O uso de solucoes extratoras que contenham sais de amonio vem-se mostrando como uma alternativa promissora para a extracao conjunta de cations, em avaliacoes da fertilidade de solos. Entretanto, a determinacao de aluminio por titulometria (tecnica usada rotineiramente na maioria dos laboratorios que analisam esse elemento em solos, no Brasil, e que determina a acidez trocavel) em extratos de solo em NH4Cl e inviavel. Isso se deve ao efeito tampao exercido pelo NH4Cl na faixa alcalina de pH, impedindo uma viragem nitida dos indicadores acido-base usados nas titulacoes com NaOH (Coscione et al., 1998). Nesse caso, em substituicao a titulacao, o aluminio pode ser determinado por espectrofotometria de absorcao atomica ou pelo metodo colorimetrico do alaranjado de xilenol (Otomo, 1963), que determina especificamente o Al trocavel. O primeiro metodo nao e usado, em geral, em laboratorios de analises de solo, pelo risco de explosoes do comburente utilizado (oxido nitroso) e elevado custo analitico. O segundo metodo foi proposto por Pritchard (1967) para uso na determinacao de aluminio em solos. Esse metodo baseia-se na complexacao dos ions Al3+ em solucao pelo xilenol, sendo a leitura da cor (amarelada) feita em espectrofotometro. Duriez & Johas (1982), trabalhando com amostras de solos brasileiros, confirmaram a simplicidade de execucao e a precisao desse metodo. Para laboratorios que processam grande numero de amostras, Coscione et al. (2001) descreveram um protocolo analitico para o elemento. O presente trabalho teve como objetivo comparar os metodos de titulometria e de espectrofotometria na determinacao de teores de aluminio trocavel extraido do solo com KCl 1 mol L-1 em diversos solos brasileiros.

Phosphorus has received considerable attention in the research of methods of soil analysis, but agreement on best methodology is lacking. Resin extractable P seems to be a superior method, but its adoption in routine soil testing is still limited worldwide. When there is a choice between several methods of analysis, if results are not comparable, greenhouse experiments under controlled conditions are used to select the soil test that is more closely related with nutrient uptake. This is done in pot experiments with soils representing a wide range of attributes that affect P reactions. A test plant is grown under conditions of proper nutrient supply except for P. The linear correlations between P uptake by plant and soil P determined by different procedures allow the ranking of methods based on the quality of prediction of P availability in soils. An example of such research for a pot experiment with fl ooded rice is shown in Figure 1. In this case, resin extractable P is compared with the Mehlich 1 extraction. The results of resin P presented a much better correlation with P absorbed by the rice plants than Mehlich 1. Several studies comparing soil P determination methods have been carried out. The literature review by Silva and Raij (1999) included papers published with soils of different countries, in which P determined by different methods was correlated with plant P uptake. The data in Table 1 indicate that the ion exchange resin method is better correlated with P uptake than the other methods and that it is suitable for all types of soils, both acidic and alkaline. The pH of the extractant solution is important for the ionexchange resin procedure as shown in Table 2. Phosphorus extraction was poor when the suspension pH was low. For soil #2, where no response to P was observed, a high value of extractable P (36 mg/dm 3 ) was obtained when the suspension

A avaliação do método modificado da resina de troca de íons para extração de Mn e Fe dos solos foi o objetivo desta pesquisa. Foram utilizadas 44 amostras de solo, cujos teores de Mn variaram de baixos a altos e de Fe de médios a altos. Como plantas-teste, utilizaram-se o milho e a soja, cultivadas em casa de vegetação. O Fe e o Mn do solo foram determinados, usando o método modificado da resina de troca de íons, DTPA, AB-DTPA, Mehlich-1 e Mehlich-3. Os coeficientes de correlação entre Mn no solo e Mn acumulado na parte aérea da soja foram: resina (0,62*), DTPA (0,58*), Mehlich-3 (0,54*), Mehlich-1 (0,51*) e AB-DTPA (0,26NS). Para o milho, houve correlação entre Mn-solo e Mn-planta somente nas amostras de solo com baixos teores desse elemento, para todos os extratores, exceto para AB-DTPA. Concluiu-se que a resina foi tão eficiente quanto os extratores DTPA, M-1 e M-3 em avaliar a disponibilidade de Mn para a soja, e que nenhum extrator foi eficiente em avaliar a disponibilidade de Fe para as plantas de milho e soja, com 53 dias de idade, cultivadas em casa de vegetação.The objective of this research was to evaluate a modified ion exchange resin method for Mn and Fe extraction from soils. Forty-four soil samples presenting low, medium, and high Mn and medium to high Fe concentrations were used. Maize and soybeans plants were grown as test plants in a pot experiment in a greenhouse. Soil samples were analyzed for Mn and Fe using the modified ion exchange resin, DTPA, AB-DTPA, Mehlich-1, and Mehlich-3 methods. The correlation coefficients between soil Mn and Mn accumulated in the soybean shoot were: ion exchange resin (0.62*), DTPA (0.57*), Mehlich-3 (0.54*), Mehlich-1 (0.51*), and AB-DTPA (0.26). For maize, significant correlation coefficients between soil Mn and plant-Mn were obtained only when low-initial Mn soil samples were considered for all extractants, except for AB-DTPA. For soybeans, the modified ion exchange resin method was as efficient as DTPA, Mehlich-1 and Mehlich-3 for the evaluation of soil Mn availability. None of the methods was efficient for evaluating the soil Fe availability for the 53 day-old maize and soybean plants grown in greenhouse.

