ABSTRACT. Rock dusts in association with organic sources have been used in agriculture to improve soil chemical characteristics and food composition. In this context, this study aimed to evaluate the effect of the rock dusts siltstone, tephrite, and olivine melilitite pure or combined and associated or not with cattle manure on the chemical composition of soybean seeds of the cultivar BRS 232 grown on a Cambisol and Nitisol subjected to these treatments and conventional fertilization. For this, an experiment was carried out with pots in a greenhouse using a Cambisol and Nitisol to cultivate the soybean from January to May 2019 until seed production. The seeds were harvested, ground, and sieved through a 1 mm mesh sieve to determine the nutrient, phytate, and crude protein contents. The effects of the rock dusts on the chemical composition of seeds were directly related to the chemical characteristics of the evaluated soils. The tested rock dusts had a more pronounced response in the Cambisol (poorer soil) than in the Nitisol (more fertile). The contents and accumulation of nutrients in the seeds, as well as the total dry matter production in both soils subjected to the treatments with the rock dusts olivine melilitite and siltstone + olivine melilitite, pure and combined with manure, were similar and, in some cases, higher than the treatments subjected to conventional fertilization. The combination of manure and rock dusts provided an increase in the concentration of nutrients in both soils, resulting in their higher availability for plants and directly reflecting on the chemical composition of seeds.

Resumo O objetivo deste trabalho foi avaliar o potencial de pó da rocha olivina melilitito, em duas granulometrias e em doses crescentes, para melhorar as características químicas do solo e o crescimento e o acúmulo de nutrientes em plantas de soja (Glycine max) e sorgo (Sorghum bicolor). Os tratamentos consistiram de três doses de olivina melilitito, equivalentes a 2,5, 5,0 e 10 Mg ha-1, nas granulometrias de pó e filler do produto comercial. Foram realizadas análises físico-químicas e mineralógicas, tendo-se utilizado, como base, instrução normativa para pó de rocha como remineralizador de solos. As plantas de soja e sorgo foram cultivadas por 60 e 45 dias, respectivamente, em casa de vegetação, em Cambissolo Háplico Alumínico e Argissolo Vermelho Distrófico sômbrico. O pó da rocha olivina melilitito aplicado nas doses crescentes e nas duas granulometrias testadas melhorou as características químicas dos dois solos estudados e promoveu o desenvolvimento das plantas. No entanto, a granulometria filler é mais eficiente que a do pó para melhorar as características químicas dos solos e o desenvolvimento e o acúmulo de nutrientes nas plantas.

Abstract The objective of this work was to evaluate the potential of olivine melilitite rock powder, in two particle sizes and in increasing rates, to improve the chemical properties of the soil and the growth and nutrient accumulation of soybean (Glycine max) and sorghum (Sorghum bicolor) plants. The treatments consisted of three rates of the rock powder, equivalent to 2.5, 5.0, and 10 Mg ha-1, in the powder and filler particle sizes of the commercial product. Physicochemical and mineralogical analyses were carried out using, as a basis, the Brazilian normative ruling on rock powder as a soil remineralizer. The soybean and sorghum plants were cultivated for 60 and 45 days, respectively, in a greenhouse on a Humic Dystrudept and a Typic Hapludult. The olivine melilitite rock powder applied in the tested increasing rates and two particle sizes improved soil chemical properties and promoted plant growth. However, the filler particle size is more efficient than that of the powder to improve soil chemical properties and plant growth and nutrient accumulation.

ABSTRACT Chemical speciation of the soil solution is an important tool to identify Al species related to phytotoxicity. In some Brazilian acid soils, the Al extractable by the KCl 1.0 mol L -1 solution (Al-KCl) exceeds 10 cmol c kg -1 and even then, in some situations, it does not cause toxicity to the plants. This study aimed to evaluate the relationship between these high concentrations of Al-KCl found in some Brazilian acid soils and the activity of the different Al chemical species in the soil solution, as well as the response of soybean and corn plants to lime application. Subsurface horizon (B) samples of five soils were collected in four states of Brazil (AC, PE, RS, and SC) from areas that had never been cultivated. The samples were then given increasing rates of limestone, equivalent to that required to neutralize 0, 0.25, 0.5, and 1.00 times the contents of H+Al and were incubated for 98 days. After that period, the soils were fertilized and planted to soybean and corn in the greenhouse for 60 and 45 days, respectively, in 2015. The experimental units consisted of 8 L pots, filled with 5 kg of soil (dry basis). After each crop, the plants and soil samples were collected to determine the leaf, stem, and root dry matter, and chemical composition. In the soil solution, cations and anions, pH, electrical conductivity, and dissolved organic carbon were quantified. The distribution of the Al species was evaluated using the program Minteq. Free Al (Al 3+ ) was the species found in highest proportion in treatments without limestone, in all soils. Application at the lowest limestone rate, equivalent to 25 % of that required for H+Al neutralization, was sufficient to decrease Al activity in the soil solution to levels considered non-toxic to plants in four of the five soils. High levels of Al-KCl are not related to manifestation of toxicity and to Al 3+ activity in the solution of Hapludult (Acre profile 9; AC9) and Hapludult (Rosario do Sul; RS) since dry matter (DM) production in these soils was little influenced by liming, unlike what occurred in the Hapludult (Pernambuco; PE), Humudepts (Bom Retiro; BR), and Kandiudox (Curitibanos; CB) soils, in which Al-KCl contents were related to Al activity in the solution and to DM production of the plants grown in them.

