ABSTRACT: The extension of the area occupied by the inter tussock stratum and tussock stratum in natural pastures is essential for the productive performance of grazing animals. Images obtained from unmanned remote sensors can provide useful information, especially because they have a high spatial resolution. Thus, this study evaluated the performance of the supervised adaptive classification applied to aerial images obtained from an onboard drone camera to map the area covered by tussocks in a natural pasture of the Pampa biome. The study was carried out in a natural pasture area managed since 1986 under different forage allowances, considering treatments of 8, 12, and 16 kg of dry matter per 100 kg live weight (% LW). An aerial image from September 2017, obtained with a Canon S100 camera onboard a drone at an altitude of 120 m, with a spatial resolution of 5 cm, was used. The random forest and support vector machine classifiers were tested associated with specific classification rules. False-color images showed considerable visual similarity in the large patterns of the vegetation distribution and the validation performed with independent samples when compared to the classified images. The tested classifiers were able to measure the area covered by the tussock stratum, which could be an indicator of the quality vegetation in a natural grassland of the Pampa biome.

RESUMO: A quantidade de área ocupada por estrato inferior e superior em pastagens naturais tem grande importância sobre o desempenho produtivo dos animais em pastejo. Imagens obtidas de sensores remotos não tripulados podem fornecer informações úteis, especialmente por possuírem alta resolução espacial. O objetivo deste trabalho foi avaliar o desempenho de classificação supervisionada adaptativa aplicada a imagem aérea obtida por câmera a bordo de drone, no mapeamento da área coberta por touceiras em pastagem natural do bioma Pampa. O estudo foi realizado em área de pastagem natural, manejada desde 1986 sob diferentes ofertas de forragem, tendo sido considerados os tratamentos 8, 12 e 16 kg de matéria seca por 100 kg de peso vivo (% PV). Foi utilizada uma imagem aérea, de setembro de 2017, obtida com uma câmera Canon S100, a bordo de um drone a 120 m de altitude, correspondendo a resolução espacial de 5 cm. Foram testados dois classificadores, Random Forest e Support Vector Machine associados a regras específicas de classificação. As imagens de falsa cor, quando comparadas às imagens classificadas, apresentaram considerável semelhança visual nos grandes padrões de distribuição da vegetação, bem como na validação feita com amostras independentes. Os classificadores testados foram capazes de mensurar a área coberta por estrato superior, podendo ser um indicador da qualidade da vegetação, em pastagem natural do bioma Pampa.

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.

RESUMO A competição de plantas daninhas é um desafio para os produtores de arroz em monocultivo no contexto de espécies resistentes a herbicidas e plantas daninhas difíceis de manejar usando o controle químico. Diversificar a rotação de culturas por meio de sistemas integrados de produção agropecuária (SIPA) pode ser uma alternativa para enfrentar esse desafio. Como o banco de sementes de plantas daninhas reflete práticas de manejo, este estudo teve como objetivo avaliar o impacto de um arrozal tradicional e quatro SIPA em terras baixas sobre o banco de sementes de plantas daninhas, em um experimento de longa duração localizado em Cristal, RS, Brasil. Os tratamentos consistiram em cinco sistemas de cultivo: T1 - monocultivo de arroz; T2 - integração arroz-pecuária; T3 - integração soja-arroz-pecuária; T4 - integração soja-milho-arroz-pecuária; e T5 - integração arroz-pecuária, em pastagens cultivadas e campo nativo. O banco de sementes foi avaliado no quarto ano experimental, outubro de 2016, em três profundidades do solo (0-5; 5-10 e 10-20 cm). No médio prazo, a diversificação do arrozal por meio de SIPA não afetou o tamanho do banco de sementes. No entanto, em T1 as sementes estavam distribuídas ao longo do perfil do solo, em contraste com os demais sistemas de cultivo, onde as sementes de plantas daninhas se acumularam na profundidade de 0-5 cm. Arranjos de SIPA que compreendem a integração de culturas de verão e pastagens hibernais diminuem a proporção de plantas daninhas ciperáceas na camada superficial do banco de sementes do solo. A diminuição do banco de sementes de arroz daninho é mais pronunciada nos arranjos de SIPA em terras baixas que integram diferentes culturas de verão em rotação com pastagens hibernais.

