Abstract: Objectives: This study has been done to investigate the effects of foliar spraying of potassium nitrate at different concentrations and times for increasing the fruit and oil productivity and quality of Jatropha curcas trees. Methodology: Jatropha curcas trees treated with three concentrations (0.5, 1.0 and 1.5%) of KNO3 either pre and/or post bloom. Changes in leaf mineral content, flowering, fruit yield and seed oil content and their chemical characteristics were determined. Several oil properties as well as oil content, acid, peroxide and iodine values were measured too. Results: The results showed that all foliar spraying with different potassium nitrate (KNO3) concentrations and times revealed a pronounced increase in leaf mineral contents. Also, KNO3 spraying enhanced fruit yield and seed physical and chemical characteristics compared with control trees. The best results, with regards to leave mineral N, P and K were found due to foliar application with 1.5% twice and 1% once. In addition spraying potassium nitrate at 1% once which superior to increase the number of flowers, fruits per inflorescences, seed weight and oil content. Total seed weight and volume were obtained under spraying potassium nitrate at 1.5% twice. Foliar spraying of potassium nitrate 1% had the highest content of seed oil and its iodine value. Meanwhile, a good oil quality that had lowest oil acidity and peroxide value was observed with potassium nitrate concentration at 1.5% compared to untreated trees (control). Conclusion: The potassium nitrate had a positive effect of leaf mineral content with improving fruit yield, seed physical and chemical properties with greatest results at 1% potassium nitrate sprayed once as compared with control.
INTRODUCTION
In Egypt, Jatropha plantations as a biofuel feedstock started as a part of its policy for safe use of treated sewage water, to expand the green stretch in the desert, producing high economic value trees. Moreover, as the population increases, waste-water represents a threat to both safety environment and population, but also represents a valuable resource which can be used for the agricultural expansion and making use of the marginal desert land. In addition, the increase in demand for biodiesel by EU markets can create a challenge for Egyptian exporters of biodiesel which is needed progressively in the future1. So, producing high quality of Jatropha oil in Egypt is very competitive prices could be considered one of few back bones of the agricultural economy and to establish a base for a new agricultural based industry.
Jatropha curcas L., as a commercially viable biofuel crop, is recognized as a promising feedstock for biodiesel production. It is one of the species that yield biodiesel and it is a multipurpose non-edible oil-yielding perennial shrub2. Jatropha plant is resistant to drought and adapted to arid/semi arid conditions which characterized by high soil salinity, low fertility and limited supply of high quality water3,4. It is adapted to a wide range of climate and soil and can be grown successfully as an agro forestry crop on waste lands and marginal lands5. Jatropha curcas is a potent oil crop that contains 30-35% oil content by seed weight and 50-60% of the kernel weight6. Seed and oil yield in Jatropha are affected by several factors, including genetics7, age of the plant, field site characteristics, such as rainfall, soil type and fertility8 and agronomic practices, such as plant spacing, pruning, irrigation and fertilization9. Meanwhile, it is limited knowledge on water requirement, lack of organized breeding programs and limited agronomic practices for inadequate investments by developing and private agencies. Also, for high yield rate, it requires more supply of water and nutrition10,11.
Foliar application of nutrients is in general helpful to satisfy plant requirement and has a high efficiency12. Potassium (K) is an essential plant nutrient that plays a very important role in plant growth and development. Its role is well documented in photosynthesis, increasing enzyme activity, improving the synthesis of protein, carbohydrates and fats, translocation of photosynthetic, enabling their ability to resist pests and diseases. Also, potassium is considered a major osmotically active action of the plant cell13 where it enhances water uptake and root permeability and acts as a guard cell controller, beside its role in increasing water use efficiency14.
Application of potassium to trees is an attractive method, especially in arid zones where a lack of water under water stress conditions in summer drastically depresses absorption of soil nutrients15. Additionally, Hiller16 reported that, it has been established in various research studies that plant leaves and other above ground parts are capable of absorbing chemicals and nutrients by plants is not a function limited to the root system. Moreover, foliar nutrition is ideally designed to provide many nutrients to a crop that may be limiting production at a time when its uptake from the soil is inefficient or non-existent17. Thus, the advantages of this technique should be explored as the smaller fertilizer use lower cost, ease of application, good quality of fertilizer used and fertilizers readily soluble in water.
