ABSTRACT Application of organic fertilizers of animal origin can increase organic carbon in the soil and increase its content in macroaggregates. This study aimed to evaluate carbon contents and fractions in two classes of soil aggregates in response to the application of organic and mineral fertilizers in an integrated crop-livestock system. The experiment was established in Concórdia, Santa Catarina State, in a Nitossolo Vermelho Eutroférrico típico, (Rhodic Kandiudox according to the WRB system) (0.00-0.05, 0.05-0.10, and 0.10-0.20 m), in an integrated crop-livestock, with corn and soybean in the summer, black oat and rye in the winter, shepherded by sheep. The design used was randomized blocks, with treatments in factorial design (5 × 3 + 1), with four replications, five sources of fertilizers, three rates and the control with no fertilization. Three organic fertilizers were applied: poultry litter, pig manure and compost; and two minerals fertilizers: M1 (formulated according to the composition of the pig slurry) and M2 (adjusted according to the composition of the poultry litter), combined with three applications rates, corresponding to 75, 100 and 150 % of the recommendation for the crop of interest, based on the element with greater demand. Total organic carbon (TOC), particulate (POC) and mineral-associated organic carbon (MAC) contents were determined in two classes of soil aggregates C1 (8.00 to 4.76 mm) and C2 (4.76 to 2.00 mm), in samples collected in the 2018/2020 crop season. Crop yields were determined in every season. The results were analyzed using analysis of variance to compare sources and polynomial regression analysis for fertilizer rates. The soil has high aggregate stability, even so, the use of organic and mineral fertilizers increased aggregation. The poultry litter organic fertilizer increases aggregation, forming largely aggregates with a size of 8.00-4.76 mm, and increases the contents of total fractions of soil organic carbon, providing the system with a more stabilized carbon. In the 0.00-0.05 m layer, organic fertilizers increased the content of total organic carbon. The stabilized fraction (MAC) showed a higher proportion of total soil organic carbon than particulate organic carbon (POC).

ABSTRACT The use of organic fertilizers from pig slurry and poultry litter can increase soil organic carbon and crop productivity. This study aimed to evaluate soil organic carbon fractions and corn yield after applying organic and mineral fertilizers. The experiment was conducted in the western region of Santa Catarina State, southern Brazil on a Nitossolo Vermelho Eutroférrico típico (Rhodic Kandiudox). The production system was an integrated crop-livestock using corn and soybean in the summer and black oat and rye with grazing by sheep in the winter. The experimental design was randomized blocks, with treatments in factorial 5 × 3 + 1, with four replications, five sources of fertilizers, three rates and the control with no fertilization. The treatments were three organic fertilizers: poultry litter, pig slurry and compost from pig slurry and two minerals fertilizer (M1 and M2). Mineral fertilizers were formulated from pig slurry (M1) and poultry litter (M2), with the application of three rates, which represent 75, 100 and 150 % of the recommendation for the crop, based on the element that is most demanding by the plant (K for soybeans and N for corn). Soil samples were collected at the layers of 0.00-0.05, 0.05-0.10 and 0.10-0.20 m in which fractions of total soil organic carbon (TOC), namely particulate (POC) and mineral-associated organic carbon (MAC) were determined. Corn yield was evaluated in the 2018/2019 and 2019/2020 seasons. The results were analyzed through analysis of variance to compare sources and polynomial regression analysis for fertilizer rates. The MAC fraction has a higher proportion of TOC and its contents were higher with increasing rates of organic and mineral fertilizers, mainly in the surface layer. Poultry litter and compost fertilizers increased TOC’s particulate fraction (POC), showing the highest levels at the highest fertilization recommendation rate. Organic and mineral fertilizers positively increase corn yield, and animal-derived fertilizers show that they can be an alternative for high crop yields.

