Abstract The sewage sludge (SS) use in agriculture has been limited by the Brazilian legislation to a few situations, mainly as a precautionary measure due to inorganic pollutants and pathogens. Thus, a large amount of SS has been accumulated in landfills, with no prospect of use, generating great concern for governments and society. Thermal treatment via pyrolysis has stood out as an option for SS recycling, transforming it into a carbon-rich product known as SS biochar (SSB). Biochar from SS showed good potential to be used for agricultural and environmental purposes. The present study aimed to evaluate the influence of pyrolysis at 300°C on the physical, chemical, morphological and mineralogical characteristics of SSB. In general, pyrolysis increased total carbon, total nitrogen, macro and micronutrient contents, except potassium. Pyrolysis also increased heavy metals (HMs) concentration in SSB. However, HMs values remained below the maximum limits allowed according to the legislation on SS agricultural use. X-ray analysis showed that both SS and SSB present silica (SiO2) as the main mineral. Pyrolysis also increased the SS surface area (SA) and porosity. In general, results of the present study prove showed that pyrolysis is a technological alternative to enable SS use as a sustainable input in agriculture.

ABSTRACT: The Cerrado (Brazilian savannah) is a biome of great socio-economic and environmental importance to Brazil. The rapid agricultural expansion in the Cerrado biome areas promoted biogeochemical cycles that affect nitrogen and carbon dynamics, leading to increased greenhouse gas (GHG) emissions. In Brazil, nitrous oxide (N2O) is the main gas in agriculture, and agricultural practices increase emissions into the atmosphere. This review aimed to assess the influence of agriculture on N2O emissions in the Cerrado region, based on existing data in the literature, and extract patterns of direct N2O emissions in different agricultural systems in the Cerrado from existing data. A systematic review of data from 36 scientific publications in the Cerrado region with several crop systems revealed that N2O emissions varied from 0.15 kg ha-1 in native cerrado to 4.84 kg ha-1 in conventional tillage. Agricultural systems, nitrogen fertilizer application, and crop residues influence N2O emissions. One of the strategies to mitigate emissions is the sustainable intensification of farming systems. Cumulative N2O emissions in the Cerrado range from 0.001 to 4.84 kg ha-1 in different land-use scenarios. Soil under the conventional tillage system (CT) had the highest emissions, with an overall average of 1.58 kg ha-1 of N2O, compared to no-till system (NT) (0.82 kg ha-1) and native Cerrado 0.15 kg ha-1. Integrated crop-livestock (ICL) systems in the Cerrado had emissions with an overall average of 1.68 kg ha-1, integrated crop-livestock-forest systems (ICLF) had 1.20 ha-1, and eucalyptus plantations had 0.48 kg ha-1.

Abstract Biochar (BCH) is a solid product, rich in carbon, obtained by heating biomass under controlled conditions of oxygenation, in a process known as pyrolysis. Its benefits are associated with improvements to the physical, chemical and biological properties of soil. Furthermore, BCH can affect the growth of phytopathogenic microorganisms. Despite research advances in this area, there is still a lack of information on the effect of BCH concentration on different soilborne microorganisms. This work evaluated the direct effect of sewage sludge biochar (SSB) on the in vitro growth of different soilborne fungi. Eight phytopathogens [Fusarium oxysporum, F. oxysporum f. sp. lycopersici (CEN 1456), Macrophomina phaseolina (429), Sclerotinia sclerotiorum, S. sclerotiorum (CEN 1147), Sclerotium rolfsii (CEN 216), Sclerotium cepivorum (CEN 1357), Rhizoctonia solani] were evaluated. Additionally, a biological control agent [Trichoderma afroharzianum (T-22)] was also studied. Microorganisms were subjected to growth in PDA (Potato-Dextrose-Agar) culture medium enriched with SSB. Biochars, produced at 300 and 500 ºC, were applied at different doses: 0.0 (control), 0.2, 0.4, 0.6, 0.8 and 1.0 (g of SSB/100 ml of PDA). Biochars showed inhibitory effects on the mycelial growth of the different fungi evaluated. It was observed that there is a certain specificity of biochar concentration that must be evaluated for the control of phytopathogens. In most cases, the 0.4 and 0.6% concentrations had a greater inhibitory effect on phytopathogens and did not affect the biological control agent. Therefore, SSB proved to be a promising product for the control of different soilborne phytopathogens.

