Material characterization and inter/intra-particle validation for DEM simulation of urea coating process

Particle coating is a common operation in the controlled-release fertilizer (CRF) industry,where a coating layer is appliedto the urea cores.A discrete element method (DEM) computer simulation was applied to model the coating process for the urea granules using measured model parameters.The accuracy of DEM input parameters for the coating material properties and the physical and mechanical characterizations of urea granules are crucial to the study of particle coating processes.Thus,to enhance the simulation accuracy,information on the material properties (urea granules) is required.In this study,the elasticity parameters,shear modulus ,coefficient of restitution (CoR),and coefficient of rolling and static friction (CoRF) and (CoSF) of urea granules are estimated experimentally in addition to the physical characteristics.The sensitivity of the angle of repose of the urea bed was investigated at different coefficients of friction.According to the obtained experimental value of the angle of repose,values of 0.2 and 0.3 for CoRF and CoSF,respectively,were adjusted to obtain consistent urea granules’ motion for simulation and the experiment.Moreover,the spray droplet sizes and velocity distributions were estimated using the video-imaging process technique.Based on this experimental characterization,elasticity parameters and spray properties were integrated into DEM simulation software as input data to perform numerical analysis of the coating process to compare simulation and experimental results,which show uniformity at three different pan speeds with a maximum deviation of 0.033 at 5 rpm.Also,consistency between DEM and experiment results was achieved in terms of average coating thickness (μm) of the selected samples and average intra-particle thickness variation ( CoV intra ).These results revealed that the coating film thickness is proportional to the rotation speed for the experiment and simulation.To enhance the inter-particle coating uniformity,the effects of the most significant parameters such as pan speed,filling ratio,particle size,spray rate,and spray angle,were examined.A low spray rate,filling ratio,and high pan speed improved the coating uniformity.The particle size and spray angle show considerable influence on the coating uniformity,where larger particle sizes and spray angles tend to reduce the inter-particle coating uniformity.

Application of Texture Measures to Study Effect of B Chromosomes on the 3D Architecture of Plant Chromatin

Background: Supernumerary chromosomes (B) comprise optional complement to basic (A) chromosome set. The presence of B-chromosomes may significantly reduce plant vigor and fertility. Potentially active genes constitute only small fraction of DNA of these chromosomes indicating that these effects are mediated by epigenetic mechanisms. One example is down-regulation of rDNA genes and condensation of their respective chromatin regions (demonstrated in squashed preparations using 2D microscopy). It may be postulated that the presence of B chromosomes leads to more extensive changes of local chromatin structure. Verification of hypothesis requires studying 3D spatial architecture of intact nuclei in tissue. Results: An image processing algorithm was developed and applied for isolation (from the confocal datasets) of regions corresponding to single nuclei. The nuclei were segmented using iterative global thresholding followed by growing and merging of regions belonging to different nuclei. The result of segmentation was verified by a human observer. Chromatin architecture was characterized quantitatively using global fluorescence intensity distribution measures (mean, variance) and local intensity distribution parameters (haraclick features, wavelet energy, run- length features). The sets of parameters corresponding to populations of nuclei with different number of B-chromo- somes were subjected to discriminate analysis. The distinct parameters were then correlated with depth in tissue at which a given nucleus was positioned. Conclusions: Combination of light microscopy with dedicated image processing and analysis framework made it possible to study chromatin architecture in nuclei containing various number of B chromosomes. These data indicate that alterations of 3D chromatin distribution occur globally in the interphase nuclei in the presence of Bs. The changes occur at the spatial scale comparable with the resolution limit of light microscopy and at larger distances.

Comparative effects of nitrogen application on growth and nitrogen use in a winter wheat/summer maize rotation system

