ABSTRACT Subsistence hunting is the main source of protein for forest reserve dwellers, contributing to the development of spurious infections by Calodium hepaticum, frequently associated with the consumption of the liver from wild mammals. The prevalence of infections by soil-transmitted helminths (STHs) and intestinal protozoa is considered an indicator of the social vulnerability of a country, besides providing information on habits, customs and quality of life of a given population. Intestinal parasites mostly affect poor rural communities with limited access to clean water and adequate sanitation. This study reports the results of a parasitological survey carried out in 2017 and 2019, in two municipalities (Xapuri and Sena Madureira) in Acre State. Stool samples were collected from 276 inhabitants. Upon receipt, each sample was divided into two aliquots. Fresh samples without preservative were processed and examined by the Kato-Katz technique. Samples fixed in 10% formalin were processed by the spontaneous sedimentation and the centrifugal sedimentation techniques. Calodium hepaticum eggs were found in three stool samples. The overall STH prevalence was 44.9%. The hookworm prevalence (19.2%) was higher than that of Ascaris lumbricoides (2.5%) and Trichuris trichiura (0.7%), an unexpected finding for municipalities belonging to the Western Brazilian Amazon. When considering parasites transmitted via the fecal-oral route, Endolimax nana and Entamoeba coli showed the highest positivity rates, of 13% and 10.9%, respectively. This study is the first report of spurious infection by C. hepaticum among forest reserve dwellers that consume undercooked liver of lowland pacas. Additionally, this is the first report of Blastocystis sp. in Acre State.

RESUMO: As divergências no temperamento dependem da reação dos animais às pessoas e à diferentes situações sociais e ambientais. Contudo, pouco se sabe acerca da influência de alterações no ambiente pastoril sobre o temperamento dos bovinos. Com isso, a hipótese de trabalho é de que o temperamento dos animais pode ser alterado se mantidos em sistemas pastoris arborizados. Para tanto, objetivou-se avaliar o efeito do componente arbóreo em ambiente pastoril sobre o temperamento de bovinos em pastejo em sistemas integrados de produção agropecuária. Foram avaliados 32 novilhos da raça Angus alocados em dois sistemas pecuária (PEC) e pecuária-floresta (PF) durante o período de dezembro de 2019 a fevereiro de 2020, no qual foi mensurado: o escore de reatividade dos animais; a velocidade de fuga e o número de vocalizações. O modelo estatístico utilizado considerou como efeito fixo de tratamentos e períodos e efeitos aleatórios dos animais, utilizando o procedimento MIXED, as médias foram comparadas pelo recurso lsmeans. A velocidade de saída e número de vocalizações foram similares entre os sistemas de produção. O escore de reatividade foi menor para os animais mantidos no sistema PF quando comparados aos do tratamento PEC. O sistema PF interfere positivamente no temperamento animal em relação ao sistema de produção PEC, observado pelo menor escore de reatividade nos animais mantidos neste sistema. Contudo, o estudo sobre a influência da integração de sistemas sobre o temperamento animal exige mais pesquisas para revelar o potencial deste modelo de produção sobre o comportamento animal.

ABSTRACT: Temperament often depends on the animals’ reaction to people, social and environmental conditions. However, little is known about the influence of changes in the pasture environment on cattle temperament. Thus, this study was designed to evaluate if an animals’ temperament changes in response to being kept in a silvopastoral system. This study evaluated the effect of the tree components in a pasture environment on the temperament of any grazing cattle in integrated crop-livestock systems. A total of thirty-two Angus steers were allocated to either a livestock (L) or livestock-forest (LF) system and observed from December 2019 to February 2020. Each animal was evaluated for their reactivity score, flight speed, and number of vocalizations. The statistical model established that the animals were random effects and that the treatments and periods were fixed effects using the MIXED procedure, and the means were compared using LSMeans. The flight speed and number of vocalizations were similar in both production systems, while the reactivity score was lower for animals kept in the LF system when compared to those in the L system. This suggested that the LF system interferes positively with the animal’s temperament in relation to the L production system. However, additional research is needed to understand the influence of the production system on animal temperament.