RESUMO No Cerrado, a maior parte dos solos possui baixa fertilidade natural. Para superar esta limitação, os agricultores empregam grandes quantidades de fertilizantes solúveis, gerando impactos ambientais. Objetivou-se avaliar a utilização de biotita sienito finamente moída (0, 600, 1.200, 1.800 e 2.400 kg ha-1) como fonte alternativa de nutrientes e cargas elétricas em Latossolo intemperizado do Cerrado. Adicionalmente, o desenvolvimento e nutrição de plantas de milho foram avaliados. Os valores de Ca + Mg, T, t, Zn, Cu, Fe e Mn no solo não foram afetados pela adição da biotita sienito, mas houve aumento no P e K disponíveis e nas cargas permanentes. A biotita não elevou os teores de P, Ca e Cu nas folhas do milho, mas aumentou os teores de N e K. Aumentos de 103, 125 e 128 % também foram detectados, respectivamente, na altura da planta, diâmetro do caule e matéria seca das folhas. A biotita sienito foi capaz de aumentar o P, K e as cargas permanentes do solo, bem como a absorção de N e K pelo milho, auxiliando no crescimento da planta.

ABSTRACT In the Brazilian Savanna, most of the soils have a low natural fertility. In order to overcome this limitation, farmers use large amounts of soluble fertilizers, causing environmental impacts. In the present study, finely ground biotite syenite (0; 600; 1,200; 1,800; and 2,400 kg ha-1) was evaluated as an alternative source of nutrients and electrical charges in a weathered Ferralsol from the Brazilian Savanna. Additionally, the development and nutrition of maize plants were analyzed. The values of Ca + Mg, T, t, Zn, Cu, Fe and Mn in the soil were not affected by the addition of biotite syenite, but the available P and K and the permanent charges were increased. The biotite did not increase the contents of P, Ca and Cu in the maize leaves, but it increased the contents of N and K. Increases of 103, 125 and 128 % were also detected, respectively, for plant height, stem diameter and leaf dry matter. The biotite syenite was able to increase the soil P, K and permanent charges, as well as the maize uptake of N and K, thus helping in the plant growth.

Resumo O uso de efluentes de esgoto tratado (EET) para fins de irrigação se destaca pelo reaproveitamento da água e pelo aporte de nutrientes ao solo, representando os dois principais benefícios ambientais. Assim, o objetivo deste trabalho foi avaliar o efeito da aplicação de EET sobre a quantidade de nutriente adicionado ao solo e alteração nos atributos químicos de um Latossolo Vermelho Amarelo na camada de 0,0 a 0,2 m, sob cultivo de pimentão, híbrido Canário F1, irrigado por gotejamento superficial. O experimento foi desenvolvido em condições de campo no período de setembro de 2015 a janeiro de 2016. O delineamento estatístico foi em blocos casualizados, com quatro repetições, com os seguintes tratamentos: água de córrego, EET, água de córrego com adubação de base, EET com adubação de base, EET com adubação de cobertura e EET com adubação de cobertura e de base, com quatro repetições. A irrigação com EET no cultivo de pimentão aumentou os teores de potássio, mas não afetou os teores de fósforo, matéria orgânica e o pH do solo ao final do ciclo de cultivo. Foram adicionados ao solo, por meio de irrigação com EET, 10 kg ha-1 de nitrogênio total,10 kg ha-1 de potássio total e 0,5 kg ha-1 de fosfato total. De maneira geral, a aplicação de EET promoveu maior produtividade de pimentão do que o uso de água de córrego, mesmo sob complementação de adubação mineral.

Abstract The use of treated sewage effluents (TSE) for irrigation purposes is a viable alternative for wastewater reuse and nutrient supply to the soil, which represent the two main environmental benefits. This work therefore evaluated the effect of the application of TSE on the quantity of nutrients added to the soil and changes in the chemical attributes of a Red-Yellow Latosol in the layer from 0.0 to 0.2 m cultivated with the bell pepper F1 Canary hybrid and surface drip irrigated. The experiment was carried out under field conditions from September 2015 to January 2016 in a randomized block statistical design with four replications, including the following treatments: river water, TSE, river water with base fertilization, TSE with base fertilization, TSE with cover fertilization, and TSE with cover and base fertilization. Irrigation of the bell pepper cultivation with TSE increased the level of potassium but did not affect the levels of phosphorus, organic matter and pH of the soil at the end of the growing cycle. The following amounts of nutrients were added to the soil by irrigation with TSE: 10 kg ha-1 of total nitrogen, 10 kg ha-1 of total potassium and 0.5 kg ha-1 of total phosphate. In general, TSE induced greater productivity of the peppers than those irrigated with river water, even when including mineral fertilization.

