Rubem Silvério de Oliveira Júnior

Rendimento de grãos e qualidade de sementes de soja após a aplicação de herbicidas dessecantes

Herbicides diquat (0.3kg ha-1), paraquat (0.4kg ha-1), amonium-gluphosinate (0.5kg ha-1) and carfentrazone-ethyl (30g ha-1) were sprayed to soybean plants at the R7,5 stage in order to study their influence on soybean grain yield and seed quality. There were no differences among treatments with regard to germination, vigor, seed health, weight of 100 seeds, seed moisture content and seed yield. Nevertheless amonium-gluphosinate and control treatments provided higher percentages of normal seedlings after accelerated aging, compared to the other treatments.

Sistemas de manejo de plantas daninhas no desenvolvimento e na produtividade da soja

The choice of the adequate moment for the desiccation of the green cover that precedes the sowing is fundamental for the success of no-till soybeans. This context, the work was aimed to study two burndown systems: desiccation immediately before sowing (AP) and anticipated desiccation (MA), composed by two burndown herbicide applications. For MA, the first application of glyphosate (1240 g ha-1) occurred between 30 and 35 days before the sowing of the crop, and the second was done just before sowing. For AP, the applications (1080 to 1260 g ha-1 of glyphosate) occurred within 48 hours prior to sowing. The trials were developed in 2003/2004 growing season, in six localities in Parana State: Sertaozinho, Campo Mourao, Iretama, Pitanga, Boa Esperanca, and Mambore, in areas with high density of weeds preceding no-till soybean sowing. Evaluations related to weed control and soybean development and grain yield were performed. MA burndown systems provided improved control of weeds after crop emergence. Soybean plants from AP areas were shorter, in comparison to ME, evidencing a delay in the shoot growth. Reduction of grain yield was verified for all localities when AP burndown system was adopted, with reductions between 15% and 50%.

Variabilidade espacial de plantas daninhas em dois sistemas de manejo de solo

Studies of spatial distribution of weeds are important in the agronomic and environmental context. The objective of this research was to describe the spatial distribution of weeds in two soil management systems. This study was accomplished in a Distroferric Red Latosol (Oxisol), located in Campo Mourao, Parana State, Brazil, in no-tillage (NT) and conventional tillage of soil (CT). A grid was established in coordinated x and y, with 128 sampling points. The studied variables were biomass of shoot weeds, density of weeds, Commelina benghalensis density and Bidens pilosa density. Exploratory data analysis was used to evaluate distribution of variables as well as to adapt them for the spatial analysis. The spatial variability was studied using geostatistics by analysis of semivariograms, kriging interpolation and constructions of maps. The ranges of biomass and density of Bidens pilosa, were larger in NT than in the CT. For plant density range was larger in the PC. The spatial distribution described by geostatistics allowed weed mapping and its site specific management and the establishment of criteria for future experiments.

Sorção do herbicida imazaquin em Latossolo sob plantio direto e convencional

Abstract – The objective of this study was to evaluate the effect of spatial variation of pH and organic matter ofa Dark Red soil, under different managements, on imazaquin herbicide sorption. Soil-water sorption partitioningcoefficient (K d ) was used in surface soil samples collected at 0–15 cm layer in a 38 ha area, under central pivotirrigation and with till and no-till management. Herbicide sorption was most strongly related to soil organic mattercontent and pH, revealing greatest sorption in lower pH values with greater soil organic matter content. Thesesamples were collected at no-till management area. The pH effects on imazaquin retention occur either bycontrolling the organic matter ionization form as also its speciation. The clay content in the whole area had novariation, however, it didn’t affect the K d values. Using multivariate regression and two independent variables(soil organic matter content and pH), the prediction of herbicide sorption by soil was good (R 2 = 0.91).Index terms: imidazolinone, site-specific management, organic matter, pH, conventional-tillage.

