ABSTRACT Grazing intensity is a preponderant factor for the success of integrated crop-livestock systems (ICLS). Management of grazing intensity impacts soil organic matter (SOM) dynamics, soil reacidification process, and amount and quality of residues added to the ICLS. Consequently, the soil mineral nitrogen (N) forms may present different behavior throughout the pasture cycle, because they are directed linked to SOM and soil acidity dynamics. This study aimed to evaluate the impact of grazing intensities and liming in the temporal variation of acidity and mineral N forms in soil surface (0.00-0.20 m) and subsurface (0.20-0.40 m), throughout the pasture cycle of an ICLS under an Oxisol in the Brazilian subtropics. The study was performed 11 years after the beginning of the field experiment, characterized by the cattle grazing in a winter pasture of oat + ryegrass during the winter and soybean cropping during the summer. The experimental design is randomized block with three replicates, where the grazing intensities are in the plots and liming is the subplots. The grazing intensities were defined as grazing sward height management, being 0.10, 0.20-0.30, and 0.40 m defined as intensive (IG), moderate (MG) and light grazing (LG), respectively. We evaluated the soil ammonium (N-NH4+), nitrate (N-NO3-), mineral N and pH at 45, 70, 156 and 192 days after pasture sowing (DAPS). Our results showed that grazing intensities only affected the soil pH at the end of pasture cycle, with MG presenting higher pH than IG and LG, regardless of liming. A decrease of soil N mineral stocks was observed throughout the pasture cycle in all managements, due to the decrease of soil N-NO3- stocks in the surface and subsurface layers and of N-NH4+ only in the surface layer. The influence of grazing intensities was only observed for N mineral forms in limed areas before the beginning of grazing. At 45 DAPS, MG and LG presented the highest and the lowest N-NH4+, respectively. At 70 DAPS, the behavior was inverse, and LG presented the highest N-NO3- stock and the MG and IG the lowest N-NO3- stocks. With such results, it is possible to conclude that there is an influence of grazing intensity and liming in the temporal variation of soil pH and mineral N forms in ICLS and this may be utilized for improvements in N fertilizer management, mainly before the starting of winter grazing.

ABSTRACT This paper aims to discuss the impact of the introduction of pastures and grazing animals in agricultural systems. For the purposes of this manuscript, we focus on within-farm integrated crop-livestock systems (ICLS), typical of Southern Brazil. These ICLS are designed to create and enhance the synergisms and emergent properties have arisen from agricultural areas where livestock activities are integrated with crops. We show that the introduction of the crop component will affect less the preceding condition than the introduction of the livestock component. While the introduction of crops in pastoral systems represents increasing diversity of the plant component, the introduction of animals would represent the entry of new flows and interactions within the system. Thus, given the new complexity levels achieved from the introduction of grazing, the probability of arising emergent properties is theoretically much higher. However, grazing management is vital in determining the success or failure of such initiative. The grazing intensity practiced during the pasture phase would affect the canopy structure and the forage availability to animals. In adequate and moderate grazing intensities, it is possible to affirm that livestock combined with crops (ICLS) has a potential positive impact. As important as the improvements that grazing animals can generate to the soil-plant components, the economic resilience remarkably increases when pasture rotations are introduced compared with purely agriculture systems, particularly in climate-risk situations. Thus, the integration of the pastoral component can enhance the sustainable intensification of food production, but it modifies simple, pure agricultural systems into more complex and knowledge-demanding production systems.

Resumo: O objetivo deste trabalho foi avaliar o impacto de intensidades de pastejo após 11 anos de um sistema de integração lavoura-pecuária, em plantio direto, na umidade do solo e em parâmetros fisiológicos da soja durante uma safra de verão afetada por seca. O experimento foi iniciado em 2001, em um Latossolo Vermelho. Os tratamentos consistiram na sucessão de soja (verão) e pastagem mista de aveia-preta + azevém (inverno), com diferentes intensidades de pastejo por bovino de corte: pastejo intensivo, com altura de pastejo de 0,10 m; pastejo moderado, com altura de pastejo de 0,20 m; e sem pastejo. No ciclo da soja, na safra 2011/2012, a precipitação foi de 40% da normal climatológica. A umidade do solo ficou dentro dos limites de água disponível, tanto em pastejo moderado quanto sem pastejo, na camada de 0,00-0,50 m, mas, em pastejo intensivo, a umidade do solo foi menor que o ponto de murcha permanente, especialmente até 0,20 m de altura de pastejo. O pastejo intensivo afetou negativamente os parâmetros fisiológicos da soja, que atingiu picos de -2.5 MPa e +6°C para potencial de água na folha e diferença entre temperatura do ar e da folha, respectivamente. O pastejo moderado ou a ausência de pastejo, durante o inverno, acarreta respostas fisiológicas similares, o que contribui para a homeostase da soja.

