Em Portugal, desde os anos 30 do século XX, os resultados da experimentação relativa à adubação potássica têm amiúde causado perplexidade entre os investigadores. Nos casos em que se esperariam respostas evidentes ao K, devido às suas baixas concentrações no solo, elas ou não se verificaram, ou tardaram a surgir, sobretudo no Sul do país. Neste trabalho de revisão, faz-se uma retrospectiva da experimentação realizada, na qual parece evidente a ineficácia da adubação potássica. Inventariaram-se as unidades-solo onde foram detectados indícios da fixação do K através de ensaios experimentais, bem como as unidades-solo submetidas a ensaios laboratoriais em que foi evidente a sua elevada capacidade de fixação do K. Relativamente à fixação, além da identificação dos solos fixadores de K, discutiram-se ainda os factores propícios à fixação deste nutriente, dos quais se salienta a composição mineralógica dos solos nas fracções argila, limo e areia fina. Por fim, com base nos estudos já realizados apontam-se estratégias a seguir na adubação potássica. Palavras-chave: filossilicatos, mineralogia das fracções do solo, potássio extraível, potássio de troca, capacidade de fixação do potássio A B S T R A C T In Portugal, since the 1930s, the results of experimentation on potassium fertilization have frequently caused perplexity among researchers. In such cases, where clear responses to K were expected due to low K concentrations in the soils, they did not occur or were very slow in manifesting themselves, particularly in the south of the country. In this review paper a retrospective of the existing experimentation was carried out where the inefficacy of K fertilization was evident. In addition, an inventory of soil types was made where evidence of K fixation had been most often detected, either through experimental trials or through laboratory tests. The laboratory data refer to the determination of soil K fixation capacity. With regard to K fixation, in addition to the identification of the K-fixing soils, the propitious factors for fixation of this nutrient are discussed, highlighting the mineralogical composition of soils in the clay, silt and fine sand fractions. Finally, based on the studies already carried out, some strategies to be followed in potassium fertilization were proposed.
R E S U M OEm Portugal, a deficiência de boro tem sido observada em quase todo o território, particularmente no interior, causando prejuízos assinaláveis nas culturas. Foi reconhecida pela primeira vez na década de 50 do séc. XX, nas vinhas do Douro (designada de 'maromba'). Desde os anos 80 vêm sendo realizados estudos sistemáticos no interior norte/centro do país para identificação e correcção desta carência em fruteiras e espécies florestais/agroflorestais. Neste trabalho de revisão faz-se uma inventariação das formações geológicas/litológicas onde mais amiúde se têm detectado as carências de boro, bem como as unidades pedológicas onde elas já foram identificadas. Enunciam-se os condicionalismos de ordem ambiental que mais potenciam o seu aparecimento. Com base em estudos efectuados nestas regiões, indica-se para algumas arbóreas a sintomatologia da deficiência e as concentrações de boro, nos solos e nas folhas, para as quais se observaram esses sintomas. Também se apresentam resultados experimentais da aplicação de boro em termos de crescimentos e de produtividade das culturas. Por último, procuraram-se explicações para perplexidades suscitadas pelas reacções das plantas aos estados de carência, ou aquando da aplicação de boro, desde o aparecimento da 'maromba' no séc. XIX até aos dias de hoje. Finaliza-se com recomendações de estratégias para corrigir a carência deste micronutriente.Palavras-chave: boro extraível, concentração foliar de boro, nível crítico no solo, sintomas de carência de boro. A B S T R A C TIn Portugal, boron deficiency has been observed almost everywhere, in particular in the interior of the country, causing severe crop damage. In the 1950's, the growth anomalies in the Douro vineyards were recognised as a boron deficiency (called ´maromba'). From the 1980's onwards systematic studies have been carried out in the northern and central interior of Portugal with the purpose of identifying and correcting this deficiency in fruit trees and forest/agroforest species. In this review paper an inventory of geological/lithological formations and soil groups is carried out where the boron shortage was most often detected. The environmental conditions that enhanced the occurrence of boron deficiency were reviewed. Based on studies carried out in these regions, the deficiency symptoms of selected trees were described, and also the boron concentrations in soils and leaves in which the symptoms had been observed were recorded. Experimental results of boron fertilisation in terms of growth or yield increase of crops were presented. Finally, an attempt is made to explain perplexities arisen from unexpected plant reactions, either due to the deficiency or to boron application, since the emergence of ´maromba' in the 19 th century until the present. In addition, some strategies for correction of scarcity of this micronutrient are suggested.
Reclamation of abandoned mining areas can be a potentially viable solution to tackle three major problems: waste mismanagement, environmental contamination, and growing food demand. This study aims to evaluate the rehabilitation of mining areas into agricultural production areas using integrated biotechnology and combining Technosols with a multipurpose (forage, food, ornamental and medicinal) drought-resistant legume, the Lablab purpureus (L.) Sweet. Two Technosols were prepared by combining gossan waste (GW) from an abandoned mining area with a mix of low-cost organic and inorganic materials. Before and after plant growth, several parameters were analysed, such as soil physicochemical characteristics, nutritional status, bioavailable concentrations of potentially hazardous elements (PHE), soil enzymatic activities, and development and accumulation of PHE in Lablab, among others. Both Technosols improved physicochemical conditions, nutritional status and microbiological activity, and reduced the bioavailability of most PHE (except As) of GW. Lablab thrived in both Technosols and showed PHE accumulation mainly in the roots, with PHE concentrations in the shoots that are safe for cattle and sheep consumption. Thus, this is a potential plant that, in conjunction with Technosols, constitutes a potential integrated biotechnology approach for the conversion of marginal lands, such as abandoned mining areas, into food-production areas.
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