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 The conservation tillage systems is based on the surface protection by crop residue and reduced soil disturbance. These two principles can favor the soil quality and promote sustainable agricultural systems. The study was developed with the objective of measure soil microbial biomass, soil basal respiration, enzymatic activity and soybean yield in conservation systems cultivated with cover crops species in the Northeastern Cerrado. The experiment was carried out in 2016/2017 and 2017/2018 cropping seasons, performed in a randomized blocks design. The treatments were soil tillage systems allocated in the main plots: no-tillage (NT) and minimum tillage (MT) and the cover crops were allocated in the subplots: Pennisetum glaucum (millet), Urochloa ruziziensis (brachiaria), Crotalaria spectabilis (C. spectabilis), Crotalaria ochroleuca (C. ochroleuca), Pennisetum glaucum + Crotalaria spectabilis (millet + C. spectabilis) and spontaneous plants with three replicates. The evaluated variables were dry mass (DM) production and nutrient accumulation in cover crops; soil biological properties, namely microbial biomass carbon and nitrogen (MBC and MBN, respectively), respiration, metabolic quotient (qCO2), dehydrogenase enzymatic activity (DH), fluorescein diacetate (FDA); and soybean yield. The higher production of dry mass and nutrient cycling occurs with the intercropping millet + C. spectabilis and single millet. The highest soybean yield occurs in succession to C. ochroleuca and intercropping of the millet + C. spectabilis. Cover crops in conservation systems improve soil microbial quality and increase soybean yield.

Resumo Os plantios de espécies florestais exóticas vêm aumentando em áreas cobertas por vegetação nativa na região nordeste do Rio Grande do Sul, o que pode alterar as dinâmicas dos nutrientes no solo. Dessa maneira, o objetivo deste estudo foi avaliar os efeitos da mudança de uso da terra sobre pH e teores de carbono orgânico total (COT), Al3+, Ca2+, Mg2+ e K+ em Cambissolo Húmico, em plantios realizados em área de campo nativo. As áreas analisadas foram pinus plantado em 1963 (P) e eucalipto em 1991 (E), comparativamente a áreas adjacentes remanescentes: de campo nativo em regeneração natural a partir de 1990 (RN), mata nativa (MN) e campo nativo (CN). As amostras de solo foram coletadas nas profundidades de 0-5, 5-10 e 10-20 cm, em oito pontos para cada área avaliada, com cálculo de médias e intervalos de confiança (95%). Em geral, CN e MN apresentaram os maiores valores de COT. O plantio “P” apresentou em relação ao CN menores teores de COT, Ca e K na camada 0-10 cm, enquanto o plantio “E” apresentou menores teores de COT em relação ao CN, indicando efeitos negativos da floresta plantada em relação à vegetação natural campestre quanto à ciclagem de carbono e nutrientes. A área RN apresentou valores desses atributos similares aos do CN e MN. Avaliações em longo prazo são importantes para verificar influências do cultivo florestal sobre atributos do solo e identificar a sustentabilidade das formas de uso do solo.

Abstract The planted forests using exotic trees are increasing areas and have replaced native vegetation in the southern Brazilian highlands, which can change the dynamics of soil nutrients. The objective was to evaluate the effects of the land use change on pH and total soil organic carbon (COT), Al3+, Ca2+, Mg2+ e K+ contents on a Humic Dystrudept under plantations established in native grassland area. The land uses evaluated were pinus established in 1963 (P) and eucalyptus planted in 1991 (E), comparatively to adjacent areas of native grassland (NP), natural regeneration since 1990 (NR), and native forest (NF). Soil samples were collected at 0-5, 5-10 and 10-20 cm depth, in eight replicates for each land use to calculate means and confidence intervals (95%). In general, NP and NF showed the highest values of TOC. “P” stand compared to NP had lower TOC, Ca and K in the 0-10 cm layer, indicating negative effects of forest plantations in comparison with natural grassland in relation to carbon and nutrient cycling. NR area showed similar values of those properties in relation to NP and NF areas. Long-term evaluations are important to verify influences of forest plantations on soil properties and identify the sustainability of these land use forms.

Abstract This study aimed to evaluate the abundance and diversity of Coleoptera in five land use systems (LUS) and the soil properties that explain the distribution of these organisms. Uses involved native forest (NF), Eucalyptus plantation (EP), perennial pasture (PA), integrated crop-livestock (ICL) and no-tillage (NT) in western Santa Catarina, Brazil. Coleopterans were sampled by the methods of pitfall traps and soil monoliths during the winter and summer. Regardless of the LUS, 1,441 individuals were captured, with Staphylinidae being the most representative family (~47%). The use of NF showed higher abundances of coleopterans. The land use systems PA, NT, and ICL obtained high values of diversity of Coleoptera families, depending on the method and season of collection. The distribution of families was influenced by the sampling season, and some soil properties such as biopores, water content and phosphorus can explain the variation of abundance among the LUS.

