-The objective of this study was to evaluate the effect of grazing intensity on herbage accumulation, animal performance, and total system yield on irrigated Tanzania grass pastures under rotational stocking. The experiment was conducted from October 1999 to January 2001, in a complete randomized block design with four replications. Treatments consisted of three grazing intensities, represented by the following quantities of green forage dry mass remaining after grazing: 1,000 (high intensity), 2,500 (intermediate intensity) and 4,000 (low intensity) kg ha −1 . Grazing cycles were of 36 days (33 rest and 3 grazing). The values observed at the end of the experiment for post grazing forage mass were close to the proposed values. Forage yield was 25,278, 36,850, and 34,144

RESUMOO objetivo deste experimento foi caracterizar e quantificar respostas de Brachiaria brizantha cv. Marandu sob níveis de infestações de cigarrinhas adultas do gênero Mahanarva (Hemiptera: Cercopidae). O ensaio foi realizado em casa de vegetação na Cidade de Piracicaba, SP, e seus tratamentos corresponderam a quatro níveis de infestações de cigarrinhas (5, 10, 20 e 40 insetos adultos vaso -1 ) mais o controle (sem cigarrinhas), distribuídos nas unidades experimentais (vasos) segundo delineamento inteiramente casualizado. O estudo compreendeu período de infestação pelo inseto e de rebrota das plantas. Avaliaram-se as seguintes variáveis-resposta: acúmulo de forragem, massa de raiz e teor de reservas orgânicas. Não foi observado efeito das cigarrinhas na massa das frações rebrote, resíduo e sistema radicular do capim-marandu (p > 0,05). A massa do resíduo e sistema radicular, assim como a concentração de carboidratos não estruturais nesses órgãos de acúmulo, sofreram influência apenas do período de rebrota (p < 0,0001). Já a concentração de nitrogênio total no resíduo e nas raízes foi influenciada pela interação entre níveis de infestação e período de rebrota (p < 0,0001 e p = 0,0521). PALAVRAS-CHAVE:Brachiaria brizantha, carboidratos não estruturais, Mahanarva, reservas orgânicas, sistema radicular.ABSTRACT REGROWTH OF MARANDU PALISADEGRASS SUBMITTED TO SPITTLEBUGS ATTACK. The objective of this experiment was to characterize and quantify responses of Brachiaria brizantha cv. Marandu under different infestation levels of adult spittlebugs of the genus Mahanarva (Hemiptera: Cercopidae). The experiment was carried out in a greenhouse, in Piracicaba, SP. Treatments corresponded to four spittlebugs infestation levels (5, 10, 20 and 40 adults pot -1 ) plus the control (unifested), distributed in the experimental units (pots) according to a completely randomized design. The study included period of infestation by insects and regrowth of plants. The following response variables were measured: forage yield, root mass and organic reserves. No significant spittlebug effect was observed on regrowth, stubble and root mass of marandu palisadegrass (p > 0.05). The stubble and root mass, as well as the nonstructural carbohydrates concentration, were influenced only during the regrowth period (p < 0.0001). The total nitrogen concentration in stubble and in roots was influenced by the interaction between infestation levels and regrowth period (p < 0.0001 and p = 0.0521).

