INFLUENCE OF SUGARCANE STRAW AND SOWING DEPTH ON THE EMERGENCE OF WEED SPECIES

ABSTRACT This study aimed to understand the influence of sowing depth and the amount of sugarcane straw on the emergence of weed species Luffa aegyptiaca Miller (Cucurbitaceae); Mucuna aterrima Piper & Tracy (Fabaceae - Leguminosae) and Ricinus communis (Euphorbiaceae). A completely randomized design with a 5 x 4 x 3 factorial layout with four replications was used, at five sowing depths (0, 2, 4, 8 and 10 cm), four different amounts of sugarcane straw (0, 5, 10 and 15 t ha-1) and three different evaluation periods (7, 14 and 21 days after sowing). After sowing, different amounts of sugarcane straw (0, 5, 10 and 15 t ha-1) were deposited on soil. Seedling emergence was analyzed at 7, 14 and 21 days after sowing, counting the number of seedlings that had emerged. At the end of the trial, weed height (cm), leaf area (cm2) and shoot dry mass (g) were measured. In relation to emergence ability, studied species presented different responses according to sowing depth and to the amount of sugarcane straw deposited on the soil. For the L.aegyptiacaand M.aterrima, no significant difference was observed in the interaction between depth and sugarcane straw, showing the adaptation of these species to no-burn sugarcane system. For R.communis, seeds placed at 0 cm of sugar cane straw depth were observed to favor the emergence of seedlings.

INTERCROPPING CORN WITH A COMBINATION OF TREE SPECIES TO CONTROL WEEDS

ABSTRACT The combination of crop residues or crop extracts is often more advantageous in controlling weeds, than the application of each residue or extract singly. This suggests that in intercropping with maize, the combination of tree species can be more advantageous than species isolated in weed control. The objective of this study was to evaluate the effects of intercropping with a combination of leguminous on the weed growth and corn yield. A randomized-block design with split plots (cultivars in plots) and five replicates was established. The cultivars BR 205 and AG 1041 were subject to the following treatments: two weedings (A), intercropping with sabiá (B), gliricidia (C), gliricidia + sabiá (D) and no weeding (E). In the B and C, 30 viable seeds m-2 of the leguminous were sown. In the D, 15 seeds of each species were sown m-2. The legumes were sown by random casting during corn planting. The sequence of the best treatments in reducing the growth of weeds is A > B = C = D = E. The sequence of the best treatments when are considered the yields of baby corn, green corn and grain is A > B > C > D > E. The cultivars do not differ in regards to the reduction in weed growth. In terms of corn yield cultivar BR 205 is the best.

Wheat Yield Loss in a Two Species Competition with Emex australis and Emex spinosa

Emex australis and E. spinosa are significant weed species in wheat and other crops. Information on the extent of competition of the Emex species will be helpful to access yield losses in wheat. Field experiments were conducted to quantify the interference of tested weed densities each as single or mixture of both at 1:1 on their growth and yield, wheat yield components and wheat grain yield losses in two consecutive years. Dry weight of both weed species increased from 3-6 g m-2 with every additional plant of weed, whereas seed number and weight per plant decreased with increasing density of either weed. Both weed species caused considerable decrease in yield components like spike bearing tillers, number of grains per spike, 1000-grain weight of wheat with increasing density population of the weeds. Based on non-linear hyperbolic regression model equation, maximum yield loss at asymptotic weed density was estimated to be 44 and 62% with E. australis, 56 and 70% with E. spinosa and 63 and 72% with mixture of both species at 1:1 during both year of study, respectively. It was concluded that E. spinosa has more competition effects on wheat crop as compared to E. australis.

Foliar flavonoids of nine species of Bauhinia

Foliar flavonoids of nine species of Bauhinia were isolated and identified. All the compounds correspond to glycosides derived from kaempferol, quercetin, isorhamnetin and myricetin. Derivatives of the latter aglyconhe seem to be rare in Bauhinia. Derivatives of isorhamnetin are commonly found in species of subgenus Bauhinia and were not detected in the two species of subgenus Phanera. Flavonoid patterns of species of the former subgenus are in general more complex than those of the latter.