Atualmente, alguns laboratórios de análise de solo determinam Al, Ca e Mg trocáveis em extratos de KCl 1 mol L-1 e K e Na na solução extratora Mehlich-1, também usada na extração de fósforo. Outros laboratórios, que empregam a resina trocadora de ânions para P, avaliam também Ca, Mg e K no extrato, não sendo possível determinar Al e Na. Dessa forma, achou-se oportuno avaliar a extração com NH4Cl 1 mol L-1 na determinação simultânea dos cinco cátions trocáveis: Al, Ca, Mg, K e Na, em comparação aos extratores KCl e Mehlich-1. Utilizaram-se amostras coletadas em áreas de cultivo de fruteiras irrigadas da região Nordeste e na área experimental da Embrapa Meio Ambiente em Jaguariúna (SP). Os métodos utilizados foram: (a) extração simultânea dos cinco cátions com NH4Cl 1 mol L-1, e (b) extração de Ca, Mg e Al com KCl 1 mol L-1, e de K e Na com o extrator Mehlich-1. A solução de NH4Cl 1 mol L-1 apresentou maior capacidade de extração de Mg do solo do que a solução de KCl 1 mol L-1; as duas soluções se equivaleram quanto à capacidade de extração de Ca e de Al. A solução de NH4Cl extraiu mais K e Na do que a solução Mehlich-1. Conclui-se que a solução de NH4Cl é uma opção conveniente para a extração de Al, Ca, Mg, K e Na trocáveis do solo.

The objective of this research was to evaluate a modified ion exchange resin method for Mn and Fe extraction from soils. Forty-four soil samples presenting low, medium, and high Mn and medium to high Fe concentrations were used. Maize and soybeans plants were grown as test plants in a pot experiment in a greenhouse. Soil samples were analyzed for Mn and Fe using the modified ion exchange resin, DTPA AB-DTPA Mehlich-1, and Mehlich-3 methods. The correlation coefficients between soil Mn and Mn accumulated in the soybean shoot were: ion exchange resin (0.62*), DTPA (0.57*), Mehlich-3 (0.54*), Mehlich-1 (0.51*), and AB-DTPA (0.26). For maize, significant correlation coefficients between soil Mn and plant-Mn were obtained only when low-initial Mn soil samples were considered for all extractants, except for AB-DTPA. For soybeans, the modified ion exchange resin method was as efficient as DTPA, Mehlich-1 and Mehlich-3 for the evaluation of soil Mn availability. None of the methods was efficient for evaluating the soil Fe availability for the 53 day-old maize and soybean plants grown in greenhouse.