ABSTRACT Weed competition is a challenge to rice monocropping growers in the context of herbicide resistant weeds and difficult weeds to manage using chemical control. Diversifying crop rotations through integrated crop-livestock systems (ICLS) can be an alternative to face this challenge. As weed seedbank reflects management practices, this study aimed to assess the impact of a traditional paddy field and four lowland ICLS on the weed seedbank, in a long-term ICLS experiment located in Cristal, RS, Brazil. Treatments consisted of five cropping systems: T1 - rice monocropping; T2 - rice-beef cattle integration; T3 - soybean-rice-beef cattle integration; T4 - Sudan grass-soybean-maize-rice-beef cattle integration; and T5 - rice-beef cattle integration in cultivated and natural grassland. The seedbank was assessed in the fourth experimental year, Oct-2016, at three soil depths (0-5; 5-10 and 10-20 cm). In a mid-term temporal scale, the diversification of paddy field through ICLS did not affect weed seedbank size. However, seeds in T1 were equally distributed along the soil profile, in contrast to the other cropping systems, where weed seeds accumulated in the 0-5 cm depth. Lowland ICLS designs that comprises the integration of summer crops with grazing winter cover crops decrease the proportion of Cyperaceae weed species in the topsoil seedbank. The depletion of weedy rice seedbank is more pronounced in lowland ICLS designs that integrates different summer crop in rotation with grazing cover crops.

ABSTRACT In an integrated crop-livestock system (ICLS), system fertilization exploits the nutrient cycling imposed by animal grazing and increases the system efficiency. An increasingly popular approach to fertilization in southern Brazil is anticipating P and K requirements for soybeans into the pasture phase. This can increase the use efficiency of these nutrients in ICLS based on meat production in winter and soybean in summer. This study aimed to evaluate the effect of fertilization strategy, grazing and soil acidity correction on herbage and animal production, soybean yield, P and K contents in soil and plant tissue, and P and K use and economic efficiency. In 2017, a field experiment was established on an Acrisol ( Argissolo Vermelho distrófico ) double-cropped with soybean and Italian ryegrass under no-tillage. Herbage and animal production, soybean yield, available P and K contents, and P and K plant tissue status were determined. Available P and K in the soil were unaffected by grazing and fertilization strategy. Conversely, system fertilization and liming increased the P and K contents of aboveground Italian ryegrass biomass. Additionally, the available K budget in the soil was 2.7 times smaller in the integrated system with system fertilization than in the specialized system with conventional fertilization, possibly due to K fixation in non-exchangeable forms. By contrast, the available P budget in the soil was not affected by treatments and was positive with all systems. The use of ICLS increased economic return, and P and K use efficiency for protein production. System fertilization did not affect soybean yield, but it increased the total herbage production of Italian ryegrass. Despite this, sheep live weight did not increase. Using ICLS in combination with system fertilization provides an effective nutrient management strategy with a higher potential for sustainable food production when compared with conventional fertilization.

