AVALIAÇÃO FENOLÓGICA DE CULTIVARES DE GIRASSOL (Helianthus annuus, L.) EM UBERABA/MG – SAFRA 2009

O girassol (Helianthus annuus, L.) tem aplicações como ração, silagem, óleo para consumo humano, ornamental e floricultura, alimentação de pássaros e é excelente matéria prima para produção de biodiesel. O objetivo do presente trabalho foi avaliar as características agronômicas de 18 genótipos de girassol na época da safrinha em Uberaba/MG. O experimento foi instalado no dia 10/03/2009 na Fazenda Experimental Getúlio Vargas – FEGT da Empresa de Pesquisa Agropecuária de Minas Gerais – EPAMIG utilizando-se o espaçamento de 0,75 m entre linhas. O ensaio foi conduzido em delineamento em blocos ao acaso (DBC). Os tratamentos foram constituídos por 18 cultivares. Houve diferença em relação ao rendimento de aquênios e somente quatro cultivares apresentaram produtividade superior à média geral. Também, foi constatada diferença em relação à altura de planta e altura de capítulo. A cultivar HLT 5004 foi inferior às demais apresentando o menor valor em massa de 1.000 aquênios. As cultivares ZENIT, EXP 1452 CL, AGROBEL 960 (T) e M 734 (T) foram superiores às demais apresentando os maiores valores de tamanho de capítulos. Quando analisado a quantidade de dias após semeadura que cada uma atingiu certo estádio reprodutivo, as cultivares apresentaram médias baixas em entrada no florescimento e no estádio reprodutivo, mostrando que são cultivares de ciclo mais curto. O girassol pode ser utilizado na época da safrinha como mais uma opção no esquema de rotação de culturas em Uberaba/MG

Decision-making on the optimum timing for nitrogen fertilization on sugarcane ratoon

Low efficiency of nitrogen from fertilizers is a major concern worldwide, threatening the sustainability of sugarcane production. The N use efficiency (NUE) by sugarcane can be improved by adopting better fertilizing management practices, reducing environmental impacts. This work evaluated the effects of varying N rates and time of application on stalks and sugar yield in ratoon harvested early in the crop season. The experimental design was a randomized block in a 2 × 4 factorial design and a control (no N) with five replications, including two application times (45 or 90 DAH – days after harvest) and four N rates (50, 100, 150, or 200 kg N ha–1). The time of N fertilizer application promoted differences in stalk yield, as the cumulative yield of two harvests was increased by 8 % (15 Mg ha–1) at 45 DAH when compared to the application at 90 DAH. The application performed at 45 DAH augmented sugar yield by 10 % (2.8 Mg ha–1 of sugar) in relation to 90 DAH. The N rates that promoted the highest sugarcane yield were, respectively, 122 and 144 kg N ha–1 in the first and second crop cycles. The average economical rates obtained for the first and second agricultural cycles were, respectively, 104 and 127 kg N ha–1, demonstrating that the gains by applying high amounts of fertilizers (rates above 150 kg N ha–1) may not cover the investment

Eficiência de fungicidas no controle do mofo branco na cultura da soja

Among the diseases that affect soybeans, white mold stands out as one of the most important currently. Chemical control has been the most effective, given the fast disease evolution and requires farmers’ close attention, primarily in relation to the time of the product being applied, this being one of the most important factors for successful disease control. Thus, this study aimed to evaluate the effectiveness of the control of white mold by applying foliar fungicides in different reproductive stages, by analyzing the progress of the disease in soybean pathosystem versus Sclerotinia sclerotiorum. The experimental area presents a crop rotation system with soybean and cotton being adopted for over 10 years and with a history of occurrence of white mold. Four treatments (Witness, Cercobin, Sumilex and Frowncide) in a randomized block design with four replications. We evaluated the incidence and disease severity in stages R5.1, R5.3 and R5.5. At the end of the experiment, the weight of sclerotia and yield were evaluated. Treatments were applied at four times every ten days from the beginning of flowering. Data were submitted to analysis of variance by F test and the means were compared by Tukey test at 5% probability. The fungicides showed efficiency in relation to the variables studied, with exception of the incidence of disease severity. The most effective fungicide against the significant gain in productivity was Frowncide. Chemical control significantly reduced the severity of the disease.Entre as doenças que incidem sobre a soja, o mofo branco se destaca como uma das mais importantes atualmente. O controle químico é mais eficaz, diante a rápida evolução da doença e requer muita atenção do produtor, principalmente em relação à época do produto a ser aplicado, sendo essencial para o sucesso do controle da doença. Assim, objetivou-se neste trabalho avaliar a eficácia do controle do mofo branco através da aplicação foliar de diferentes fungicidas em diferentes estádios reprodutivos, por meio da análise do progresso da doença no patossistema soja versus Sclerotinia sclerotiorum. A área experimental apresenta sistema de rotação de culturas com soja e algodão sendo adotado há mais de 10 anos e com histórico de ocorrência de mofo branco. Foram testados quatro tratamentos (Testemunha, Cercobin, Sumilex e Frowncide) em delineamento em blocos casualizados com quatro repetições. Avaliou-se a incidência e severidade da doença nos estádios R5.1, R5.3 e R5.5. Ao final do experimento, avaliou-se o peso de escleródios e a produtividade. Os tratamentos foram aplicados em quatro vezes a cada dez dias a partir do inicio do florescimento da cultura, via terrestre. Os dados foram submetidos a analise de variância pelo teste F e as médias foram comparadas pelo teste de Tukey a 5% de probabilidade. Os fungicidas apresentaram eficiência em relação às variáveis estudadas, com exceção da incidência da severidade da doença. O fungicida mais eficiente em relação ao ganho significativo de produtividade foi o Frowncide. O controle químico reduz significativamente a severidade da doença