Abstract This study is based on the importance of biological control methods and the lack of information on the effect of biochar (BCH) from sewage sludge associated or not with Trichoderma harzianum on the control of Macrophomina phaseolina in the bean crop (Phaseolus vulgaris, cv. BRS Estilo). Biochar from sewage sludge, pyrolyzed at 500 ºC and used in low concentration (0.5%), has a direct effect on the in vitro control of M. phaseolina. However, higher BCH concentrations stimulated the growth of the pathogen. In culture medium with or without BCH, T. harzianum (strain 1306) inhibited the mycelial growth of M. phaseolina. The addition of BCH + T. harzianum reduced the deleterious effects caused by M. phaseolina on bean plants. This study demonstrated that joint application of BCH from sewage sludge + T. harzianum considerably increased the fresh and dry mass of bean plants, inoculated or not with M. phaseolina.

ABSTRACT The study of labile carbon fractions (LCF) provides an understanding of the behavior of soil organic matter (SOM) under different soil management systems and cover crops. The aim of this study was to assess the effect of different soil management systems with respect to tillage, cover crop and phosphate fertilization on the amount of the LCF of SOM. Treatments consisted of conventional tillage (CT) and no-tillage (NT) with millet as the cover crop and a no-tillage system with velvet bean at two phosphorus dosages. Soil samples were collected and analyzed for organic carbon (OC), C oxidizable by KMnO4 (C-KMnO4), particulate OC (POC), microbial biomass carbon and light SOM in the 0.0-0.05, 0.05-0.10 and 0.10-0.20 m soil layers. The Carbon Management Index (CMI) was calculated to evaluate the impacts of soil management treatments on the quality of the SOM. The different LCFs are sensitive to different soil management systems, and there are significant correlations between them. C-KMnO4 is considered the best indicator of OC carbon lability. In the soil surface layers, the CT reduced the carbon content in all of the labile fractions of the SOM. The use of phosphorus led to the accumulation of OC and carbon in the different soil fractions regardless of the tillage system or cover crop. The application of phosphate fertilizer improved the ability of the NTsystem to promote soil quality, as assessed by the CMI.

Resumo O objetivo deste trabalho foi avaliar o efeito de cultivos de milho (Zea mays) em monocultura e consorciado com forrageiras nas propriedades microbiológicas de solo e na disponibilidade de nitrogênio, em plantio direto, no Cerrado. O experimento foi realizado nas safras de 2007/2008 até 2010/2011, em Latossolo Vermelho-Amarelo distrófico. Utilizou-se o delineamento de blocos ao acaso, com três repetições e os seguintes tratamentos: milho em monocultura; milho em consórcio com Panicum maximum; milho em consórcio com Urochloa humidicola; P. maximum em monocultura; e U. humidicola em monocultura. Amostras de solos foram retiradas nas profundidades de 0,00-0,05, 0,05-0,10, 0,10-0,20 e 0,20-0,30 m, no início e no final da última safra. Os cultivos consorciados de milho aumentaram o nitrogênio disponível no solo, mas não alteraram os conteúdos totais de nitrogênio e carbono orgânico, quando comparado ao cultivo do milho em monocultura. O consórcio de milho com P. maximum aumentou o nitrogênio da biomassa microbiana e o quociente microbiano de nitrogênio no solo, em comparação ao milho em monocultura, bem como o carbono da biomassa microbiana, na camada superficial do solo, quando comparado ao consórcio com U. humidicola.

