Eficiência do uso de radiação solar incidente por plantas de amora-preta submetidas a diferentes manejos de poda

Abstract

The blackberry (Rubus spp.) Crop has been consolidating and gaining market share in recent years due to its attractive characteristics, mainly for family agriculture and small farms, presenting as main obstacle the seasonality in the harvest, which reduces the prices paid in the period of harvest. Solar radiation is the main source of energy for terrestrial processes, and the radiation balance corresponds to the available energy for the processes of growth, development, photosynthesis among others, being influenced by the albedo which has great impact on the availability of energy in the environment , since it represents the ability of a surface to reflect solar radiation, also affecting the conversion efficiency of solar radiation in dry mass, since it is dependent on the photosynthetically active radiation absorbed by a crop. The present work aims to evaluate the influence of pruning times on the albedo, and to determine the solar radiation conversion efficiency and productivity in the blackberry crop when submitted to different intensities and pruning seasons. The experiment was carried out in a commercial orchard in the municipality of Morro Redondo, Rio Grande, State of Rio Grande do Sul, Brazil, with a randomized block design with five replications, each plot consisting of six plants, in a 3X2 factorial scheme, three seasons and two pruning intensities. Pruning was carried out on 07/18; 10/08 and 01/09 of 2016, each season being submitted to two pruning intensities, short (secondary branches with 15cm in length) and long (secondary branches with 30cm in length). The daily variation of the albedo shows to be more stable in sunny day in comparison with the cloudy day. The albedo presents an inverse behavior in relation to the leaf area index of the blackberry cultivated on vegetated surface between the lines. The average albedo for the crop cycle was 0.24 for pruning in July, 0.23 for pruning in August and 0.21 for pruning in September. The phases of green berry and ripe berry are the phases of the blackberry cycle in which the highest amounts of solar radiation are accumulated. Plants pruned in July have more time to accumulate solar radiation during their cycle, while plants that received pruning in September accumulate greater radiation balance. The pruning season affected the conversion efficiency of solar radiation in dry mass and the production of dry mass of the fruits, so that the pruning performed on July 18 provides greater efficiency than the pruning performed on September 1st. Blackberry plants pruned on September 1 show the same conversion efficiency of solar radiation in dry mass and dry mass production of fruits than plants pruned in the normal period (August 10). The pruning intensity did not affect the conversion efficiency of the solar radiation in dry mass and the dry mass production of the fruits. The yield per plant and the estimated productivity are not affected by the intensity and the season of pruning. The average weight of the fruits was higher in the plants that received short pruning.