Abstract The objective of this work was to evaluate the influence of colored shade mesh and plant density on the morphological characteristics of Corymbia citriodora seedlings. The highest radiation efficiency was found in the blue mesh, 7.01 g MJ-1 and 5.72 g MJ-1 for average and high density respectively. For dry matter and leaf area index at high density, the treatment without mesh followed by the red mesh was the best. The chlorophyll index did not differ between treatments, with mean values of 206.4, 59.1 and 262.0 for chlorophyll a, b and total, respectively. Using principal component analysis, we found the total variance to be 70%. The use of colored shade mesh and plant density altered the radiation use efficiency and dry matter accumulation. Leaf area index was affected only by plant density. The red mesh resulted in the most similar values to the treatment without mesh.

Abstract: Despite its economic importance, the microclimate in soybean canopies has not yet been studied in detail. Such a study can yield valuable information regarding the interaction of a crop with its environment. In this context, the aim of this study was to evaluate the solar radiation dynamic and yield responses for each canopy strata for two soybean cultivars with determined and undetermined growth habits. A field study was conducted during the 2013/2014 and 2014/2015 growing seasons in the city of Frederico Westphalen, Rio Grande do Sul, Brazil. The cultivar NA6411, with a determinate growth habit, presented a greater interception of radiation in the middle and lower canopies strata which results in higher soybean yield when compared to the cultivar TEC6029, and thus, can be recommended for cultivation in crop production systems. The contribution of the middle and upper canopy strata to the total yield formation was greater than that observed in the lower canopy strata due to the greater interception of solar radiation by these strata. To increase soybean yields, new studies regarding the microclimatic conditions of the soybean canopy should be developed to improve the maximum potential yield of the new soybean cultivars.

Abstract: The objective of the study was to evaluate the growth and production efficiency of forage-grain dual-purpose wheat in two arrangements and four agroforestry systems (Intercrop-I and Intercrop-II), as well as to evaluate crop management for the wheat crops in two planting seasons (Crop Season I-2014 and Crop Season II-2015. The experiment was conducted in a randomized complete block design, factorial scheme 7x2x2, with seven cultivation systems Eucalyptus urophylla x Eucalyptus grandis Intercrop-II and Intercrop-I; Peltophorum dubium Intercrop-II and Intercrop-I; P. rigida Intercrop-I; S. parahyba Intercrop-I; a wheat monoculture with no tree species present; and two harvest management techniques (with and without harvesting of the forage species). Agroforestry systems generated shading for wheat plants, with a higher phyllochron and lower values of leaf area index of those individuals kept under trees with higher crown shading (non-deciduous trees) due to the lower transmissivity of solar radiation. The systems composed with Schizolobium parahyba in Intercrop-I and Parapiptadenia rigida in Intercrop-I provide a minor phyllochron to the wheat, resulting in a higher leaf area index and dry matter yield. Thus, the cultivation of tree species and dual-skilled agricultural crops, such as wheat, provides promising alternatives for the future use of land in tropical countries.

Resumo O objetivo deste trabalho foi determinar o crescimento, a eficiência do uso da radiação solar e a proteína bruta do sorgo forrageiro submetido a diferentes manejos de cortes. Foi utilizado um esquema unifatorial em delineamento de blocos casualizados (manejo de cortes), que variou do tratamento sem corte até quatro cortes. O primeiro corte ocorreu 44 dias após a semeadura, o segundo 23 dias após o rebrote, o terceiro 25 dias após o rebrote e o último após 40 dias do rebrote. A eficiência do uso da radiação solar do sorgo forrageiro reduziu com o aumento do número de cortes. A proteína bruta das plantas de sorgo aumentou com o manejo de cortes. Portanto, para a cultura do sorgo forrageiro, recomenda-se restringir o manejo de cortes para até três vezes durante o ciclo, desde que exista potencial produtivo de biomassa, e esses cortes devem ocorrer a cada 25 dias, dependendo do acréscimo de matéria seca. Não se recomenda a realização de mais do que três cortes, devido à baixa eficiência na utilização da radiação solar, à reduzida acumulação de matéria seca e à baixa qualidade desse material.

