ABSTRACT Soil nutrient availability and interpretations of nutrient contents are based on the results obtained from specific extraction methods used in routine testing laboratories. The development of new extraction methods and new extractants with better accuracy is particularly important to determine the correct fertilizer rates to be applied. For this purpose, this study aims to synthesize, characterize and evaluate the predictive capacity of cellulose acetate film containing calcinated layered double hydroxide (CAF-LDH-c), as a new extractant and a new method of P extraction in soils. Different analyses techniques were used to characterize the CAF-LDH-c sample, including X-ray diffraction, attenuated total reflectance Fourier transform infrared spectroscopy, and scanning electronic microscopy. Soils were collected from twelve areas with different management and initial availability of P. The soils were subjected to six rates of P and were cultivated with plants. The predictive capacity of CAF-LDH-c, as a new extractant of P in different soils, was evaluated and compared to Mehlich-1 (M-1), Mehlich-3 (M-3), and Mixed Exchange Resin (MER) extractants. Chemical analyses performed on CAF-LDH-c showed that LDH in powder form was incorporated into the cellulose acetate film. There was a linear relation between P uptake by plants and extractable soil P in the soil by CAF-LDH-c, M-1, M-3, and MER extractants. The significant correlations between extracted P in the soil and P uptake by plants for CAF-LDH-c showed the efficacy of the new extractor and the newly proposed method for different types of soils. The results from the present study confirm the possibility of using CAF-LDH-c extractant as a new methodology to evaluate the availability of P in the soil for plant cultivation.

ABSTRACT Studies aimed at mitigating environmental impacts have received attention in recent years. The use of biochar obtained from the pyrolysis is an alternative for the recovery of organic materials that usually are directly discarded in the environment. Biochar has the potential to recover nutrients from wastewater, and in the latter case, the reuse or recycling of biochar as a controlled-release fertilizer could be an option. However, the adsorption characteristics of the ions into different biochars have not been known. The aim of this study was to evaluate the ions adsorption in biochar derived from discarded potatoes, as well as to make physical and chemical characterization of the produced materials. The biochar derived from discarded potatoes was produced by pyrolysis at 450 °C under an N2 atmosphere. In order to define its ionic profile, the adsorption of HnPO4(3–n)–, Ca2+, Mg2+, and Al3+ was tested in pure biochar, as well as adsorption of HnPO4(3–n)–in biochar after it was doped with Al3+. The desorption of these ions was tested by washing with deionized water, and the KCl (1.0 mol·L–1) and Mehlich-1 extractors. In absolute values, the adsorption order of the ions was Al3+ (in acid pH value) = Ca2+ > Al3+ > HnPO4(3–n)–(biochar doped with Al3+) > Mg2+ > HnPO4(3–n)– (biochar without doping). The adsorption of HnPO4(3–n)– was positively influenced by the doping of biochar with Al3+. The biochar has preferential characteristics for cations adsorption, and the doping process can aid in adsorption of anions.

RESUMO As florestas da costa atlântica brasileira são pouco estudadas quanto às quantidades e à dinâmica de nutrientes. Os objetivos deste trabalho foram estimar os teores e conteúdos de carbono orgânico, Ca, Mg, K, Na, P e N no solo e na serapilheira dos ambientes de encosta e fundos de vale do Parque Nacional da Tijuca, Rio de Janeiro, RJ. Os processos de ciclagem de nutrientes nas encostas (ambientes mais oligotróficos) e dos fundos de vale (ambientes menos oligotróficos) também foram comparados. Foram estabelecidas 15 parcelas de amostragem, cada uma com 100 m², 10 em encostas (vertentes do Conde, das Cobras e da Tijuca), e cinco em fundos de vale (fundos de vale 1 e 2). O compartimento solo (nutrientes trocáveis/disponíveis e totais até a profundidade de 0,30 m) e o compartimento serapilheira (separada em horizontes O1 e O2) foram avaliados. O teor de carbono orgânico total no solo das encostas foi maior que o nos fundos de vale. Nas encostas, a serapilheira também apresentou maior biomassa, com separação nítida dos horizontes O1 e O2, o que não ocorreu nos fundos de vale. Aparentemente, a disponibilidade de nutrientes nos dois ambientes foi o que gerou tais diferenças, com a tendência de aumento nos teores no solo nos fundos de vale. Diferenças entre fundos de vale e encostas foram mais evidentes para o K. Os resultados deste estudo caracterizaram a área estudada como oligotrófica, embora com considerável potencial de reposição dos elementos perdidos por lixiviação.

