The errors in the activation energies of solid-state reactions determined with the Piloyan method are more larger than those previously assumed in the literature. On the other hand, the errors in the kinetic parameters are strongly dependent on the kinetic law obeyed by the reaction. A theoretical explanation of this behaviour is given.
Application of the appropriate N fertilizer rate for wheat production is needed to improve and sustain productivity. Different methods have been developed over time to estimate these needs. The objective of this work was to evaluate the relationship basal N rate at planting — NDVI (normalized difference vegetative index) by means of a spline regression to estimate further N needs of spring wheat. Experiments were established in two planting systems; permanent beds and conventional in solid stands. Three flat N rates (25, 50, and 75 kg N ha
, and 30, 60 and 90 kg Nha
for permanent beds and conventional planting, respectively) plus an unfertilized check plot were applied according to three N timing treatments (whole rate at planting or end of tillering, and split at planting and at the end of tillering). Before the application of N treatments at the end of tillering, plots were divided into two halves to apply variable N rates according to the first segment of the spline model. Results indicated that parameter estimates from the spline regression vary within each planting system. However, variable N rates estimated for each year and location were lower than flat N rates. In spite of those differential fertilizer rates, grain yield resulting for the application of variable N rates were similar to flat N rates. Pooled data analysis suggests that NDVI readings greater than 0.56 and 0.65 for permanent beds and conventional planting, respectively, the application of N fertilizer at the end of tillering can be excluded as grain yield will not be modified.
Authors:J. Criado, L. Perez-Maqueda, and A. Ortega
The cyclic and Controlled Rate Thermal Analysis method (CRTA) has been used. The two rates automatically selected in the cyclic
curve are small enough to allow the two states of the sample to be compared have nearly the same reacted fraction. Thus, the
activation energy can be calculated without previous knowledge of the actual reaction mechanism.
Provided that the activation energy,E, is known, a procedure has been developed for determining the kinetic law obeyed by the reaction by means of master curves
that represent the values of the reacted fraction, α, as a function of−E/R(1/T-1/T0.5),T0.5 being the temperature at which α=0.5. This procedure has been tested by studying the thermal decomposition reaction of BaCO3.
It has been shown the ability of the Sample Controlled Reaction Temperature (SCRT) method for both discriminate the kinetic
law and calculate the activation energy of the reaction. This thermal decomposition is best described by a Johnson–Mehl–Avrami
kinetic model (with n = 2) with an activation energy of nuclei growth which fall in the range 52–59 kJ mol−1. The process is not a single-step because the initial rate of decomposition is likely to be limited by nucleation. The results
reported here constitute the first attempt to use the new SCRT method to study the kinetic of the thermal decomposition of
Authors:A. Ortega, L. Pérez-Maqueda, and J. Criado
It has been demonstrated that a single plot of the values of Δlnα1/2/Δln(1-α) (taken from a single α−T curve obtained under a controlled linear increase of the reaction rate) as a function of the corresponding values of Δ(1/T)/Δln(1−α) permits the simultaneous determination of both the activation energy and the kinetic model in accordance with a
solid state reaction.
Authors:A. Limon-Ortega, E. Villaseñor-Mir, and E. Espitia-Rangel
L.) grain production in the Central Highlands of Mexico occurs under rainfed conditions. Traditionally this crop has been planted by conventional means in solid stands combined with heavy tillage and lack of ground cover. These practices have been leading to soil erosion in the sloping lands, frequent drought stress, and water logging after occasional heavy rainstorms in the low lands. To ameliorate those constrains, farmers have started to replace the traditional planting system by the planting system on narrow raised beds. However, information on N management and varieties is needed. This 5-yr study was conducted from 1999 to 2003 to test a set of eight wheat genotypes using a raised-bed system to evaluate their performance as affected by N fertilizer management. Three N rates (40, 70 and 100 kg N ha
) were applied at planting, at the end of tillering-early jointing, and split at planting and at the end of tillering-early jointing. Treatments included an unfertilized check plot. Results indicated that the optimum N fertilizer rate for wheat grain production varies from 0 to 40 kg N ha
) depending upon the variety. Nitrogen timing practices had no effect on grain yield but on N use efficiency (NUE). The split application of 40 kg N ha
increased the NUE. Higher N rates reduced the NUE irrespective of the N timing practice. According to the differential performance among varieties, this study showed that the planting system on narrow raised beds is a variety-specific technology. The relative grain yield, stability, and NUE, indicated that Tlaxcala F2000, Nahuatl F2000 and Romoga F96 are the most adequate varieties for the planting system on narrow raised beds in the Central Highlands of Mexico.
Authors:J. Criado, M. Gonzalez, A. Ortega, and C. Real
It has been demonstrated that the kinetic data on solid-state reactions show a good fitting to the expressiong(α)=kt, regardless of the nature of theg(α) function previously assumed for performance of the calculations. Moreover, the activation energy value obtained from the
Arrhenius law is quite independent of the kinetic function assumed.
Authors:L. Hernan, J. Morales, A. Ortega, and J. L. Tirado
The kinetics of thermal decomposition of CoOOH have been studied by analysis of isothermal weight loss data under vacuum. The comparison of linear correlation coefficients of different kinetic expressions applied to these data does not allow an understanding of the mechanism, even when significance tests are performed (t test). A single value of the activation energy (193 kJ mol−1) is obtained from the Arrhenius plots, and is relatively independent of the choice of rate law. On the other hand, a change in the mechanism of formation of Co3O4 with temperature cannot be inferred from analysis of isothermal data. Thus, the statement of some authors that from formal kinetics it is possible to distinguish the proton and electron transfers involved in the transformation appears unacceptable.