Abstract: The objective of this work was to evaluate the impact of grazing intensities after 11 years of an integrated crop-livestock system, under no-tillage, on soil moisture and soybean physiological parameters during a summer season affected by drought. The experiment was established in 2001 on a Rhodic Hapludox. Treatments consisted in the succession of soybean (summer) and a mixed pasture of black oat + Italian ryegrass (winter), under different beef-cattle grazing intensities: intensive grazing, with 0.10-m pasture height; moderate grazing, with 0.20-m pasture height; and no grazing. During the soybean cycle, in the 2011/2012 crop season, rainfall was 40% of the climatological normal. The soil moisture was within the limits of available water both under moderate grazing and no grazing, at 0.00-0.50-m soil depth, but, under intensive grazing, it was below the permanent wilting point, especially up to the grazing height of 0.20 m. Intensive grazing affected negatively the plant physiology parameters, reaching peaks of -2.5 MPa and +6°C for leaf water potential and leaf-air temperature difference, respectively. Moderate grazing or the absence of grazing, during the winter season, results in similar physiological responses, contributing to soybean plant homeostasis.

Resumo:O objetivo deste trabalho foi avaliar o efeito da intensidade de pastejo na decomposição dos resíduos da pastagem utilizada como cultura de cobertura, do esterco e da soja, bem como a liberação de C e N desses resíduos, em um sistema integrado de produção de soja e bovinos de corte, em plantio direto e em longo-prazo. O experimento foi iniciado em 2001, com soja cultivada no verão e aveia-preta + azevém no inverno. Os tratamentos consistiram de quatro alturas de pasto (10, 20, 30 e 40 cm), além de uma área sem pastejo, como controle. Em 2009-2011, resíduos da pastagem, do esterco, e do caule e das folhas de soja foram alocados em sacos de decomposição feitos com malha de nylon e decompostos até 258 dias. Com o aumento da intensidade de pastejo, a matéria seca residual da pastagem diminuiu e a do esterco aumentou. A concentração de lignina e as taxas de liberação de C da pastagem e do esterco foram menores com a intensidade de pastejo moderada. A liberação de C e N do resíduo de soja não é afetada pela intensidade de pastejo. A intensidade moderada de pastejo produz resíduos de maior qualidade, tanto para a pastagem quanto para o esterco. Já a quantidade total de C e N liberada é influenciada pela maior quantidade de matéria seca residual produzida quando a pastagem foi submetida ao pastejo leve ou não foi pastejada.

Abstract:The objective of this work was to evaluate the effect of grazing intensity on the decomposition of cover crop pasture, dung, and soybean residues, as well as the C and N release rates from these residues in a long-term integrated soybean-beef cattle system under no-tillage. The experiment was initiated in 2001, with soybean cultivated in summer and black oat + Italian ryegrass in winter. The treatments consisted of four sward heights (10, 20, 30, and 40 cm), plus an ungrazed area, as the control. In 2009-2011, residues from pasture, dung, and soybean stems and leaves were placed in nylon-mesh litter bags and allowed to decompose for up to 258 days. With increasing grazing intensity, residual dry matter of the pasture decreased and that of dung increased. Pasture and dung lignin concentrations and C release rates were lower with moderate grazing intensity. C and N release rates from soybean residues are not affected by grazing intensity. The moderate grazing intensity produces higher quality residues, both for pasture and dung. Total C and N release is influenced by the greater residual dry matter produced when pastures were either lightly grazed or ungrazed.

