CRESCIMENTO INICIAL E CONCENTRAÇÃO DE NUTRIENTES EM CLONES DE Eucalyptus urophylla x Eucalyptus grandis SOB INTERFERÊNCIA DE PLANTAS DANINHAS

A presença de plantas daninhas em plantios de eucalipto, especialmente nos dois primeiros anos, pode acarretar grandes prejuízos à produtividade, pois reduz a eficiência de aproveitamento dos recursos de crescimento pela cultura. Assim, objetivou-se com este trabalho avaliar os efeitos da interferência de plantas daninhas sobre o crescimento inicial de dois clones de Eucalyptus urophylla x Eucalyptus grandis e a concentração foliar de nutrientes na cultura e nas plantas daninhas. O experimento foi instalado em esquema fatorial 2 x 5 + 7, sendo dois clones de híbridos de Eucalyptus urophylla x Eucalyptus grandis, identificados como CNB001 e CNB016, em competição com cinco plantas daninhas Urochloa decumbens (capim-braquiária), Ipomoea nil (corda-de-viola), Commelina diffusa (trapoeraba), Spermacoce latifolia (erva-quente) e Panicum maximum (capim-colonião). Adicionalmente, foram cultivados os dois clones de eucalipto e as cinco plantas daninhas em monocultivo como padrão de comparação, no delineamento inteiramente casualizado, com quatro repetições. Foram avaliados eucalipto através da altura de plantas, o diâmetro do coleto, o número de ramos, a área foliar, a matéria seca e, o teor foliar de nutrientes do eucalipto, bem como o teor de nutrientes nas folhas das plantas daninhas. O clone CNB001 apresentou crescimento inicial superior ao clone CNB016, no entanto, livre da interferência de plantas daninhas, verificaram-se teores foliares semelhantes para a maioria dos nutrientes em ambos os genótipos. O clone CNB016 mostrou maior sensibilidade à interferência negativa das plantas daninhas que o clone CNB001, sendo seu crescimento inicial mais afetado por Ipomoea nil e a concentração de nutrientes reduzida pelas espécies Panicum maximum, Urochloa decumbens e Commelina diffusa. Panicum maximum apresentou maior interferência com o clone CNB001, enquanto Ipomoea nil pouco influenciou o crescimento e o teor de nutrientes deste híbrido. As plantas daninhas apresentaram elevada capacidade de extrair nutrientes do solo, mesmo em convivência com os clones de Eucalyptus urophylla x Eucalyptus grandis. A interferência imposta à cultura é dependente da espécie infestante e do genótipo de eucalipto.

Glyphosate-resistant hairy fleabane competition in RR® soybean.

2014

Interference and management of parthenium: The world's most important invasive weed

Parthenium (Parthenium hysterophorus L.) is one of the most aggressive herbaceous weeds of the Asteraceae family. It is widely distributed, almost across the world and has become the most important invasive weed. Comprehensive information on interference and control of this devastating species is required to facilitate better management decisions. A broad review on the interference and management of this weed is presented here. Inspite of its non-tropical origin, parthenium grows quite successfully under a wide range of environmental conditions. It is spreading rapidly in Australia, Western Africa, Asia, and Caribbean countries, and has become a serious weed of pastures, wastelands, roadsides, railwaysides, water courses, and agricultural crops. The infestations of parthenium have been reported to reduce grain and forage yields by 40–90%. The spread of parthenium has been attributed to its allelopathic activity, strong competitiveness for soil moisture and nutrients, and its capability to exploit natural biodiversity. Allelochemicals released from parthenium has been reported to decrease germination and growth of agronomic crops, vegetables, trees, and many other weed species. Growth promoting effects of parthenium extracts at low concentrations have also been reported in certain crops. Many pre- and post-emergence herbicides have been evaluated for the control of parthenium in cropped and non-cropped areas. The most effective herbicides are clomazone, metribuzin, atrazine, glyphosate, metsulfuron methyl, butachlor, bentazone, dicamba, and metsulfuron methyl. Extracts, residues, and essential oils of many allelopathic herbs (Cassia, Amaranthus, and Xanthium species), grasses (Imperata and Desmostachya species), and trees (Eucalyptus, Azadirachta, Mangifera species, etc.) have demonstrated inhibitory activities on seed germination and seedling growth of parthenium. Metabolites of several fungi, e.g., Fusarium oxysporun and Fusarium monilifonne, exhibit bioherbicidal activity against seeds and seedlings of this weed. Intercropping, displacement by competitive plant species like Cassia species, bisset bluegrass, florgen blugress, buffelgrass, along with the use of biological control agents like Mexican beetle, seed-feeding and stem-boring weevils, stem-galling and leaf-mining moth, and sap-feeding plant hopper, have been reported as possible strategies for the management of parthenium. An appropriate integration of these approaches could help minimize spread of parthenium and provide sustainable weed management with reduced environmental concerns.

