Sustainable approach for seed stimulating and sowing date to enhance field emergence and growth of sorghum (Sorghum bicolor L. Moench)

Sorghum cultivation is often accompanied by low field emergence rates and weak seedlings, which may be due to genetic or environmental stress. A factorial experiment was conducted in the spring and fall seasons of 2022 using a randomized complete block design with split-plot arrangement and four replications. Planting dates (spring season: Feb. 15th, Mar. 1st, 15th, and Apr. 1st, 15th; fall season: Jun. 15th, Jul. 1st, 15th, and Aug. 1st, 15th) were allocated to the main plots. Seeds stimulation treatments (35% banana peel extract + 100 mg L−1 citric acid and distilled water soaking treatment only) were allocated to the subplots. The interaction treatment (banana peel extract + citric acid) with the planting date of April 15 showed the highest field emergence (74.2%), 75% flowering (86.0 day), plant height (163.9 cm), and days to physiological and complete maturity (111.0 and 131.0 day), respectively. The banana peel extract + citric acid soaking treatment with the planting date of July 1st showed the highest field emergence (91.3%), plant height (185.1 cm), leaf area index (7.6), and dry weight per plant (398.8 g). It can be concluded that the seeds primed with banana peel extract + citric acid before planting improved growth characteristics and could be a solution to environmental challenges, which also promote the concept of sustainable agriculture. It can be recommended seeds soaking with a combination of banana peel extract and citric acid to enhance emergence and growth when planting in April 15th for the spring season and July 1st for the fall season.


Introduction
Low field emergence leads to weak growth.Seed priming is used to improve crop performance under a wide range of environmental conditions such as temperature or soil salinity [1,2,3,4], leading to good field 1325 (2024) 012012 IOP Publishing doi:10.1088/1755-1315/1325/1/012012 2 establishment by increasing field emergence rate, improving seedling growth, reducing the time to emergence, and increasing uniformity [5,6,7,8].Exposing seeds to priming treatments makes them have rapid emergence when re-imbibed under normal growth conditions or exposed to different types of stress [9,10,11,12].Seed vigour and the ability of resulting plants to grow under biotic and abiotic stresses have been improved by soaking seeds in various nutrient solutions [13,14,15].Seeds are primed by soaking them in natural or manufactured solutions to tolerate stress, increase germination rate, field emergence rate, improve seedling competitiveness, uniformity of seedling emergence and growth, and harvest the crop at the same time [16,17,18,19].Germination and seedling growth indicators can be improved in a wide range of environmental conditions when seeds are soaked in licorice extract, potassium nitrate, or both, in addition to using licorice extract as an alternative to gibberellin to stimulate germination [20].
The presence of high levels of potassium and growth stimulants, as well as amino acids such as Ltryptophan, has shown significant effects on various biological characteristics of plants, including a high seed germination rate.Banana peels have demonstrated substantial effects in this regard [21,22,23].As for citric acid, it is a water-soluble organic acid and one of the most important non-enzymatic antioxidants.It plays a role in mitigating and enhancing plant tolerance to environmental stress, stimulating photosynthetic processes, generating energy compounds for plants, and increasing carbohydrate synthesis and accumulation.Treating maize seeds with citric acid at a concentration of 100 mg L -1 effectively improved the percentage of field emergence compared to soaking with ascorbic acid and distilled water treatment [18,19].
Early planting in the spring leads to short plant height due to low temperatures, which generally reduces growth.However, late planting in the fall means that crop maturity coincides with the time of rainfall.A study concluded that seeds vigour was associated with the planting date.And the seeds resulting from the planting date in July 15 th had higher vigour compared to the seeds produced from the two planting dates in 15 th of June or August, and excelled in vitality and vigour tests of seeds and growth traits during the spring and fall seasons [24].The vitality and vigor of the seeds are related to the activity level of the enzyme system and the metabolic processes in the seeds before and during its initiation of germination or field emergence, which is reflected in the stages of growth and subsequent phenotypic and physiological changes.Temperature, relative humidity, and length of photoperiod affect the vitality and vigour of the seeds and the formation and growth of the plant, which are indirectly related to the appropriate date for planting [25,26,27,28,29].The study aimed to improve field emergence and growth by priming the seeds before planting at different dates.And using environmentally approachable agricultural practices that promote the concept of sustainable agriculture.

