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Zucchini (Cucúrbita pepo L.) has a great economic and productive potential in the semi-arid region of Brazil, due to the wide acceptance by consumers and quick financial return. The nitrate (NO3 -) assimilation process in C3 plants such as zucchini is related to photorespiration, and Si accumulated near the stomata reduces the transpiration rate, making the photosynthesis cycle more efficient. The objective of this study was to evaluate the interaction between nitrogen and silicon fertilization on growth, chlorophyll index, and chlorophyll a fluorescence of zucchini plants. The treatments were distributed in a split-plot scheme in a randomized block design with three replicates. The plot was arranged by silicon levels (0 and 6 g/plant) and the subplots constituted by five nitrogen levels (30, 60, 90, 120 and 150 kg ha-1). Leaf, stem and total dry masses, chlorophyll a, chlorophyll b, total chlorophyll, chlorophyll a/b ratio and chlorophyll a fluorescence were evaluated. The highest dry matter productions in zucchini were obtained in treatments without Si. Si and N application together positively influences the chlorophyll a/b ratio of zucchini plants. The interaction between Si and N positively influences the maximum fluorescence, variable fluorescence and quantum yield of photosystem II of zucchini plants. RESUMEN El calabacín (Cucurbita pepo L.) presenta un gran potencial económico y productivo en la región semiárida de Brasil, debido a su amplia aceptación por los consumidores y su rápido rendimiento financiero., El proceso de asimilación de nitrato (NO3 -) en plantas C3 como el calabacín estaría relacionado en parte con la fotorrespiración, y el Si acumulado cerca de los estomas reduce la tasa de transpiración, haciendo que el ciclo de fotosíntesis sea más eficiente. Por lo tanto, el objetivo de este estudio fue evaluar la interacción entre el nitrógeno y la fertilización con silicio en el crecimiento, el índice de clorofila y la fluorescencia de la clorofila a en plantas de calabacín. Los tratamientos se distribuyeron en un esquema de parcelas divididas en un diseño de bloques al azar con tres repeticiones. La parcela se formó por niveles de silicio (0 y 6 g/planta) y las subparcelas constituidas por cinco niveles de nitrógeno (30, 60, 90, 120 y 150 kg ha-1), totalizando 30 parcelas experimentales. Se evaluaron masas de hojas, tallos y secas totales, clorofila a, clorofila b, clorofila total, clorofila a/b y fluorescencia de la clorofila a. Las mayores producciones de materia seca de calabacín se obtuvieron en tratamientos sin Si. La aplicación de Si y N juntos influye positivamente en la proporción de clorofila a/b de las plantas de calabacín. La interacción entre Si y N influye positivamente en la fluorescencia máxima, la fluorescencia variable y el rendimiento cuántico del fotosistema II de plantas de calabacín.

In semiarid areas producing corn in the State of Paraiba (Brazil), despite the social and economic importance of this culture associated with some types of stress mainly in semiarid regions, as well as the soils of these regions, which in many cases have a low organic matter content, generally

The correct management of organic fertilization has been shown as an extremely viable alternative in the production of vegetables, providing high yields concomitant to the reduction of synthetic fertilizers. The improvement of the production can be interpreted by the physiological behavior, favored by the organic fertilization with the supply of nutrients. Thus, an experiment was carried out to evaluate the gas exchange and Soil-Plant Analyses Development (SPAD) chlorophyll content in tomato plants according to types of organic fertilizers and biofertilizer doses. The experimental design was completely randomized with treatments distributed in factorial arrangement (3 x 5), referring to organic fertilizer types (T1: earthworm humus; T2: goat manure and T3: cattle manure) and biofertilizer concentrations (600, 800, 1000, 1200 and 1400 ml), with four replications. The gas exchange and the SPAD chlorophyll content in tomato plants depend on the type of organic fertilizer and the concentration of biofertilizer. It was possible to observe that increasing doses of biofertilizer in the substrate with low organic concentration increase the gas exchange in tomato plants, while high doses together with more concentrated organic fertilizers reduce these characteristics. Key words: Alternative fertilizer, Lycopersicon esculentum, photosynthesis, organic fertilizer.

Zucchini (Cucurbita pepo L.) is a horticultural crop of great socioeconomic importance in Brazil and in the world. However, inappropriate fertilization management, such as over-fertilization of soils, may become a limiting factor for its development. Thus, the aim of this study was to evaluate the morpho-physiological behavior of zucchini submitted to nitrogen (N) doses applied via soil and foliar application of silicon (Si). The treatments were distributed in split-plot scheme in a randomized block design, with three replications. The plot was formed by silicon levels (0.0 and 6.0 g plant-1) and the subplots constituted by five nitrogen levels (30, 60, 90, 120 and 150 kg ha-1), adding up to 30 experimental units. Gas exchanges and growth parameters were assessed at 35 days after planting. The data were submitted to analysis of variance by the F test and in the cases of significance was performed a polynomial regression analysis for the nitrogen factor and Tukey test for the silicon factor. The supply of Si positively enhances the effects of N on growth characteristics and gas exchanges of zucchini. The simultaneous application of Si and N does not influence the leaf area of zucchini. The N dose of 93.9 kg ha-1 provides greater assimilation of CO2 in zucchini plants under the conditions in which the experiment was performed.