Research On Methods And Techniques For Measuring The Available Nitrogen And Phosphorus In Soil Using The Integrated Reaction Flow Analysis

Available nitrogen and phosphorus in soil can directly be absorbed and utilized by crops.Fertilization plays a crucial role in regulating and maintaining the available nitrogen and phosphorus in soil to support the crop growth.However,the excessive use of fertilizer will left off over the soil by leaching and surface runoff.The excessive available nitrogen and phosphorus pollutes the rivers,lakes and groundwater,seriously threatening the human health.The theoretical technology of traditional lab-based methods for measuring soil available nitrogen and phosphorus involves the photoelectric detection and absorption spectrum.It always has a high sensitivity if the soil sample is measured in the lab.Normally,before taking the absorption spectrum,both soil available nitrogen and phosphorus are needed to extract from soil using different extractants.In the actual measurement process,a manual operation with the professional skill is essentially required.With the development of technology in automation,control and photoelectric detection,flow analysis technology allows instrument to continuously analyze the available nitrogen and phosphorus in soil,instead of human operation.Compared with the lab-based analysis method of soil available nitrogen and phosphorus,the flow analysis method can greatly reduce the errors caused by operators,avoiding potential harmful chemicals and realizing the rapid quantitative determination of the soil available nitrogen and phosphorus.As we known,the precision agriculture and efforts to prevent the non-point source pollution are intensively recommended.The automatic measurement of soil available nitrogen and phosphorus is the future development trends.This thesis mainly focuses on an integrated reaction flow analysis method to improve the measurement efficiency of soil available nitrogen and phosphorus.Firstly,an absorbance compensation algorithm was proposed to improve the accuracy of soil available nitrogen and phosphorus detected by the multi-channel soil nutrient analysis instrument.The measurement results of soil available nitrogen and phosphorus associated with the multi-channel instrument established the recommendation indexes of soil nutrient abundance and deficiency in maize planting area.In order to meet the requirements of a large number of soil measurements,an automatic instrument is urgently developed.So the integrated reaction flow analysis method has been proposed to determine the soil available nitrogen and phosphorus through automatically adding the reagents for chemical reactions.Compared with common flow injection method,both sample and reagent solutions are firstly mixed and reacted in a chemical reaction chamber,then the chemical reaction reaches to the steady state through the water bath pool with a constant temperature before measuring the soil available nitrogen and phosphorus in the photoelectric detection unit.Flexible parameter configuration improves the versatility and portability of this integrated reaction flow analysis instrument.The main research contents and novelties are listed as follows:(1)In order to avoid the existing inconsistency among the channels of the multi-channel instrument.An absorbance compensation algorithm was adopted to improve the accuracy of this instrument.Firstly,the blank solution was placed in the channel to establish the calibration coefficient.Then the standard solution was placed in the channel to establish the absorbance compensation coefficient of each channel.After the absorbance compensation algorithm was applied to the multi-channel instrument,the maximum relative standard deviations of absorbance in each channel,measured the ammonium nitrogen,available phosphorus and available potassium are 1.22%,1.27%and 1.00%,respectively.Compared with the common method,the correlation coefficients of ammonium nitrogen from the soil in 3 counties,Yongcheng,Tangyin and Zhongmu were 0.9190,0.9087 and 0.9133,respectively,and the correlation coefficients of soil available phosphorus were 0.923 1,0.9033 and 0.9301,respectively.(2)The novel integrated chemical reaction flow analysis method was firstly proposed to realize automatic sampling and photoelectric detection for measuring the available nitrogen and phosphorus in soil.This novel system is mainly composed of a syringe pump,peristaltic pumps,pinch valves,solenoid valves,sample loop rings,chemical reaction chamber,uniform spiral rings,ultrasonic level switches,constant temperature photoelectric detection unit and water bath pool,etc.Accurately sampling the soil available nitrogen and phosphorus solutions is done by the syringe pump and sample loop ring.The chemical reaction takes place in the chemical reaction chamber that the repeated perturbation is pushed by the peristaltic pump in order to make the solution react uniformly.After that,the solution is heated by the water bath pool,then it is analyzed in the photoelectric detection unit.The optical path length in the photoelectric unit can be replaced with the lengths of 10nm,20nm and 30nm,according to the concentrations of the detected samples.The chemical reaction chamber and sample pipelines are cleaned automatically by controlling the pinch valves.The integrated reaction flow analysis system realizes the continuously multiple samples measurement,without replacing the pipelines.According to the measured solutions,the cleaning procedures and light sources are automatically selected,and the brightness of light source is adjusted programmatically,in order to realize the automatic measurement of ammonium nitrogen,nitrate and available phosphorus for multiple samples continuously.After calibration,the relative standard deviation was 0.5 15%.The correlation coefficients were 0.99256,0.99794 and 0.99736,respectively.And the detection limits were 0.01 mg/L,0.59 mg/L and 0.007 mg/L with the recovery rate of 99?118%.(3)In order to solve the light source stability for running a long time,the blank sample absolution subtraction method was designed.At the same time,the pipeline of the integrated reaction flow analysis was optimized to improve the efficiency of soil nitrate measurement.Two sample channels were occupied by the cleaning and blank solution respectively.The sample solution and the blank solution were measured and recorded as the background signals.Finally,the actual measurement value of soil nitrate nitrogen using the integrated reaction flow analysis was subtracted by the blank solution.Compared with conventional measurement,the correlation coefficient of the soil nitrate nitrogen was 0.94403.(4)A flexible parameter configuration method was developed to improve the versatility of this instrument based on the integrated reaction flow analysis method for soil available nitrogen and phosphorus measurement.Compared with the conventional measurement method,the correlation coefficient from the sodium sulfate and sodium bicarbonate ammonium extractant and nessler's reagent reaction for soil ammonium nitrogen is 0.91499,the correlation coefficient from the calcium chloride extractant for soil ammonium nitrate and available phosphorus were 0.99828,0.85129 and 0.99206,respectively.