ABSTRACT. The objective was to evaluate the production of Megathyrsus maximus genotypes (Syn. Panicum maximum), under different levels of water in the soil. This was a 5x5 factorial completely randomized design conducted in a greenhouse, combining five genotypes of M. maximus (B55, C10 and PM30, cv. Massai and cv. BRS Tamani) and five levels of soil field capacities (20%, 40%, 60%, 100% and 140%), with three replications. Dry matter production was evaluated: leaf, stem, dead material, root, shoot and total dry matters, as well as the number of tillers and leaf:stem and aboveground:root ratios. The qualitative factor (genotypes) was subjected to Duncan test at 5% probability. The quantitative factor (% field capacity) was subjected to regression, adopting 5% as a critical level of probability. There was no interaction between the factors for any of the evaluated characteristics. Significant differences among the genotypes were detected for tiller number, dead material dry mass, root and total dry mass and leaf:stem ratio. There was no significant effect of the percentage of field capacity on most of the characteristics, except for leaf:stem and aboveground:root ratios. Cultivar Massai showed the best forage production compared to the other genotypes, regardless of the percentage of field capacity evaluated. In general, the evaluated genotypes were more tolerant to excess water stress than to water deficit.

Resumo: O objetivo deste trabalho foi avaliar as características morfogenéticas, estruturais, fisiológicas e produtivas do amendoim-forrageiro submetido a diferentes níveis de sombreamento artificial no campo. O amendoim-forrageiro 'Amarillo MG-100' foi plantado em abril de 2015, e as avaliações foram realizadas de maio de 2017 a abril de 2018. Os tratamentos foram: 0, 30, 45 e 75% de sombreamento artificial. Não houve efeito significativo do sombreamento sobre as características morfogenéticas do amendoim-forrageiro. O sombreamento aumentou o comprimento final da folha e a altura do dossel e diminuiu o índice de área foliar e o número de estolões. A fotossíntese, a taxa de transpiração, a condutância estomática, a clorofila b e a temperatura das folhas aumentaram quadraticamente em função do sombreamento. Houve efeito linear positivo sobre o tamanho do ciclo de crescimento e efeito quadrático sobre a produção de massa de matéria seca, com o máximo a 30% de sombra. O amendoim-forrageiro colhido a 95% de interceptação luminosa (11 cm de altura) apresenta adaptação ao sombreamento de até 45%, com aumento do tamanho das folhas, da altura do dossel, da taxa fotossintética, da condutância estomática, da taxa de transpiração e da clorofila b. Além disso, as plantas sob sombreamento de 30% apresentam maior rendimento do que aquelas que crescem sob a luz do sol.

Abstract: The objective of this work was to evaluate the morphogenetic, structural, physiological, and productive traits of forage peanut (Arachis pintoi) subjected to different levels of artificial shading in the field. The 'Amarillo MG-100' forage peanut was planted in April 2015, and the evaluations were carried out from May 2017 to April 2018. The treatments were: 0, 30, 45, and 75% of artificial shading. There was no significant effect of shading on the morphogenetic traits of forage peanut. Shading increased final leaf length and canopy height and decreased the leaf area index and number of stolons. Photosynthesis, transpiration rate, stomatal conductance, chlorophyll b, and leaf temperature increased quadratically as a function of shading. There was a linear positive effect on the growing cycle length and a quadratic effect on the production of dry matter mass, with the maximum at 30% shade. Forage peanut harvested at 95% light interception (11-cm height) shows adaptation to shading up to 45%, with increased leaf size, canopy height, photosynthetic rate, stomatal conductance, transpiration rate, and chlorophyll b. In addition, plants at 30% shading show a higher yield than those growing under full sun.