ABSTRACT Studies on lability of soil phosphorus (P) under integrated crop-livestock systems (ICLS) are still scarce, especially for deep soil layers (more than 0.20 m depth) and different managements in the crop and livestock phase. Distinct management in these phases may lead to a different distribution of soil P pools according to its lability (labile, moderately labile, less labile and residual) and, consequently, the P availability for plant nutrition. This study aimed to determine the soil P pools, by P fractionation and its distribution in lability classes. In a long-term ICLS experiment of grain and sheep production established in 2003, in Southern Brazil, we sampled in 2017 the 0.00-0.05, 0.05-0.10, 0.10-0.20, 0.20-0.26, 0.26-0.30 and 0.30-0.40 m layers of a Red Dystrophic Acrisol ( Argissolo Vermelho distrófico ) under two cropping systems in the summer (soybean/corn rotation and soybean/soybean succession), two grazing intensities (moderate and low) and two methods (continuous and rotational) in winter. Fractionation of P consisted of sequential extractions with anionic exchange resin, NaHCO 3 0.5 mol L -1 , NaOH 0.1 mol L -1 , HCl 1 mol L -1 , and NaOH 0.5 mol L -1 . The fractions were grouped in four different pools: labile, moderated labile, less labile and residual P. The soybean/soybean succession increased the labile pool of soil P in the 0.00-0.10 m layer compared to the soybean/corn rotation, regardless of the management of the livestock phase. Meanwhile, the management of the livestock phase also influenced soil P lability, regardless of the management of the crop phase. Low grazing intensity increased the levels of labile soil P in the 0.00-0.05 m layer, in comparison with the moderate grazing intensity and regardless of the grazing method. Grazing methods did not impact the soil P lability or content. The greater soil P availability in the soybean/soybean succession can be attributed to the higher quality (low carbon/nitrogen ratio) of the residue, while in the low grazing intensity to the higher forage dry matter production. Such management benefits nutrient cycling and consequently the P availability to the plants, being important to decrease production costs with the reduction and/or greater use efficiency of phosphate fertilizers.

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.

ABSTRACT Under integrated crop-livestock production systems (ICLS), plant and animal residues are important nutrient stocks for plant growth. Grazing management, by affecting the numbers of both plants and animals and the quality of residues, will influence nutrient release rates. The objective of this study was to evaluate the impact of grazing intensity on Ca and Mg release from pasture, dung, and soybean residues in a long-term no-till integrated soybean-cattle system. The experiment was established in May 2001 in a Latossolo Vermelho Distroférrico (Rhodic Hapludox). Treatments were a gradient of grazing intensity, determined by managing a black oat + Italian ryegrass pasture at 10, 20, 30, and 40 cm grazing height and no-grazing (NG), followed by soybean cropping. Ca and Mg release rates were determined in two entire cycles (2009/11). Moderate grazing (20 and 30 cm sward height) led to greater Ca and Mg release rates from pasture and dung residues, with low average half-life values (13 and 3 days for Ca and 16 and 6 days for Mg for pasture and dung, respectively). Grazing compared with NG resulted in greater Ca and Mg release from pasture and dung residues. Grazing intensity did not affect Ca and Mg release rates or amounts from soybean residues, but Ca and Mg release rates were greater from soybean leaves than from stems. Although moderate grazing intensities produce higher quality residues and higher calcium and magnesium release rates, a higher total nutrient amount is released by light grazing intensity and no-grazing, determined by higher residue production. Grazing intensity is, then, important for nutrient dynamics in the soil-plant-animal continuum.

ABSTRACT The Pampa biome is an important ecosystem in Brazil that is highly relevant to livestock production. The objective of this study was to analyze the potential use of vegetation indices to discriminate grazing intensities on natural grasslands in the Pampa biome. Moderate Resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) images from Jan to Dec, 2000 to 2013 series, were analyzed for natural grassland experimental units managed under high (forage allowance of 5 ± 2 % live weight – LW), moderate (13 ± 5 % LW) and low grazing intensity (19 ± 7 % LW). Regardless of intensity, the temporal profiles showed lower NDVI and EVI during winter, increased values in spring because of summer species regrowth, slightly decreased values in summer, especially in years when there is a water deficit, and increased values in the fall associated with the beginning of winter forage development. The average temporal profiles of moderate grazing intensity exhibited greater vegetation index values compared with low and high grazing intensities. The temporal profiles of less vegetation index were associated with lower green biomass accumulation caused by the negative impact of stocking rates on the leaf area index under high grazing intensity and a floristic composition with a predominance of tussocks under low grazing intensity. Vegetation indices can be used for distinguishing moderate grazing intensity from low and high intensities. The average EVI values can discriminate moderate grazing intensity during any season, and the NDVI values can discriminate moderate grazing intensity during spring and winter.