Abstract The objective of this work was to evaluate the effects of corn (Zea mays) in monoculture and intercropped with forage on soil microbiological properties and nitrogen availability under no-tillage in the Cerrado (Brazilian savanna). The experiment was carried out from the 2007/2008 to the 2010/2011 crop season, in a Latossolo Vermelho-Amarelo distrófico (Typic Haplustox). A randomized complete block design with three replicates was used, with the following treatments: corn in monoculture; corn intercropped with Panicum maximum; corn intercropped with Urochloa humidicola; P. maximum in monoculture; and U. humidicola in monoculture. Soil samples were taken at 0.00-0.05, 0.05-0.10, 0.10-0.20, and 0.20-0.30-m soil depths, in the begining and in the end of the last crop season. The intercropping systems of corn increased soil nitrogen availability, but did not alter total nitrogen and organic carbon contents in the soil, when compared to corn in monoculture. Corn intercropped with P. maximum increased soil microbial biomass nitrogen and microbial nitrogen quotient, in comparison to corn in monoculture, as well soil as microbial biomass carbon in the surface soil layer, when compared to corn intercropped with U. humidicola.

Resumo O objetivo deste trabalho foi avaliar indicadores da qualidade do solo, obtidos de diferentes bases de dados, para comparar sistemas de manejo do solo no Cerrado. Três critérios foram utilizados para a seleção de indicadores físicos, químicos e biológicos do solo: o conjunto completo de indicadores obtido, com 36 parâmetros, entre os quais todas as propriedades físicas, químicas e biológicas foram determinadas; um subconjunto de indicadores selecionados por análise de componentes principais (20 parâmetros); e um subconjunto de indicadores com alguma frequência de uso na literatura (16 parâmetros). Esses indicadores foram obtidos a partir dos seguintes sistemas de manejo: plantio direto, preparo convencional e cerrado nativo. As amostras de solo foram coletadas a 0,0-0,1 m de profundidade, e os indicadores de qualidade do solo foram submetidos à análise de variância e suas médias foram comparadas. A incorporação do solo de cerrado nativo à agricultura diminuiu a qualidade do solo. Os indicadores mais comumente utilizados na literatura científica são suficientemente sensíveis para detectar diferenças de qualidade do solo de acordo com o uso da terra. Portanto, a seleção de um conjunto mínimo de dados representativos pode ser mais útil do que um conjunto complexo de atributos, para comparar sistemas de manejo quanto à qualidade do solo.

Abstract The objective of this work was to assess soil quality indicators obtained with different datasets to compare soil management systems in the Brazilian Cerrado. Three criteria were used to select soil physical, chemical, and biological indicators: the full set of indicators obtained, with 36 parameters, for which all the physical, chemical, and biological soil properties were determined; a subset of indicators selected by principal component analysis (20 parameters); and a subset of indicators with some frequency of use in the literature (16 parameters). These indicators were obtained from the following management systems: no-tillage, conventional tillage, and native cerrado vegetation. Soil samples were collected at 0.0-0.1-m soil depth, and soil quality indicators were subjected to analysis of variance and their means were compared. The incorporation of soil native cerrado into agriculture decreased soil quality. The most commonly used indicators in the scientific literature are sensitive enough to detect differences in soil quality according to land use. Therefore, the selection of a minimum set of representative data can be more useful than a complex set of properties to compare management systems as to their soil quality.

Resumo O objetivo deste trabalho foi avaliar os efeitos de sistemas de manejo do solo, de plantas de cobertura e da fertilização fosfatada nas frações húmicas do solo, em experimento de longa duração. Os tratamentos consistiram de sistemas de preparo convencional e de plantio direto com milheto (Pennisetum glaucum) ou com mucuna-preta (Mucuna aterrima) como planta de cobertura, sob duas doses de fósforo: 0 e 100 kg ha-1 de P2O5 por ano. As amostras de solo foram coletadas após 11 anos da implantação do experimento e analisadas quanto aos teores de carbono orgânico total e de carbono das frações humificadas no solo, nas camadas de 0,00-0,05, 0,05-0,10 e 0,10-0,20 m de profundidade. As frações humificadas são sensíveis ao manejo do solo, exceto o ácido fúlvico livre, que foi a única que não diminuiu seus conteúdos de carbono na camada superficial do solo (0,00-0,05 cm) com o plantio convencional. As principais alterações ocorreram na camada superficial, em que o plantio direto com milheto como planta de cobertura promoveu os maiores teores de carbono nas frações húmicas. A fertilização fosfatada por longo tempo sob plantio direto, com milheto como planta de cobertura, promove o acúmulo de carbono orgânico nas frações húmicas do solo.