Abstract The purpose of this study is to determine the growth, the solar radiation use efficiency, and the gross protein of sorghum forage under different cutting management. A unifactorial design in random blocks (cutting management) was used, varying from no-cut treatment to four cuts. The first cut occurred 44 days after sowing, the second one after 23 days of regrowth, the third one after 25 days of regrowth, and the last one after 40 days of regrowth. The efficiency of the sorghum forage's solar radiation use reduces as the number of cuts increases. The sorghum forage's gross protein increases with cutting management. Therefore, for a sorghum forage crop, it is recommended to restrain the cutting management up to three times during the crop cycle, since it has the biomass potential production, and the cuts should be made at every 25 days, depending on the increase of dry mass. After that, the cutting management should not be done, mainly due to the low radiation use efficiency, reduced dry mass accumulation, and low material quality.

Abstract Sugarcane (Sacharum officinarum L.) monocropping has had a great socio-economic and environmental impact in Brazil, and agroforestry systems have been considered as an alternative for more sustainable production; however, there is a lack of field research under such conditions. The aim of this study was to evaluate the growth rates, radiation use efficiency and yield traits in sugarcane cultivated in the understory of Aleurites fordii, in two agroforestry arrangements and monocropping systems. A field experiment was conducted from July 2015 to June 2016 in the city of Frederico Westphalen, Rio Grande do Sul, Brazil. The radiation use efficiency, assimilate partitioning, leaf area index, absolute growth rate, net assimilation rate, number of tillers, plant height, % of intercepted solar radiation, extinction coefficient, and yield in each system was evaluated. In agroforestry systems, the dynamic interactions between multiple plant species change with the time and can result in unique microclimates. The use of agroforestry systems in 12 x 12m arrangements should be prioritized because it enables greater yields and radiation availability in the understory. This study sought to provide new sustainable alternatives for farmers in order to increase the diversification of the rural property and maintain the preservation of existing agroecosystems.

Abstract Soybean (Glycine max L.) monocropping have had a great socio-economic and environmental impact on the world and agroforestry systems has been considered an alternative for more sustainable production. The aim of this study was to evaluate the effect of different arrangements of agroforestry systems of the species E. urophylla x E. grandis and P. dubium and the pruning of the trees on the dynamics of solar radiation and soybean yield. A field experiment was conducted in Southern Brazil. In order to achieve the objective of the study, the solar radiation transmissivity and the productive performance of the soybean were evaluated. In this study, the soybean yield was determined by the arrangement of the agroforestry system and forest species utilized. The soybean crop cultivated in the understory of the P. dubium trees showed the highest yield response. The use of silvicultural practices for the management of forest species should be considered to generate the balance of the productive system. In this context, tree pruning is a viable side for agroforestry systems, as it promotes an increase in the incidence of solar radiation in the understory, resulting in an increase in soybean yield, especially when integrated with P. dubium.

RESUMO Esse trabalho teve como objetivo determinar o efeito da idade e do espaçamento de plantio na produção de biomassa das espécies florestais: Acacia mearnsii De Wild, Eucalyptus grandis W. Hill ex Maiden, Mimosa scabrella Benth e Ateleia glazioviana Baill. Foram considerados plantios com diferentes espaçamentos: 2,0×1,0 m, 2,0×1,5 m, 3,0×1,0 m e 3,0×1,5 m, nas idades de 1, 3 e 5 anos após o plantio. O trabalho foi instalado em delineamento experimental de blocos completos casualizados. A determinação da biomassa aérea consistiu na colheita e pesagem das diferentes partes das árvores. Os espaçamentos de plantio influenciam na produção de biomassa das partes das espécies florestais, nas diferentes idades após o plantio. Os espaçamentos mais adensados proporcionam maiores quantidades de biomassa que os menos adensados. As espécies florestais diferenciam-se em relação à produção de biomassa. O Eucalyptus grandis (325,1 t ha-1) apresenta a maior produção, seguido da Acacia mearnsii (239,3 t ha-1), Mimosa scabrella (53,4 t ha-1) e Ateleia glazioviana (32,1 t ha-1). A madeira apresenta a maior participação na biomassa total ao longo do tempo, sendo constatada a crescente proporção percentual ao longo das classes etárias, seguido do galho, folha e casca.

