Efeito da poda na arquitetura da planta, produtividade e qualidade de sementes de malva (Urena lobata L.)

Abstract

Mallow (Urena lobata L.) is a crop of socioeconomic relevance in Amazonas, cultivated for fiber production. However, currently the limiting factor in the chain is the supply of the main input, the seeds. Therefore, the objective of this work was to evaluate the effect of different pruning practices on the growth (height, stem and canopy diameter) and development (phenology - vegetative growth, flowering, immature fruits, mature fruits) of plants and on the productivity of mallow seeds. A randomized block design (RBD) was established with five treatments and four replications, as follows: T1: pruning to 80 cm at 3 months; T2: pruning at 80 cm at 3 months and 130 cm at 5 months; T3: pruning at 80 cm at 3 months, at 100 cm at 4 months and at 130 cm at 5 months; T4: pruning by 80 cm at 3 months, by 110 cm at 5 months and by 140 cm at 6 months; T5: pruning by 80 cm at 3 months, by 100 cm at 4 months, by 120 cm at 5 months and by 140 cm at 6 months. The results were subjected to the F test (5%) or Kruskal Wallis (5%) and Tukey test or regression analysis. Pruning management affects plant growth by reducing height up to 11 months after sowing, which favors the mitigation of lodging and facilitates harvesting by reducing the height of the mallow. This reduction in height occurs mainly in plants pruned up to six months after sowing. It also affects the diameter of the canopy, a greater number of prunings possibly contributes to greater branching of lateral sprouts, resulting in a denser and smaller canopy, which is also an advantageous characteristic for seed production. The implementation of mallow seed production in the field four months before the drought in Amazonas affects the phenological phases of the species, making the sowing time a limiting factor for the production of mallow seeds in Amazonas. Although a satisfactory plant stand has been achieved, there is still sufficient rainfall for germination and initial growth, incipient vegetative growth makes commercial seed production impossible. This is because drought after four months of cultivation induces early flowering and fruiting. Pruning after six months of cultivation, implemented four months before the dry period eliminates flowers and fruits. The high rainfall from 7 to 11 months after sowing, a period in which the beginning of flowering and fruiting was expected, caused the resumption of the vegetative growth phenophase, prolonging the crop cycle. Pruning management for up to six months of cultivation does not influence the productivity of mallow seeds in a prolonged cultivation cycle (15 months). Therefore, future work is recommended to include studies with different pruning management with sowing at the beginning of the rainy season in Amazonas, including pruning at the end of the annual cycle to analyze the perennial conduction of the mallow crop.