Phosphorus sources residual effects on tifton 85 production and nutritive value cultivated in a tropical weathered soil

Acid reactions and low available phosphorus in tropical soils limit forage yield. The aim was to evaluate soil chemical characteristics pH, P and Mg, forage nutritive values, critical soil and plant P levels and the residual effect of each source. The experiment was in a greenhouse with a Rhodic Haplustox, loam texture. Experimental design was a 5 x 4 factorial with five replicates which phosphate fertilizers were triple superphosphate, reactive rock phosphates Gafsa and Arad, and fused magnesium phosphate powder and coarse, applied at rates of 30, 60, 90 and 120 mg kg-1 P and a control treatment without P. The effectiveness of rock phosphates increased due to their residual effect. The coarse fused magnesium phosphate resulted in the lowest efficiency. The P critical level in soil and plant were 18 mg kg-1 and 2.4 g kg-1, respectively. The increase of phosphorus rates provided an increase in crude protein content

Precision production environments for sugarcane fields

Sugarcane (saccharum spp.) in Brazil is managed on the basis of “production environments”. These “production environments” are used for many purposes, such as variety allocation, application of fertilizers and definition of the planting and harvesting periods. A quality classification is essential to ensure high economic returns. However, the classification is carried out by few and, most of the time, non-representative soil samples, showing unreal local conditions of soil spatial variability and resulting in classifications that are imprecise. One of the important tools in the precision agriculture technological package is the apparent electrical conductivity (ECa) sensors that can quickly map soil spatial variability with high-resolution and at low-cost. The aim of the present work was to show that soil ECa maps are able to assist classification of the "production environments" in sugarcane fields and rapidly and accurately reflect the yield potential. Two sugarcane fields (35 and 100 ha) were mapped with an electromagnetic induction sensor to measure soil ECa and were sampled by a dense sampling grid. The results showed that the ECa technique was able to reflect mainly the spatial variability of the clay content, evidencing regions with different yield potentials, guiding soil sampling to soil classification that is both more secure and more accurate. Furthermore, ECa allowed for more precise classification, where new “production environments”, different from those previously defined by the traditional sampling methods, were revealed. Thus, sugarcane growers will be able to allocate suitable varieties and fertilize their agricultural fields in a coherent way with higher quality, guaranteeing greater sustainability and economic return on their production

Efficiency of nitrogen sources and rates on growth and dry matter yield of tifton 85