Resumo O plantio de pinus em áreas de campo natural (NG) pode alterar as formas e estoques de carbono orgânico (OC) do solo. Visando quantificar essas alterações, foram determinados os teores e estoques de OC total (TOC) e das frações particulada (POC) e associadas aos minerais (MAC) em cinco camadas, entre 0,0 e 0,4 m de profundidade, do solo sob usos com NG e plantios de pinus aos cinco (P5), 16 (P16) e 21 (P21) anos. O estudo foi realizado em áreas de Cambissolo Húmico na região do planalto sul de Santa Catarina. O teor de TOC, nas diferentes camadas e usos, variou entre 15,0 e 44,5 g kg-1 e seu estoque, na soma das camadas, entre 86 e 144 Mg ha-1. O teor de POC variou entre 2,1 a 23,2 g kg-1 e seu estoque, entre 7,4 e 21,8 Mg ha-1, enquanto o teor de MAC variou entre 12,2 e 23,7 g kg-1 e seu estoque, entre 79 e 122 Mg ha-1. Em geral, os teores e estoques de TOC e das frações MAC e POC do solo aumentam com a idade dos plantios de pinus até 21 anos. Os teores de TOC e POC e o estoque dessa fração, em geral diminuem com a profundidade do solo sob NG e P5 e P21, mas o teor de MAC e os estoques dessa fração e do TOC geralmente não variam entre as camadas até 0,40 m de profundidade.

Abstract Pine plantations on former natural grassland (NG) areas can change the forms and stocks of organic carbon (OC) in the soil. To quantify these changes, the contents and stocks of the total OC (TOC), consisting of particulate OC (POC) and the mineral-associated OC (MAC) fractions, were determined in five layers, at depths between 0.0 and 0.40 m, in soil under NG and pine plantations aged five (P5), 16 (P16) and 21 (P21) years. The study was carried out in areas of Cambissolo Húmico, dystrophic, on the southern plateau of Santa Catarina state. The TOC content in the different layers and under different land uses ranged from 15.0 to 44.5 g kg-1 and the TOC stock, in all layers together, from 86 to 144 Mg ha-1. The POC content varied from 2.1 to 23.2 g kg-1 and the POC stock from 7.4 to 21.8 Mg ha-1, while the MAC content varied between 12.2 and 23.7 g kg-1 and MAC stock between 79 and 122 Mg ha-1. In general, the TOC stocks and contents and MAC and POC fractions in the soil increase with the age of the pine plantations up to 21 years. The TOC and POC contents and POC stock usually decrease with depth under NG, P5 and P21, whereas the MAC content and MAC and TOC stocks generally remain unchanged in layers to a depth of 0.40 m.

ABSTRACT Use of organic fertilizers in integrated crop-livestock (iCL) systems may affect soil phosphorus fractions. This study aimed to determine phosphorus fractions in the soil under the iCL system after six years of application of organic or mineral fertilizers. The experiment was conducted on a Rhodic Kandiudox (Nitossolo Vermelho Distroférrico) in a randomized block design, using a 5 × 3 + 1 factorial scheme, with four replicates. The treatments consisted of three organic fertilizers (poultry litter, pig slurry, and compost) and two mineral fertilizers (M1, equivalent to pig slurry; and M2, equivalent to poultry litter) in interaction with three application rates, corresponding to 75, 100, and 150 % of the fertilizer recommendation for the crop of interest and a control (with no fertilizer). Soil sampling was performed in the 0.00-0.05, 0.05-0.10, and 0.10-0.20 m layers for determination of the phosphorus fractions. Successive use of organic or mineral fertilizers for six years in the iCL system considerably raises the labile and moderately labile P fractions up to the 0.20 m depth and, with less intensity, raises the non-labile fractions up to the 0.10 m depth. The soil P increase associated with fertilizer input raises soybean and corn yields, and it does not exceed the critical P limit according to local environmental legislation.