ABSTRACT The forests of Brazilian Atlantic coast are poorly studied in terms of nutrient pools and dynamics. The purpose of this study was to determine the amounts and contents of organic carbon and Ca, Mg, K, Na, P, and N in the soil and the litter layer on slopes and in valley bottoms in Tijuca National Park, Rio de Janeiro, Brazil. The nutrient cycling process on slopes (more oligotrophic environments) and valley bottoms (less oligotrophic environments) was also compared. Samples were collected from 15 plots (100 m² each), 10 on slopes (Conde, Cobras and Tijuca) and five in valley bottoms (Valley bottom 1 and 2). The soil compartment (exchangeable/available and total nutrient contents to a depth of 0.30 m) and litter compartment (O1 and O2 horizons) were evaluated. The total organic carbon content in the soil and litter biomass on slopes were higher than in the valley bottoms. On slopes, there was a clear separation of horizons O1 and O2 in the litter layer, unlike the valley bottoms, probably due to a higher nutrient content in these positions. The difference in nutrient availability was most evident for K. These results characterize the study area as oligotrophic, although it has considerable potential for replacement of nutrients lost by leaching.

ABSTRACT: Vale do Rio Doce shoot dieback (VRDSD) is an anomaly whose cause seems to be associated with hypoxic conditions and their consequences (excess Mn and Fe) triggered by elevation of the water table in areas with poor drainage. Different plants have distinct survival strategies under this form of stress. The objective of this study was to understand the physiological responses involved in the differential tolerance of eucalyptus clones to VRDSD and their relationship to hypoxia and excess Mn. A hydroponic experiment was carried out using a 2 × 2 × 2 factorial arrangement, two eucalyptus clones with different levels of tolerance to VRDSD (sensitive Urograndis hybrid - 1213; and the tolerant Rio Claro hybrid - Eucalyptus grandis x unknown - 2719), two concentrations of O2 (8 and 4 mg L-1), and two Mn concentrations (1.39 and 300 mg L-1) in a randomized block design (RBD) with three replicates. Forty-day-old clones were maintained in Clark nutrient solution for 30 days. After this period, the treatments were applied for 11 days. Plant gaseous exchange shoot and root production, and the quantity of enzymes related to oxidative stress in leaves and roots were evaluated. In the tolerant clone, reactive oxygen species (ROS) were produced under hypoxic conditions, accompanied by reduction in production of dry matter, malondialdehyde (MDA), and in activity of the enzyme alcohol dehydrogenase (ADH). However, this clone had greater production of superoxide dismutase (SOD) under these conditions, an enzyme responsible for detoxification of ROS, which acts as part of the Low Oxygen Quiescence Syndrome (LOQS). In contrast, sensitive clones did not exhibit expressive reductions in growth or changes in the leaf/root ratio. These clones formed large quantities of adventitious roots and had high levels of MDA and ADH and low levels of SOD. Therefore, sensitive clones appear not to be prepared for detoxification of ROS and other toxic metabolites, but rather adopt morphological escape mechanisms, the Low Oxygen Escape Syndrome (LOES), in response to hypoxia. Thus, the period of soil waterlogging may cause the death of large numbers of roots in sensitive clones, limiting their ability to absorb water and nutrients and culminating in the death of these plants. Excess Mn seems to aggravate the damage caused by hypoxia, but it is not the causal agent of VRDSD.

RESUMO A cenoura está entre as principais olerícolas consumidas no Brasil, onde as cultivares utilizadas atualmente apresentam elevado potencial produtivo e demanda nutricional, o que exige constantes ajustes dos programas de fertilização da cultura. Objetivou-se determinar valores de referência e índices diagnósticos pelo método DRIS para três fases fenológicas da cultura da cenoura (cerca de 40 e 70 dias após a semeadura e na colheita), bem como verificar a possibilidade de diagnose precoce de limitação nutricional. Para determinação das normas DRIS, obteve-se um banco de dados a partir da amostragem de folhas, produtividade de raízes e teores foliares de N, P, K, Ca, Mg, S, B, Cu, Mn e Zn, em lavouras comerciais de cenoura. A ordem de limitação nutricional foi gerada em função do potencial de resposta à adubação e da faixa ótima dos teores foliares. Os valores referência de K, Ca, Mg, S e Mn mostraram-se semelhantes em todas épocas de amostragem. Os de N, P, B, Cu e Zn variaram, reforçando a ideia de padronização da época de amostragem para esses nutrientes. O Mn, K e Mg foram os nutrientes mais limitantes por deficiência, enquanto Zn e B foram os menos limitantes. Para K, Ca, Mg, S e Mn, há concordância entre a diagnose realizada nas fases precoces e a efetuada na colheita, o que indica possibilidade de diagnose precoce da limitação desses nutrientes.