ABSTRACT. The aim of this study was to evaluate the addition of macauba palm cake (Acrocomia aculeata) on the chemical composition, fermentation and aerobic stability of elephant grass silages (Pennisetum purpureum). The experiment was performed in a completely randomized design with four replicates. The treatments were composed of six levels of macauba palm cake (0, 6, 12, 18, 24, 30%) as additive to elephant grass silage. Dry matter and ethereal extract content of the silage increased linearly with the inclusion of the additive. Addition levels of 15.54% would provide 35% of dry mass, and the limit of 7.00% of ethereal extract in the silage could be obtained with 10.47%. The neutral detergent fiber content reduced linearly from 68.97 to 52.59%, but lignin increased linearly from 6.56 to 7.70%. There was a reduction of 0.17% in the ammoniacal nitrogen content for each 1% of cake. The minimum value of dry matter losses (1.33%) was estimated to the inclusion level of 23.70%. The aerobic stability increased with inclusions between 18 and 24% of cake. The use of levels between 10 and 15% of macauba palm cake are sufficient to optimize dry matter and ethereal extract contents of the silages and to provide a high aerobic stability with minimum losses.

ABSTRACT In experiments with selection of perennial plants, the initial performance is expected to be maintained throughout the productive life. The probability of repeating the agronomic response can be evaluated by the repeatability coefficient. The objective was to estimate repeatability coefficients of agronomic characteristics in Panicum maximum Jacq. using different methods and identify the best combinations between harvests according to the genotypic stabilization. Seventeen genotypes were evaluated in a randomized complete block design with three replicates. The coefficients of repeatability were estimated by the methods: ANOVA, structural analysis based on the mean of the correlation coefficients (SACOR), analysis of principal components based on the covariance matrix (PCCOV) and correlation matrix (PCCOR). In the genotypic stabilization, coefficients estimated by ANOVA and PCCOR were used. For total DM, repeatability coefficients ranged from 0.3500 to 0.4300 by the ANOVA and PCCOR methods, respectively. High repeatability coefficients were found for the characteristic leaf DM, while low coefficients were observed for leaf and stem percentages and leaf:stem ratio. For the genotypic stabilization of total DM and leaf:stem ratio, the best coefficients were observed for the combination of harvests 5 to 8. There are variations in the estimate of repeatability by different methods and the highest coefficients were those of the principal components based on the correlation and covariance matrices. For the genotypic stabilization, the best coefficients of repeatability and determination were observed for the harvests performed in the second rainy period.

RESUMO. O experimento foi conduzido, objetivando-se avaliar estratégias de manejo em pastos de capim-mombaça (Panicum maximum) sob lotação intermitente, submetidos a diferentes alturas de resíduo. O delineamento utilizado foi em blocos casualizados, com dois tratamentos (duas diferentes alturas de resíduo pós-pastejo - 30 e 50 cm) e três repetições. Foram avaliadas a altura do pasto no pré e no pós-pastejo, a massa e o acúmulo de forragem, os períodos de descanso, de ocupação, a produção dos componentes morfológicos do pasto, a produção de leite e a qualidade da forragem. Os dados foram submetidos à análise de variância e as médias foram comparadas pelo teste F a 5% de probabilidade. Para tratamentos com intensidade de pastejo mais severa, notou-se maior intervalo de pastejo. Encontrou-se maior acúmulo de forragem para pastos manejados com altura de 50 cm de resíduo de pastejo. Para massa de forragem no pós-pastejo, obteve-se maior produção e maior porcentagem de folhas para o resíduo de 50 cm, bem como maiores teores de PB e digestibilidade para folhas e colmos, e menores teores de lignina e FDN. Para manejo de pastos de capim-mombaça, recomenda-se a altura de 50 cm de resíduo, por promover maior produção de leite por animal e maior número de ciclos de pastejo, garantindo melhor aproveitamento da área.

ABSTRACT. This study was conducted to evaluate management strategies in Mombaça grass pastures (Panicum maximum) under intermittent grazing subjected to different residual heights. A randomized-block design with two treatments (two post-grazing residual heights: 30 and 50 cm) and three replications was adopted. Pasture heights pre- and post-grazing, forage mass and accumulation, rest and occupation periods, pasture morphological components, milk yield and quality forage were evaluated. The data were submitted to analysis of variance and the means were compared by the F test at 5% probability. A longer grazing interval was observed in the treatments under the more severe grazing intensity. For forage mass post-grazing, larger production and higher percentage of leaves were found with the 50 cm residue, as well as higher crude protein contents and digestibility of leaves and stems and lower lignin and neutral detergent fiber contents. The residual height of 50 cm is recommended for the management of Mombaça grass pasture, as it provides greater milk yield per animal and a larger number of grazing cycles, ensuring better use of the area.

