El reemplazo por las migraciones: natalidad y fecundidad de los extranjeros en España

Resulta muy difícil estimar el aporte al crecimiento natural de las personas venidas de fueras y nuevos residentes, de acuerdo con la propuesta de Naciones Unidas. Históricamente, No ha habido acuerdo acerca de la fecundidad de los migrantes. Andorka consideró que la migración producía un efecto depresor en la fecundidad. Estudios sobre la fecundidad de los migrantes internos en la sociedad catalana han mostrado el contraste entre un creciente indicador sintético de fecundidad (ISF) y un efecto reducido en la fecundidad longitudinal. Un intento de explicación basado en el tiempo, nacimientos pospuestos y adaptación, se presenta. Se trata de una combinación de la propuesta de Andorka del efecto depresor de la fecundidad, con un segundo tiempo de recuperación en destino. Esta Hipótesis en dos Tiempos (H2T) tiene carácter tentativo. Considera sólo un efecto de calendario. Se utilizan datos oficiales de la Encuesta de Fecundidad de 1999, de un Censo anterior y de natalidad. La H2T se considera una explicación posible de las altas tasas de natalidad de Europa y América.Estimaciones sobre la evolución de los nacimientos futuros de mujeres extranjeras, en al menos dos escenarios, son contemplados al final del artículo.

Documento sobre salud sexual y reproductiva en la adolescencia

El grup ha analitzat els problemes existents quant a la salut sexual i reproductiva en l'adolescència i la validesa del consentimentinformat dels menors. Aquesta qüestió requereix un debat social informat, encaminat a assolir el consens suficient per portar a terme les actuacions necessàries -d'acord amb la normativa ja existent per a la majoria dels supòsits- que protegeixin l'interès del menor, considerat en la nostra legislació com sempre preferent.

Alteração de atributos físicos em latossolo com aplicação superficial de escória de aciaria, lama cal, lodos de esgoto e calcário

Os resíduos industriais e urbanos podem atuar como condicionadores do solo, pois possuem a capacidade de alterar suas propriedades físicas. Contudo, não há referência para os atributos físicos do solo quando esses resíduos são aplicados sobre a superfície do solo no sistema plantio direto. O objetivo deste trabalho foi avaliar o efeito da aplicação superficial de escória de aciaria, lama cal, lodos de esgoto e calcário nos atributos físicos de um Latossolo Vermelho distrófico sob sistema plantio direto. Os tratamentos foram constituídos por quatro resíduos: lodos de esgoto centrifugado - LC e de biodigestor - LB, escória de aciaria - E, e lama cal - Lcal, interagindo com quatro doses (0, 2, 4 e 8 t ha-1, aplicadas na forma seca) mais uma testemunha (controle), constituída da aplicação de 2 t ha-1 de calcário. O delineamento experimental foi em blocos casualizados no esquema fatorial 4 x 4 + 1, com quatro repetições. A presença de Ca na composição de lama cal, lodo de esgoto centrifugado, escória de aciaria e calcário permite o aumento da agregação das partículas, diâmetro médio ponderado, índice de estabilidade de agregados, porosidade e retenção de água, sendo essas alterações distintas para cada fonte, dose e profundidade de reação no solo. A aplicação superficial da lama cal na dose de 8 t ha-1, após 27 meses de reação, proporcionou a maior agregação das partículas no solo, desde a superfície até 40 cm de profundidade.