Variabilidade espacial da resistência do solo à penetração e da taxa de estratificação de carbono orgânico do solo em um Latossolo Vermelho eutroférrico

The compaction and the quality of the soil are constantly questioned for the definition of the no-till soil management. This study was aimed at evaluating the spatial variability of the soil resistance to penetration, bulk density and soil organic carbon stratification ratio in layers on a clayey Typic Eutrothox, in contiguous areas of no-tillage with rotation of cultures and no-tillage with succession of cultures associated the chiselling. The study was set up from May to June of 2002, in Palotina, west region of the state of Parana, Brazil. The samples for determination the soil bulk density, soil resistance to penetration and soil organic carbon stratification ratio were obtained in 120 points in 2 x 5m grid, in the 0.40m depth. Soil resistance to penetration measures were made three times, in a period of 10 days, initiate after having interrupted precipitation. The soil bulk density did not explain the spatial dependence of the compaction of the soil. The soil resistance to penetration and soil organic carbon stratification ratio presented range of 17m. The temporal variation of the spatial dependence of the soil resistance to penetration happens in the 0.05-0.20m layers. Similares spatial e dependence of the soil resistance to penetration and soil organic carbon stratification ratio reveals the importance of the quality of the soil in the spatial and temporary stabilization of the compaction of the soil expresses for the soil resistance to penetration in no-tillage systems.

Persistência e fitotoxicidade de herbicidas aplicados na soja sobre o girassol em sucessão

O objetivo deste trabalho foi avaliar o efeito residual dos herbicidas imazaquin, imazethapyr e diclosulam aplicados na cultura da soja sobre o girassol em sucessao. Nas parcelas, foi semeado o girassol aos 60 e 90 dias apos a aplicacao (DAA) do imazaquin e do diclosulam e 45 e 75 DAA do imazethapyr. As subparcelas foram compostas pelos herbicidas imazaquin (150 g/ha), imazethapyr (70 g/ha) e diclosulam (33,6 g/ha) aplicados na cultura da soja, alem da testemunha (sem aplicacao). O girassol, semeado aos 90 e aos 75 dias apos a aplicacao do imazaquin e do imazethapyr na cultura da soja, respectivamente, nao apresenta sintomas de fitotoxicidade. O diclosulam causa reducao total do estande de girassol nas duas epocas de semeadura. A lesao causada pelos herbicidas ao girassol, observada na produtividade da cultura, e maior em ordem decrescente de fitotoxicidade: diclosulam > imazaquin > imazethapyr.

Evidence of High Gene Flow Between Samples of Horseweed (Conyza canadensis) and Hairy Fleabane (Conyza bonariensis) as Revealed by Isozyme Polymorphisms

Abstract Native polyacrylamide gel electrophoresis was used to identify polymorphisms in &agr;- and &bgr;-esterases loci and electrophoresis in starch gel to identify polymorphism in malate dehydrogenase (MDH; EC 1.1.1.37) and acid phosphatase (ACP; EC 3.1.3.2) isozymes loci in leaf tissues from samples of horseweed and hairy fleabane populations to determine genetic diversity and population structure. Similar or differential genetic divergence between the two species may guide specific use of herbicides. For samples of plants with high genetic similarity it is possible to adopt similar mechanisms and processes for their control. The proportion of polymorphic loci was 57.14, 50.0, and 53.6%, in samples of horseweed and hairy fleabane, for EST, MDH, and ACP isozymes, respectively. A comparison of the diversity parameters in the two species showed that the number of alleles is similar in the horseweed and hairy fleabane plants. The estimated heterozygosity in horseweed and hairy fleabane was also very close. A relatively low level of population differentiation was detected between horseweed and hairy fleabane (Fst  =  0.0199), which suggests a substantial genetic exchange among the two species. Accordingly, estimate of gene flow was high (Nm  =  12.3172) for the alleles of the loci Est, Mdh, and Acp. The Nei’s identity (I) values also was high (I  =  0.9561) indicating very high similarity between the two Conyza species. AMOVA showed higher genetic variation within (95%) than among (5%) the two samples. The low genetic structure and high value of genetic identity was an important indication that alleles are exchanged between horseweed and hairy fleabane populations, and provides additional evidence of occurrence of outcrossing between populations or dispersion of samples of one for other site. Nomenclature: Hairy fleabane, Conyza bonariensis (L.) Cronq.; horseweed, Conyza canadensis (L.) Cronq.