Temporal dynamics of two species of Chaetophoraceae (Chlorophyta) in tropical streams of São Paulo State, Southeastern Brazil

Temporal dynamics of the chaetophoracean green algae Chaetophora elegans (Roth) C.A. Agardh and Stigeoclonium amoenum Kützing populations was investigated biweekly during late autumn trhough early spring (April to October) in two tropical streams from northwestern São Paulo State, southeastern Brazil. Abundances of one population of each species was evaluated by the quadrat technique in terms of percent cover and frequency. The fluctuations were related to the following stream variables: temperature, turbidity, specific conductance, pH, oxygen saturation, depth, substratum type, current velocity, irradiance and nutrients. Percent cover and frequency of C. elegans had lower values throughout the study period and was positively correlated to rainfall. Other correlations (i.e. positive of percent cover with depth and current velocity and negative with irradiance) were consistently found, reinforcing the strong influence of rainfall. On the other hand, percent cover and frequency of S. amoenum had higher values, with maximum growth from June to September. Percent cover was negatively correlated to rainfall. Results suggest the precipitation regime as the most important driving force to temporal changes in both populations, but playing different roles in each one. The gelatinous thallus of C. elegans seem to be favored by the increment of current velocity, since higher flows can improve the nutrient uptake by means of reduction in diffusion shell without promoting excessive drag force. In contrast, tufts of S. amoenum are, presumably, more exposed to drag force, and, consequently, more susceptible to mechanical damage effects due to higher current velocities.

Lognormal abundance distribution of woody species in a cerrado fragment (São Carlos, southeastern Brazil)

The lognormal distribution model is frequently found in communities, especially those which are rich in species and influenced by many environmental factors, as those of the cerrado. We tested the hypothesis that the abundance distribution of woody plant species in a cerrado fragment fits the lognormal model. We placed 20 lines in a cerrado fragment and sampled, with the point-quarter method, 800 individuals with stem perimeter equal or larger than 3 cm. We plotted the abundance-class histogram of the species, verified its normality with the Kolmogorov-Smirnov test, and estimated the expected number of woody species for this community. Of the 63 obtained species, Anadenanthera falcata (with 185 species), Eriotheca gracilipes (43), Stryphnodendron obovatum (37), and Miconia albicans (36) were the most abundant ones. Twelve species were represented by only one individual. We did not reject the null hypotheses that the distribution of woody component species was normal and, thus, their abundances fitted the lognormal model. Therefore, with our work, we can predict that cerrado plant communities fit the lognormal model. If this pattern is maintained in other cerrado communities, there would be implications for the conservation of this vegetation type, because rare species are susceptible of extinction, and implications to their structure, because the dominant species may act as keystone species.

Water relations of tree species growing on a rock outcrop in the "Parque Estadual de Itapuã", RS

Water relations of the tree species Myrsine umbellata Mart. ex A. DC., Dodonaea viscosa Jacq. and Erythroxylum argentinum O. E. Schulz, growing on a rock outcrop in the "Parque Estadual de Itapuã" (RS), were studied. Environmental (precipitation, temperature, soil water) and plant (water potential, vapor pressure deficit, stomatal conductance, transpiration, leaf specific hydraulic conductance, osmotic potential and cell wall elasticity) parameters were collected in five periods and pooled into two sets of data: wet and dry periods. Myrsine umbellata showed great stability of the plant parameters, including the maintenance of high pre-dawn (psiwpd) and mid-day (psiwmd) water potentials in the dry period (-0.48 and -1.12 MPa, respectively), suggesting the presence of a deep root system. Dodonaea viscosa and E. argentinum reached lower psiwpd (-1.41 and -1.97 MPa, respectively) and a greater degree of stomatal closure in the dry period, suggesting a shallower root system. Differential exposure to soil drought was also corroborated by differential drought effects on the whole-plant leaf specific hydraulic conductance (Gt). Correlation analysis pointed to weak correlations between psiwpd and g s. Erythroxylum argentinum was the only species to show osmotic adjustment in response to drought. It is suggested that M. umbellata has low tolerance to water deficits, adopting an avoidance behavior. The much lower values of psiw reached by D. viscosa and E. argentinum suggest a greater tolerance to drought by these species.

