Flooded rice yield as affected by levels of water salinity in different stages of its cycle

Losses of productivity of flooded rice in the State of Rio Grande do Sul, Brazil, may occur in the Coastal Plains and in the Southern region due to the use of saline water from coastal rivers, ponds and the Laguna dos Patos lagoon, and the sensibility of the plants are variable according to its stage of development. The purpose of this research was to evaluate the production of rice grains and its components, spikelet sterility and the phenological development of rice at different levels of salinity in different periods of its cycle. The experiment was conducted in a greenhouse, in pots filled with 11 dm³ of an Albaqualf. The levels of salinity were 0.3 (control), 0.75, 1.5, 3.0 and 4.5 dS m-1 kept in the water layer by adding a salt solution of sodium chloride, except for the control, in different periods of rice development: tillering initiation to panicle initiation; tillering initiation to full flowering; tillering initiation to physiological maturity; panicle initiation to full flowering; panicle initiation to physiological maturity and full flowering to physiological maturity. The number of panicles per pot, the number of spikelets per panicle, the 1,000-kernel weight, the spikelet sterility, the grain yield and phenology were evaluated. All characteristics were negatively affected, in a quadratic manner, with increased salinity in all periods of rice development. Among the yield components evaluated, the one most closely related to grain yields of rice was the spikelet sterility.

Dry matter production and nutrient accumulation after successive crops of lettuce, tomato, rice, and andropogongrass in a substrate with zeolite

Zeolites are hydrated crystalline aluminosilicate minerals of natural occurrence, structured in rigid third dimension net that can be used as slow release plant-nutrient source. The main objective of this study was to evaluate the effects of plant growth substrate under zeolite application, enriched with N, P and K, on dry matter yield and on nutrient contents in consecutive crops of lettuce, tomato, rice, and andropogon grass. The experiment was carried out in a greenhouse, with 3 kg pots with an inert substrate, evaluated in a randomized block design with three replications. Treatments consisted of four types of enrichment of concentrated natural zeolite: concentrated zeolite (Z) only, zeolite + KNO3 (ZNK), zeolite + K2HPO4 (ZPK) and zeolite + H3PO4 + apatite (ZP), and a control grown in substrate fertilized with a zeolite-free nutrient solution. Four levels of enriched zeolite were tested: 20, 40, 80, and 160 g/pot. Four successive crops were grown on the same substrate in each pot: lettuce, tomato, rice, and andropogon grass. Results indicated that N, P and K enriched zeolite was an adequate slow-release nutrient source for plants. The total dry matter production of above-ground biomass of four successive crops followed a descending order: ZP > ZPK > ZNK > Z.

Brachiaria species affecting soil nitrification

Nitrification can lead to substantial losses of the applied N through nitrate leaching and N2O emission. The regulation of nitrification may be a strategy to improve fertilizer N recovery and increase its agronomic efficiency. The objective of this study was to evaluate the inhibiting capacity of nitrification in soil by Brachiaria species. The greenhouse experiment was conducted using pots with 10 dm³ of a Red Latosol sample. The treatments consisted of the cultivation of three forage species (Brachiaria brizantha, B. ruziziensis and B. decumbens) and four n rates (0, 100, 200, and 300 mg/pot), and the control (without plants). In the absence of the forage plants, all N fertilization levels raised the N-NO3- soil levels, as a result of nitrification. The mineralization of organic matter supplied much of the N requirement of the forage plants and nitrification was influenced in the rhizosphere of B. brizantha; however, this effect was not high enough to alter the N-NH4+ level in the total soil volume of the pot.

Industrial and urban organic wastes increase soil microbial activity and biomass

Microbial processes have been used as indicators of soil quality, due to the high sensitivity to small changes in management to evaluate, e.g., the impact of applying organic residues to the soil. In an experiment in a completely randomized factorial design 6 x 13 + 4, (pot without soil and residue or absolute control) the effect of following organic wastes was evaluated: pulp mill sludge, petrochemical complex sludge, municipal sewage sludge, dairy factory sewage sludge, waste from pulp industry and control (soil without organic waste) after 2, 4, 6, 12, 14, 20, 28, 36, 44, 60, 74, 86, and 98 days of incubation on some soil microbial properties, with four replications. The soil microbial activity was highly sensitive to the carbon/nitrogen ratio of the organic wastes. The amount of mineralized carbon was proportional to the quantity of soil-applied carbon. The average carbon dioxide emanating from the soil with pulp mill sludge, corresponding to soil basal respiration, was 0.141 mg C-CO2 100 g-1 soil h-1. This value is 6.4 times higher than in the control, resulting in a significant increase in the metabolic quotient from 0.005 in the control to 0.025 mg C-CO2 g-1 Cmic h-1 in the soil with pulp mill sludge. The metabolic quotient in the other treatments did not differ from the control (p < 0.01), demonstrating that these organic wastes cause no disturbance in the microbial community.

