Fitossociologia Da Comunidade De Plantas Daninhas Na Cultura Da Soja Transgênica Sob Dois Sistemas De Preparo Do Solo

Abstract

Edson Aparecido dos SANTOS 5 RESUMOObjetivou-se com este trabalho realizar o levantamento fitossociológico de plantas daninhas antes e após aplicação de herbicidas pós-emergentes na cultura da soja transgênica. Os tratamentos foram distribuídos em blocos casualizados com os herbicidas: lactofen + chlorimuron-ethyl (150 + 50 g ha ) nos sistemas de plantio direto e convencional. As amostragens de plantas daninhas ocorreram em quatro épocas: antes da aplicação dos herbicidas (estádio V 2 ); aos sete dias após aplicação dos herbicidas (estádio V 4 ); no início do florescimento da cultura (R1) e em pré-colheita da soja (estádio R8), utilizando quadrado inventário (0,25 m²) jogado ao acaso nas parcelas por duas vezes. As espécies vegetais amostradas foram identificadas, contadas e pesadas para obtenção dos parâmetros fitossociológicos. ABSTRACTThis objective of this work was to carry out a phytosociological assessment of the weed communiy before and after post-emergents herbicides application on transgenic soy crop. The treatments were arranged in random blocks by using: lactofen + chlorimuron-ethyl (150 + 50 g ha -1 ), imazethapyr + fomesafen (100 + 250 g ha -1 ) and glyphosate (1000 g ha -1 ) under no-tillage and conventional systems. The weed community sampling occurred in four seasons: before herbicide application (V 2 stage); seven days after herbicide application (V 4 stage); at the beginning of flowerage (R 1 ) and at soy pre-harvest (R 8 stage), using the inventory square method applied through a square of 0.25 m², randomly placed twice. The species found were identified, counted and weighed to obtain phytosociological parameters. The families that showed higher density, abundance and importance value index in the area were: Brachiaria plantaginea, Euphorbia heterophylla, Ipomoea sp., Cyperus rotundus and Digitaria horizontalis, meanwhile B. plantaginea and C. rotundus showed higher importance value index under conventional system and B. plantaginea and D. horizontalis showed importance value index under no-tillage systems. Comparing the systems, at the end of the crop cycle, the management using only glyphosate under conventional system allowed a significative C. rotundus infestation. Under no-tillage system, at the same season, B. plantaginea predominated followed by D. horizontalis wasn't present in parcels treated with imazethapyr + fomesafen.

Crop management and its effects on weed occurrences

“…The families with the highest occurrence rates were Poaceae and Asteraceae, followed by Amaranthaceae and Euphorbiaceae (Table 1). Similar to these data, weed phytosociology in soybean cultivation was verified in two soil management systems, with high density of the species Brachiaria plantaginea, Euphorbia heterophylla, Ipomoea sp., Cyperus rotundus, and Digitaria horizontalis (Fialho et al 2011). Additionally, in an area where there was resistant soybean and susceptible to glyphosate, 16 weed species belonging to 10 families were found, the main species belonging to Poaceae and Asteraceae, with 5 and 3 species, respectively.…”