Background and objectives: Creating a suitable afforestation, it is essential to have a nursery with optimized conditions and management that can produce seedlings with desirable quantitative and qualitative traits. Improving seedlings and soil characteristics through nursery soil management plays an important role in the success of afforestation programs. In recent years, the use of fertilizers to increase the quantitative and qualitative growth of seedlings in nurseries has expanded, but the evaluation of the effectiveness and use of these fertilizers in different forest species, especially in semi-arid regions in Iran, is still limited. This study aims to investigate the effect of 5 types of fertilizers, including vermicompost and animal manure (as organic fertilizers), biofertilizers, bio-chemical fertilizers, and chemical fertilizers, and their method of use (fertilizer application at the beginning of the growing season and fertilizer application at intervals of 20 days), primarily on some characteristics of broadleaf and coniferous seedlings in a nursery in a semi-arid region of Iran.

Methodology: This research was conducted in the forest nursery of the General Directorate of Natural Resources of Zanjan Province, located 5 km from the Zanjan-Tabriz road, with a longitude of 48°24´52´´ and a latitude of 41°36´44´´. The climate of the region is semi-arid according to the Köppen climate classification and the Demarton index. The experiment was conducted in a completely randomized design with different fertilizer treatments, and seedlings of different species. The fertilizer treatments included biological fertilizers (Biorganic and Silicic), chemical fertilizers (urea, ammonium sulfate, potassium fulvaben), bio-chemical fertilizers (including several types of chemical and biological fertilizers), vermicompost, and cow manure. Five three-year-old species including juniper (Juniperus excelsa M.Bieb.), silver cypress (Cupressus arizonica Greene.), hawthorn (Crataegus monogyna Jacq.), hackberry (Celtis caucasica Willd.) and pistachio (Pistacia atlantica Desf.) were planted in pots with the same soil. A total of 275 seedlings were replanted in pots with the same soil composition with five replications for species and five replications for fertilizers. Soil chemical properties including pH, carbon, phosphorus, potassium, and nitrogen, and traits of seedlings (root length and volume, stem diameter and length) In order to analyze the data obtained from the characteristics of seedlings and also the chemical properties of soil, first the normality of the data was examined using the Kolmogorov-Smirnov test and the homogeneity of variance was examined using the Levene test. The effect of different soil fertilizers on the quantitative characteristics of seedlings and the chemical properties of soils was carried out using the one-way analysis of variance (ANOVA) test. Also, the Tukey test was used to compare the desired means.

Results: Carbon, phosphorus and nitrogen in the organic fertilizer treatment (livestock and vermicompost), showed appropriate values. In the Juniper, the highest and lowest amounts of carbon, phosphorus and nitrogen in the soil were in the biological-chemical-gradual treatment and the biological and biological-gradual treatment, respectively. In the silver cypress, the amounts of the mentioned elements in the gradual vermicompost and gradual biological treatment showed the lowest values compared to many other treatments. In hackberry, the growth of seedlings in the chemical fertilizer treatment was lower than in other treatments, carbon, potassium and nitrogen showed the highest values in the chemical treatment. The three mentioned elements in the soil of corm seedlings in the vermicompost treatment showed the highest values. All species except silver cypress dried in the bio-chemical treatment. In the juniper, the control treatment showed the highest growth in root length and volume. The highest growth in collar diameter and root volume of silver cypress was observed in the vermicompost treatment with 3.4 cm and 8.34 cm3, respectively. Hawthorn and sedge were sensitive to biological and biochemical treatments, but they responded positively to other fertilizers, especially organic fertilizers. The highest growth of the studied characteristics in corm seedlings occurred in chemical, vermicompost and livestock treatments, while biofertilizer had a lesser effect. In seedlings of this species, the highest collar diameter and root volume were observed in the vermicompost treatment with 1.4 cm and 2.7 cm3, respectively.

Conclusion: The results of this study showed that the effectiveness of various fertilizers in a semi-arid climate such as Zanjan depends on the plant species, the nature of the fertilizer, and the method of its application. In general, organic fertilizers provided a more suitable substrate for the establishment of most seedlings in the semi-arid climate of the region. Species with slower initial growth or sensitive to drought stress, such as Crataegus monogyna, Celtis caucasica, and Pistacia atlantica, showed a more significant response to the use of organic fertilizers, especially in a gradual manner. While Juniperus excelsa and Cupressus arizonica species were less dependent on these types of fertilizers. Chemical fertilizers, especially in broadleaf seedlings, increased yield and improved soil properties, but due care should be taken in their use with regard to environmental impacts and procurement costs. Also, given that bio-chemical fertilizer applied once for some species caused most seedlings to dry out, and then bio-fertilizer also caused poor seedling growth performance in most species, the use of these types of fertilizers in similar nurseries is not recommended. In addition, based on the results, the gradual application of fertilizers, especially organic fertilizers, leads to a more appropriate balance of soil nutritional elements, while gently releasing elements and more stable growth of most seedlings.