Materials and Methods
A field experiment was conducted in the fields of the Directorate of Horticulture, Ministry of Agriculture, in the spring season and in the fields of the College of Agricultural Engineering Sciences, University of Baghdad, in the fall season in 2022.A randomize complete block design with split-plot arrangement was applied with four replications.The first factor was soaking of seeds before planting (100 mg L -1 citric acid + 35% aqueous banana peel extract in addition to distilled water soaking treatment only).The second factor was five planting dates in the spring season (Feb.15 th ; Mar. 1 st , 15 th and Apr. 1 st , 15 th ) and in the fall season (Jun.15 th ; Jul. 1 st , 15 th and Aug. 1 st , 15 th ).The main and sub-plots were occupied by treatments of planting dates and seeds soaking, respectively, randomly.Data and simple correlation coefficient were statistically analyzed.Means were compared by using least significant difference test (LSD) at 5% probability level [30].The statistical program Genstat was used.Note: Only, soaking seeds in distilled water before planting in February 15 th gave no data for all traits.
The aqueous banana peel extract was prepared by cutting the banana peels after washing them thoroughly with distilled water into pieces (3×3 cm) and soaking 100 g of them in a liter of distilled water for 7 days at room temperature, taking care to open the bottle cap once a day to remove the accumulated gases in the bottle.The transformation of the transparent yellow liquid into a dark color begins with the continuation of the reaction and then it turns into an opaque black liquid or the float of the banana peels and the liquid settles at the bottom or the appearance of a sweet and sour smell of the liquid, which is an indicator of the completion of the decomposition [31].Then, liquid filtered using a filter paper with a diameter of (150 ml) and a Büchner funnel.The volume of the aqueous extract reached 900 ml and the volume was completed to 1000 ml with distilled water to obtain a concentration of 10% of the extract.The required concentrations were prepared by taking (15, 25, and 35) ml of the aqueous extract and completing the volume to 100 ml distilled water.It was stored in the refrigerator at a temperature of 5°C until use.Citric acid concentrations (C 6 H 8 O 7 , molecular weight 192.12, purity 99% from Avonchem) were prepared by dissolving the acid in water to prepare the required concentrations.The seeds soaking period was 12 hours [15] at room temperature on paper towels in Petri dishes.

Soil preparation and planting
The soil was well-plowed and leveled, and the subplots (4 m long × 3 m wide) were divided into five rows with a spacing of 70 cm between the rows and 10 cm between the holes.The distance between each main plot and the next was 1 m, and between each replication and the next was 1.5 m.A total of 436 kg ha-1 of DAP fertilizer (46% N and 18% P) was applied in one application.A total of 696 kg ha -1 of urea fertilizer was applied in two applications, the first one was at planting and the second one at 40 days after planting [32].The fertilizer was applied by side-dressing 10 cm from the planting row.The seeds of Inqath cultivar were used, which is an improved cultivar that was approved in 2002 by the Agricultural Research Directorate, Ministry of Agriculture.It is suitable for cultivation in both the spring and fall seasons in central and southern Iraq.Three seeds were planted in each hole at a depth of 3 cm.After emergence, the seedlings were thinned to one plant per hole, resulting in a plant density of 142857 plants ha-1.Weeds were manually controlled as needed.Grainy diazinon (10%) insecticide was used to control the stalk borer at a rate of 6 kg ha-1.The insecticide was applied to the growing tip of the plant twice, once as a preventive control at the 4-5 leaf stage, and the second time 15 days after the first treatment.

Traits studied 2.2.1 Field emergence ratio
450 seeds were sown per treatment in four replications.Seedlings emerging up the soil surface were counted since first irrigation till 15 and 10 days for the spring and fall seasons, respectively.

Days to 75% flowering (day)
Days from date of first irrigation until 75% flowering of plants were recorded.

