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[Objective] The aim of this paper is to explore the relationship between the main chemical components of flue-cured tobacco and soil chemical properties. [Method] All of 235 tobacco leaf samples and soil samples were collected from typical aromatic tobacco growing areas in Yunnan province. The main soil factors affecting the chemical quality of Yunnan fragrant tobacco leaves were studied by correlation analysis, stepwise regression analysis and principal component analysis. [Result] The contents of total sugar and reducing sugar in Yunnan tobacco were 30.87% and 27.21, respectively ;the contents of total nitrogen, nicotine and potassium were in the appropriate range, which were 1.91, 2.63% and 1.91% respectively ;The results showed that the pH value of the main tobacco planting soils in Yunnan was moderate, with an average of 6.3. The contents of total nitrogen, total phosphorus, available molybdenum and available sulfur were in the rich level. The contents of total potassium and humic acid were on the low level. The contents of organic matter, fulvic acid, available boron, water-soluble chloride ion, salt content and CEC (total amount of cation exchange) were in the middle level. The contents of total sugar, reducing sugar, starch and potassium in tobacco leaves were significantly positive correlation with total potassium in soil. Two sugar difference and sugar alkali ratio were significantly positive correlation with soil available molybdenum content. Two sugar difference was significantly positive correlation with soil humic acid content, and was significantly negative correlation with soil chloride ion content. [Conclusion] The contents of total potassium, available molybdenum, humic acid and water-soluble chloride ion in tobacco growing soil of Yunnan tobacco growing areas are the most important indicators affecting the chemical quality of tobacco leaves in Yunnan. [ABSTRACT FROM AUTHOR]

In order to study the characteristics of microplastics and its response relationship with mulching years, irrigation methods in the farmland soil of Hetao Irrigation District, field sampling and indoor experiments were used in combination for in-depth study. This paper mainly analyzed the current situation of plastic film mulching in Hetao Irrigation District by considering the effects of mulching years (5, 10, 20 a) and irrigation methods (drip irrigation and surface irrigation under film mulching). The abundance, type, color, particle size and other distribution characteristics of microplastics in the farmland soil were analyzed and other microplastic surface features and attachments also were observed and discussed, which was supported by scanning the electric microscope and energy spectrometer. The results showed that the average abundance of microplastics in soil under the different mulching years (5, 10, 20 a) in Hetao Irrigation District was 2 526.00, 4 352.80, 6 070.00 pieces/kg. The maximum microplastic was 2133.50 pieces/kg in every layer of soil appeared at 0-10 cm soil layer by mulching 20 a, and the minimum microplastic was 678.00 pieces/kg at 20-30 cm soil layer by mulching 5 a. The average annual increasing rate of microplastics was 14.46% in the early stage (5-10 a), while the increasing rate in the later stage (10-20 a) was 3.95%. The abundance of soil microplastics was affected by different plastic-mulching years and irrigation methods. The abundance of microplastic in drip irrigation farmland was slightly larger than the surface irrigation farmland, and it decreased with the increase of soil depth. By further analysis, the major categories of microplastics were fibers (23.34%), fragments (26.31%), films (38.57%) and grains (11.78%); the colors of microplastics included black, transparent, green, red, blue, etc., with the proportions 24.56%, 23.83%, 19.34%, 16.52% and 15.75% respectively. In the 0-10 cm soil layer, the main color of microplastics was black and it accounted for 30.25% of the total microplastic; in the >10-20 and >20-30 cm soil layer, the main color of microplastics were transparent, accounted for 30.15% and 29.23% of the total microplastic. The particle size exhibited a downward trend with the increase of the mulching years, and the majority of particle size less than 1 mm. In addition, with the increase of mulching years, microplastics particle size in >0-10, >10-20, >20-30 cm soil layer was gradually decreased, and there was no significant relationship between size and irrigation method (P>0.05). The surface features of microplastic samples were rough and irregular pores existed on it, and fiber, thin film and fragments microplastics had regular micropores, while the grain microplastic surface pores were irregular and concave. The porous properties of microplastics in soil made the characteristic of greater specific surface area carried by it. This characteristic could increase the adsorption of other pollutants and microorganisms from the soil; and there were stable iron oxides and rare earth elements on the surface. The research is of great significance to clarify the distribution and harm of microplastics in the soil of the Hetao Irrigation District. [ABSTRACT FROM AUTHOR]

