EFFECT OF SEED SOAKING WITH A GROWTH REGULATOR (ATONIK) AND SEEDING DATES ON THE VEGETATIVE GROWTH CHARACTERISTICS OF SORGHUM BICOLOR L.

A field experiment was carried out during the spring and fall seasons of 2021 at Al-Hamidiya Research Station of the College of Agriculture, With the aim of studying the effect of soaking seeds with Atonik growth regulator and seeding dates on growth characteristics and plant nutrients content for three varieties of sorghum. A randomized complete block design with split-split plot arrangement was used with three replications. The main plot included seeding dates for both spring and fall seasons, while the sub-plot included the concentrations of the growth regulator (Atonk) which are 0, 2.5-and 5-ml L -1 , while the three varieties (Inqath, Lelu and Giza 113) were allocated to the sub-sub plots. The results showed the superiority of the cultivar Inqath in most of the studied traits such as leaf area, plant content of chlorophyll and plant content of potassium, phosphorous and nitrogen (4406, 3888 cm 2 and 58.36 59.17 spad) for both seasons, respectively. Whereas, Giza 113 cultivar outperformed in terms of plant height for both seasons. The plants which seeds soaked at a concentration of 5 ml L -1 also outperformed in all studied traits seeding date had a significant effects for both seasons. The interaction between the studied factors had a significant effect for most of the traits.


INTRODUCTION
Sorghum (Sorghum bicolor L.) is an important crop that is widely cultivated for the purpose of forage and grain production and ranks fifth in the world after wheat, rice, maize and barley in terms of economic importance (13).The global production of sorghum reached about 68.9 million tons for an area of 49.9 million hectares (14).In Iraq, the total production of sorghum during spring and fall seasons was 473.1 thousand tons, with an area of 128.8 thousand hectares (12).The application of the latest technology to predict future events of environmental changes, the world, at the beginning of the third millennium, is still unable to find solutions to meet the challenges of climate change, drought and the lack of water resources responsible for the deterioration of one-third of agricultural land and the problem of food deficit.It is expected in the coming decades to see more changes in temperature, and changes in the water levels of rivers and seas, The repercussions of the climate change problem in the arid and semiarid areas in which Iraq is located on food security became clear.Therefore, interest in managing the crop by improving its germination or shortening its growth cycle is among the important objectives to bring about a tangible increase in the quantity of the crop and improve its quality.Currently, developing countries contribute two-thirds of the world's cereal production through the successful management of drought-tolerant crops, which are the first line of defense against agroenvironmental changes.The Development of crop management systems, such as appropriate seeding dates and important nutrients, must be matched by the production of high-quality grains (7, 21).In terms of quantity and quality; the change of the growing season and the seeding dates limit the growth of certain varieties of sorghum in a very large way in their production areas, as most varieties of spring sorghum suffer from the deterioration of their germination and fall to the deterioration of their production as a result of the lack of water imports and the change in temperatures between the spring and fall seasons (8,18).The productivity cultivars it does not achieve the highest production unless ideal environmental conditions with, as choosing best date for seeding the optimal crop is no less important with the variety or nutrition, as well as determining the optimal date for the crop growth is the basis for the success of sorghum cultivation because it provides the ideal conditions for growth and yield, (8,11).To mitigate its effects, it requires the use of environmentally safe materials that contribute to improving the germination and growth of varieties, such as growth regulators (Atonik), leading to the completion of the seeds part of the metabolic processes during activation by soaking before sowing, which helps sorghum plants to withstand environmental stress conditions and enhance the plant's self-resistance.Experiments have proven that growth regulators play an important role in improving root growth characteristics (15,19).As well as preserving leaves from aging, as well as chlorophyll and preserving protein from decomposition and getting rid of free radicals in plant tissues exposed to stress (22) This study was aimed to investigate of seeds soaking with a growth regulator and seeding dates on the vegetative traits of sorghum .

