Biomass components of Pennisetum purpureum cv. Roxo managed at different growth ages and seasons

Rev. Bras. Saúde Prod. Anim., Salvador, v.19, n.1, p.11-22 jan./mar., 2018 http://dx.doi.org/10.1590/S1519-99402018000100002 ISSN 1519 9940 Biomass components of Pennisetum purpureum cv. Roxo managed at different growth ages and seasons Componentes da biomassa em “Pennisetum purpureum” cv. Roxo manejado sob diferentes idades e épocas de crescimento MARANHÃO, Theyson Duarte1*; CÂNDIDO, Magno José Duarte1; LOPES, Marcos Neves1; POMPEU, Roberto Claudio Fernandes Franco2; CARNEIRO, Maria Socorro de Souza1; FURTADO, Rafael Nogueira1; SILVA, Rafael Rodrigues da1; SILVEIRA, Francisco Gleyson Alves da1 1 Universidade Federal do Ceará, Centro de Ciências Agrárias, Departamento de Zootecnia, Fortaleza, Ceará, Brasil. 2 Embrapa Caprinos e Ovinos, Sobral, Ceará, Brasil. *Endereço para correspondência: SUMMARY RESUMO This study was carried out aiming to evaluate the biomass components of elephant grass cv. Roxo at seven growth ages, during rainy, transition and dry seasons. A completely randomized design was adopted with a split plot arrangement over time. The treatments consisted of seven growth ages (9, 18, 27, 36, 45, 54 and 63) and three seasons (rainy, transition and dry). The variables green forage biomass, dead forage biomass, green stem biomass and green leaf blade biomass showed positive linear responses to age and had their magnitude influenced by the evaluated seasons. The live/dead material ratio showed a decreasing linear response as a function of age. The leaf blade/stem ratio showed a negative linear adjustment in the rainy season, reaching a critical value of 1.0 at 59 days, and it showed a quadratic adjustment in the transition season, with the maximum point at 27.53 days; however, this ratio was not influenced by age in the dry season, revealing an average value of 2.22 ± 0.27. The canopy height and leaf area index showed a positive linear response to age in the three seasons. Tiller population density showed quadratic behaviour for age, with maximum estimated values of 134 and 110 til. m-2 at 31.24 and 37.40 days in the rainy and dry seasons, respectively. Rainfall seasonality influences the magnitude of the daily increase of the distinct biomass components of Pennisetum purpureum cv. Roxo. Objetivou-se avaliar os componentes da biomassa em capim-elefante cv. Roxo em sete idades de crescimento, nas épocas chuvosa, transição e seca. Adotou-se um delineamento inteiramente casualizado, em arranjo de parcelas subdivididas no tempo. Os tratamentos consistiram em sete idades de crescimentos (9; 18; 27; 36; 45; 54 e 63 dias) e três épocas (chuvosa, transição e seca). As variáveis biomassa de forragem verde, forragem morta, colmo verde e de lâmina foliar verde apresentaram resposta linear positiva para o fator idade e tiveram suas magnitudes influenciadas pelas épocas de avaliação. A relação material vivo/material morto respondeu de forma linear decrescente em função das idades. A relação lâmina foliar/colmo apresentou ajuste linear negativo na época chuvosa, atingindo valor crítico de 1,0 aos 59 dias e ajuste quadrático na época de transição, com ponto de máxima aos 27,53 dias, e não foi influenciada pelo fator idade na época seca, com valor médio de 2,22±0,27. A altura do dossel e o índice de área foliar responderam de forma linear positiva para o fator idade, nas três épocas. A densidade populacional de perfilhos apresentou comportamento quadrático para o fator idade, com valores máximos estimados em 134 e 110 perf. m-2 aos 31,24 e 37,40 dias de idade nas épocas chuvosa e seca, respectivamente. A sazonalidade da precipitação pluvial influencia a magnitude do incremento diário nos distintos componentes da biomassa em Pennisetum purpureum cv. Roxo. Keywords: canopy structure, elephant grass, seasonality Palavras-chave: estacionalidade, estrutura do dossel, Pennisetum purpureum 11 Rev. Bras. Saúde Prod. Anim., Salvador, v.19, n.1, p.11-22 jan./mar., 2018 http://dx.doi.org/10.1590/S1519-99402018000100002 INTRODUCTION Elephant grass (Pennisetum purpureum) is widespread in tropical and subtropical regions, and it can be managed under grazing or cutting, due to its good agronomic characteristics, such as adaptation to different soil and climatic conditions, high productivity, perenniality, and responsiveness to management. The morphophysiological characteristics are conditioned by the abiotic factors to which the canopy is submitted, since, although the expression of morphogenic characteristics is genetically determined, its magnitude is influenced by extrinsic factors, and thus morphogenesis is the determining event for the canopy structure (CHAPMAN & LEMAIRE, 1993). However, morphological modifications of the structural components of the canopy, implied in the qualitative characteristics of the biomass, are detrimental to the accumulation of carbon in plant organs of lower nutritional value during forage development. In tropical regions, the variability of rainfall is the most inductive abiotic factor of phenotypic plasticity of forage plants managed under waterless conditions. Biomass production is another variable strongly influenced by climatic changes. Alencar et al. (2009), working with six grasses of different genera, verified effects of the seasonality on the variable total forage biomass. The recommendations in the literature for the ideal cutting time of P. purpureum are based on variables such as height, chronological age or number of internodes (ANDRADE & GOMIDE, 1971); however, such recommendations are used for canopies under optimal conditions for the ISSN 1519 9940 development of the culture. It is also difficult to find models in the literature that allow an estimation of the ideal cutting time of this grass in different edaphoclimatic conditions with satisfactory levels of precision, including both productive and qualitative indexes. This study aimed to evaluate the biomass components of elephant grass cv. Roxo at seven growth ages, during rainy, transition and dry seasons. MATERIAL AND METHODS The study was carried out in a canopy of elephant grass (Pennisetum purpureum) cv. Roxo established in 2007, cultivated in sandstone yellow clay soil, belonging to the Núcleo de Ensino e Estudos em Forragicultura of the Departamento de Zootecnia of the Centro de Ciências Agrárias of Universidade Federal do Ceará – NEEF/DZ/CCA/UFC, located in Fortaleza, CE. According to Köeppen's classification, the region has an Aw' rainy tropical climate type. Cumulative rainfalls of 373.30, 17.30 and 9.60 mm for the rainy, transition and dry seasons were recorded, respectively. The potential evapotranspiration of the crop was estimated as 39.43, 46.11 and 52.58 mm day-1 for the rainy, transition and dry seasons, respectively (Figure 1). The treatments consisted of seven growth ages (9, 18, 27, 36, 45, 54 and 63 days) and three seasons (rainy, transition and dry) with three replicates (plots of 3.0 x 3.5 m). A completely randomised design with a split plot arrang (...truncated)