Research On Nitrogen And Potassium Nutrient Diagnosis Method Of Greenhouse Cucumber Based On Sap Ions And Stem Puncture Characteristics

Cucumber is the main cultivated crop in facility agriculture.Its planting scale in China is only second to that of tomato,ranking first in the world.Therefore,accurate analysis of nitrogen and potassium nutrition of greenhouse cucumber,so as to improve fertilizer utilization rate and cucumber yield and quality,is of great significance for maintaining national food safety,promoting the development of smart management and control of greenhouse in China,and realizing agricultural modernization in China.At present,the greenhouse cucumber information acquisition and accurate analysis of nitrogen and potassium nutrition still have large deficiencies,lacking the information perception mode of dialogue with crops.First of all,the interaction mechanism between the nutrient elements required by crops is unknown,which leads to the phenomenon of homospectral heterogeneity in the accurate analysis of nitrogen and potassium nutrition of crops.Secondly,as the only channel between root and leaf,the response mechanism of cucumber stem growth and development to external nutrient conditions has not been widely concerned.There are relatively few studies on using the K⁺content in the stem apoplast sap to accurately analyze the cucumber’s nutritional status,and there is a lack of methods and devices to detect nitrogen and potassium information while causing less damage to the plant.Therefore,based on the research of domestic and foreign scholars,this research takes greenhouse cucumbers as the research object to study the above issues,and uses minimally invasive crop body information acquisition and wearable nitrogen and potassium information detection devices to achieve accurate analysis of crop nitrogen and potassium nutrition.The specific research contents are as follows:（1）Taking"Jinyou No.1"cucumber as the experimental object,the change rule of growth indexes such as morphology,photosynthesis,dry matter accumulation and root development of greenhouse cucumber,as well as the content of H₂O₂ in cucumber leaves and stems,the activity of related enzymes and the transport of carbohydrate substances under nitrogen and potassium stress was studied.The results showed that nitrogen had a very significant effect on the growth of cucumber stems,and the stems also had a positive response to external stimuli.Under the independent and combined stresses of high nitrogen,the biomass accumulation of cucumber stems was inhibited,while under the independent and combined stresses of low nitrogen,the dry weight of cucumber stems increased by at least 23.01%.When a large amount of H₂O₂ is accumulated in the leaves,the H₂O₂ in the stems remains at a relatively low level,but the leaves and stems have similar content of MDA,which indicates that the stems are more sensitive to stress than the leaves.Secondly,the K⁺concentration in cucumber stem apoplast sap is mainly related to the external potassium supply.Under LN treatment and HN treatment,the K⁺content in apoplast sap changed little.However,the K⁺concentration under LK,LNLK and HNLK treatment decreased by 23.77%,37.32%and 51.92%respectively,while the K⁺concentration under HK,LNHK and HNHK treatment increased by at least 54%.It can be seen that it is feasible to detect nitrogen and potassium nutrition information of cucumber through stem characteristics and potassium ion content in apoplast sap.（2）By analyzing the microstructure characteristics of cucumber stems in greenhouse,it is found that the diameter of the middle stems is 7000μM,compared with the upper stem,it is less affected by surface burr and contour,and easier to conduct puncture operation.Compared with the lower stem,the physiological activities of middle stem such as growth and metabolism are more vigorous and the perception of the supply of nitrogen,potassium and other elements is more sensitive.Therefore,the middle stalk was selected for the analysis of puncture mechanical properties,and most of the cucumber stalks could be healed within 25 hours without being affected by puncture.The research shows that the mechanical properties of stems are mainly affected by nitrogen application,so we built a crop nitrogen detection model based on the mechanical properties of stems.The results showed that the R² of the nitrogen detection model based on the penetrability of stem epidermis under different potassium stress were 96.55%,95.09%and 90.9%,respectively,which had a good detection effect.However,the detection effect of epidermis brittleness and epidermis toughness on multiple treatments is poor,and the nitrogen detection model based on epidermis fracture depth is vulnerable to interference,while the nitrogen detection model based on stem penetration is more harmful to crops.Therefore,we finally chose to build a nitrogen detection model based on the penetration of stem epidermis,and added the influence factors related to potassium.It was found through validation that the R² and RMSE of the detected and measured values of nitrogen nutrition based on 1:1 straight line of the nitrogen detection model based on the penetrability of stem epidermis under the conditions of low potassium,normal potassium and high potassium were 0.9956and 5.8%,0.9942 and 6.8%,0.9915 and 7.5%respectively.This study greatly promoted the application of stem characteristics in crop stress physiology.