Early growth of common bean cropped over ruzigrass residues

Ruzigrass (Brachiaria ruziziensis, syn. Urochloa ruziziensis) is used as a cover crop in tropical regions because it has a high yield potential, is widely adapted and has a vigorous root system. However, it may affect early growth of the next crop due to allelopathy and competition for soil nitrate. A greenhouse experiment was conducted in glass-walled pots with soil to determine the effect of ruzigrass residues on the initial growth and mineral nutrition of common bean (Phaseolus vulgaris). Ruzigrass was grown in the pots for 50 days and chemically desiccated. Then, common bean was grown: without ruzigrass residues; with ruzigrass shoots placed on the soil surface; with ruzigrass roots left in the soil; and with ruzigrass shoots and roots left undisturbed. Root growth of common bean was decreased by ruzigrass residues, but shoot biomass was not affected when it was grown in the presence of ruzigrass shoots or roots alone. In pots where ruzigrass residues were undisturbed, common bean biomass yield was decreased. Nitrogen concentration in common bean shoot was not affected by ruzigrass shoot on the soil surface, an evidence that the observed decrease in common bean growth probably was due to allelopathic effects rather than competition for nitrogen.

WHEAT HERBAGE AMENDMENTS ALTER EMERGENCE DYNAMICS, SEEDLING GROWTH OF LAMBSQUARTER AND SOIL PROPERTIES

ABSTRACT Crop allelopathy is a potential tool for weed management but allelopathic potential often varies among cultivars and developmental stages of crop. Bioassays were conducted to appraise the allelopathic potential of herbage (incorporated at 8 g kg-1 soil) of different hexaploid wheat (Triticum aestivum) cultivars (Millat-2011, AARI-2011, Lasani-2008 and Faisalabad-2008) collected at different crop growth stages [tillering (Z-30), anthesis (Z-60) and maturity (Z-90)] against lambsquarter (Chenopodium album). Mean emergence time taken by lambsquarter was prolonged over control by anthesis and maturity stage herbage of all wheat cultivars. Final emergence percentage was dropped by 3-17% in response to different growth stages of herbage collection. Maximum suppression in shoot (45 and 78%) and root (60 and 90%) length, and seedling dry biomass (65 and 96%) of lambsquarter over control was recorded under the amendment of anthesis and maturity stages herbage of wheat cultivars. Total chlorophyll contents declined in response to herbage collected at anthesis and maturity stage of all wheat cultivars over control. Phenolic contents on the other hand were increased. Activities of enzymatic antioxidants also varied among all wheat cultivars, and declined by the incorporation of tillering, anthesis and maturity stage herbage. Wheat herbage induced lipid peroxidation in lambsquarter seedling and higher malondialdehyde content (0.56 and 0.77 nmol g-1 FW) was observed by the incorporation of wheat cultivars herbage collected at anthesis and maturity stage, respectively. Anthesis and maturity stage herbage of wheat cultivars Millat-2011, AARI-2011 and Lasani-2008 was more phytotoxic than Faisalabad-2008. Moreover, tillering stage herbage of all wheat cultivars had less inhibitory potential against emergence, seedling growth and biochemical attributes of lambsquarter. Wheat herbage amendment increased the soil pH, phenolic, organic carbon and nitrogen contents as compared to control.

Eucalypt Growth Submitted to Management of Urochloa spp.

The objective of this work was to evaluate the initial growth and the physiological characteristics of eucalypt submitted to different managements of signalgrass. The experiment was conducted in a protected environment, using a randomized blocks design with five repetitions. The treatments were arranged in a (5 x 2) + 1 factorial design, and the first factor corresponded to the types of weed management (no control; chemical control keeping the signalgrass shoot on the soil; chemical control with removal of the signalgrass shoot; mechanical control keeping the signalgrass shoot on the soil, and mechanical control with removal of the signalgrass shoot); the second factor corresponded to the two weeds species (U. brizantha and U. decumbens) and a control relative to the eucalypt in monoculture. The eucalypt growth was not affected by the presence of the Urochloa species until 50 days after treatments (DAT). However, the coexistence of these species with eucalypt for 107 DAT reduced the collar diameter, total dry matter, and the leaf area, but did not alter the characteristics related to photosynthesis and transpiration. The control method adopted, with removal or maintenance of the signalgrass shoot, regardless of species, did not change the initial eucalypt growth. It can be concluded that the coexistence of eucalypt with Urochloa decumbens or Urochloa brizantha for 105 days reduces the eucalypt growth. However, the use of chemical or mechanical control, with or without removal of signalgrass residue, were effective methods to prevent interference of these weeds.

