Effects of Different Nitrogen Fertilizer Levels on Sunflower Growth and Yield Attributes

MATERIALS AND METHODS

Site description and soil properties: The study was conducted in Kinyinya, Bujumbura in Burundi. The soils in the site are predominantly Schists, Precambrian lava and dolomitic limestone, with soil texture chemical properties as: P^HH₂O (5.72), P^HKCl (4.44), C (1.40%), N-NH⁺⁴ (0.0036%), N-NO₃-(0.0034%) and P (6 mg kg^–1).

Experiment design: The experiment was carried out in lysimeters, where nine treatments were considered. These are T1: NPK (0-0-0), set as control treatment, T2: NPK(30-50-30), T3: NPK (40-50-30), T4: NPK (50-50-30), T5: NPK (60-50-30), T6: NPK (70-50-30), T7: NPK (80-50-30), T8: NPK (90-50-30) and T9: NPK (100-50-30). These treatments were set in randomized complete block design with 3 replications for each. During the growth period, diseases and pests were controlled through insecticide and fungicide application and all treatments had the same agricultural management practices.

Sampling and data collection: Plant were sampled and monitored in vigorous growth and harvesting period to determine the following:

The harvested production was dried at 70°C till constant dry weight was achieved, in a forced-air oven for two days.

Statistical analysis: The data acquired were processed and analyzed using advanced Excel 2007 and SPSS 15. A comparison among treatments were conducted (p<0.05) by using least significant difference (LSD) at 5% level.

RESULTS AND DISCUSSION

Effects nitrogen fertilizers on plant height: Plant height is an important morphological character that acts as a potent indicator of available growth resources in its vicinity. This study revealed that treatment T9 enhances plant height significantly (p<0.05) with a mean of 142.6 cm, followed by T8 (132.2 cm), While the control treatment (T1) showed the smallest plant by 75.29 cm (Fig. 1).

The higher performance of T9 may be attributed to the higher nitrogen level used under a conducive environment, hence enough nutrients for plant growth. These results support those of Mostafa and Abo-Baker¹¹, who reported increased sun flower growth due to higher rate application of nitrogen. Similar experimental results were attained by Shah and Khanday¹² as well as Sarkar and Mallick¹³.

Nitrogen fertilizers effects on sunflower head diameter: There was generally an increase in head diameter with applied nitrogen. The highest increase was observed for treatment T9 (54.87 cm), which significantly differed (p<0.05) from other treatments.

Fig. 1:	Effect of different nitrogen levels on plant height

Fig. 2:	Effects nitrogen fertilizers on sunflower head diameter

This was followed by treatment T8 (52.28 cm), which exceeded (p<0.05) the control Treatment (T1). This last (T1) recorded a minimum value of head diameter (23.53 cm) (Fig. 2).

These finding are in agreement with those of Iqbal et al.¹⁴ and Munir et al.¹⁵. Generally, larger heads harvested with higher Nitrogen application and were associated with more number of grains thus giving more yields.

Influences of nitrogen different rates on sunflower stem girth: Sunflower stem girth increased sharply as the level of nitrogen fertilizer increases (Fig. 3). Treatment T9 (6.06 cm) got the highest stem girth, followed by T7 (6.02 cm) and T8 (5.89 cm), while T1 (2.92 cm) got the smallest stem girth.

The enhanced stem girth for treatment T9 (Fig. 3) could be due to the applied higher nitrogen level which increased available plant nutrient, hence an improved sunflower stem girth. These results support those of Osman and Awed¹⁶, who reported increased stem girth with applied higher nitrogen rate.

Fig. 3:	Effect of different nitrogen levels on sunflower stem girth

Fig. 4:	Effect of different nitrogen levels on pair leaf number

Nitrogen’s effects on pair leaves number: The yield of sunflower can be projected from pair leaves. In this study, the highest pair leaves number was attained under treatment T9 (Fig. 4), with a significant difference (p<0.05) from the control treatment (T1).The treatments T8 and T7 were the following and significantly exceed (p<0.05) the control treatment (T1) which was having a lowest number of pairs leaves.

Even though nitrogen fertilization improved the pair leaves number, treatment T9 was the most effective treatment in increasing the number of pair leaves. As reported by Ali et al.¹⁷, this was due to the used nitrogen fertilizer which could stimulate vegetative growth and obviously increased the number of pair leaves.