Influence of soil properties on the abundance of plant species in ferruginous rocky soils vegetation, southeastern Brazil

Ferruginous "campos rupestres" are a particular type of vegetation growing on iron-rich primary soils. We investigated the influence of soil properties on plant species abundance at two sites of ferruginous "campos rupestres" and one site of quartzitic "campo rupestre", all of them in "Quadrilátero Ferrífero", in Minas Gerais State, southeastern Brazil. In each site, 30 quadrats were sampled to assess plant species composition and abundance, and soil samples were taken to perform chemical and physical analyses. The analyzed soils are strongly acidic and presented low fertility and high levels of metallic cations; a principal component analysis of soil data showed a clear segregation among sites due mainly to fertility and heavy metals content, especially Cu, Zn, and Pb. The canonical correspondence analysis indicated a strong correlation between plant species abundance and soil properties, also segregating the sites.

Evaluation of techniques for C and ASG banding of the mitotic chromosomes of Anastrepha species (Diptera, Tephritidae)

Methods previously described by Canovai et al. (Caryologia 47: 241-247, 1994) which produced C and ASG bands in mitotic chromosomes of Ceratitis capitata were applied to the chromosomes of several Anastrepha species. Metaphase plate yield was substantially increased by use of imaginal disks together with cerebral ganglia. The C-bands were quite prominent allowing the resolution of tiny blocks of heterochromatin. The ASG method produced G-like banded chromosomes, which permitted recognition of each individual chromosome. These simple techniques do not require special equipment and may be valuable for karyotype variability studies in fruit flies and other Diptera

Attraction to amino acids by Lymnaea acuminata, the snail host of Fasciola species

Adult Lymnaea acuminata (average length 20-22 mm) were collected locally from lakes and low-lying submerged fields from Gorakhpur. The chemoattraction studies were made in round glass aquaria measuring 30 cm in diameter and filled to a depth of 10 mm with 500 ml dechlorinated tap water. Each aquarium was divided into four concentric zones. At the starting time of the assay 10 snails were placed on the circumference of outermost zone 0. Snail attractant pellets (SAP) were added simultaneously in the center of central zone 3. SAP of different amino acids were prepared at concentrations of 10, 20, 50, 80 and 100 mM/2% agar solution and, subsequently, spread to a uniform thickness of 5 mm. After cooling, SAP were cut in small pieces of 5 mm in diameter. Lymnaea acuminata's attraction to amino acids was studied using different amino acid concentrations in SAP. Pellets containing amino acids with non-polar R groups (proline and tryptophan), a charged polar group (arginine) and uncharged polar R groups (serine, citrulline and asparagine) were tested. The snails were more attracted to the uncharged polar R group amino acid serine than to other groups of amino acids. The preferred amino acid concentration was 80 mM. The attraction of snails to different amino acids was concentration dependent. Snails could discriminate amongst the different amino acids at > or = 50 mM.

Evaluation of iron bioavailability in a mixture of cereals, seeds, and grains ("Human Ration")

Iron bioavailability was evaluated in three mixtures of cereals, seeds, and grains ("Human Ration"): light, regular, and homemade provided to rats. The animals received an iron depletion diet for 21 days, followed by a repletion diet containing 12 mg·kg-1 of iron for 14 days. The hemoglobin regeneration efficiency and the relative biological value did not differ between the light mixture and control group. The iron bioavailability of the light mixture of cereals, seeds, and grains and the control group were 99.99±27.62 and 80.02±36.63, respectively, while the regular and homemade mixtures of cereals, seeds, and grains showed lower iron bioavailability, 50.12±35.53 and 66.66±15.44, respectively; the iron content of the diet with light cereal mixture light was statistically similar to that of the control (ferrous sulfate 99.99±27.62). The high content of tannin (202.81±19.53 mg·100-1) in the diet with the regular cereal mixture may have contributed to its low iron bioavailability. The higher intake of soluble fiber by the animals fed the light mixture (21.15±0.92 g) was moderately correlated (r=0.5712, p=0.0018) with the concentration of propionate in the caecal bulk (65.49±11.08 µmol/g). The short chain fatty acids produced by soluble fiber fermentation, associated with the low-content of tannin may have improved iron solubility and absorption in the light cereal mixture diet. The iron bioavailability in the light mixture of cereals, seeds, and grains was similar to that of ferrous sulfate.