RESUMO: Este estudo teve como objetivo avaliar a estrutura da vegetação e o desempenho de novilhas em recria e vacas de descarte em pastagens naturais manejadas em sistema de pastejo rotacionado com lotes “ponta” e “rapador” no período primavera-verão. Os tratamentos foram diferentes intervalos de descanso de 402 e 252 graus-dia (GD), os quais favorecem o crescimento de gramíneas de diferentes grupos funcionais. O delineamento experimental foi em blocos ao acaso com dois tratamentos e três repetições. Os animais de teste foram 24 novilhas no grupo “ponta” e 24 vacas no grupo “rapador”. No estrato entre touceiras, as alturas do pasto maiores que 16 cm foram predominantes em ambos os tratamentos, sendo 1.3 vezes mais frequente no tratamento 402 GD em relação ao tratamento 252 GD. A taxa de lotação média foi 22% maior no tratamento com 252 GD. Embora não tenham sido observadas diferenças para o ganho médio diário de novilhas (0,227 kg.dia-1) e vacas (0,336 kg.dia-1) entre os tratamentos, o ganho de peso por área no período experimental foi maior no tratamento 252 GD. Apesar do sistema de manejo com lotes “ponta” e “rapador” não proporcionar mudanças significativas na estrutura da pastagem, ele permite atingir metas de desempenho satisfatórias em áreas de pastagens naturais.

ABSTRACT: This study evaluated the structure of vegetation and the performance of rearing heifers and cull cows in Campos grasslands managed in the rotational stocking method with first-last stocking in the spring-summer period. The treatments were different rest intervals of 402 and 252 degrees-day, which favor the growth of different functional groups of grasses. A completely randomized block design with two treatments and three repetitions was used. The test animals were 24 heifers in the “first” group and 24 cows in the “last” group. In the stratum between tussock grasses, sward heights greater than 0.16 m were predominant in both treatments, it was 1.3 times more frequent in the 402 DD treatment compared to the 252 DD treatment. Average stocking rate was 22% higher in the 252 DD treatment. Although, no differences were observed for the average daily gain of heifers (0.227 kg.day-1) and cows (0.336 kg.day-1) between treatments, the weight gain per area in the experimental period was greater in the 252 DD treatment. Despite the management system with first and last stoking does not provide significant changes in the structure of the pasture, it allowed to achieve satisfactory performance goals in areas of Campos grassland.

ABSTRACT High acidity and low soil P availability in the soils from the Pampa natural grasslands generally limit the forage growth and economic return. Thus, to increase the economic return and avoid environmental degradation and biodiversity loss due to replacement by intensive cropping systems, it is essential to improve the soil P availability. This study aimed to diagnose the nutritional status of the pluri-specific natural grasslands amended with different history of P sources. Additionally, we also try to indicate the most appropriate range of soil P availability for maximizing forage growth. The experiment started in 1997 in an area of Pampa natural grasslands in the state of Rio Grande do Sul, Brazil. The treatments evaluated the application of Gafsa hyperphosphate (HP) and triple superphosphate (SP) for four years (1997, 1998, 2002, and 2010). Soil and aboveground biomass sampling were performed five times from October 2010 to March 2011 to access aboveground biomass production, botanical composition, soil available P, and N and P nutrition index. Greater P availability in the soil amended with SP produced more forage and resulted in a higher P accumulation than in the soil amended with HP. The ideal range of soil P availability in the soils of natural grasslands ranged from 14 to 20 mg kg˗1, varying for different plant species. The species Paspalum plicatulum and Aristida laevis produce less aboveground biomass and accumulate less P in their tissue than Dichantelium sabulorum and Eustachys uliginosa, and P. notatum. Therefore, areas of natural grasslands dominated by D. sabulorum, E. uliginosa and P. notatum demand higher soil P availability to maintain high forage production. Soil P fertilization of pluri-specific natural grasslands in the Brazilian Pampa biome must consider the dominant forage species in the area and the soil P availability.

