Daytime Net Radiation on Cowpea and Castor Bean in the County of Areia-PB and Garanhuns-PE

Abstract

O saldo de radiacao (Rn) e a energia utilizada em diversos processos que ocorrem no sistema solo-planta-atmosfera, a exemplo da evapotranspiracao; no entanto, sua medicao direta nao esta disponivel para a maioria das estacoes meteorologicas do Brasil. Dessa forma, o presente trabalho objetivou determinar a relacao entre o Rn e a radiacao solar global incidente (Rg) sobre dosseis de caupi e mamona. Os dados de Rn e Rg foram coletados de experimentos realizados durante os anos de 2002 e 2003 (caupi), de 2004 e 2005 (mamona) em Areia-PB (6 o 58 ’ S, 35 o 41 ’ W e 620 m), e de 2009 (mamona) em Garanhuns-PE (8 o 53’ S, 36 o 29’ W e 842 m). Os dados foram integrados durante o periodo diurno, das 6 as 18h, e depois foi obtida a relacao Rn/Rg para cada dia. Obtiveram-se equacoes com elevado R 2 (acima de 0,93), indices d e c (acima de 0,90), e baixo RQME (abaixo de 0,83), indicando boa precisao da estimativa do Rn em funcao do Rg nas culturas do caupi e da mamona. A equacao geral para mamona foi Rn = 0,5965 Rg (R 2 = 0,943) e para caupi foi Rn = 0,7822 Rg (R 2 = 0,976). O Rn, em dosseis de caupi e mamona, pode ser estimado satisfatoriamente a partir da Rg. 800x600 Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:Table Normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Calibri,sans-serif;} A B S T R A C T Net radiation (Rn) is the quantity of radiant energy used in many process occurring in the soil-plant-atmosphere continuum, such as evapotranspiration, however, its direct measurement is not available for most weather stations in Brazil. Thus, the objective of this work was to determine the relationship between Rn and incident solar radiation (Rg) in cowpea and castor bean canopies. The Rn and Rg data were collected from experiments conducted during in the years 2002 and 2003 (cowpea), 2004 and 2005 (castor bean) in Areia, PB (6 o 58’ S, 35 o 41’ W e 620 m), and 2009 (castor bean) in Garanhuns-PE (8 o 53’ S, 36 o 29’ W e 842 m). Were performed daily sums of Rn and Rg, from 6 to 18h, and then it was calculated the Rn/Rg ratio for each day. Models with high R 2 (above 0.93), d and c indices (above 0.90) and low RMSE (below 0.83) were obtained in test between measured and estimated values, indicating precision to estimate Rn in cowpea and castor bean canopies as a function of Rg. The general linear function for castor bean and cowpea were Rn = 0.5965 Rg (R 2 = 0.943) and Rn = 0.7822 Rg (R 2 = 0.976), respectively. Net radiation can be satisfactorily estimated from incoming solar radiation for both crops. Key words: Evapotranspiration, Solar Radiation, Vigna unguiculata, Ricinus communis