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 Avaliaram-se os efeitos de níveis de correção da fertilidade do solo (testemunha, calagem, adubação e calagem + adubação) e da idade de rebrota (21, 28, 35, 42, 49, 56, 63, 70, 77 e 84 dias) sobre a dinâmica de crescimento e rendimento de forragem de Trachypogon plumosus em Roraima. O aumento da idade de rebrota resultou em maiores rendimentos de matéria seca (MS), taxa absoluta de crescimento (TAC), taxa de assimilação líquida (TAL), razão de área foliar (RAF) e índice de área foliar (IAF), ocorrendo o inverso quanto à taxa média de crescimento (TMC). A gramínea mostrou-se responsiva à melhoria da fertilidade do solo. A calagem + adubação ou a adubação proporcionaram maiores rendimentos de MS (1.934 e 1.661 kg ha-1), TAC (36,6 e 31,5 kg ha-1 dia-1), TMC (32,5 e 27,9 kg ha-1 dia-1), TAL (4,993 e 4,152 g/m2), RAF (152,9 e 140,9 cm2/g) e IAF (2,42 e 2,14). Para otimizar a eficiência de utilização da forragem produzida e reduzir perdas por senescência da gramínea, o período mais adequado de sua utilização, durante o período chuvoso, situa-se entre 56 e 63 dias com o uso de adubação e calagem + adubação e entre 63 a 70 dias para a testemunha e a calagem.

Abstract We assessed the effects of levels of soil fertility correction (control, liming, fertilization and liming + fertilization) and of regrowth ages (21, 28, 35, 42, 49, 56, 63, 70, 77, and 84 days) on growth dynamic and forage yield of Trachypogon plumosus in the Roraima´s savannas. Dry matter (DM) yields, absolute growth rate (AGR), net assimilation rate (NAR), and leaf area ratio (LAR) increased consistently with regrowth age, while the crop growth rate (CGR) was inversely proportional to regrowth age. The grass showed high responsivity to soil fertility improvement. Liming + fertilization or fertilization alone provided higher DM yields (1,934 and 1,661 kg ha-1), AGR (36.6 and 31.5 kg ha-1.day), CGR (32.5 and 27.9 kg ha-1.day), NAR (4.993 e 4.152 g/m2), LAR (152.9 and 140.9 cm2/g), and LAI (2.42 and 2.14). Regrowth intervals of 56 to 63 days for liming + fertilized and fertilized pastures, and 63 to 70 days for control or liming pastures were appropriate to provide maximum forage yields, growth rates and to prevent larger losses relative to senescence and leaf death.

RESUMO O objetivo deste trabalho foi avaliar o efeito de diferentes intensidades de pastejo sob a produção de forragem e o desempenho animal de novilhos superprecoces mantidos sob pastejo contínuo em sistema integrado de produção agropecuária. Os tratamentos consistiram das alturas de manejo de pasto de 10; 20; 30 e 40 cm; e de um tratamento sem pastejo. Os pastos eram constituídos de aveia-preta (Avena strigosa Schreb.) e azevém anual (Lolium multiflorum Lam.) em sucessão a cultura da soja (Glycine max (L.) Merr.). As variáveis massa de forragem, oferta de forragem e palhada residual se ajustaram de forma positiva e linear ao incremento da altura do pasto (P≤0,0001). O desempenho individual de novilhos apresentou resposta quadrática (P = 0,0017) e foi otimizado com o incremento na altura do pasto até valores próximos a 30 cm, com ganho de peso por animal de aproximadamente 1,0 kg dia-1. O mesmo foi observado para o peso vivo ao abate e as características de carcaça (P≤0,0305). Os resultados sugerem que alturas próximas a 30 cm permitem maiores ganhos individuais, devido ao aumento da quantidade de forragem disponível por animal e a melhor qualidade da forragem consumida, não havendo comprometimento da palhada residual destinada à cultura subsequente.