ABSTRACT Carrot is one of the most consumed vegetables in Brazil, where the cultivars currently grown present a high yield potential and nutritional demand, which require constant adjustments in fertilization programs for the crop. This study aimed at determining reference values and diagnostic indices by using the DRIS method in three phenological stages of the carrot crop (around 40 and 70 days after sowing and at harvest), as well as evaluating the possibility of early diagnosis for nutritional limitations. For determining the DRIS norms, a database was obtained from leaf samplings, root yields and leaf contents of N, P, K, Ca, Mg, S, B, Cu, Mn and Zn, in carrot commercial fields. The nutritional limitation order was generated as a function of the fertilization response and optimum range of leaf contents. The reference values for K, Ca, Mg, S and Mn were similar in all sampling times. N, P, B, Cu and Zn varied with the stages sampled, indicating the need to standardize the sampling times for these nutrients. Mn, K and Mg were the most limiting nutrients for the crop growth, while Zn and B were the least limiting. There was a correlation between the diagnoses performed at early stages and those performed at harvest for K, Ca, Mg, S and Mn, indicating the possibility of early diagnosis for the deficiency of these nutrients.

O nitrogênio e um dos nutrientes mais demandados pelas espécies vegetais, sua presença no solo, sob formas orgânicas ou minerais disponíveis para as plantas, está vinculada à qualidade e quantidade dos resíduos vegetais aportados ao solo. O estudo teve o objetivo de avaliar a influência do cultivo do eucalipto e da acácia na composição das formas orgânicas e inorgânicas de N e, na abundância natural de 15N em um Argissolo Amarelo. Para isso, foram coletadas amostras de solo e serapilheira em monocultivos do Eucalyptus urograndis (clone do Eucalyptus urophylla S. T. Blake x Eucalyptus grandis W. Hill ex Spreng) de ciclo curto (sete anos), sistemas de cultivo de rotação com acácia (Acacia mangium Willd.) após monocultivo de eucalipto, monocultivo de eucalipto de ciclo longo (24 anos) e mata nativa (Mata Atlântica) como condição original de solo do litoral Norte do Espírito do Santo. Foram avaliados os teores de C orgânico total, N total, N-NH4 +, N-NO3 -, relação C/N, fracionamento do N orgânico e abundância natural de 15N no solo e serapilheira. Das formas de N-orgânico hidrolisado, o N-amino foi a fração que apresentou maior contribuição (39%), seguida pela fração de N-não identificado (27%), da fração N-amida (18%) e N-hexosamina (15%). O povoamento de acácia promoveu menor abundância natural de 15N e maiores teores de N total e C orgânico no solo e aumentou as formas orgânicas de N-hidrolisado, quando comparado àqueles de eucalipto de ciclo curto. Isso indica o aumento de formas lábeis de N orgânico no solo para as plantas e redução da humificação da matéria orgânica do solo (MOS) de acácia. Nesse sentido, a rotação de cultivos florestais com acácia após eucalipto de ciclo curto contribuiu para o aumento de formas orgânicas no solo, importantes para a nutrição de plantas, por serem potenciais fontes de nutrientes às plantas em curto período de tempo.

The nutrients nitrogen and one of the most demanded by plant species, and its presence in soil under organic or mineral forms available to plants is linked to quality and quatity of plant residues added to the soil. The study aimed to evaluate the influence of cultivation of eucalyptus and acacia in the composition of organic and inorganic N forms and the natural abundance of 15N in an Ultisol. For this, we collected soil and litter samples in continuous short-rotation eucalypt (Eucalyptus urophylla x Eucalyptus grandis hybrid) (seven years) compared to a rotation system including acacia (Acacia mangium Willd.) after short-rotation eucalypt; and long-rotation eucalypt (24 years). A native vegetation (Atlantic Forest) was used as a reference for the original site condition representative for the northern coast of Espírito Santo state. To do so, we evaluated the content of total organic C, total N, N-NH4 +, N-NO3 -, C/N ratio, fractionation of organic N and 15N natural abundance in soil and litter. Among the forms of organic-N hydrolyzed, the N-amino was the fraction with the highest contribution of organic N (39%), followed by the fraction of N-unidentified (27%), the fraction of N-amide (18%) and N-hexosamine (15%). The acacia plantation presented smaller natural abundance of 15N and higher levels of total N and soil organic C, and increased organic forms of N-hydrolyzed, when compared to the eucalyptus short-rotation soil. This indicates the increase of labile N-organic forms in the soil for the plants and reduction of humification of soil organic matter (SOM) of acacia. Thus, the crops rotation with acacia after eucalyptus contributed to the increase of organic forms in the soil, important for the nutrition of plants, because they are potential sources of nutrients to the plants in a short-time period.