Plant height (cm)
The height of ten randomly taken plants was measured from the midlines of each experimental unit, starting from the soil surface to the apex after flowering was completed.

Leaf area index
It was calculated by dividing the leaf area of the plant by the land area it occupies, for an average of five plants.

Days to physiological maturity (day)
Days from date of first irrigation until physiological maturity were recorded.Plants reach this stage when the black layer forms at the base of the seeds.The grain moisture content ranges between 25-40%.

Dry weight per plant (g) after harvest
It was weighted when plants reached the stage of maturity, as 5 plants from midlines were cut randomly from soil surface, and placed inside a perforated paper bag in an electric oven at a temperature of 70 °C for a period of (2-4) days until the weight stabilized.

Field emergence percentage (%)
Seeds soaked in banana peel extract + citric acid outperformed seeds soaked in distilled water only in both seasons (Table 1).The reason for this may be the organic acids found in banana peel extract [23].It's activated the process of energy conversion in living cells and provide the energy needed for germination.Organic acids also promote root growth and increase nutrient absorption efficiency from the soil, which helps to stimulate plant growth.Banana peel extract is rich in potassium and growth promoters essential for plant growth [34], and citric acid is one of the most important organic acids in the respiratory pathways of plant cells and is also essential for various biochemical and physiological processes [35].And germination rate increased by up to 50% in field crops when citric acid was used to soak seeds as a preplanting treatment [36].
The planting date of April 15 th outperformed all other dates significantly with 72.4% emergence rate.The planting date of March 1 st gave the lowest percentage of field emergence, which was 14.9% in the spring season.The superiority of the planting date of April 15 th may be due to the favorable climatic conditions, as the average temperature during that period was (20.96°C) (Table 2).Climatic factors such as humidity, temperature, and carbon dioxide have variable effects on soil processes and their various characteristics related to soil fertility and productivity.Seed germination depends primarily on soil temperature, which may be rapid and reduce seeds loss, or the opposite may occur, depending on the rise or fall of soil temperature.However, high humidity coinciding with low temperature at the germination stage increases the activity of living organisms that attack the seeds and leads to the failure of its germination [37].
The interaction between either treatment of seeds soaked in banana peel extract + citric acid or treatment of soaking in distilled water only and planting date of April 15 th outperformed all other interactions with the highest average (74.2 and 70.6%), which did not differ significantly from each other.On the other hand, the interaction between seeds soaked in distilled water and planting date of February 15 th gave the lowest percentage of field emergence in the spring season.
Planting date of June 15 th outperformed most dates significantly and gave the highest average of 84.6%, which did not differ significantly from dates of July 1 st and 15 th compared to date of August 15 th which gave the lowest average of 66.8%.The reason may be due to the suitability of temperatures during the field emergence period, as their average ranged from (33.26°C), (34.35°C), and (34.70°C) for dates of June 15 th , July 1 st and 15 th , respectively (Table 2).

