Yazhen Shen

Biodegradation of a biochar-modified waterborne polyacrylate membrane coating for controlled-release fertilizer and its effects on soil bacterial community profiles

Biochar-modified polyacrylate-like polymers are promising waterborne polymer-based membrane coatings for controlled-release fertilizers. However, the effect of these membrane polymers on paddy soil is unknown. A soil incubation experiment was conducted using Fourier transform infrared photoacoustic spectroscopy to monitor the changes in the polymer-coated membranes in paddy soil, and Biolog EcoPlates and polymerase chain reaction-denaturing gradient gel electrophoresis were used to detect the effects of the membranes on soil bacterial community profiles. Compared to unmodified membranes, the biodegradation rate of the biochar-modified membrane was slower, and the membrane was more intact, which improved and guaranteed the controlled release of nutrients. Compared to the soil without membranes, the biochar-modified membranes, as well as unmodified ones, showed no significant impacts on the composition diversity of soil dominant bacterial community. The activity and functional diversity of soil culturable microbial community during the early stage of incubation were reduced by biochar-modified membranes due to the release of small amount of soluble organic materials but were both recovered in the 12th month of the incubation period. Therefore, the biochar-modified waterborne polyacrylate was environmentally friendly, demonstrating its potential both in the development of coated controlled-release fertilizers and in the utilization of crop residue.

Soil Microbial Responses to Experimental Warming and Nitrogen Addition in a Temperate Steppe of Northern China

The responses of soil microbes to global warming and nitrogen enrichment can profoundly affect terrestrial ecosystem functions and the ecosystem feedbacks to climate change. However, the interactive effect of warming and nitrogen enrichment on soil microbial community is unclear. In this study, individual and interactive effects of experimental warming and nitrogen addition on the soil microbial community were investigated in a long-term field experiment in a temperate steppe of northern China. The field experiment started in 2006 and soils were sampled in 2010 and analyzed for phospholipid fatty acids to characterize the soil microbial communities. Some soil chemical properties were also determined. Five-year experimental warming significantly increased soil total microbial biomass and the proportion of Gram-negative bacteria in the soils. Long-term nitrogen addition decreased soil microbial biomass at the 0-10 cm soil depth and the relative abundance of arbuscular mycorrhizal fungi in the soils. Little interactive effect on soil microbes was detected when experimental warming and nitrogen addition were combined. Soil microbial biomass positively correlated with soil total C and N, but basically did not relate to the soil C/N ratio and pH. Our results suggest that future global warming or nitrogen enrichment may significantly change the soil microbial communities in the temperate steppes in northern China.

Application of Nano FeIII–Tannic Acid Complexes in Modifying Aqueous Acrylic Latex for Controlled-Release Coated Urea

Acrylic latexes are valuable waterborne materials used in controlled-release fertilizers. Controlled-release urea coated with these latexes releases a large amount of nutrients, making it difficult to meet the requirement of plants. Herein, FeIII-tannic acid (TA) complexes were blended with acrylic latex and subsequently reassembled on a surface of polyacrylate particles. These complexes remarkably retarded the release of urea (the preliminary solubility was decreased from 22.3 to 0.8%) via decreasing the coating tackiness (Tg was increased from 4.17 to 6.42 °C), increasing the coating strength (tensile stress was improved from 3.88 to 4.45 MPa), and promoting the formation of denser structures (surface tension was decreased from 37.37 to 35.94 mN/m). Overall, our findings showed that a simple blending of FeIII-TA complexes with acrylic latex produces excellent coatings that delay the release of urea, which demonstrates great potential for use in controlled-release fertilizers coated with waterborne polymers.

Application of FTIR-PAS and Raman spectroscopies for the determination of organic matter in farmland soils

