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  • Author or Editor: Ricardo Fernández-Escobar x
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María José Jiménez-Moreno and Ricardo Fernández-Escobar

Mist-rooted ‘Picual’ olive cuttings growing in 1.1-L pots containing a mixture of washed sand and perlite were used to induce symptoms of phosphorus (P) deficiency and toxicity and to determine the nutritional status to which these symptoms occur. Plants were growing in a growth chamber at 25 °C day/15 °C night with a 14-hour photoperiod. From late spring to the autumn, plants were placed in a shade house protected from the rain. In the first experiment, plants received the application of 0, 100, 200, or 400 ppm P, and in the second experiment, 0, 12.5, 25, 50, 100, or 200 ppm P. Shoot growth was measured weekly and leaf samples were collected at different dates to determine P concentration. At the end of each experiment, plants were harvested and P was determined to obtain the P uptake by the plants. Phosphorus uptake efficiency (PUE) was estimated as PUE = (P uptake/P applied) × 100. P content increased in plants with the amount of P applied, and accumulated mainly in the roots. Vegetative growth showed a quadratic response, indicating a reduction of growth at the lowers and highest doses of P application. Leaf P concentration below or above which shoot growth was reduced was 0.11% to 0.13%. Symptoms of P deficiency and toxicity were observed in only a few plants. Leaf P concentration of deficient plants was 0.025%, and that of toxicity 0.21%. Toxicity symptoms were similar to that of zinc (Zn) deficiency. PUE was very low, 1.34% to 4.45%, suggesting the low P requirements of the olive.

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William H. Krueger and Ricardo Fernandez Escobar

The relationship between changes in Photosynthetically Active Radiation (PAR), specific leaf weight, nitrogen per leaf area and fruit size at harvest were investigated within the canopy of Manzanillo olive. Increasing PAR in the tree canopy related linearly to increasing: specific leaf weight, nitrogen per leaf area and fruit size at harvest for samples collected adjacent to where the light measurements were made. From these results it appears as though specific leaf weight, and nitrogen per leaf area may be useful indicators for determining if light intensity is a limiting factor on fruit sizing within the canopy of Manzanillo olive. These and additional data will be discussed.

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Ricardo Fernández-Escobar, Miguel A. Sánchez-Zamora, Jorge M. García-Novelo and Concepción Molina-Soria

The determination of nutrient removal from olive orchards could be of interest to estimate tree consumption and to provide information about the amount of nutrients to be applied when leaf analysis indicates the need for fertilization. In this work, nutrient removal from yield and pruning was determined from the control plots of two olive orchards located in different locations, in which two long-term experiments dealing with nitrogen fertilization were conducted. The trees from these plots received only potassium fertilizers during the 7 years of the experiments, because the previous season’s leaf analysis showed that the other nutrients were always above the threshold of sufficiency. Potassium was the most abundant element in the harvested fruits with an average of 4.42 g·kg−1 fresh fruit, which represents more than 50% of the mineral composition of the olive fruit, whereas calcium was the more abundant element in the pruning material with an average of 12.0 g·kg−1 and 6.87 g·kg−1, depending on the location, which represents more than 50% of the mineral composition of the pruning material. Nitrogen was the second more abundant element in both fruits (2.87 g·kg−1) and pruning material (6.87 and 5.40 g·kg−1, depending on the location), representing ≈35% of the mineral composition of both fruit and pruning material. The other nutrients were removed only in very small amounts. Expressed per hectare, the amounts of nutrients removed annually were: 57.9 kg·ha−1 per year calcium (Ca), 54.4 kg·ha−1 per year nitrogen (N), 45.5 kg·ha−1 per year potassium (K), 6.87 kg·ha−1 per year phosphorus (P), 3.79 kg·ha−1 per year magnesium (Mg), 0.12 kg·ha−1 per year copper (Cu), 0.11 kg·ha−1 per year boron (B), 0.08 kg·ha−1 per year manganese, and 0.05 kg·ha−1 per year zinc (Zn). These data show that olive trees remove small amounts of nutrients and, therefore, the need for fertilization is relatively low.

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M. Teresa Gómez-Casero, Francisca López-Granados, José M. Peña-Barragán, Montserrat Jurado-Expósito, Luis García-Torres and Ricardo Fernández-Escobar

Hyperspectral reflectance curves of olive (Olea europaea L.) trees under different N or K treatments, and the best wavelengths or vegetation indices to discriminate between different N or K applications using discriminant analysis were investigated. Field hyperspectral studies were carried out in two olive orchards located at Cabra and Lucena (southern Spain) for N and K experiments, respectively, in 2004 and 2005. At Cabra, olive trees have been fertilized since 1993, and annual applications of N per tree consisted of 0 kg (N0), 0.5 kg [N1 (normal)], or 1 kg [N2 (high)]. At Lucena, olive trees were fertilized since 1997, with 0%, 2.5%, and 5% K2CO3. Hyperspectral measurements were collected for each N and K treatments using a handheld field spectroradiometer (spectral range, 400–900 nm) in July of both years. To determine the nutritional status, a leaf analysis was carried out in July 2004 and 2005 at both locations. At Cabra, leaf N concentrations under N0 treatment were below the critical threshold, indicating nutritional deficiencies. Reflectance curves corresponding to N1 and N2 showed higher reflectance values in the near-infrared (NIR) plateau than N0 treatments. Wavelengths within the NIR region (from 710–900 nm) were selected in both years for discriminating between N treatments, with an overall accuracy of up to 99.2%. At Lucena, when K was not applied, leaf K content was below the critical threshold, indicating that olive trees were under a nutritional deficiency. Wavelengths from 710 to 890 nm, and the normalized difference vegetation index {NDVI = [(R780 – R670)/(R780 + R670]} were selected for discriminating K treatments with an overall accuracy of up to 94.4%. Classification matrices for cross-validation classified and misclassified cases into the nearest category. The results suggest that the induction of N or K nutritional deficiency for more than 10 years in olive trees resulted in different leaf nutrient contents, and this consistently affected hyperspectral reflectance curves, mainly in the NIR region. These results are promising and could provide information for further work on the identification of N- or K-deficient olive trees using remote sensing.