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Search Results: 1 - 10 of 16624 matches for " Competition for the soil "
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Potencial de espécies utilizadas como adubo verde no manejo integrado de plantas daninhas
Erasmo, E.A.L.;Azevedo, W.R.;Sarmento, R.A.;Cunha, A.M.;Garcia, S.L.R.;
Planta Daninha , 2004, DOI: 10.1590/S0100-83582004000300002
Abstract: this work was carried out at the experimental station of the university of tocantins, gurupi-to, brazil, to evaluate the interference of eight species frequently used as green manure (mucuna aterrima, mucuna pruriens, crotalaria ochroleuca, crotalaria spectabilis, canavalia ensiformis, cajanus cajan, pennisetum americanum and sorghum bicolor, hybrid br304) in the weed community, for sixty days under field conditions. the most frequent weed species in the experimental area were digitaria horizontalis, hyptis lophanta and amaranthus spinosus. samplings were made at 15, 30, 45 and 60 days after formation of green manure covering, using a square sampler of 0.25 m2. the weeds were identified, collected, dried and weighed. the experimental design consisted of nine treatments distributed in randomized blocks with four replicates. it was verified that c. spectabilis, s. bicolor, c. ochroleuca m. aterrima and m. pruriens reduced significantly the number and dry matter weight of the weeds evaluated, especially h.lophanta and a. spinosus, while p. americanum was the least efficient.
Adsorption of Cd, Cu, Ni and Zn in tropical soils under competitive and non-competitive systems
Moreira, Cindy Silva;Alleoni, Luís Reynaldo Ferracciú;
Scientia Agricola , 2010, DOI: 10.1590/S0103-90162010000300008
Abstract: the adsorption of heavy metals in soils affects their behavior in the environment and their bioavailability to plants. the knowledge of the adsorption mechanisms in competitive systems allows a more realistic evaluation of the metals' behavior in the soil than the single metal adsorption. the objectives of this study were (i) to evaluate cd, cu, ni, and zn adsorption in 14 surface samples (0-0.2 m) of representative soils of the brazilian humid-tropical region, in competitive and non-competitive systems, and (ii) to establish metal affinity sequences for each soil, based in the maximum adsorption capacity (mac) estimated by the langmuir model. the rhodic eutrudox, the kandiudalf eutrudox, the arenic hapludalf, the arenic hapludult and the typic argiudoll had the highest metals' adsorption capacity, whereas the typic quartzipsamment and the sandy-textured arenic hapludult had the lowest values. in general, the mac values for metals were lower in the competitive than in the non-competitive system. in the non-competitive system, the most common affinity sequence was cu > zn > ni > cd, whereas the most common sequence was cu > cd > zn > ni in the competitive system. in general, the langmuir model fitted well the adsorption data of metals on the studied soils.
The Growth of Two Species of Subalpine Co-nifer Saplings in Response to Soil Warming and Inter-Competition in Mt. Gongga on the South-Eastern Fringe of the Qinghai-Tibetan Plateau, China  [PDF]
Hongtao Song, Song Cheng, Yinsheng Zhang
World Journal of Engineering and Technology (WJET) , 2016, DOI: 10.4236/wjet.2016.43039
Abstract: In conjunction with global climate change, soil temperatures have been recorded to be increasing more rapidly than air temperatures at Mt. Gongga, China. Plant density is also increasing, and a means of combining the effects of changes in soil temperature and competition on the growth and regeneration of the constructive coniferous species seedlings in the subalpine ecotones is needed. Thus, a split-plot design experiment was conducted with Sargent spruce (Picea brachytyla) and Purple cone spruce (P. purpurea) saplings, using four soil temperatures (control Tsoil = 11.9 ± 0.3, low Tsoil = 13.4 ± 0.140, intermediate?Tsoil = 15.4 ± 0.1, high Tsoil = 16.4 ± 0.2) and three plant densities (one, two and three saplings per pot), in the subalpine ecotone. Soil temperatures were controlled through a cable heating system. After two growing seasons under the soil temperature treatments, 107 Sargent spruce saplings and 110 of the same-aged Purple cone spruce saplings were harvested. The results showed that Sargent spruce grew faster and with a greater biomass productivity than Purple cone spruce. Increased soil temperature significantly increased leaf biomass, branch biomass, above-ground biomass, and total plant biomass for developing crown architecture in Sargent spruce, whereas plant competition (i.e., higher density) notably caused a decline in leaf biomass, branch biomass, and above-ground biomass. Purple cone spruce did not respond to either an increases in soil temperature or plant competition. Neither plant species was influenced by the interaction of soil temperature and plant competition. These results suggest that Sargent spruce may expand the upper and lower limits of its distribution as global warming continues, but the expansion is likely to be restricted by plant competition in the future, including that from Purple cone spruce. Below-ground, fine root biomass does not change with soil warming although other sized roots do in both species. This signifies that light availability is more important in
Biocombustibles y Seguridad Alimentaria
Oliveri,EA; Dalto,P; Santiago,LC; Guerrero,ME;
Diaeta , 2009,
Abstract: the basic task of delimiting the concept of "biofuel" carries some problems in itself. we can refer to it as a generic notion including any organic substance used by man as a source of energy (e.g. firewood) and/or refer to the phenomenon as it is developing under the current circumstances, making reference to the outcome of complex systems of biomass transformation (e.g. bioethanol, biodiesel). the debate about biofuels has been occupying a considerable space for quite a long time on the media (newspapers, magazines, tv), but the information is given in a very disorderly way, mostly as the expression of parties in disagreement. on the one hand, there are people who seem to express only the benefits of the model, making reference to countries such as argentina (due to its characteristics) as privileged performers of this new initiative. on the other hand, there are those who warn about a renewed expansionist effort of developed countries in their search for taking possession of natural resources. the task of taking a vision beyond superficial assumptions, aimed at providing clear evidence of the current stage, cannot be ignored. the mere suspicion of a competition for territory to harvest crops intended to energy production, versus the pursuit to use that territory to obtain food, deserves a very careful examination. the present paper tries to explore the main aspects of the biofuel phenomenon, its production ways, and their connection with food supply safety, starting from the description of four interrelated dimensions: food availability, access to food, stability in the use of natural resources and biological utilization of food and nutrients. the "food vs. energy" dilemma will go on until a solid research platform analyzing all the factors related to this subject is available. it is essential to sponsor interdisciplinary studies, and governments are, for sure, the main players.