The application of fertilizer in agricultural production has become universally common for achieving high crop yields and economic benefits, but it has potential impacts on food safety, energy crisis and environmental pollution. Optimal management of fertilization is thus necessary for maintaining sustainable agriculture. Two-year（2013–2015） field experiment was conducted, in Yangling（108°24′E, 34°20′N, and 521 m a.s.l.）, Shaanxi Province, China, to explore the effects of different nitrogen（N） applications on biomass accumulation, crop N uptake, nitrate N（NO_3~–-N） distribution, yield, and N use with a winter wheat/summer maize rotation system. The N applications consisted of conventional urea（U）（at 80（U80）, 160（U160）, and 240（U240） kg N ha^（–1）; 40% applied as a basal fertilizer and 60% top-dressed at jointing stage） and controlled-release urea（CRU）（at 60（C60）, 120（C120）, 180（C180）, and 240（C240） kg N ha~（^（–1））; all applied as a basal fertilizer） with no N application as a control（CK）. The continuous release of N from CRU matched well with the N demands of crop throughout entire growing stages. Soil NO_3~–-N content varied less and peaked shallower in CRU than that in urea treatments. The differences, however, were smaller in winter wheat than that in summer maize seasons. The average yield of summer maize was the highest in C120 in CRU treatments and in U160 in urea treatments, and apparent N use efficiency（NUE） and N agronomic efficiency（NAE） were higher in C120 than in U160 by averages of 22.67 and 41.91%, respectively. The average yield of winter wheat was the highest in C180 in CRU treatments and in U240 in urea treatments with C180 increasing NUE and NAE by averages of 14.89 and 35.62% over U240, respectively. The annual yields under the two N fertilizers were the highest in C120 and U160. The results suggested that CRU as a basal fertilizer once could be a promising alternative of urea as split application in semiarid areas.

Kinetic and thermodynamic effects of moisture content and temperature on the ammonia volatilization of soil fertilized with urea

The traditional qualitative analysis of the individual factors on the kinetic and thermodynamic parameters cannot sufficiently reveal the mechanism underlying ammonia volatilization in soil.This study aimed to determine the effects of temperature,moisture content,and their interaction on the kinetic and thermodynamic parameters,which revealed the key control mechanism underlying ammonia volatilization,modified the traditional Arrhenius model,and established a quantitative prediction model of cumulative NH_(3)-N loss(CNL).Laboratory culture experiments were conducted under different temperatures(T)(15℃,20℃,25℃and 35℃)and moisture contents(θ)(60%,80%,and 100%field capacities).Soil ammonia volatilization was also measured every 2 d.Results showed that the effects of individual factors and their interaction on the values of reaction rate(K_(N)),Activation free energy(ΔG),and activation entropy(ΔS)followed the descending order of T>θ>T·θ,whereas those of activation enthalpy(ΔH)and activation degree(lgN)followed the descending order ofθ>T>T·θ.The interaction showed significant effect on K_(N)value and insignificant effect on all the thermodynamic parameters.The effects of water and temperature were mainly observed during the preparatory stage and the most critical transition state stage of the chemical reaction,respectively.Given thatΔH>0,ΔG>0,andΔS>0,ammonia volatilization is found to be an endothermic reaction controlled by enthalpy.The new K_(N)(T)-2 model with the determination coefficient(R^(2))of 0.999 was more accurate than the traditional Arrhenius model with the R^(2)of 0.936.The new NH_(3)(T,θ)model with the mean absolute percentage error(MAPE)of 4.17%was more accurate than the traditional NH_(3)(T)model with the MAPE of 7.11%.These results supplemented the control mechanism underlying ammonia volatilization in soil fertilized with urea and improved the prediction accuracy of CNL.

Effect of γ-PGA Coated Urea on N-Release Rate and Tomato Growth

The anionic polymer γ-polyglutamic acid （γ-PGA） was used to coat urea and slow its dissolution. Three types of slow release urea （SRU） fertilizers （polymer coated urea with pore constriction, polymer coated urea with enzyme inhibitor and polymer coated urea with pore constriction and enzyme inhibitor） were prepared and tested for the N-release rate. After using SRU, the effect on the tomato growth was analyzed. The extracts of SRU were analyzed for NH3/NH4＋-N and NO3--N. The N-release rate was used to determine the optimum ratio of ingredients. The results show that the three types of SRU met the dissolution rate standards recommended by the Com- mittee of European Normalization. γ-PGA SRU increased the chlorophyll content of tomato （flowering stage） by an average of 100% compared with that grew in untreated urea. The results from soil analysis （0-60 cm in tomato pots） indicate that the content of NH3/NH4＋-N in SRU-treated pots was 25%-61% higher than that in soil from urea-treated pots during the growing period, while the content of NO3--N was nearly 50% lower after the tomato had been harvested. Newly formulated SRU fertilizer increases nitrogen up- take and reduces loss of applied nitrogen. Plant growth is enhanced, a valu- able resource is conserved, and the aquatic environment benefits from de- creased level of nitrate in agricultural run-off.