| Subsurface irrigation could directly supply water to the roots of crops,so that the water use efficiency is highly,which has obvious water-saving and yield-increasing effects.However,there are problems such as high energy consumption of the system,environmental pollution and soil degradation,because the plastic drip irrigation tapes and emitters are difficult to recycle and degrade.These problems would restrict the large-scale application of this irrigation technology.Therefore,this paper uses the reference of the experience of ancient pitcher irrigation,combine the basic requirements of modern water-saving irrigation technology（water-saving,energy-saving and environmentally friendly）,the porous ceramic emitters was prepared.Material formulation and performance of porous ceramic emitters was studied systematically;the outflow mechanism of the emitter in the soil under zero pressure and micro pressure was revealed;the reasonable value of the key technical parameters of field application of porous ceramic emitter was determined;finally,the effect of saving water,increasing production and improving quality of porous ceramic root irrigation technology was comprehensively analyzed and evaluated.The main results were listed as follows:（1）Two kinds of material formulations suit for preparing porous ceramic emitters are preferred,and porous ceramic emitters/drip irrigation pipes of three different structures are developed.The diatomite porous ceramic was prepared by a sintering technology using clay,diatomite,and calcium sulfate and silica sol as raw materials.The porous ceramic irrigation emitter showed the best performance when the sintering temperature was 1 075°C and the content of diatomite was 15%.Under such conditions,the porous ceramics had the Vickers hardness of 448 MPa,the open porosity of 26.3%,but its linear shrinkage only 4.9%.Quartz-based ceramic emitter was fabricated using quartz with different particle size,talcum powder,and dextrin and silica sol as raw materials.The open porosity and mean pore size decreased as particle size decreased.The optimum sintering temperature was1200°C,and the suitable particle size of quartz in the raw material was 38-75 um.Based on the studies of diatomite porous ceramics and sand-based porous ceramics,bypass porous ceramic emitter（up-tube form;down-tube form）,inter-tube porous ceramic emitter and porous ceramic patch were developed.The up-tube form bypass porous ceramic emitter which was sintered at 1200°C has a discharge of 0.72 L/h at a working pressure of 20 cm.The inter-tube porous ceramic emitter was prepared by using quartz with a diameter of 38-75 um which had a small in manufacturing deviation and discharge.In order to meet the requirements of different crops,the discharge of porous ceramic patch-type subsurface drip irrigation pipe（CP-SDIP）can be adjusted by changing the material of the ceramic water-seepage pad which is the core component.The CP-SDIL pressure-discharge relationship is linear,and the flow region index is one.Therefore,discharge from the CP-SDIL is extremely sensitive to working pressure.Since the discharge is sensitive to pressure,it changes as the soil water potential changes.（2）The outflow process model of microporous ceramic emitter was established,and the outflow mechanism of the emitter under negative pressure,no pressure and micro pressure was clarified.The outflow mechanism of porous ceramic emitter is different from the subsurface drip irrigation belt.Water contents in the wetting zone of porous ceramic root irrigation change slightly.But water contents of subsurface irrigation increased continuously,and then got decreased after stopping irrigation because of soil water redistribution.Because porous ceramic infiltration irrigation is a continuous irrigation method,so it could provide a constant water moisture environment for crops.But subsurface drip irrigation is a passive and intermittent irrigation method,so water moisture environment for crops is alternate drying-wetting.When the working pressure of the porous ceramic emitter is non-pressure,the basic cause of soil water content change is the change of the emitter discharge change,which decreases gradually with the increase of water contents around the emitter.When the soil water content is saturated,the emitter discharge would be stopped.When the soil moisture is dissipated,the flow would recover from emitter again,and the discharge is approximately equal to soil evaporation capacity.Therefore,the emitter discharge would supply the soil water content in time.When the working pressure of the porous ceramic emitter is micro-pressure,discharge of ceramic emitter in the soil decreased gradually with time and finally stabilized.On the contrary,the soil water content around the emitter increased rapidly,tending to approach saturation.The change of soil water potential was the direct cause for changing of emitter discharge.When the designed flow rate higher than soil saturated hydraulic conductivity,a saturated zone formed around the emitter and a certain positive pressure was