RESUMO: Objetivou-se avaliar, por meio de correlação parcial, o grau de associação entre o acúmulo de forragem e as características morfogênicas do capim-tanzânia (Panicum maximum Jacq.) desfolhado com 95% de interceptação luminosa e adubado com nitrogênio em diferentes densidades de planta. O delineamento foi em blocos completos casualizados, com 12 tratamentos e duas repetições em esquema fatorial 4 × 3, constituído por 4 doses de nitrogênio (0, 80, 160 e 320kg ha-1 ano-1) e três densidades de plantas (9, 25 e 49 plantas m-2). As colheitas foram realizadas a 25cm do nível do solo quando as parcelas interceptavam 95% da luz incidente. Os coeficientes de correlação simples foram altos e positivos, entre o acúmulo de forragem e as taxas de alongamento de folha e de colmo e aparecimento de folha. Já a associação do acúmulo com a duração da vida das folhas foi alta e negativa. O estudo dos coeficientes de correlação parcial implicou em mudanças consideráveis na estrutura da correlação, onde a associação com o alongamento de colmos assumiu valor negativo e estatisticamente igual a zero, indicando não haver relação de causa e efeito entre estas variáveis. Resultado semelhante foi observado para a associação entre o acúmulo de forragem e o aparecimento de folhas e a duração da vida da folha. á a correlação parcial entre o acúmulo e o alongamento de folhas foi diferente de zero e positiva. Nesse contexto, em dosséis forrageiros de capim-tanzânia desfolhados com 95% de interceptação de luz, a taxa de alongamento foliar é a variável morfogênica que apresenta maior grau de associação com o acúmulo de forragem.

ABSTRACT: The objective of this study was to evaluate, through partial correlation analysis, the degree of association between herbage accumulation and morphogenetic traits of ‘Tanzania’ grass (Panicum maximum Jacq.) defoliated with 95% of light interception and fertilized with nitrogen, under different planting densities. The experiment was carried out in a randomized complete design with 12 treatments and two replicates, in a 4 × 3 factorial arrangement consisting of four nitrogen rates (0, 80, 160, and 320kg ha-1 Yr-1) and three planting densities (9, 25, and 49 plants m-2). Harvests were performed at 25cm above the soil, when the plots intercepted 95% of the incident light. The simple correlation coefficients between herbage accumulation and leaf and stem elongation rates and leaf appearance rate were high and positive. Correlation between herbage accumulation and leaf lifespan; however, was high and negative. The study of partial correlation coefficients revealed considerable changes in the correlation structure, whereby the association with stem elongation had a negative value statistically equal to zero, indicating no relationship between these variables. A similar result was observed for the correlations between herbage accumulation and leaf appearance and leaf lifespan. The partial correlation between accumulation and leaf elongation was different from zero and positive indicating a strong association. In Guinea grass cv. ‘Tanzania’ canopies defoliated at 95% light interception, leaf elongation is the morphogenetic variable with the highest strength of association with herbage accumulation.

RESUMO: O lançamento de forrageiras resultantes de programas de melhoramento genético tem sido importante fonte de liberação de novas forrageiras mais adaptadas e competitivas. Nessas situações, a avaliação do valor genético é essencial quando se objetiva ranquear os genótipos com base no valor genotípico, isento dos efeitos ambientais. O objetivo com este trabalho foi estimar e avaliar o valor genotípico de características agronômicas e de valor nutritivo de três progênies de P. maximum, resultantes do cruzamento entre duas progenitoras sexuais e as cultivares ‘Mombaça’ e ‘Tanzânia’. O experimento foi implantado em teste clonal no delineamento em blocos incompletos com três tratamentos (progênies 1, 2 e 3) com duas repetições (clones). Os híbridos foram manejados por meio de cortes na altura de 25cm do nível do solo por um ano, realizando seis cortes. A progênie 2 proporcionou melhores resultados para produção de folhas, rebrota, altura de planta e baixa incidência de mancha foliar causada por Bipolaris maydis. As progênies 1 e 3 apresentaram, em média, melhores resultados para características qualitativas como proteína bruta e digestibilidade e menor teor de lignina. As progênies híbridas de P. maximum apresentam características forrageiras de interesse para o melhoramento, sendo que a utilização do capim-mombaça como parental proporciona maior produção de folhas e resistência à mancha foliar, ao passo que o capim-tanzânia como parental proporciona melhoria da qualidade da forragem.

