Influence of Nitrogen on Growth and Flowering of Zinnia elegans Cv. Meteor

MATERIALS AND METHODS

The effect of various levels of nitrogen on growth and flowering of Zinnia Cv. Meteor was determined in the Floriculture Research Area, Institute of Horticultural Sciences, University of Agriculture, Faisalabad, during the year 2002.

The seeds of Zinnia elegans Cv. Meteor were sown in earthen pots and nursery was transplanted in large sized pots, with one plant per pot, after one month of sowing of seeds. Pots were filled with properly prepared medium containing normal soil, silt and farm yard manure in the ratio of 1:1:1. Nitrogen was applied @ 0, 5, 10, 15 and 20 g pot^-1 using urea (46%) as source of nitrogen. These doses were equivalent to 0, 50, 100, 150 and 200 kg h^-1 application of nitrogen, respectively.

Fertilizer was applied in two splits: first half at the time of transplanting and the remaining half one month after transplanting. Data were collected on various vegetative and floral characteristics including plant growth rate per week (cm), plant height (cm), number of lateral shoots, length of lateral shoots (cm), number of leaves per plant, leaf area (cm²), emergence of first flower (days), total number of flowers, size of flowers (cm²) and blooming period (days).

Data were statistically analyzed by performing Analysis of Variance technique^[6] and interpreted according to Duncan’s Multiple Range test at 5% level of probability.

RESULTS AND DISCUSSION

Nitrogen application significantly affected the vegetative (Table 1) and floral characteristics (Table 2) of Zinnia elegans Cv. Meteor. Growth rate was maximum (6.7 cm per week) when Zinnia plants were supplied with 15 g (T₃) or 20 g (T₄) nitrogen per pot, although, results were statistically non-significant for nitrogen application @ 10,15 and 20 g pot^-1. Application of 5 g N per pot resulted less growth rate (5.7 cm per week) as compared to 10, 15 and 20 g N application. Yet, the results were significantly different from the control i.e. minimum growth rate (4.7 cm per week) was recorded in plants grown without application of nitrogen fertilizer. Results revealed that growth rate of Zinnia was increased by increasing the dose of nitrogen, as already reported by John et al.^[2] that increasing the dose of nitrogen from 50 to 150 kg ha^-1, resulted in more vigorous growth in Zinnia Cv. Giant flowered crimson.

Maximum plant height (51.8 cm) was recorded in plants supplied with 20 g N/pot, while, minimum plant height (40.5 cm) was observed in plants grown without nitrogen (control). Nitrogen application @ 10 and 15 g pot^-1 resulted in plants having statistically similar height i.e. 45.8 and 47.7 cm, respectively. Almost similar trend was observed for number of lateral shoots per plant i.e. number of lateral shoots increased with increasing nitrogen application. Minimum number of laterals (4.5 per pant) were found in control, while, maximum number of laterals (7.0 laterals per plant) were observed in plants supplied with 20 g N/pot. Nitrogen application @ 5, 10 or 15 g pot^-1 resulted in 5.2, 5.8 and 6.0 lateral shoots per plant, respectively. Length of lateral shoots was positively correlated with the rate of nitrogen application. Plants supplied with 20 g N/pot had lateral shoots of maximum size (26.0 cm). Length of lateral shoots decreased gradually with reduction in nitrogen application rate i.e. 24.5, 24.2, 22.9 and 22.2 cm, in plants receiving 15, 10, 5 and 0 g N/pot, respectively.

Number of leaves was maximum (65.7) in plants with maximum height i.e. in plants supplied with 20 g N/pot. Plant supplied with 5 g N/pot produced 43.4 leaves, statistically similar to those produced by the plants with no fertilizer application (41.4 leaves). Leaf area increased gradually with increasing the dose of nitrogen i.e. minimum (31.8 cm²) in control and maximum (44.4 cm²) in plants receiving nitrogen @ 20 g pot^-1. No significant difference in leaf area was observed in plants supplied with 5, 10 or 15 g N/pot. These findings are confirmed by John et al.^[2] who reported that plant height and number of branches per plant were maximum when nitrogen was applied @ 150 kg ha^-1.

Data on reproductive behavior of Zinnia plants (Table 2) shows significant impact of nitrogen application on various parameters. Emergence of first flower was delayed gradually with increasing the dose of nitrogen. Flowers emerged earliest i.e. after 22 days of transplanting, in plants receiving 10 g N/pot, although, results were statistically similar to plants supplied with 5 g N/pot. Higher doses i.e. 15 g and 20 g N/pot delayed flowering and flowers emerged even later than the control plants. Results revealed that higher the dose of nitrogen longer was the period required for flowering, as already stated by Shah et al.^[3]. Moderate doses of nitrogen increased flowering in Zinnia i.e. more flowers were produced by plants receiving 10 g (13.5 flowers per plant) and 5 g (12.6 flowers per plant) nitrogen per pot, than those supplied with 15 g (11.7 flowers per plant) and 20 g (10.8 flowers per plant) nitrogen per pot. Higher doses of nitrogen had negative impact on flowering of Zinnia. Size of Zinnia flowers was affected significantly by nitrogen application. Flowers of maximum size (8.0 cm²) were observed in plants treated with 10 g N/pot. Statistically similar results were recorded when nitrogen was applied @ 5 g (6.9 cm²) and 15 g (7.6 cm²) nitrogen per pot.

Table 1:	Effect of nitrogen on vegetative characteristics of Zinnia elegans Cv. Meteor
Means with same letter(s) in a column are statistically non-significant

Table 2:	Effect of nitrogen on floral characteristics of Zinnia elegans Cv. Meteor
Means with same letter(s) in a column are statistically non-significant

Higher dose of nitrogen (20 g pot^-1) reduced flower size to 6.6 cm², comparable to control plants (6.3 cm²). These results do not verify the findings of John et al.^[2] who reported more number of flowers per plant with increased diameter, in plants supplied with higher dose of nitrogen (150 kg ha^-1). Zinnia plants fertilized with moderate dose of nitrogen i.e. 10 g pot^-1 bloomed for a longer duration (65.4 days) than all other treatments. Plants supplied with 5, 15 and 20 g N/pot bloomed for 62.3, 60.4 and 60.7 days, respectively which are statistically similar with each other.

Positive relationship occurs between nitrogen application rate and vegetative growth (plant growth rate, plant height, number and size of lateral shoots, number of leaves and leaf area) i.e. growth increased with increasing the dose of nitrogen. But, flowering behaviour was negatively correlated with nitrogen application. Optimum doses of nitrogen (10 to 15 g pot^-1) resulted in optimum vegetative growth and best reproductive growth behavior. Therefore, optimum use of N fertilizer would help better towards vigorous growth of Zinnia elegans, to keep your plants healthy and attractive and to obtain a large number of good quality blooms.