Vegetable crops grown continuously in greenhouse are vulnerable to phytosanitary problems or changes in the physical and chemical conditions of the soil such as salinization. One alternative to minimize these problems is to grow crops without soil using different substrates. A mixture of perlite and composted willow sawdust has been used successfully with tomatoes (Lycopersicum esculentum Mill), but the behavior of this substrate when reused is unknown. Factorial trials with tomato pot crops cv. Topacio were developed, and in each experiment, water content at 10, 50 and 100 cm, bulk density, pH, electrical conductivity and exchangeable cations were determined. From a physical perspective, reuse of the substrate did not substantially modify the total available water and aeration was higher than that considered as ideal. Reuse caused a light acidification and increased the C/N ratio with a loss of exchangeable cation capacity for Ca 2+ and Na + . This modification of the substrate did not affect the yield. Key words: Lycopersicum esculentum, willow sawdust, fertirrigation, pot crop, crop substrates. ResumenAlteraciones en las propiedades físicas y físico-químicas de un sustrato a base de serrín compostado y perlita con cultivos policíclicos de tomate El cultivo intensivo de hortalizas bajo invernadero puede inducir problemas fitosanitarios o de salinización del suelo, por lo que una alternativa es la realización de cultivos en sustrato. Una mezcla que permite cumplir con los criterios de aireación y retención de agua es la de serrín compostado de Salicáceas con perlita agrícola. Por otra parte, el cultivo de tomate (Lycopersicum esculentum Mill) en varios ciclos cortos presenta resultados productivos promisorios, aunque supone un mayor costo que el planteo tradicional, especialmente por el uso de sustratos. Para abaratar estos costos es necesario evaluar si el reuso del sustrato no altera sus propiedades físicas y físico-químicas. Con este objetivo se desarrollaron experimentos polifactoriales en macetas cultivadas con tomate cv. Topacio. En cada tratamiento se midió el contenido hídrico a tensiones de 10, 50 y 100 cm, densidad aparente, pH, conductividad eléc-trica y cationes intercambiables. Desde el punto de vista físico, la reutilización del sustrato no modificó sustancialmente el agua total disponible, aunque esta disponibilidad sí presentó variaciones en profundidad. En cuanto a la aireación, fue superior a la considerada ideal, pero ello no implica problemas al cultivo siempre que no se altere el agua total disponible. Con la reutilización se produjo una ligera acidificación del sustrato, un notable incremento en la relación C/N y una pérdida gradual de la capacidad de intercambio de cationes y de bases de Ca 2+ y de Na + . Ninguna de estas modificaciones afecta al rendimiento del cultivo de tomate, siendo importante destacar que el Ca 2+ es absorbido preferentemente por el cultivo y por ello se debe realizar un incremento en su aporte mediante fertirrigación.Palabras clave: Lycopersicum esculentum...

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Euxesta sp. (corn-silk fly) is a highly polyphagous insect genus that affects horticultural crops, fruit trees, and industrial crops. It causes huge economic losses in sweet corn (maize). Damage is caused by larvae feeding on corn silk, kernels and the remainder of the cob. Chemical treatments applied to maize crops are often not effective; therefore, efforts to control the fly must focus on finding alternative methods, such as biological control. The aim of this work was to determine the effects of Euxestophaga argentinensis (Hymenoptera, Figitidae) parasitism on corn-silk fly larvae, in two different planting dates: late winter and late summer. Samples were taken during spring and autumn in a commercial Bt sweet corn for two consecutive years. A total of 20 ears of corn per sample were collected at random and were placed in plastic trays, stored at 22 ± 2°C and 70 ± 5% RH and exposed to a 14:10 h photoperiod. Euxesta eluta and Euxesta mazorca pupae were separated, placed in separate plastic vials and periodically checked for emergence of adult flies and parasitoids. E. eluta has greater potential to damage sweet corn crops than E. mazorca. Parasitism was higher in late winter than in late summer, while only E. eluta was parasitized.

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