The amount of nitrogen applied and nutritional status of olive plants affect nitrogen uptake efficiency
Abstract Mist-rooted ‘Picual’ olive cuttings were used to test the hypothesis that both the amount of nitrogen applied and the nutritional status of olive plants may affect nitrogen uptake efficiency (NUE). Plants were placed in a greenhouse at 30/15 °C (day/night) with a 14 h photoperiod. Two different experiments were developed. In the first, plants were subjected to the application of 0, 50, 100, 200, 400, 600 or 800 ppm N. In the second experiment, the aim was to obtain three groups of plants differentiated by the nutritional status. Each group received 0, 50 or 100 ppm N, according to the results obtained in the first experiment. When plants of each group differed in their nitrogen content, they were subjected to additional nitrogen application either via foliar or to the soil. At the end of each experiment, plants were harvested and nitrogen was determined in leaves, stems and roots to obtain the nitrogen uptake by the plants. Nitrogen uptake efficiency (NUE) was estimated as NUE = (N uptake/N applied) × 100. Nitrogen content of the plant, vegetative growth and leaf chlorophyll content increased from 0 to 100 ppm N applied, decreasing at higher doses of N application. Consequently, NUE exponentially decreases with the amount of N applied above 100 ppm, with values ranging from 45.9% at 100 ppm to 4.1% at 800 ppm N. The method of nitrogen application, foliar or to the soil, does not affect nitrogen uptake, but the contrary occurs with the nutritional status of the plant. Nitrogen deficient plants were able to uptake more fertilizer nitrogen that well-nourished plants, with a significant reduction in NUE. Consequently systematic, annual applications of large amounts of fertilizer nitrogen may cause nitrogen over-fertilization and negative effects in both the plant and the environment.