ABSTRACT South American natural grasslands are composed of several species with different growth strategies, with variations in specific leaf area (SLA), leaf dry matter content (LDMC), specific root length (SRL) and specific root area (SRA). The objective of this study was characterizing in grasses cultivated with different levels of phosphorus (P) in the soil if species with higher leaf and root area production per unit of dry matter have higher tissue P concentration, P use efficiency and higher dry matter yield. The plant species were grown in a greenhouse in pots with 5 kg of soil in a completely randomized design with four replicates and two conditions of P availability: addition of 60 mg kg-1 soil and without addition of P. The species with the highest SRA had a higher leaf and root P concentration. The higher production of leaf or root surface area per unit of dry matter did not represent higher tissue P use efficiency. The group formed by species of genre Paspalum had a higher leaf and root P use efficiency, therefore, areas composed of this genre are preferred for P fertilization.

Abstract Background: South American rattlesnakes are represented in Brazil by a single species, Crotalus durissus, which has public health importance due to the severity of its envenomation and to its wide geographical distribution. The species is subdivided into several subspecies, but the current classification is controversial. In Brazil, the venoms of C. d. terrificus and C. d. collilineatus are used for hyperimmunization of horses for antivenom production, even though the distinction of these two subspecies are mostly by their geographical distribution. In this context, we described a comparative compositional and functional characterization of individual C. d. collilineatus and C. d. terrificus venoms from three Brazilian states. Methods: We compared the compositional patterns of C. d. terrificus and C. d. collilineatus individual venoms by 1-DE and RP-HPLC. For functional analyzes, the enzymatic activities of PLA2, LAAO, and coagulant activity were evaluated. Finally, the immunorecognition of venom toxins by the crotalic antivenom produced at Butantan Institute was evaluated using Western blotting. Results: The protein profile of individual venoms from C. d. collilineatus and C. d. terrificus showed a comparable overall composition, despite some intraspecific variation, especially regarding crotamine and LAAO. Interestingly, HPLC analysis showed a geographic pattern concerning PLA2. In addition, a remarkable intraspecific variation was also observed in PLA2, LAAO and coagulant activities. The immunorecognition pattern of individual venoms from C. d. collilineatus and C. d. terrificus by crotalic antivenom produced at Butantan Institute was similar. Conclusions: The results highlighted the individual variability among the venoms of C. durissus ssp. specimens. Importantly, our data point to a geographical variation of C. durissus ssp. venom profile, regardless of the subspecies, as evidenced by PLA2 isoforms complexity, which may explain the increase in venom neurotoxicity from Northeastern through Southern Brazil reported for the species.

RESUMO: O estudo objetivou avaliar o efeito de dois intervalos de descanso entre pastoreios nas características estruturais do pasto e desempenho de novilhas de corte em pastagens naturais manejadas em pastejo rotativo. Os tratamentos foram dois intervalos entre pastejos de 375 e 750 GD (graus dia), baseados na soma térmica da duração de elongação foliar média de gramíneas de grupos de captura e conservação dos recursos dominantes de uma pastagem natural. O experimento foi conduzido no período de outubro de 2015 a março de 2016, com duração de 151 dias e os períodos experimentais divididos em primavera e verão. Foram utilizadas 24 novilhas teste da raça Braford, com idade inicial na média de 12 meses, e de peso corporal médio de 220 kg (± 27,8). A Massa de forragem total (FMt) pré-pastejo foi em média de 3791 kgMSha-1 e não diferiu entre tratamentos e estação, o mesmo ocorreu com a FM de estrato não touceira. A taxa de lotação média foi de 469 kgha-1 em ambos os tratamentos. O ganho médio diário variou apenas entre estações, com médias de 0,102 kganimal-1dia-1 na primavera e 0,372 kganimal-1dia-1 no verão. O ganho por área durante os 151 dias de avaliação foi em média de 103 kgha-1. As pastagens naturais submetidas a intervalos de descanso entre pastoreios baseados na elongação foliar de gramíneas dominantes, independente do tratamento utilizado, proporcionam ritmos de ganhos médios diários compatíveis com a meta de peso corporal, a ser atingida aos 24 meses, para que as novilhas possam ser acasaladas.

