Influência das condições climáticas e da cobertura plástica do solo no crescimento e produtividade do meloeiro.

Abstract

Cultural practices are relevant factors for a successful melon crop, and in this concern the use of synthetic mulching has become a standing practice, mainly after polyethylene films had become available in the market. The utilization of these films by the producers of the Brazilian Northeast region has been increasing lately and had become an important alternate practice for controlling water expenditure in crops, chiefly in the semi-arid regions, where small rainfall amounts and high temperatures are common. In this context, this work aimed at evaluating, in the melon crop, the effects of solar radiation (incident and reflected) and air and soil temperatures, as well as plant growth in function of accumulated degree-days, and determining the relation of this measure to yield in the crops influenced by polyethylene film (black, silvered, yellow and brown) covered soil and uncovered soil conditions. The study was carried out through two experiments: one with the hybrid Goldex (May to June 2003) and the other with the hybrid Torreon (August to October 2003). According to the results, polyethylene film mulching affected radiation balance and air and soil temperatures, with these variables reaching higher values in the second experiment. The increase in number of leaves, leaf area index and shoot dry matter production were slow up to 400 degree-days (accumulated) for both hybrids, with the values of these variables becoming intensive in the flowering and fruiting stages. This increase was greater in the treatments with polyethylene films than in the uncovered soil treatment. Polyethylene film mulching affected both absolute and relative crop growth rates, with the relative rate decreasing along the crop cycle. In the Goldex crop, the marketable yield was negatively correlated with the number of accumulated degree-days (to reach the maximum number of leaves) and with the maximum leaf area index; also, there was positive correlation between the accumulated degree-days (to reach the maximum shoot dry matter) and the non-marketable (refuse) and total yields. In the Torreon crop, there was positive correlation between the maximum leaf area index and the nonmarketable yield, as well as between the number of accumulated degree-days (to reach the maximum shoot dry matter) and the total, export class and national class yields.