AMINO ACID APPLICATION CAN BE AN ALTERNATIVE TO PREVENT GLYPHOSATE INJURY IN GLYPHOSATE-RESISTANT SOYBEANS

Glyphosate-resistant (GR) soybeans have continuously increased; however, this expansion significantly increased the use of glyphosate and therefore, in some cases, has resulted in injury symptoms observed in GR soybean, known as “yellow flashing”. Previous reports of interference of glyphosate with nutrient availability and utilization by GR soybean may be linked to this injury symptom. Also, because glyphosate interferes with amino acid synthesis, supplementation with exogenous amino acids may help GR soybean recover from adverse effects of glyphosate. Therefore, an experiment was designed to evaluate different amino acid concentrations. Near-isogenic and GR soybean varieties were grown in the greenhouse in two soils with and without glyphosate at different rates and amino acids were foliarly applied with and without glyphosate. In general, the photosynthetic variables, nutrient contents, and shoot and root dry biomass parameters were affected by glyphosate, however, use of amino acid formulations suppressed harmful effects of glyphosate on these parameters.

ATIVIDADE RESIDUAL DE IMAZAQUIN E ALACHLOR+ATRAZINE PARA PLANTIO SEQÜENCIAL DE CANOLA

The objective of this work was to evaluate the carryover potential of the herbicides imazaquin (150 and 300g eq. acid ha-1) and alachlor+atrazine (1430+1430 and 2860+2860g ha-1), applied respectively to soybeans and corn crops, aiming at determining the smallest period of time between utilization of these products and canola planting date succeding these crops. Soil samples were collected at 15, 30, 60, 90 and 120 days after application (DAA) of the herbicides on field and ten canola seeds were sown in each pot. Canola germination was reduced up to 30DAA of imazaquin applied at recommended rate (150g eq. acid ha-1) and up to 60DAA at double the recommended rate. In relation to plant growth, imazaquin inhibited in 30 and 32.5% (rates of 150 and 300eq. acid ha-1, respectively) canola shoot dry biomass production, in soil samples collected at 15DAA. Nevertheless, after 30DAA, no visual symptoms of phytotoxicity were shown. For alachlor+atrazine, the effects on germination and growth were more intense in samples collected up to 30DAA, but phytotoxicity symptoms decreased gradually and after 90DAA no negative effects were observed for the parameters evaluated. The results suggest that canola can be planted 90 days after spraying imazaquin and alachlor+atrazine, with no damage to emergence or crop development derived from residues of these herbicides present in soil.

Seletividade de herbicidas aplicados em pré-emergência na cultura do algodão

The cultivation of cotton has great economic and social importance as it is the most widely used fibre in the textile sector. It is however a crop that is highly sensitive tweeds, and there are few selective herbicides for the crop. With this in mind, this study aimed to evaluate the selectivity of herbicides applied to pre-emergent cotton crops. The herbicides, alachlor, S-metolachlor, diuron, prometryne, trifluralin and oxyfluorfen were applied both individually and in mixture to the variety FMT-701 in the towns of Diamantino and Campos de Julio, Mato Grosso. The experimental design used was of randomized blocks with 16 treatments and four replications. To evaluate selectivity, assessments were made for height at 36, 66 and 150 days after application (DAA), for phytotoxicity at 14, 21, 29 and 36 DAA, for growth at 21 and 49 DAA, for the number of bolls at 141 DAA and for cotton-seed yield at 193 DAA. The data were submitted to joint-analysis and the Scott-Knott cluster test (p>0.05). The results indicated that some treatments resulted in lower plant height in certain evaluations, and that a large part of the treatments caused injury in the initial stage of cultivation. It was found that the treatments did not produce significant differences for the characteristics of plant growth, number of bolls and cotton-seed yield, proving that all the treatments assessed may be used in weed management.