Therefore, the present investigation was carried out to study the effects of foliar spraying of potassium nitrate at different concentrations and times on leaves mineral contents and fruit and oil productivity and quality of Jatropha curcas trees grown under low quality soil and treated sewage water (Suez conditions).
MATERIALS AND METHODS
Plant material: This study was carried out during the two successive seasons of 2014 and 2015 in a private orchard of Jatropha curcas trees (4 years old) grown under Suez Government conditions, Egypt, to study the effect of foliar sprays of potassium form such as potassium nitrate (KNO3) at different concentrations and times on leave mineral contents, fruit yield, seed properties, seed oil content and its quality characteristics.
The selected Jatropha trees were uniform in vigor and size, planted at 2×4 m apart. All trees received the same horticultural practices in the orchard. The treatments were carried out by spraying the chosen trees with potassium nitrate (KNO3) at three different concentrations (0.5, 1.0 and 1.5%), while untreated trees (control) were sprayed with only water. Each treatment consists of three replicates and each replicate were two trees. All trees under the study were sprayed two times, first at full bloom (once) and second after fruit set (twice).
Water: Jatropha trees were irrigated by a drip irrigation system. Plot consisted of 14 lateral lines, 35 m long, 4 m between the rows and 2 m among trees with two drippers for each (dripper discharge 8 L h–1). Irrigation process was carried 3 days weekly with total amount ranged from 32-40 L day–1 tree–1. Experimental plots were irrigated by secondary treated sewage water (Table 1).
| Table 1: | Chemical characteristics of the investigated soil and water |
| Table 2: | Hydro-physical characteristics of the investigated soil |
Soil: The CaCO3 were determined18 and the organic matter was determined19 after soil water constants such as field capacity and wilting point were measured20 and available water was getting by subtracting. Soil and irrigation water analysis are given in Table 1 and 2. The following parameters were measured in both seasons.
Leaf mineral contents: At the end of each growing season during the first week of September, leaf samples were collected, washed and dried at 70°C until constant weight and then grounded for determining the following nutrient elements (Percentage as dry weight); N, P and K were determined according to AOAC21.
Number of inflorescence per shoot: During the peak flowering period (May-June), the number of inflorescence present in a shoot was counted.
Number of flowers per inflorescence: The inflorescences in each individual shoot were tagged just before their emergence and the total number of flowers per inflorescence were counted.
Number of fruits per inflorescence: During the peak fruiting period, total number of fruits per inflorescence present on each plant were counted and average fruits per inflorescence was calculated.
Fruit yield: At maturity stage of two seasons (mid October), fruits of each tree were separately harvested, then weighed and yield as kilogram per tree was estimated.
Seed characteristics: Thirty seed per each tree were randomly selected for carrying out the seed measurements as follow:
| • | Seed dimensions: Seed length and diameter (cm) |
| • | Seed parameters: 100 seed weight (g) and 100 seed volume (cm3) |
Seed oil content (%): The seeds were ground using mortar and pestle and 20 g of coarse seed powder was taken for oil extraction. Commonly used solvent extraction method in Soxhlet apparatus was applied, using petroleum ether (boiling point: 40-60°C) as solvent for extraction of the oil method according to De Pena et al.22.
Chemical analysis of oil: Determinations for peroxide, iodine and oil acidity were carried out using22, standard analytical methods.
Statistical analysis: All obtained data during both 2014 and 2015 experimental seasons were subjected to analysis of variances (ANOVA) according to Snedecor and Cochran23 using MSTAT program. Least Significant Difference (LSD) was used to compare between means of treatments according to Duncan24 at probability of 5%.