Days to 75% flowering (day)
Soaking seeds in distilled water reduced the time to reach 75% flowering, while soaking seeds in 35% banana peel extract + 100 mg L -1 citric acid increased the time in the spring season.The results were reversed in the fall season (Table 3).The variation in the results between the two seasons is due to the failure of germination in the distilled water treatment at the planting date of February 15 th .The positive role of the stimulation process can be observed in this regard.The reason for this may be that the stimulation treatments are rich in growth promoters such as proteins, essential amino acids, and polyunsaturated fatty acids.It has an effect on the biological aspects of the plant [38] and the role of citric acid in improving the nutritional status of the plant, and then improves growth traits [39].And may be that soaking treatment with citric acid affects the root to a greater extent than other parts, which affects the absorption and transport of nutrients from the soil, and this improves plant growth.Significant differences were observed between all planting dates in the spring season, with the planting date of April 15 th giving the shortest duration, while the longest duration was for the planting date of March 1 st .The reason for this may be the climatic diversity, characterized by the rise and fall of temperatures, light intensity, and the length and shortness of the photoperiod.This, in turn, has a major impact on the duration required from planting until flowering.The average temperature during that period was between 20.72°C for the February 15 th planting date and 21.38°C for the March 1 st planting date (Table 2).
The seeds soaked in banana peel extract + citric acid and planted on February 15 th gave the highest interaction value of 130.0 days.
The planting date of July 15 th required fewer days to reach 75% flowering (64.5 day), while the planting date of August 15 th required more days to reach 75% flowering (85.1 day).The reason for the early flowering of the plants planted on July 15 th is the high temperature and the long photoperiod, which had an average temperature of (36.35°C) (Table 2).High temperature accelerates the flowering of plants, while low temperature affects the disruption of physiological processes such as the water system, mineral nutrition, photosynthesis, and respiration in the plant.
The results showed that the seeds soaked in the best treatment and planted on July 15 th required fewer days to reach 75% flowering, with an average of 62.0 day.Compared to seeds soaked in distilled water and planted on August 15 th with an average of 86.0 day.The reason for the superiority of the stimulation treatment is that banana peel contains a group of important elements, including phosphorus, calcium, and magnesium.These elements are important for building healthy roots and shoots, strengthening stems, producing flowers and fruits, and supporting proper photosynthesis.This reflects a healthy growth of the plant from all aspects.Soaking in citric acid enhances the activity of antioxidant enzymes and has a role in protecting cell membranes.This leads to improving the ability of seedlings to resist environmental stress and maintaining the functional activity of many major metabolic enzymes [40].The seeds soaked in banana peel extract + citric acid outperformed the seeds soaked in distilled water in both seasons (Table 4).This may be due to the high content of natural phenolic compounds in banana peel extract, including antioxidants such as vitamins, flavonoids, and nutrients, as well as the effect of tryptophan, which increases hormone levels and then stimulates cell division [41,42].Citric acid acts as a substitute for phosphorus fertilizer, which enhances root and plant growth [43].
The planting date of April 15 th had the highest average height of 163.9 cm, which was not significantly different from the planting date of April 1 st , which had a mean of 161.7 cm.The lowest average was for the planting date of March 1 st .The reason for this is the suitability of the climatic conditions, which helped to improve the efficiency of photosynthesis and then increase the efficiency of plant dry weight, which helped to increase plant height.The average temperature during that period was 35.67°C (Table 2).
The interaction between banana peel extract + citric acid + planting date of April 15 th had the highest values (163.9 cm).The outperformed treatment did not differ significantly from the treatment of soaking seeds in distilled water + April 15 th , which had an average of 162.5 cm, and the planting date of April 1 st , which had an average of 162.4 cm.
The planting date of August 1 st had the highest plant height of 177.1 cm, which was not significantly different from the planting dates of July 1 st and August 15 th , which had an average of 176.1 and 176.0 cm.The reason for this may be the suitability of the environmental conditions that prevailed during the planting date.The plant was able to spend most of its life within appropriate temperatures, moderate humidity, and appropriate photoperiod, which helped to divide and elongate the stem cells.This is in contrast to the planting date of June 15 th , which had the lowest average, which is supported by the average temperature of 34.55°C.The treatment of soaking seeds in banana peel extract + citric acid and planted on July 1 st had an average height of 185.1 cm, compared to the treatment of soaking seeds in distilled water + June 15 th , which had the lowest value of 162.6 cm.

Leaf area index
The seeds soaked in banana peel extract + citric acid outperformed the seeds soaked in distilled water only in both seasons (Table 5).The third planting date, March 15 th , had the highest average (7.5), and the lowest average was for the planting date of April 1 st .The reason for the superiority of the stimulation treatments and the planting date is the superiority of the treatments and the same date in leaf area.The factors that increase LAI are the length of time that the leaf area remains effective, in addition to increasing leaf area.Photosynthetic efficiency is high at low light levels, as it receives a sufficient amount of light to achieve reasonable rates of photosynthesis, rather than receiving large amounts of light that it cannot extract effectively due to photo saturation [44].
As for the interaction treatment between banana peel extract + citric acid and planted on February 15 th , it gave the highest value (7.7) and did not differ significantly from several other treatments.
The planting date of July 1 st was significantly superior in LAI, which reached 7.0, compared to the planting date of August 1 st , which gave the lowest average (4.2) (Table 5).The interaction between the seeds soaked in banana peel extract + citric acid and planted on July 1 st was significantly superior (7.6).The lowest average was at the interaction between the seeds soaked in distilled water and planted on August 1 st , with an average of 3.5.This may be due to the superiority in the trait of plant height, effective leaf area, and photosynthetic efficiency, which had a positive effect on increasing dry weight of the plant and thus increasing the growth rate of the crop.

