Entre os fitopatógenos habitantes do solo, o Pythium sp. é um dos mais agressivos e de difícil controle e acomete diversas culturas comerciais. Na cultura do pepino (Cucumis sativus L.) causa podridão de colo e conseqüente tombamento de plântulas. O controle deste fitopatógeno é baseado em alternativas culturais, por o tratamento químico de sementes não ser efetivo. A adição de compostos orgânicos promove alterações químicas, físicas e biológicas no solo e alterações nutricionais nas plantas. O chorume de suínos apresenta-se como uma alternativa de controle deste fitopatógeno, devido a sua disponibilidade e ao seu potencial nutricional. No entanto, o pH do solo influencia na liberação de diferentes compostos pelo chorume de suínos e, consequentemente, na sua ação sobre os patógenos. Para o gênero Pythium, não existem relatos de utilização de chorume de suínos como alternativa de controle aplicado em diferentes níveis de pH do solo. Este trabalho avaliou o efeito da aplicação de chorume de suínos em solo com diferentes níveis de pH, sobre o controle da doença, sobre o desenvolvimento do fitopatógeno e sua influência nas características químicas e biológicas do solo. Três diferentes situações foram testadas, sendo em todas mantidas a aplicação de 0, 5, 10 e 15% de chorume. Em experimentos com arranjo inteiramente casualizado. Em placas de Petry, avaliou-se a aplicação dos volumes de chorume de suínos em solo com pH 4,8, 6,3 e 8,4, com 1, 2 e 3 dias de incubação sobre o crescimento micelial do Pythium sp. No solo com pH 8,4 o crescimento das colônias foi superior em todos os períodos testados, e em solo pH 4,8 e 6,3 com até dois dias de desenvolvimento, as colônias tiveram um crescimento micelial inibido. Em experimentos inteiramente casualizado, com incubação hermética dos mesmos volumes de chorume de suínos, por quatro dias em solo com pH 4,8, 6,3 e 8,4, obteve-se menor índice de tombamento de plantas no solo pH 4,8. Em outra situação, avaliou-se em experimentos com blocos ao acaso o efeito de diferentes volumes de chorume de suínos sobre o tombamento de plantas de pepino em vasos. A aplicação deste em solo com dois diferentes níveis de pH (pH 4,8 e 6,3), revelou menor número de plantas de pepino tombadas no solo com pH 4,8. Em todas as situações o efeito fungitóxico dos ácidos graxos voláteis, liberados pelo chorume de suínos, quando aplicado em solo com maior nível de acidez, foi apontado como a principal causa da obtenção destes resultados. / Among the soilborne plant pathogens, the Pythium sp. is one of the most aggressive and difficult to control and affects several crops. In the culture of cucumber (Cucumis sativus L.) causes collar rot and subsequent damping-off. Control of this pathogen is based on cultural alternatives for the chemical treatment of seed not be effective. The addition of organic compounds promotes chemical changes in soil physical and biological and nutritional changes in plants. The swine manure is presented as an alternative to control this pathogen due to its availability and its nutritional potential. However, soil pH influences the release of different compounds by swine manure and consequently in its action on pathogens. For the genus Pythium, there are no reports of use of swine manure as an alternative control applied at different levels of soil pH. This study evaluated the effect of swine manure in soil with different pH levels on disease control on the development of the pathogen and its influence on chemical and biological soil. Three different situations were tested, and all maintained in the application of 0, 5, 10 and 15% manure. In experiments with randomized arrangement. In Petry plates, evaluated the implementation of the volumes of swine manure in soil with pH 4.8, 6.3 and 8.4, 1, 2 and 3 days of incubation on the mycelial growth of Pythium sp. In soil with pH 8.4 the growth of colonies was higher in all periods tested, and soil pH 4.8 and 6.3 with up to two days of development, the colonies had inhibited growth. In randomized experiments, with incubation hermetic same volumes of swine manure, for four days in soil with pH 4.8, 6.3 and 8.4, we obtained a smaller rate of damping of plants in soil pH 4.8. In another situation, it was evaluated in experiments with randomized block the effect of different amounts of swine manure on the registration of cucumber plants in pots. The application of soil with two different pH levels (pH 4.8 and 6.3) revealed a lower number of cucumber plants having fallen to the ground with pH 4.8. In all cases, the antifungal effect of volatile fatty acids, released by swine manure, when applied to soil with higher acidity level, he was appointed as the main cause of getting these results.