ABSTRACT The aim of this study was to determine the effect of age and plant spacing on biomass production of four forestry tree species: Acacia mearnsii De Wild, Eucalyptus grandis W. Hill ex Maiden, Mimosa scabrella Benth, and Ateleia glazioviana Baill. The following spacings of plants at the ages of 1, 3, and 5 years after planting were considered: 2.0 × 1.0 m, 2.0 × 1.5 m, 3.0 × 1.0 m, and 3.0 × 1.5 m. The study was installed in randomized complete block design. Biomass was determined by weighing different components of the trees after harvesting. Plant spacing affected biomass production of forestry trees at different ages after planting. Dense spacings produced larger quantities of biomass than less dense spacing. The tree species differed in biomass production: Eucalyptus grandis produced the largest quantity (325.1 t ha-1), followed by Acacia mearnsii (239.3 t ha-1), Mimosa scabrella (53.4 t ha-1), and Ateleia glazioviana (32.1 t ha-1). Wood biomass represented the biomass component with the largest production over time, which showed an increasing proportion throughout the age groups, followed branch, leaf, and bark biomass.

ABSTRACT The objective of this experiment was to determine the conversion efficiency of intercepted photosynthetically active radiation into biomass of Acacia mearnsii De Wild. seedlings. A forest species, plastic tubes (90 cm3), and 11 evaluation periods (up to 180 days after emergence) were used in this study. The leaf area index (LAI), total dry biomass (BIO), global solar radiation (GSR), cumulative intercepted photosynthetically active radiation (PARic), and conversion efficiency of radiation (εb) were determined using a pyranometer (LI200X, LICOR). The value of εb in BIO seedlings of Acacia mearnsii was 7.76 g MJ-1. LAI was directly related to the efficiency of PARic, and this influenced the development, production potential and accumulation of BIO. The value of GSR flow was 11.81 MJ m-2 day-1, while the value inside the greenhouse was 6.26 MJ m-2 day-1.

RESUMO A verificação das modificações que ocorrem na planta, em função da aclimatação ao sombreamento, auxilia na seleção de espécies forrageiras adequadas para o uso em sistemas agroflorestais. O objetivo deste estudo foi avaliar a morfoanatomia foliar de azevém (Lolium multiflorum Lam.), no sub-bosque de espécies arbóreas em sistemas agroflorestais. O experimento foi conduzido no município de Frederico Westphalen, RS, entre junho e setembro de 2012, em delineamento experimental de blocos ao acaso. O azevém anual foi semeado em três ambientes: radiação solar plena, sub-bosque de angico-vermelho (Parapiptadenia rigida Benth.) e canafístula (Peltophorum dubium Spr. Taubert), com três repetições. As espécies florestais foram distribuídas em cinco renques, separados por 6,0 m cada. Foram avaliadas as seguintes variáveis: radiação fotossinteticamente ativa incidente (RFAi), transmissividade da RFAi, área foliar específica, espessura do mesofilo foliar, espessura da parede periclinal externa mais cutícula, tamanho do estômato e densidade estomática. A presença das espécies florestais provoca alterações nas condições luminosas do ambiente de produção do azevém e ocasiona ajustes nas folhas dessa espécie, os quais resultam no aumento da área foliar específica, na diminuição do mesofilo e na espessura da parede periclinal externa mais cutícula, bem como no aumento da quantidade e tamanho dos estômatos. Esses ajustes resultam da capacidade de aclimatação do azevém, que nas condições de baixa luminosidade, altera sua morfologia em busca de radiação solar e aumenta a área fotossintética.

