9 research outputs found

    Genetic variation in a progeny test of Eucalyptus camaldulensis in Ethiopia

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    Fire-free land preparation as an alternative to slash-and-burn agriculture in the bragantina region, eastern Amazon: crop performance and nitrogen dynamics.

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    In the Amazon region, shifting cultivation with slash buming which is practiced by at least 500,000 small farmers, has been considered one of the main activities responsible for deforestation. To considerably reduce deforestation rates the leveI of sustainability of the shifting cultivation systems, has to be increased and technologies perrnitting an increase in the period used for cultivation of an area to three or more years need to be employed. Thus, the present study had the following objectives: I) to evaluate the effects of tire-free land preparation on crop performance and nitrogen dynarnics; 2) to evaluate the importance of chemical ferti!izer use in systems without the use of tire and 3) to select rice, maize, cowpea and cassava cultivars suitable for mulch systems. The studies were conducted in the community of Cumaru in the municipality of Igarapé Açu (Parå, Brazil) on two neighboring sites with 4-year-old (FV4y) and l G-year-old fallow vegetation (FVIOy). Three treatments for land preparation were tested with and without fertilizer. The treatments were: I) buming ± NPK fertilization; 2) mulching ± NPK fertilization; 3) incorporation of the fallow vegetation biomass into the soi! ± NPK fertilization. Rice was planted followed by cowpea and cassava in two consecutive cropping periods. Yield characteristics of the crops as well as the nitrogen dynamics in the soil and the nitrogen uptake by the crops were evaluated. Furtherrnore, screening experiments were set up to evaluate the yield characteristics of a total of 8 rice, 18 maize, 21 cowpea and 5 cassava cultivars under mulch conditions with and without fertilizer application...Doctoral Dissertation (Doctor of Agricultural Sciences) - George-August-University Göttingen, Göttingen

    Fire-free land preparation as an alternative to slash-and-burn agriculture in the bragantina region, eastern Amazon: crop performance and phosphorus dynamics.

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    Shifting cultivation is the most important agricultural land-use system in the Amazon region and the slash-and-bum practice is the traditional method for land preparation used by small farmers. During slash and buming, however, high amounts of nutrients are lost through volatilization. This fact, exacerbate by reduced fallow time, decreases the total nutrient stock offallow systems and compromises the system's sustainability. The objectives of this study were: I) to evaluate the effects of fire-free land preparation on crop performance and phosphorus dynamics; 2) to evaluate the importance of the use of chemical fertilizer in systems without the use of fire and 3) to select rice, maize, cowpea and cassava cultivars suitable for mulch systems. The studies were conducted in the community of Cumaru in the municipality of Igarapé Açu (Parå, Brazil) on two neighboring sites with 4-year-old (FV4y) and 10-year-old fallow vegetation (FVIOy). Three treatments for land preparation were tested with and without fertilizer. The treatments were: I) buming ± NPK fertilization; 2) mulching ± NPK fertilization; 3) incorporation of the fallow vegetation biomass into the soil ± NPK fertilization. Rice was planted followed by cowpea and cassava in two consecutive cropping periods. Yield characteristics of the crops as well as the phosphorus dynamics in the soil and uptake by the crops were evaluated. Furthermore, screening experiments were set up to evaluate the yield characteristics of a total of 8 rice, 18 maize, 21 cowpea and 5 cassava cultivars under mulch conditions with and without fertilizer application...Doctoral Dissertation (Doctor of Agricultural Sciences) - George-August-University Göttingen, Göttingen