ABSTRACT: This study aimed to evaluate the effect of two rest intervals between grazing on the structural characteristics of pasture and performance of beef heifers in Campos grassland under rotational grazing. The treatments were two intervals between 375 and 750 DD (degree-days) grazing, based on the cumulative thermal sum for leaf expansion of native grasses belonging to capture and conservation groups of resources dominant in a natural grassland. The experiment was conducted during 151 days from October 2015 to March 2016, and twenty-four Braford heifers tests mean age = 12 months; mean body weight = 220kg (± 27.8) were used. The pre-grazing total forage mass (FMt) was on average 3791 kgMSha-1 and did not differ between treatments and season, the same occurred with the non-tussock FM. The average stocking rate was 469 kg ha-1 in both treatments. The average daily gain varied only between seasons, 0.102 kg animal-1 day-1 during spring and 0.372 kg animal-1 day-1 during summer. During the 151 evaluation days, the gain per area was a 103 kgha-1. The use of rest intervals between grazing based on the leaf elongation of dominant grasses, when applied to the areas of Campos grasslands, provided nutritional conditions to reach the target body weight for breeding 24 months old beef heifers.

The natural grasslands that form part of the "Campos" of South America contain a large number of species at the paddock level (high α diversity), but little differentiation among paddocks (low β diversity). Thus, forage resources at the farm level have slightly different seasonal growth peaks, in part due to the low frequency of fertilization, the lack of differential grazing management and mowing of these plant communities. To stimulate diversification of these forage resources, it is possible to take advantage of differential responses of each type of plant community to changes in their use. Characterizing species by functional traits allows to orient the use of forage resources according their functional composition, thus increasing the diversity of vegetation types, which favors differentiation of growth peaks among paddocks. After an initial division between C3 and C4 species, 63 Poaceae species were classified into eight groups or plant functional types (PFT) according to their preferred degree of soil fertility and use intensity. Based on the leaf dry matter content (LDMC) measured in experiments in Brazil, Uruguay and Argentina, we distinguished four PFT, two for C3 species and two for C4 species, with LDMC less than or equal to 300 mg/g. The species of these four PFT are adapted to fertile environments and intensive defoliation. Fertilizing and using more intensively vegetation dominated by species with these low LDMC can diversify the use value of paddocks, thus facilitating use of forage resources at the farm level.

Los pastizales naturales que forman parte de los "Campos" de América del Sur se caracterizan por tener un gran número de especies a nivel de potrero (alta diversidad α) y una diferenciación entre potreros relativamente baja (baja diversidad β). Esto significa que, a nivel de predio, se dispone de un conjunto de recursos forrajeros con picos de crecimiento estacionales poco diferenciados. En parte, esto es consecuencia del uso escaso de prácticas diferenciales de fertilización, de manejo del pastoreo y de corte sobre dichas comunidades vegetales. Para incentivar la diversificación de los recursos forrajeros (aumentar la diversidad β) se puede aprovechar la respuesta diferencial de los pastizales frente a cambios en su uso. Caracterizar las especies a través de sus rasgos funcionales permite orientar el uso del recurso al aplicar el tratamiento adecuado a su composición, aumentar la diversidad de tipos de vegetación y favorecer, de esta manera, el escalonamiento de la producción entre distintos potreros. Luego de una primera división entre especies C3 y C4, se clasificaron 63 Poáceas en 8 grupos o tipos funcionales de plantas (PFT) según su preferencia por sitios más o menos fértiles e intensidades de uso más o menos altas. Sobre la base de los valores de contenido en materia seca foliar (LDMC) obtenidos en varios experimentos en Brasil, Uruguay y Argentina se separaron cuatro PFT, dos de especies en C3 y otros dos de especies en C4, que presentan valores inferiores o muy cercanos a 300 mg/g. Las especies de estos cuatro PFT están adaptadas a ambientes fértiles y defoliadas con gran intensidad, a diferencia de los cuatro PFT restantes. Fertilizar y usar de forma más intensa la vegetación donde dominan las especies con esas bajas LDMC permitirá diversificar el valor de uso de los potreros, lo que facilita el aprovechamiento de los recursos forrajeros a nivel de predio.