Effects of light stress on the growth of the epiphytic orchid Cattleya forbesii Lindl. X Laelia tenebrosa Rolfe

Considering the performance of CAM epiphytes under high levels of radiation or in shaded environments, with growth rate proportional to light intensity, the objective of this work was to evaluate the effects of long-term light stress on the growth of a Brazilian epiphytic orchid, Cattleya forbesii Lindl. X Laelia tenebrosa Rolfe. Two groups of plants were used in the first experiment, one under 90% (@ 1,650 µmol.m-2.s-1) of Photosynthetically Active Radiation (PAR) and the other maintained under 22.5% (@ 400 µmol.m-2.s-1). In the second experiment the diffusive resistance, transpiration rate and fluorescence levels were monitored for plants that were under 22.5% of PAR, under 90% and plants transferred from 22.5 to 90%. Our results show that light intensity interfered with growth and development of this orchid. Data on the changes in pseudobulb volume throughout the time course of growth suggest that water and reserves stored in the back shoots are translocated to the current shoot. Regarding stomatal resistance, plants under 22.5% of PAR reached a largest stomatal aperture during the night, whereas those under 90% only after dawn. After transfer from 22.5% PAR to 90% PAR the ratio of Fv/Fm decreased from approximately 0.8 to 0.7. This suggests the limitation of photoprotection mechanisms in the leaf and the results observed after the transfer of plants from 22.5% to 90% reinforce the possibility that a photoinhibition is reflected in a decrease in growth rate.

Seedling growth of fifteen Brazilian tropical tree species differing in successional status

Growth of seedlings of fifteen tropical tree species representative, at the adult stage, of different successional positions, was studied under field conditions. Seedlings were grown in three treatments: full sun (FS), artificial shade imposed by neutral screens (AS) and natural shade imposed by a closed canopy in a Forest Reserve in Southeast Brazil (NS). Most of the studied species survived in both shade treatments, although their growth was severely affected. Decreases in height, internode numbers, dry weight, leaf area, root:shoot ratio (R:S) and increases in leaf mass ratio (LMR), leaf area ratio (LAR) and specific leaf area (SLA) were common responses to shade. Relative growth rates (RGRs) and net assimilation rates (NARs) were consistently lower in the shaded treatments than in full sun. RGR was significantly correlated with NAR in the FS and NS treatments, whereas it was correlated with LAR in the AS treatment. Natural shade had more severe effects than artificial shade on leaf area reduction and RGR. Between-species differences in R:S, LMR, SLA and LAR were not related to the successional status of species. However, there was a tendency for early-successional species to have higher RGRs than late successional ones, regardless of the light environment. Late-successional species also showed less pronounced responses to shade than early ones. The characteristics presented by the late-successional species may be associated with shade tolerance, enabling their persistence under dense canopies.

Allelopathic interference of Sapindus saponaria root and mature leaf aqueous extracts on diaspore germination and seedling growth of Lactuca sativa and Allium cepa

Sapindus saponaria (soapberry) is a species that presents a great diversity of chemical compounds, such as saponins; however, few studies have examined the allelopathic effect of this species. Therefore, this study provides an evaluation of the allelopathic potential of aqueous extracts of the roots and mature leaves of S. saponaria on the germination of diaspores and seedlings growth of lettuce (Lactuca sativa) and onion (Allium cepa). The aqueous extract was prepared in the proportion of 100 g of dry plant material in 1,000 mL of distilled water (a concentration of 10% w v-1), and diluted with distilled water to 7.5, 5.0 and 2.5% concentrations. The mature leaf extracts caused delay and decrease in the germination process of the lettuce and onion diaspores, with inhibitory effect concentration-dependent, while the root extracts showed no allelopathic effects on the germination process. Both extracts caused abnormalities and inhibited the growth of shoot and root seedlings.

Germination, initial growth, and biomass allocation in three native Cerrado species

The parameters of germination, initial growth, and biomass allocation of three native plant species of Cerrado (Copaifera langsdorffii, Dipteryx alata and Kielmeyera coriacea) were established. The species had germination percentages above 88% and average germination times longer than 139 hours. The average time for the opening of the first leaf pair was more than 538 hours for all three species. The average root length of C. langsdorffii and D. alata seedlings after 80 days of growth was around 40cm, four times larger than the average shoot length (<10cm), although the root and shoot biomasses were similar for both species. The average root length (>20cm) of K. coriacea seedlings was four times larger than the average shoot length (<5cm), and the root biomass was 243% greater than the shoot biomass. Increase in seedling biomass was sustained primarily by the cotyledons in C. langsdorffii and D. alata, which acted as reserve organs and showed progressive weight reductions. Increase in seedling biomass in K. coriacea was sustained primarily by photosynthesis, since the cotyledons showed no significant weight reduction, acting primarily as photosynthetic organs. The length of the root systems was at least four times larger than the length of the shoots parts in all three species. Higher investment in root length rather than in root biomass suggest that the initial growth of these species is primarily to ensure access to water resources, apparently putting off the function of the radicular system as storage organ.