RESUMO O Al trocável é tradicionalmente quantificado no extrato da solução de KCl 1 mol L-1; entretanto, nem sempre o Al provém unicamente de formas trocáveis desse elemento. Este trabalho objetivou investigar as formas de Al presentes em solos ácidos de várias regiões brasileiras, com distintas mineralogias, buscando elucidar se todo o Al-KCl corresponde às formas trocáveis do elemento. Foram testados os seguintes extratores para Al: Método tradicional (KCl 1 mol L-1), e variações desse método (curvas de titulação potenciométrica, método das extrações sucessivas e tamponado a pH 5), KCl 0,1 mol L-1, CaCl2 0,01 mol L-1, oxalato de amônio 0,2 mol L-1, pirofosfato de sódio 0,1 mol L-1 e CuCl2 0,5 mol L-1. A quantificação do elemento foi feita por titulação e, ou, por espectrofotometria de absorção atômica (EAA), quando pertinente. Foram analisadas amostras de dois horizontes (A e B) de perfis de solo de cinco estados brasileiros (AC, PE, BA, RS e SC). Dois perfis de solo de Santa Catarina, com níveis mais baixos de Al-KCl, foram utilizados como referência de solos mais intemperizados, com mineralogia caulinítica. Os resultados demonstraram que, particularmente nos solos ácidos com esmectitas, o KCl 1 mol L-1 extrai outras formas de Al além da trocável, superestimando seus valores, não sendo, portanto, um extrator indicado para a maioria dos solos analisados neste estudo. No entanto, a utilização dessa solução, porém mais diluída (KCl 0,1 mol L-1), teve menor efeito na dissolução desses compostos, podendo indicar de forma mais realista os teores de Al trocáveis do solo. As demais variações desse método (tampão pH 5, método potenciométrico e extrações sucessivas) não se evidenciaram adequadas para determinar esse elemento por extraírem quantidades similares ou até mais altas, quando comparadas com o método tradicional. Os altos teores de Al quantificados nos extratos de oxalato de amônio, cloreto de cobre e pirofosfato de sódio indicaram a participação expressiva de formas inorgânicas amorfas e de baixa cristalinidade, que contribuíram para a superestimação dos teores de Al nos solos estudados.

ABSTRACT Exchangeable Al is normally quantified in the extract of 1.0 mol L-1KCl, but Al does not always come solely from exchangeable forms of the element. The objective of this study was to quantify Al forms existing in acid soils in order to elucidate if all Al-KCl comes from exchangeable forms. Soils samples with different mineralogical compositions were collected from many regions of Brazil. The following Al extractants were evaluated: the traditional method (1.0 mol L-1 KCl) and some variations of it (potentiometric titration curves, method of successive extractions, and 1.0 mol L-1 KCl buffered at pH 5.0), 0.1 mol L-1 KCl, 0.01 mol L-1CaCl2, 0.2 mol L-1 ammonium oxalate, 0.1 mol L-1 sodium pyrophosphate, and 0.5 mol L-1CuCl2. Aluminum was quantified by titration, or by atomic absorption spectroscopy when pertinent. Samples from A and B horizons were used that were collected from five Brazilian states: Acre, Bahia, Pernambuco, Santa Catarina, and Rio Grande do Sul. Two additional soil profiles with lower contents of Al and essentially kaolinitic mineralogy were used as a reference of more weathered soils. Results showed that especially in acid soils with smectite, 1.0 mol L-1 KCl extracts other forms of Al in addition to the exchangeable form, which makes this solution inappropriate for estimating exchangeable Al for most soils studied. However, use of this solution in a more dilute form (0.1 mol L-1 KCl) had a smaller effect on the dissolution of these compounds and is a more reliable indicator of exchangeable Al levels. The other variations of this method (buffer pH 5, and potentiometric and successive extraction methods) were not suitable for determining this element because they extracted similar or even higher amounts when compared to the traditional method. The high contents of Al quantified by ammonium oxalate, copper chloride, and sodium pyrophosphate extractants showed the expressive participation of amorphous inorganic forms and low crystallinity, which contributed to overestimating the levels of Al in the soils studied.