RESULTS AND DISCUSSION
Leaf mineral contents: Results in Fig. 1 revealed that, leaf mineral content of N, P and K were significantly increased by all spraying treatments as compared with control. As for nitrogen content in leaves, it was significantly affected by different spraying treatments. Foliar spraying of potassium nitrate at 1.5%, twice gave the highest value for average of both seasons of leave nitrogen content since it was 1.26 followed by using potassium nitrate at 1.5% once, which recorded (1.21). On the contrary, control treatment recorded the lowest value in this respect which gave (0.82). Regarding P content in leaves, results in Fig. 2 cleared that all spraying treatments improved P content in leaves as compared untreated trees. Foliar potassium nitrate at 1.5 and 1% once achieve the highest value since it was (0.30 and 0.29), respectively, followed by foliar spraying with potassium nitrate at 1 and 1.5% twice which gave (0.25 and 0.27), respectively. Meanwhile control treatment recorded the lowest one in this respect (0.19). Concerning leaves content of K, the results showed that K content in Jatropha leaves was significantly affected with different potassium spraying.
| Fig. 1: | Effect of foliar spraying by KNO3 at different rates on N, P and K of leaf content of Jatropha curcas trees. Values are the means of the two seasons. The letters represents LSD level according to Duncan24 (p≤0.05) |
| Fig. 2: | Effect of No. of foliar spraying by KNO3 on N, P and K the leaf content of Jatropha curcas trees. Values are the means of the two seasons. The letters represents LSD level according to Duncan24 (p≤0.05) |
| Fig. 3: | Number of fruit/inflorescence of Jatropha curcas trees treated with foliar spray of KNO3 at 0.5, 1.0 and 1.5% once and/or twice. Values are the means of the two seasons. The letters represents LSD level according to Duncan24 (p≤0.05) |
Foliar potassium at 1.5% twice registered the highest potassium content in leaves (0.79). Meanwhile, control treatment gave the lowest one in this respect since it was (0.45). In addition other treatments were in between ranges. Generally, spraying potassium nitrate twice was more effective than once sprays which registered the highest leaves N and K content in both seasons while spraying potassium nitrate once recorded the highest one concerning leaves P content.
Flowering properties: Data illustrated in Fig. 3-5 indicated that the effect of foliar sprays of potassium nitrate (KNO3) on flowering properties as well as a number of inflorescences per shoot, number of flowers per inflorescence and number of fruits per inflorescence. Obtained data revealed that the number of inflorescences per shoot at flowering stage was significantly influenced by different treatments as compared with control.
| Fig. 4: | Number of inflorescence of Jatropha curcas trees treated with foliar spray of KNO3 at 0.5, 1.0 and 1.5% once or twice. Values are the means of the two seasons. The letters represents LSD level according to Duncan24 (p≤0.05) |
| Fig. 5: | Number of flowers/inflorescence of Jatropha curcas trees treated with foliar spray of KNO3 at 0.5, 1.0 and 1.5% once or twice. Values are the means of two seasons. The letters represents LSD level according to Duncan24 (p≤0.05) |
Regarding number of fruits per inflorescence, data in Fig. 3 illustrated that all spraying treatments significantly increased the number of fruits per inflorescence as compared with control. Foliar sprays of potassium nitrate at 0.5% sprays once or 0.5 and 1.5 sprays twice recorded the highest number of fruits per inflorescence (17.33, 17.33 and 17.33), respectively. On the contrast, control treatment registered the lowest value in this respect since it was (11.67). Moreover, other treatments were in between ranges.
Figure 4 shows that, the maximum number of inflorescences per shoot was recorded by using of foliar potassium nitrate at 0.5% at once or twice sprays since it was (2.66 and 2.66), respectively. Meanwhile, the minimum number of inflorescence per shoot was found under control treatment which gave (1.33). Concerning the number of flowers per inflorescence according to the data illustrated in Fig. 5. It is cleared that total flowers per inflorescence were highly significantly affected by different application treatments of potassium as compared with control. Foliar sprays of potassium nitrate at 1% sprays twice recorded the highest value in this respect since it was (102.7). On the other contrary control treatment gave the lowest one in this respect (80.33).
Fruit yield and seed physical parameters: Data presented in Fig. 6 revealed that, fruit yield expressed as weight (kilogram per tree) was significantly increased in all different spraying treatments as compared with control. Untreated trees (control) had the lowest yield as (kilogram per tree) since it was 1.88 kilogram per tree. On the otherwise, trees received KNO3 at 0.5 or 1.5% twice sprays exhibited 2.95 and 2.96 kg, respectively, followed by potassium nitrate sprays at 1% once or twice which recorded 2.91 and 2.92 kg, respectively.