Abstract The objective of this work was to evaluate the effects of soil management systems, cover crops, and phosphate fertilization on soil humic fractions in a long-term experiment. The treatments consisted of conventional tillage and no-tillage with pearl millet (Pennisetum glaucum) or velvet bean (Mucuna aterrima) as cover crops, at two doses of phosphorous: 0 and 100 kg ha-1 P2O5 per year. Soil samples were taken 11 years after the establishment of the experiment and analyzed for soil total organic carbon and carbon content of humic fractions at 0.00-0.05, 0.05-0.10, and 0.10-0.20-m depths. The humic fractions are sensitive to soil management, except free fulvic acid, which was the only one that did not reduce its carbon contents on the surface layer (0.00-0.05 m) with conventional tillage. The main changes occurred on the soil surface layer, in which the no-tillage system with pearl millet as a cover crop provided the highest carbon levels in humic fractions. Long-term phosphate fertilization under no-tillage, with pearl millet as a cover crop, promotes the accumulation of organic carbon in soil humic fractions.

ABSTRACT Changes in carbon stocks in different compartments of soil organic matter of a clayey Latossolo Vermelho Distrófico (Typic Haplustox), caused by the substitution of native savanna vegetation (cerrado sensu stricto) by agroecosystems, were assessed after 31 years of cultivation. Under native vegetation, a stock of 164.5 Mg ha-1 C was estimated in the 0.00-1.00 m layer. After 31 years of cultivation, these changes in soil C stocks were detected to a depth of 0.60 m. In the case of substitution of cerrado sensu stricto by no-tillage soybean-corn rotation, a reduction of at least 11 % of the soil C pools was observed. However, the adoption of no-tillage as an alternative to tillage with a moldboard plow (conventional system) reduced CO2 emissions by up to 12 %.

ABSTRACT The use of cover crops has recently increased and represents an essential practice for the sustainability of no-tillage systems in the Cerrado region. However, there is little information on the effects of nitrogen fertilization and cover crop use on nitrogen soil fractions. This study assessed changes in the N forms in soil cropped to cover crops prior to corn growing. The experiment consisted of a randomized complete block design arranged in split-plots with three replications. Cover crops were tested in the plots, and the N topdressing fertilization was assessed in the subplots. The following cover species were planted in succession to corn for eight years: Urochloa ruziziensis, Canavalia brasiliensis M. ex Benth, Cajanus cajan (L.) Millsp, and Sorghum bicolor (L.) Moench. After corn harvesting, the soil was sampled at depths of 0.00-0.10 and 0.10-0.20 m. The cover crops showed different effects at different soil depths. The soil cultivated with U. ruziziensis showed higher contents of total-N and particulate-N than the soil cultivated with C. cajan. Particulate-N was the most sensitive to changes in the soil management among the fractions of N assessed. The soil under N topdressing showed a lower content of available-N in the 0.10-0.20 m layer, which may be caused by the season in which the sampling was conducted or the greater uptake of the available-N by corn.

As veredas são ecossistemas tropicais úmidos, geralmente associados a solos hidromórficos e afloramento do lençol freático. Os solos desses ecossistemas sofrem alterações conforme o uso das áreas do entorno dessas veredas. Este trabalho teve como objetivo determinar as frações da matéria orgânica do solo (MOS) em áreas úmidas (veredas) adjacentes a ambientes conservados e antropizados (em áreas agrícolas e pastagens), no bioma Cerrado. Amostras de solo foram coletadas nas profundidades de 0-10 e 10-20 cm, ao longo de linhas de referência dispostas, segundo sua posição no relevo, nas posições superior, média e inferior de uma das vertentes, acompanhando o sentido da linha de drenagem da vereda. Foram determinados o C orgânico total e N total do solo, bem como a relação C:N, teores de C, N e relações C:N das frações particulada e associada a minerais (da MOS), além do C das frações ácidos fúlvicos, ácidos húmicos e humina e relação entre ácidos húmicos e fúlvicos. O uso agropecuário da terra no entorno das veredas promoveu diminuição dos teores de C das frações da MOS, de forma mais pronunciada na porção inferior da vertente. Nessa porção, em superfície, os níveis de C orgânico contidos nas substâncias húmicas e na fração particulada da MOS, do mesmo modo que o C orgânico total do solo, foram reduzidos na vereda vizinha a áreas de cultivo.