ABSTRACT: Visual symptoms of Zn deficiency, induced by excessive P applications, have been observed in commercial orchid nurseries. The supply of other metallic micronutrients, such as Fe and Mn, may also be inadequate in the plant due to high application rates of P. The aim of this study was to investigate this interaction in the nutrition of Phalaenopsis plants. Experimental treatments consisted of three P rates (0.0, 0.5, and 1.0 g L-1) and three Zn rates (0.00, 0.35, and 0.70 g L-1), as well as fertilization with other basic nutrients, and a control treatment with the fertilizer B&G Orchidée(r), at 1.0 g L-1. Dry matter production was evaluated, as well as the levels of P, Zn, Fe, and Mn in both shoots and roots. Higher P rates induced higher shoot dry matter production. However, symptoms of Zn deficiency were observed in plants treated with the highest P rate in the absence of Zn. With increasing P rates, Zn concentrations in the shoots decreased more markedly than in roots, with accumulation of the element in the roots, indicating low Zn translocation to the shoot. A much higher Mn content in shoots (661 mg kg-1) than in roots (75 mg kg-1) suggested that the species is highly tolerant to this micronutrient. The Fe concentrations in the plant were much higher than those indicated in the literature as critical levels for this genus.

ABSTRACT Univariate methods for diagnosing nutritional status such as the sufficiency range and the critical level for garlic crops are very susceptible to the effects of dilution and accumulation of nutrients. Therefore, this study aimed to establish bivariate and multivariate norms for this crop using the Diagnosis and Recommendation Integrated System (DRIS) and Nutritional Composition Diagnosis (CND), respectively. The criteria used were nutritional status and the sufficiency range, and then the diagnoses were compared. The study was performed in the region of Alto Paranaíba, MG, Brazil, during the crop seasons 2012 and 2013. Samples comprised 99 commercial fields of garlic, cultivated with the cultivar “Ito” and mostly established in Latossolo Vermelho-Amarelo Distrófico (Oxisol). Copper and K were the nutrients with the highest number of fields diagnosed as limiting by lack (LF) and limiting by excess (LE), respectively. The DRIS method presented greater tendency to diagnose LF, while the CND tended towards LE. The sufficiency range of both methods presented narrow ranges in relation to those suggested by the literature. Moreover, all ranges produced by the CND method provided narrower ranges than the DRIS method. The CND method showed better performance than DRIS in distinguishing crop yield covered by different diagnoses. Turning to the criterion of evaluation, the study found that nutritional status gave a better performance than sufficiency range in terms of distinguishing diagnoses regarding yield.

ABSTRACT Given the increase in crop yields and the expansion of agriculture in low fertility soils, deficiency of micronutrients, such as iron, in plants grown in tropical soils has been observed. The aim of this study was to evaluate Fe availability and Fe uptake by corn (Zea mays L.) plants in 13 different soils, at two depths. Iron was extracted by Mehlich-1, Mehlich-3, and CaCl2 (Fe-CC) and was fractionated in forms related to low (Feo) and high (Fed) crystallinity pedogenic oxyhydroxides, and organic matter (Fep) using ammonium oxalate, dithionite-citrate, and sodium pyrophosphate, respectively. In order to relate Fe availability to soil properties and plant growth, an experiment was carried out in a semi-hydroponic system in which part of the roots developed in a nutrient solution (without Fe) and part in the soil (the only source of Fe). Forty-five days after seeding, we quantified shoot dry matter and leaf Fe concentration and content. Fed levels were high, from 5 to 132 g kg-1, and Feo and Fe-CC levels were low, indicating the predominance of Fe as crystalline oxyhydroxides and a low content of Fe readily available to plants. The extraction solutions showed significant correlations with various soil properties, many common to both, indicating that they act similarly. The correlation between the Mehlich-1 and Mehlich-3 extraction solutions was highly significant. However, these two extraction methods were inefficient in predicting Fe availability to plants. There was a positive correlation between dry matter and Fe levels in plant shoots, even within the ranges considered adequate in the soil and in the plant. Dry matter production and leaf Fe concentration and content were positively correlated with Fep concentration, indicating that the Fe fraction related to soil organic matter most contributes to Fe availability to plants.

