Changes in the Content of Nutrients, Starch and Protein in On and Off Years in Three Local Olive Cultivars in Kermanshah, West of Iran

Abstract

Introduction Olive (Olea europaea L.) is the most famous species of Oleaceae family that has edible fruits. The olive tree has a tendency to alternate bearing, leading often to the production of massive fruit yield in one year (on) and a very low fruit yield in the next year (off). Knowing the changes of nutrients in different stages of olive fruit growth and development in the “on” and “off” years provides the possibility of timely and correct application of fertilizers. This research was conducted in order to investigate the changes in the concentration of mineral elements, starch, and protein of olive fruit in the on and off-years. Materials and Methods This research was carried out in the years 2018-2019 at Olive Dalaho Research Station in 2018 and 2019 at Dalahu Olive Research Station in Kermanshah (Lat. 32° 30´ N, Long. 45° 51´, Alt. 560 m.), west of Iran. The experiment was carried out in the form of a randomized complete block design with three replications and three local olive varieties, namely Deira, Zagros and Meshkat. All tested 11-year-old trees were under similar conditions in terms of pruning, drip irrigation, fertilization and pest and disease control. Measurement were carried out on N, P, K, Zn, B, starch, and protein in young leaves, fruits, old leaves, and roots from the time of kernel hardening (in early June) until fruit ripening (in mid-November) every 40 days using both "on" and "off" year trees. The samples included 20 broad leaves from the middle part of one-year-old and newly-formed vegetative branches, the growing fruits of the current year, and the feeding roots of 30 cm depth under the canopy of the tree crown. Measurements on potassium concentration were made by a flame photometer (model PFP7 made by JENWAY, England), phosphorus by colorimetric method using spectrophotometer, nitrogen and protein by Kjeldahl method, boron and zinc elements using an atomic absorption device (Perking Elmer model 31/40). Starch concentration of the dry matter was measured by Morley's method. Results and Discussion Monthly changes of mineral elements in leaves and young fruits, starch, and protein concentration in old leaves and roots were significant in the on and off years. The monthly changes in the concentration of the mineral elements corresponded to the pattern of the fruit growth curve (double sigmoid). The concentration of N, K, B, and Zn in young leaves decreased from the beginning of June to the middle of July (the time of endocarp hardening) and then increased slightly. The monthly changes in concentration of mineral elements in leaves and young fruits, starch, and protein in old leaves and roots were significant in the on and off years. The monthly changes of the mineral elements corresponded to the pattern of the fruit growth curve (double sigmoid). The concentration of N, K, B and Zn in young leaves decreased from the beginning of June to the middle of July (the time of endocarp hardening) and then increased slightly. Mashkat cultivar had the highest and Deira and Zagros cultivars had the lowest concentration of nitrogen in young leaves. The concentration of nitrogen has a direct effect on vegetative growth, fruit formation, fruit yield, and shoot growth. There was a positive and significant relationship between fruit nitrogen and phosphorus and zinc concentration of the fruit, but young leaf nitrogen had a negative and significant correlation with phosphorus and zincof the fruit. Deira cultivar had the highest and Meshkat the lowest zinc concentration of the young leaves. Zinc plays a significant role in the function of enzymatic systems, synthesis of nucleic acids, protein and auxin metabolism. There was a positive correlation between phosphorus concentration in young leaves with phosphorus concentration in fruit and leaf starch, but there was a negative correlation with leaf and root protein concentration. The concentration of starch in the old leaves and roots increased and then decreased in the on-year until June. The concentration of root starch decreased slowly from June to November in off-year trees. The concentration of protein in old leaves and roots followed a double sigmoid curve, it decreased sharply until mid-July. From the mid-July to the end of August, the protein concentration of the old leaves slowly and strongly in old leaves and roots, respectively. Conclusions Considering the observed changes in the concentration of mineral elements in the leaves and fruits according to the fruit growth pattern, especially in the spring, soil application of nitrogen, phosphorus, and potassium in January (before flowering), foliar spraying of nitrogen, potassium, zinc, and boron in June (after fruit set) and nitrogen and potassium amendments in August (after endocarp hardening) is recommended for the olive orchards of the studied region.

Keywords

• alternative bearing
• fruit
• growth pattern
• plant nutrition.