Balanços energéticos agropecuários: uma importante ferramenta como indicativo de sustentabilidade de agroecossistemas.

No Brasil, pouca atenção se tem dado às formas e caminhos com que os fluxos energéticos se distribuem nos sistemas produtivos. Na agropecuária, a atenção tem sido voltada a novas fontes de energia (biomassa) ou em tecnologia alternativa, visando a racionalização do uso de energia fóssil ou elétrica. Entretanto, a agricultura tem se desenvolvido baseada fortemente na utilização intensiva de máquinas agrícolas, com conseqüente uso de combustíveis fósseis. Um fator de estrangulamento muito forte no consumo energético geral tem sido a utilização massiva de fertilizantes derivados do petróleo nos agroecossistemas. Estudos de Balanços Energéticos visam determinar os pontos de estrangulamento energético fundamentando a busca por tecnologias poupadoras de energia, especialmente aquelas de origem fóssil (combustível, fertilizante, agrotóxicos, energia despendida na fabricação das máquinas e implementos, etc.). No Brasil, a Região Sul, é onde se encontram vários trabalhos buscando uma agricultura mais auto-sustentável, do ponto de vista da utilização da energia. Em vista da possibilidade de eventuais futuras crises energéticas, o presente trabalho procura analisar o estado-da-arte dos estudos em Balanço Energético, no Brasil e no Mundo, como uma ferramenta de indicação da sustentabilidade dos sistemas agropecuários

Determinação da capacidade de troca de cátions, do solo por fotometria de chama

O presente trabalho relata os dados obtidos sobre a determinação da capacidade de troca de cátions do solo, através da determinação do cálcio por fotometria de chama. A amostra de solo (2g) foi prèviamente saturada com íons cálcio, o excesso do reagente foi lavado e o cálcio deslocado do solo, mediante extração com solução normal de acetato de amônio pH 7. A determinação do cálcio, contido no extrato, foi feita mediante o emprêgo do fotômetro de chama Coleman modêlo 21. Os dados obtidos, demonstraram que a técnica adotada, além de sua simplicidade e rapidez, fornece resultados cuja precisão é satisfatória.This paper describes a method for determining cation exchange capacity of soils (C.E.C.).Two grams sample of 9 different soils were placed in a percolation tube with diammeter of 15 mm and lenght of 200 mm. Twenty mililiters of normal calcium acetate solution pH = 7,0 were percolated through the soil. Excess of calcium acetate was washed with ethyl alcohol 80% (80 parts of alcohol plus 20 parts of water, in volume) by suction. Adsorbed calcium was extratecd with 50 ml of normal ammonium acetate solution (pH - 7,0) by suction. Calcium extratecd by ammonium acetate solution was determined by photometry.The method described is very rapid and afford a good precision, according to table 1

Distribuição volumétrica e diâmetro de gotas de pontas de pulverização de energia hidráulica para controle de corda-de-viola

As pontas de pulverização são responsáveis pela formação das gotas, e cada ponta apresenta características próprias relacionadas ao espectro de gotas e perfil de deposição, específicas para determinados alvos. Este trabalho teve o objetivo de caracterizar o diâmetro e a uniformidade das gotas e o perfil de distribuição volumétrica das pontas de pulverização AI 110015 e TTI 110015, bem como seu efeito sobre a mortalidade de corda-de-viola, com herbicida pré-emergente, associado ou não a adjuvantes. Avaliou-se o número de plantas emergidas e os pesos secos da parte aérea e radicular das plantas. Os perfis de distribuição volumétrica para a altura de 40 cm foram avaliados em mesa de deposição. A partir dos perfis de distribuição, simulou-se o padrão de deposição ao longo da barra de pulverização. O espectro do diâmetro de gotas foi determinado em analisador de tamanho de partículas por difração de luz laser . O herbicida diuron + hexazinona foi eficiente no controle em préemergência de corda-de-viola, podendo ser utilizado polimetil siloxano organomodificado ou óleo mineral como adjuvantes, associados às pontas de pulverização AI 110015 ou TTI 110015. O uso de adjuvantes proporcionou aumento no diâmetro mediano volumétrico e redução na porcentagem de gotas com diâmetro inferior a 100 µm. O espaçamento sugerido entre os bicos na barra de pulverização foi de 70 cm para o modelo AI 110015 e 80 cm para o modelo TTI 110015.Nozzles are responsible for the formation of drops, with each side presenting its own characteristics related to droplet deposition spectrum and profile specific to certain targets. This study aimed to characterize the diameter and uniformity of the droplets and volumetric distribution profile of nozzles AI 110015 and 110015 TTI, as well as their effect on the mortality of scarlet morningglory, using pre-emergent herbicide, alone or combined with adjuvants. The number of emerging plants and dry weight of shoot and root growth were evaluated. Volumetric distribution profiles for a 40cm height were evaluated in a table deposition. Based on the distribution profiles, a deposition pattern was simulated along the spray boom. Droplet diameter spectrum was determined in a particle size analyzer by laser light diffraction. The herbicide mixture diuron + hexazinone was effective in controlling pre-emergence scarlet morningglory, and organo-modified polymethyl siloxane or mineral oil may be used as adjuvants, in association with nozzles AI 110015 or 110015 TTI. The use of adjuvants allowed the increase in volume median diameter and reduction in the percentage of droplets with diameter below 100 micrometers. The suggested spacing between nozzles on the spray bar was 70 cm for AI 110015 and 80 cm for the TTI 110015

