Radiation balance in the sweet sorghum crop

Abstract

The fluxes of incident solar radiation (K↓), reflected (K↑) and net radiation (Rn) were measured during the growing cicle of two fields of sweet sorghum (Sorghum bicolor L.), cvs. BR-501 and BR-503, maintained under convenient irrigation level. Resultant data allowed to estimate the crop albedo (r = K↑ /K↓) as well as the estimates of Rn as a function of K↓ or k↓ (1- r). Both cultivars showed a mean albedo/day of 0.23. The estimates of Rn for cultivar BR-501 were Rn = 0.55 K↓ - 3.25 and Rn = 0.51 K↓ + 2.55 respectively in the periods before and after heading. For the same periods the cultivar BR-503 showed the following equations: Rn = 0.40 K↓ + 66.50 and Rn = 0.44 K↓ + 38.10. Analysis of data also demonstrated that the inclusion of the albedo did not improve the relationship between Rn and K↓, and that the equations above presented reasonable degree of confidence in the calculation of evapotranspiration in sweet sorghum.