Razão entre radiação fotossinteticamente ativa e radiação global no cultivo do tomateiro em casa-de-vegetação

Abstract

RESUMOPropôs-se, com este trabalho, determinar e analisar as variações da razão entre a radiação fotossinteticamente ativa (RFA) e a radiação global (Rg) durante o período de crescimento do tomateiro (Lycopersicon esculentum Mill., cv. Duradoro) cultivado em substrato de areia sob condições de ambiente protegido. Medições de Rg e RFA foram conduzidas no interior de uma casa-de-vegetação, coberta com filme plástico de polietileno, durante a estação seca, em Viçosa, MG. Paralelamente, a Rg foi medida também em uma estação meteorológica automática. A razão RFA/Rg sofreu uma redução de 1,691 para 1,574 mol MJ -1 , no período compreendido entre as 1ª e 9ª semanas após o transplante e se manteve praticamente estável entre as 9ª e 13ª semanas, oscilando entre 1,571 e 1,587 mol MJ -1 . Posteriormente, com a ocorrência da alternância de condições de céu claro para dias nublados, a RFA/Rg sofreu aumentos consideráveis (1,93 e 2,07 mol MJ -1 ), os quais estão próximos dos obtidos em outras localidades do Brasil. Com base nos resultados, é possível afirmar que ocorreu efeito pouco expressivo da expansão foliar da cultura em reflexões múltiplas da radiação solar no interior do ambiente protegido e um efeito marcante da nebulosidade na razão RFA/Rg. Palavras-chave: ambiente protegido, Lycopersicon esculentum, radiação solarRatio between photosynthetically active radiation and global radiation during tomato growth inside greenhouse ABSTRACTIt was proposed in this study to determine and analyze variations in the ratio between photosynthetically active radiation (PAR) and global solar radiation (GR) during the growth season of tomato (Lycopersicon esculentum Mill., cv. Duradoro) crop in sand substract under protected cultivation. Measurements of GR and PAR were conducted inside of a single layer polyethylene greenhouse during the dry season in Viçosa, Minas Gerais, Brazil. Simultaneously, the GR was measured in an automatic weather station. The PAR/GR ratio decreased from 1.691 to 1.574 mol MJ -1 , from the first to the ninth week after transplanting, and was relatively constant, oscillating between 1.571 and 1.587 from the ninth to the thirteenth week. Thereafter, when clear sky conditions changed to cloudy days, the PAR/GR ratio increased considerably (1.93 e 2.07 mol MJ -1 ), reaching values near to those determined in other Brazilian locations. Based on results it is possible to affirm that little effect of leaf expansion on multiple reflections of solar radiation inside the greenhouse occurred, but a remarkable influence of the clouds in the PAR/GR ratio was verified.

Vineyard microclimate and yield under different plastic covers

“…The average PAR/SR ratio under BPF ranged from 0.32 to 0.36, between 2012 and 2014. Steidle Neto et al (2008) found similar values of PAR/SR ratio (0.36) with transparent polyethylene, which was close to the results obtained by Cardoso et al (2008). Under BSS, PAR/SR was higher compared to under BPF and varied from 0.40 to 0.47 ( Fig.…”

Relationship between photosynthetically active radiation and global radiation in Petrolina and Brasília, Brazil

“…All the PAR/Rs ratios for Petrolina were higher than those for Brasília because PAR was slightly higher in the former city (Figures 1A and B). Therefore, Petrolina, located in the Caatinga biome, has more PAR, the energy available for photosynthetic processes, than in Brasília, located in the Cerrado biome, and other localities from Brazil (36 -49%), observed in the works of Assis & Mendez (1989), Almeida & Landsberg (2003), Steidle Neto et al (2008), Escobedo et al (2011) and Aguiar et al (2012).…”

“…Although its importance is widely recognized, PAR is usually not measured in the weather station networks in Brazil and worldwide. To overcome this problem, researchers use different PAR estimation techniques, among which the most used technique to obtain PAR is through simple linear regression with global solar radiation (Rs) (Al-Shooshan, 1997;Jacovides et al, 2007;Steidle Neto et al, 2008;Escobedo et al, 2009;Galvani, 2009;Escobedo et al, 2011;Wang et al, 2014;Pashiardis et al, 2017;Chukwujindu et al, 2018).…”