RESUMOEm Sistemas Integrados de Produção Agropecuária, a presença dos animais em pastejo pode provocar alterações na produção das culturas subsequentes. Com o objetivo de verificar como diferentes manejos do pasto poderiam afetar o cultivo de soja, a 9ª fase de lavoura em rotação pecuária/lavoura foi avaliada. Os tratamentos foram intensidades de pastejo (10; 20; 30; 40 cm de altura do pasto), aplicados desde 2001, em pasto misto de aveia e azevém anual, além de área sem pastejo utilizada como testemunha. O delineamento experimental foi de blocos ao acaso, com três repetições. Houve diferença na população inicial de plantas e na massa do nódulo (P<0,05), porém, o número e a massa de nódulos por planta foi semelhante (P>0,05). O rendimento de soja foi diferente entre os tratamentos, porém, não houve diferença entre áreas pastejadas e não pastejadas. Houve diferença para cobertura e frequência de espécies indesejáveis entre tratamentos (P>0,05). Em conclusão, diferentes intensidades de pastejo afetam os parâmetros de rendimento e desenvolvimento da soja, mas apenas a intensidade de pastejo de 10 cm pode comprometer a safra de soja subsequente.

ABSTRACTGrazing livestock in integrated crop-livestock systems can cause impacts in the subsequent crop cycle. Aiming to investigate how grazing could affect soybean, the 9th crop cycle of a pasture/soybean rotation was assessed. Treatments were grazing intensities (10, 20, 30 and 40 cm of sward height) applied since 2001 in a mixed of oat and annual ryegrass; and an additional no grazing area as control. Treatments were arranged in a completely randomized block design with three replicates. Grazing affected soybean population and the mass of individual nodules (P<0.05), while the number and mass of nodules per plant were similar (P>0.05). Soybean yield showed differences among treatments, but no difference was found between grazed and non-grazed areas. Grazing intensities impact the coverage and frequency of weeds (P>0.05). In conclusion, grazing intensity impacts different parameters of soybean yield and development, but only the grazing intensity of 10 cm can jeopardize the succeeding soybean crop.

The objective of this study was to evaluate the chemical composition of the forage apparently consumed by steers in a natural grassland on region of Campanha, in Rio Grande do Sul, Brazil, subjected or not to different inputs: NP - natural pasture without inputs; FNP - fertilized natural pasture and INP - improved natural grassland with fertilization and over-seeded with cultivated winter species. Three Angus steers testers and a variable number of regulator animals per experimental unit were utilized in order to maintain 13 kg of DM/100 kg of live weight (LW) as forage allowance. One time at each season, hand plucking samples were performed along the daily grazing time simulating forage harvested by the animals. The collected samples after drying and grind were submitted to chemical analysis to determine the forage quality. Except in winter and spring, the values of neutral detergent fiber were higher than the critical value of 550 g/kg of DM, which could limit forage intake, demonstrating that the values of forage on offer provided (15.6; 13.7; 13.5; 15.8 kg of DM/100 kg of LW/day in summer, autumn, winter and spring, respectively) were not restrictive to intake. The oversowing of winter cultivated species or fertilization positively alter the degradable fiber content. The seasons had marked influence on the chemical composition of forage apparently consumed; positively increasing some fractions of forage chemical composition in the seasons in which native or cultivated winter species increased their participation. The forage chemical composition is the determining factor in animal performance in natural pasture.

The overseeding of ryegrass (Lolium multiflorum Lam) on sub-tropical native pastures increases the availability and quality of forage in the cold season. However, soil chemical amendment and nitrogen use can affect the floristic composition, with consequences to the primary and secondary production. In a randomized complete block design with three replications, the effect of nitrogen fertilization (40, 90 and 140 kg/ha of nitrogen) on native pasture overseeded with ryegrass in two consecutive years was assessed regarding production and composition of pasture and performance of beef calves. In both years, the forage accumulation rate and forage production responded linearly to the increase in nitrogen rates as a result of increased participation of ryegrass. The lower efficiency of responses in 2008 was due to the increased participation of dead material and the reduction of ryegrass in the forage sward. In 2007 there was an increasing substitution of the participation of native grasses by ryegrass with increasing nitrogen rates. Native legumes and other species were almost not affected by nitrogen fertilization. The average daily weight gain of the animals responded linearly to nitrogen rates in 2007, and quadratically in 2008. The stocking rate and gain per hectare increased linearly in both years, with greater responses in 2007. The production and composition of forage and livestock production are improved by the use of nitrogen, but the efficiency of responses can be affected by sowing date and nitrogen fertilization.