The abiotic environment of Heliamphora nutans (Sarraceniaceae): pedological and microclimatic observations on Roraima Tepui
Adlassnig, Wolfram;Pranji, Kornelija;Mayer, Edith;Steinhauser, Georg;Hejjas, Flora;Lichtscheidl, Irene K.;
Brazilian Archives of Biology and Technology , 2010, DOI: 10.1590/S1516-89132010000200022
Abstract: the aim of this study was the study of the abiotic environment of the carnivorous pitcher plant heliamphora nutans (sarraceniaceae), including the microclimate and the geochemistry of the soil of the growing sites on roraima tepui and discuss their relevance within the recent model of carnivorous plant ecology. the soil was peaty and low in nutrients. the microclimate on the site was very balanced, with moderately cool temperatures, a constant high humidity and very low wind speed. heliamphora was not exposed to any recognizable climatic stress. previous macroclimatic measurements reflected the growth conditions of heliamphora only incorrectly, since humidity decreased drastically with height. the apparent conflict with the common model of carnivorous plant ecology was caused by the dense surrounding vegetation. however, the leaf coverage of these non carnivorous plants was too low to cause significant insolation decrease for heliamphora. furthermore, the temperature regime of the pitcher fluid was more balanced than the temperature of the leaf. this may improve conditions for the growth of microorganisms in the pitcher fluid that contribute to the degredation of the plant's prey.
Reten??o e dessor??o competitivas de anions inorganicos em gibbsita natural de solo
Pozza, Adélia Aziz Alexandre;Curi, Nilton;Costa, Enio Tarso de Souza;Guilherme, Luiz Roberto Guimar?es;Marques, Jo?o José Granate de Sá e Melo;Motta, Paulo Emílio Ferreira da;
Pesquisa Agropecuária Brasileira , 2007, DOI: 10.1590/S0100-204X2007001100015
Abstract: the objective of this work was to quantify the competitive retention and desorption of nitrate, sulfate, silicate and phosphate anions on gibbsitic clay fraction of a melanic gleisol. samples of clay fraction were shaken in centrifuge tubes with 30 mmolc l-1 nacl solution containing these anions in quantities equivalent to 30% of the respective maximum adsorption capacity exhibited by clay. for comparative purposes, samples were also shaken with the same solution containing 1 mmolc l-1 of each mentioned anion. the tubes were centrifuged and the anionic concentrations in supernatants were determined. the dessorption was performed by shaking the residual clay fraction in centrifuge tubes with nacl solution and quantifying the released anions. in another experiment, with the silicon phosphorus previously adsorbed to gibbsite, p and si were added in the sequence, intercalated for evaluating the capacity of desorpting the previously adsorbed anion. the phosphate was preferentially adsorbed in relation to the other studied anions and the previous silicon application reduced the phosphate fixation. the silicon application previously to phosphate favours the bioavailability of p in highly weathered soils.