ABSTRACT The aim of this study was to evaluate the effects of different grazing intensities on forage production and animal performance of yearling steers kept under permanent grazing in an integrated crop-livestock system. The treatments consisted of areas with sward heights of 10; 20; 30 and 40 cm, and one treatment with no grazing. The pastures were of bristle oat (Avena strigosa Schreb.) and annual ryegrass (Lolium multiflorum Lam.) following soybean (Glycine max (L.) Merr.). The variables forage mass, forage allowance and residual straw showed a positive and linear fit to the increasing sward height (P≤0.0001). Average daily gain of steers displayed a quadratic response (P = 0.0017), being optimal with increases in grazing height up to values of near 30 cm, showing a weight gain per animal of approximately 1.0 kg day-1. A similar response was seen for live weight at slaughter and carcass characteristics (P≤0.0305). The results suggest that sward heights close to 30 cm provide greater individual gains, due to the increase in forage available to each animal and the better quality of the consumed forage without compromising the residual straw destined for the following crop.

ABSTRACT: Irrigated rice in the state of Rio Grande do Sul (Brazil) has shown significant growth in yield in recent years due to improved management practices, especially in regard to fertilizer use. However, the response curves that led to the current fertilizer recommendations do not consider integrated systems prevailing in rice-producing regions that have adopted the practice of integrated crop-livestock systems. The aim of the present study was to evaluate the effectiveness of current fertilizer recommendations for irrigated rice in lowland soils in Rio Grande do Sul under integrated crop-livestock systems for different periods of time. The experiments were performed in the 2012/2013 growing season on four farms in the state with different forage species under cattle grazing. In these areas, fertilizer recommendations were made based on previous soil analyses, and treatments consisted of fractions of the currently recommended application rates. At the end of the crop cycle, the percentages of maximum technical efficiency (PMTE) and maximum economic efficiency (PMEE) of NPK fertilizers, and increases in yield and net income provided by PMEE were determined. Rice yield increased and fertilizer response decreased over time in a rice-beef cattle integrated system. The highest incomes with fertilization of irrigated rice occurred at lower application rates than those recommended by soil analysis.

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.

RESUMO Busca-se nos Sistemas Integrados de Produção Agropecuária (SIPA) maior ciclagem do nitrogênio (N). Este trabalho objetivou avaliar a adubação antecipada em azevém pastejado por ovinos no índice de nutrição nitrogenada (INN) das culturas de verão em SIPA. O estudo foi realizado em um protocolo de longa duração manejado, no período de inverno, sob dois métodos de pastoreio, contínuo e rotativo, e duas intensidades de pastejo, moderada e baixa, com quatro repetições. No verão, a área foi subdividida em dois sistemas de cultivos, soja e rotação soja/milho. A fertilização foi feita na fase pastagem, com 75 kg de N e 60 kg de P2O5 e K2O ha-1. Avaliaram-se a massa de forragem residual (MFR) da pastagem e o rendimento, o teor de N e o INN da fitomassa das culturas de verão. No milho, houve efeito das intensidades de pastejo para INN, ao contrário da soja. Não houve efeito dos métodos de pastoreio. A MFR é importante fonte de N para a cultura de verão subsequente. Menores intensidades de pastejo geraram maiores MFR e INN para a cultura do milho. A adubação antecipada não influenciou a soja, pois essa atende parte da sua demanda por N pela fixação biológica.