ABSTRACT The verification of changes that occur in the plant, due to the acclimatization to the shading, assists in the selection of forage species suitable for use in agroforestry systems. The aim of this study was to evaluate the leaf morphoanatomy of ryegrass (Lolium multiflorum Lam.) in the tree species understory in agroforestry systems. The experiment was conducted in Frederico Westphalen, RS, Brazil, between June and September 2012, in an experimental design of randomized blocks. The annual ryegrass was sown in three environments: full sunlight, understory of angico-vermelho (Parapiptadenia rigida Benth.), and canafístula (Peltophorum dubium Spr. Taubert), with three replications. Forest species were distributed in five lines, separated by 6.0 m. The following variables were evaluated: incident photosynthetically active radiation (RFAi), transmissivity of RFAi, specific leaf area, leaf mesophyll thickness, thickness of outer periclinal wall + cuticle, stomatal size, and stomatal density. The presence of forest species causes changes in the lighting conditions of the production environment of ryegrass and causes adjustments in the leaves of this species, which result in increased specific leaf area, decreased mesophyll and thickness of the outer periclinal wall + cuticle, as well as increased amount and size of the stomata. These adjustments result from the acclimation capacity of ryegrass, which, in low-light conditions, alter their morphology to capture more solar radiation and increase the photosynthetic area.

RESUMO Com o propósito de compreender e relacionar o desempenho fisiológico das plantas às adversidades meteorológicas, objetivou-se determinar a resposta fisiológica de plantas de cidró (Aloysia triphylla) submetidas a diferentes níveis de reposição hídrica no verão e inverno. O trabalho foi desenvolvido em ambiente protegido, no município de Frederico Westphalen-RS. O delineamento utilizado foi blocos completos ao acaso em um esquema fatorial 2x4x2, sendo duas estações do ano (verão e inverno), quatro disponibilidades hídricas (50, 75, 100, 125% da ETo) e duas faces da folha (abaxial e adaxial), com quatro repetições. Avaliou-se a resistência à difusão de vapor pelos estômatos (s/cm), transpiração (µg/cm2/s) e a temperatura da folha (°C), em ambas as faces da folha, no período compreendido entre 10 às 11, 13 às 14 e 16 às 17 horas, aos 45 dias após o início da estação. A resposta fisiológica das plantas de cidró foi influenciada pelo nível de reposição hídrica, de forma diferenciada entre as estações do ano. A estação do verão foi responsável pelos maiores valores de radiação fotossinteticamente ativa incidente, temperatura da folha, transpiração e resistência à difusão de vapor pelos estômatos. A redução na disponibilidade hídrica promoveu o aumento nos valores de resistência estomática ao fluxo de vapor, reduzindo a taxa de transpiração das folhas. A radiação fotossinteticamente ativa incidente, temperatura da folha e transpiração apresentaram maiores valores na face abaxial da espécie estudada.

ABSTRACT We aimed to determine the response of cidró (Aloysia triphylla) submitted to different water replacement levels in summer and winter, in order to understand and relate the plant physiological performance under adverse weather conditions. The research was developed in a protected environment, in the city of Frederico Westphalen, Rio Grande do Sul State, Brazil. The experimental design was completely randomized, arranged in a 2x4x2 factorial scheme, two seasons of the year (summer and winter), four water availability (50, 75, 100, 125% of ETo) and two faces of leaf (abaxial and adaxial), with four replications. There were evaluated stomatal vapor diffusion resistance (s/cm), transpiration (µg/cm2/s) and leaf temperature (°C), on both faces of the leaf from 10 a.m. to 11 a.m., 1 p.m. to 2 p.m. and 4 p.m. to 5 p.m., 45 days after the beginning of the season. We concluded that the physiological response of cidró plants was influenced by water replacement levels, in a different way according to the seasons of the year. The summer season was responsible for the highest values of incident photosynthetically active radiation, leaf temperature, transpiration and stomatal vapor diffusion resistance. The reduction in water availability promoted the increase in values for stomatal resistance to vapor flow, reducing leaf transpiration rate. The incident photosynthetically active radiation, leaf temperature and transpiration showed highest values on the abaxial face of the studied species.