Sample size for measurement of root traits on common bean by image analysis

Evaluation of root traits may be facilitated if they are assessed on samples of the root system. The objective of this work was to determine the sample size of the root system in order to estimate root traits of common bean (Phaseolus vulgaris L.) cultivars by digital image analysis. One plant was grown per pot and harvested at pod setting, with 64 and 16 pots corresponding to two and four cultivars in the first and second experiments, respectively. Root samples were scanned up to the completeness of the root system and the root area and length were estimated. Scanning a root sample demanded 21 minutes, and scanning the entire root system demanded 4 hours and 53 minutes. In the first experiment, root area and length estimated with two samples showed, respectively, a correlation of 0.977 and 0.860, with these traits measured in the entire root. In the second experiment, the correlation was 0.889 and 0.915. The increase in the correlation with more than two samples was negligible. The two samples corresponded to 13.4% and 16.9% of total root mass (excluding taproot and nodules) in the first and second experiments. Taproot stands for a high proportion of root mass and must be deducted on root trait estimations. Samples with nearly 15% of total root mass produce reliable root trait estimates.

Impact of direct seeding mulch-based cropping systems on soil nematodes in a long-term experiment in Madagascar

The objective of this work was to assess the effects of conventional tillage and of different direct seeding mulch-based cropping systems (DMC) on soil nematofauna characteristics. The long-term field experiment was carried out in the highlands of Madagascar on an andic Dystrustept soil. Soil samples were taken once a year during three successive years (14 to 16 years after installation of the treatments) from a 0-5-cm soil layer of a conventional tillage system and of three kinds of DMC: direct seeding on mulch from rotation soybean-maize residues; direct seeding of maize-maize rotation on living mulch of silverleaf (Desmodium uncinatum); direct seeding of bean (Phaseolus vulgaris)-soybean rotation on living mulch of kikuyu grass (Pennisetum clandestinum). The samples were compared with samples from natural fallows. The soil nematofauna, characterized by the abundance of different trophic groups and indices (MI, maturity index; EI and SI, enrichment and structure indices), allowed the discrimination of the different cropping systems. The different DMC treatments had a more complex soil food web than the tillage treatment: SI and MI were significantly greater in DMC systems. Moreover, DMC with dead mulch had a lower density of free-living nematodes than DMC with living mulch, which suggested a lower microbial activity.

Phosphorus utilization by corn as affected by green manure, nitrogen and phosphorus fertilizers

The objective of this work was to evaluate the utilization by corn plants of P from triple superphosphate fertilizer labeled with 32P (32P‑TSP), and of P from soil as affected by N rates and by the green manures (GM) sunn hemp (Crotalaria juncea) and millet (Pennisetum glaucum). The experiment was carried out using pots filled with 5 kg Oxisol (Rhodic Hapludox). A completely randomized design was used, in a 4x4x2 factorial arrangement, with four replicates. The treatments were: four P rates as TSP (0, 0.175, 0.350, and 0.700 g P per pot); four N rates as urea (0, 0.75, 1.50, and 2.25 g N per pot); and sunn hemp or millet as green manure. The additions of N and P by the GM were taken into account. After grain physiologic maturation, corn dry matter, P contents, accumulated P, and P recovery in the different treatments were measured. 32P‑TSP recovery by corn increased with N increasing rates, and decreased with increasing rates of 32P‑TSP. The mineral fertilizer provides most of the accumulated P by corn plants. The recovery of 32P‑TSP by corn was 13.12% in average. The green manure species influence the assimilation of 32P‑TSP by the plants.

One pot obtention of a tetrabutylammonium hydroxide solution for ironporphyrin-OH- interaction studies in organic solvents

In this work we report the obtention of a tetrabutylammonium hydroxide (TBAOH) solution in acetonitrile in a one pot process in order to study the interaction ironporphyrinOH- in non-aqueous systems. All the reactions were carried out under dry argon atmosphere to prevent the contamination of the solution with CO2, which leads to the formation of (TBA)2CO3.

Preparation, spectroscopic and acidity properties of two hydrazones: an organic lab experiment

An undergraduate organic lab experiment is described based on the preparation of two readily accessible hydrazones. The UV-visible spectra of these N-H acids and of their conjugate bases are employed to illustrate the importance of through-conjugation in determining their acid strength and their internal charge-transfer-band transitions.

Aplicação de fósforo para imobilização química do cádmio em solo contaminado

The objective of the study was to evaluate the effect of phosphorus on the Cd availability to plants of a contaminated soil using 109Cd isotope and chemical extractants. The experiment was set in a randomized block design and the soil was labeled with 222 KBq of 109Cd per pot and received 5 rates of P as triple superphosphate, growing lettuce plants as test crop. The use of phosphorus reduced pH of soil which altered the Cd availability in DTPA and Mehlich extractants. The lettuce Cd content decreased but its accumulation and L value increased in all treatments compared to the control, demonstrating the inefficiency of phosphorus in reducing the Cd availability.