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Mammoth cultivars of flue-cured tobacco flower under short-day photoperiods, thereby increasing the potential number of leaves per plant. Field experiments were conducted in 1991 and 1992 at the Virginia Tech Southern Piedmont Agricultural Experiment Station near Blackstone, Virginia to determine the influence of nitrogen rate on nitrogen use efficiency and its components on two mammoth cultivars and a conventional cultivar. Experiments were also conducted to determine the effects of leaf number, time of topping, and nitrogen rate on yield, quality, and other agronomic characteristics. Nitrogen uptake, utilization, and use efficiencies decreased while nitrogen accumulation increased as nitrogen rates increased from 67 to 112 kg ha⁻¹. Mammoth cultivars were more efficient than the conventional cultivar for nitrogen uptake, utilization, and use. Only NC 27 NF benefits from increasing nitrogen above the recommended rate. Yield increased by 17 percent as the leaf number increased from 20 to 36. In contrast, both agronomic traits and chemical characteristics decreased accordingly. The ratio of nitrogen to nicotine that was unacceptable at leaf numbers above 28. Yield, value, and quality decreased as topping was delayed by seven to 21 days. Yield was reduced by 30 kg per hectare per day when topping was delayed by 21 days after the conventional cultivar reached the bud stage. Leaf lengths and widths of mammoth cultivars were larger than the conventional cultivar. Mammoth cultivars were higher yielding and had better quality at 112 kg ha⁻¹ N when compared to the conventional cultivar, although these differences were not significant. / Master of Science

The enhancing effect of K on alfalfa (Medicago sativa L.) yield has frequently been reported, but the nature of this influence has not been clearly shown. It was assumed that K contributed either to increased leaf expansion, thereby resulting in a larger photosynthetic surface, or to higher CO₂ assimilation rates per unit leaf area. Sand culture technique for growing plants was used in two greenhouse experiments, while field plants were grown in plots with soil differing in available K. Yield increases were consistently obtained with high K. Added K increased plant height and leaves per plant and per plot, The rate of leaf accumulation was higher as K increased. Leaf size and weight per unit area also increased, as did stomatal number and aperture. Larger epidermal cells and greater numbers per leaf were observed with high K nutrition. Percent K in plants was associated with rate of K application. Net photosynthesis rates of excised leaves increased with potassium application, but all K levels had similar light compensation points. Leaves from plants with added K had lower CO₂ compensation points, indicating higher efficiency of CO₂ assimilation. Based on these data, K appears to function both to increase the effective photosynthetic surface through greater leaf initiation and development and to increase the rate of CO₂ utilization per unit leaf area. The latter increase probably results from greater CO₂ diffusion into substomatal cavities. / Ph. D.

An experiment was conducted at the Eastern Virginia Research Station, Warsaw, comparing the effects of fall applications of nitrogen (N), (0, 28, 56 kg/ha) from fish-solubles (FS) and spring applications of N (0, 56 kg/ha) from NH₄NO₃ on yield and components of yield of four cultivars each of barley (Hordeum vulgare) and wheat (Triticum aestivum). Both barley and wheat expressed significant yield responses to FS. The NH₄NO₃ application increased yields in both crops, although the increase in wheat was not statistically significant. Interactions between the barley cultivars and N source or rates were nonexistent; however cultivar yield and thousand kernel weight (Mkw) did express interactions with the nitrogen levels and sources in wheat. Cultivars of both crops displayed significant differences for almost every analyzed trait. Both crops responded similarly in the effect of N rates and sources on components of yield, with the greatest response being an increase in spikes/61 cm as the N rates increase. In barley, the increasing rates of N caused a slight increase in kernels/spike, while there was very little effect in wheat. In wheat, the spring application of NH₄NO₃ decreased Mkw, but there was no such effect in barley. Samples of the ten best heads taken from the plots provided useful estimates of kernels/spike in wheat, Mkw in both crops, and of cultivar yield in barley. / Master of Science

LD2668 .T4 1947 C7 / Master of Science

Call number: LD2668 .T4 1953 R3 / Master of Science

Call number: LD2668 .T4 1959 C43