As for seed length and diameter (cm), it could be noticed from Fig. 7 that, seed length and diameter was significantly affected by different potassium nitrate application at both seasons under study. The highest significant value of seed length and diameter were found due to using potassium nitrate at 1.5% spraying once which recorded (2.20 and 2.12 cm) for seed length and diameter, respectively. On the otherwise, the obtained results indicated that untreated trees exhibited the lowest values in this respect since it was (2.05 and 1.98 cm) for seed length and width cm, respectively.
Figure 8 clearly showed that all different spraying treatments significantly increased the average of 100 seed weight (g) and volume (cm3) during both seasons of study.
| Fig. 6: | Fruit yield of Jatropha curcas trees treated with foliar spray of KNO3 at 0.5, 1.0 and 1.5% once or twice. Values are the means of the two seasons. The letters represents LSD level according to Duncan24 (p≤0.05) |
| Fig. 7: | Seed dimensions (Length and diameter) of Jatropha curcas trees treated with foliar spray of KNO3 at 0.5, 1.0 and 1.5% once or twice. Values are the means of two seasons. The letters represents LSD level according to Duncan24 (p≤0.05) |
| Fig. 8: | Seed parameters (weight and volume) of 100 seeds of Jatropha curcas trees treated with foliar spray of KNO3 at 0.5, 1.0 and 1.5% once and/or twice. Values are the means of the two seasons. The letters represents LSD level according to Duncan24 (p≤0.05) |
The highest average of two seasons for 100 seed weight was recorded by using foliar potassium nitrate at 1.5% sprays once since it was (49.06 g) followed by 1% sprays once or twice which recorded (45.23 and 45.25 g), respectively. On the other contrary, control treatment gave the lowest one in this respect (37.00 g). Meanwhile, other treatments showed the average values which were in between the previous range.
Concerning the average volume (cm3) of 100 seeds, data in Fig. 8 revealed that spraying potassium nitrate at 1 and 1.5 once and 1.5 twice recorded the highest 100 seed volume than other treatments which being (80.00, 80.12 and 82.33 cm3), respectively. Meanwhile, the lowest one in this respect (65.00 cm3) was obtained under control treatment.
| Fig. 9: | Seed oil content of Jatropha curcas trees treated with foliar spray of KNO3 at 0.5, 1.0 and 1.5% once or twice. Values are the means of the two seasons. The letters represents LSD level according to Duncan24 (p≤0.05) |
| Fig. 10: | Oil acid value of Jatropha curcas trees treated with foliar spray of KNO3 at 0.5, 1.0 and 1.5% once or twice. Values are the means of the twos seasons. The letters represents LSD level according to Duncan24 (p≤0.05) |
Seed oil content and chemical properties of oil seed: The physical and chemical characteristics of Jatropha seed oil can varied depends on environmental factors, genetics and the maturity of the seeds. The oil content of Jatropha seeds varied significantly after spraying treatment with different concentrations of potassium nitrate (Fig. 9). Different spraying treatments (once and twice) produced significantly higher seed oil content as compared to control. On the other side, spraying KNO3 twice showed an increase in the seed oil content compared to spraying once. The highest percentage of seed oil content was observed at potassium nitrate sprayed twice 1% (24.29%) followed by 1.5% sprayed once. Meanwhile, untreated trees (control) recorded the lowest percent (21.15) of oil content.
Chemical properties of seeds oil: The chemical properties of seed oil are the most important properties that described the present condition of the oil. The various number of test parameters like: Acid value, peroxide value and iodine value had been estimated. The acid value of Jatropha seeds oil which valuable measure of oil quality in Fig. 10 showed significant effect by different concentrations of potassium nitrate compared to control (untreated trees). The lowest oil acidity (6.23) recorded by 1.5% potassium nitrate spraying once followed by 1% ( 6.34) sprays twice. Untreated trees (control) clarified the highest percent of seed oil acid value (7.67).