Atualmente, alguns laboratórios de análise de solo determinam Al, Ca e Mg trocáveis em extratos de KCl 1 mol L-1 e K e Na na solução extratora Mehlich-1, também usada na extração de fósforo. Outros laboratórios, que empregam a resina trocadora de ânions para P, avaliam também Ca, Mg e K no extrato, não sendo possível determinar Al e Na. Dessa forma, achou-se oportuno avaliar a extração com NH4Cl 1 mol L-1 na determinação simultânea dos cinco cátions trocáveis: Al, Ca, Mg, K e Na, em comparação aos extratores KCl e Mehlich-1. Utilizaram-se amostras coletadas em áreas de cultivo de fruteiras irrigadas da região Nordeste e na área experimental da Embrapa Meio Ambiente em Jaguariúna (SP). Os métodos utilizados foram: (a) extração simultânea dos cinco cátions com NH4Cl 1 mol L-1, e (b) extração de Ca, Mg e Al com KCl 1 mol L-1, e de K e Na com o extrator Mehlich-1. A solução de NH4Cl 1 mol L-1 apresentou maior capacidade de extração de Mg do solo do que a solução de KCl 1 mol L-1; as duas soluções se equivaleram quanto à capacidade de extração de Ca e de Al. A solução de NH4Cl extraiu mais K e Na do que a solução Mehlich-1. Conclui-se que a solução de NH4Cl é uma opção conveniente para a extração de Al, Ca, Mg, K e Na trocáveis do solo.Currently, part of the soil testing laboratories of Brazil determine exchangeable Al, Ca, and Mg in a 1 mol L-1 KCl soil extract and exchangeable sodium and potassium in the Mehlich-1 soil extract, which is also used for phosphorus extraction. Other laboratories use an anion exchange resin for P and also determine Ca, Mg and K in the same extract, while Al and Na cannot be determined. For this reason, it was considered a good opportunity to evaluate the simultaneous extraction of the five exchangeable cations: Al, Ca, Mg, K, and Na in a 1 mol L-1 NH4Cl solution, and compare the results with those obtained with potassium chloride and Mehlich-1 extractants. The soil samples used were from Northeastern Brazil fruit growing region and from the Embrapa Environment Experimental Station, located in Jaguariúna County, São Paulo State. The employed methods were: (a) simultaneous extraction of the five cations with a 1 mol L-1 NH4Cl; (b) extraction of Ca, Mg, and Al with 1 mol L-1 KCl; and (c) extraction of K and Na with the Mehlich-1 solution. The NH4Cl solution has a higher Mg extraction capacity than KCl, but they present similar Ca and Al extraction ability. The NH4Cl solution extracted more K and Na than the Mehlich-1 solution. It is concluded that the ammonium chloride solution is a convenient alternative for the extraction of exchangeable Al, Ca, Mg, K, and Na from soils.

Probably the cheapest and most widely used chemical analysis employed in agriculture, soil testing is often not properly appreciated for the advantages it has for economically sound fertilizer recommendation for crops. In fact, soil testing is not only useful, but it becomes indispensable for this purpose, considering that it is used to determine unfavorable soil reaction and nutrient deficiencies and excesses that affect plant growth. To demonstrate how soil analysis and the economy of fertilizer use are interrelated, a quadratic model was used to show the magnitude of economic returns under different conditions, using soil analysis as starting point. The parameters used in the quadratic response model used were the sufficiency index of a nutrient obtained by soil analysis, the expected or maximum yield, and the nutrient rate to achieve this yield. Using the sufficiency index of the nutrient in the soil, the cost of the nutrient unit, and the value of the crop unit as inputs for the model, profits and return to investment ratios were calculated for several conditions, covering the range of yield levels, fertilizer costs, and crop values found in agriculture. Profits are higher for nutrients applied when they are more deficient in soils, under conditions of higher maximum yields and also when crop value are higher. The results point to the importance of the proper evaluation of soil fertility and to the removal of yield limiting factors. On the basis of the concepts presented on the economics of fertilizer use, the following cases were discussed: fertilizer use in extensive low value crops; policies to increase crop production with fertilizers; fertilizer use under conditions of limited capital; fertilizer recommendation for precision agriculture; choice of adequate fertilizer blends; fertilization as a sound environmental practice.

The increasing use of the ICP-AES (inductively coupled plasma atomic emission spectrophotometry) as a multielement Analytical technique has stressed the preference for the use of multinutrient extractants in routine soil analysis. However, few studies relating the extraction of zinc (Zn) from soil with such extractants and the absorption of the element by plants have been published. Two experiments under greenhouse conditions were carried out in order to determine the efficiency of some multinutrient extractants for the determination of available Zn in 44 soils from the State of Sao Paulo, Brazil, for corn and soybean. All soil samples were limed to increase the CEC's base saturation at pH 7 to 70%. Twenty-two soil samples with DTPA (diethylenetriaminepentaacetic acid) extractable Zn concentration lower than 0.6 mg dm(-3) received either the application of B, Cu, Mn, Zn or of these micronutrients excluding Zn. The remaining 22 soil samples, with Zn concentration above 0.6 mg dm(-3), received application of three micronutrients (B, Cu and Mn). Macronutrients were applied to all pots as needed for crop development. Zinc was extracted from the soils before each planting using the extracting solutions, DTPA, Mehlich 1 (M-1), Mehlich 3 (M-3) and AB-DTPA (ammonium bicarbonate-DTPA) and determined by ICP-AES. The results showed significant correlations between plant Zn concentration and soil Zn concentration. The correlation values between soil-Zn and plant-Zn were of 0.74 (M-3), 0.73 (DTPA), 0.62 (AB-DTPA) and 0.61 (M-1) for corn, and of 0.71 (DTPA), 0.63 (M-1), 0.58 (M-3) and 0.46 (AB-DTPA) for soybean. Thus, the DTPA solution was the most efficient extractant for the determination of bioavailable Zn when both crops are considered together.