Monitoraram-se variáveis relacionadas à produção e à estrutura de pastos de aveia-preta (Avena strigosa, Schreb) e azevém (Lolium multiflorum, Lam) manejados em quatro alturas (10, 20, 30 e 40 cm), em pastejo contínuo com lotação variável (put and take). Utilizaram-se novilhos de corte mestiços de aproximadamente 10 meses de idade com peso médio inicial de 190 kg, em delineamento de blocos completos casualizados com três repetições. Investigou-se o tipo de distribuição das frequências de altura em seis datas, bem como o potencial de predição da massa seca de forragem por meio da altura do pasto. A massa de forragem aumentou de forma linear de acordo com a altura do pasto: cada 1 cm de aumento na altura acima de 10 cm correspondeu a um acréscimo de cerca de 107 kg de MS/ha na massa de forragem. Não houve efeito da altura do pasto na taxa de acúmulo (55,8 kg de MS/ha.dia) nem na produção total de matéria seca (8.210 kg de MS/ha). A distribuição das frequências ajustou ao modelo normal em apenas uma das 96 séries analisadas. A distribuição tipo Gamma foi a que mais frequentemente se ajustou aos dados de altura do pasto, porém, uma vez iniciado o pastejo, a heterogeneidade no pasto foi tão alta que a distribuição das alturas não se ajustou a nenhum dos modelos estudados. É possível estimar a massa seca de forragem existente no pasto por meio de sua altura média, assim, sugere-se estabelecer alturas variáveis ao longo do ciclo de pastejo, com o intuito de se administrar a heterogeneidade causada pelo animal.

It was monitored variables related to production and structure of oat (Avena strigosa Schreb) and ryegrass (Lolium multiflorum Lam) pastures managed at four sward heights (10, 20, 30, and 40 cm) on continuous grazing with variable stocking (put and take). It was used crossbred beef steers at approximately 10 months of age and an average initial weight 190 kg in a complete random block design with three replicates. The type of sward height distribution in six different sample dates as well as the forage dry mass prediction through sward heights were investigated. Forage mass linearly increased according to the sward height: for each 1-cm increase of the height above 10 cm, there was an approximately 107 kg DM/ha addition in the forage mass. There was no effect of sward height on the accumulation rate (55.8 kg DM/ha) neither on the dry matter total production (8,210 kg of DM/ha). Frequency distributions fitted to the normal model in only one out of the 96 analyzed data series. Gamma type distribution was the one that was the most frequently adjusted to sward height data, however, once grazing was started, pasture heterogeneity was so high that height distribution did not fit any of the investigated models. It is possible to estimate forage dry mass on the pasture by its average height so it is suggested to establish variable heights over the grazing cycle aiming to manage the heterogeneity caused by the animal.

Com o objetivo de avaliar o efeito da estrutura de uma pastagem nativa nos parâmetros que compõem o processo de ingestão de forragem de ovelhas e bezerras em pastejo, foram estabelecidas quatro alturas de pasto (4, 8, 12 e 16 cm), em delineamento estatístico inteiramente casualizado, com quatro tratamentos e duas repetições no tempo e no espaço. A massa do bocado e a taxa de ingestão foram estimados por diferença de peso vivo corrigido para a perda de peso metabólico, durante 45 minutos. Os movimentos mandibulares de apreensão e mastigação foram registrados pelo aparelho IGER Behaviour Recorder. A profundidade do bocado foi obtida em 40 perfilhos marcados por unidade experimental, em medições realizadas antes e após o pastejo. Observou-se correlação positiva entre a altura do pasto e a massa de forragem, e negativa com a densidade de forragem. A profundidade de bocados apresentou relação linear e positiva com o aumento da altura do pasto e não diferiu entre espécies animais. Acima de 9,5 cm de altura do pasto, a profundidade do bocado das ovelhas não compensou a pouca densidade de forragem nos estratos mais superiores, o que reduziu a massa do bocado. A mesma resposta foi observada a partir da altura do pasto de 11,4 cm para as bezerras. Com o aumento da massa do bocado, houve diminuição na taxa de bocados e aumento na taxa de mastigação. A taxa de ingestão foi maior nas alturas em que a massa de bocados foi também superior, o que evidencia a correlação positiva entre as duas variáveis. Nessas condições, para aumentar o consumo de ovelhas e bezerras em campo nativo, a estrutura ideal de manejo requer manutenção de altura do pasto entre 9,5 e 11,4 cm, respectivamente.

