Effect of nitrogen and phosphorus levels on vegetative growth of chrysanthemum (Chrysanthemum morifolium Ramat.) cv. Snowball

Introduction

Chrysanthemum (Chrysanthemum morifolium Ramat.) is one of the most important ornamental flowering crops cultivated worldwide for cut flowers, loose flowers, garden decoration, and landscaping purposes. The crop is highly valued for its wide range of flower forms, colours, and adaptability to diverse agro-climatic conditions. The growth, flowering, yield, and quality of chrysanthemum are greatly influenced by nutrient management practices, making balanced fertilization an essential component of its successful cultivation (Karik and Tunturk, 2019) [5] . Chrysanthemum is considered a heavy feeder because of its shallow root system, which limits nutrient uptake from deeper soil layers. Consequently, an adequate and balanced supply of nutrients is necessary to sustain vigorous vegetative growth and optimum flower production (Gu et al., 2022; Hosseinzadeh et al., 2015) [3,4] . Although varietal characteristics largely determine flower quality, environmental conditions, soil fertility status, and nutrient availability also play significant roles in influencing plant growth and productivity. Therefore, the selection of appropriate fertilizer doses according to cultivar requirements and local soil conditions is crucial for maximizing crop performance (Shahrajabian et al., 2019) [9] . Among essential plant nutrients, nitrogen (N) and phosphorus (P) are particularly important for chrysanthemum growth. Nitrogen is a major constituent of amino acids, proteins, nucleic acids, and chlorophyll, and is directly involved in photosynthesis and vegetative development. Adequate nitrogen nutrition promotes plant height, leaf production, branching, and overall plant vigor.

Phosphorus, on the other hand, plays a vital role in energy transfer, root development, cell division, and metabolic activities. It is an integral component of nucleic acids, phospholipids, and several enzymes that regulate plant growth and development (Li et al., 2019; Chaitra et al., 2018) [6,1] . Previous studies have demonstrated that growth, flowering, yield, and quality attributes of chrysanthemum can be significantly improved through the application of appropriate levels of nitrogen, phosphorus, and other nutrients. Variations in fertilizer doses have been reported to influence vegetative growth, flower production, and overall crop performance in different chrysanthemum cultivars (Rajan et al., 2019; Choudhary et al., 2022) [8,2] . However, nutrient requirements vary among cultivars and environmental conditions, making it necessary to identify optimum fertilizer levels for specific cultivars under local growing conditions. Considering the importance of balanced nutrition and the limited information available for chrysanthemum cv. Snowball under the agro-climatic conditions of Prayagraj, the present investigation was undertaken to evaluate the effects of different levels of nitrogen and phosphorus on vegetative growth parameters, namely plant height, plant spread, number of branches per plant, and number of leaves per plant, and to determine the optimum nutrient combination for achieving maximum growth.

Materials and Methods

The experiment was conducted during the winter season of 2009-10 at the Research Farm of the Department of Horticulture, Sam Higginbottom Institute of Agriculture, Technology and Sciences (SHUATS), Prayagraj, India. The experimental soil was sandy loam with pH 7.1, organic carbon 0.48%, available nitrogen 0.25 kg ha⁻¹, available phosphorus 181.6 kg ha⁻¹, and available potassium 28.69 kg ha⁻¹. The experiment was laid out in a factorial randomized block design (FRBD) with four nitrogen levels (0, 40, 60, and 80 kg N ha⁻¹) and three phosphorus levels (0, 100, and 150 kg P₂O₅ ha⁻¹), resulting in 12 treatment combinations (Table 1). Each treatment was replicated three times. Potassium was applied uniformly at 100 kg K₂O ha⁻¹ in all plots. Rooted cuttings of chrysanthemum cv. Snowball were transplanted on 30 October 2009. Nitrogen was supplied through urea and phosphorus through single super phosphate. Half of the nitrogen along with the full dose of phosphorus and potassium was applied as basal fertilizer before transplanting, while the remaining nitrogen was applied as top dressing 20 days after transplanting. Recommended agronomic practices, including irrigation, weeding, and plant protection measures, were followed uniformly for all treatments throughout the crop growth period. Five plants were randomly selected and tagged in each plot for recording observations. Growth parameters including plant height (cm), plant spread (cm), number of branches per plant, and number of leaves per plant were recorded at 30, 45, 60, and 75 days after transplanting (DAT). Plant height was measured from the soil surface to the apex of the plant. Plant spread was recorded as the average of east-west and north-south canopy spread. The numbers of branches and leaves were counted manually.