MATERIALS AND METHODS
A field experiment was carried out during the spring and fall seasons of 2021 at Al-Hamidiya Research Station of the College of Agriculture within 43˚ east longitude, 33˚ north latitude, and 34.1 m above sea level, to study the response of three cultivars of sorghum to soaking with Atonik growth regulator and seeding dates in growth characteristics and plant nutrients content.A randomized complete plot design within a split-split plot arrangement was used with three replications.The main plots included seeding dates during spring (15/3, 1/4 and 15/4), whereas for (fall) seeding dates 1/7, 10/7 and 20/7.The sub-plots included three concentrations of Atonik nutrient solution (0 control, 2.5-, and 5-ml l -1 ), while the three varieties (Inqath, Lelu and Giza 113) were allocated to the sub-sub plot.The number of experimental units was 81, resulting from the all combination of the study factors.Field operations were carried out for the soil of the field, including plowing, smoothing and leveling, where the length of the row was 3 m, and the area of the experimental unit was (3 x 2.5 m) and included five rows, the distance between one line and another was 50 cm, and the distance between hills (plants) was 25 cm.The plant density is 80,000 plants ha -1 .The experiment land was fertilized with triple super phosphate fertilizer at a rate of 100 kg ha -1 P (46% P 2 O 5 ) at once upon leveling before seeding, Whereas, nitrogen fertilizer was added at a rate of 200 kg ha -1 in the form of urea (46% N) in three batches, the first at seeding, the second after three weeks, and the third at the beginning of head formation (17).After completing the field operations and preparing the experimental units, the seeds were soaked with the nutrient solution Atonik according to the aforementioned concentrations for a period of eight hours and planted according to the seeding dates under study, by placing three seeds in the hill and giving them a calm irrigation to ensure that the seeds do not drift, then the seedlings thinned after two weeks of emergence to one plant per hill.Crop service operations were carried out by irrigation and weeding as needed (20).

Statistical analysis
The data were statistically analyzed using the statistical program Genstat, by the method of analysis of variance according to randomized complete block design within split-split plot.The least significant difference (L.S.D) test used to compare the means at the probability level of 0.05 (9).

RESULTS AND DISCUSSION
Plant height : The results showed that the cultivars differed significantly in this trait, as the plants of the cultivar Giza 113 recorded the highest average of 279.2 and 286 cm for both spring and fall seasons, respectively (Table 1), it differed significantly from the other two cultivars (Inqath and Lilo), The reason of the differences cultivars in this trait is due to genetis cultivars in their genetic structure or the extent of their response to environmental conditions, and its reflection on the characteristics of vegetative growth.These results are in agreement with those found by Abood and Abduihameed (3) and Abood et al. (2).The results also indicate that soaking sorghum seeds with nutrient solution (Atonik) had a significant effects by increasing the average of this trait, As the plants soaked their seeds in the nutrient solution at a concentration of 5 ml L -1 had the highest average plant height of 194.7 and 211.2 cm for both seasons, respectively, compared with the (the control treatment), which recorded the lowest mean for plant height of 181.7 and 195.8 cm for the two seasons respectively.The reason could be attributed to the role of Atonik in the synthesis of tryptophan, which is the raw material for the manufacture of IAA necessary for cell elongation.This result is consistent with the findings of Borowski and Blamowski (10).The difference in seeding dates had a significant effect on plant height, as the plants grown in the late spring season (15/4) and early in the fall season (1/7) achieved the highest plant height average (196.8 and 216.4 cm) for both dates and seasons, respectively (Table 1).It is known that sorghum plants are plants of determinant growth type, so the reason for the difference in plant height under the influence of dates may be due to the difference in temperatures, photoperiod and relative humidity that led to the variation of plants of different dates and their response to environmental conditions and the reflection of this on this characteristic.This results agreed with the results of Kadhim (16) on maize and Ajaj et al. (5) on sorghum, who found a significant difference in plant height when seeding at different dates.The results also indicated that there was a significant interaction between seeding dates and Atonik concentrations in the spring season only, as plants of the late date and soaked in concentration 