ABSTRACT: Genetic breeding of forage plants has increasingly contributed to the release of more productive plants. In this regard, evaluating the genotypic value is essential when aiming to rank genotypes based on the mean free of environmental factors. Therefore, this study aimed to predict the genotypic value of agronomic and nutritive value characters of three progenies of Panicum maximum. Hybrids were evaluated in a clonal test in an incomplete-randomized design with three treatments (progenies 1, 2, and 3) and two replications (clones). Six harvests were performed at 25cm from the ground level throughout one year. Progeny 2 provided better results for total and leaf dry mass yield, regrowth, and height, and lower incidence of leaf spot. Progenies 1 and 3 had a better response for qualitative characters such as higher crude protein and digestibility and lower lignin and fiber content. Hybrid progenies of P. maximum have forage characters of interest for breeding, and when using ‘Mombaça’ grass as parents, the progeny stands out for leaf production and resistance to leaf spot and for ‘Tanzania’ grass as parent has resulted in better forage quality.

The objective of this study was to evaluate the genotypic stability of agronomic traits in hybrids of Panicum maximum. Hybrids originating from the crosses between two sexual parents and cultivars Mombasa and Tanzania were evaluated in an incomplete-block design. Evaluated traits were total dry matter, leaf dry matter, stem dry matter, percentage of leaves, and leaf:stem ratio. These traits were evaluated in six harvests. Overall, higher repeatability was observed for the traits total dry matter and leaf dry matter, especially when harvests 4, 5, and 6, occurring in spring and summer, were evaluated. The leaf dry matter was the trait that provided the greatest repeatability and determination. The repeatability of stem dry matter, percentage of leaves, and leaf:stem ratio had a low magnitude, even when the coefficient was estimated based on the harvests of better stabilization for the other variables. The hybrids achieved genotypic stabilization in the harvests made in the second rainy season. Harvests made in the rainy season provide greater repeatability and determination, and the inclusion of the dry-season harvest is detrimental to the process of selection of low-repeatability traits such as percentage of leaves.

RESUMO: Cultivares do gênero Nopalea são conhecidos no Brasil por serem tolerantes ao ataque cochonilha carmim, tornando o cultivo desse gênero uma alternativa promissora para mitigar os efeitos negativos deste inseto sobre a produção de biomassa. Com o objetivo de caracterizar morfologicamente variedades de palma forrageira e identificar características morfológicas que podem ser o foco em programas de melhoramento genético, um experimento foi conduzido em delineamento de blocos casualizados com 11 tratamentos e quatro repetições. A variedade Alagoas apresentou os maiores valores de peso, área e volume de cladódios. As variedades Negro Michoacan F7 e V7, Tamazunchale V12 apresentaram os maiores valores de índice de área cladódio, volume total de cladódios e produção total de massa fresca. As variedades Negro Michoacan V7 e F7 apresentaram maior eficiência do uso de água e produção de massa seca. O volume de cladódios apresentou o maior coeficiente de correlação com a massa fresca de cladódios. Visando a liberação de variedades para a produção de biomassa, as variedades Negros Michoacan F7, V7 e V12 Tamazunchale podem substituir a variedade Miúda. O número e cladódios índice de área podem ser utilizados como critério para seleção de variedades superiores em programas de melhoramento.

ABSTRACT: Cultivars of the genus Nopalea are known in Brazil for being tolerant to cochineal carmine attacks, thus making the cultivation of this genus a promising alternative for mitigating the negative effects of this insect on the production of biomass. With the objectives of characterizing morphologically spineless forage cactus varieties and identify morphological characteristics that may be the focus in spineless forage cactus breeding programs, an experiment was conducted in a completely randomized block design with 11 treatments and four replications. The variety Alagoas showed the highest values of weight, area and volume of cladodes. The varieties Negro Michoacan F7 and V7, Tamazunchale V12 showed the highest values of the cladode area index, the total volume of cladodes and total fresh mass production. The varieties Negro Michoacan V7 and F7 presented the highest water use efficiency and dry mass yield. Cladode volume showed the highest correlation coefficients with the fresh weight of cladodes. Aiming the release of varieties for biomass production, varieties Negro Michoacan F7, V7 and Tamazunchale V12 may substitute the Miúda variety. The number and cladode area index may be used as criteria for selection of superior varieties in breeding programs.