RESUMO A literatura existente para a fertilização da cultura da cenoura recomenda, de modo geral, doses de nutrientes para expectativas de produtividades inferiores às obtidas atualmente. Além do mais, a recomendação considera somente os resultados da análise química do solo e não contempla efeitos como dos resíduos culturais ou variações da produtividade. Objetivou-se, com este trabalho, propor um sistema de recomendação de nutrientes para a cultura da cenoura (FERTICALC Cenoura), que abranja o suprimento de nutrientes pelos resíduos culturais, a variação da produtividade almejada, os atributos químicos do solo e a época de cultivo (inverno ou verão). Para obter dados necessários à modelagem do requerimento nutricional, amostraram-se 210 talhões de cultivo de cenoura na região do Alto Paranaíba, MG. Com essas amostragens, determinaram-se o teor de matéria seca das raízes, o coeficiente de utilização biológica dos nutrientes nas raízes e o índice de colheita dos nutrientes para os cultivos de verão e inverno. Para modelar o suprimento de nutrientes pelo solo, realizou-se revisão na literatura buscando trabalhos relacionados ao tema. O modelo foi desenvolvido para recomendação de macronutrientes e B. Para os micronutrientes catiônicos, o sistema informa somente a exportação e extração da cultura. O FERTICALC desenvolvido pode auxiliar na recomendação de nutrientes para a cultura da cenoura. Como vantagens em relação às tabelas de recomendação oficiais citam-se a variação contínua das doses de nutrientes com a produtividade e com características do solo e de acordo com dados de eficiência de extração de cultivares modernas e de maior produtividade.

ABSTRACT The literature on fertilization for carrot growing usually recommends nutrient application rates for yield expectations lower than the yields currently obtained. Moreover, the recommendation only considers the results of soil chemical analysis and does not include effects such as crop residues or variations in yield levels. The aim of this study was to propose a fertilizer recommendation system for carrot cultivation (FERTICALC Carrot) which includes consideration of the nutrient supply by crop residues, variation in intended yield, soil chemical properties, and the growing season (winter or summer). To obtain the data necessary for modeling nutritional requirements, 210 carrot production stands were sampled in the region of Alto Paranaíba, State of Minas Gerais, Brazil. The dry matter content of the roots, the coefficient of biological utilization of nutrients in the roots, and the nutrient harvest index for summer and winter crops were determined for these samples. To model the nutrient supply by the soil, the literature was surveyed in regard to this theme. A modeling system was developed for recommendation of macronutrients and B. For cationic micronutrients, the system only reports crop nutrient export and extraction. The FERTICALC which was developed proved to be efficient for fertilizer recommendation for carrot cultivation. Advantages in relation to official fertilizer recommendation tables are continuous variation of nutrient application rates in accordance with soil properties and in accordance with data regarding the extraction efficiency of modern, higher yielding cultivars.

RESUMO Ácidos húmicos (AH) são componentes principais das substâncias húmicas (SH), as quais são encontradas em praticamente todos os solos, sedimentos e corpos d’água. Elas apresentam papel fundamental na maioria, se não todas, as propriedades químicas e físicas do ambiente. Apesar de sua importância, a elevada complexidade dos AH (e das SH, em geral) fazem deles um sistema pouco compreendido. Portanto, compreender as propriedades físico-químicas e as interações dos AH se faz crucial para determinar o papel fundamental dessas substâncias no ambiente e obter detalhes estruturais. Surfactantes catiônicos são conhecidos por interagirem com AH por interações tanto eletrostáticas (cabeça polar) quanto hidrofóbicas (cauda apolar). Como os surfactantes representam um sistema muito bem conhecido e caracterizado, eles representam ótimas escolhas como sondas moleculares para estudar os AH. Avaliou-se a interação entre surfactantes catiônicos com AH pela técnica de titulação calorimétrica isotérmica visando obter informações sobre a estrutura básica dos AH, a natureza dessa interação e se AH de diferentes origens apresentam estruturas básicas diferentes. Ao contrário do que o modelo supramolecular prega, a estrutura dos AH não é fracamente retida, podendo separar-se dependendo das condições do meio ao que forem submetidas. A estrutura dos AH não sofreu nenhuma divisão ou mudança conformacional durante a interação com os surfactantes catiônicos. Parece existir uma estrutura básica dos AH que é mantida virtualmente a mesma apesar das diferentes origens ou composições desses AH.

