Study On Nutrient Detection Of Soil Using Laser-induced Breakdown Spectroscopy

The status of soil nutrients plays a crucial role in the effective supply and food security.Quickly and accurately detection of soil nutrients,and then fertilizing accordingly is one of the main goals for precision agriculture.Laser-induced breakdown spectroscopy(LIBS)has attracted a lot of attention and become a research hot-spot in the field of soil detection due to its advantages,such as no or simple sample preparation,rapid analysis,and convenient operation.However,as for the soil nutrients detection by LIBS,both the accuracy and sensitivity are less than satisfactory usually,which can be easily affected by matrix effect,spectral interference and weak spectral intensity.Therefore,it is urgent to address these problems so as to improve the practicability of LIBS technology.This paper studied the matrix effect,spectral interference,available elements and spectral enhancement in the detection of macro-and micro-nutrients in soil.The details are as follows:Partial least-square regression(PLSR)is proposed to combine with LIBS to solve matrix effect and self-absorption effect in the analyses of macronutrients.Robust quantitative analysis models by PLSR were established.The macronutrient elements N,P,K,Ca,Mg and Na were analyzed quantitatively with high precision,whose coefficients(R~2)were all above 0.99.And compared to the standard calibration method,the average relative errors were greatly improved from 21.24～35.86%to 0.17～3.84%.LIBS assisted by laser-induced fluoresence(LIF)was introduced to solve the spectral interference and poor sensitivity of micronutrients.The micronutrient elements Fe,Mn,B,Zn and Cu in the soil were detected.The R~2s of the analytical elements were all improved to 0.99,and the limits of detection(Lo Ds)were 23 mg/kg,1.23 mg/kg,0.36 mg/kg,0.48mg/kg and 1.21 mg/kg,respectively,which were satisfied the environmental quality standard for soils in China.High-sensitivity determination of available N,P and K elements were conducted.By ultrasonic vibration extraction and centrifugal separation,available N,P and K in soil were prepared successfully.And the optimal Lo Ds of 23 mg/kg,0.23 mg/kg and 36 mg/kg were obtained respectively.Nanoparticles were used to enhance the spectral intensity of LIBS successfully.The used nanoparticles were prepared by pulsed laser irradiation,which were ultrapure and had a diameter of around 15 nm.Quantitative analyses of the element Fe,Mn,Cu and Zn were conducted by transforming the solid soil sample into solution.The R~2s of Fe,Mn,Cu and Zn were all above 0.98,and the Lo Ds were 35 mg/kg,7.9 mg/kg,0.29 mg/kg,and 1.16mg/kg,respectively.Compared to other spectral enhancement methods,the enhancement of nanoparticle-enhanced LIBS(NELIBS)was remarkable,and no extra devices were needed,which may promote the field application of LIBS.The self-developed portable LIBS equipment was used to analyze the actual soil samples around the laboratory.To compared with previous laboratory studies,the soil samples were collected,taken back to laboratory,and prepared following standard procedures.Standard calibration method and PLSR method were adopted to analyze Fe,Ca,Mn and Mg elements,respectively.The PLSR method showed higher accuracy,whose R~2s were above 0.98.In a nutshell,the studies conducted in this paper significantly improved the accuracy and detection sensitivity of LIBS in the field of soil nutrient detection.The related results provided technical and theoretical support for the practical application of LIBS in the analysis of soil nutrients.