Rafael Magallanes-Quintanar

Soil Nitrogen Fertilization Effects on Phytoextraction of Cadmium and Lead by Tobacco (Nicotiana tabacum L.)

ABSTRACT A greenhouse experiment using 24 plastic pots filled with 6 kg of Pb- and Cd-contaminated soil was carried out. In all 24 pots, soils were heavy metal–contaminated with 10 mg Cd kg−1 soil and 500 mg of Pb kg−1 soil by using CdCl and PbNO3. Two-month-old tobacco (Nicotiana tabacum L.) plants were used to extract these heavy metals. Results showed that tobacco is able to remove Cd and Pb from contaminated soils and concentrate them in its harvestable part, that is, it could be very useful in phytoextraction of these heavy metals. Increasing additions of ammonium nitrate to soil (50, 100, and 150 mg N kg−1 soil) significantly (p ≤ .05) increased aboveground Cd and Pb accumulation during a 50-day experimental period, whereas increasing additions of urea to soil (50 and 100 mg N kg−1 soil) did not show these effects at the same significance levels. Increasing additions of ammonium nitrate to soil shows as dry matter increases, both accumulated Cd and accumulated Pb also increase when tobacco plants are growing under Pb- and Cd-contaminated soil conditions. Higher Pb concentrations depress Cd/Pb ratios for concentrations and accumulations, suggesting that Pb negatively affects Cd concentration and/or accumulation.

Preliminary compositional nutrient diagnosis norms for cowpea (Vigna unguiculata (L.) Walp.) grown on desert calcareous soil

This study calculated the compositional nutrient diagnosis (CND) norms of cowpea (Vigna unguiculata (L.) Walp.), as well as identified significant nutrient interactions of this crop growing in an irrigated calcareous desert soil. Three genotypes were distributed in rows in a 2-ha field. The soil showed high heterogeneity in its chemical properties. For statistical analysis, 86 foliar composite samples from healthy plants were used. Preliminary CND norms were developed using a cumulative variance ratio function and the χ2 distribution function. Means and standard deviations of row-centered log ratios VX of five nutrients (N, P, K, Ca, and Mg) and a filling value R, which included all nutrients not chemically analyzed. Preliminary CND norms are: VN*=0.174±0.095, VP*=−2.172±0.234, VK*=−0.007±0.267, VCa*=−0.022±0.146, VMg*=−1.710±0.132, and VR5*=3.728±0.084. These CND norms are associated with dry bean yields higher than 1.88 t ha−1, and are associated with the following foliar concentrations: 26.2 g N kg−1, 2.5 g P kg−1, 22.9 g K kg−1, 21.6 g Ca kg−1, and 4 g Mg kg−1. Cowpea plants growing in desert calcareous soils took up lower amounts of N, P, and K than those considered as optimum in a previous report. Six interactions were strongly indicated for cowpea through principal component analyses: positive for Ca–Mg, and negative for N–Ca, N–Mg, Ca–P, Mg–P, and K–P. Furthermore, two interactions were identified using simple correlations, negative N–P and positive K–Ca.

Compositional Nutrient Diagnosis in Maize Grown in a Calcareous Soil

ABSTRACT Preliminary compositional nutrient diagnosis (CND) norms for maize (Zea mays L.) were developed from a small database as means and standard deviations of row-centered log ratios V X of five nutrients [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg)] and a filling value R, which comprised all nutrients not chemically analyzed and quantified in 72 leaves of hybrid ‘Pioneer 3044.’ Norms were derived from maize grain yields higher than 7.7 t ha−1. Principal-component analysis performed using CND nutrient indexes allowed us to identify an antagonism between N and Mg explained by the calcareous nature of the soil and the relevant N fertilization with ammonium (NH4 +), and a positive interaction between P and K, and P-Ca and K-Ca antagonisms. Maize plants tended to take up lower amounts of N and K and higher amount of Mg in our calcareous soil than the concentrations of these nutrients reported to be optimum.