O agrupamento de genótipos, via análise de variáveis canônicas, é importante ferramenta para o melhoramento e permite reunir indivíduos com características afins que, associadas ao melhor desempenho agronômico, podem ser indicativas do perfil ideal de planta para a região. Nesse sentido, objetivou-se definir, por meio do uso de análise canônica, o perfil agronômico de plantas de Panicummaximum adaptadas à região do agreste. O experimento foi conduzido em delineamento inteiramente casualizado com 28 tratamentos, 22 genótipos de P. maximum e os cultivares Mombasa, Tanzânia, Massai, Milênio, BRS Zuri e BRS Tamanie trêsrepetições, em parcelas de 4 m². Foram realizados cinco cortes por parcela e avaliadas as características: altura de planta, massa seca total, massa seca de folhas, massa seca de colmos, massa seca de material morto, relação folha/colmo, porcentagem de folhas e densidade volumétrica da forragem.A análise de variáveis canônicas foi realizada com base na média fenotípica dos caracteres avaliados e na matriz de variâncias e covariâncias residuais. O genótipo PM34 apresentou maior média paramassa seca de folhas nas condições do Agreste Alagoano (em média, 53% superior aoscultivares Mombasa, Tanzânia, Milênio e Massai). Foi possível resumir a variação observada em oito caracteres agronômicos em apenas duas variáveis canônicas, que acumularam 81,44% da variação dos dados. O ideótipo de planta adaptada às condições do Agreste deve apresentar, além de alta produção de folhas, porte alto, alta porcentagem de folhas, alta relação folha/colmo e valores intermediários de densidade volumétrica de forragem.

Grouping of genotypes by canonical variable analysis is an important tool in breeding. It allows the grouping of individuals with similar characteristics that are associated with superior agronomic performance and may indicate the ideal profile of a plant for the region. The objective of the present study was to define, by canonical analysis, the agronomic profile of Panicum maximum plants adapted to the Agreste region. The experiment was conducted in a completely randomized design with 28 treatments, 22 genotypes of Panicum maximum, and cultivars Mombasa, Tanzania, Massai, Milenio, BRS Zuri, and BRS Tamani in triplicate in 4-m² plots. Plots were harvested five times and the following traits were evaluated: plant height; total, leaf, and stem; dead dry matter yields; leaf:stem ratio; leaf percentage; and volumetric density of forage. The analysis of canonical variables was performed based on the phenotypic means of the evaluated traits and on the residual variance and covariance matrix. Genotype PM34 showed higher mean leaf dry matter yield under the conditions of the Agreste of Alagoas (on average 53% higher than cultivars Mombasa, Tanzania, Milenio and Massai). It was possible to summarize the variation observed in eight agronomic characteristics in only two canonical variables accounting for 81.44 % of the data variation. The ideotype plant adapted to the conditions of the Agreste should be tall and present high leaf yield, leaf percentage, and leaf:stem ratio, and intermediate values of volumetric density of forage.

O experimento foi conduzido objetivando-se determinar os coeficientes de repetibilidade, por quatro métodos (Análise de Variância, de Componentes principais - matriz de correlação e covariância e a Análise estrutural), o número de cortes necessários para aumento de acurácia e a estabilização fenotípica de características de produção em acessos de Panicum maximum. O experimento foi conduzido em delineamento inteiramente casualizado com 35 genótipos e três repetições. Foram realizados cinco cortes e as amostras foram pesadas e secas para obtenção da produção de matéria seca total, de colmo, folhas e material morto. Os coeficientes de repetibilidade nos diferentes métodos, para todas as características, oscilaram entre 0,1867 e 0,6583. As estimativas da repetibilidade obtidas pelo método da análise de variância foram quase sempre menores que as obtidas pelos demais métodos. Pelo método dos componentes principais (baseado na matriz de covariância), as estimativas foram sempre maiores em relação aos demais métodos. Portanto, é possível recomendar esse método para estimativas do coeficiente de repetibilidade para as características avaliadas nesse estudo. Considerando satisfatórios os níveis de 80 ou 90% de confiabilidade para avaliação da superioridade relativa dos acessos para todas as características avaliadas, as cinco medições realizadas são suficientes para escolha do melhor acesso.

