Calibration Of Correction Factor Of Soil Nitrate Nitrogen Measurement By Ultraviolet Spectrophotometry

Soil nitrate nitrogen plays an important role in nitrogen nutrient management in dry cropland.Ultraviolet spectrophotometric determination of soil nitrate nitrogen has the advantages of simple operation,fast measurement and less interference factors,which are favored by most laboratories.However,the correction factor in UV spectrophotometry is affected by the extractant,wavelength selection,and soil type.Therefore,it is necessary to optimize the correction factors in the national standard?GB/T 32737-2016?method.In this study,eight types of soil?Air dried and fresh soil?in different ecological regions from east to west in Inner Mongolia were selected to investigate the influence of extractant type,wavelength selection and soil type on the correction factor in nitrate determination using UV spectrophotometry.The results are as follows:?1?Extractants and wavelengths have an important impact on the correction factors for fresh soil and air-dried soil samples.There is no correlation for the corrected factor values between the CaCl₂ and KCl extracts in air-dried and fresh soil samples.There is a significant correlation for the correction factors between 210 nm and 220 nm wavelength.The correction factor at 210 nm is generally higher than 220 nm.Different soil types have different effects on correction factors in different extractants and wavelengths.?2?The calibration factors of air-dried soil samples other than Alkalinzed solonchaks with KCl as extractant at 210 nm and 220 nm were 3.42 and 2.77,while the correction factor values of Alkalinzed solonchaks were 5.99 and 3.64,respectively.The correction factors of CaCl₂ as extractant at 210 nm and 220 nm were 4.40 and 2.92,while the correction factors of alkalized saline soil were 14.17 and 6.81,respectively.?3?The correction factor of fresh soil samples is greatly affected by soil type and needs to be determined according to different soil types.When KCl is the extractant,the correction factors of Subalpine meadow black soils and Castano-cinnamon soils are 9.27 and 6.23 at 210 nm and 220 nm,respectively.The correction factors of brown forest soils and Meadow soils are 26.46 and 13.10.The correction factors of the Castanozems and the Aeolian soils are 4.02 and 2.97,and the correction factors of the Alkalinzed solonchaks are 56.33 and 30.16,respectively.When the extractant is CaCl₂,the correction factors of Subalpine meadow black soils and Castano-cinnamon soils are 10.49 and 6.89 at 210 nm and 220 nm,and the correction factors of brown forest soils and Meadow soils are 20.24 and 12.36.The correction factors of the Castanozems are 16.93 and 9.25.The correction factors of the Aeolian soils are 3.66 and 2.80,and the correction factors of Alkalinzed solonchaks are 65.53 and 32.07,respectively.?4?Compared with Phenol two sulfonic acid spectrophotometry,nitrate determination by UV method?KCl as the extractant with 220 nm wavelength?has the highest accuracy in both air-dried and fresh soil samples.Flow analysis method and the reflectometry method further confirmed their reliability.