Balanço de radiação como subsídio ao cultivo do milho nos tabuleiros costeiros de Alagoas

Abstract

The radiation balance in the maize crop was analyzed via three agro-meteorological experiments conducted at the Agrarian Science Center (CECA) at the Federal University of Alagoas (UFAL), Rio Largo, AL (09º28’02”S; 35º49’43”W;127m). Two experiments were conducted in dry conditions and one in irrigated conditions in the Coastal Trays region. All of the instruments used to monitor the meteorological variables were connected to an automatic data gathering system, 21XL, of Campbell Scientific. The cultivating of the BR 106 maize variety reached a maximum height and a maximum foliage index in the phenological phase of maize tassel emissions. A total radiation estimate (Rn) was established as a function of global radiation (Rg) and photosynthetically active radiation (PAR) as a function of global radiation. The relationship between the radiation components and maize growth parameters were also determined, especially as a result of leaf area index (LAI). An estimate of maize growth parameters was defined as follows: the height of the plant as a result of the day after the emergency, the leaf area index as a result of the day after the emergency and the leaf área index as a result of the height of the plant. The variation of the global solar radiation between the plants (RgS2) and the row of planting (RgS1) was analyzed throughout the day as a result of LAI. It was found that with LAI equal to 0.67 the percentage of radiation transmitted into the surface was 98% for RgS1 and 97% for RgS2. With the LAI at 1.35, that transmission was 70% and 53% for RgS1 and RgS2, respectively. With the LAI at 2.00 a transmission of 58% was found for RgS1 and 32% for RgS2. On average the total radiation was 10.70 MJm-2; 11.91 MJm-2 and 13.63 MJm-2 , for the years 2000, 2001 and 2002, respectively. The radiation efficiency (Rn/Rg) was an average of 74% for the first two experiments and 77% for the last planting. The average albedos schedule in the reproductive planting phase 2000 and 2001, showed similar rhythms, while in the reproductive phase of the 2002 planting, the average albedos schedule between the phases were different. A lower average albedos schedule was found in the phenological emergency. This phenomenon was observed during the three cultivations, with the global radiation reflection on the naked soil being more credited.