Ciência Rural (Jun 1998)
Dessecação do campo nativo para semeadura direta da cultura da soja Native pasture desiccation for no-till soybeans seeding
Abstract
Para avaliar doses do herbicida glyphosate, isolado ou misturado com 2,4-D, na dessecação do campo nativo para semeadura direta de soja, foi conduzido um experimento no compus da UFSM. Os tratamentos foram: glyphosate a 360, 720 e 1080g ha-1 de equivalente ácido, isolado ou em mistura com 200g ha-1 de 2,4-D éster, aspergidos em dois volumes de calda (50 e 200l ha-1), além de testemunha sem controle. A aspersão dos herbicidas ocorreu em 30/10/95 e a semeadura da soja em 27/12/95. Das 57 espécies presentes no campo nativo, as principais foram: Paspalum notatum var. notatum biótipos "C" e "D", Vernonia polyanthes, Vernonia nudiflora, Eryngium horridum e Baccharis trimera. Os resultados mostram que o uso de 2,4-D e a redução do volume de calda de 200 para 50l ha-1 não melhoraram a eficácia de controle do glyphosate, que mostrou controle geral de 48, 73 e 90% para as doses de 360, 720 e 1080g ha-1. O glyphosate mostrou controle ineficiente de V. polyanthes, V. nudiflora e E. horridum, independente da dose ou mistura com 2,4-D, sendo eficiente para B. trimera à 720 e 1080g ha-1. Houve controle do Paspalum de 54, 79 e 93% para o glyphosate à 360, 720 e 1080g ha-1 . O rendimento médio de grãos de soja foi de 1762, 2502, 2690 e 2793 kg ha-1, para testemunha e glyphosate a 360, 720 e 1080g ha-1. Conclui-se que, para semeadura direta de soja sobre campo nativo, a dose de 1080g ha-1 de glyphosate é adequada.The objective of this study was to evaluate rates of glyphosate herbicide applyed alone or in mixture with 2,4-D ester herbicide, to control nativo pasture before planting soybeans in a no-till system. The following treatments were tested: glyphosate at 360, 720, and 1080g ha-1 of acid equivalent, alone or in mixture with 200g ha-1 of 2,4-D, sprayed at two volumes (50 and 200l ha-1), and unsprayed control. Herbicides were sprayed in 10/30/95 and soybean was seeded in 12/27/95 in study carried out at the Federal University of Santa Maria campus. Santa Maria, RS, Brazil. The main plant species out of the 57 identified were Paspalum notatum var. notatum biotypes "C" and "D", Vernonia nudiflora, Vernonia polyanthes, Eryngium horridum e Baccharis trimera. The reduction in the spray volume from 200 to 50l ha-1 and mixing with 2,4-D did not affect the efficacy of glyphosate, which showed general control of 48, 73, and 90% using 360, 720. and 1080g ha-1. respectively. Glyphosate did not control V. nudiflora, V. polyanthes and E. horridum, but controlled B. trimera at rates of 720 and 1080g ha-1. There were 54, 79, and 93% control of Paspalum spp. using 360, 720, and l080g ha-1 of glyphosate, respectively. Soybeans yields were 1762, 2502, 2690, and 2793 kg ha-1 for unsprayed and 360, 720, and 1080g ha-1 of glyphosate, respectively. It is concluded that for soybean seeding over native pasture, the rate of 1080g ha-1 of glyphosate is adequate.
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