Em solos ácidos de ambiente mais tropical com esmectitas, assim como em solos altamente tamponados de ambiente subtropical, contendo esmectita com hidroxi-Al entrecamadas (EHE) e, ou, vermiculita com hidroxi-Al entrecamadas (VHE), os teores de Al-KCl podem ser excepcionalmente altos; entretanto, em alguns casos não se manifestam efeitos fitotóxicos do elemento nas culturas. O Al "trocável" é tradicionalmente quantificado no extrato da solução de KCl 1 mol L-1 (Al-KCl), mas nem sempre esse elemento provém unicamente de formas trocáveis. Este trabalho objetivou investigar relações entre o Al extraído com solução de KCl e de oxalato de amônio com a mineralogia da fração argila. A quantificação do Al nos extratos de KCl e oxalato de amônio foi feita, respectivamente, por titulação com NaOH 0,02 mol L-1 padronizado e por espectrofotometria de absorção atômica. Foram utilizadas amostras de dois horizontes (A e B) de 12 perfis de solo de cinco estados brasileiros (AC, PE, BA, RS e SC), com diferentes características mineralógicas, todos com teores de Al-KCl superior a 4 cmol c kg-1 no horizonte B. Dois perfis de SC (Rancho Queimado e Curitibanos), com níveis mais baixos de Al-KCl, foram incluídos para comparação. Os altos teores de Al-KCl evidenciaram-se relacionados com a mineralogia dos solos estudados. Nos solos ácidos com mais esmectitas, drenagem moderada ou imperfeita e oscilação do lençol freático houve evidências morfológicas, confirmadas pelas análises mineralógicas, de que no clima atual ocorre um processo de destruição de argilas, liberando Al que precipita como compostos amorfos. A alta concentração salina da solução de KCl dissolve parcialmente tais compostos, superestimando as formas trocáveis desse elemento, principalmente nos horizontes subsuperficiais. Nos solos ácidos do ambiente subtropical, os teores de Al-KCl também foram altos, embora com valores mais baixos do que nos com predomínio de esmectitas. Parte do Al-KCl nesses solos parece provir da dissolução de compostos orgânicos e de Al presente em entrecamadas de argilominerais 2:1. Os resultados demonstraram que o KCl 1 mol L-1 não foi adequado para estimar o Al "trocável" na maioria dos solos estudados.

In acid soils of a more tropical environment containing smectites, as well as in highly buffered subtropical soils containing Al hydroxide interlayered smectite (HIS) or vermiculite (HIV), the values of exchangeable Al, extracted by KCl solution (Al-KCl), may be exceptionally high, but not always toxic to the crops. This "exchangeable" Al does not come solely from electrostatic sites. This study aimed to evaluate the relationship between the Al extracted from the soil by KCl and ammonium oxalate solutions, and clay mineralogy. Soil samples collected in both the A and B horizons of 12 profiles coming from five Brazilian states were used, showing different soil mineralogical characteristics, with Al-KCl always higher than 4.0 cmol c kg-1 in the B horizon. Additional samples from two highly weathered soils of the State of Santa Catarina (one Hapludult from Rancho Queimado and one Hapludox from Curitibanos) containing lower values of Al-KCl were also included. Al in the KCl and ammonium oxalate extracts was determined titrimetrically (with NaOH 0.02 mol L-1) and by atomic absorption spectroscopy, respectively. Al extracted by KCl was closely related to the soil clay mineralogy. In the acid soils containing higher quantities of smectites, deficient drainage, and oscillation of the groundwater level, mineralogical analysis showed morphological evidence of clay destruction with subsequent release of Al that precipitates in amorphous forms. The high electrolytic concentration of the KCl solution partially dissolves such Al compounds, overestimating the values of exchangeable Al, especially in the subsurface horizons. In the more weathered acid soils of the subtropical environment, the values of Al-KCl were also high, but lower than those found in soils with smectites as the main clay mineral. Part of the Al-KCl in these soils seems to come from the dissolution of organic compounds and also from Al located in the interlayer of 2:1 clay minerals. Thus, Al extracted by KCl 1 mol L-1 did not adequately estimate exchangeable Al in most of the soils studied.