Aiming to evaluate the influence of native pasture structure in the intake process of grazing ewes and calves, four sward heights (4, 8, 12 and 16 cm) were established. A completely randomized design with four treatments and two replicates in time and space was used. Bite mass and forage intake were estimated by the short-term weight changes technique, corrected for the rate of insensible weight loss, during a 45 minutes test. The grazing and mastication jaw movements were registered by the IGER Behaviour Recorder device. Bite depth was obtained through 40 tillers marked in each experimental unit, by measurements carried before and after grazing. A positive correlation was observed between sward height and herbage mass, and negative between sward height and herbage bulk density. Bite depth fitted positively and linearly with increasing sward height, being not different between animal species. Ewe bite mass increased with increasing sward height up to 9.5 cm, then decreasing due to the low bulk density in the superior stratum. The same response was observed with calves, but bite mass reached a plateau only at 11.4 cm sward height. Bite rate decreased and mastication rate increased with increasing bite mass. Intake rate was greater at the sward height in which bite mass was also superior, indicating the positive correlation between these two variables. Under those conditions, to optimize the intake of sheep and calves, in native pasture, the ideal structure for management requires the maintenance of sward heights between 9.5 and 11.4 cm.

Avaliou-se o desempenho de cordeiros em pastagem de azevém anual (Lolium multiflorum Lam.) manejada em duas intensidades (moderada e baixa, 2,5 ou 5,0 vezes o potencial de consumo) e dois métodos de pastejo (lotação rotacionada ou contínua) durante 113 dias. O delineamento experimental foi o de blocos casualizados, em esquema fatorial 2 × 2 × 4 com quatro repetições. Não houve interação métodos × intensidades de pastejo e, portanto, seus efeitos foram analisados de forma independente. A intensidade de pastejo moderada resultou em menor oferta de forragem, menor massa média e menor altura da pastagem. As características qualitativas da forragem também foram afetadas positivamente pela intensidade moderada. A altura e a massa de forragem foram maiores no pastejo sob lotação rotacionada, mas a qualidade da forragem foi melhor nos piquetes de lotação contínua. As ofertas de forragem não diferiram entre os métodos de pastejo e proporcionaram condições necessárias para a comparação de todas as variáveis. O ganho médio diário e a carga animal foram afetados tanto pelo método quanto pela intensidade de pastejo. O ganho por área foi maior para a intensidade de pastejo moderada, no entanto, não foi influenciado pelo método de pastejo. A quantidade de forragem ofertada para o animal é o principal determinante da produtividade do sistema, independentemente do método de pastejo. A intensidade de pastejo baixa foi mais adequada para o manejo, pois refletiu em melhor ganho por animal.

This work measured lamb performance in a ryegrass pasture (Lolium multiflorum Lam.) under different grazing intensities and methods. The pasture was used from July 12th to November 1st of 2003 (total of 113 days). The treatments were two grazing intensities (moderate and low) in rotational and continuous stocking. The moderate and low grazing intensities were represented, respectively, by forage allowance of 2.5 and 5 fold the intake potential. It was used a factorial arrangement (2 intensities × 2 methods × 4 replicates) in a complete randomized block design. There was no interaction among grazing methods and grazing intensities and they were analyzed separately. The moderate grazing intensity provided the lower forage allowance, lower herbage mass and lower pasture height. This intensity affected positively the qualitative characteristics of pasture as well. Regarding the grazing methods, the height and the herbage mass were larger under rotational stocking, while the forage quality was higher under continuous stocking. There was no difference of forage allowance between methods, and the necessary conditions to compare all the variables measured were reached. There were significant differences between average daily gain and stocking rates on both, grazing methods and intensities. The gain/hectare was better under moderate grazing intensity, but no difference was identified under grazing methods for this intensity. The amount of forage available for the animal is the central key for the productivity, despite the grazing method used. Low grazing intensity was considered more appropriate for pasture management because it allows better gain per animal.