Resumo: O objetivo deste trabalho foi avaliar o efeito da aplicação de fertilizantes organominerais e minerais em solos com fertilidade construída sobre o índice de manejo de carbono (IMC) e as frações e o estoque de carbono. O experimento foi realizado em um Cambissolo e em um Nitossolo sob sistema plantio direto, por três anos agrícolas. Os tratamentos consistiram de dois fertilizantes organominerais e de dois fertilizantes minerais nas formas sólidas e fluídas, além do controle sem adubação. A aplicação de fertilizantes organominerais e minerais, nas formas sólidas e fluídas, às diferentes classes de solo com fertilidade construída, promoveu alterações no carbono orgânico total, particulado e associado aos minerais, bem como nos estoques de carbono e no IMC. Nos tratamentos com fertilizante mineral fluído e fertilizante organomineral sólido, houve alterações apenas no Cambissolo, em razão do menor grau de intemperização deste solo. Os maiores valores do IMC, com fertilizante mineral fluido no Cambissolo, permitem inferir sobre qual seria a melhor prática de manejo para o aumento e a manutenção de carbono no sistema solo-planta, justificada pelos resultados de produtividade de trigo, sorgo e milho, que foram semelhantes aos obtidos com os outros fertilizantes.

Abstract: The objective of this work was to evaluate the effect of the application of organomineral and mineral fertilizers to highly fertile soils on the carbon management index (CMI) and carbon fractions and stock. The experiment was carried out on an Oxisol and Inceptisol, under no-tillage, in three crop seasons. The treatments consisted of two organomineral fertilizers and of two mineral fertilizers in solid and fluid forms, besides a control without fertilization. The application of organomineral and mineral fertilizers, in solid and fluid forms, to the different soil classes with high fertility promoted changes in total organic carbon, particulate organic carbon, and carbon associated with minerals, as well as in carbon stocks and the CMI. In the treatments with fluid mineral fertilizer and solid organomineral fertilizer, such changes occurred only in the Inceptisol due to the lower degree of weathering of this soil. The higher values of the CMI, with the fluid mineral fertilizer in the Inceptisol, allow inferring on which would be the best management practice aiming at the increase and maintenance of carbon in the soil-plant system, based on the yield results of wheat, sorghum, and corn, which were similar to those obtained with the other fertilizers.

ABSTRACT Studies of the successive application of manure as fertilizer and its combined effect with long-term soil management systems are important to the identification of the interdependence of physical attributes. The aim of this study was to evaluate changes in the physical properties of a Rhodic Kandiudox under management systems employing successive applications of pig slurry and poultry litter, and select physical indicators that distinguish these systems using canonical discriminant analysis (CDA). The systems consisting of treatments including land use, management and the application time of organic fertilizers are described as follows: silage maize under no-tillage (NT-M7 years); silage maize under conventional tillage (CT-M20 years); annual pasture with chisel plowing (CP-P3 years); annual pasture with chisel plowing (CP-P15 years); perennial pasture without tillage (NT-PP20 years); and no-tillage yerba mate (NT-YM20 years) and were compared with native forest (NF) and native pasture (NP). Soil samples were collected from the layers at the following depths: 0.0-0.05, 0.05-0.10, and 0.10-0.20 m, and were analyzed for bulk density, porosity, aggregation, flocculation, penetration resistance, water availability and total clay content. Canonical discriminant analysis was an important tool in the study of physical indicators of soil quality. Organic fertilization, along with soil management, influences soil structure and its porosity. Total porosity was the most important physical property in the distinction of areas with management systems and application times of manure for the 0.0-0.05 and 0.10-0.20 m layers. Soil aeration and micropores differentiated areas in the 0.05-0.10 m layer. Animal trampling and machinery traffic were the main factors inducing compaction of this clayey soil.

RESUMO Objetivou-se avaliar a influência da estruturação espacial e de variáveis ambientais sobre a organização florístico-estrutural do componente arbóreo em uma Floresta Ombrófila Mista Aluvial no sul do Brasil. Para isso, foram alocadas 48 parcelas de 200 m2 no remanescente amostrado, localizado em Lages-SC. Todos os indivíduos dentro das parcelas com diâmetro na altura do peito (DAP) igual ou superior a 5 cm foram identificados. Foram mensuradas variáveis ambientais e espaciais em cada parcela. Os dados foram analisados por meio de Correlograma de Mantel, Particionamento da Variância, Análises de Redundância, análise de Coordenadas Principais de Matrizes Vizinhas e testes de correlação. Foram amostrados 1.462 indivíduos pertencentes a 66 espécies. Conjuntamente, as variáveis ambientais e espaciais explicaram 24,13% da variação total, sendo que a maior parte (15,22%) se encontrou espacialmente estruturada. Dentre as variáveis ambientais, a topografia (desnível máximo) e a fertilidade do solo (soma de bases e P) foram significativas. Conclui-se que o componente arbóreo está organizado na forma de um gradiente florístico-estrutural. Ainda, os resultados sugerem que o regime de inundação do rio e a presença de zonas de maior encharcamento do solo foram relevantes na definição de micro-hábitat, que influenciaram na distribuição das espécies.