RESUMO: A utilização da madeira para fins energéticos é elevada no país, motivada principalmente pela diversidade de espécies que apresentam potencialidade de geração de energia. Esse trabalho teve como objetivo determinar o efeito da idade e do espaçamento de plantio nas propriedades energéticas em diferentes compartimentos da biomassa: madeira, casca e galho da espécie Ateleia glazioviana Baill, distribuída em diferentes espaçamentos: 2,0x1,0m, 2,0x1,5m, 3,0x1,0m e 3,0x1,5m, no 1º, 3º e 5º ano após o plantio. O presente trabalho foi realizado em um experimento instalado em delineamento experimental de blocos completos casualizados em três repetições. Foram determinadas as variáveis biomassa (BIO), poder calorífico superior (PCS), massa específica básica (ME), produtividade energética (PE), densidade energética (DE), teor de carbono fixo (CF), teor de material volátil (MV) e teor de cinzas (CZ). Concluiu-se que as diferentes idades das árvores influenciam significativamente todas as variáveis analisadas, proporcionando uma distribuição crescente da BIO, PE, CF, ME e DE, sem tendência a estabilização ao longo do tempo. Os quatro espaçamentos de plantio induzem a diferentes produções de BIO e PE, com uma tendência de redução dos seus valores com o aumento do espaçamento, em todos os períodos avaliados. Os quatro compartimentos das árvores induzem a um efeito significativo das variáveis BIO, PE, PCS, CF, MV e CZ.

ABSTRACT: The use of wood for energy purposes is common in Brazil, motivated mainly by the diversity of species that present a potential for energy production. The objective of this study was to determine the effects of tree age and spacing on the energy properties of different components of the biomass: wood, bark, and branch of the species Ateleia glazioviana Baill, distributed at different spacings: 2.0 × 1.0m, 2.0 × 1.5m, 3.0 × 1.0m, and 3.0 × 1.5m in the 1st, 3rd, and 5th year after the planting. The experiment was carried out in a randomized complete block design with three replications. The following variables were determined: biomass (BIO), gross calorific power (GCV), basic density (BD), energy productivity (EP), energy density (ED), fixed carbon content (FCC), volatile material content (VMC), and ash content (AC). Different tree ages significantly affected all analyzed variables, increasing the distribution of BIO, EP, AC, BD, and ED with no tendency to stabilize over time. The four tree spacings induced different levels of BIO and EP, with a trend toward lower values with increasing tree spacing for all assessed periods. The four components of the trees had a significant effect on the variables BIO, EP, GCV, FCC, VMC, and AC.

RESUMO O trabalho teve como objetivo avaliar o comportamento fisiológico em diferentes horários do dia e o nível de dependência entre variáveis fisiológicas e elementos meteorológicos em mudas de Aleurites fordii. O experimento foi conduzido em casa de vegetação, utilizando-se delineamento experimental inteiramente casualizado, em esquema unifatorial composto por 10 horários de avaliação (das 8 às 17h, com intervalo de 1h entre as avaliações) e três repetições. Cada repetição era constituída por três plantas de avaliação, totalizando nove mudas, as quais estavam dispostas sobre bordadura dupla. Foram avaliadas as características: temperatura da folha (ºC), radiação solar fotossinteticamente ativa (ìmol S-1 m-2), resistência estomática (S cm-1) e transpiração (mmol H2O s-1 m-2) ao longo de um dia típico, com uso de um porômetro digital LI-1600 LI-COR. As medidas da temperatura e umidade relativa do ar foram determinadas dentro do ambiente protegido, utilizando-se um termohigrógrafo. As avaliações foram realizadas aos 244 dias após a semeadura, entre 8:00 e 17:00h, com intervalo de 60 minutos, totalizando 10 avaliações. O comportamento fisiológico das mudas de Aleurites fordii é afetado pelo horário do dia. De modo geral, as variáveis fisiológicas estudadas são altamente dependentes dos elementos meteorológicos. A temperatura do ambiente protegido e a umidade relativa do ar são os elementos meteorológicos que mais influenciam o comportamento fisiológico das mudas de Aleurites fordii.