Weed-soybean interference studies in Brazil

Recently, a notable shift in weed patterns has occurred in some soybean growing regions, as a result of tillage system change and herbicide use. The weed communities are very diversified and strongly interfere with soybean growth and productivity, especially when the shading of superior leaves of the canopy occurs. Some changes to certain agricultural practices, such as cultivars, row spacing and sowing density, were studied and were considered suitable for the establishment of an integrated weed management system under Brazilian conditions. -from Author

EFFECTS of MINERAL NUTRITION on INTER- and INTRASPECIFIC INTERFERENCE of PEANUT (Arachis hypogaea L.) and HAIRY BEGGARTICKS (Bidens pilosa L.)

The present work was carried out to study the effects of mineral nutrition on peanut (Arachis hypogaea L) cv. IAC Runner-886 and hairy beggarticks (Bidens pilosa L) growth, when submitted to inter- and intraspecific competition. The treatments consisted of two peanut plants per pot, two hairy beggarticks per pot and one plant of each species per pot. The plants were nourished with Hoagland and Arnon (1950) complete solution, or without potassium, or without phosphorus or without nitrogen. Sixty days after planting, no inter- or intraspecific competition effect on growth characteristics of peanut was verified and nutrition was not a limiting factor to the culture. No interaction between competition and nutrition effects was observed for both species. The weed suffered more negative effects from intraspecific competition and nutrition. The absence of N had a pronounced effect compared to the other elements, resulting in a reduction in all the evaluated characteristics. The deficiency of nutrients and competition affected the weed more than the crop, showing that peanut was more competitive than hairy beggarticks.

Statistical analysis and reduction of multiple access interference in MC-CDMA systems

Multicarrier code division multiple access (MC-CDMA) is a very promising candidate for the multiple access scheme in fourth generation wireless communi- cation systems. During asynchronous transmission, multiple access interference (MAI) is a major challenge for MC-CDMA systems and significantly affects their performance. The main objectives of this thesis are to analyze the MAI in asyn- chronous MC-CDMA, and to develop robust techniques to reduce the MAI effect. Focus is first on the statistical analysis of MAI in asynchronous MC-CDMA. A new statistical model of MAI is developed. In the new model, the derivation of MAI can be applied to different distributions of timing offset, and the MAI power is modelled as a Gamma distributed random variable. By applying the new statistical model of MAI, a new computer simulation model is proposed. This model is based on the modelling of a multiuser system as a single user system followed by an additive noise component representing the MAI, which enables the new simulation model to significantly reduce the computation load during computer simulations. MAI reduction using slow frequency hopping (SFH) technique is the topic of the second part of the thesis. Two subsystems are considered. The first sub- system involves subcarrier frequency hopping as a group, which is referred to as GSFH/MC-CDMA. In the second subsystem, the condition of group hopping is dropped, resulting in a more general system, namely individual subcarrier frequency hopping MC-CDMA (ISFH/MC-CDMA). This research found that with the introduction of SFH, both of GSFH/MC-CDMA and ISFH/MC-CDMA sys- tems generate less MAI power than the basic MC-CDMA system during asyn- chronous transmission. Because of this, both SFH systems are shown to outper- form MC-CDMA in terms of BER. This improvement, however, is at the expense of spectral widening. In the third part of this thesis, base station polarization diversity, as another MAI reduction technique, is introduced to asynchronous MC-CDMA. The com- bined system is referred to as Pol/MC-CDMA. In this part a new optimum com- bining technique namely maximal signal-to-MAI ratio combining (MSMAIRC) is proposed to combine the signals in two base station antennas. With the applica- tion of MSMAIRC and in the absents of additive white Gaussian noise (AWGN), the resulting signal-to-MAI ratio (SMAIR) is not only maximized but also in- dependent of cross polarization discrimination (XPD) and antenna angle. In the case when AWGN is present, the performance of MSMAIRC is still affected by the XPD and antenna angle, but to a much lesser degree than the traditional maximal ratio combining (MRC). Furthermore, this research found that the BER performance for Pol/MC-CDMA can be further improved by changing the angle between the two receiving antennas. Hence the optimum antenna angles for both MSMAIRC and MRC are derived and their effects on the BER performance are compared. With the derived optimum antenna angle, the Pol/MC-CDMA system is able to obtain the lowest BER for a given XPD.