ABSTRACT This study aimed to evaluate the influence of spatial structure and environmental variables on floristic-structural organization of the tree component, in an Alluvial Araucaria Forest, in southern Brazil. To do so, 48 200 m2 sampling units were allocated in the study area, located in the municipality of Lages, SC state. All trees within the sampling units, with diameter at breast height (dbh) equal to or greater than 5 cm were identified. The environmental and spatial variables were measured in each sampling unit. The data were analyzed through Mantel Correlogram, Variation Partitioning, Redundancy Analysis, analysis of Principal Coordinates of Neighbor Matrices and correlation tests. A total of 1,462 individuals, belong to 66 species, were sampled. Together, the environmental and spatial variables explained 24.13% of total variation, with the largest part (15.22%) being spatially structured. The significant environmental variables were topography (maximum elevation difference) and fertility (bases sum and P). It is possible to conclude that the tree component is organized as a floristic-structural gradient. Furthermore, the results suggest that the inundation regime and the presence of flood prone areas were relevant for micro-habitat definitions, that influenced the distribution of species.

Resumo: O objetivo deste trabalho foi avaliar as aplicações superficial e injetada de dejeto líquido de suínos e ureia ao solo, quanto aos seus efeitos sobre as propriedades físicas de um Nitossolo Vermelho distroférrico, em um sistema de semeadura direta. Os tratamentos foram: dejeto injetado no sulco, com injetor de dejeto líquido de suínos (IDLS); dejeto em superfície, aplicado às linhas com o IDLS erguido; ureia injetada, por meio de abertura do sulco com o IDLS, e distribuída manualmente; e milho, em semeadura direta, como controle. A semeadura e a injeção de dejeto líquido ou de ureia não modificam o teor de carbono orgânico, o pH e a agregação, mas alteram a densidade e a porosidade do solo na linha mobilizada, e aumentam os macroporos.

Abstract: The objective of this work was to evaluate the superficial and injected applications of swine slurry and urea to the soil, regarding their effects on the physical properties of a Nitossolo Vermelho distroférrico under a no-tillage system. The treatments were: injected slurry into the groove with a liquid swine slurry injector (LSSI); slurry on surface, applied on the lines by the LSSI kept raised; urea injected by opening the groove with the LSSI and distributed manually; and corn, under no-tillage, as a control. Sowing and the injection of liquid slurry or urea do not modify the organic carbon content, pH, and aggregation, but alter the soil bulk density and porosity in the mobilized line, and increase the macropores.

ABSTRACT: Springtails (Collembola) are soil organisms with wide morphological diversity and are sensitive to alterations in the soil, regardless of whether they are human-caused or not. The aim of this study was to evaluate the influence of land use on the morphological diversity of springtails and verify their relationships with soil physical, chemical, and microbiological properties. Samples were collected in the eastern region of Santa Catarina, in three municipalities: Joinville, Blumenau, and Timbó. They included the following land use systems (LUSs): native forest (NF), Eucalyptus plantation (EP), pasture (PA), integrated crop-livestock (ICL), and no tillage (NT). Samples were collected to determine soil properties, and pitfall traps were set in the winter and summer at the same points. The captured springtails were counted and morphotyped, observing features such as presence or absence of ocelli and setae, pigmentation, antenna length, and furcula length. The data were analyzed based on abundance, the Shannon-Wiener (H') and Margalef diversity indices, Pielou's evenness index (J), morphotype richness, modified Soil Biological Quality index (QBS), and Principal Component Analysis (PCA). Springtails abundance was higher in ICL and PA, whereas morphotype richness was higher in NF and ICL in the winter. The Shannon-Wiener and Margalef indices were higher in the winter in NF. In the summer, only H' differed significantly among the LUSs and was higher in NF. The QBS values did not precisely follow the human intervention gradient in either of the two periods. The PCA showed difference among the periods and LUSs. In the winter, the occurrence of morphotypes was related to soil microbiological and chemical properties, whereas in the summer, the distribution of morphotypes was explained by soil physical and chemical properties. Morphological diversity analysis is a good alternative to study springtail distribution and soil biological quality, especially when associated with multivariate techniques.