Resumo Embora a ovinocultura tenha despertado o interesse de criadouros no estado do Acre nas últimas quatro décadas, pouco se conhece sobre a ocorrência de helmintoses no plantel de ovinos dessa região. O objetivo do presente estudo foi avaliar a possibilidade de ocorrência de helmintíases não intestinais entre ovinos abatidos no município de Rio Branco. Foram inspecionados 110 fígados de ovinos em dois abates (julho de 2014 e março de 2015) em um abatedouro no município de Rio Branco. Fígados com lesões macroscópicas foram fotografados com posterior análise histopatológica por microscopia de luz. Nas lesões macroscópicas foram encontrados pequenos nódulos apresentando características inflamatórias com áreas de fibrose, aparentemente calcificadas, sugerindo uma reação granulomatosa. Dos 110 fígados avaliados, observou-se 110 nódulos no total; estes nódulos têm um tamanho médio de 0,5 cm. A análise histopatológica mostrou alterações na arquitetura do lóbulo hepático, com múltiplos focos de necrose, além da formação de abscessos hepáticos constituídos por polimorfonucleares. Duas amostras revelaram a presença de helmintos da Classe Nematoda e ovos de Capillaria sp. identificados pela morfologia típica e morfometria. Esse resultado parece ser o primeiro registro de Capillaria sp. em fígado de ovino no Brasil, o que é um importante alerta para a vigilância no controle sanitário animal e o seu papel zoonótico para humanos.

Abstract Although sheep farming has grown in the state of Acre over the past four decades, little is known about occurrences of helminthiases in the herds of this region. The objective of the study was to assess the occurrences of non-intestinal helminthiasis among sheep slaughtered in Rio Branco. A total of 110 sheep livers were inspected from two slaughter batches (july 2014 and march 2015) in a slaughterhouse in Rio Branco. Livers with macroscopic lesions were photographed and were then subjected to histopathological analysis under an optical microscope. The macroscopic lesions showed small nodes with inflammatory characteristics and areas of fibrosis, which appeared to be calcified, thus suggesting a granulomatous reaction. Of the 110 evaluated livers, we noticed 110 nodules in total; these nodules have an average size of 0.5 cm. The histopathological analysis showed alterations to the architecture of the hepatic lobe, with multiple foci of necrosis and polymorphonuclear cells. Two samples revealed the presence of helminths from Nematode class and Capillaria sp. eggs identified by the typical morphology and morphometry. This seems to be the first report of Capillaria sp. in sheep livers in Brazil, and it serves as an important alert regarding animal health surveillance and control and regarding the Capillaria sp. zoonotic role in humans.

O objetivo foi avaliar o desempenho de novilhas de corte em pastagem natural sob pastoreio contínuo e rotativo no outono-inverno. Os tratamentos foram distribuídos em um delineamento inteiramente casualizado, conduzidos utilizando a massa de forragem acima de oito cm e 50% da massa de lâminas foliares das touceiras. Os animais foram novilhas Brangus com peso médio inicial de 258kg. As variáveis avaliadas foram massa de forragem disponibilizada (MFd), massa de lâminas foliares das touceiras (MLFt) oferta de forragem disponibilizada (OFd), altura do estrato inferior (Hinf), proteína bruta (PB), fibra em detergente neutro (FDN), digestibilidade da matéria orgânica (DISMO), nutrientes digestíveis totais (NDT), ganho médio diário (GMD), escore de condição corporal (CC), escore do trato reprodutivo (ETR) e taxa de lotação (TL). MFd, Hinf, DISMO e NDT foram decrescentes e OFd, PB e FDN semelhantes ao longo do período experimental. O GMD foi positivo apenas no terceiro período, enquanto que CC, ETR e TL decresceram. O manejo da pastagem natural sob pastoreio contínuo ou rotativo, no outono-inverno, utilizando a massa de forragem acima de oito cm e 50% da massa de lâminas foliares das touceiras, não possibilita o desenvolvimento corporal adequado para acasalamento de novilhas de corte aos 24 meses.