Effectiveness of plant growth promoting rhizobacteria in facilitating lead and nutrient uptake by little seed canary grass

We investigated the effectiveness of Nitroxin inoculation on lead (Pb) and nutrient uptakes by little seed canary grass. The factors tested included inoculation (or not) with Nitroxin and different soil concentrations of Pb (0, 200, 400 and 800mgPbkg-1 soil). Increasing soil concentrations of Pb decreased stem, leaf and root dry weights. Shoot phosphorus concentrations increased in parallel with increasing soil Pb concentrations. Nitroxin inoculation did not alter the phosphorus concentration of the roots. The Pb translocation factor was >1 in inoculated treatments in the Pb soil concentration range of 200 to 400mgkg-1; the translocation factor for 800mgPbkg‑1 with no inoculation of Nitroxin was, however, <1. Our results indicated that the Pb bioaccumulation factor for little seed canary grass was <1, indicating that it is a Pb excluding plant.

Critical levels of organic acids on seed germination and seedling growth of wheat

The objective of this study was to determine the responses of the wheat cultivars CD 108 and CD 111 for tolerance to organic acids. The effects of five concentrations of the three main acids formed in the soil were studied: acetic acid (0, 4, 8, 12 and 16 mM), propionic acid (0, 4, 8, 12 and 16 mM) and butyric acid (0, 2, 4, 8 and 12 mM). Tests included germination, shoot length, root length and dry weight of shoot and root. The variable root length is the most responsive variable for all the acids tested and the critical level of toxicity of acetic, propionic and butyric acids, which reduced root length by at least 50% was 9.0, 8.5 and 4.0 mM respectively. It was concluded that the presence of acetic, propionic and butyric acids in the germination substratum of wheat seeds of the cultivars CD 111 and CD 108 reduced seedling development, mainly by reducing the length of the radicles.

The influence of light spectra, UV-A, and growth regulators on the in vitro seed germination of Senecio cineraria DC.

This study was carried out to investigate the effects of light spectra, additional UV-A, and different growth regulators on the in vitro germination of Senecio cineraria DC. Seeds were surface-sterilized and inoculated in MS medium to evaluate the following light spectra: white, white plus UV-A, blue, green, red or darkness. The maximum germinability was obtained using MS0 medium under white light (30%) and MS + 0.3 mg L-1 GA3 in the absence of light (30.5%). S. cineraria seeds were indifferent to light. Blue and green lights inhibited germination. Different concentrations of gibberellic acid (GA3) (0.1; 0.4; 0.6; 0.8; 1.0 and 2.0 mg L-1) and indole-3-acetic acid IAA (0.1; 0.3 and 1.0 mg L-1) were evaluated under white light and darkness. No concentration of GA3 enhanced seed germination percentage under white light. However, when the seeds were maintained in darkness, GA3 improved germination responses in all tested concentrations, except at 1.0 mg L-1. Under white light, these concentrations also increased the germination time and reduced germination rate. Germination rate, under light or darkness, was lower using IAA compared with GA3.

Root growth of Arabidopsis thaliana (L.) Heynh. treated with humic acids isolated from typical soils of Rio de Janeiro state, Brazil

Humic substances isolated from soil organic matter had been used as stimulators of plant metabolism. Arabidopsis thaliana (L.) Heynh. with only five chromosomes, short cycle and size, is an important model to evaluate the physiological effects of these substances, which are qualitatively and quantitatively influenced by morphogenesis, mineralogy and chemistry of soils. The objective of this study was to evaluate the ambience effects on bioactivity of humic acids. A and B horizons of four typical soils of the North Fluminense were sampled. After isolation and purification, humic acids were applied to plants in increasing concentrations. The number and length of lateral roots and main root length were evaluated and, subsequently, the concentrations of maximum stimulation were determined by dose-response curves and regression equations. The results showed that more stable humic acids isolated from soil in less advanced stages of weathering, high activity clay and high base saturation resulted in better physiological stimulants for Arabidopsis.