Effects of nitrogen on yield and grains number: The yield is an index closely linked to different rates of fertilizers applied. While grains number is the most important yield component that a breeder should consider when selecting for higher yields under non-stress conditions as well as for the contribution of oil content.

Table 1:	Influence of nitrogen different rate on yield and sunflower grains number

Table 2:	Correlation coefficient between analyzed parameters
*,**Significant at p<0.05 and 0.01, respectively

As seen in Table 1, there were significant differences between treatments for full grains. Specifically, treatment T9, with 821 grains, got the maximum full grains, followed by T8 and T7 with 814 and 686 grains, respectively. The minimum was recorded for treatment T1 with 188 full grains. The reduced full grain number in T1 was probably due to the shortage of N which affects the plant development and growth as reported by Wajid et al.¹⁸ and Khaliq and Cheema¹⁹. The full grains ration under treatment T4 (76.27%) was ranked as the highest, while the one of T1 (71.1%) was the lowest.

The number of empty grain were more under treatment T8 (312), followed by T9 (294), while T1 (148) got the lowest value. The ratio of empty grains was highest in T1 (44.05%) and least under treatment T4 (23.73%). Similarly, the total grains number was maximum for T8 (1126), followed by T9 (1115) and minimum for T1 (336). On the other hand, the total grains yield weight of treatment T9 (2886.1 kg ha^–1) was highest and significantly exceeded the control treatment (564.4 kg ha^–1) and others. The highest total grains yield weight obtained under T9 may be ascribed to the applied higher level of nitrogen which could improve synthesis of sufficient photosynthases²⁰. These results are in agreement with the finding of Hocking et al.²¹ and Mahal et al.²² and supported by Ozer et al.²³, who highlighted higher grain yields weight with increased nitrogen rates.

Table 1 shows that the treatment leading to the maximum total yield weight does not necessarily translate into maximum parameters attained. Specifically, the treatment leading to maximum total grains yield and weight did not correspond to maximum full grains number or empty grains number. In essence, if a treatment has the highest proportion of a parameter, its proportion for other parameters was not obviously the highest. Moreover, the treatment with the maximum for some parameters, was not necessary the highest one in the proportion of these parameters. Considering each aspect factor, treatment T9: NPK (100-50-30) was the most effective than other treatments. This illuminated that T9 could improve growth and yield parameters. It might be due to the used higher nitrogen rate which could supply effective and adequate nutrients during sunflower’s growth.

Correlation coefficient of analyzed parameters: The correlation coefficient is a measure that determines the degree to which two variables linearly depend on each other. In the present study, the correlation coefficients between two investigated variables are displayed in Table 2.

There exist a strong and positive correlation between parameters as attested by the high significance (p<0.01) and correlation coefficients attained. Specifically, total full grains number and head diameter have a very high and strong correlation with other parameters by p<0.01.

Generally, the correlation coefficient was noticeably higher between total full grain number and total grain number and total full grain number and total grain yield weight with respective R² = 0.988 and R² = 0.970. The lowest (R² = 0.683) is between total grain number and total grain yield weight. Similar positive correlation were found in research by Tiwari and Upadhyay²⁴ and Ertek et al.²⁵.

CONCLUSION

The experimental outcomes showed that the sunflower plant growth parameters and yield attributes were increased significantly with the increase of nitrogen fertilizers. Treatment T9 with NPK (100-50-30) was the most effective and could not only enhance significantly the plant height and head diameter, but also increase stem girth, leaves pair number, grains number, full grains number and remarkably increased total grains yield weight. Treatment T9 could also effectively improve the ratio of sunflower different parts. Likewise, all the analyzed parameters were highly and positively correlated. Considering all tested index in this research, T9, NPK (100-30-50), was the most effective treatment in improving the growth characteristics and yield attributes of sunflower plant. This suggested that treatment T9 could improve sunflower growth parameters and yield attributes in Burundi country. Further research may be required in this area for more improvement of this crop.

SIGNIFICANCE STATEMENT

This study revealed the effect of nitrogen on sunflower cultivation especially on degraded soils of Kinyinya in Burundi. This will help the researchers, extension workers and farmers navigate between the height, weight and diameter of sunflower in an attempt to optimize production and demystify non productivity of degraded soils. Thus a paradigm shift in sunflower production in Burundi.

ACKNOWLEDGMENT

This research work was funded by the University of Burundi, Burundi.