Influência de silicato e calcário na decomposição de resíduos culturais e disponibilidade de nutrientes ao feijoeiro

A disponibilidade do Si pelo silicato de Ca poderá aumentar a formação de polifenóis, os quais tornariam possível a maior persistência dos resíduos culturais em superfície. Com esse intuito, procurou-se avaliar a ação do silicato e do calcário na decomposição de diferentes resíduos culturais e a liberação de nutrientes para o desenvolvimento do feijoeiro. O delineamento experimental empregado foi o de blocos casualizados em esquema fatorial 3 x 5, com quatro repetições. Os tratamentos foram constituídos de três espécies de plantas de cobertura: milheto (Pennisetum americanum), braquiária (Brachiaria brizantha) e guandu-anão (Cajanus cajan L.) e cinco níveis proporcionais de silicato de cálcio: 0, 25, 50, 75 e 100 %, aplicado nas doses crescentes de 0, 2,31, 4,63, 6,96 e 9,27 g/vaso, respectivamente, balanceadas com carbonato de cálcio e carbonato de magnésio, de forma que as quantidades de Ca e Mg em cada tratamento fossem iguais, calculados para atingir uma saturação por bases no solo de 70 %. A aplicação de silicato de Ca não interferiu na decomposição do resíduo cultural de braquiária, guandu e milheto. O teor de Mg disponível no solo foi reduzido pela aplicação de silicato de Ca, o que induz menor absorção pelas plantas de cobertura e eventual disponibilização após sua decomposição. O crescimento do feijoeiro foi favorecido pela aplicação de silicato de Ca, sendo as doses de 2,31 e 6,95 g/vaso de silicato com o resíduo cultural de braquiária os tratamentos que apresentaram maior eficiência.

The use of total luminescence spectroscopy in the investigation of the effects of different rice management practices on humic substances of a planosol

In the Earth's carbon cycle, C stocks in the soil are higher than in vegetation and atmosphere. Maintaining and conserving organic C concentrations in the soil by specific management practices can improve soil fertility and productivity. The aim of this study was to evaluate the impact of agricultural management techniques and influence of water regime (flooded or drained) on the structure of humic substances by excitation/emission matrix fluorescence. Six samples of a Planosol (Planossolo by the Brazilian System of Soil Classification) were collected from a rice field. Humic substances (HS) were extracted from flooded and drained soil under different agricultural management techniques: conventional tillage, reduced tillage and grassland. Two peaks at a long emission wavelength were observed in the EEM spectra of HA whereas those of the corresponding FA contained a unique fluorophore at an intermediate excitation/emission wavelength pair (EEWP) value. The fluorescence intensity measured by total luminescence (FI TL) of HA was lower than that of the corresponding FA. A comparison of all samples (i.e., the HA values compared to each other) revealed only slight differences in the EEWP position, but the FI TL values were significantly different. In this soil, anoxic conditions and reduced tillage (little plowing) seem to favor a higher degree of humification of the soil organic matter compared with aerated conditions and conventional tillage.

Phosphorous forms in cultivated indian black earth (anthrosols) of varying texture in the brazilian Amazon

Despite the agricultural importance of Indian Black Earth (IBE) in the Amazon region, there are few studies that report on the relation between soil texture and chemical fertility of IBE. These soils of pre-Colombian origin, with high contents of P, Ca and other nutrients are found across the Amazon valley. IBE profiles were studied to evaluate the total contents of P, its primary chemical forms and the P transformation phases in areas with IBE soils of variable texture and in adjacent reference soils. The soil texture strongly influenced soil fertility, changing in terms of transformation of the primary P forms and, consequently, predominant P forms in IBE. Soils with texture varying between clay and heavy clay had higher total P contents and primary Ca-P forms. Highest P-Al and lowest total P amounts were observed at the site Rio Preto da Eva, where texture varies from sandy loam to sandy clay loam. In the IBE with clay texture the amounts of soluble P, extracted with NH4Cl were highest, although different from Mehlich 1-extractable amounts.

