freezing time;the water storage pit irrigation has a larger freezing depth than the ground irrigation,and the melting thawing speed is fast.(2)The spatial distribution characteristics of soil profile quality water content under the condition of water storage pit irrigation are: in the unstable freezing stage,the moisture content increases first and then decreases with the depth of soil layer and the distance from the pit wall,and the water distribution is elliptical on the whole,with the increase of water content,the soil moisture content increases and the wetting range is enlarged.Whether or not the pit is covered has little effect on the distribution of moisture content after irrigation.The moisture content of surface irrigation decreases with the increase of soil depth,and the horizontal distribution is uniform.In the stable freezing stage,the water content decreases with the depth of soil layer and the distance from the pit wall,and is distributed along the storage pit on the whole.With the increase of the water content,the soil moisture content in the soil layer above 40 cm rises continuously;the soil moisture content in the pit covers the soil and the soil water content is higher than that in the pit,and the water distribution of the ground irrigation is more uniform.In the stage of thawing,the water content of the vertical soil increased first and then decreased,and increased with the increase of the distance from the tree trunk in the radial direction;the irrigation amount had little effect on the soil water content;the water content of the soil covered soil covered the soil was larger than that of the uncovered soil,and the water retention of the soil was increased;the water storage pit irrigation was concentrated in the middle and deep soil.The water content of surface irrigation decreased from top to bottom and distributed evenly.(3)Under the condition of water storage pit irrigation,the dynamic change of soil water content with time is that the soil moisture content increases first and then decreases with the increase of depth in the unstable freezing stage.As time goes on,the atmosphere temperature decreases,the surface soil water begins to freeze,and the soil moisture content in the frozen area increases gradually to the stable freezing stage.The depth of the freezing is maximum,and the distribution of soil water content decreases with the increase of depth,and the distribution of soil water content increases first and then decreases with the increase of depth.As a whole,the quantity of water content in the soil layer above 60 cm rises first and then decreases with the change of time..With the increase of water content,the time of the increase of surface water content is postponed,the range of high water content area is reduced;the pit cover postpones the time of water abrupt increase and reduces the range of high water value area,and the water content of soil irrigation soil irrigation is slow with time.(4)The diurnal variation of soil temperature in the orchard under the condition of water storage pit irrigation is as follows: 4 the soil temperature decreases and then decreases with the passage of time.The soil temperature decreases with a sinusoidal distribution;the change amplitude of soil temperature decreases with the increase of soil depth in the same day;in the unstable freezing stage and the stable freezing stage,the soil above 40 cm The temperature of the layer increased with the increase of irrigation volume.During the thawing and thawing stage,the temperature of 40 cm soil layer decreased with the increase of irrigation volume.The temperature diurnal variation of 10-20 cm soil layer in the whole freeze-thaw period can be fitted by sine function formula,and the fitting correlation coefficient R2 is higher than 0.76.(5)The daily variation of soil temperature in the orchard under the condition of water storage pit irrigation was as follows: the soil temperature decreased first and then increased with the increase of soil depth,and the depth of the same soil layer decreased with the increase of the soil depth,and the mean value increased and the standard deviation decreased continuously.(6)The spatial distribution of soil temperature in the orchard under the condition of water storage pit irrigation is: in the unstable freezing stage,the soil temperature increases with the increase of soil depth,and increases first and then decreases with the increase of the pit wall distance from the storage pit.With the increase of the irrigation amount,the soil temperature increases and the low temperature range near the pit wall decreases.The temperature difference on the section is also decreasing.In the stable freezing stage,with the increase of the depth of the soil layer,the temperature increases first and then decreases with the increase of the pit wall distance,and the low temperature range near the pit wall decreases with the increase of the amount of irrigation.In the stage of thawing,the spatial distribution characteristics of the soil temperature profile are consistent with the distribution characteristics of the first two stages.With the increase of the irrigation amount,the soil temperature at the same point is basically unchanged.The temperature of the soil profile is basically up to 0 degrees centigrade except the surface soil;the soil temperature can be raised and the low temperature range can be reduced by the cover of the pit.Small temperature difference.