ABSTRACT Humic acids (HA) are a component of humic substances (HS), which are found in nearly all soils, sediments, and waters. They play a key role in many, if not most, chemical and physical properties in their environment. Despite the importance of HA, their high complexity makes them a poorly understood system. Therefore, understanding the physicochemical properties and interactions of HA is crucial for determining their fundamental role and obtaining structural details. Cationic surfactants are known to interact electrostatically and hydrophobically with HA. Because they are a very well-known and characterized system, they offer a good choice as molecular probes for studying HA. The objective of this study was to evaluate the interaction between cationic surfactants and HA through isothermal titration calorimetry in a thermodynamic manner, aiming to obtain information about the basic structure of HA, the nature of this interaction, and if HA from different origins show different basic structures. Contrary to what the supramolecular model asserts, HA structure is not loosely held, though it may separate depending on the conditions the HA are subjected to in their milieu. It did not show any division or conformational change when interacting with surfactants. The basic structure of the HA remains virtually the same regardless of the different sources and compositions of these HA.

O uso da concentração foliar de nitrogênio total como indicador para diagnose nutricional apresenta algumas limitações. O objetivo deste trabalho foi determinar a confiabilidade da concentração de N total como indicador do status do nutriente para clones de eucalipto e compará-la com indicadores alternativos. Conduziu-se um experimento de casa de vegetação em delineamento de blocos ao acaso, em um arranjo fatorial 2 × 6, com mudas de dois clones de eucalipto (140 dias) e seis doses de N em solução nutritiva. Também foi conduzido um experimento de campo em delineamento inteiramente casualizado, em um arranjo fatorial 2 × 2 × 2 × 3, com duas épocas, duas regiões, dois clones jovens (aproximadamente dois anos) e três posições de amostragem das folhas na copa. As áreas de campo (regiões) tinham contrastantes propriedades físicas e químicas do solo e suas concentrações de N total, N-NH+4 e N-NO−3, foram determinadas em cinco camadas do solo, até 1 m de profundidade. Avaliaram-se como indicadores do status de N da planta, em raízes e folhas, concentrações de N total, N-NH+4 e N-NO−3, clorofila, razão N/P e leituras do medidor de clorofila nas folhas. Amônio (raiz) e N-NO−3, (raiz e folha) previram eficientemente os requerimentos de N para as mudas de eucalipto em casa de vegetação. Similarmente, N/P foliar, valores de clorofila e leituras do medidor de clorofila forneceram bons resultados em casa de vegetação. Entretanto, N/P foliar não refletiu o status de N do solo, e o uso do medidor de clorofila não pode ser generalizado para diferentes genótipos. A concentração foliar de N total não é um indicador ideal, mas essa e os níveis de clorofila melhor representam o status de N do solo para os clones jovens de eucalipto em condições de campo.

The use of leaf total nitrogen concentration as an indicator for nutritional diagnosis has some limitations. The objective of this study was to determine the reliability of total N concentration as an indicator of N status for eucalyptus clones, and to compare it with alternative indicators. A greenhouse experiment was carried out in a randomized complete block design in a 2 × 6 factorial arrangement with plantlets of two eucalyptus clones (140 days old) and six levels of N in the nutrient solution. In addition, a field experiment was carried out in a completely randomized design in a 2 × 2 × 2 × 3 factorial arrangement, consisting of two seasons, two regions, two young clones (approximately two years old), and three positions of crown leaf sampling. The field areas (regions) had contrasting soil physical and chemical properties, and their soil contents for total N, NH+4-N, and NO−3-N were determined in five soil layers, up to a depth of 1.0 m. We evaluated the following indicators of plant N status in roots and leaves: contents of total N, NH+4-N, NO−3-N, and chlorophyll; N/P ratio; and chlorophyll meter readings on the leaves. Ammonium (root) and NO−3-N (root and leaf) efficiently predicted N requirements for eucalyptus plantlets in the greenhouse. Similarly, leaf N/P, chlorophyll values, and chlorophyll meter readings provided good results in the greenhouse. However, leaf N/P did not reflect the soil N status, and the use of the chlorophyll meter could not be generalized for different genotypes. Leaf total N concentration is not an ideal indicator, but it and the chlorophyll levels best represent the soil N status for young eucalyptus clones under field conditions.

