Effect of ammonium sulfate (NH4)2SO4 as nitrogen source on crop production
The statistical analyses performed during all four seasons showed significant differences on all studied features (Table 2). Results obtained in the current investigation suggest that ammounium sulfate [(NH4)2SO4] impacts positively on plant height, number of branches per plant, fruiting zone length, seed yield per plant, seed yield per hectare and oil percentage with the increased levels of nitrogen (Table 2). The maximum plant height, number of branches per plant, fruiting zone length, seed yield per plant, seed yield per hectare and oil contents were recorded in the presence of 30 kg/ha ammonium sulfate compared to control plants of canola. Correlation analysis was performed in order to evaluate the agronomic characteristics after the ammonuim sulfate treatment and it was found that signficant results have been achieved with respect to the ammounium sulfate treatments and plant height (0.998), number of branches per plant (0.953), fruiting zone length (0.987), seed yield per plant (0.994), seed yield per hactare (0.994) (Table 3). Another important factor that must be taken into account is the Sulfur element since it plays an important role in the synthesis of proteins which in turn affects the oil contents in canola seeds 21. Hence, the balanced application of S and N is vital with the objective of further improving the canola seeds quality and production 21. Karamanoset al. 22 suggested that the optimal ratio of N:S ranging from 7:1 to 5:1 can maximize canola production. In fact, a study conducted by Brennan and M.D.A, 2008 and proven that the canola production can be extremely limited in case of sulfur deficiency in soil 23. The supply of artificial sulfur promotes the nitrogen uptake efficiency of canola production and consequently elevates the level of protein in leaves: this will definitely enhance the crop productivity and yield 24.
Our results are in agreement with those reported by Chienet al. 25 in which the plant height and number of branches were boosted when higher rates of ammonium sulfate were applied. Other researchers have reported similar results in which they have indicated that the 1000-seed weight increases proportionately with sulfur and nitrogen levels 26. Others have suggested that biological yield increases significantly when increasing the nitrogen and sulfur rates 27.
Influence of NH4NO3 as nitrogen source on canola plants
The ammonium nitrate treatment has considerably influenced the crop’s agronomic and quality traits compared to the control canola plants in th field. The recorded results including the maximum plant height (194 cm), number of branches per plant (9), fruiting zone length (156.2 mm), seed yield per plant (42.4g) and seed yield per hectare (1007.2 kg) showed an increase in all of the aforementioned agronomic attributes (Table 2), except for the oil percentage that has decreased by 0.8 percentage point when NH4NO3(100 kg/ha) treatment was applied (Table 2). The correlation coefficient between the ammonium nitrate rates and agronomic characteristics have indicated that the morphological traits were positively affected when nitrogen nutrient was added in a form of NH4NO3. A high positive correlation was also observed between yield attributes and ammonium nitrate rates for plant height (0.987), number of branches per plant (0.887), fruiting zone length (0.957), seed yield per plant (0.953), and seed yield per hactare (0.953), while negative correlation with oil contents was detected (Table 3). From these findings it can be concluded that a nutrient deficiency (nitrogen) can severely hampers canola productivity 28,29. Furthermore, the canola yields can be enhanced by a better management of nitrogen at the optimum growth stages of canola 2,16. Nitrogen is an essential plant nutrient that simulates its meristematic activity, cell elongation, and elevates the photosynthesis of canola. These factors will ultimately boost growth and yield of the canola plant 30. A pervious study published by Khan, S., et al, 2018, they haves demonstrated that 3.8qt/ha (Quintal/hectare) oil yield was achieved through rigorous application of 60 kg of nitrogen per hectare 31. Similar findings have been made in other studies highlighting the importance of nitrogen supplementation in the refinement of the rapeseed yields in diverse agro- climatic conditions 32.
As far as we know, Nitrogen has strongly and significantly correlated with the seed yield per hectare, plant height, number of branches per plant, fruiting zone length, and number of seed per plant, in addition to the enhancement of the number of pods per seed, 1000 seed weight, biological yield, seed yield , and oil yield 27,32. On this basis, it can be concluded that the canola production depends on the selection of the correct dose, source, and timing of nitrogen fertilizer application. Unbalanced application of nitrogen fertilizer may adversely affect the canola production 6. The source of nitrogen fertilizer may also change the plant N uptake and soil N availability and hence impacting the ultimate canola productivity 33. In our experiments, two sources of nitrogen were tested and compared one with another. The subsequent results showed that ammonium nitrate had significantly contributed to the enhancement of canola production comparing to the ammonium sulfate 34. It has been reported elsewhere that the application of ammonium sulfate reduces the pH of the soil as well as dissolution of many other nutrients resulting in negative impacts on plant growth and development compared to ammonium nitrate 35.
Effect of foliar application of Gibberellic acid and potassium fertilizer on canola yield and yield components
The influence of various treatments related to the application of gibberellic acid and potassium fertilizer were also studied in accordance with the yield parameters of canola. The results of the present study provide evidence that all the agronomic traits and oil percentage tend to increase with increasing levels of foliar application of K and GA3 solely or combined in comparaison with the unsprayed plants. A significant increase was recorded using different treatements of GA3 and K in plant height, number of branches per plant, fruiting zone length, seed yield per plant, seed yield/ha and seed oil percentage compared to control (T1-T10).