The aim of this study was to evaluate the performance of beef heifers in natural grassland under continuous and rotational grazing during the autumn-winter period. The treatments were distributed in a completely randomized design and conducted using the forage mass above eight cm and 50% of the leaf blades mass of tussocks. The animals were Brangus beef heifers with initial body weight of 258kg. The variables evaluated were available forage mass (FMa), leaf blades mass of tussocks (LBMt), real forage allowance (FAr), sward height of the lower stratum (HLS), crude protein (CP), neutral detergent fiber (NDF), organic matter digestibility (OMD), total digestible nutrients (TDN), average daily gain (ADG), body condition score (BCS), reproductive tract score (RTS) and stocking rate (SR). FMa, HLS, OMD and TDN decreased while FAr, CP and NDF were similar during the experimental period. The ADG was positive only at third experimental period while BCS, RTS and SR decreased over time. The natural grassland management under continuous and rotational grazing during the autumn-winter period, using the forage mass above 8cm and 50% of the leaf blades mass of tussocks, does not allow the adequate corporal development for breeding the beef heifers at 24 months old.

A maioria das pastagens naturais no bioma Campos no sul do Brasil cresce em solos com baixa disponibilidade de fósforo (P), mas com altos teores de P total e de P orgânico. Este trabalho objetivou avaliar as alterações nas formas de P no solo, ao longo de um ciclo de crescimento de pastagens naturais, decorrentes da aplicação de fontes de fosfato. Em três experimentos instalados em áreas de pastagem natural, foi aplicado P nas formas de hiperfosfato de Gafsa, superfosfato triplo e testemunha, arranjados em blocos casualizados com três repetições. Nos experimentos instalados no município de Candiota, RS, em pastagens naturais sob Luvissolo Úmbrico e Neossolo Litólico, foram aplicados 100 kg ha-1 de P2O5 em setembro de 2010. Na pastagem sob Argissolo Vermelho no município de Santa Maria, RS, foram aplicados 180, 90, 100 e 100 kg ha-1 de P2O5 nos anos de 1997, 1998, 2002 e 2010, respectivamente. Amostras de solo foram coletadas (0-10 cm) ao longo da estação de crescimento da pastagem (0, 55, 116, 171 e 232 dias, após aplicação do fosfato em Candiota; e 0, 50, 83, 129, 159 e 186 dias, após aplicação do fosfato em Santa Maria). Foram analisados os teores de P disponível por resina de troca aniônica, o P imobilizado na biomassa microbiana do solo, o P extraído por NaOH 0,1 mol L-1, o P orgânico total e o P total. Os teores de P disponível aumentaram rapidamente com a aplicação de fosfato solúvel, mas no final do período de avaliação esses se equivaleram ao do fosfato natural, que foi semelhante à testemunha. A aplicação de fertilizantes fosfatados sob pastagens naturais com baixa disponibilidade de P aumentou a importância das frações inorgânicas lábeis às plantas, tornando-as menos dependentes da mineralização das frações orgânicas. As frações orgânicas, inclusive o P microbiano, não são bons indicadores da biodisponibilidade de P em pastagens naturais sob Argissolos, Neossolos e Luvissolos do sul do Brasil fertilizadas com fosfatos.