generated.Therefore,the infiltration rate was less than the designed flow rate.On the contrary,when the designed flow rate was smaller than soil saturated hydraulic conductivity,the soil water potential around the emitter would be negative pressure and promoted the outflow of emitter,and the infiltration rate would be bigger than designed flow rate.Soil water content around emitters had an appreciable negative effect on emitter infiltration rate in the soil.There was a feedback regulation relationship between the water content and emitter discharge.Therefore,when the porous ceramic emitter is used as the core component of the irrigation system.Under the condition of suitable working pressure and design flow are choose,the emitter discharge can replenish its water requirement according to the crop in real time,achieving the purpose of continuous and adaptive irrigation.（3）The application parameters of microporous ceramic emitters were proposed,and the technical parameters of vegetable and forest fruit irrigation were preliminarily determined for different soil textures.Soil texture has significant effect on emitter discharge,soil matrix potential around the emitter,and wetting front.For 12 different soil textures,aspect ratio of the wetting front is basically between 1.01-2.13.In sandy soil,the wetting front mainly appears as an ellipse;but in the clay,the wetting front is closer to a circle.As irrigation time increases,emitter discharge gradually decreases to a stable value;however,emitter discharge in different texture soils is quite different.Both the working pressure head and ceramic hydraulic conductivity have significant impact on the discharge of emitters in soil,and the deep percolation water losses.When the working pressure head and ceramic hydraulic conductivity are higher,the stable discharge（emitter discharge in soil at 120 h）is greater.The relationship between the working pressure head,ceramic hydraulic conductivity,and stable discharge is developed as a power function.Based on the combination of numerical simulation and experimental research,according to the law of soil water movement,combined with the distribution characteristics of crop roots,to meet the water requirements of crops,and considering the risk of deep leakage,a method for determining the application parameters of microporous ceramic emitters was proposed.For the four representative soils such as sand,loam,clay and sandy clay loam,the irrigation technical parameters（work pressure,design flow and depth）of fruit trees（apples）and vegetables（tomato and cucumber）were preliminarily determined.For apples:the suitable working pressure,design flow rate and depth of ceramic emitters in sandy clay loam are 40-50 cm,1.16-1.20 L h-1 and 25 cm,respectively;20-50 cm and0.72-0.98 L h-1 and 45 cm in loam,respectively;in silty clay loam,the irrigation technical parameters is 40-50 cm,1.79-2.08 L h-1 and 45 cm respectively;due to the high risk of deep percolation,ceramic emitters are not recommended to be used in sand.For tomato and cucumber:the suitable working pressure,design flow and buried depth of ceramic emitters in sandy clay loam are 0 cm,L h-1 and 25 cm,respectively;0 cm,0 L h-1 and 15 cm in loam,respectively;10 cm,0.006 L h-1 and 25 cm in clay,respectively;0-20 cm,0-0.03 L h-1 and15 cm in sand,respectively.（4）A microporous ceramic root irrigation system was constructed and applied in the field.Porous ceramic root irrigation and subsurface drip irrigation can effectively promote the growth of new shoots of apple trees,and improve the apple fruit index（single fruit weight,volume and transverse diameter）while ensuring the quality of apples.The length of new shoots treated with porous ceramic root irrigation with a depth of 40 cm was 15.9%（5.90 cm）higher than that of subsurface drip irrigation,and the fruit index and quality index（VC content,titratable acid,etc.）were comparable.Under the condition that the irrigation amount is basically the same,in two years,the apple yields of ceramic root irrigation treatment with a depth of 40 cm are increased compared with the subsurface drip irrigation,with an average yield increase of 7.6%（119 kg）and the highest water use efficiency（4.69 kg/m3）.According to the average purchase price of apples（6 yuan/kg）in2017 and 2018,farmers can increase annual income by 709 yuan/year（compared with subsurface drip irrigation）,4418 yuan/year（no irrigation）.The comprehensive index of apples under the ceramic root irrigation treatment with a depth of 40 cm reached the maximum.It is considered that the ceramic root irrigation technology is used to irrigate the mountain apples in the Loess Plateau,the buried depth of emitter could be 40 cm.It can not only promote the increase of production and efficiency of apples,but also increase the farmers’income while ensuring the good quality of apples.This paper will provide theoretical guidance and technical support for the promotion and application of porous ceramic root irrigation technology and porous ceramic emitter/drip irrigation belt. |
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