The experiment aimed at determining repeatability coefficients for four methods (analysis of variance, principal components-correlation and covariance matrices and structural analysis), number of harvests necessary to increase accuracy and phenotypic stability of yield characteristics of accessions of Panicum maximum. The experiment was conducted in a completely randomized design with 35 genotypes and three replications. Five cuts were made and material was weighed and dried to obtain total, stem, leaf and dead forage dry matter yields. The repeatability coefficients in the different methods, for the evaluated characteristics, ranged from 0.1867 and 0.6583. The estimates of repeatability coefficients obtained for the evaluated characteristics by analysis of variance were generally smaller than the ones obtained with the other methods. By the principal components (based on the covariance matrix), the estimates were usually larger than those for the other methods. Therefore, it is possible to recommend this method to estimate the coefficient of repeatability for traits evaluated in this study. Considering that levels of 80 or 90% of confidence in the evaluation of the relative superiority of the accessions for all the evaluated characteristics are satisfactory, five harvests are sufficient for the choice of the best accession.

Objetivou-se avaliar as características morfogênicas e estruturais bem como a produção de biomassa de plantas de Panicum maximumcv. Massai sob doses de nitrogênio. O experimento foi instalado em delineamento de blocos casualizados com quatro tratamentos (0, 80, 160 e 240 kg de N/ha) e quatro repetições, em parcelas de 4 m2. A adubação nitrogenada foi aplicada parceladamente, de acordo como os tratamentos. Plantas de capim-massai responderam linear e positivamente à adubação nitrogenada com aumento significativo nas taxas de alongamento, aparecimento e senescência de folhas e alongamento de colmo bem como no número de folhas vivas por perfilhos e no comprimento final da lâmina. Por outro lado, a adubação nitrogenada diminui o filocrono e a duração de vida das folhas em capim-massai, o que indica efeito direto do nitrogênio no fluxo de tecidos. Observou-se efeito linear e positivo da adubação nitrogenada para massa seca total, de folhas e de colmos, não tendo sido observado efeito para massa seca de material morto. A adubação nitrogenda influencia o perfilhamento, a morfogênese e a produção de biomassa em plantas de capim-massai.

The objective of this study was to evaluate the morphogenetic and structural characteristics, as well as the biomass of Panicum maximumcv. Massai plants under nitrogen levels. The experiment was conducted in a randomized block design with four treatments (0, 80, 160 and 240 kg N/ha) and four replications in plots of 4 m2. The nitrogen was applied according to the treatments. Massaigrass plants responded linear and positively to N fertilization with a significant increase in the rates of elongation, appearance and senescence of leaves, stem elongation, and number of live leaves per tiller and the final length of the blade. On the other hand, the nitrogen decreased the phyllochron and leaf life span of the massaigrass, indicating a direct effect of nitrogen flow in the tissues. There was positive and linear effect of N fertilization on total dry matter of leaf and stem, but there was no effect on dry matter of dead material. Nitrogen fertilization influences tillering, morphogenesis and biomass production in massaigrass plants.

This study was carried out with the objective of estimating the genetic parameters of agronomic traits in Panicum maximum hybrids. Genotypes obtained from the crosses between the sexual plants S10 and S12 and cultivars Tanzania and Mombasa were evaluated. The design was an incomplete blocks design with two replicates (clones) and 33 blocks. Each block was constituted by three lines or plots with nine plants each, which were evaluated in six harvests. All the characters presented low broad sense heritabilities for both the individual harvest and for the mean of harvests and a large difference between the heritability and the individual repeatability coefficient, which may be due to the high permanent environmental variance, mainly for forage dry matter and leaf dry matter. On the other hand, the percentage of leaves also presented low repeatability and permanent environmental variance. The genotypic coefficients of variation were high, except for leaf percentage, but they were also associated with high residual coefficients of variation. Both the broad sense heritabilities per harvest and for the mean of harvests were of moderate magnitude for the agronomic traits evaluated in hybrid individuals of P. maximum. On the other hand, there is variability for selection of important characters such as total and leaf dry matter yields and selection for leaf percentage needs a greater number of harvests to improve selection efficiency. The genotypes presented great variability for Bipolaris maydis leaf spot incidence and this character can be included in the P. maximum breeding program.