Most natural pastures in the Campos biome in Southern Brazil grow in soils with low phosphorus (P) availability, but with high contents of total and organic P. The present study aimed to evaluate the changes in forms of soil P resulting from the application of phosphate sources over a growth cycle of natural pastures. In three experiments under natural pasture, P was applied in the form of Gafsa rock phosphate, triple superphosphate, and a control treatment in a randomized block design with three replications. In the trials carried out in natural pastures in the municipality of Candiota (RS) in an Alfisol and an Entisol, 100 kg ha-1 of P2O5 was applied in September 2010. In natural pasture in an Ultisol in the municipality of Santa Maria (RS), 180, 90, 100, and 100 kg ha-1 of P2O5 were applied in the years 1997, 1998, 2002, and 2010, respectively. Soil samples were collected (0-10 cm) throughout the natural grassland growing season (0, 55, 116, 171, and 232 days after P application at Candiota and 0, 50, 83, 129, 159, and 186 days after application of phosphate at Santa Maria). The levels of available P were analyzed by anion exchange resin, as well as P immobilized in the soil microbial biomass, P extracted by 0.1 mol L-1 NaOH, total organic P, and total P. The available P content increased rapidly with the application of soluble phosphate, but at the end of the evaluation period it was equivalent to the Gafsa rock phosphate, which was similar to the control. The application of phosphate fertilizers on natural pastures with low P availability increased the importance of the labile inorganic P forms to the plants, making them less dependent on the mineralization of organic P fractions. The organic fractions, including microbial P, are not good indicators of the bioavailability of P in natural pastures under Alfisols, Entisols, and Ultisols in Southern Brazil fertilized with phosphates.

Em ecossistemas de pastagens naturais deficientes em P disponível, a imobilização temporária do P na biomassa microbiana e sua posterior mineralização podem ser considerados mecanismo potencial de suprimento de P às plantas. O objetivo deste trabalho foi avaliar a influência da queima e do pastejo da vegetação campestre sobre a dinâmica do P no solo, com ênfase no conteúdo de P imobilizado na biomassa microbiana. Os tratamentos consistiram da associação do pastejo (presença ou ausência) e da queima (ausência ou presença) numa pastagem natural manejada há 13 anos com histórico de queimadas e de pastejo nas posições de relevo de encosta (Argissolo) e de baixada (Planossolo). A queima e o pastejo foram arranjados em delineamento completamente casualizado com quatro repetições. Coletaram-se amostras de solo na camada de 0-10 cm em duas épocas, durante a estação de crescimento da pastagem natural, sempre logo após o pastejo. A carga animal utilizada foi calculada adotando-se uma taxa de utilização de 20-35 % da massa de forragem. Determinaram-se o teor de P armazenado na biomassa microbiana do solo, o teor de P total e o de P orgânico total. A análise estatística dos resultados foi baseada em análise de variância via testes de aleatorização. O teor de P microbiano do solo sob pastagem natural variou de 11,4 a 57,3 mg kg-1, representando, em média, 38 e 32 % do P orgânico total do solo, na primeira e na segunda coleta, respectivamente. O P imobilizado na biomassa microbiana constitui a reserva potencial de P capaz de suprir a demanda de espécies nativas nas pastagens naturais, além de ser indicador mais sensível que o teor de P orgânico total do solo para detectar as alterações promovidas pelo pastejo. O manejo das pastagens naturais com fogo diminui a amplitude do incremento de P microbiano decorrente do pastejo.

In natural grassland ecosystems deficient in available P, the temporary immobilization of P in microbial biomass and its subsequent mineralization can be considered a potential mechanism of P supply to plants. The purpose of this study was to evaluate the influence of burning and grazing of grassland vegetation on the dynamics of soil P, with emphasis on the content of P immobilized in microbial biomass. The treatments consisted of the combination of grazing (presence or absence) and burning (presence or absence) in a natural grassland on slope and lowlands after 13 years under a management involving burning and grazing. Burning and grazing were arranged in a completely randomized design with four replications. Soil samples were collected from the 0-10 cm layer twice during the growing period of native pasture, always immediately after grazing. The stocking rate was calculated based on a utilization rate of 20-35 % of existing forage mass. The P content stored in the soil microbial biomass, the total P content and total organic P in soil were determined. The statistical analysis was based on analysis of variance by randomization tests. The microbial P content of natural pasture ranged from 11.4 to 57.3 mg kg-1, representing on average 38 and 32 % of total organic P in soil in the first and second evaluation, respectively. The P immobilized in microbial biomass is a potential reserve of P that can meet the demand for native species in natural pastures, and is a more sensitive indicator than the total organic P content of the soil to detect changes induced by grazing. Management of natural pastures with fire decreases the amplitude of the increase in microbial P due to grazing.