O extrator Mehlich-1 (M-1), assim como o Fosfato Monocálcico em ácido acético (FMCa), tem na acidez e na troca de ligantes - seja do sulfato do extrator pelo fosfato do solo ou do fosfato do extrator pelo sulfato do solo - os mecanismos de extração do P e do S disponíveis. Em solos argilosos, com maior poder de adsorção de P, ou menor valor de P-remanescente (P-rem), o que corresponde a solos com maior Poder-Tampão de Fosfato (PTF), mais tamponados para a acidez, o pH inicialmente baixo dos extratores é, durante o seu contato com o solo, aumentado em direção àquele do solo, e o sulfato do M-1 ou o fosfato do FMCa é adsorvido por sítios de adsorção ocupados ou não por esses ânions. Tal fato faz com que o extrator perca seu poder de extração, fenômeno conhecido como desgaste de extrator, objetivo de estudo deste trabalho. Escolheram-se 20 amostras de solos, de modo a cobrir a faixa do P-rem (0 a 60 mg L-1). Como medida do PTF, foi utilizado o P-rem. Os teores de P e de S disponíveis das amostras dos solos pelo M-1 e FMCa, de demais nutrientes e de matéria orgânica (MO) foram determinados. Para a determinação do desgaste dos extratores, após o período de repouso, foram medidos o pH e os teores de P e de S em ambos os extratos-solos. Houve efeito pouco expressivo, embora significativo, do desgaste da acidez dos extratores M-1 e FMCa com a diminuição do valor de P-rem. Observou-se para o M-1 um modelo linear plateau para desgaste descontínuo do teor do P, com a diminuição da concentração do P-rem ou aumento do PTF, sugerindo que se deve adotar um modelo também descontínuo para a interpretação do P-disponível de solos com diferentes valores de P-rem. Entretanto, observou-se resposta linear-contínua entre as variáveis P no extrato-solo e P-rem para o extrator FMCa, o que evidenciou desgaste crescente desse extrator com o aumento do PTF do solo, indicando a validade da relação linear entre o S disponível do solo e o PTF, estimado pelo P-rem, como atualmente adotada.

The Mehlich-1 (M-1) extractant and Monocalcium Phosphate in acetic acid (MCPa) have mechanisms for extraction of available P and S in acidity and in ligand exchange, whether of the sulfate of the extractant by the phosphate of the soil, or of the phosphate of the extractant by the sulfate of the soil. In clayey soils, with greater P adsorption capacity, or lower remaining P (Rem-P) value, which corresponds to soils with greater Phosphate Buffer Capacity (PBC), more buffered for acidity, the initially low pH of the extractants increases over their time of contact with the soil in the direction of the pH of the soil; and the sulfate of the M-1 or the phosphate of the MCPa is adsorbed by adsorption sites occupied by these anions or not. This situation makes the extractant lose its extraction capacity, a phenomenon known as loss of extraction capacity or consumption of the extractant, the object of this study. Twenty soil samples were chosen so as to cover the range of Rem-P (0 to 60 mg L-1). Rem-P was used as a measure of the PBC. The P and S contents available from the soil samples through M-1 and MCPa, and the contents of other nutrients and of organic matter were determined. For determination of loss of extraction capacity, after the rest period, the pH and the P and S contents were measured in both the extracts-soils. Although significant, the loss of extraction capacity of the acidity of the M-1 and MCPa extractants with reduction in the Rem-P value did not have a very expressive effect. A “linear plateau” model was observed for the M-1 for discontinuous loss of extraction capacity of the P content in accordance with reduction in the concentration of the Rem-P or increase in the PBC, suggesting that a discontinuous model should also be adopted for interpretation of available P of soils with different Rem-P values. In contrast, a continuous linear response was observed between the P variables in the extract-soil and Rem-P for the MCPa extractor, which shows increasing loss of extraction capacity of this extractor with an increase in the PBC of the soil, indicating the validity of the linear relationship between the available S of the soil and the PBC, estimated by Rem-P, as currently adopted.

