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The nitrogen requirements of lettuce (Lactuca sativa L.) cultivars for obtaining plants of a high phenotypical quality and low nitrate foliar content were studied in this research. Butterhead (Divina and Prima cvs.) and loose-leaf (Grand Rapids and Brisa cvs.) lettuces were grown in a modified hydroponic floating system. Plants were subjected to four treatments differential of nitrogen and are in mg of nitrogen L-1 : solution 1: 100 NO 3-N; solution 2:150 NO 3-N and 50 NH 4 +-N; solution 3: 200 NO 3-N and 100 NH 4 +-N; solution 4: 250 NO 3-N and 150 NH 4 +-N meanwhile as base solution was used modified Hoagland II solution. Cultivar responses to treatments were different so much in growth as foliar nitrate content. While the greatest growth was observed in 'Grand Rapids' and 'Brisa' in solution 1 with the lowest nitrogen content in which NO 3-N only was supplied, the opposite was observed in 'Divina' and 'Prima' in solution 4 and where NO 3 and NH 4 + were supplied. These results showed that the nutritional requirements cultivars are different. Moreover, greatest plant growth was observed in cultivars where the foliar nitrate content was highest. High levels of nitrate in vegetable crops have been associated with human health problem. The four cultivars in all treatments showed foliar nitrate contents below the limits established by the European Commission Legislation. This study permit to optimize the growth under such conditions.

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A tissue analysis trial for the diagnosis of nitrogen level was performed during the 2001 growing season in Paine County, Metropolitan Region, Chile. Seven-year-old `Hass' avocado (Persea americana Mill.) trees were soil treated with urea at rates of 0, 333, 666, and 999 g N/tree, split in two applications (2 and 4 months after fruit set). Each treatment was applied to three randomly selected trees. Fifty spring flush leaves and fifteen fruit peduncles were taken per tree 4 months after application. Two months later, 70 panicles per tree were taken, and nitrogen concentration in these samples was determined by Kjeldahl digestion. Differences between treatments were better detected in peduncle and inflorescence samples than in leaf samples. The relationship between nitrogen dose and nitrogen concentration in the tissue was R2 = 0.67, 0.65, and 0.56 in peduncle, leaf, and inflorescence, respectively. Consequently, peduncle appears a promising tissue, probably better than leaf, for diagnosing the nitrogen status of avocado trees.

Resumen -El objetivo de este trabajo fue evaluar la relación existente entre la concentración de N, P y K del extracto peciolar, la lámina y la raíz, para determinar el estado nutricional de la vid. El ensayo se desarrolló entre diciembre de 2006 y febrero de 2007. Se validó la metodología de extracto peciolar para Vitis vinifera 'Red Globe', en plantas de un año de edad autoenraizadas, creciendo en macetas, a partir de tres ensayos de fertilización utilizando N, P 2 O 5 y K 2 O. En el extracto peciolar, se evaluó nitrato, fosfato y potasio, y en láminas y raíces, nitrógeno, fósforo y potasio. El análisis del extracto peciolar fue más sensible que el de la lámina y la raíz para determinar el estatus de nitrato y nitrógeno. Mientras que el análisis de la lámina representa mejor la respuesta de la planta a la fertilización con fósforo y potasio. El extracto peciolar puede detectar antagonismos entre elementos en altas dosis de fertilización.Términos para indexación: Vitis vinifera, análisis de savia, análisis de tejido, diagnóstico nutricional, 'Red Globe'. Petiole extract chemical analysis to evaluate nutritional status in grapevineAbstract -The objective of this work was to evaluate the relationship between N, P and K concentration in petiole extract, blades and roots, to determine the nutritional status in grapevine. The experiment was done between December 2006 and February 2007. Three fertilization trials with N, P 2 O 5 and K 2 O in one-year-old Vitis vinifera 'Red Globe' plants, grown in containers, were established. Nitrate, phosphate and potassium concentration were evaluated in the petiole extract, and nitrogen, phosphorus and potassium were determined in blades and roots. Petiole extract analysis was more sensitive than blade and root analysis to determine nitrate and nitrogen status. Meanwhile, blade analysis showed better plant response to fertilization with phosphorus and potassium. Petiole extract analysis can indicate the antagonism between nutrients under high doses of fertilization.