（3）The flexible potassium ion sensor was studied,the Co Ni C composite was prepared,and the morphology and load of the composite were tested.The performance of the K⁺selective interdigital electrode was investigated through potential response test,electrochemical impedance test,chronopotentiometry,anti-interference and water layer test.The results show that the K⁺selective electrode prepared in this study has good stability and reliability,and has an ideal linear response in the range of 0.1-2 g/L.The R² of the working curve equation is 0.9947,and the slope is 50.336 m V/dec.The K⁺selective interdigital electrode modified with the composite material has a far higher selectivity to K⁺than the interfering ions,which proves that the prepared electrode has good recognition specificity for K⁺ions and strong anti-interference ability.Moreover,after the composite material is successfully modified,the signal conversion efficiency and electric capacity of the electrode are significantly improved,the formation of the water layer between the selective film and the substrate is effectively prevented.In the actual test,the R² and RMSE of the detected and measured values of the electrode based on the 1:1 straight line reached 0.9884 and 85.137 mg/L respectively,which proved that the electrode can fully meet the detection requirements of the actual scene.Moreover,at different growth stages,the electrode has a good detection effect on the K⁺content in the apoplast sap under different nitrogen treatments.At the same time,the electrode has strong adaptability and can be used to detect a variety of greenhouse crops.The study of potassium ion selective electrode plays an important role in accurately obtaining the true physiological state of crops by using the information in the body of crops and exploring the response mechanism of crops to adversity,which provides a theoretical basis for the detection of potassium nutrition by wearable devices.（4）The prepared potassium ion selective electrode still has good performance in micro detection,and the slope of the working equation reaches 46.782.However,due to the instability of the droplet on the electrode surface,the electrode micro detection is greatly difficult.Therefore,in order to improve the stability and accuracy of the electrode in micro detection,a structural design of an asymmetric three rib microfluidic chip was proposed and fabricated.The simulation results of liquid flow in the microchannel show that the asymmetric three rib microfluidic chip increased the accuracy and stability of electrode detection.The volume fraction of extracellular body fluid in the detection room was 98.2%,while the volume fraction of flushing fluid in the detection room was 89.7%.The prepared microfluidic chip ensures that the electrode can fully contact with the droplets during micro detection,thus realizing the pure and quantitative detection of samples,and significantly improving the detection accuracy and stability.The R² of the ion selective electrode for detecting trace potassium solution is 0.9341.The slope of the electrode is 54.65,which is 16.8%and8.6%higher than that of micro detection and immersion detection respectively.In the actual test,the microfluidic ion selective electrode showed a good detection effect,which can fully meet the detection requirements.（5）A wearable detection device for crop nitrogen and potassium information was designed.The R2 of the strain and force relationship model of the nylon fixed base is0.9993,which is larger than that of the photosensitive resin fixed base（0.9971）.Moreover,the strain range of the nylon base is 29 to 412 microstrains,which is larger than that of the photosensitive resin（19 to 240）.Therefore,nylon was chosen as the printing material of the base.Moreover,the maximum relative error of wearable detection device for cucumber nitrogen nutrition detection is 22.8%,the minimum relative error is 1.2%,and the average relative error is 11.2%.Among them,under the conditions of nitrogen application levels of 50%to 150%,the average relative error was6.5%,while under the conditions of nitrogen application levels of 25%and 175%,the average relative error reached 22.9%.This indicated that the device was not suitable for situations of severe nitrogen deficiency or excessive use.After installing the wearable detection device,the stem diameter,leaf area and plant height of cucumbers decreased by 4.89%,6.19%and 2.69%respectively compared with those of cucumbers without the device.In addition,the maximum shear force of cucumber stems after 17 days of installation decreased by 10.66%compared with stems without the device,while the epidermis shear force of stems increased by 11.43%.It can be seen that the device has a good detection effect and little influence on crop growth,which is conducive to long-term monitoring of crops.（6）A diagnosis method of nitrogen and potassium nutrition based on flexible electrode and mechanical properties of stem has been established,which can not only achieve the acquisition of apoplastic sap under the condition of less damage to crops,but also detect the penetrability of cucumber stem epidermis by using the deformation characteristics of fixed base under the effect of puncture reverse force,realizing the diagnosis of cucumber nitrogen nutrition in greenhouse.The diagnosis method based on minimally invasive information acquisition inside the object uses flexible potassium ion sensor,detection model based on stem mechanics and wearable detection device to achieve rapid,low-cost acquisition and accurate analysis of nitrogen and potassium nutrition information of greenhouse cucumber.