In soil analysis, Raman spectroscopy is not as widely used as infrared spectroscopy mainly owing to fluorescence interferences. This paper investigated the feasibility of Fourier-transform infrared photoacoustic (FTIR-PAS) and Raman spectroscopies for predicting soil organic matter (SOM) using partial least squares regression (PLSR) analysis. 194 farmland soil samples were collected and scanned with FTIR and Raman spectrometers in the spectral range of 4000-400cm(-1) and 180-3200cm(-1), respectively. For the PLSR models, the combined dataset was split into 146 samples as the calibration set (75%) and 48 samples as the validation set (25%). The optimal number of analytical factors was determined using a leave-one-out cross-validation. The results showed that SOM could be predicted using FTIR-PAS and Raman spectroscopies independently, with R(2)>0.70 and RPD>1.8 for the validation sets. In comparison to the single applications of FTIR-PAS and Raman spectroscopies, accurate prediction of SOM was made by combining FTIR-PAS and Raman spectroscopies, with R(2)=0.81 and RPD=2.18 for the validation sets. By statistically assessing large amounts of PLS models, model-population analysis confirmed that the accuracy of the PLS model can be increased by combining FTIR-PAS and Raman spectroscopies. In conclusion, the combination of FTIR-PAS and Raman spectroscopies is a promising alternative for soil characterization, especially for the prediction of SOM, owing to the availability of complementary information from both FTIR-PAS (polar vibrations) and Raman spectroscopy (non-polar vibrations).

Rapid Determination of N Isotope Labeled Nitrate Using Fourier Transform Infrared Attenuated Total Reflection Spectroscopy

Abstract Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy was utilized to quantify nitrate contents, 14NO3-N and 15NO3-N in KNO3 solution and soil. The results showed that the characteristic band of nitrate in solution and soil was 1200–1500 cm−1, and about 35 cm−1 of red shift was observed in the characteristic band of 15NO3− compared with 14NO3−. The intensity of the characteristic band of nitrate increased with the nitrate concentration and with less interference involved. The linear regression was made between the first principal component of characteristic band and nitrate-N content with a correlation coefficients of 0.9840, which indicated that FTIR-ATR spectroscopy was feasible for rapid monitoring of nitrate in solution and soil. Furthermore, based on the red shift of 15NO3− absorption, partial least squares (PLS) method was employed to predict the nitrate -N labeled with different N-isotope in solution and soil. As a result, all the prediction models were excellent. For 14NO3-N and 15NO3-N in solution, the determination coefficients (R2) were 0.9980 and 0.9982, respectively, and corresponding RPD were 6.44 and 4.76, respectively. For 14NO3-N and 15NO3-N in soil, the determination coefficients (R2) were 0.9794 and 0.9679, respectively, and the corresponding RPD were 5.75 and 4.78, respectively. Therefore, FTIR-ATR spectroscopy can be applied for rapid monitoring different N-isotope labeled nitrate in solution and soil, which provides a new method for in situ and fast analysis of nitrification process in soil.

Rapid Determination of Nitrate in Chinese Cabbage Using Fourier Transforms Mid-infrared Spectroscopy

Abstract The nitrate content in Chinese cabbage was rapidly predicted using the techniques of mid-infrared spectroscopy (diffusion reflectance spectroscopy, photoacoustic spectroscopy and attenuated total reflectance spectroscopy). There existed interferences in the characteristic bands of nitrate (1200–1500 cm−1) for all the infrared spectra. The interferences for diffusion reflectance spectra were strongest, followed by photoacoustic spectra, and the weakest for the attenuated total reflectance spectra, which were also verified by the principal component regressions between infrared spectra and nitrate content in Chinese cabbage, and the coefficient (R2) were 0.4003, 0.4874 and 0.8741, respectively. Based on attenuated total reflectance spectra, the chemometrics method of partial least squares was involved to improve the prediction model of nitrate, the prediction accuracy was significantly decreased, the coefficient was 0.8851, and the RPD value was 3.19. Therefore, the technique of mid-infrared attenuated total reflectance spectroscopy was feasible for rapid monitoring of nitrate in Chinese cabbage.

Thermal post-treatment alters nutrient release from a controlled-release fertilizer coated with a waterborne polymer

Controlled-release fertilizers (CRF) use a controlled-release technology to enhance the nutrient use efficiency of crops. Many factors affect the release of nutrients from the waterborne polymer-coated CRF, but the effects of thermal post-treatments remain unclear. In this study, a waterborne polyacrylate-coated CRF was post-treated at different temperatures (30 °C, 60 °C, and 80 °C) and durations (2, 4, 8, 12, and 24 h) after being developed in the Wurster fluidized bed. To characterize the polyacrylate membrane, and hence to analyze the mechanism of nutrient release, Fourier transform mid-infrared spectroscopy, scanning electron microscopy, and atomic force microscopy were employed. The nutrient-release model of CRF post-treated at 30 °C was the inverse “L” curve, but an increased duration of the post-treatment had no effect. The nutrient-release model was “S” curve and nutrient-release period was enhanced at higher post-treatment temperatures, and increased post-treatment duration lengthened slowed nutrient release due to a more compact membrane and a smoother membrane surface as well as a promoted crosslinking action. CRF equipped with specified nutrient-release behaviors can be achieved by optimizing the thermal post-treatment parameters, which can contribute to the development and application of waterborne polymer-coated CRF and controlled-release technologies.

