A. Jakelaitis

Persistência de sulfentrazone em Argissolo Vermelho-Amarelo cultivado com cana-de-açúcar

The objective of this study was to evaluate sulfentrazone persistence in Typic Hapludalf and its effect on the microbiota of soil cultivated with sugar-cane. The treatments consisted of herbicide application only in 2003, in 2003 with reapplication in 2004 and control without herbicide. Herbicide distribution in the soil profile (0-10 and 10-20 cm of depth) and persistence in 467/24, 517/74, 550/107 and 640/197 days after application (DAA), were studied in the split-plots and split-split-plots, respectively. Indirect quantification of the residues was accomplished by bioassay and C-CO2 evolution together with microbial biomass (CBM) determination were evaluated in soil collected 640/197 DAA. Reduction of dry mass of the aerial part of Sorghum vulgare was verified during the entire evaluated period when the herbicide was applied in 2003 and reapplied in 2004. Most of the residues were detected at the depth of 010 cm, with their leaching potential in the soil being of little significance under environmental conditions. Sulfentrazone influenced the evolution of C-CO2 and CBM of the soil, with the largest accumulated value of C-CO2 being observed for the treatment without herbicide application. Sulfentrazone presented high persistence in PVA, with a negative effect on soil microorganisms, but without posing leaching risks in its profile.

Persistência e lixiviação de ametryn e trifloxysulfuron-sodium em solo cultivado com cana-de-açúcar

The aim of the work was to evaluate the behavior of the ametryn + trifloxysulfuron-sodium commercial mixture in sugar-cane crop, as related to leaching potential and persistence in the environment. The Typic Haplufalf soil area was divided into two sub areas where the sugar-cane varieties SP 79 1011 and SP 80 1816 were cultivated. The treatments were constituted by pre and post-emergence applications of the commercial herbicide mixtures in 2003 and 2003 + 2004, with four soil samplings 0-0.10 and 0.10-0.20 m deep. Bioassay and High Performance Liquid Chromatography (HPLC) methods were used to evaluate the residues. Both methods were found satisfactory for evaluation of the commercial mixture residue, although the bioassay use did not allow evaluating the compounds separatedly. According to the data obtained from the simultaneous analysis of ametryn and trifloxysulfuron-sodium by HPLC, most of the ametryn residues remained in the soil layer 0-0.10 m deep, persisting for over 180 days after application (DAA), in soil sprayed in 2003 + 2004. Ametryn residues in 0.10 - 0.20 m deep, were as well found for the treatments sprayed in 2003 + 2004 and showed the risks of leaching and contaminating water with this herbicide. For the treatments sprayed only in 2003, a significant residual effect was not detected 490 days after application. Differences in residual effect among cultivated sub areas with the variety SP 79 1011 and SP 80 1816 were due to the different amounts of clay and organic matter in the soil. Residues of trifloxysulfuron-sodium were not found in any period of the soil sampling, as the limit of quantification by HPLC (0.06 mg L-1) is higher than the used dose of this herbicide (37 g ha-1).

Atividade microbiana e produção de milho (Zea mays) e de Brachiaria brizantha sob diferentes métodos de controle de plantas daninhas

This study aimed to evaluate the effects of atrazine + nicosulfuron on soil microbial activity and biomass production of corn and Brachiaria brizantha intercroping. The treatments were constituted of corn and B. brizantha intercropping, treated with atrazine (1,500 g ha-1), or with atrazine + nicosulfuron (0, 4 and 32 g ha-1) and two controls represented by intercropping control with and without weeds. Herbicides were applied 30 days after corn emergence (DAE). The experiment was arranged in a randomized block design, with four replicates. Microbial biomass (MB), respiration and metabolic quotient (qCO2) obtained from soil samples seven days after herbicide application on corn flowerage and pre-harvesting were evaluated. No-treated soil samples were collected in field and treated with atrazine (1,500 g ha-1) + nicosulfuron (0, 2, 4, 8, 16 and 32 g ha-1 ) under laboratory condition. Weed and B. brizantha dry matter and corn grain yield were evaluated at corn pre- harvesting. Methods of control did not influence respiration, MB nor qCO2 but higher MB in flowerage and higher qCO2 were observed after seven days of application. Higher weed dry matter production was observed in the control treated only with atrazine. Forage yield of B. brizantha was superior in the control plots without weeds, while corn grain yield was superior both in the control plots without weeds and treated with nicosulfuron.

Períodos de interferência de plantas daninhas na cultura do feijoeiro-comum (Phaseolus vulgaris L.)