Veredas are humid tropical ecosystems, generally associated to hydromorphic soils and a shallow water table. The soils of these ecosystems are affected by the use of the areas around these veredas. The objective of this study was to determine soil organic matter (SOM) fractions in veredas adjacent to preserved (native savanna) and disturbed environments (agricultural areas and pastures) in the Cerrado biome. Soil samples were collected from the 0-10 and 10-20 cm layers along reference lines drawn along the relief following the upper, middle and lower positions of one of the slopes, in the direction of the draining line of the vereda. The soil analysis determined: total soil OC, total nitrogen and C:N ratio; C and N contents and C:N ratio in particulate and mineral-associated fractions (of SOM); fulvic acids, humic acids and humin fractions and ratio between humic and fulvic acids. The agricultural use around the veredas induced changes in the SOM fractions, more pronounced in the lower part of the slope. In the soil surface of this part, the OC levels in the humic substances and the particulate fraction of SOM, as well as total soil OC were reduced in the vereda next to crop fields.

Plantas de coberturas são fundamentais para sustentabilidade do sistema de plantio direto em regiões tropicais. No entanto, ainda há pouca informação sobre os efeitos dessas plantas e da adubação nitrogenada sobre as frações da matéria orgânica do solo. O objetivo deste trabalho foi avaliar o efeito de plantas de cobertura com composição química diferenciada e da aplicação de N em cobertura nas frações lábeis e humificadas da matéria orgânica de um Latossolo sob plantio direto no Cerrado. O estudo foi realizado em delineamento de blocos ao acaso, com parcelas divididas e três repetições. Foram utilizadas quatro plantas de cobertura nas parcelas e presença ou ausência de fertilização nitrogenada em cobertura na subparcela. As seguintes plantas de cobertura foram utilizadas em sucessão ao milho, por oito anos: Urochloa ruziziensis ; Canavalia brasiliensis M. ex Benth; Cajanus cajan (L.) Millsp; e Sorghum bicolor (L.) Moench. Em geral, o uso da U. ruziziensis resultou nos maiores teores de C no solo com destaque para o C nas frações ácido húmico e C orgânico particulado, que são indicadores da qualidade da matéria orgânica do solo. O C das substâncias húmicas e o C orgânico associados aos minerais apresentaram as maiores proporções do C orgânico total e demonstraram a forte interação da matéria orgânica com os óxidos de Fe e Al e a caulinita, que predominam nesses solos intemperizados do Cerrado.

Cover plants are essential for the sustainability of no-tillage systems in tropical regions. However, information on the effects of these plants and N fertilization on soil organic matter fractions is still scarce. This study evaluated the effect of cover crops with different chemical composition and of N topdressing on the labile and humified organic matter fractions of an Oxisol of the Cerrado (savanna-like vegetation). The study in a randomized complete block design was arranged in split-plots with three replications. Four cover species were tested in the plots and the presence or absence of N topdressing in the subplot. The following cover species were planted in succession to corn for eight years: Urochloa ruziziensis; Canavalia brasiliensis M. ex Benth; Cajanus cajan (L.) Millsp; and Sorghum bicolor (L.) Moench. In general, the cultivation of U. ruziziensis increased soil C levels, particularly of C in the humic acid and particulate organic C fractions, which are quality indicators of soil organic matter. The C in humic substances and mineral organic C accounted for the highest proportions of total organic C, demonstrating the strong interaction between organic matter, Fe and Al oxides and kaolinite, which are predominant in these weathered soils of the Cerrado.

Several methods exist for determining soil organic carbon, and each one has its own advantages and limitations. Consequently, a comparison of the experimental results obtained when these methods are employed is hampered, causing problems in the comparison of carbon stocks in soils. This study aimed at evaluating the analytical procedures used in the determination of carbon and their relationships with soil mineralogy and texture. Wet combustion methods, including Walkley-Black, Mebius and Colorimetric determination as well as dry combustion methods, such as Elemental and Gravimetric Analysis were used. Quantitative textural and mineralogical (kaolinite, goethite and gibbsite) analyses were also carried out. The wet digestion methods underestimated the concentration of organic carbon, while the gravimetric method overestimated. Soil mineralogy interfered with the determination of carbon, with emphasis on the gravimetric method that was greatly influenced by gibbsite.