5 ml L -1 recorded the highest average plant height (206.1 cm).The results also showed a significant interaction between the cultivars and seeding dates for both seasons, as the Giza 113 plants planted on date 4 / 15 and 1/7 gave a higher mean plant height of 296.2 and 303.5 cm for both spring and fall seasons, respectively.The three-way interaction between the study factors was significant in plant height for the fall season only.Leaf area (cm 2 plant -1 ) The results indicate that the cultivars differed significantly in the average leaf area, as the plants of the cultivar Inqath recorded the highest mean of the leaf area amounted to 4406 and 3888 cm 2 for the spring and fall seasons, respectively).While plants of the two cultivars Lilo and Giza113 recorded the lowest average of 4248 and 3032 cm 2 for both cultivars and for the two seasons respectively (Table 2).The reason for the differences among in cultivars in this trait is due to the variation between cultivars in their genetic composition and length of vegetative growth.This result is in agreement with the results of Ahmad and Abood (4).Increasing the concentration of the nutrient solution (Atonik) for soaking the seeds led to a significant increase in the average leaf area compared to the control treatment for both seasons (Table 2).The highest mean of this trait was in plants whose seeds were soaked at a concentration of 5 ml L -1 with an average of 4442 and 3762 cm2 for the two seasons, respectively, which did not differ significantly with the treatment of 2.5 ml L -1 and it differed significantly with the control treatment.The results indicate that the seeding dates differed significantly in the average leaf area of the two seasons (Table 2), as the plants grown in the second date 1/4 of spring season and 10/7 of the fall season outperformed by giving their plants the highest leaf area of 4471 and 3794 cm 2 respectively.While the plants of the first date (15/3) for the spring season and the last date (20/7) for the fall season recorded the lowest average of 3245 and 3346 cm 2 respectively and that may be due to the appropriate environmental conditions for the stages of growth when seeding on dates that outperformed the characteristic of leaf area, which was positively reflected on the characteristics of vegetative growth of the plant, including leaf area.These results are in agreement with the results of Ajaj et al. (5), who indicated that the leaf area varies according to the seeding dates.
The results also indicated that there were significant differences for this trait due to the effect of the interaction between seeding dates and Atonik concentrations in the fall season only.The plants seeded on 1/7 with seeds soaking at a concentration of 5 ml L -1 recorded the highest average of 3980 cm 2 .The results indicate that the sorghum cultivars under were significantly different in this trait, as the plants of the cultivar Inqath outperformed with the highest mean for the trait that reached 58.36 and 59.17 spad for both spring and fall seasons, respectively (Table 3).While the Giza 113 plants recorded the lowest average of 50.99 and 58.25 Spad for both seasons, respectively.This difference could be due to the cultivar differences in their genetic structure, this result is in agreement with the results of Abood et al and Abood and Salh (1).The results indicated that the chlorophyll content of the leaves increased significantly with the increasing of the concentration of the Atonik solution , as the concentration of 5 ml L -1 had the highest mean for the character 58.68 and 60.33 Spad for both seasons respectively and did not differed significantly from the treatment of 2.5 ml L -1 in the fall season.respectively.Perhaps the reason for the increase in the content of chlorophyll in the leaves by increasing the content of the nutrient solution is due to the role of this substance in increasing the activity of the photosynthesis process and the absorption of nutrients such as nitrogen, which is the basic building block of amino acids.seeding dates had a significant effect on the chlorophyll index for the spring and fall seasons, as the plants planted on  The results indicate that sorghum cultivars differed significantly in their potassium content in leaves for both spring and fall seasons (Table 4).The cultivar Inqath had the highest average of the potassium content of leaves for the spring and fall seasons, which was 1.68 and 1.70 %, respectively, it differed significantly from Giza 113, which recorded the lowest mean for this trait (1.67 and 1.65 %) respectively.The potassium percentage in the leaves increased significantly with an increase in the Atonik concentrations of a solution, the highest concentration of 5 ml L -1 outperformed for both seasons with 1.69 and 1.71% for the two seasons respectively.While the control treatment recorded the lowest average.The results