Objetivou-se nesta pesquisa determinar os periodos de interferencia de plantas daninhas no feijoeiro-comum (Phaseolus vulgaris L.) cultivado em plantio direto, em Rolim de Moura-RO. Dois ensaios foram conduzidos simultaneamente; no primeiro a cultura permaneceu livre da competicao com plantas daninhas desde a emergencia ate os 7; 14; 21; 28; 35; 42; 49 e 64 dias; no segundo a cultura permaneceu em competicao com a comunidade infestante pelos periodos citados no primeiro ensaio. O delineamento utilizado foi de blocos ao acaso, com quatro repeticoes. A Digitaria horizontalis e Zea mays foram as especies que apresentaram maior importância. A D. horizontalis atingiu altas frequencias relativas, dominância relativa e densidade de ate 95,3%. A Z. mays apesar dos baixos indices de densidade e frequencia relativa, apresentou alta dominância relativa pelo grande acumulo de massa seca. O rendimento de graos do feijoeiro foi afetado pela convivencia com as plantas daninhas. Assumindo perdas de 5% no rendimento de graos do feijoeiro pela interferencia da comunidade infestante o periodo anterior a interferencia foi de quatro dias, onde nao foi necessaria a realizacao do controle. O periodo total de prevencao da interferencia foi de dezoito dias apos a emergencia (DAE) e o periodo critico de prevencao da interferencia situou-se entre os quatro e os dezoito DAE. Neste periodo ate 18 DAE a convivencia do feijoeiro com plantas daninhas ocasionou diminuicao no rendimento da cultura por competirem pelos recursos do meio, onde houve necessidade de serem controladas.

Inoculação das sementes e adubações nitrogenada e molíbdica do feijoeiro-comum, em Rolim de Moura, RO

The aim of this study was to evaluate the effects of seed inoculation with Rhizobium tropici and nitrogen and molybdenum fertilization on the performance of the common-bean (Phaseolus vulgaris L.). A complete randomized block design with four replicates was used, in a factorial arrangement 2x2x2, with the combinations of absence and presence of seed inoculation and nitrogen (N) and molybdenum (Mo) fertilization. Seeds inoculation was just before sowing with a peat inoculante composed by the strain CIAT 899 (SEMIA 4077), N was provided at sowing (10 kg.ha-1) and coverage (50 kg.ha-1) when the plants showed the third trifoliate sheet expand and Mo was applied by foliar spraying with 60 g.ha-1 when plants were at beginning of flowering . No effect of treatments on the dry mass of roots and the number of pods per plant was observed. N fertilization reduced nodulation of plants, however, N fertilization lead to an increase in height and dry mass of bean shoots. It was also observed that plants fertilized with N but in the absence of Mo shoed heavier grains. The interactions between N and Mo fertilization with inoculation of seed negatively affected the leaf N content and the number of grains per pod. The inoculation of seed in beans provided grain yields similar to those provided by the treatment with N fertilization.

Atividade residual no solo da mistura comercial dos herbicidas fluazifop-p-butil e fomesafen utilizados no cultivo convencional e direto do feijoeiro

The residual activity of the commercial mixtures of the herbicides fluazifop-p-butyl and fomesafen was evaluated in Typic Hapludalfs soil in bean cultivated under tillage and no-tillage systems. The bean plant was cultivated under the tillage system over corn straw (3.6 t ha1) Brachiaria brizantha (15 t ha-1) and corn straw + B. brizantha (8.1 t ha-1). Under the tillage system, bean was planted after incorporation into the soil of the corn straws + B. brizantha originating from the consortium. The commercial herbicide mixture (500 mL ha-1 ) was applied 30 days after bean emergence. In soil samples collected at 10, 29, 47, 72 and 119 days after herbicide application (DAA), persistence was evaluated in the soil using the bioassay method and Sorghum vulgare as control. It was verified that Typic Hapludalfs soil has a high sorption capacity for fluazifop-p-butyl and fomesafen. Regardless of the type and amount of straw over the surface soil, under no tillage system, no herbicide residual effect on soil was verified after 10 DAA. However, when the straw was incorporated into the soil, under the tillage system, phytotoxicity symptoms, and reduced height and dry mass aerial part of S. vulgare persisted after 72 DAA of the herbicides. The absence of residual symptoms in the control plant, when the herbicides were applied under no tillage system, was attributed to straw retention, preventing its contact with the soil.

Interação entre herbicida e inseticida sobre o milho-pipoca (Zea mays), as plantas daninhas e a lagarta-do-cartucho

This study aimed to evaluate the effect of the tank-mixture herbicide nicosulfuron combined with the insecticide chlorpirifos on the popcorn cultivar UFVM2, weeds and fall armyworm. The experiment was arranged in a randomized complete block design, in a (5x2)+3 factorial scheme and four replications. The first factor consisted of nicosulfuron doses (0, 10, 20, 30, and 40 g ha-1) + atrazine (1.200 g ha-1) + oil (900 g ha-1) and the second of doses of the insecticide chlorpirifos (0 and 240 g ha-1). Three additional treatments were evaluated: two controls, with and without weeding, both without insecticide, and one control with weeding and insecticide. The interaction between the nicosulfuron and chlorpirifos doses in the control of the fall armyworm was not significant. The tank-mixture formed by the chlorpirifos and herbicides caused intoxication to popcorn plants, mainly at nicosulfuron rates (10, 20 and 40 g ha-1). Chlorpirifos did not interfere in herbicide efficiency in controlling weed, nor in the final stand, number of ears, and production and expansion capacity of the popcorn grains.