ABSTRACT Greater nitrogen (N) cycling is sought through Integrated Crop-Livestock Systems (ICLS). The aim of this study was to evaluate the effect of early fertilization of nitrogen applied to ryegrass grazed by sheep on the nitrogen nutrition index (NNI) of summer crops in ICLS. This study was carried out in a long-term protocol managed in the winter under two stocking methods, continuous and rotational, and two grazing intensities, moderate and low, with four replications. In summer, the area was divided into two cropping systems - soybean monoculture and a soybean/maize rotation. Fertilization was carried out in the pasture phase with 75 kg N and 60 kg P2O5 and K2O ha-1. Residual forage mass (RFM) of pasture, and phytomass yield, N content, and NNI of the summer crops were evaluated. An effect of grazing intensities was found on the maize NNI, but not on soybean. There was no effect from grazing methods. The RFM is an important source of N for the subsequent summer crop. Lower grazing intensities generate higher RFM and NNI for maize. Early fertilization did not affect soybean, because it meets part of its N demand by biological nitrogen fixation.

RESUMO Urina e fezes de ovinos são componentes importantes do ciclo do N em pastagens, mas pouco se sabe sobre o efeito desses nas emissões de óxido nitroso (N2O) para atmosfera. Um estudo foi conduzido para quantificar as emissões de N-N2O provenientes das excretas de ovinos sobre uma pastagem de azevém num Argissolo Vermelho Distrófico típico no sul do Brasil. Quatro doses de N-urina (161, 242, 323 e 403 kg ha-1 N) e uma de N-fezes (13 kg ha-1 N) foram aplicadas, além de um tratamento-controle sem aplicação de excretas. O fator de emissão de N-N2O (FE = % do N adicionado emitido na forma de N-N2O) foi calculado para urina e fezes, levando em consideração os fluxos de N2O determinados no período de 39 dias. Os FEs da urina e fezes foram utilizados para estimar as emissões de N-N2O num período de 90 dias da pastagem no inverno, sob duas intensidades de pastejo (2,5 e 5,0 vezes o potencial de consumo dos ovinos). Os fluxos de N-N2O variaram de 4 a 353 µg m-2 h-1. Os fluxos mais elevados de N-N2O ocorreram 16 dias após a aplicação da urina e das fezes, quando os teores mais elevados de nitrato ocorreram e a porosidade preenchida por água excedeu 60 %. O FE médio da urina foi 0,25 % do N aplicado, muito superior ao verificado para as fezes (0,06 %). Considerando o período de 90 dias de utilização da pastagem no inverno, estimou-se que a emissão de N-N2O foi de 0,54 kg ha-1 na intensidade de pastejo baixa e de 0,62 kg ha-1 na intensidade de pastejo moderada. Entre as excretas, a urina foi o principal contribuinte para a emissão de N-N2O (media de 36 %), enquanto as fezes foram responsáveis por menos do que 0,1 % das emissões totais de N-N2O do solo.

ABSTRACT Livestock urine and dung are important components of the N cycle in pastures, but little information on its effect on soil nitrous oxide (N2O) emissions is available. We conducted a short-term (39-day) trial to quantify the direct N2O-N emissions from sheep excreta on an experimental area of ryegrass pasture growing on a Typic Paleudult in southern Brazil. Four rates of urine-N (161, 242, 323, and 403 kg ha-1 N) and one of dung-N (13 kg ha-1 N) were applied, as well as a control plot receiving no excreta. The N2O-N emission factor (EF = % of added N released as N2O-N) for urine and dung was calculated, taking into account the N2O fluxes in the field, over a period of 39 days. The EF value of the urine and dung was used to estimate the emissions of N2O-N over a 90-day period of pasture in the winter under two grazing intensities (2.5 or 5.0 times the herbage intake potential of grazing lambs). The soil N2O-N fluxes ranged from 4 to 353 µg m-2h-1. The highest N2O-N fluxes occurred 16 days after application of urine and dung, when the highest soil nitrate content was also recorded and the water-filled pore space exceeded 60 %. The mean EF for urine was 0.25 % of applied N, much higher than that for dung (0.06 %). We found that N2O-N emissions for the 90-day winter pasture period were 0.54 kg ha-1 for low grazing intensity and 0.62 kg ha-1 for moderate grazing intensity. Comparison of the two forms of excreta show that urine was the main contributor to N2O-N emissions (mean of 36 %), whereas dung was responsible for less than 0.1 % of total soil N2O-N emissions.