The recorded data were subjected to analysis of variance (ANOVA) appropriate for a factorial randomized block design following the procedure described by Fisher (1950). Treatment means were compared using the critical difference (CD) test at the 5% probability level.

Results and Discussion

Plant height

Plant height was significantly influenced by nitrogen, phosphorus and their interaction at 45, 60 and 75 DAT, whereas treatment effects were non-significant at 30 DAT (Supplementary Tables S1 andS2). At 75 DAT, the maximum plant height (35.78 cm) was recorded under N₂P₁ (60 kg N ha⁻¹ + 100 kg P₂O₅ ha⁻¹), followed by N₂P₂ (34.84 cm), while the minimum value (32.89 cm) was observed in the control treatment (N₀P₀) (Table 2). A similar trend was observed throughout the crop growth period, where N₂P₁ consistently recorded the highest plant height at 30 DAT (16.66 cm), 45 DAT (25.43 cm) and 60 DAT (34.50 cm), compared with 11.74, 21.44 and 31.45 cm, respectively, under the control treatment (Supplementary Tables 1 and2). The increase in plant height with nitrogen application up to 60 kg ha⁻¹ and phosphorus application up to 100 kg P₂O₅ ha⁻¹ may be attributed to enhanced chlorophyll synthesis, photosynthetic activity, protein formation and cell elongation. However, further increase in nutrient levels resulted in a slight decline in plant height.

Plant spread

Nitrogen, phosphorus and their interaction significantly affected plant spread at 45, 60 and 75 DAT, whereas interaction effects were non-significant at 30 DAT (Supplementary Tables S3 andS4). At 75 DAT, N₂P₁ produced the maximum plant spread (36.47 cm), followed by N₂P₂ (34.65 cm), whereas the control treatment recorded the minimum value (30.34 cm) (Table 2). The superiority of N₂P₁ was evident throughout the growth period, recording plant spread values of 20.65, 24.57 and 32.69 cm at 30, 45 and 60 DAT, respectively, compared with 13.53, 20.69 and 27.76 cm under the control treatment (Supplementary Tables 3 and4). The improved plant spread under optimum nutrient application may be due to enhanced vegetative growth, greater assimilate production and efficient translocation of photosynthates to developing tissues. The decline observed at higher nutrient levels suggests that excessive fertilization was less effective in promoting canopy development.

Number of branches per plant

The number of branches per plant was significantly affected by nitrogen and phosphorus at 45, 60 and 75 DAT, while treatment effects were non-significant at 30 DAT (Supplementary Tables S5 andS6). The highest number of branches per plant at 75 DAT was recorded under N₂P₁ (19.89), followed by N₂P₂ (19.77), whereas the lowest value (14.64) was observed in the control treatment (Table 2). The same treatment also produced the highest number of branches at 30 DAT (4.41), 45 DAT (6.71) and 60 DAT (12.82), compared with 2.56, 4.59 and 8.46 branches plant⁻¹, respectively, under the control treatment (Supplementary Tables 5 and6). The increased branching under optimum nutrient supply may be attributed to enhanced meristematic activity and greater availability of metabolites required for vegetative growth. Phosphorus-mediated improvement in root development and nutrient uptake may have further contributed to branch formation.

