In South Texas, most of tomato (Lycopersicon esculentum Mill.) crops are produced on plastic mulch due to the elevated temperatures and solar radiations. The study objectives were to; Determine the suitable planting dates for increasing tomato varieties production under different planting dates in early spring and late winter, and evaluate the influence of using the plastic mulch (black and white. In the Spring season, nine tomato varieties (four rounds and five roma) were grown. The round varieties were the Torero, Mykonos, Shourouq, and TAM Hot-Ty, and the roma varieties were Prunus, Rio Grande, Seri, DRP-8551, and SV8579TE. The best five varieties from the spring season and two more varieties were selected for evaluation in the fall including; SV8579ET, Mykonos, DRP-8551, TAM-HOT-T4, Shourouq, Tycoon, and Everglade. All the tomato varieties were evaluated during the Spring season under three different planting dates (from late-February till late-March) and three mulching treatments (black, white plastic mulch, and bare soil); and during the fall season during two planting dates (from early to midSeptember) and two mulching treatments (black and white plastic mulch). Higher average marketable yields were observed in the spring season than the fall season. The best varieties during the spring season were DRP-8551, SV8597TE, Shourouq, and Seri with yields ranging from 68,630 to 57,237 kg/ha, whereas the best varieties in the fall; were DRP-8551, SV8597TE, and Tycoon with yields ranging from 47,123 to 60,674 kg/ha. In both seasons, white plastic mulch resulted in higher yields compared to the black and bare tomato yields.

Concentration dynamics and nutrient accumulation in above ground biomass components of Cedrela odorata L. in Costa Rica. Present study was conducted aiming to study nutrient concentration and accumulation dyna mics on Cedrela odorata L. (Meliaceae) trees to improve knowledge and management on tropical forestry plantations. False time series (chrono sequences) from 15 stands on Tropical Very Humid Forest of Costa Rica were used to determine aboveground biomass, nutrient concentration and to estimate nutrient accumulation on aboveground biomass components of selected trees. As a result, nutrient concentration showed a trend to decrease and followed the order nitrogen > potassium > magnesium > calcium > sulfur > phosphorus for macro nutriments, while minor elements followed the order iron > boron > zinc RESUMENSe planteó el presente estudio con el objetivo de estudiar la dinámica de la concentración y la acumulación de nutrimentos en árboles de Cedrela odorata L. (Meliaceae), para mejorar el conocimiento y la gestión de las plantaciones forestales tropicales. Mediante una serie falsa de tiempo (crono secuencia) compuesta por 15 plantaciones en bosque Muy Húmedo Tropical de Costa Rica, se determinó la biomasa aérea, la concentración de nutrimentos y se estimó su acumulación en los componentes de la biomasa en árboles seleccionados. Como resultado se obtuvo que la concentración de los nutrimentos presentó tendencia a disminuir en el orden: nitró-geno > potasio > magnesio > calcio > azufre > fósforo para los macro nutrimentos, mientras que los micro elementos siguen la secuencia hierro > boro > zinc > manganeso > cobre > aluminio. 1 Autor para correspondencia. Correo electrónico:

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