Environmental and agricultural benefits of a management system designed for sandy loam soils of the humid tropics

A sustainable management of soils with low natural fertility on family farms in the humid tropics is a great challenge and overcoming it would be an enormous benefit for the environment and the farmers. The objective of this study was to assess the environmental and agronomic benefits of alley cropping, based on the evaluation of C sequestration, soil quality indicators, and corn yields. Combinations of four legumes were used in alley cropping systems in the following treatments: Clitoria fairchildiana + Cajanus cajan; Acacia mangium + Cajanus cajan; Leucaena leucocephala + Cajanus cajan; Clitoria fairchildiana + Leucaena leucocephala; Leucaena leucocephala + Acacia mangium and a control. Corn was used as a cash crop. The C content was determined in the different compartments of soil organic matter, CEC, available P, base saturation, percentage of water saturation, the period of the root hospitality factor below the critical level and corn yield. It was concluded that alley cropping could substitute the slash and burn system in the humid tropics. The main environmental benefit of alley cropping is the maintenance of a dynamic equilibrium between C input and output that could sustain up to 10 Mg ha-1 of C in the litter layer, decreasing atmospheric CO2 levels. Alley cropping is also beneficial from the agricultural point of view, because it increases base saturation and decreases physical resistance to root penetration in the soil layer 0 - 10 cm, which ensures the increase and sustainability of corn yield.

Radionuclides and heavy metal contents in phosphogypsum samples in comparison to cerrado soils

Phosphogysum (PG) or agricultural gypsum, a solid waste from the phosphate fertilizer industry, is used as soil amendment, especially on soils in the Cerrado region, in Brazil. This material may however contain natural radionuclides and metals which can be transferred to soils, plants and water sources. This paper presents and discusses the results of physical and chemical analyses that characterized samples of PG and compares them to the results found in two typical soils of the Cerrado, a clayey and sandy one. These analyses included: solid waste classification, evaluation of organic matter content and of P, K, Ca, Mg, and Al concentrations and of the mineralogical composition. Natural radionuclides and metal concentrations in PG and soil samples were also measured. Phosphogypsum was classified as Class II A - Not Dangerous, Not Inert, Not Corrosive and Not Reactive. The organic matter content in the soil samples was low and potential acidity high. In the mean, the specific 226Ra activity in the phosphogypsum samples (252 Bq kg-1) was below the maximum level recommended by USEPA, which is 370 Bq kg-1 for agricultural use. In addition, this study verified that natural radionuclides and metals concentrations in PG were lower than in the clayey Oxisol of Sete Lagoas, Minas Gerais, Brazil. These results indicated that the application of phosphogypsum as soil amendment in agriculture would not cause a significant impact on the environment.

Spatial variability of soil chemical properties after coffee tree removal

Assessing the spatial variability of soil chemical properties has become an important aspect of soil management strategies with a view to higher crop yields with minimal environmental degradation. This study was carried out at the Centro Experimental of the Instituto Agronomico, in Campinas, São Paulo, Brazil. The aim was to characterize the spatial variability of chemical properties of a Rhodic Hapludox on a recently bulldozer-cleaned area after over 30 years of coffee cultivation. Soil samples were collected in a 20 x 20 m grid with 36 sampling points across a 1 ha area in the layers 0.0-0.2 and 0.2-0.4 m to measure the following chemical properties: pH, organic matter, K+, P, Ca2+, Mg2+, potential acidity, NH4-N, and NO3-N. Descriptive statistics were applied to assess the central tendency and dispersion moments. Geostatistical methods were applied to evaluate and to model the spatial variability of variables by calculating semivariograms and kriging interpolation. Spatial dependence patterns defined by spherical model adjusted semivariograms were made for all cited soil properties. Moderate to strong degrees of spatial dependence were found between 31 and 60 m. It was still possible to map soil spatial variability properties in the layers 0-20 cm and 20-40 cm after plant removal with bulldozers.

The effect of plantation silviculture on soil organic matter and particle-size fractions in Amazonia

Eucalyptus grandis and other clonal plantations cover about 3.5 million ha in Brazil. The impacts of intensively-managed short-rotation forestry on soil aggregate structure and Carbon (C) dynamics are largely undocumented in tropical ecosystems. Long-term sustainability of these systems is probably in part linked to maintenance of soil organic matter and good soil structure and aggregation, especially in areas with low-fertility soils. This study investigated soil aggregate dynamics on a clay soil and a sandy soil, each with a Eucalyptus plantation and an adjacent primary forest. Silvicultural management did not reduce total C stocks, and did not change soil bulk density. Aggregates of the managed soils did not decrease in mass as hypothesized, which indicates that soil cultivation in 6 year cycles did not cause large decreases in soil aggregation in either soil texture. Silt, clay, and C of the sandy plantation soil shifted to greater aggregate protection, which may represent a decrease in C availability. The organic matter in the clay plantation soil increased in the fractions considered less protected while this shift from C to structural forms considered more protected was not observed.

