Investigation of different fertilizer management effect on nutritional status of apple by compositional nutrient diagnosis

Introduction: Apples are the world's largest commercial fruit orchard. According to the World Food Agriculture Organization in 2017, Iran is one of the top three apple producers in the world. Nutrition is one of the important factors that affect the quality and quantity of fruit. This study was conducted to evaluate and compare different fertilizer management on the nutritional status of apple trees in 1397-1398 at Razi University of Kermanshah (34◦ 19′ N and 47◦ and 7′ E).
Materials and Methods: This research was conducted to a complete randomized block design in a four-year-old high-density apple orchard with Gala cultivar based on M9. Different managements included mineral, organic, and integrated systems. In the chemical management, 65 g urea, 38 g triple superphosphate, and 60 g KCl per tree plus the foliar application of ferrous, zinc, and calcium were used. Inorganic management 5 kg compost, 0.5 kg farmyard manure (cow), and 5 kg biochar per tree were used. The integrated management included chemical fertilizers +biochar, chemical fertilizers +compost, chemical fertilizers + farmyard manure, and compost + biochar. The balance of nutrients in apple leaf nutrients was investigated using the compositional nutrient diagnosis (CND) method.
Results and Discussion: The coefficient of determination (R2) of the third-order equation model for all elements was in the range of 0.79-0.89. The cutoff points of the curves (-b/3a) for nitrogen 7.98, phosphorus 7.64, potassium 7.12, calcium 7.82, magnesium 8.00, ferrous 7.87, zinc 7.98, copper 7.79, manganese 7.41 and residual value (R9) 8.11 kg were obtained. In general, the average fruit yield for different elements are so closed and ranged from 7.12 to 8.11 (on average of 7.77± 0.31) related to potassium and R9, respectively. According to the Cate-Nelson method, fruit yield equals 8.75 kg was chosen as critical fruit yield to grouping the groups into high- and low- fruit yield subgroups. The control, farmyard manure, and compost treatments belonged to a low- fruit yield subgroup. While integrated treatments as well as chemical fertilizers and biochar treatments grouped in the high- fruit yield subgroup. The results indicated that in the high-fruit yield subgroup the average of compositional nutrient diagnosis norms (V*(x)) were positive for nitrogen, potassium, calcium, and magnesium besides negative for phosphorus, ferrous, copper, and manganese. The balance index (r2) indicated the imbalances of nutrients under different fertilizer management. After the application of different fertilizers, some indices were changed from the most negative amounts to the most positive amounts. These changes were found for the ferrous index in chemical management, calcium index in organic management, and nitrogen and phosphorus indices in integrated management (in comparison with the application of only chemical fertilizers). In integrated management calcium, magnesium, and ferrous indices were increased from -0.17, -0.42, and -1.24 in untreated trees to 0.15, 0.07, and 0.15, respectively
Conclusions: it is necessary to consider micronutrients’ deficiency in the future fertilizer management of the studied apple orchard. Among macronutrients calcium, phosphorus, magnesium, and potassium in mineral fertilizer management should be considered. The potassium deficiency was one of the limiting factors to produce apple fruit in organic and integrated fertilizer management. Based on the fruit yield, the application of chemical fertilizers or biochar was recommended. For the integrated management, chemical fertilizer +biochar, chemical fertilizer + farmyard manure, and chemical fertilizer +compost were suggested regarding the available fertilizers.