We examined the possibility of using mixed cation–anion exchange resinspre-treated with two organic acid ligands, acetate (R-ACET) and tartrate(R-TART) for extraction of phytoavailable Fe, Mn, Cu and Zn using theconventional diethylenetriaminepentaacetic acid (DTPA) as a referenceextractant. In each soil, variable amounts of Fe, Mn, Cu and Zn were extractedby the different extractants. The amounts of Fe, Mn, Cu and Zn did not followprediction based on stability constants of metal-organic complexes. The R-ACETwas a slightly better predictor of soybean uptake of Cu and Mn, and dry matter(DM) yield responses to Cu than either DTPA or R-TART, though differencesbetweenR-ACET and DTPA were not significant. However, soybean DM yield response to Znwas best predicted by DTPA, while Zn uptake correlated more strongly with DTPAthan R-ACET and R-TART extractable Zn. These results suggest that R-ACET may beused as an alternative extractant for Fe, Mn, Cu and Zn in strongly weatheredtropical soils, but it was not superior to DTPA.

Neste trabalho, avaliou-se a influência da mineralogia e o histórico de uso na adsorção e formas de P em Latossolos. Empregaram-se cinco Latossolos (LAx, LAd, LVw e dois LVdf, desenvolvidos de gabro, LVdfg, e de tufito, LVdft), de modo a abranger uma ampla faixa de proporções de hematita, goethita, caulinita (Ct) e gibbsita (Gb). Estes solos foram coletados em áreas nunca cultivadas e em áreas adjacentes já cultivadas por longos períodos, onde receberam calagens e adubações fosfatadas periódicas. Procedeu-se à caracterização física, química e mineralógica, envolvendo: granulometria, Fe em formas menos cristalinas (Feo), óxidos livres (Fed) e "totais" (Fes), além do fracionamento e disponibilidade de P. Com o uso da difração de raios-x, obteve-se a composição mineralógica das frações: argila desferrificada e argila ferro-concentrada, e, por análise térmica diferencial, a razão Ct/(Ct + Gb), na fração argila desferrificada. A adsorção de P foi estudada, empregando-se 24 h de agitação e concentrações de 0; 5; 10; 15; 25; 50; 75; 100 e 200 mg L-1, para calcular a isoterma de adsorção, de onde se obteve a capacidade máxima de adsorção de fósforo (CMAF). Os resultados mostraram que, à medida que a mineralogia dos Latossolos tornou-se mais oxídica, aumentaram a adsorção de P, o teor total e as formas ligadas mais fortemente a Al e Fe. O cultivo influenciou, de modo diferenciado, a adsorção de P e aumentou as formas de P ligado a Ca em todos os solos. As formas pouco lábeis de P predominaram nos Latossolos estudados, destacando-se as orgânicas associadas a compostos húmicos naqueles não cultivados e as inorgânicas ligadas a Fe e Al nos cultivados.

In the process of phosphate rock acidulation, several impure P compounds may be formed along with the desirable Ca and NH4 phosphates. Such compounds normally reduce the content of water-soluble P and thus the agronomic effectiveness of commercial fertilizers. In order to study this problem, a greenhouse experiment consisting of three consecutive corn crops was conducted in samples of a Red-Yellow Latosol (Typical Hapludox) in a completely randomized design (6 x 2 x 2), with four replicates. Six commercial fertilizers were added to 2 kg of soil at a rate of 70 mg kg-1 P, based on the content of soluble P in neutral ammonium citrate plus water (NAC + H2O) of the fertilizers. Fertilizer application occurred either in the original form or leached to remove the water-soluble fraction, either by mixing the fertilizer with the whole soil in the pots or with only 1 % of its volume. The corn plants were harvested 40 days after emergence to determine the shoot dry matter and accumulated P. For the first crop and localized application, the elimination of water-soluble P from the original fertilizers resulted in less bioavailable P for the plants. For the second and third crops, the effects of P source, leaching and application methods were not as evident as for the first, suggesting that the tested P sources may have similar efficiencies when considering successive cropping. The conclusion was drawn that the water-insoluble but NAC-soluble fractions of commercial P fertilizers are not necessarily inert because they can provide P in the long run.