Selective detection of fluoride based on a pyridinium n-phenolate-calix[4]pyrrole displacement assay: an undergraduate laboratory experiment

A two-step experiment is proposed for a third year class in experimental organic chemistry. Over a period of five weeks, the students synthesized calix[4]pyrrole, a receptor that is highly selective for fluoride, and a pyridinium N-phenolate dye. Subsequently, the students used the synthesized compounds to investigate a displacement assay on the basis of the competition in acetonitrile between fluoride and the dye for calix[4]pyrrole. The experiment increased the students' skills in organic synthesis and in the characterization of organic compounds, provided a very attractive and accessible illustration of important supramolecular phenomena, and allowed the study of a chromogenic chemosensor.

An undergraduate level experiment on the synthesis of Au nanoparticles and their size-dependent optical and catalytic properties

The synthesis of gold nanoparticles (Au NPs) 15, 26, and 34 nm in diameter, followed by the investigation of their size-dependent optical and catalytic properties, is described herein as an undergraduate level experiment. The proposed experiment covers concepts on the synthesis, stabilization, and characterization of Au NPs, their size-dependent optical and catalytic properties at the nanoscale, chemical kinetics, and the role of a catalyst. The experiment should be performed by groups of two or three students in three lab sessions of 3 h each and organized as follows: i) synthesis of Au NPs of different sizes and investigation of their optical properties; ii) evaluation of their catalytic activity; and iii) data analysis and discussion. We believe that this activity enables students to integrate these multidisciplinary concepts in a single experiment as well as to become introduced/familiarized with an active research field and current literature in the areas of nanoparticle synthesis and catalysis.

SÍNTESE DE ÁCIDOS CUMARINO-3-CARBOXÍLICOS E SUA APLICAÇÃO NA SÍNTESE TOTAL DA AIAPINA, CUMARINA E UMBELIFERONA

The synthesis of 3-coumarin-carboxylic acids and their application to the total synthesis of the natural products ayapin, coumarin, and umbeliferone in undergraduate organic chemistry experiments is described herein. The synthetic approach consists of a one-pot cyclization between salyciladehydes and Meldrum's acid in water to produce the above mentioned acids, followed by decarboxylation under basic or radical conditions.

Effect of population densities of Heterodera glycines race 3 on leaf area, photosynthesis and yield of soybean

The effect of Heterodera glycines on photosynthesis, leaf area and yield of soybean (Glycine max) was studied in two experiments carried out under greenhouse condition. Soybean seeds were sown in 1.5 l (Experiment 1) or 5.0 l (Experiment 2) clay pots filled with a mixture of field soil + sand (1:1) sterilized with methyl bromide. Eight days after sowing, seedlings were thinned to one per pot, and one day later inoculated with 0; 1.200; 3.600; 10.800; 32.400 or 97.200 J2 juveniles of H. glycines. Experiment 1 was carried out during the first 45 days of the inoculation while Experiment 2 was conducted during the whole cycle of the crop. Measurements of photosynthetic rate, stomatic conductance, chlorophyll fluorescence, leaf color, leaf area, and chlorophyll leaf content were taken at ten-day intervals throughout the experiments. Data on fresh root weight, top dry weight, grain yield, number of eggs/gram of roots, and nematode reproduction factor were obtained at the end of the trials. Each treatment was replicated ten times. There was a marked reduction in both photosynthetic rate and chlorophyll content, as well as an evident yellowing of the leaves of the infected plants. Even at the lowest Pi, the effects of H. glycines on the top dry weight or grain yield were quite severe. Despite the parasitism, soybean yield was highly correlated with the integrated leaf area and, accordingly, the use of this parameter was suggested for the design of potential damage prediction models that include physiological aspects of nematode-diseased plants.

Harmonical oscillator and electro-mechanical analogy: an interdiscinary experiment to high precision mass variation measurements

In general, the traditional Physics courses needs examples of the aplications of the Physics concepts in other areas such as Chemistry and Biology. This lacks tend to demotivate Chemistry and Biology students regarding to deal with Physical concepts developed in classroom. In this work, the analogy among mechanic and electric oscillators is investigated to be applied in Chemistry and Biology areas, showing to be valuable due to its aplication in techniques that aims to measure mass variation with high precision. This measure could be made in a direct or indirect way. These techniques are known as electrogravimetric techniques and they are important in biosensor aplications. Thus, this paper explores the electromechanic analogy in an interdisciplinary way involving areas like Physics, Chemistry and Biology. Based on this analogy, it is proposed an experiment that can be applied in different ways, i.e. by an basic approach or more deeper, depending on the students specific formation, in other words, Physics, Chemistry or Biology.