Days to physiological maturity (day)
Soaking in distilled water gave a shorter time to reach the physiological maturity stage compared to the treatment of soaking seeds in banana peel extract + citric acid in the spring season.The results were opposite in the fall season (Table 6).The reason for the difference in results between the two seasons may be due to the failure of germination when treating the distilled water soak and planted on February 15 th .This confirms the role of banana peel extract + citric acid in the process of seeds stimulation.The sowing date of March 1 st gave the highest average of 147.4 day, while the date of April 15 th gave the lowest rate of 112.5 day.The combination of soaking seeds in banana peel extract + citric acid and the sowing date of February 15 th gave the highest value of interaction of 149.8 day.This may be due to the suitability of environmental conditions at that time, as the average temperature during that period was (25.10 °C) (Table 2).
The sowing date of July 15 th arrived at physiological maturity earlier by an average of (81.6 day), unlike the date of August 15 th which was delayed by an average of (122.4 day).The reason for the superiority of the sowing date of July 15 th may be due to the high temperature, which made the plant complete its life cycle in a short growth period, as the average temperature during that period was (33.08 °C) (Table 2).Late planting encourages flowering and early maturity due to the short photoperiod compared to early planting, in which the photoperiod has not reached the critical threshold that encourages flowering [45], and those seeds soaked in banana peel extract + citric acid and planted on July 15 th arrived at physiological maturity earlier by an average of (77.3 day) compared to seeds soaked in distilled water and planted on the August 15 th , with an average of 124.0 day.

Days to full maturity (day)
Seeds soaked in banana peel extract + citric acid gave the highest average of (155.4 day) compared to the treatment of stimulation with distilled water, which reached (122.7 day) for the spring season.In the fall season, the results were reversed by the effect of the two soaking treatments, as the treatment of stimulation with banana peel extract + citric acid needed a shorter time to reach full maturity (Table 7).This is because the treatment of soaking in distilled water and planted on February 15 th had zero germination rate, which had a major impact on the difference between the rates of soaking in banana peel extract and citric acid.The date of March 1 st exceeded by giving the highest value to reach full maturity with an average of 167.4 day, while the date of April 15 th gave the lowest average of 132.5 day.
A significant interaction was found between the combination of soaking in banana peel extract + citric acid and the sowing date of February 15 th , and it gave the highest rate to reach full maturity (169.8 day).The reason for the superiority is that the stimulation treatments and sowing dates are the same treatments that are superior at days to physiological maturity (Table 6).This is reinforced by the positive significant correlation between full maturity and the days to physiological maturity, as the correlation coefficient reached (0.999) (Table 8).
The sowing date of July 15 th exceeded with an average of 103.1 day, while the date of August 15 th achieved an average of 151.9 day.This is due to the superiority of the same date at days to physiological maturity (Table 6).And the seeds soaked in banana peel extract + citric acid which were planted on July 15 th took fewer days to reach the full maturity stage with an average of (99.3 day) compared to the seeds soaked in distilled water which were planted on August 15 th with an average of (153.8 day).