ABSTRACT The objective of this work was to evaluate the physiological behavior at different times of the day and the level of dependence between physiological variables and meteorological elements in Aleurites fordii seedlings. The experiment was conducted in a greenhouse, using a completely randomized experimental design, in a uniform scheme composed of 10 evaluation times (from 8 am to 5 pm, with an interval of 1h between evaluations) and three replications. Each replicate consisted of three evaluation plants, totaling nine seedlings, which were arranged on a double border. The following characteristics were evaluated: leaf temperature (ºC), photosynthetically active solar radiation ((mol S-1 m-2), stomatal resistance (S cm-1), and transpiration (mmol H2O s-1 m-2) over a typical day, using a LI-1600 LI-COR digital porometer. The temperature and relative humidity were measured inside the greenhouse, using a thermohygrograph. The evaluations were performed at 244 days after sowing, between 8:00 and 17:00, with an interval of 60 minutes, totaling 10 evaluations. The physiological changes of Aleurites fordii seedlings are affected by the time of day. In general, the physiological variables are highly dependent on meteorological elements. The temperature of the greenhouse and the relative humidity are the meteorological elements that most influence the physiological behavior of Aleurites fordii seedlings.

RESUMO A eficiência de conversão da radiação solar é uma variável frequentemente utilizada em modelos de simulação do crescimento das culturas, pois a produção de biomassa, e consequentemente, o acúmulo de carbono, estão relacionados com a eficiência de conversão da energia radiante em química pela planta, através do processo da fotossíntese. Dessa maneira, o objetivo deste trabalho foi determinar a eficiência de conversão da radiação solar fotossinteticamente ativa interceptada (RFAi) no acúmulo de carbono na parte aérea de Ilex paraguariensis, em cultivo consorciado (Ilex paraguariensis A. St. Hil. e Pinus elliottii Engelm) e solteiro. A eficiência de conversão da RFAi em carbono acumulado foi calculado a partir da relação entre o acúmulo de carbono e a RFAi envolvida. A maior eficiência de conversão (eb) de radiação solar fotossinteticamente ativa interceptada no acúmulo de carbono na parte aérea em plantas de erva-mate é obtida no sistema de cultivo consorciado.

ABSTRACT The efficiency of solar radiation conversion is a variable often used in crop growth simulation models in which the production of biomass and, consequently, carbon accumulation are related to the conversion of radiant energy into chemical compounds by plants through the process of photosynthesis. The goal of this study was to determine the efficiency of conversion of intercepted photosynthetically active radiation (PARi) into carbon accumulation in shoots of Ilex paraguariensis in intercropping (Ilex paraguariensis A. St. Hil. and Pinus elliottii Engelm) and monoculture. The conversion efficiency of PAR in accumulated carbon was calculated based on the ratio between the accumulated carbon and the PARi involved in the process. Our results demonstrate that the higher conversion efficiency (eb) of photosynthetically active solar radiation intercepted in carbon in yerba mate sprouts was obtained in the intercropping scenario.

RESUMO Esse trabalho teve como objetivo determinar o efeito da idade e do espaçamento de plantio nas propriedades energéticas de diferentes compartimentos da biomassa de Eucalyptus grandis W. Hill ex Maiden, distribuída em diferentes espaçamentos: 2,0x1,0 m, 2,0x1,5 m, 3,0x1,0 m e 3,0x1,5 m, no 1º, 3º e 5º ano após o plantio. O presente trabalho foi realizado em um experimento instalado em delineamento experimental de blocos completos casualizados em três repetições. Foram determinadas as variáveis biomassa (BIO), poder calorífico superior (PCS), massa específica básica (ME), produtividade energética (PE), densidade energética (DE), teor de carbono fixo (CF), teor de material volátil (MV) e teor de cinzas (CZ). As idades proporcionam um efeito em todas as variáveis analisadas, sendo que no 5º ano após o plantio, são verificados os maiores valores de BIO, PE, ME, DE e CF. Os espaçamentos de plantio induzem a diferentes produções de BIO e PE, com uma tendência de redução dos valores com o aumento do espaçamento de plantio, em todos os períodos avaliados. Os compartimentos das árvores influenciam nas variáveis BIO, PCS, PE, CF, MV e CZ. Do ponto de vista energético, quanto maior a idade e menor o espaçamento de plantio, melhores são as propriedades energéticas da biomassa.