Results are presented in Fig. 11 illustrated the effect of spraying potassium nitrate on oil quality as well as iodine value which measure the average amount of unsaturation of fats and oils. Spraying of different concentrations of potassium nitrate once showed a higher iodine value compared to spray twice. The highest iodine value which due to its high content of unsaturated fatty acids obtained by potassium nitrate 1% (102.6) have followed by 1.5% (101.6) then 0.5% (95.57) sprayed once.
The results in Fig. 12 showed that peroxide value of the Jatropha curcas seed oil affected with different concentrations of potassium nitrate compared to control. The lowest peroxide value obtained by 1.5% potassium nitrate (4.52) twice spray compared to untreated trees (control) which recorded the highest peroxide value (12.13).
| Fig. 11: | Oil peroxide value of Jatropha curcas trees treated with foliar spray of KNO3 at 0.5, 1.0 and 1.5% once or twice. Values are the means of the two seasons. The letters represents LSD level according to Duncan24 (p≤0.05) |
| Fig. 12: | Oil iodine value of Jatropha curcas trees treated with foliar spray of KKNO3 at 0.5, 1.0 and 1.5% once or twice. Values are the means of the two seasons. The letters represents LSD level according to Duncan24 (p≤0.05) |
DISCUSSION
The obtained results, regarding the influence of spraying potassium nitrate on leaf mineral content are in agreement with those obtained by El-Razek et al.25 found that spraying mango trees with sward (25% potassium) raised leaf mineral content of N, P and K. Furthermore, Taha et al.26 on mango tree showed that all different potassium forms applications had a positive effect on improve leave mineral content, also Hegazi et al.27 on picual olive trees cleared that sprayed potassium nitrate enhance nutritional status of trees. On the other hand, the improvement in leave mineral content under foliar potassium sprays due to shorten the time required for uptake compared to soil application28. In addition, Southwick et al.29 indicated that uptake of K from foliar spray may be more predictable and efficient than uptake from the soil. Also, foliar spray of KNO3 may be attributed to the best uptake of N, P, K and Ca. Concerning flowering, fruit set and yield the obtained results are in harmony with these of Montenegro et al.30, who found that fertilization of J. carcus plants with nitrogen and potassium at a dose of 150+120 kg ha–1 increased fruit and seed production by more than 90%, as compared with the unfertilized control. Moreover, Rojas et al.31 found that spraying of KNO3 at (6%) on mango trees during September-October significantly increased the percentage of flowering/shoots and the number of mixed panicle. Similar results was found with Rajput and Singh32 who noticed that spraying of KNO3 significantly increased the flowering percentage of mango.
Generally, potassium nitrate concentrations especially in combination with urea gave better results for most of the flowering and yield parameters of ‘Tommy Atkins’ mango33,34 is claimed that KNO3 at 4% had improved flowering and fruiting in mango. In addition, the results of the present investigation are in agreement with the findings of El-Fangary35, Mostafa and Saleh36 and Sarrwy et al.37 who found that spraying potassium using different forms had a positive effect yield as number or fruits weight of citrus trees. The highest flowering and fruit yield which was obtained by foliar spray of KNO3 may be attributed to the best uptake of N, P, K and Ca. There is no doubt that K, as important nutritional elements, plays its part in regulation of many physiological criteria in plant which in turn affect the resulted total yield. In addition, foliar potassium spray’s success in preventing the leaf contents of K and other mineral nutrients from declining to low levels during fruit set38,39.
| Fig. 13(a-d): | Regression equation between the main Jatropha characteristics and KNO3 at different concentration |
Regarding seed physical and chemical characteristics as well as (seed weight, volume, dimension and oil quantity and quality). The results of the investigation lend support to the findings of Inglese et al.12 who found that foliar application of KNO3, during the second and the third phase of olive growth improved the fresh weight and the flesh to pit ratio40,41 on olive trees reported that potassium fertilization improved yield and quality as well as fruit weight, flesh to pit ratio and oil content of olive fruit. In addition, Sarrwy et al.37 on citrus trees concluded that enhanced fruit physical and chemical characteristics were obtained by sprayed both KNO3 and KTS at 1.5% concentrations. The beneficial effects of potassium nitrate on fruit and oil quality may be attributed to their vital role in stimulating cell division and elongation as well as the biosynthesis and enhancing fruiting of trees42.
