ABSTRACT Grafting in tomato is a regular production practice aimed to control vascular diseases. Even though grafted plants are more expensive, when a vigorous rootstock is used the plants can be trained using multiple leading shoots, reducing the number of plants per hectare. Seeking to reduce direct labor cost and the cost of the plants, this experiment tested 29,000, 26,000, 23,000 and 20,000 leading shoots/ha, training the plants with either 3 or 4 leading shoots each. Plants were grown in a polyethylene-covered greenhouse, transplanting at the end of January; the harvest was done from May until August, quantifying yield, fruit size and leaf area, analyzing the data with quadratic regression. Yield increased from 81 to 103 t/ha when comparing the lowest and the highest density of shoots/ha, but the difference between the training systems was only 4 t/ha. When the two extremes of the density were compared (29,000 vs 20,000 shoots/ha), leaf area increase by 2%, the equatorial fruit diameter increased from 7.4 to 7.8 cm, and the weight increased from 178 to 199 g/fruit. The training system showed difference of 0.1 cm in fruit diameter, while the leaf area and fruit weight were not affected. While the lowest density of shoots per hectare had a 30% reduction in direct labor cost, the largest net profit margin was observed when using 3 shoots/plant and 29,000 shoots/ha.

RESUMEN El uso de plantas injertadas en tomate es una práctica habitual que busca controlar enfermedades vasculares. Aun cuando las plantas injertadas son más caras, cuando se usa un portainjerto vigoroso es posible conducir en multi-ejes, usando una baja densidad de plantas por hectárea. Con el objetivo de disminuir los costos directos en mano de obra y el valor de las plantas, se evaluó densidades de 29.000, 26.000, 23.000 y 20.000 ejes/ha, con conducción a 3 y 4 ejes por planta. El cultivo se realizó en un invernadero con cubierta de polietileno, trasplantando a fines de enero; se cosechó entre mayo y agosto (fines de otoño e inverno), cuantificando el rendimiento, tamaño del fruto y área foliar, analizando los datos con regresión cuadrática. El rendimiento aumentó de 81 a 103 t/ha entre la menor y la mayor densidad de ejes/ha, pero solo se presentó una diferencia de 4 t/ha entre los sistemas de conducción. Comparando los niveles extremos de densidad (29.000 y 20.000 ejes/ha), área foliar aumentó en 2%, y diámetro ecuatorial del fruto aumentó de 7,4 a 7,8 cm, y peso aumentó de 178 a 199 g/fruto. El sistema de conducción generó diferencias de 0.1 cm en el diámetro del fruto, mientras que el área foliar y el peso del fruto no fueron afectados. A pesar que la baja densidad genera una reducción del 30% en el costo de mano de obra directa, el mayor margen neto se estimó para la conducción en 3 ejes, a una densidad de 29.000 ejes/ha.

Microbiological bioassays of nitrification and nitrogen mineralization have been used for evaluation of soil quality on metal-contaminated soils. We evaluated the effectiveness of nitrification and nitrogen mineralization bioassays as quality indicators of soil degradation caused by metal contamination. We performed standard tests based on protocols of ISO 14238 (2012) and ISO 15685 (2012) on 90 soil samples collected from agricultural areas in central Chile that were historically contaminated by mining activities. Potential nitrification rate (PNR) was best explained by pH and organic matter content (OM) (R²=0.32), while nitrogen mineralization (Nmin) was best explained by OM and clay content (R²=0.44). Following normalization of the bioassays responses with respect to OM yielded significant correlations between PNR and pH and total Cu content (R²=0.22), and between Nmin and clay and total Cu contents (R²=0.19). However, inasmuch as total Cu content improved the regression model showing the inhibitory effect of Cu in both bioassays, it accounted for a mere small proportion of the variance. This was despite the wide range of Cu contents in the soils studied (51-2878 mg kg-1). Hence, due to the known sensitivity of the nitrification and nitrogen mineralization process to physicochemical characteristics of soils, these bioassays seem to have limited applicability for metal toxicity assessment in metal-contaminated soils.

Salinity is well known to reduce plant growth and yield by reducing water availability; it does so by interfering with both nutrient uptake and translocation. The objective was to determine the nitrate and potassium contents in xylem sap and the root-shoot transportation of both as a function of the salinity of the nutritional solution provided. We compared NO3-and K+ contents and flux in xylem sap collected from cut stems of tomato seedlings, based on electric conductivity (EC) tests among five nutrition solutions for soilless crops ranging from medium to high salinity. The EC was 2.2, 3.5, 4.5, 6, and 12 dS m-1. The concentration of nitrates and potassium in the xylem sap remained constant, while the external concentration in the rhizosphere varied greatly. Notwithstanding, the xylematic flux was strongly affected by the salinity of the nutritional solution: at maximum salinity, EC reached 3.5 dS m-1; at minimum, EC was 12 dS m-1. For similar reasons, the longest NO3- and K+ transportation distance between root and shoot was achieved when the EC read 3.5 dS m-1, but was reduced by up to 80% when EC was 12 dS m-1.