Biomass components and structure of massai grass fertilized with nitrogen and grazed by sheep

M.N. Lopes https://orcid.org/0000-0002-1562-3919 M.J.D. Cândido https://orcid.org/0000-0003-3573-6053 R.C.F.F. Pompeu http://dx.doi.org/10.1590/1678-4162-10051 https://orcid.org/0000-0002-4099-3575 R.G. Silva https://orcid.org/0000-0002-0062-7554 M.S.S. Carneiro Arq. Bras. Med. Vet. Zootec., v.71, n.4, p.1411-1420, 2019 https://orcid.org/0000-0002-6887-7111 L.B. Morais Neto https://orcid.org/0000-0002-2293-7393 M.J.A. Peixoto https://orcid.org/0000-0003-1367-2095 Biomass components and structure of massai grass fertilized with T.C.F. Carvalho https://orcid.org/0000-0002-3141-0550 nitrogen and grazed by sheep [Componentes da biomassa e estrutura do capim-massai adubado com nitrogênio e pastejado por ovinos] M.N. Lopes1, M.J.D. Cândido1, R.C.F.F. Pompeu2, R.G. Silva3, M.S.S. Carneiro1, L.B. Morais Neto1, M.J.A. Peixoto4, T.C.F. Carvalho5 1 Universidade Federal do Ceará - Fortaleza, CE 2 Embrapa Caprinos e Ovinos - Sobral, CE 3 Instituto Federal de Educação, Ciência e Tecnologia do Ceará - Limoeiro do Norte, CE 4 Secretaria do Desenvolvimento Agrário do Ceará - Fortaleza, CE 5 Aluna de pós-graduação - Universidade Estadual do Ceará - Fortaleza, CE ABSTRACT To evaluate the biomass components of massai grass subjected to nitrogen (N) fertilization levels (control - 0; 400; 800 and 1200 kg ha-1 year-1 of N) and under rotational stocking with sheep, this study was undertaken using a completely randomized design with measurements repeated in time. A quadratic response was observed reaching maximum values as the levels of nitrogen fertilization increased for green forage biomass, green leaf biomass, green stem biomass (5,172.9; 4,146.3; 1,033.9 kg ha-1 cycle-1, respectively), forage total density (179.1 kg ha-1 cm-1), canopy height (36.8 cm) and live material/dead material ratio (4.0) at levels 896; 934; 797; 879.2; 751.4 and 1,161 kg ha-1 year-1 of N, respectively. For all variables, oscillation was observed between the grazing cycles studied. Nitrogen fertilization has a positive response on the biomass components and canopy structure of massai grass. Keywords: forage production, green leaf biomass, nitrogen fertilization, Panicum maximum RESUMO Objetivou-se avaliar os componentes da biomassa do capim-massai sob lotação rotativa com ovinos e adubado com doses de nitrogênio (controle - 0; 400; 800 e 1200 kg de N ha-1 ano-1), em delineamento inteiramente ao acaso, com medidas repetidas no tempo. Constatou-se resposta quadrática, alcançando valores máximos com o incremento das doses de nitrogênio para as produções de biomassa de forragem verde, de lâmina foliar verde, de colmo verde (5172,9; 4146,3; 1033,9 kg ha-1 ciclo-1, respectivamente) e para a densidade total de forragem (179,1 kg ha-1 cm-1), altura do dossel (36,8 cm) e relação material vivo/material morto (4,0) nas doses 896; 934; 797; 879,2; 751,4 e 1161 kg ha-1 ano-1 de N, respectivamente. Para todas as variáveis, verificou-se oscilação entre os ciclos de pastejo estudados. A adubação nitrogenada exerce respostas positivas sobre os componentes da biomassa e a estrutura do dossel do capim-massai. Palavras-chave: adubação nitrogenada, biomassa de folha verde, Panicum maximum, produção de forragem  INTRODUCTION The maximization of biomass production up to the productive genetic potential of forages reflects from specific conditions such as light, Recebido em 18 de maio de 2017 Aceito em 11 de dezembro de 2018 E-mail: humidity, nutrient availability, temperature and management. Soil fertility is one of the main factors influencing the quality and biomass production of forage plants. Among the nutrients, nitrogen plays an important role in increasing productivity (Alves et al., 2008; Pompeu et al., Lopes et al. Forage biomass production is the main component that defines the carrying capacity of pastures, hence the relevance of knowledge of its components to understand how the management practices (fertilization, irrigation, adjustment of animal load and others) influence them. The response potential of forages to fertilization, especially nitrogen, is an important aspect in the selection of cultivars for intensive livestock systems in pasture. Massai grass, a forage of the genus Panicum maximum introduced in 2001 by Embrapa has revealed important characteristics in studies conducted by Martuscello et al. (2006) and Lopes et al. (2011a), regarding the production of leaf biomass, leaf blade / stem ratio, high capacity to emit leaves and tillers, among other characteristics, in response to nitrogen fertilization under greenhouse conditions. However, studies with the purpose of evaluating the biomass components and canopy structure of the massai grass under intensive management conditions in rotational stocking with sheep and fertilized with nitrogen under irrigation are still incipient. Due to the above, this research was carried out with the objective of studying the massai grass managed under rotational stocking with sheep and fertilized with nitrogen through the evaluation of the biomass components and canopy structure. MATERIAL AND METHODS The experiment was carried out on a pasture of Panicum maximum cv. Massai, at the Nucleus of Teaching and Studies in Forage Crop of the Animal Science Department of the Agricultural Sciences Center of the Federal University of Ceará - NEEF / DZ / CCA / UFC, in Fortaleza CE. Fortaleza is located at an average altitude of 21 meters, with the following geographic coordinates: latitude south of 03° 45' 47'', longitude west of 38° 31' 23'', with climate type Aw', tropical rainforest, according to the Köeppen classification. The monthly average temperature (maximum average, average and minimum average), precipitation and insolation of the experimental period are shown in Figure 1. 35,0 Temperatura (o C) 30,0 25,0 20,0 15,0 10,0 5,0 37,8 3,0 2,0 5,2 Setembro Outubro Novembro 0,0 Agosto 500 450 400 350 300 250 200 150 100 50 0 Precipitação (mm) e Insolação (horas) 2010; Magalhães et al., 2006) and in the quality of the forage produced (Chagas and Botelho, 2005), besides providing greater regrowth vigor by accelerating the recovery capacity of the defoliated plants, guaranteeing persistence and perenniality of the pastures throughout the successive cycles of grazing or cutting. Meses Precipitação Mensal Temperatura Média Insolação Mensal Temperatura Média Mínima Temperatura Média Máxima Figure 1. Climatic data of the experimental period in Fortaleza - CE, in 2009. 1412 Arq. Bras. Med. Vet. Zootec., v.71, n.4, p.1411-1420, 2019 Biomass components… The soil of the experimental area is classified as yellow Argisol, having as its source material sandy-clay sediments of the barreira formation (Sistema…, 1999). The soil analysis (0-20 cm depth) carried out at the beginning of the experiment presented the following chemical characteristics: 9 mg dm-3 P; 15.64mg dm-3 K; 1.3cmolc dm-3 Ca2+; 1.2 cmolc dm-3 Mg2+; 0.35cmolc dm-3 of Al3+; 0.10 cmolc dm-3 of Na+; organic m (...truncated)