Moreover, potassium is an essential plant nutrient that plays avery important role in plant growth and development. Its role is well documented in photosynthesis, increasing enzyme activity, improving synthesis of protein, carbohydrates and fats. Also, potassium (K) is well recognized as the essential plant nutrient with the strongest influence on many quality parameters of fruits43. Although, K is not a constituent of any functional molecules or plant structures, it is involved in numerous biochemical and physiological processes vital to plant growth, yield and quality44, in addition to its role in stomatal regulation of transpiration45.
Furthermore, the increased of oil quantity and quality due to foliar sprayed potassium nitrate. It also has a relationship to synthesis of protein and fats, synthesis of chlorophyll, stimulation of adenosine triphosphate formation and photosynthesis, anabolism and metabolism of carbohydrates, translocation of photosynthetic. In addition potassium used to increase of lipids synthesis in oil crops. It also can contribute in action of approximately 60 enzymes.
Figure 13 illustrated the relation between spraying by KNO3 and oil content, acid value, peroxide value and iodine value. Positive regression equation was obtained between KNO3 concentration and both oil content and iodine value, where the oil content is significant at 5% level and with iodine value is not. While, acid value showed negative significant linear correlation with KNO3 concentration (Fig. 13). It is clear that negative correlation was obtained between KNO3 from side and peroxide value from the other one but this equation was polynomial one form the 3rd degree and get R2 significant at 1%. This finding could attributed to the concentration of KNO3 had not get good effect on the peroxide value more than 1% KNO3. Data was supported by getting simple correlation between KNO3 concentration from side and leaf content from N, P, K and flower characters flowers, number of flowers/inflorescences and number of fruit/inflorescences. Significantly correlation coefficient were obtained with value 0.961**, 0.967** and 0.985** for leaf content from N, P and K, respectively. While, r value were 0.865**, 0.570* and 0.624* for flowers, number of flowers/inflorescences and number of fruit/inflorescences, respectively.
CONCLUSION
In summary, the results of this study indicated that:
| • | All foliar application of potassium nitrate had a positive effect on increased Jatropha leaf mineral content and improved yield, seed physical and chemical properties as compared with control of Jatropha carcus trees grown under suez conditions |
| • | The best treatment to increase the number of flowers, fruits per inflorescences, seed weight and oil content was under spraying potassium nitrate at 1% once |
| • | Meanwhile, total seed yield and volume were obtained under spraying potassium nitrate at 1.5% twice |
SIGNIFICANCE STATEMENTS
| • | The objective of this study was to investigate the effects of foliar spraying of potassium nitrate at different concentrations and times for increasing the fruit and oil productivity and quality of Jatropha curcas trees |
| • | The methodology including treating Jatropha curcas trees with three concentrations (0.5, 1.0 and 1.5%) of KNO3 either pre and/or post bloom. Changes in leaf mineral content, flowering, fruit yield and seed oil content and their chemical characteristics were determined. Several oil properties as well as oil content, acid, peroxide and iodine values were measured too |
| • | The results showed that all foliar spraying with different potassium nitrate (KNO3) concentrations and times revealed a pronounced increase in leaf mineral contents |
| • | Foliar spraying of potassium nitrate 1% had the highest content of seed oil and its iodine value and leave mineral N, P and K. Meanwhile, good oil quality that had lowest oil acidity and peroxide value was observed with potassium nitrate concentration at 1.5% compared to untreated trees (control) |
| • | The potassium nitrate had a positive effect of leaf mineral content with improving fruit yield, seed physical and chemical properties with greatest results at 1% potassium nitrate sprayed once |
ACKNOWLEDGMENT
The researchers are grateful and express their deep thanks to those who have contributed to this study especially to National Research Centre who financed the project of "Plantation and Potential Applications of Jojoba and Jatropha Trees Under Sinai Peninsula Conditions" (Cod. No. 10060109).