also showed that seeding dates differed significantly in potassium content in sorghum leaves for the fall season, the third date (20/7) recorded the highest average of potassium in leaves (1.71%), while the first date (1/7) recorded the lowest average for the trait (1.64%).The results showed that the interaction between seeding dates and Atonik solution concentrations had a significant effect on this trait for both spring and fall seasons (Table 4).Where the treatment of seeds soaked with 5 ml L -1 and planted on the second date 1 / 4 for the spring seeding and the first date 1/7 for the fall seeding recorded the highest average of 1.71 and 1.74% respectively.. The results indicated the effect of the three-way interaction between the study factors in the spring season, where the plants of the cultivar Inqath of their seeds soaked with 5 ml L -1 and planted on the second date 1/4 recorded the highest percentage of potassium in the leaves of 1.79% for the spring season, while the plants of the cultivar Giza 113 soaked its seeds with distilled water only and planted on the first date 15/3 recorded lowest average for the trait of 1.55%.The results indicate that sorghum cultivars differed significantly in their phosphorous content in leaves for both spring and fall seasons (Table 5).The cultivar Inqath gave the highest average of the phosphorous content of leaves for the spring and fall seasons, which was 0.50 and 0.47 %, respectively, it differed significantly from the other cultivars, as the cultivar Giza 113 for the two seasons recorded the lowest average for this trait (0.43 and 0.44) %, respectively.These results are in agreement with the results of Al-Fahdawi (6).The percentage of phosphorous in the leaves increased significantly with an increases in the Atonik concentrations of a solution, the highest concentration of 5 ml L -1 outperformed for both seasons with 0.47 and 0.48% respectively, which did not differed significantly with plants whose seeds were soaked with 2.5 ml L -1 .Whereas, The results also showed that the seeding dates had a significant effect on the phosphorous content of the sorghum leaves for the fall seeding, as the second and third dates (10/7 and 20/7) for the fall seeding scored the highest average for leaves Nitrogen content(%): The averages of nitrogen content in leaves differed significantly by increasing the concentrations of soaking seeds with Atonik, as the concentration of 5 ml L -1 gave the highest mean (2.57 and 2.44%) for spring and fall seasons, respectively (Table 6).While the control treatment recorded the lowest mean of 2.25 and 2.16% for the spring and fall seasons, respectively.The results showed that seeding dates had a significant effect on nitrogen content in leaves for the fall season only, as the second date 10/7 was significantly superiored in the nitrogen content in plant leaves, and recorded the highest average of 2.33%, while the first date 1/7 recorded the lowest average of 2.28%.The results also showed that the interaction between seeding dates and Atonik solution concentrations was significant for both seasons.The plants planted on 15/3 and 1/7 for both seasons of spring and fall and their seeds soaked with 5 ml L -1 recorded the highest average of nitrogen in leaves 2.63 and 2.53% for the two seasons respectively, while the plants planted at the same time and soaked with distilled water only recorded the lowest average of 2.25 and 2.00% for the two seasons, respectively.The results also showed that the interaction between seeding dates and cultivars for the spring and fall seasons was significant, as the cultivar Inqath planted on 1/4 and 10/7 in the spring and fall seasons outperformed with the highest average of 2.92 and 2.49% for the two seasons, respectively.While the second date (15/4) for the spring season and the first date (1/7) for the fall season of Giza 113 plants recorded the lowest average ( 2.25 and 2.19%) for both seasons, respectively.The interaction between the concentrations of Atonik solution and the cultivars was significant for the spring season only.The cultivar Inqath and its seeds soaked with a concentration of 5 ml L -1 of Atonik solution recorded the highest average of 3.17%, while the plants of the Giza cultivar soaked with distilled water (the control treatment) recorded the lowest mean of 2.23%.The three-way interaction between the study factors was significant (Table 6), The plants grown on the first date 15/3 in the spring season and the first date 1/7 in the fall season for the cultivar Inqath and their seeds soaked with 5 ml liter -1 recorded the highest average nitrogen content in leaves, which was 3.33 and 2.98% for the two seasons, respectively.While the Giza 113 plants, planted on dates 15/3 and 1/7 for both spring and fall seasons, and their seeds treated with distilled water only, recorded the lowest average of 2.22 and 2.00% respectively.