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The nutritional status of plants in different regions depends on many factors. The most important of them are soil and climate, and along with these two main factors, agricultural management, the most important of which is fertilization, is one of the factors affecting the nutritional status of agricultural and horticultural plants. This research was conducted in selected orchards in 18 regions of 16 provinces of Iran, including Guillan, Ilam, Tehran, South Kerman, North Khorasan, Khuzestan, Fars, Qom, Kermanshah, Kohgiluyeh and Boyer Ahmad, Golestan, Mazandaran, Markazi, Yazd, South Khorasan and Qazvin. Before the start of the research, soil sampling was carried out at two depths of 0-30 cm and 30-60 cm in March plant sampling was carried out in August, and fertilizer recommendation instructions were prepared by the Soil and Water Research Institute (SWRI), Karaj, Iran based on the results of soil tests and leaf tests, the age of the orchards and the type of cultivar and were made available to researchers for applying fertilizer treatments. Also, during the research, recommendations related to orchard management, including improving the irrigation system, combating pests and diseases, managing the orchard floor, and removing by-products were provided by the progress report from the researchers. The present study focused on the role of nutrients in olive yield using Pearson correlation data and principal component analysis (PCA) and identified the limiting and effective factors. Based on the results, the yield of olive orchards is strongly influenced by nutritional management and the balance of nutrients. The analyses showed that attention to the direct and indirect effects of elements and nutritional interactions is essential to achieve optimal yield. According to the results, the balance in the consumption of nutrients in olive orchards should be considered. Based on the data, the most limiting and effective nutrients in olive orchards in the studied regions are nitrogen, phosphorus, potassium, calcium, and boron. Calcium was identified as a key factor in improving the yield in the orchards of the studied regions in Fars, Golestan, Safiabad Dezful, and Isfahan provinces. Boron was identified as an important nutrient in improving the yield in the orchards of the studied regions in Fars, Golestan, Qom, Kohgiluyeh, and Boyer Ahmad provinces. Nitrogen was identified as an important nutrient in improving the yield in the orchards of the studied regions in Qazvin, Ilam and Markazi provinces, phosphorus was identified as an important nutritional element in improving yield in the orchards of Ilam, Markazi, South Khorasan, Isfahan and Kohgiluyeh and Boyer Ahmad provinces, and potassium was identified as an important nutrient in improving the yield in the orchards of Qazvin, Ilam, Markazi, South Khorasan, Isfahan, Qom, South Kerman province and Kohgiluyeh and Boyer Ahmad provinces. As can be seen, potassium is an important nutrient in improving the yield in a wider range of the studied regions. In terms of yield-limiting elements in the studied orchards, calcium and boron had the greatest impact on yield reduction. As, based on the results, calcium was identified as a yield-limiting element in the studied olive orchards in the provinces of Qazvin, South Khorasan, Tehran, Kohgiluyeh and Boyer-Ahmad, while boron element was identified as a yield-limiting nutrient in the olive orchards of Qazvin, Ilam, Markazi, South Khorasan, and Tehran. Therefore, in general, potassium is more abundant in the studied orchards in terms of its effect on yield improvement, and in contrast, boron is more abundant in the studied orchards in terms of its effect on yield reduction, and it is necessary to consider them in soil fertility management programs and olive orchard nutrition in Iran.
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