Levantamento de plantas daninhas em soja cultivada sob diferentes espaçamentos em savana amazônica.

Abstract

The management of weeds in the soybean crop, through the reduction of the planting spacing, appears as an important factor of cultivation on which the success of the production depends. The objective of this study was to evaluate the floristic, ecological and phytosociological compositions of weeds in soybean cultivation under different spacings in an Amazonian savannah area, in Boa Vista, RR, Brazil. The cultivar BRS 7980 was sown in a conventional system, in four blocks with three different spacings (45, 55 and 65 cm) between rows. Weed sampling was carried out through an iron square (0.25 m2), which was randomly thrown four times in each block, totaling 4.0 m2 of sampled area. A total of 16 weed species were recorded, distributed in ten genera and five families, of which Fabaceae and Malvaceae predominated. Four species were present in all spacings: MimosapudicaL.,Urochloa decumbensStapf.,Calopogonium muconoidesDesv. eWaltheria communisA.St.-Hil. The different spacings were not indicators of the floristic composition of weeds. The low similarity index between the species indicated that the plant community was affected by the different spacings used.Urochloa decumbensStapf. obtained greater prominence in the phytosociological parameters evaluated, requiring special attention in the control. The highest weed dry mass was obtained at 55 and 65 cm spacings. The predominant propagation type, life form and life cycle were by seeds, herbs and perennials, respectively. The predominant photosynthetic route was the C3 type, especially at 45 cm. Therefore, the cultivation of soybeans with a spacing of 45 cm between rows causes a reduction in the ecological and phytosociological composition of weeds in an area of ​​Amazonian savannah. The different spacings between rows are not indicators of the floristic composition of weeds in soybean cultivation in the Amazon savanna