ABSTRACT Changes in land use management in agricultural areas can affect the biodiversity of spider families. This study aimed to evaluate spider diversity in different land use systems with capture by two sampling methods, and to identify soil properties that can modulate the occurrence of spiders. Five land use systems, representative of traditional agricultural areas, were evaluated in the west of Santa Catarina, Brazil, to establish a scale of land use intensity: native forest, eucalyptus reforestation areas, pastures, crop-livestock integration areas, and annual crops under no-tillage. The collection methods were manual from soil monoliths and soil traps. Altogether 479 individuals were captured, which were distributed among 20 families, 40 genera, and 8 species. Principal component analysis separated the land use systems and showed an association of spider families with land use in the two sampling methods. There was reduction in spider diversity as the intensity of land use increased. The manual collection method was more efficient for families of soil spiders, whereas traps were more efficient for epigeic spiders. The Lycosidae family was more resistant to environmental pressures, while Oonopidae and Amaurobiidae were more sensitive to environmental modifications. The differences in the spider communities were explained by the following soil properties: organic matter, mean weight-diameter of soil aggregates, and resistance to penetration, which were associated with the degree of anthropic intervention in the land use systems.

RESUMO Devido à grande área ocupada com reflorestamentos de pinus no sul do Brasil, considera-se necessário avaliar o impacto dessa cultura no estoque de carbono orgânico do solo, especialmente com relação às frações das substâncias húmicas (SH). Nesse contexto, o presente trabalho teve como objetivo avaliar as alterações na quantidade e proporção das substâncias húmicas da matéria orgânica em solo representativo do Planalto Catarinense devido à substituição da vegetação natural por povoamentos de Pinus taeda. Foram avaliadas quatro situações de uso em áreas localizadas no município de Ponte Alta, sendo uma de campo natural (CN) e três plantios de Pinus taeda com idades de 5 (P05), 16 (P16) e 21 (P21) anos em segunda rotação, em solo classificado como Cambissolo Húmico distrófico. Amostras de solos compostas por sete sub amostras foram coletadas em sete pontos amostrais dentro de cada área nas camadas de 0-5 cm, 5-10 cm, 10-20 cm, 20-30 cm e 30-40 cm de profundidade. Os teores de carbono das SH da matéria orgânica do solo (MOS) foram determinados através de fracionamento químico resultante da solubilização em meios ácido e básico. Os teores e proporções das SH da MOS variaram significativamente em função da situação de uso e profundidade analisados, evidenciando maiores quantidades na camada superficial e seu aumento com a idade do pinus. Em geral, os maiores valores de C nas frações e camadas avaliadas foram observados no P21 e os menores no P05.

ABSTRACT Due to the great area occupied with Pinus sp. plantations in southern Brazil, it is considered necessary to evaluate the impact of this kind of crop on soil organic carbon stock, specially related to fractions from humic substances (HS). On this context, this work aims to evaluate the changes on humic substances quantity and the proportion of organic matter on representative soil of the highlands in Santa Catarina state due to replacement of natural grassland by Pinus taeda stands. Four situations of soil use on areas located in Ponte Alta town were evaluated, being one of natural grasslands(CN) and tree of Pinus taeda forests with 5 (P05), 16 (P16) and 21 (P21) years old on second rotation, on soil classified as Humic Dystrupept. Soil samples composed by seven subsamples were collected on seven points inside every area in the 0-5 cm, 5-10 cm, 10-20 cm, 20-30 cm, 30-40 cm layers. The carbon contents of HS in the SOM were determined by chemical fractionating resulted from alkaline or acid extraction. The HS contents and proportions varied according to the soil use and depth analyzed, showing more quantity in the surface layer and its increasing with pinus age. In general, the highest levels of C on fractions and layers evaluated were observed on P21 and the lowest on P05 uses.