Number of leaves per plant

The number of leaves per plant increased significantly with nitrogen and phosphorus application at 45, 60 and 75 DAT, whereas treatment effects were non-significant at 30 DAT (Supplementary Tables S7 andS8). At 75 DAT, the maximum number of leaves per plant (129.41) was recorded under N₂P₁, followed closely by N₂P₂ (129.20), while the minimum value (121.11) was recorded in the control treatment (Table 2). The superiority of N₂P₁ was maintained throughout the crop growth period, recording 25.85, 50.89 and 121.61 leaves plant⁻¹ at 30, 45 and 60 DAT, respectively, compared with 18.64, 35.65 and 83.92 leaves plant⁻¹ under the control treatment (Supplementary Tables 7 and8). Increased leaf production under optimum nitrogen and phosphorus nutrition may be attributed to enhanced photosynthetic activity, chlorophyll synthesis, protein formation and metabolic regulation. The results indicate that application of 60 kg N ha⁻¹ and 100 kg P₂O₅ ha⁻¹ was most effective in promoting vegetative growth of chrysanthemum cv. Snowball under the conditions of the present study.

Discussion

Nitrogen and phosphorus significantly influenced vegetative growth of chrysanthemum cv. Snowball. The superior performance of the treatment combination N₂P₁ (60 kg N ha⁻¹ + 100 kg P₂O₅ ha⁻¹) in terms of plant height, plant spread, number of branches, and number of leaves indicates that balanced nutrient application promoted vigorous vegetative growth. Nitrogen is a major constituent of chlorophyll, amino acids, proteins, and nucleic acids and plays a key role in photosynthesis and cell division. Adequate nitrogen availability therefore enhances vegetative growth and canopy development. Phosphorus is involved in energy transfer, root growth, and various metabolic processes, thereby improving nutrient uptake and utilization efficiency (Marschner, 2012) [7] . The improvement in growth parameters observed with increasing nitrogen up to 60 kg ha⁻¹ and phosphorus up to 100 kg P₂O₅ ha⁻¹ may be attributed to enhanced photosynthetic activity, increased assimilate production, and efficient translocation of metabolites to actively growing tissues. Similar beneficial effects of balanced nitrogen and phosphorus nutrition on vegetative growth of chrysanthemum have been reported by Chaitra et al. (2018) [1] and Rajan et al. (2019) [8] . The increase in branch and leaf production under optimum nutrient supply could be associated with enhanced meristematic activity and improved synthesis of structural compounds required for vegetative development.A slight decline in growth parameters at higher nitrogen and phosphorus levels suggests that nutrient application beyond the optimum requirement did not further improve plant growth. Similar observations have been reported in chrysanthemum and other ornamental crops, where excessive fertilizer application resulted in reduced nutrientuse efficiency and marginal growth responses (Taiz et al., 2015) [10] . Therefore, balanced fertilization appears to be more important than increasing fertilizer dose beyond the crop requirement.The present findings indicate that application of 60 kg N ha⁻¹ and 100 kg P₂O₅ ha⁻¹ provides an optimum nutrient combination for promoting vegetative growth of chrysanthemum cv. Snowball under the agroclimatic conditions of Prayagraj.

Conclusion

The present study demonstrated that nitrogen and phosphorus significantly influenced the vegetative growth of chrysanthemum cv. Snowball. Among the nutrient combinations evaluated, application of 60 kg N ha⁻¹ and 100 kg P₂O₅ ha⁻¹ (N₂P₁) consistently produced the highest plant height, plant spread, number of branches per plant, and number of leaves per plant throughout the growth period. Further increases in nitrogen and phosphorus levels did not result in additional growth improvement. Therefore, application of 60 kg N ha⁻¹ and 100 kg P₂O₅ ha⁻¹, together with 100 kg K₂O ha⁻¹, may be recommended for promoting optimum vegetative growth of chrysanthemum cv. Snowball under the agro-climatic conditions of Prayagraj, India.

Acknowledgement

AcknowledgementThe author gratefully acknowledges the Department of Horticulture, School of Agriculture, Sam Higginbottom Institute of Agriculture, Technology and Sciences (SHIATS), Allahabad, Uttar Pradesh, India, for providing the necessary facilities and support for conducting the research.

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