Relação da radiação fotossinteticamente ativa no acúmulo de biomassa de frutos de coqueiro-anão-verde no Leste do Pará em dois regimes hídricos

Abstract

The green dwarf coconut palm (Cocos nucifera L.) is of great socio-economic importance due to the growing demand for its products and by-products, contributing to the increase in plantations in the north and northeast regions. However, information to help understand how the plant is affected by meteorological variables is scarce for the Amazon region. The aim of this study was to determine the radiation use efficiency (EUR) of the green dwarf coconut palm in the municipality of Santa Izabel do Pará. The study was conducted in an irrigated (I) and non-irrigated (NI) commercial plantation of dwarf-green coconut trees, located on the Reunidas Sococo farm in the municipality of Santa Izabel do Pará (01º 13' 40.16“ S; 48º 02' 54.35” W). A micrometeorological tower was installed in each area with sensors for rainfall (PP), incident global radiation (Rg), photosynthetically active radiation (PAR) transmitted below the canopy of a plant in each area. The leaf area index was estimated by adapting the method developed for oil palm by Hardon et al. (1969) and the efficiency of radiation use by Monteith's methodology (1977). The study period was from October 2020 to February 2024. The daily average PAR was 8.30 MJ m-² dia-1, ranging from 4.27 to 11.04 MJ m-² dia-1in the non-irrigated area. In the irrigated area, an average of 7.66 MJ m-² dia-1was obtained, with a variation of 4.05 to 10.54 MJ/m².day-1. Intercepted PAR showed a direct and linear relationship with incident PAR, a relationship that varies throughout the day due to the amount of radiation available, but with an average of 84% interception by the canopy. EUR was divided into two phases: in the first phases, it was 0.16g for each MJ accumulated in the irrigated area and 0.12g for the non-irrigated area; in the second phase, these values corresponded to 0.64g and 0.62g, respectively. The seasonality of EUR over the months of the year was also directly related to the amount of PAR that was intercepted by the plant, which in turn varied throughout the year according to the seasonality of the region. These results show that environmental conditions influence the production and development of the plant and are fundamental to understanding the interaction of the dwarf-green coconut palm with photosynthetically active radiation.