    The woody flora and soils of seven Brazilian Amazonian dry savanna areas

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    This study compares the soils, floristic composition, phytosociological structure and history of seven Brazilian savannas in the Amazon basin: those at Alter do Chao, Amapa, Roraima and SE Humaita are islands in rain forest; and those at Chapada dos Parecis, Redencao, and Carolina are on the periphery (northern border) of the central Brazilian savannas (the so-called 'cerrado'). A total of 26 transects were sampled by the PCQ method (for trees with dbh greater than or equal to 5 cm) and additional tree species were recorded by 'wide patrolling'. A total of 101 species were recorded from the transects and another 43 species were recorded by 'wide patrolling'. Byrsonima crassifolia, B. coccolobifolia, Curatella americana, Salvertia convallariodora and Plathymenia reticulata occurred in most or all sites, but no species occurred in all transects. The number of species in the isolated savannas decreased with the distance from the central Brazilian core savanna area. Both cluster analysis (based on the S0rensen Similarity Index) and ordination (DCA), showed that the disjunct and non-isolated peripheral areas were in floristically distinct groups. Five surface soil samples (0 - 10 cm) were collected from each of the 26 transects. Two soil cores (up to 4 m depth), one located in the savanna and the other from the nearest forest present, were taken from each study site for carbon isotope analysis. All the sites had acidic soils (pH 4.5 - 5.2) and a wide range of concentrations of aluminium (0.12 - 1.49 meq 100g-1); most of the other soil properties varied significantly within study sites. An ordination (PCA) distinguished the soils from Amapa, Alter do Chao, Redencao and Roraima, but did not distinguish the disjunct sites from non-isolated peripheral ones. The soil delta 13C values of all the disjunct savannas indicated a vegetation change in the past from C3 to C4 plants, showing that forest (or at least a vegetation with few C4 plants) formely covered these sites. 14C dating indicated that the disjunct savannas are of relatively recent origin, e.g. Humaita was dated at about 2,000 years BP, and hence that they are not remnants of a more widespread Pleistocene savanna in the Amazon

    Écologie de reproduction des populations de tourterelle en milieu phoenicicole

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    Ecologie de reproduction des populations de tourterelle en milieu phoenicicole. Nous avons menĂ© une Ă©tude sur l'Ă©cologie de la reproduction des populations de tourterelles dans le milieu phĂ©nicicole. Nous avons examinĂ© l'impact des diffĂ©rents composants du paysage sur la distribution et l'abondance de trois espĂšces de ColumbidĂ©s le long de gradients urbains-ruraux dans la rĂ©gion de Biskra. Nos rĂ©sultats ont montrĂ© que l'abondance de la tourterelle turque Ă©tait plus Ă©levĂ©e dans les zones fortement urbanisĂ©es et positivement corrĂ©lĂ©e avec la couverture du bĂąti, tandis que les tourterelles maillĂ©es et les tourterelles des bois Ă©taient plus abondantes lorsque les zones bĂąties Ă©taient faiblement reprĂ©sentĂ©es dans le paysage. Pour chaque espĂšce, nous avons identifiĂ© les trois meilleurs modĂšles explicatifs de leur abondance. Dans cette Ă©tude, nous avons examinĂ© les facteurs qui dĂ©terminent la survie des nids de trois espĂšces sympatriques des colombidĂ©s dans un habitat oasien. En 2019, nous avons surveillĂ© un total de 225 nids dans les six stations (Palmeraies) d’études : 68 nids de tourterelle maillĂ©e, 65 nids de tourterelle turque et 92 nids de tourterelle des bois. Nos rĂ©sultats ont montrĂ© que l'Ăąge du nid est un prĂ©dictif important du taux de survie car l'effet de l'Ăąge du nid est restĂ© significatif pour les trois espĂšces de tourterelle. Tandis que, pour les tourterelles maillĂ©es, l'Ăąge du nid, la distance par rapport au champ de cĂ©rĂ©ales et la hauteur du nid sont tous des facteurs significatifs. La survie des nids pour toutes ces trois espĂšces Ă©tait plus faible durant la pĂ©riode d'incubation par rapport Ă  la pĂ©riode de nidification. Pour dĂ©terminer les effets des caractĂ©ristiques des palmiers, du micro-habitat et de la prĂ©sence humaine sur la sĂ©lection des habitats de nidification par la tourterelle des bois. Nos rĂ©sultats ont montrĂ© que la Streptopeliaturtur prĂ©fĂšre les palmiers de plus grande hauteur, avec une moyenne de 13,10 ± 0,17 m, et un diamĂštre de tronc plus important, avec une moyenne de 2,83 ± 0,05 m. En ce qui concerne les caractĂ©ristiques du micro-habitat, les tourterelles des bois ont optĂ© pour un milieu dans lequel la couverture des palmiers se situe entre 67,02 % et 82,09 %, tandis que la hauteur de la strate herbacĂ©e atteint jusqu'Ă  70,05 cm. Cependant, l’emplacement des palmiers portants des nids doivent ĂȘtre distant des bordures qui existent au niveau de la palmeraie par une moyenne de 84.08±4.73 m. Mots clĂ©s :Ă©cologie de reproduction, milieu phoenicicole,,composants du paysag
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