This experiment was carried out with the objectives of determining repeatability coefficients, the number of harvests necessary to increase accuracy and the genotypic stability of yield characteristics in Brachiaria brizantha cultivars in the northeast region of Brazil in the period from July 2009 to March 2011. The experimental design used was completely randomized with three treatments (Brachiaria brizantha var. Marandu, Xaraés and Piatã) and three replications. Each plot was harvested seven times: five in the rainy season and two in the dry season. Immediately after each harvest, the forage was weighed and dried to obtain total, stem, leaf and dead dry matter yields. For the estimation of the repeatability coefficient, analysis of variance, principal components (correlation and covariance matrices) and structural analyses were used. The repeatability coefficients (r) obtained by the different methods, for all characteristics evaluated, varied from 0.009 to 0.837. The estimates of the repeatability coefficients obtained for all characteristics evaluated by the method of analyses of variance were almost always lower than those obtained by the other methods. By the principal components method (based on the covariance matrix), the estimates were always higher than those from other methods. Considering that levels of 80 or 90% confidence are satisfactory in the evaluation of the relative superiority of the cultivars for all the evaluated characteristics, with the exception of dead matter yield, the seven harvests are sufficient for the choice of the best cultivar to be used in the northeast region of Brazil.

Objetivou-se com este trabalho avaliar o efeito de doses de nitrogênio (N) e densidades de plantas (D) sobre a dinâmica de perfilhamento do capim-tanzânia (Panicum maximum Jacq.). O delineamento foi em blocos casualizados, com 12 tratamentos e duas repetições em esquema fatorial 4 × 3, com quatro doses de N (0, 80, 160 ou 320 kg ha-1 ano-1) e três densidades de plantas (9, 25 ou 49 plantas m-2). O número de perfilhos foi maior na densidade de 9 plantas m-2 e nas maiores doses de N, principalmente na segunda e terceira gerações. O N influenciou quadraticamente as taxas de aparecimento de perfilhos basilares e totais, que também foram influenciadas pela densidade de plantas e pela interação N × D. A taxa de aparecimento de perfilhos aéreos, no entanto, não foi influenciada pelos fatores avaliados. A taxa de mortalidade de perfilhos totais foi influenciada de forma quadrática pelas doses de N e pelas densidades de plantas. A taxa de mortalidade de perfilhos basilares respondeu quadraticamente à densidade de plantas, enquanto a taxa de mortalidade de perfilhos aéreos aumentou de linearmente com a adubação. Pastos implantados em densidades baixas ou intermediárias adubados com nitrogênio apresentam padrão mais intenso de renovação de perfilhos.

This study evaluated the influence of nitrogen levels (N) and plant density (D) on the tillering dynamics of Tanzania guinea grass (Panicum maximum Jacq.). Treatments were arranged in a completely randomized block design with 12 treatments and two replicates in a factorial scheme (4 × 3) with four levels of N (0, 80, 160 or 320 kg ha-1 N) and three plant densities (9, 25, and 49 plant m-2). Higher number of tillers was observed in the treatment with 9 plants m-2 and under higher levels of N, especially in the second and third generations. Still, the N influenced quadratically the appearance rate of basal and total tillers, which were also affected by plant density and interaction N × D. However, the appearance rate of aerial tiller was not influenced by factors evaluated. The mortality rate of total tiller was influenced quadratically by the nitrogen levels and plant densities. The mortality rate of basal tiller responded quadratically to plant density, whereas the mortality rate of aerial tiller increased linearly with fertilization. Pastures with low or intermediate densities fertilized with nitrogen, presented a more intense pattern of tiller renewal.