Rodrigo Neves

Efeitos do manejo mecânico e químico da aveia-preta no milho em sucessão e no controle do capim-papuã

n†The objective of this experiment was to evaluate the effects of mechanical and chemical management of oat straw and of sowing dates of maize after oat desiccation on maize grain yield and on alexandergrass (Brachiaria plantaginea Link) infestation. In 1997/98, treatments were composed by two mechanical management systems of oat (rolled or not) and bare area as the control, by two herbicides (glyphosate and paraquat) applied to desiccate oat straw and by two maize sowing dates after desiccation (one and 15 days). In the 1998/99†growing season, five management systems of oat straw (rolled, cleared and desiccated with glyphosate, glufosinate and paraquat) and a bare area used as check were tested. Delay of maize sowing date in 15 days after oat straw desiccation increased N accumulation, dry matter production per plant and grain yield of maize. Maize grain yield in succession to oat was not influenced by management system of oat straw. Rolling oat straw provided the best control of alexandergrass infestation.

Redução na dose do herbicida aplicado em pós-emergência associada a espaçamento reduzido da cultura de soja para controle de Brachiaria plantaginea

Integration of certain crop management practices with chemical weed control could allow a rate reduction of the herbicide to be applied, without significant changes in weed control levels and soybean grain yields. This research aimed to evaluate reduction in the recommended rate of a formulated mixture of fluazifop-p-butyl plus fomesafen, associated with reduction in soybean row width, on alexandergrass (Brachiaria plantaginea) control and crop grain yield. The experiment was conducted at EEA/UFRGS, Eldorado do Sul-RS, during the growing season of 1997/98. Soybean cultivar tested was BR 16, sowed under a no-till system. The treatments consisted of three row widths (20, 40 and 60 cm), and five rates of the herbicide mixture [fluazifop-p-butyl (200 g L-1) + fomesafen (250 g L1)], applied at the recommended rate of 1.0 L ha-1 (100%) and reduced rates (75, 50, and 25% of the recommended rate) plus a check. Alexandergrass control was visually evaluated at 8 and 17 days after herbicide applications, by obtaining its dry matter weight, as well as the soybean grain yield. The results showed that, for a moderate alexandergrass infestation, soybean row width does not affect weed control when the herbicide is sprayed at the recommended rate. For late herbicide applications, 40 cm row width allows a reduction of herbicide rate up to 50%, without affecting alexandergrass control and a decrease up to 75% of the herbicide rate, without reducing soybean grain yield; reduction of herbicide rate is conditioned to application time and row width used; with reduced row widths application must be performed earlier so that a sufficient amount of the product reaches the weeds.

Ação dos herbicidas atrazine e glufosinate de amônio no aproveitamento de nitrogênio pelas plantas de milho

Plant absorption of nitrogen (N) present in soil or supplied through fertilization is regulated by a complex of enzymes that act in a jointly and ordered way in the plant. The purpose of this research was to investigate the effects of the herbicides atrazine and ammonium glufosinate in N absorption by plants and their effects on corn plant traits. In one of the experiments (experiment 1), three atrazine rates were tested (0, 200, and 2000 g a.i. ha-1), three ammonium glufosinate rates (0, 40, and 80 g a.i. ha-1), and two N rates (0 and 90 kg ha-1). In another experiment (experiment 2), three herbicide treatments were tested (atrazine, 200 g a.i. ha-1; ammonium glufosinate, 40 g a.i. ha-1; atrazine + glufosinate, 200 + 40 g a.i. ha-1; and a check), two N sources (urea and ammonium nitrate), and two N rates (0 and 100 kg ha-1). Effects of the treatments were evaluated at 10 and 20 days after herbicide application (DAA) in experiment 1, and when corn plants presented 10 developed leaves (15 DAA) and at tasseling (40 DAA) in experiment 2. Statistical analyses revealed that N side dressing application in corn promotes an increase in most of the grain yield components and increases grain yield by 35%, and that such effects occur regardless of the N source used, urea or ammonium nitrate. There was no interaction effect among factors related to herbicides that are inhibitors of photosystem II (atrazine) and to herbicides inhibitors of the glutamine synthesis (ammonium glufosinate) and N side-dressing application in corn. The use of these herbicides in reduced rates, applied alone or in combination, did not affect grain yield nor yield components. Atrazine shows little consistency in affecting chlorophyll and N contents in corn; nevertheless, in some cases, its action is favorable, especially when used at the recommended rate or even when sprayed alone. Ammonium glufosinate, applied at reduced rates, in general does not affect N content in corn; however, in some situations, chlorophyll content is affected and, when used at 80 g a.i. ha-1, promotes N content increase in the corn tissue.

Ação de herbicidas sistémicos não-seletivos sobre a progénie de soja quando aplicados durante a fase reprodutiva das plantas-mãe

The purpose of ihis research was to evaluate germination of soybean seeds and initial development of seediings, whose mother plants were treated with sub-rates of svstemic nonselective herbicides during late stages of development. Field, laboratory, and greenhouse experiments were carried oui ai Agronomy School of UFRGS, in Porto Alegre, RS, during the period 1995/97. Treatments consisted offield appiications of the herbicides 2,4-D at rates of 5 and l0g/ha a. e., imazapvr at 25 and 50g/ha a.e., and sulfosate at 25 and 50g/ha a.e. The se herbicides were sprayed eiiher at beginning of flowering (R1 stage) or at beginning ofpod development (R3 stage) of soybean plants. It was proved that appiication of imazapyr on sovbean plants at beginning of pod development decreased germination of seeds formed on those plants. The appiication of 2,4-D and sulfosate did not ajfect soybean seed germination, at tested rates, independentiy if appiied eiiher at beginning of flowering or pod development of the mother plants. Seediing izeight, dry matter of shoots, of roots and total dry matter of seediings of the progeny were not affected by herbicides appiied at Ri and Rs stages of sovbean plants. However, sprayings of herbicides 2,4-D (at 5 and l0g/ha a.e.), imazapyr (at 25 and 50g/ha a.e.), and sulfosate (at 25 and 50g/ha a.e.), appiied at beginning of pod development of mother plants, in general reduced hvpocotyl and root lengtli of sovbean seed-lings of tire progeny.