Forrageiras do gênero Cynodon são conhecidas por sua capacidade de resposta a altas doses de nitrogênio (N). Em condições tropicais o N pode se tornar um problema ambiental e financeiro devido à sua baixa eficiência de uso pelas plantas, principalmente como resultado de perdas por volatilização e/ou lixiviação. Portanto, objetivou-se com este trabalho avaliar fontes e doses de N no crescimento e produção de matéria seca do Tifton 85, bem como mudanças nas frações do carbono (C) no solo. Um experimento foi conduzido de 2012 a 2014, e constituiu de um fatorial em um delineamento de blocos ao acaso, onde os tratamentos foram a associação de duas fontes de N (nitrato de amônio [NA] e ureia), e cinco doses do nutriente (0, 60, 120, 180 e 240 kg ha-1 N por corte) aplicadas a cada 30 dias. Neste experimento foram utilizados NA e ureia enriquecidos com 15N como uma ferramenta para quantificar a recuperação do N advindo do fertilizante, nas plantas e no sistema solo-planta. As plantas foram cortadas para avaliar a produção de matéria seca, concentração de N na parte aérea e recuperação. O índice de área foliar (LAI), radiação fotossinteticamente ativa interceptada (PARi) e índice de clorofila (CI) foram mensurados no dia anterior ao corte. As amostras de solo foram coletadas nas parcelas que receberam NA e foram fracionadas em carbono orgânico particulado (POC), fração leve livre (FLF) e fração mineral (C-min); O teor de C nas frações foi quantificado. Os resultados demonstraram que o NA pode ser uma fonte mais eficiente somente quando a quantidade de precipitação é insuficiente para incorporar o fertilizante ao solo, resultando em maior produção de forragem, na somatória dos dois anos ambas as fontes produziram a mesma quantidade de matéria seca onde a maior produtividade 37,2 Mg ha-1, foi atingida com a dose de 210 kg ha-1 N por corte. Por outro lado, a quantidade de N recuperado pelo sistema de planta+solo foi maior quando a ureia foi utilizada, com destaque para a quantidade de N no solo, onde a ureia foi capaz de manter 10% mais N que o NA, a recuperação do nutriente diminuiu à medida que as doses foram elevadas. Nenhuma alteração no conteúdo de C foi notada devido às diferentes doses de N utilizadas, no entanto o POC e o C-min foram mais sensíveis às mudanças na camada de 0-0,1 m do que na camada de 0,1-0,2 m.Cynodon hybrids are known by their ability to respond to high rates of nitrogen (N). In tropical conditions, N may become an environmental and financial issue due to its low efficiency of use by plants, mainly as a result of losses by volatilization and/or leaching. Therefore, the aims with this work were to evaluate N sources and rates on growth and dry matter yield of Tifton 85 and to determine changes in soil carbon (C) fractions in response to N fertilization. The 2-yr field experiment was conducted from 2012 to 2014, and consisted of a factorial design. Treatments were a combination of two sources of N (ammonium nitrate [AN] and urea) and five rates of the nutrient (0, 60, 120, 180 and 240 kg ha-1 N per cut) applied broadcast every 30 days. This study used AN and urea enriched with 15N as a tool to quantify the recovery of N derived from fertilizer in plants and the soil-plant system. Forage was cut at 30-d intervals for dry matter yield, shoot N concentration determinations and N recovery. The leaf area index (LAI), photosynthetic active radiation intercepted (PARi) and chlorophyll index (CI) were evaluated on the day before clipping. Soil samples were collected in plots receiving AN and they were fractionated in to particulate organic carbon (POC), free light fraction (FLF) and mineral fraction (C-min); The C concentration of the various fractions was determined. Results showed that AN was a more efficient source only when the amount of precipitation is insufficient to incorporate the fertilizer to the soil, resulting in increased production, in the sum of the two years both sources produced the same amount of dry matter in which the highest productivity, 37.2 t ha-1 , was achieved at the rate of 210 kg ha-1 N per cutting. On the other hand, the amount of N recovered by the plant+soil system was higher when urea was used, especially the amount of N in the soil, where urea was able to maintain 10% more N than AN, the nutrient recovery decreased as the rates were increased. No change in soil C concentration was detected in response to the different N rates used, however the POC and the C-min were more sensitive to changes in the layer of 0-0.1 m than the layer from 0.1-0.2 m.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Growth and nutritional disorders of eggplant cultivated in nutrients solutions with suppressed macronutrients

The objective was to evaluate the effects of omitting macronutrients in the nutrients solution on growth characteristics and nutritional status of eggplants. The treatments were complete nutrients solution and solutions with nutrient omission: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). The experiment was carried out under greenhouse conditions with three replicates in a completely random design. Plant height, number of leaves per plant, leaf area, relative chlorophyll index, photosynthesis rate, stomatal conductance, dry matter, concentration levels of macronutrients in plant aerial part and root system, and nutritional disorders were evaluated. Omitting elements interfered in the concentration of elements in the various plant tissues and this had as consequences limited vegetative growth, reduced dry matter and led to the development of the typical deficiency symptoms of each element. Although potassium was the most demanded of all elements, nitrogen and calcium were the most growth limiting ones

Relação entre o fluxo luminoso interceptado em diferentes épocas no índice de área foliar de diferentes forrageiras

The objective was to evaluate the leaf area index of six different grasses. The experiment was installed at the Instituto Federal de Tecnologia e Educacao of Uberaba, using a randomized block design with split plots in time. The plots were sown: Brachiaria decumbens cv. Basilisk, Brachiaria brizantha cv. Marandu, Panicum maximum cv. Mombasa, Panicum maximum cv. Tanzania, Brachiaria brizantha cv. Xaraes, Cynodon dactylon hb. Tifton and the plots, ten seasons of evaluation in 10 x 6 factorial arrangement with four replications. Rates of leaf area of each forage at different times of year were evaluated. Compared to other forage species, Panicum maximum had a higher leaf area index when subjected to periodic fertilization and irrigation. Only in the late fall Brachiaria Xaraes IAF had increased, but did not differ significantly from the others