Initial growth of maize in response to application of rock phosphate, vermicompost and endophytic bacteria

Due to the high energy requirement and demand for non-renewable resources for the production of chemical fertilizers, added also to the environmental impact caused by the use of such products, it is important to intensify research on bio-based agricultural inputs. The use of nitrogen-fixing endophytic and phosphate solubilizing bacteria can provide these nutrients to the plants from the air and poorly soluble phosphorus sources, such as phosphate rock. The objective of this study was to evaluate the nutrition and initial growth of maize (Zea mays L.) in response to the inoculation of nitrogen-fixing and rock phosphate solubilizing endophytic bacteria, in single or mixed formulation, applied with vermicompost. The treatments containing bacteria, both diazotrophic and phosphate solubilizing, when compared to controls, showed higher levels of leaf nitrogen and phosphorus in maize, as well as higher growth characteristics. The application of vermicompost showed synergistic effect when combined with endophytic bacteria. Thus, the innovation of the combination of the studied factors may contribute to the early development of maize.

Production of cabbage grown in pots containing legumes' root and shoot

Roots effect is not generally considered in studies assessing the performance of crops in response to green manuring. However, such effect can contribute to a better understanding of crop rotation. The aim of this study was to assess the effect of root and shoot of two legumes on the production of cabbage. The experiment was conducted in pots of 10 liters containing substrate of 2:1 soil/sand. The experiment was arranged in a factorial scheme (2x3 + 2) in a randomized block design with five replicates using two legume species (Crotalaria juncea L. and Canavalia ensiformis L), three plant parts (root, shoot, or whole plant), and two additional treatments (mineral fertilization with 100% and 50% of the recommended dose of N for growing cabbage). Pots with legume treatments received mineral fertilizer with 50% of the recommended dose of N for growing cabbage. The experimental plot consisted of a pot containing one plant of cabbage. Legumes were grown in pots and harvested at 78 days. The root biomass was determined in extra pots. Production was assessed using head fresh and dry weight. The application of the whole plant of both legume species reduced cabbage production. However, root or shoot of both legume species was equivalent to 50% of mineral N fertilization required for the cultivation of cabbage.

Soybean growth and yield after single tillage and species mixture of cover plants

The use of cover crops is important for the agricultural crop and soil management in order to improve the system and, consequently, to increase yield. Therefore, the present study analyzed the effect of crop residues of black oat (Avena strigosa Schreb.) (BO) and a cocktail (CO) of BO, forage turnip (Raphanus sativus L.) (FT) and common vetch (Vicia sativa L.) (V) on the emergence speed index (ESI), seedling emergence speed (SES) plant height and soybean yield in different intervals between cover crop desiccation with glyphosate 480 (3 L ha-1) and BRS 232 cultivar sowing. Plots of 5 x 2.5 m with 1 m of border received four treatments with BO cover crops and four with CO as well as a control for each cover crop, at random, with five replications. The plots were desiccated in intervals of 1, 10, 20 and 30 days before soybean seeding. The harvest was manual while yield was adjusted to 13% of moisture content. The experimental design was completely randomized with splitplots and means compared by the Scott and Knott test at 5% of significance. The results showed that CO of cover crops can be recommended for soybean to obtain a more vigorous seedling emergence, from 10 days after cover crop desiccation.

Growth and yield of Coffea arabica L. in Northwest Fluminense: 2nd harvest

In recent years, several new coffee cultivars recommended for different regions have been released. However, the performance of these varieties in many traditionally producing regions is unknown. Difference of climate and soil may jeopardize the productivity of the new cultivars and cause losses to farmers. The objective of this study is to evaluate the vegetative growth and productive genotypes of C. arabica in the conditions of the Northwestern Rio de Janeiro State, Brazil. The experiment was settled in 2007, in Panorama 1 Farm, located in the municipality of Varre Sai, RJ. Twenty-five genotypes of C. arabica were planted in a spacing of 2.5 × 0.8 m, using a completely randomized design with five replications and eight plants per plot. There were eight measurements of vegetative growth represented by plant height, stem diameter and number of plagiotropic branches. Assessments of productivity were also performed in years 2009 and 2010. There was a positive phenotypic correlation among vegetative characteristics and between vegetative characteristics and yield in the first harvest, while in the second harvest only the number of plagiotropic branches was positively correlated with yield. Up to date, the genotypes Catucaí amarelo 2 SL, Catiguá MG 02, Acauã, Palma II, Sabiá 398, IPR 103/ Iapar, IPR 100/Iapar, H 419-10-6-2-12-1, Catucaí amarelo 24 / 137, Iapar 59, Catucaí amarelo 20/15, H 419-10-6-2-5-10-1 and H 419-10-6-2-5-1 had the highest average yield after two harvests.