Macrofauna edáfica em estádios sucessionais de Floresta Estacional Semidecidual e pastagem mista em Pinheiral (RJ): Rio de Janeiro State

Entre os diferentes tipos de organismos da macrofauna do solo, distribuídos em diversos tipos de habitats, com variados hábitos alimentares e ciclos de vida, alguns são capazes de responder rapidamente às alterações ambientais e, por isso, considerados bons indicadores do funcionamento dos ecossistemas. O presente trabalho teve como objetivo avaliar o efeito dos seguintes estádios sucessionais de Floresta Estacional Semidecidual Submontana do domínio ecológico da Mata Atlântica: floresta secundária estádio inicial (FSEI), floresta secundária estádio médio (FSEM), floresta secundária estádio avançado (FSEA) e uma área de pasto misto manejado (PMM) sobre a densidade, diversidade e composição da comunidade da macrofauna edáfica em duas épocas do ano, no município de Pinheiral (RJ). Para amostragem da macrofauna, foram retiradas oito amostras da serapilheira e da camada superficial (0-10 cm) do solo pelo método recomendado pelo programa Tropical Soil Biology and Fertility (TSBF), com adaptações. Predominaram Isoptera, Formicidae e Oligochaeta em FSEI, FSEM e FSEA e Formicidae e Oligochaeta em PMM. Não houve diferença significativa na densidade da macrofauna edáfica entre as áreas. Os maiores valores dos estimadores de diversidade utilizados (equabilidade de Pielou, riqueza total e média) foram encontrados em FSEA. Os valores de riqueza total mostraram aumento gradual de acordo com o estádio de sucessão, desde PMM até FSEI. Constatou-se maior número de indivíduos no solo do que na serapilheira em todas as áreas de floresta, nas duas épocas. Pela análise de componentes principais (ACP) realizada para os períodos seco e chuvoso, foi possível identificar maiores diferenças na composição das comunidades entre os estádios sucessionais para o período chuvoso. Nesta época, os estádios FSEM e FSEA estiveram associados a uma maior diversidade de invertebrados saprófagos e predadores do que PMM e FSEI, demonstrando influência do processo sucessional sobre a comunidade da macrofauna do solo.

Alterations of soil chemical properties by eucalyptus cultivation in five regions in the Rio Doce Valley

Little is currently known about modifications in edaphic characteristics caused by short-rotation eucalyptus and the impacts of these alterations on the sustainability of eucalyptus wood production. This study was carried out to identify theses changes at five sites of eucalyptus plantation in the region of the Rio Doce Valley, state of Minas Gerais, Brazil. Areas with more than three previous eucalyptus cycles, adjacent to pasture land or native forest, were chosen. Soil samples were collected and soil fertility analyzed by routine methods and other fractionation methods in order to measure alterations in the K, Ca and Mg contents as a consequence of eucalyptus cultivation. In the eucalyptus areas, reductions in the exchangeable Ca2+, Mg2+ and K+ contents and pH were observed and increased Al3+ and H + Al contents. Of all nutrients, only P contents (Mehlich-1 P) increased in the eucalyptus areas. The reduction in exchangeable forms and in medium-term soil nutrient pools indicates the need for higher nutrient rates than the currently applied in order to prevent nutritional limitations and soil nutrient exhaustion. After several eucalyptus rotations there was a recovery in the SOM content in comparison to degraded pasture soils, although not to the level of the native forest soil. The positive correlation between effective CEC and medium-term non-exchangeable Ca, Mg and K with SOM emphasizes the need for adequate fertilizer and plant residue management to sustain or even increase forest productivity in future cycles.

