Avalia??o de plantas forrageiras tropicais sob sombreamentos no outono e inverno

O presente trabalho foi realizado com apoio da Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - Brasil (CAPES) - C?digo de Financiamento 001.Os sistemas de integra??o lavoura-pecu?ria-floresta, tamb?m conhecidos como agrossilvipastoris, podem contribuir positivamente para os sistemas de produ??o animal e s?o alternativas eficientes de uso da terra na recupera??o de ?reas degradadas. No entanto, a toler?ncia de gram?neas e leguminosas ao sombreamento depende da sua capacidade morfofisiol?gica para se adaptar a determinado n?vel de radia??o, conhecido como plasticidade fenot?pica. O objetivo com este trabalho foi avaliar o comportamento de quatro cultivares de plantas forrageiras tropicais sob diferentes n?veis de sombreamento e manejadas a 95% de intercepta??o luminosa (IL), ao longo do outono e inverno de 2019. Foram realizados quatro experimentos com quatro esp?cies forrageiras tropicais: Brachiaria spp. cv. Mavuno (capim-mavuno), Panicum maximum Jack cv. BRS Zuri (capim-zuri), Panicum maximum cv. BRS Tamani (capim-tamani) e Arachis pintoi cv. Amarillo (amendoim forrageiro). Cada experimento foi realizado em delineamento inteiramente casualizado (DIC), com seis repeti??es, submetidos aos n?veis de sombreamento artificial de 47% com radia??o fotossint?ticamente ativa (RFA) de 353 ?mol m-2s-1, de 64% com RFA de 242 ?mol m-2s-1, 74% com RFA de 172 ?mol m-2s-1 e o tratamento controle com as plantas cultivadas sem sombreamento, com RFA de 668 ?mol m-2s-1. As plantas foram mantidas sob regime de corte ao atingir 95% de IL. Durante o experimento foram realizadas avalia??es morfog?nicas para determina??o das vari?veis-respostas: taxa de aparecimento foliar, filocrono, taxa de alongamento foliar, taxa de senesc?ncia foliar, dura??o de vida da folha, taxa de alongamento do colmo/caule para todas as forrageiras e tamb?m a taxa de alongamento em largura e taxa de alongamento do pec?olo para o amendoim forrageiro. Antes do corte tamb?m foram realizadas as avalia??es estruturais, referentes ao n?mero de folhas vivas por perfilho, comprimento final da folha e do colmo ou caule, altura final das plantas, o ?ndice de ?rea foliar, densidade de perfilhos e o peso m?dio dos perfilhos. Tamb?m foram realizadas an?lises fisiol?gicas referentes aos teores de clorofila a e b, taxa fotossint?tica, condut?ncia estom?tica, taxa transpirat?ria, efici?ncia no uso da ?gua e temperatura da folha. Posteriormente, ap?s o corte foi determinada a composi??o morfol?gica (propor??o de folhas, colmo ou caule, material senescente e infloresc?ncia) e a produ??o de massa seca total de cada esp?cie forrageira sob os diferentes n?veis de sombreamento. Todos os dados foram analisados no programa estat?stico Statistical Analysis System - SAS 9.1. As m?dias das caracter?sticas morfog?nicas, morfofisiol?gicas e produtivas foram submetidas ? an?lise de vari?ncia e posteriormente ? an?lise de regress?o linear e quadr?tica a 5% de probabilidade. O capim-mavuno apresentou adapta??o aos sombreamentos de 47%, 64% e 74% ao longo do outono e inverno, visto que a produ??o de massa seca n?o diminuiu mesmo com a restri??o luminosa imposta pelos n?veis de sombreamentos nas plantas e houve aumentos no ?ndice de ?rea foliar, na propor??o de folhas, no teor de clorofila a e b e na taxa fotossint?tica nos sistemas sombreados. O capim-zuri apresenta alta adapta??o ao sombreamento de 64%, visto que nesta condi??o houve maior produ??o de massa seca, maiores propor??es de folhas e da taxa de aparecimento foliar e aumentos nos teores de clorofila que consequentemente proporcionaram maiores taxas fotossint?ticas sob este n?vel de sombreamento. O capim-tamani apresentou grande toler?ncia aos sombreamentos de 47% e 64%, aumentando a produ??o de massa seca, a taxa fotossint?tica, a clorofila a e b, a taxa de aparecimento foliar, a propor??o de folhas e a rela??o folha/colmo da composi??o morfol?gica, quando comparado as plantas sem sombreamento. Foi verificado tamb?m que o capim-tamani pode ser sombreado em at? 74% sem reduzir a produ??o em compara??o com as plantas que crescem sem sombreamento. O amendoim forrageiro apresentou grande adapta??o ao sombreamento a 47%, aumentando a produ??o de massa seca, a taxa fotossint?tica, a propor??o de folhas e a rela??o folha/ caule quando comparado as plantas sem sombreamento e com sombreamento de 64 e 74%. Com isso o capim-tamani quando comparado com outros capins, apresenta maior adapta??o aos diferentes n?veis de sombreamento durante a esta??o outono e inverno, seguido pelo capim zuri e o capim mavuno. J? a leguminosa amendoim forrageiro durante a esta??o outono e inverno, apresenta toler?ncia a baixos n?veis de sombreamento.Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq)Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES)Funda??o de Amparo ? Pesquisa do Estado de Minas Gerais (FAPEMIG)Disserta??o (Mestrado) ? Programa de P?s-Gradua??o em Produ??o Vegetal, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2020.The crop-livestock-forest integration systems, also known as agrosilvipastoris, can contribute positively to animal production systems and are efficient alternatives for land use in the recovery of degraded areas. However, the tolerance of grasses and legumes to shading depends on their morphophysiological capacity to adapt to a certain level of radiation, known as phenotypic plasticity. The objective of this work was to evaluate the behavior of four cultivars of tropical forage plants under different levels of shading and managed at 95% light interception (IL), throughout the fall and winter of 2019. Four experiments were carried out with four forage species tropical: Brachiaria spp. cv. Mavuno (mavuno grass), Panicum maximum Jack cv. BRS Zuri (zuri grass), Panicum maximum cv. BRS Tamani (tamani grass) and Arachis pintoi cv. Amarillo (forage peanut). Each experiment was carried out in a completely randomized design (DIC), with six replications, subjected to artificial shading levels of 47% with photosynthetically active radiation (RFA) of 353 ?mol m-2s-1, 64% with RFA of 242 ?mol m- 2s-1, 74% with RFA of 172 ?mol m-2s-1 and the control treatment with plants grown without shading, with RFA of 668 ?mol m-2s-1. The plants were kept under a cutting regime when reaching 95% IL. During the experiment, morphogenic evaluations were performed to determine the response variables: leaf appearance rate, phyllochron, leaf elongation rate, leaf senescence rate, leaf life duration, stem / stem elongation rate for all forages and also the rate of elongation in width and the rate of elongation of the petiole for forage peanut. Before cutting, structural evaluations were also carried out, referring to the number of live leaves per tiller, final length of the leaf and stem or stem, final height of the plants, the leaf area index, tiller density and the average weight of tillers. Physiological analyzes were also carried out regarding the levels of chlorophyll a and b, photosynthetic rate, stomatal conductance, transpiratory rate, water use efficiency and leaf temperature. Subsequently, after cutting, the morphological composition (proportion of leaves, stem or stem, senescent material and inflorescence) and the production of total dry mass of each forage species were determined under the different levels of shading. All data were analyzed using the statistical program Statistical Analysis System - SAS 9.1. The means of the morphogenic, morphophysiological and productive characteristics were subjected to analysis of variance and subsequently to the analysis of linear and quadratic regression at 5% probability. The mavuno grass showed adaptation to the shading of 47%, 64% and 74% throughout autumn and winter, since the production of dry mass did not decrease even with the light restriction imposed by the levels of shading in the plants and there were increases in the index leaf area, leaf proportion, chlorophyll content a and b and photosynthetic rate in shaded systems. Zuri grass has a high adaptation to shading of 64%, since in this condition there was greater production of dry mass, higher proportions of leaves and the rate of leaf appearance and increases in chlorophyll contents which consequently provided higher photosynthetic rates under this level of shading. Tamani grass showed great tolerance to shading of 47% and 64%, increasing dry mass production, photosynthetic rate, chlorophyll a and b, leaf appearance rate, leaf proportion and leaf / stem ratio of the morphological composition, when compared to plants without shading. It was also found that tamani grass can be shaded by up to 74% without reducing production compared to plants that grow without shading. Forage peanuts showed great adaptation to shading at 47%, increasing the dry matter production, the photosynthetic rate, the proportion of leaves and the leaf / stem ratio when compared to plants without shading and with shading of 64 and 74%. As a result, tamani grass, when compared to other grasses, shows greater adaptation to different levels of shade during the autumn and winter season, followed by zuri grass and mavuno grass. The forage peanut legume during the autumn and winter season, tolerates low levels of shading