ABSTRACT This study aimed to determine the effect of planting age and spacing on energy properties of different compartments of the biomass of Eucalyptus grandis W. Hill ex Maiden, disseminated in different spacings: 2.0 x 1.0 m, 2.0 x 1.5 m, 3.0 x 1.0 m e 3.0 x 1.5 m, in the 1st, 3rd and 5th year after the planting. The present study was carried out as an experiment installed in an experimental design of randomized complete blocks in three replications. Variables determined were Biomass (BIO), Gross Calorific Value (GCV), Basic Density (BD), Energy Productivity (EP), Energy Density (ED), Fixed Carbon Content (FCC), Volatile Material Content (VMC), and Ash Content (AC). Ages have an effect on all studied variables, and in the 5th year after planting, the largest BIO, EP, BD, ED and FCC values are checked. The planting spacings induce different productions of BIO and EP, with a trend towards lower values with increasing planting spacing in all assessed periods. The compartments of trees influence BIO, GCV, FCC, VMC and AC variables. Regarding to energy, the higher the age and lower the planting spacing, the better the energy properties of biomass.

RESUMO Objetivou-se, com este trabalho, avaliar o efeito de doses e de fontes de nitrogênio sobre as variáveis morfológicas relacionadas com a produtividade de dois cultivares de girassol. O delineamento utilizado foi o de blocos ao acaso, em esquema fatorial 5 x 2 x 2, com cinco doses de adubação nitrogenada (0, 40, 80, 120 e 160 kg ha-1), duas fontes de nitrogênio (N), fertilizante convencional (ureia), com 44% de N e fertilizante nitrogenado de liberação lenta, com 26% de N, e dois cultivares de girassol (Olisun 3 e Aguará 6), com três repetições. Avaliaram-se altura de plantas, índice de área foliar, interceptação de radiação global, massa de mil aquênios, diâmetro do capítulo, produtividade de aquênios e estimou-se o teor de clorofila. Doses crescentes de N promovem aumento do índice de área foliar e de interceptação da radiação global, do florescimento pleno e da produtividade do girassol, de forma diferenciada entre cultivares. O fertilizante nitrogenado de liberação lenta possibilita índice de área foliar, no início de enchimento de aquênios, maior que o obtido por uso de ureia, a partir da dose de 120 kg ha-1 de N. O cultivar Olisun 3 apresenta maior índice de área foliar no florescimento pleno e maior produtividade, a partir das doses de 80 e de 120 kg ha-1 de N, respectivamente.

ABSTRACT The objective of this study was to evaluate the effect of doses and sources of nitrogen on themorphological variables related to yield of two sunflower cultivars. The design was randomized blocks in a factorial design 5 x 2 x 2, with five doses of nitrogen (0, 40, 80, 120 and 160 kg ha-1), two sources of nitrogen (N), fertilizer conventional (urea), with 44% N, and the fertilizer nitrogenated of slow-release, with 26% N, and two sunflower cultivars (Olisun 3 and Aguará 6) with three replications. Was evaluated theplant height, leaf area index, global radiation interception, thousand achenes weight, diameter of achenes, yield and estimate the chlorophyll content. Increasing doses of N promotes an increase in the leaf area index and interception of global radiation at flowering full and the sunflower yield, in a differentiated way between cultivars. The use of fertilizer nitrogenated of slow-release provides higher leaf area index in the beginning of achenes filling, compared the use of urea, from the dose of 120 Kg ha-1 N. The cultivar Olisun 3 shows greater leaf area index at flowering full and yield, from the doses of 80 and 120 kg ha-1 N, respectively.