The measurement values of plant-height in all of the treatments were higher than the control plant during a four-year period (2014 to 2018). Significant differences were also observed among the treatments (F=81.913; p≤ 0.0000, F=99.79; p≤ 0.0000, F=86.782; p≤ 0.0000, and F=101.34; p≤ 0.0000) during all seasons (Table 4). The maximum plant-height was reported when combined GA3 (30kg/ha) and K (6 g/m2) ( T10 followed by T9, T8 and so on) (Table 4) were applied. However, both T4 (GA3 0 and K 6.0) and T8 (GA3 10kg/ha and K 2.0g/m2) showed an almost insignificant variation in the plant-height meseaurements compared to other treatments.
The foliar application of K and GA3 significantly affected the number of branches per canola plant comparing to the control one (T1). The highest number of branches per plant were recorded in T10 (30GA3g/ha+6.0 g/m2 K) which appeared to have the same trend as that reported for canola plant-height measurements (Table 5). A considerable rise in the fruiting zone length (cm) was also observed when combined foliar applications were applied (T10). The significant differences among the treatments (F=101.814; p≤ 0.0000, F=123.32; p≤ 0.0000, F=126.62; p≤ 0.0000 and F=122.4; p≤ 0.0000) were also noted for over four years of the study (Table 6). As
Another agronomic trait was affected when foliar applications of K and GA3 were applied ( individually or combined) is the number of seeds per plant: it was found that canola plants produce more number of seeds per plant when combined GA3 and K were applied (T10) during the four seasons of 2014-2018 (Table 7). This parameter seemed to be improved immeasurably in all treatments (T2-T10) compared to the control plant (T1). Therefore, it can be concluded that improvement of this agronomic parameter can be successfully attained when increased rates of the foliar (K and GA3) were applied.
Since seed yield ha-1 is considered as the main interest for canola breeders, higher rates of the foliar (K and GA3) were applied (individually or combined) with respect to non-sprayed plants (T1); the obtained results of this investigation indicate that high seed yield occurs in all treatments (T2-T10), particularly, when increased rates of the foliar were applicable.
This important rise in seed yield/ha (883.2) was recorded with 30 kg/ha GA3 and 6 g/m2 K foliar application (T10). The significant differences were also detected among the following treatments (F=44.576; p≤ 0.0000, F=49.903; p≤ 0.0000, F=48.765; p≤ 0.0000 and F=51.273; p≤ 0.0000) applied during the experimental period (Table 8).
The changes in oil percentages, in response to K and GA3 application were also investigated. The highest oil percentage was observed at the T10 treatment followed by T3 and T5 during the four cropping seasons of 2014-18 (Table 9).
In view of the aforementioned findings, it can be concluded that combined form of GA3 and K (T10) presents a potential strategy to enhance growth performance of canola. The promoting effect of gibberellic acid and potassium treatments contribute to the metabolic and other physiological processes leading to better crop yields. Interestingly, for the majority of the studied traits, the K application (T4) acts similarly and almost insignificantly to the combined application (T8) of K (3.5g/m2) and GA3 (15g/ha), this could be attributed to the key role of K in improving canola yields (Table 4-9).
GA3 and K fertilizer application is necessary to increase the vegetative and reproductive growth of canola plant36. These fertilizers could be involved in improving defence mechanisms of canola plant which may consequenlty affect the seed yield. Similar results have been reported using these same treatments on sesame plant 28. Likewise, foliar application of potassium and gibberelic acid alone or in combination incerases the plant vegetative and reproductive growth of the plant resulting in the enhancement of the yield per unit 37. In fact, in a study reported by Imran and A.A. Khan, 2017, the application of K fertilizer not only enhances the yield per unit, fresh nut and karnel dry mass (spliting percentage), it also reduces the blank percentage 38. It was also observed that in absence of gibberellic acid applications, the blank percentage and spliting percentage could be ameliorated 39.
Jan et al (2019) reported that high concentrations of potassium K and Zing Zn after the simultaneous foliar applications of GA3 and K separately or in combination could be found in canola plant leaves 40. The evidences of this study suggest that the interactive effects of GA3 and K can be employed in the aim of improving morphological aspects and yield attributes of canola. It can also be expected that these interactive effects may elevate the plant resistance against various biotic and abiotic stresses, carbohydrate translocation,and the photosynthesis process 39. Khan et al (2019) also mentioned that these fertlizers (GA3 and K) might strengthen the defence mechanism of the plant which ultimately impacts the plant growth and yield 41,42. In short, with appropriate application of nitrogen fertilizers, GA3, and K, canola yeilds can be substantially improved.
Ethic statements
This study does not involve any wild or endangered species of plants. Moreover, it does not encompass the collection of any new plant material. The study is only related to the field performance of a canola genotype under different growth treatments. The seeds of canola were collected from nuclear institute of Agriculture (NIA) tandojam. The evaluated genotype is a cultivated species and is a released variety in Pakistan. The experiment was conducted in line with institutional and national policies.