Envelhecimento de resíduos vegetais sobre o solo e os reflexos na eficácia de herbicidas aplicados em pré-emergência

Abstract

RESUMOCom o objetivo de avaliar os efeitos do envelhecimento dos resíduos vegetais de diferentes espécies [sorgo de cobertura (Sorghum bicolor x S. sudanensis 'Cober Exp'), milheto forrageiro (Pennisetum americanum 'BN2'), capim-pé-de-galinha (Eleusine coracana) e capim-braquiária (Brachiaria brizantha)], no controle de Ipomoea grandifolia, pelos herbicidas diclosulam e imazaquin, aplicados em pré-emergência, foi desenvolvido experimento em casa de vegetação, no período de agosto a dezembro de 2004. Foram realizadas determinações químicas nos materiais vegetais em decomposição. A eficácia do herbicida diclosulam não foi afetada pelo envelhecimento da palha de nenhuma das coberturas estudadas. Pelo contrário, a associação desse herbicida a qualquer dos resíduos vegetais estudados, principalmente o de capimbraquiária, favoreceu o controle da planta daninha. O imazaquin teve o potencial de controle influenciado pelas coberturas de milheto forrageiro e capim-braquiária, aos 90 dias após a deposição dos resíduos vegetais sobre o solo. Tal comportamento pode ser atribuído ao enriquecimento de celulose e lignina nos materiais vegetais de milheto forrageiro e capim braquiária.Palavras-chave: constituição química, decomposição, Ipomoea grandifolia, palha, sistema de semeadura direta, herbicidas residuais ABSTRACT CROP RESIDUES AGING ON SOIL AND THEIR EFFECTS ON PRE-EMERGENCE HERBICIDESAn experiment was conducted from August to December 2004 under greenhouse conditions to evaluate the effects of aging residues of different plant species [coverage sorghum (Sorghum bicolor x S. sudanensis 'Cober Exp'), forage millet (Pennisetum americanum 'BN2'), finger millet (Eleusine coracana) and St. Lucia Grass (Brachiaria brizantha)], on the control of Ipomoea grandifolia using the pre-emergence herbicides diclosulam and imazaquin. Crop residues were subjected to chemical analyses. The efficiency of diclosulam was not affected by any of the residues. On the other hand, in association with residues of any of the species, but especially with St. Lucia Grass, this herbicide showed increased weed control efficiency. The control potential of imazaquin was influenced by forage millet and St Lucia Grass residues 90 days after laying residues on the soil. This behavior may be due to cellulose and lignin increase in both forage millet and St. Lucia Grass.

Sulfentrazone efficiency on Ipomoea hederifolia and Ipomoea quamoclit as influenced by rain and sugarcane straw

“…It is possible that sugarcane straw remaining on the soil surface may create a favorable environment for the seed germination and the development of these weeds due to a reduced daily temperature range, increased soil moisture retention, and improved physical and chemical soil attributes. Correia and Durigan (2004) reported that the emergence of Ipomoea grandifolia, I. hederifolia, and I. quamoclit was not influenced by straw at the levels included in their study (5, 10, and 15 t ha -1 ). Contrary to this finding, however, an increased number of I. quamoclit seedlings emerged, and a greater biomass accumulation was observed, in the presence of mulch compared to treatment without straw.…”

“…The effect of straw on herbicide efficacy depends on the physical and chemical attributes of the herbicides, such as solubility, vapor pressure, and polarity (Rodrigues, 1993). Rain or irrigation, time following the application of herbicide, and changes in the chemical constitution of the decomposing plant material may also strongly influence herbicide retention by straw (Correia et al, 2007). When straw remains on the soil, herbicides are potentially lost by photodegradation, volatilization, and even adsorption to plant residues.…”

Seed bank and control of Rottboellia exaltata using clomazone alone and in combination with other herbicides

“…Depending on the physical and chemical characteristics of herbicides, such as solubility, vapor pressure and polarity, straw cover can have a greater or lesser influence on herbicidal effectiveness (Rodrigues, 1993). The timing and amount of rainfall or irrigation after herbicide application as well as changes in the chemical composition of decaying plant materials can greatly influence herbicide retention by straw cover (Correia et al, 2007). The herbicide on the straw that is not transferred into the soil is subject to losses from photodegradation, volatilization, and adsorption onto plant litter whose degree of decomposition or age can affect its ability to adsorb herbicides (Mersie et al, 2006).…”

S-metolachlor efficacy on the control of Brachiaria decumbens, Digitaria horizontalis, and Panicum maximum in mechanically green harvested sugarcane

“…This capacity is dependent on the physical and chemical characteristics of the herbicide, such as its water solubility, vapor pressure, and molecule polarity (Rodrigues, 1993). After herbicide application, the amount and period when rainfall or irrigation occurs, as well as modifications occurring in the decomposing plant residues, are also important factors regarding the retention of the herbicide by the crop residue (Correia et al, 2007). When retained by the crop residue, herbicide losses are likely to occur due to photo degradation, volatilization, and its adsorption by plant residues.…”