SCALE-INVARIANCE OF NORMALIZED YEARLY MEAN GRAIN YIELD ANOMALY SERIES

In crop science, tools of non-linear dynamics, fractals, chaos, intermittency and self-organized criticality may be employed and applied to the analysis of spatial variability and temporal behavior of agro-meteorological variables, soil properties, plant attributes, commercial yields, and prices of the agricultural products in order to gain knowledge about underlying complex processes. A search on the occurrence of particular scaling laws in Mexicos normalized yearly mean grain yield anomaly series of maize (Zea mays L.), beans (Phaseolus vulgaris L.), wheat (Triticum aestivum L.) and rice (Oriza sativa L.), using a variography approach is reported in this work. Additionally, power spectrum determination, time-frequency analysis, and estimation of Lyapunov exponent were performed for each profile in order to obtain useful information on the frequency contents and signs at which important frequencies occur as well as to determine their sensitivity to initial conditions. Fractal analysis gives us the order maize

COMPARISON AMONG BOLTZMANN AND CUBIC POLYNOMIAL MODELS FOR ESTIMATION OF COMPOSITIONAL NUTRIENT DIAGNOSIS STANDARDS: OPUNTIA FICUS-INDICA L. CASE

Compositional Nutrient Diagnosis technique involves a yield target for discriminating between high- and low-yield subpopulations when developing norms. Traditionally, this yield value is estimated by finding the inflection point of the cumulative variance ratio function versus yield relationship through a third-order equation. However, yield targets frequently lie outside of the experimental yield range. A comparison among traditional (unrestricted) and restricted cubic model, and restricted and unrestricted Boltzmann equations was performed using a database (n = 360) of fresh matter yield and nutrient concentrations in one–year old cladodes of Opuntia ficus-indica L. The unrestricted Boltzmann equation resulted to have the best goodness-of-fit. The yield target was 27.01 kg plant−1 associated to the unrestricted Boltzmann equation for phosphorus cumulative variance ratio function versus yield relationship. Proposed nutrient optimum concentrations are: 11.4 g kg−1 for nitrogen (N), 3.4 g kg−1 for phosphorus (P), 42.3 g kg−1 for potassium (K), 42.5 g kg−1 for calcium (Ca), and 16.2 g kg−1 for magnesium (Mg).

Time-Frequency Analysis of a Pulsed Excitation and Its Application in Randles Model

Many electrochemical systems can be studied using equivalent circuit models. One simple model is the Randles circuit, which consists of a resistance connected in series with a parallel combination of a capacitance and another resistance. This second resistance is called polarization resistance, and for many practical applications, it is very important to estimate its value. Using a special form of a pulsed excitation, we show that it is possible to estimate a value for the polarization resistance with a very simple calculation. A time-frequency analysis of the proposed pulsed excitation showed not only the zero frequency content of the signal but also the time when this zero frequency occurs. Using Laplace analysis, we show also that the transient current through the capacitance is zero, when the frequency contents of the pulse is zero. In this way it is possible to estimate the value of the resistive component of an electrochemical cell. Experimental results show an approximation error of less than 0.5%. We conclude this is an alternative technique to estimate the polarization resistance.

A Lowpass Pulsed Excitation and Method for Polarization Resistance Measurements

A new method to measure the polarization resistance on electrochemical cells is proposed. The method is based on the application of a new pulsed excitation, which exhibits low pass frequency contents, and time domain analysis. In other pulsed excitation methods, curve fitting algorithms are used to find values for equivalent RC models. In our approach using this pulsed excitation, single values of potential and current measurements, at a very precise time, are needed to obtain the value of the polarization resistance. A numerical simulation was first developed and then, the method was tested using equivalent analog circuits and electrochemical cells. The pulsed excitation method was also compared with electrochemical impedance measurements, where the modulus of the impedance, at the minimum testing frequency, was taken as an estimation of the polarization resistance. According to the experimental results, the proposed method can be used in new instrumentation designs, where the main goal is to obtain a value of the polarization resistance.