Fitomassa de adubos verdes e controle de plantas daninhas em diferentes densidades populacionias de leguminosas
Fernandes, Marcelo Ferreira;Barreto, Ant?nio Carlos;Emídio Filho, Jo?o;
Pesquisa Agropecuária Brasileira , 1999, DOI: 10.1590/S0100-204X1999000900009
Abstract: the objective of this study was to evaluate the dry matter yields of calopogonium mucunoides, stizolobium aterrimum, stizolobium deeringeanum variety "rajada", canavalia ensiformis, cajanus cajan, crotalaria breviflora and c. spectabilis in relation to the sowing densities of 10, 20, 40, 80 and 160 seeds m-2, and the yield of weeds grown in these legume densities. this study was carried out from may to august 1996, in a coastal tableland area of the antonio martins experimental station (emdagro/embrapa-cpatc), at lagarto, state of sergipe, brazil. the number of survival plants and the dry matter yields were determined when each species reached the flowering stage. the highest increments of dry matter yield in response to increasing levels of sowing density were observed in plants of crotalaria spectabilis and c. breviflora followed by c. mucunoides, s. aterrimum and s. deeringeanum. a negative response to the increasing sowing densities was observed in canavalia ensiformis and sowing densities did not affect the dry matter yield of cajanus cajan plants. linear and positive responses of c. spectabilis, c. breviflora and c. mucunoides, and quadratic responses of c. ensiformis, c. cajan and s. deeringeanum were obtained for number of plants in response to increasing sowing density. no equations were found to express the relation between the number of survival plants and sowing densities of s. aterrimum, but the survival of this species at high populations was very low. s. aterrimum and c. ensiformis showed the best weed inhibition, even in the lower sowing densities.
Efeito de cascas de café e de arroz dispostas nas camadas do solo sobre a germina??o e o crescimento inicial do caruru-de-mancha
Santos, J.C.F.;Souza, I.F.;Mendes, A.N.G.;Morais, A.R.;Concei??o, H.E.O.;Marinho, J.T.S.;
Planta Daninha , 2001, DOI: 10.1590/S0100-83582001000200007
Abstract: studies of plant residue effects involving mulches to control weeds in perennial crops are difficult to carry out due to the need to differentiate between allelopathy and competition. many researches, nowadays, refer to criteria proving allelopathy. this work was established under greenhouse conditions to determine the allelopathic effects of coffee and rice husks on amaranthus viridis through their arrangements in soil layers. the experimental design was a randomized block with four replications, arranged in a 3 x 3 factorial scheme, with coffee and rice husks and expanded vermiculite being one factor and their residues placed on the top and incorporated into the soil surface and into the bottom, as the other factor. one additional treatment without mulching was used. overall, plant residues inhibited seed germination and stimulated growth of slender amaranth. rice husk showed lower emergent velocity index and seed germination than coffee husk. coffee husk placed on the top provided greater growth and higher dry matter weight of slender amaranth, followed by husk incorporation into the soil surface.
Características de plantas de arroz e a habilidade competitiva com plantas daninhas
Balbinot Jr., A.A.;Fleck, N.G.;Barbosa Neto, J.F.;Rizzardi, M.A.;
Planta Daninha , 2003, DOI: 10.1590/S0100-83582003000200001
Abstract: competitive hability of plants for the use of environmental resources is affected by their morpho-physiological characteristics. there is no agreement on which rice plant characteristic is the most important in determining its competitive ability against weeds. this research aimed to identify flooded rice plant characteristics that contribute the most to its competitiveness. thus, a field experiment was carried out during the 2000/01 growing season in cachoeirinha, rs, to compare the behavior of eight rice genotypes, grown in the absence or presence of the eea 406 rice genotypes, simulating a red rice infestation. rice plant characteristics in the absence of competition were evaluated and at harvesting time, grain yield decrease was determined for each rice genotype, due to competition effect. the analysis of multiple linear regression and simple linear correlation showed that the ability of a cultivar to shadow the soil 60 days after seeding (das) was the variable more closely related to its competitive potential, and that this characteristic was especially associated with rice plant shoot matter accumulation at 15 das.
Potencial da utiliza??o de coberturas vegetais de sorgo e milheto na supress?o de plantas daninhas em condi??o de campo: I - plantas em desenvolvimento vegetativo
Vidal, R.A.;Trezzi, M.M.;
Planta Daninha , 2004, DOI: 10.1590/S0100-83582004000200007
Abstract: the capacity of supression of weed infestation by cultivation of cover crops can occur during the vegetative growth of the species cultivated as cover crops, at the early stages of development, or after their desiccation. competition and allelopathic effects performed, during the coexistence of the cover crop with the weeds can be responsible for the supressive effect. two experiments were carried out under field conditions, in 1999/2000 and 2000/2001, at the experimental station of agronomy college, at the federal university of rio grande do sul (ufrgs), brazil, in a randomized block design with four replications, to determine the effects of living plants of sorghum genotypes with distinct capacity of production of hydrophobic root extracts, on supressing weeds. in 1999/2000, the treatments consisted of the rs 11, br 601, and br 304 sorghum genotypes, representative of three classes of hydrophobic root extracts production in laboratory, comum rs pearl millet genotype and a check without crops. in 2000/2001, the treatments were the result of combinations of genotype factors and weed position ( rows or interrows). in the two experimental years, the density and growth of weeds (sidrh, bidss, and brapl) were similar between sorghum genotypes and of these with pearl millet. this occurred regardless of the place evaluated, in the total area or individually in the rows or interrows, indicating lack of suppressive effect of hydrophobic exsudates under field conditions. in the first trial, thirty days after seeding, reduction of 41% of infestation and 74% of weed total dry mass were observed, while in the second trial, 14 days after seeding, no differences were observed between sorghum and pearl millet areas and the check without cover crops. weed density in rows was inversely proportional to living sorghum plant population in these places.
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