Os Latossolos apresentam, de modo geral, baixos teores de P disponível; no entanto, a influência do material de origem parece ser decisiva na definição do estoque e da forma de P predominante nesses solos. O objetivo deste trabalho foi avaliar a disponibilidade de P, pelos extratores Mehlich-1 (M-1) e Resina de Troca Iônica (RTI), em amostras de horizontes B de Latossolos Férricos e Perférricos desenvolvidos a partir de diferentes materiais de origem. Para tanto, além da caracterização física e química dos solos, foram realizadas 10 extrações sequenciais com os extratores M-1 e RTI em amostras de horizonte B coletadas entre 0,8 e 1,0 m de profundidade. Os teores totais de Ca, P, Fe, Al e Ti foram determinados após digestão com os ácidos nítrico, fluorídrico e perclórico. Os efeitos das extrações sequenciais de P sobre os óxidos de Fe também foram avaliados a partir das análises com ditionito-citrato-bicarbonato e oxalato ácido de amônio. A maior semelhança observada entre os teores de P acumulado após as extrações sequenciais com M-1 e RTI nos solos desenvolvidos de tufito é indicativo da predominância de P-Ca. Os maiores teores de P extraídos pela RTI após uma única extração relevam sua maior eficiência na remoção de P em solos bastante intemperizados como os Latossolos estudados e, ainda, ressalta a elevada sensibilidade do extrator M-1 em solos altamente tamponados. Além disso, uma única extração com o extrator M-1 ou RTI não é suficiente para estimar o fator quantidade de P lábil nesses solos.

In general, Latosols have low levels of available P, however, the influence of the parent material seems to be decisive in defining the pool and predominant form of P in these soils. This study evaluated P availability by extraction with Mehlich-1 (M-1) and Ion Exchange Resin (IER), from samples of B horizons of Ferric and Perferric Latosols developed from different parent materials. To this end, in addition to the physical and chemical characterization of soils, 10 sequential extractions were performed with M-1 and IER from samples of B horizons (depth between 0.8 and 1.0 m). Total contents of Ca, P, Fe, Al, and Ti were determined after digestion with nitric, hydrofluoric and perchloric acids. The effects of sequential P extractions on Fe oxides were also evaluated from the analyses of dithionite-citrate-bicarbonate and ammonium acid oxalate. The high similarity between contents of P accumulated after sequential extractions with M-1 and IER in soils developed on tuffite indicated a predominance of P-Ca. Higher contents of P after a single IER extraction show greater efficiency in P removal from highly weathered soils, as from the Latosols studied here. The P contents also show the high sensitivity of extractant M-1 in highly buffered soils. Furthermore, a single extraction with extractant M-1 or IER is not sufficient to estimate the amount of labile P in these soils.

O nitrogênio é requerido em grandes quantidades pelo eucalipto; entretanto, as repostas à aplicação desse nutriente são divergentes. O objetivo deste trabalho foi avaliar o comportamento diferenciado em crescimento, na nutrição mineral e nas trocas gasosas de clones de eucalipto supridos com N. Os tratamentos consistiram de dois clones de eucalipto (VM-01 e I-144) e seis doses de N (0; 0,74; 2,93; 4,39; 5,85; e 8 mmol L-1 de NH4NO3), dispostos em delineamento de blocos casualizados com cinco repetições. O clone VM-01 foi superior em altura e altura/diâmetro do colo e teve maiores concentrações foliares de todos os macronutrientes e de Cu, Fe, Mo e Zn. Em termos de produção de matéria seca da raiz e total, raiz/parte aérea e diâmetro do colo, bem como em condutância estomática e transpiração, o clone I-144 teve melhor performance. O desempenho dos clones foi claramente diferenciado, e o crescimento do I-144, independetemente de menor concentração foliar de N, foi em geral melhor que do VM-01.

Eucalyptus requires large amounts of nitrogen (N); however, it responds in diverse manners to the application of this nutrient. The aim of this study was to evaluate the differential performance in growth, mineral nutrition, and gas exchanges of N-fertilized Eucalyptus clones. The treatments consisted of two Eucalyptus clones (VM-01 and I-144) and six N application rates (0, 0.74, 2.93, 4.39, 5.85, and 8 mmol L-1 NH4NO3) arranged in a randomized complete block design with five replications. VM-01 had greater plant height and greater height/collar diameter ratio, as well as higher leaf concentrations of all macronutrients and of Cu, Fe, Mo, and Zn. In terms of total and root dry matter production, root/shoot ratio, and collar diameter, as well as stomatal conductance and transpiration, I-144 performed better. The performance of the clones was clearly differentiated, and the growth of I-144, despite lower leaf N concentration, was in general better than VM-01.