Spittlebugs are the main pest of tropical pastures and Marandu palisade grass (Urochloa brizantha cv. Marandu) is the most representative cultivated pasture in the tropics. Our objective was to characterize Marandu palisade grass responses subjected to Mahanarva (Hemiptera: Cercopidae) attack and to estimate the losses in terms of beef production from pasture-based systems. A set of five experiments were carried out. Three consecutive years of monitoring showed that Mahanarva spittlebugs increased their abundance after first rains with three to four peaks throughout the wet season. A decrease of 66% on herbage yield was observed in the greenhouse trial, with an average decrease of 61% on pools of calcium, magnesium, phosphorus, sulfur, potassium, crude protein, neutral-detergent fiber and in vitro digestible dry matter of Marandu palisade grass. Results from field experiments corroborated with greenhouse trial showing decreases on herbage yield varying from 31 to 43% depending on level of fertilization and grazing severity of Marandu palisade grass. Finally, an unprecedented 154-ha field experiment indicated that Mahanarva decreases 74% the beef productivity (i.e. kg body weight ha −1) of Nellore heifers grazing Marandu palisade grass. Brazil has the largest commercial beef cattle herd and is one of the top beef exporters in the world 1. Brazilian beef represents 20% of all global beef trading and, together with other agricultural commodities, it sums to about 21% of gross domestic product in Brazil 2. Beef cattle production in Brazil is characterized by pasture-based systems of which almost 90% of the cattle slaughtered comes from 3. However, despite highly representative, pasture-based livestock systems are extensive and conducted with low technology inputs resulting in low stocking rates (SR) and animal performance (i.e. average daily gain, ADG). Studies have reported beef production greater than 1,500 kg of body weight (BW) ha year −1 whilst the Brazilian average is much lower at about 150 kg BW ha year −14. Many factors stand out as key drivers for this poor productivity, among them: inadequate grazing management strategies, low soil fertility, and pest damage 5. The 215 million head of cattle in Brazil occupy approximately 160 million hectares composed by 70% of cultivated pasture species and 30% of native grasslands 6,7. Marandu palisade grass {Brachiaria brizantha (Hochst. ex A. Rich.) R. D. Webster [syn. Urochloa brizantha (A. Rich.) Stapf]} is the most representative of the cultivated pasture species, grown in about 50 million hectares in the country 8. It was launched by Embrapa in 1984 as an alternative to signal grass (Brachiaria decumbens cv. Basilisk, syn. Urochloa decumbens Stapf R.D. Webster) owing to its higher herbage yield and, mainly because of its resistance to "pasture spittlebugs" such as Notozulia entreriana (Berg, 1879), Deois flavopicta (Stål, 1854) and Deois schach (Fabricius, 1787) (Hemiptera: Cercopidae) 9. However, from the mid-1990s, spittlebugs from the genus Mahanarva have been r...

Aos meus pais Euvaldo Rebouças Pereira de Almeida e Eliane Dias de Castro, e à minha família, pelo apoio e carinho. À companheira Ana Paula Oeda Rodrigues pelo amor, dedicação, e infinita paciência. Ao Professor Moacyr Corsi pela amizade, confiança e exemplo profissional. Aos amigos de Piracicaba Felipe Pecinatto Daltro e Guilhermo Francklin de Souza Congio, pela amizade e companhia e discussões desde a graduação. Aos irmãos de São Paulo, Bruno Iyda Saggese, Caio Cesar do Amaral, Felipe Teixeira Gonçalves e João Pedro Marcondes Mourão, por sempre terem sido parte da família. Aos amigos, companheiros de pós-graduação, Ricardo Cazerta Duarte Goulart, Mariana Pares Andreucci e Fernando Masello Junqueira Franco e Alonso José de Resende Júnior. Ao amigo Miguel Miiti Shiota pela contribuição especial na viabilização deste trabalho. Aos amigos Linicius Schiavuzzo Mendes e Tiago Alves Corrêa. Aos todos os integrantes do grupo de estágio Projeto CAPIM, desde os atuais alunos de graduação, até os ex-integrantes, pela amizade contínua ao longo de todos esses oito anos de convivência, pela colaboração com a minha formação, pelo companheirismo, e pelo trabalho em conjunto até o último minuto. A todos colegas do programa de pós graduação em Ciência Animal e Pastagens, pelo exemplo de dedicação, pela solicitude sempre que preciso e pela troca de experiências e informações. Aos membros da comissão de pesquisa, Prof. Dr. Flávio Augusto Portela Santos e Prof. Dr. Carlos Guilherme Silveira Pedreira pela colaboração e boa vontade.