Redox index of soil carbon stability

As an alternative to the relatively complex and expensive spectroscopic methods, the redox properties of humic acids, determined by potentiometric titrations, have been used to evaluate the stability of soil organic C. The objective of the present study was to establish a Redox Index of C Stability (RICS) and to correlate it with some properties of the humic acids extracted from different modal soils in Brazil (distinct weathering stages or management) to facilitate system comparison. The RICS was efficient for soil comparison and variations were comparable to those of the chemical and spectroscopic methods used for humic acid characterization. The values of soil pH, point of zero salt effect, sum of bases, exchangeable Ca content, weathering index, as well as the humic acid O/C ratio, quinone and semiquinone free radical contents, aromatic C and fluorescence intensity were closely related with the RICS. The RICS was higher in less weathered soils, with more active clays and higher fertility. The RICS values of soils under long-term sugarcane management were ranked in decreasing order: unburned, burned with vinasse, burned without vinasse.

Nitrogen fertilizer use efficiency, recovery and leaching of an alexandergrass pasture

Nitrogen usually determines the productive potential of forage crops, although it is highly unstable in the environment. Studies on recovery rates and use efficiency are important for more reliable fertilizer recommendations to reduce costs and avoid environmental pollution. The purpose of this study was to evaluate N use efficiency and recovery rate of Alexandergrass pasture (Brachiaria - Syn. Urochloa plantaginea) as well as N-NO3- and N-NH4+ soil concentrations using different levels of N fertilization under two grazing intensities. The experiment was arranged in a randomized block design in a factorial scheme with three replications. Treatments consisted of three N rates (0, 200 and 400 kg ha-1 N) and two grazing intensities termed low mass (LM; forage mass of 2,000 kg ha-1 of DM) and high mass (HM; forage mass of 3,600 kg ha-1 of DM) under continuous stocking and variable stocking rates. Results of N fertilization with 200 kg ha-1 were better than with 400 kg ha-1 N. There was a significant effect of N rates on soil N-NO3-concentration with higher levels in the first layer of the soil profile in the treatment with 400 kg ha-1 N. Grazing intensity also affected soil N-NO3- concentration, by increasing the levels under the higher stocking rate (lower forage mass).

Physical and chemical attributes of archaeological soils developed from shell middens in the Região dos Lagos, Rio de Janeiro, Brazil

In prehistoric times, innumerous shell middens, called "sambaquis", consisting mainly of remains of marine organisms, were built along the Brazilian coast. Although the scientific community took interest in these anthropic formations, especially since the nineteenth century, their pedological context is still poorly understood. The purpose of this study was to characterize and identify the physical and chemical changes induced by soil-forming processes, as well as to compare the morphology of shell midden soils with other, already described, anthropogenic soils of Brazil. Four soil profiles developed from shell middens in the Região dos Lagos - RJ were morphologically described and the physical and chemical properties determined. The chemical analysis showed that Ca, Mn, Mg, and particularly P and Zn are indicators of anthropic horizons of midden soils, as in the Amazon Dark Earths (Terras Pretas de Índio). After the deposition of P-rich material, P reaction and leaching can mask or disturb the evidence of in situ man-made strata, but mineralogical and chemical studies of phosphate forms can elucidate the apparent complexity. Lower phosphate-rich strata without direct anthropic inputs indicate P leaching and precipitation in secondary forms. The total and bioavailable contents of Ca, Mg, Zn, Mn, Cu, P, and organic C of midden soils were much higher than of regional soils without influence of ancient human settlements, demonstrating that the high fertility persisted for long periods, at some sites for more than 4000 years. The physical analysis showed that wind-blown sand contributed significantly to increase the sand fraction in the analyzed soils (texture classes sand, sandy loam and sandy clay loam) and that the aeolian sand accumulation occurred simultaneously with the midden formation.