Application And Calibration Of Nuclear Magnetic Resonance (NMR) Soil Moisture Analyzer In The Filed

Soil moisture is one of the driving factors of the loess plateau ecosystem.Quantifying its quantitative characteristics is the basis of studying the material circulation and energy transformation in the regional ecosystem.At present,the main methods to measure soil moisture include drying method,neutron method and time domain reflection method?TDR?.These methods not only take time and labor,but also disturb the soil,resulting in inaccurate determination results.In recent years,a non-contact method for the direct determination of soil moisture and porosity,namely nuclear magnetic resonance?NMR?method,has gained wide attention.However,there is still a lack of research on the accuracy and application of this method.This paper,by using nuclear magnetic resonance?NMR?soil moisture meter to the secretary-general of protect the grass and corn,acacia,apple,soil moisture and porosity were determined and analyzed the basic physical properties of soil and nuclear magnetic resonance?NMR?method,the relationship of the measured values,and is compared with drying method and the ring knife method,nuclear magnetic resonance?NMR?method was established the relationship between the measured value and the traditional way to measure values as well as the establishment of soil moisture meter calibration formula,the main results were as follows:?1?There is a positive correlation between the moisture measurement value of the NMR method and soil organic matter,clay and sand,and a negative correlation between the mean weight diameter and silt;the T₂ value?transverse relaxation time?and there is a clear negative correlation between soil organic matter,clay and sand,and a positive correlation between the mean weight diameter and silt.?2?The T₂ value of NMR method reflects the porosity of soil,and the correlation coefficient with the non-capillary porosity of soil is the highest.The distribution size of T₂ value ranges from 1.76 ms-8.80 ms,and it is mainly distributed between 2.00 ms-3.50 ms.As the Tr value?the amount of time between two spin echo sequences at a given measurement frequency?increased,there was no significant difference in T₂value of NMR method,indicating that the adjusted Tr value NMR moisture meter had no effect on the measurement of T₂ value.?3?The water calibration curve of the NMR moisture meter is y=1.38+1.37,R² is 0.95,y is calibration value?mass water content?,x is the measured value.As the Tr value increases,the moisture measurement value of the NMR method tends to be stable.In order to ensure the accuracy of the data,the Tr value is adjusted to 6 s.?4?Precautions for using the instrument:Keep the probe in direct contact with the soil.In addition,covering the probe with a shielding aluminum foil can improve the accuracy of the measurement data.