Crop rotation and genetic resistance reduce risk of damage from Fusarium wilt in lettuce

Fusarium wilt of lettuce, caused by the soilborne fungus Fusarium oxysporum f. sp. lactucae, affects all major lettuce production areas in California and Arizona. In trials at UC Davis, we found that lettuce cultivars differ significantly in susceptibility to the disease, with some leaf and romaine types highly resistant under all test conditions. For more susceptible cultivars, disease severity is strongly influenced by inoculum levels and ambient temperature. Management of Fusarium wilt requires an integrated approach that includes crop rotation to reduce soil inoculum levels and the use of resistant cultivars during the warmest planting windows

Biodiversity of Fusarium species in Mexico associated with ear rot in maize, and their identification using a phylogenetic approach

Fusariumproliferatum, F. subglutinans, and F. verticillioides are known causes of ear and kernel rot in maize worldwide. In Mexico, only F. verticillioides and F. subglutinans, have been reported previously as causal agents of this disease. However, Fusarium isolates with different morphological characteristics to the species that are known to cause this disease were obtained in the Highland-Valley region of this country from symptomatic and symptomless ears of native and commercial maize genotypes. Moreover, while the morphological studies were not sufficient to identify the correct taxonomic position at the species level, analyses based in the Internal Transcribed Spacer region and the Nuclear Large Subunit Ribosomal partial sequences allowed for the identification of F. subglutinans, F. solani, and F. verticillioides, as well as four species (F. chlamydosporum, F. napiforme, F. poae, and F. pseudonygamai) that had not previously been reported to be associated with ear rot. In addition, F. napiforme and F. solani were absent from symptomless kernels. Phylogenetic analysis showed genetic changes in F. napiforme, and F. pseudonygamai isolates because they were not true clones, and probably constitute separate sibling species. The results of this study suggest that the biodiversity of Fusarium species involved in ear rot in Mexico is greater than that reported previously in other places in the world. This new knowledge will permit a better understanding of the relationship between all the species involved in ear rot disease and their relationship with maize

Distribution pattern, surface tension and contact angle of herbicides associated to adjuvants on spraying and control of Ipomoea hederifolia under rainfall incidence

ABSTRACT Scarlet Morning Glory is considered to be an infesting weed that affects several crops and causes serious damage. The application of chemical herbicides, which is the primary control method, requires a broad knowledge of the various characteristics of the solution and application technology for a more efficient phytosanitary treatment. Therefore this study aimed to characterize the effect of rainfall incidence on the control of Ipomoea hederifolia, considering droplet size, surface tension, contact angle of droplets formed by herbicides liquid on vegetal and artificial surfaces, associated to adjuvants and the volumetric distribution profile of the spray jet. The addition of the adjuvants to the herbicide spraying liquid improved the application quality, as it influenced the angle formed by the spray by broadening the deposition band of the spray nozzle and thus the possible distance between the nozzles on spray boom and due the changes at droplet size, which contribute to a safety application. The rainfall occurrence affected negatively the weed control with the different spraying liquids and also the dry matter weight, suggesting that the phytosanitary product applied was washed off

Distribución volumétrica, simetría del chorro y diámetro de gotas de las boquillas TF-VS2

El conocimiento de las características de las diferentes boquillas de pulverización tiene una importancia imprescindible para la adecuada y correcta recomendación de su uso. El objetivo de este trabajo fue determinar el espaciamiento máximo en la barra horizontal de pulverización, la simetría del chorro y el diámetro de gotas en boquillas de pulverización TF-VS2. El trabajo fue realizado en mesa de deposición, en donde fueron utilizadas las presiones de 100, 200 y 300 kPa en las alturas de trabajo de 40 y 50 cm. La simetría del chorro fue determinada en función de dos metodologías (empírica y trigonométrica). También se determinó el tamaño de las gotas, utilizando el método de difracción de rayos laser, en función de dos caldos de pulverización constituidos por agua y por agua con adyuvante en las tres presiones de trabajo ya descritas. Los espaciamientos máximos entre las boquillas en la barra de pulverización no pueden rebasar los 70 y 82 cm, admitiéndose el CV de un 10% para las alturas de 40 y de 50 cm respectivamente. La mayor presión proporcionó el menor diámetro mediano volumétrico (DMV) y la peor uniformidad de gotas, además del mayor porcentaje de gotas susceptibles a deriva, así como también aumentó la simetría entre los chorros.The knowledge of spray distribution pattern and analysis of droplets size of spray hydraulic nozzles turbo Floodjet TF-VS2 to adapt the spacing on spray boom are very important for a proper and correct use and recommendations. The aim of this study was to determine the maximum spacing on the horizontal spraying boom held on a patternator to the tips TF-VS2, under pressures of 100, 200 and 300 kPa in heights of work of 40 and 50 cm. Symmetry of spraying fan was determined due empirical and trigonometric methodology. It was also determined the droplets size by means of laser diffraction, with two spray liquids consisting of water and water plus adjuvant under three work pressures, described above. The maximum spacing between nozzles should be 70 and 82cm assuming the coefficient of variation of 10% for the heights of 40 and 50cm respectively. The higher pressure of work provided the lowest volume median diameter (VMD) and the worst uniformity of drops, beyond the higher percentage of drops susceptible to drift and improve the spray symmetry