Radiation and energy balance of lettuce culture inside a polyethylene greenhouse

Abstract

1VALÉRIA DE ALMEIDA FRISINA 2 e JOÃO FRANCISCO ESCOBEDO 3 RESUMO -Objetivou-se, neste trabalho, determinar os balanços de radiação e energia da cultura de alface (Lactuca sativa, L. cv. Verônica) em estufa de polietileno. O experimento foi realizado em uma estufa tipo túnel alto com cobertura de polietileno (100 mm de espessura) e em uma área externa, ambas com 35 m 2 . Durante o ciclo da cultura, foram monitoradas as radiações global e refletida, saldo de radiação, fluxo de calor no solo e temperatura do ar (seca e úmida) nos dois meios. Utilizou-se um Datalogger que operou na freqüência de 1 Hz, armazenando médias de cinco minutos. A partir das integrações diárias das irradiâncias global (K¯) e refletida (K), verificou-se que a transmissividade média da radiação global (K¯in / K¯ex) foi aproximadamente constante, em torno de 79,59%, enquanto a razão das radiações refletidas (Kin / Kex) foi igual a 69,21% com coeficiente de variação de 8,47%. As curvas normalizadas do saldo de radiação de ondas curtas em relação à radiação global (K* / K¯), nos dois meios, mostraram ser aproximadamente constantes no início do ciclo e decrescentes no final. A relação (Rn/ K¯) foi maior no meio externo, em torno de 12%, a partir da fase em que a superfície verde da cultura cobriu o solo. O balanço médio (L*) de radiação de ondas longas foi maior no exterior, em torno de 50%. O balanço de energia, estimado em termos de fluxos verticais, mostrou, em média, que: no exterior, 83,07% do saldo de radiação foi convertido em calor latente (LE), 18,00% em fluxo de calor no solo (G) e 9,96% em calor sensível (H), enquanto que, no interior da estufa, 58,71% do saldo de radiação foi convertido em LE, 42,68% em H e 28,79% em G.Termos para indexação: radiação global, radiação refletida, saldo de radiação, fluxos de calor. RADIATION AND ENERGY BALANCE OF LETTUCE CULTURE INSIDE A POLYETHYLENE GREENHOUSEABSTRACT -The objective of this paper was to describe the radiation and energy balance, during the lettuce (Lactuca sativa, L. cv. Verônica) crop cycle inside a polyethylene greenhouse. The radiation and energy balance was made inside a tunnel greenhouse with polyethylene cover (100 mm) and in an external area, both areas with 35 m 2 . Global, reflected and net radiation, soil heat flux and air temperature (dry and humid) were measured during the crop cycle. A Datalogger, which operated at 1 Hz frequency, storing 5 minutes averages was utilized. The global (K¯) and reflected (K) radiations showed that the average transmission of global radiation (K¯in / K¯ex) was almost constant, near to 79.59%, while the average ratio of reflected radiation (Kin / Kex) was 69.21% with 8.47% standard-deviation. The normalized curves of short-wave net radiation, in relation to the global radiation (K*/ K¯), found for both environments, were almost constant at the beginning of cycle; this relation decreased in the final stage of culture. The normalized relation (Rn/ K¯) was bigger in the external area, about 12%, when the green culture covered the soil surface. The ...

Micrometeorological Characterization of Protected Environments for Plant Production

“…Some other researchers assessed photosynthetically active radiation and its relationship with global solar radiation in a canopy of alfalfa, according to the leaf area index (França et al, 1997), the radiation balance in snap bean crops with and without polyethylene covering (Souza and Escobedo, 1997), the effect of different types of coverage, in mini-greenhouses, in the attenuation of solar radiation and light (Sentelhas et al, 1998), and the albedo and the radiation balance estimates in snap beans under a plastic cover and external environment (Souza et al, 1999). Other issues like the radiation balance and energy of lettuce cultivation in a polyethylene greenhouse (Frisina and Escobedo, 1999), the transmissivity of solar radiation in greenhouses covered with blue and transparent PVC films (Sentelhas et al, 1999), the efficiency of the use of photosynthetically active radiation by tomato crop in different environments (Radin et al, 2003), tomato morphological changes in response to reduced solar radiation in plastic greenhouse environments (Reisser Júnior et al, 2003), and the use of meshes and shading in protected environments and their effect on global and photosynthetically active solar radiation (Guiselini et al, 2004b), were also studied. Aspects like changes in the radiation balance in a protected environment with light-diffusing polyethylene cover (Sousa et al, 2005), solar radiation in protected environments cultivated with tomato in the summer-autumn seasons of Rio Grande do Sul (Beckmann et al, 2006), and the ratio between photosynthetically active radiation and global radiation in greenhouse tomato cultivation (Steidle Neto et al, 2008) were presented.…”