Study On The Basic Characteristics Of Ecological Conservation Substrate And Its Water Transport Characteristics

The ecological and environmental problems in the northwest of China are becoming increasingly serious,the desertification area is growing,the utilization rate of land resources is low,and there is a lack of industrialized large-scale planting conditions.Based on conservation brick technology,the study explores high-quality substrates and related theoretical characteristics with industrialization as the way forward;based on the actual situation in northwest China,it responds to the development of Gobi ecological agriculture and taps the ecological functions carried by agriculture,aiming to change the current situation of resources and environment with modern agricultural technology.Through the investigation of the western region of the river and the upper reaches of the Yellow River,we narrowed down the scope of the search by physical indexes such as falling fragmentation and density,selected suitable materials(sandy soil,coconut coir,artificial peat)to prepare the conservation brick substrate,improved the water retention capacity of the substrate,and explored the hydraulic and infiltration characteristics.Combined with the relevant mathematical methods to select the best,to create a lightweight,high-quality solid substrate;then set the flow rate of 0.8L/h,1.2L/h,1.6L/h,2.0L/h,etc.,combined with the optimal substrate for drip irrigation double point source simulation test,to explore the water transport characteristics of the brick substrate in the soil,to lay the foundation for the irrigation technology management of this substrate.The main research results are as follows:(1)By replacing the soil substrate fraction with coconut coir,we obtained several groups of lightweight conservation brick substrates(breezy soil:coconut coir:organic fertilizer:artificial peat=3.5:3.5:3:1 or 3:4:3:1 or 2:5:3:1)with certain resistance to falling and shattering,and their masses were reduced by 63.17%on average compared with the group of all-breezy soil substrates.In terms of physicochemical properties,most of these initially screened groups met the specifications and were better cultivation substrates.(2)According to the analysis of the water characteristics curve of the substrate,it was found that the water holding and water supply capacity of the initially screened substrate increased significantly,with an average increase of 9.91%in total effective water content and an average increase of 9.87%in capillary pore space;coconut bran changed the pore size distribution ratio and specific water capacity of the substrate and reduced its drainage capacity.In addition,combined with the water content monitoring,it was found that coconut bran not only increased the saturated water content of the substrate,but also impeded the deep infiltration of water,and the substrate made of the mass ratio of the substrate part of wind-sand soil:coconut bran=1:1 blocked the infiltration most obviously.The infiltration model fitting found that R~2≥0.89922,the fitting effect is better and can reflect the actual process of substrate infiltration more accurately;according to the gray correlation analysis,the infiltration performance of the substrate with the mass ratio of substrate part of sandy soil:coconut coir=2:5 is the best.(3)Through the comprehensive evaluation of coordinates,the group of wind-sand soil:coconut bran:organic fertilizer:artificial peat with mass ratio=2:5:3:1 has the best performance in terms of water retention and water permeability,stability and nutrient content.Therefore,in practical production consideration and construction,this ratio is recommended to initially meet the conditions of industrial pavement transportation and high quality standardization.(4)When the drip head spacing is certain,the greater the drip head flow,the greater the horizontal wetting front transport distance,the smaller the vertical wetting front transport distance;irrigation water increases,both horizontal and vertical wetting front transport distance increases.The intersection location(intersection surface)is approximately in the middle of the two drip heads,water content and wetting fronts are roughly symmetrical distribution with the intersection surface as the axis,the shape of the wetting body is from two semi-ellipsoidal shape into a more uniform"peanut shell"shape.The wetting front intersection time is related to the drip head flow,and its negative correlation;intersection will accelerate the transport of wetting fronts on the intersection surface.(5)The water distribution in the wetted body of the intersection area was based on the location of the brick substrate as the front value,and the water content contour of the intersection area showed a distribution similar to the"several"shape.Under the same irrigation conditions,the water content of the intersection surface decreases with increasing depth;the higher the drip head flow rate,the higher the water content of the shallow layer in the intersection area.After the end of irrigation,the location of the highest water content is closer to the soil surface as the drip head flow rate increases,and the approximate change range is the substrate layer.In addition,the water was redistributed through a certain time,and its highest water content location was located near the bottom soil layer of the brick(near the vertical depth of 12 cm),which provides some guidance for the irrigation management of this substrate.