Rapid lower-cost detection methods for soil macronutrient, including soil samping, sample pretreatment and nutrient determination, are urgently needed. In this paper, a prototype soil rapid pretreatment device was introduced for the ion-selective electrode (ISE) based in-situ soil nitrate-nitrogen detection. Necessary pretreatment steps of soil weighting, extracting and filtration were achieved in the integrated device. The mechanical structure of the device was composed of 4 major components, including a two-dimensional work bench, a high-speed centrifuge, a liquid pump and a self-designed electric control unit. The two-dimensional work bench was built with a vertical sliding table and a rotary table. On the purpose of eliminating the “suspension disturbance” of ISE, the centrifuge was used to obtain the clear soil extract solution. The peristaltic liquid pump, which conducted the quantitative injection of the soil extractant solution into centrifugal tube, was involved for the soil extractant injection and stirring. The electric control unit consisted of a microprocessor of STM32F103 and its interface circuit, which was used for the precise control of the two-dimensional work bench. The soil moisture sensor was applied to reduce the interference of soil water content. Net weight of the testing sample could be calculated. According to the testing results, the displacement accuracy of the vertical sliding table was less than 0.1 cm, while the root mean square error (RMSE) and mean relative error (MRE) were less than 0.04 cm and 0.4% respectively. The one-way displacement of 10 cm consumed less than 5 s. The accuracy of the angular movement for the rotary table was 1°. The rotating speed was calculated through the ratio between rotation angle and time, which could reach 10°/s. The two-dimensional work bench possessed good repeatability with the coefficient of variation (CV) of less than 0.40%. The accuracy of the liquid pump was also evaluated. Two injection volumes of 12.5 and 25 mL were selected. A volume accuracy of 0.2 mL was obtained. The RMSE, the MRE and the injection time were examined to be 0.07 mL, 0.24% and 13 s, respectively. The continuous injection operation possessed a high repeatability with the CV of less than 0.1%. Therefore, the extractant injection performance was verified to be reliable and accurate. The performance of the self-designed device was estimated in the nitrate-nitrogen detection of wet soil. Comparisons were conducted among 3 groups of ISE-based detections and the standard spectrometric detection. The 3 groups of ISE-based detections included the fast pretreatment group, the soil suspension group and the conventional pretreatment group. The fast pretreatment group was processed by the self-developed pretreatment device discussed above. Samples of the soil suspension group were prepared without filtration operation. The conventional pretreatment group was conducted under the national site-specific soil testing recommendation. Compared with the standard spectrometric detection, the poor detection accuracy with the biggest absolute error (AE) of 76.86 mg/kg was determined in the soil suspension group. The slope of regression equation was 2.27, which indicated a non-negligible deviation from the real condition. As expected, the ISE detection, conducted by the self-designed device, was much closer to the standard spectrometric. The adjusted determination coefficient (R2) of the regression equation was 0.87 and the equation slope was 1.31, which was less than 2.27 obviously. The average AE was decreased to be 20.97 mg/kg. The RMSE of 22.34 mg/kg was found. Meanwhile, the labor intensity was greatly reduced. However, the fast pretreatment group still exhibited the obvious difference with the conventional pretreatment group. In all, the device discussed in this study demonstrates a promising result, which might provide references for the ISE applications of in-situ soil macronutrient rapid detections. Further modification on the mechanical structure for extracting is required to enhance its performance. [ABSTRACT FROM AUTHOR]