In Situ Measurement of Ammonia Concentration in Soil Headspace Using Fourier Transform Mid-Infrared Photoacoustic Spectroscopy

Ammonia (NH3) volatilization is one of the important pathways of nitrogen loss in alkaline soil, and the NH3 concentration in soil headspace is directly linked with the NH3 volatilization. Ammonia was characterized by Fourier transform mid-infrared photoacoustic spectroscopy (FTIR-PAS) and two typical absorption bands in the region of 850–1200 cm−1 were observed, which could be used for the prediction of NH3 concentration in the soil headspace. An alkaline soil from North China was involved in the soil incubation, pot and field experiments under three fertilization treatments (control without N input (CK), urea and coated urea). Ammonia concentrations in the soil headspace were determined in each experiment. In the soil incubation experiment, the NH3 emissions were initiated by the N input, reached the highest concentration on day 2, and decreased to the level as measured in CK after 8 d, with significantly higher NH3 emissions in the urea treatment compared to coated urea treatment, especially during the first 4 d. The NH3 concentration in soil headspace of the pot experiment showed the similar dynamics as that in the incubation experiment; however, the NH3 concentration in the soil headspace in the field experiment demonstrated a significantly different emission pattern with those of the incubation and pot experiments, and there was a 4-d delay for the NH3 concentration. Therefore, the NH3 concentration in the incubation and pot experiments could not be directly used to model the real NH3 emission in the field due to the differences in fertilization method and application rate as well as soil temperature and soil disturbance. It was recommended that light irrigation in the second week after fertilization and involvement of controlled release coated urea could be used to significantly decrease N loss from the perspective of NH3 volatilization.

Characterization of the Release of Urea from Coated Fertilizer by Fourier Transform Infrared Spectroscopy with Attenuated Total Reflectance

The development of a simple and cost-effective method for the determination of the release of coated urea has significant implications. Fourier-transform infrared spectroscopy with attenuated total reflectance was employed to determine the release of urea through univariate and multivariate calibration. The results indicated that univariate calibration did not accurately predict the release of urea, whereas partial least squares based on multivariate calibration performed significantly better. Partial least squares had the highest accuracy when the band located at 1420–1520 per centimeter was employed as the input. Moreover, the accuracy was further improved when segmented partial least squares models were developed at low and high urea concentrations. Unsegmented and segmented partial least squares models were employed, and release values were comparable to those measured by colorimetry. This work demonstrated the use of infrared spectroscopy and partial least squares to characterize the release of coated urea.

Evaluation of net nitrification rates in paddy soil using mid-infrared attenuated total reflectance spectroscopy

Colorimetry is a conventional method for the determination of soil nitrification rates, and it demands pretreatments and chemical reagents, which make it time and cost consuming. Fourier transform infrared attenuated total reflectance spectroscopy (FTIR-ATR) as a simple and fast method was employed in this study, and the feasibility of determination of nitrate contents by FTIR-ATR under different soil conditions was investigated. It was found that the second-order derivatives of nitrate characteristic bands (1270–1320 cm−1) were proportional to nitrate contents, and an excellent correlation coefficient of 0.9751 was obtained, indicating that FTIR-ATR combined with second-order derivatives could be well used for quantification of nitrate. The nitrate-N contents determined by FTIR-ATR and colorimetry increased with increasing incubation time under different treatments including soil temperature, moisture, pH and nitrogen application rate; in most cases, the values obtained by FTIR-ATR were slightly higher than those obtained by colorimetry after 50% incubation. The abiotic immobilization of nitrate and Fe interference in the colorimetric procedure might contribute to this difference. Thus, FTIR-ATR combined with second-order derivatives can be used as an alternative option for fast determination of nitrate under varied conditions in paddy soils.