Dry weight per plant (g) after harvest
The seeds soaked in banana peel extract + citric acid (211.04 g plant -1 ) exceeded the seeds soaked in distilled water (179.73g) (Table 9).The sowing date of April 15 th outperformed with the highest average (238.46g) compared to the dates of March 1 st and 15 th .The reason is due to the superiority of the same date in the trait of plant height, Table (4).This is reinforced by the value of the significant correlation between dry weight per plant and plant height, as the correlation coefficient value reached (0.991), Table (8).
The seeds soaked in distilled water which were planted on April 15 th exceeded and gave (245.62 g).Perhaps the reason may be due to an increase in stem diameter.The treatment of soaking in banana peel extract + citric acid and planted on July 1 st gave the highest average of 398.8 g, while the seeds soaked in distilled water and planted on July 1 st gave the lowest average of 245.8 g.This may be due to the superiority of the same interaction treatment in the trait of leaf area index, Table (5).This is reinforced by the positive significant correlation between the traits, as the correlation coefficient reached (0.285), Table (8).9) and days to full maturity (Table 7), which have a positive relationship with this trait.This is reinforced by the value of the positive significant correlation between crop growth rate and plant dry weight and days to full maturity (0.947 and 0.862) respectively (Table 8).Only, soaking seeds in distilled water before planting in February 15 th gave no data for all traits.The sowing date of the July 1 st outperformed with 42.09 g m -2 day -1 , while the August 15 th gave the lowest average (26.43 g m -2 day -1 ) in the fall season (Fig 4).The treatment of soaking seeds in banana peel extract + citric acid which was planted on the July 1 st exceeded by an average of 52.52 g m -2 day -1 compared to the seeds soaked in banana peel extract + citric acid which was planted on the August 15 th , which gave an average of 25.43 g m -2 day -1 (Fig 5).The reason for the difference in plant growth rate may be due to the effect of the sowing date on crop growth processes as a result of providing the appropriate environmental conditions of temperature, light, etc., which are reflected in the efficiency of the photosynthesis process, and thus the production of effective vegetative parts that end with an increase in plant dry weight.There is a positive significant correlation between the trait of crop growth rate and leaf area index and plant dry weight, with a correlation coefficient of (0.411 and 0.866) respectively (Table 8).

Conclusions
The results showed the possibility of using environmentally approachable agricultural practices that promote the concept of sustainable agriculture, and this would contribute to enhancing food security, especially if these practices were transformed into a solution to environmental challenges.The seeds stimulated with banana peel extract and citric acid responded to sowing dates to a higher extent than seeds stimulated in distilled water only, indicating that seeds stimulation may have improved plant growth under a wide environmental range.It can be recommended that using of banana peel extract with citric acid as alternative materials to growth regulators increases the stimulation of seeds with poor germination such as sorghum seeds.And to adopt the date of planting on April 15 th when planting in the spring season and the date of July 1 st when planting in the fall season.
1) W1 = Dry weight of the first sample.W2 = Dry weight of the next sample (harvest stage).T1 = Time of the first dry weight sample.T2 = Time of the next dry weight sample.SA = Area occupied by the plant.

Table 1 .
Effect of seeds stimulation with banana peel extract and citric acid, planting date and their interaction on field emergence ratio (%) in sorghum LSD 0.05 , Least significant difference test at probability level of 0.05; N.S: Non-significant at P≤0.05

Table 2 .
Temperature data for the spring and fall seasons.

Table 3 .
Effect of seeds stimulation with banana peel extract and citric acid, planting date and their interaction on days to 75% flowering (day)

Spring season 2022 Fall season 2022 Planting date Seeds stimulation
LSD 0.05 , Least significant difference test at probability level of 0.05

Table 4 .
Effect of seeds stimulation with banana peel extract and citric acid, planting date and their interaction on plant height (cm) in sorghum Spring

Table 5 .
Effect of seeds stimulation with banana peel extract and citric acid, planting date and their interaction on leaf area index in sorghum LSD 0.05 , Least significant difference test at probability level of 0.05

Table 6 .
Effect of seeds stimulation with banana peel extract and citric acid, planting date and their interaction on days to physiological maturity (day) in sorghum LSD 0.05 , Least significant difference test at probability level of 0.05

Table 7 .
Effect of seeds stimulation with banana peel extract and citric acid, planting date and their interaction on days to full maturity (day) in sorghum

Table 8 .
Simple correlation coefficient between traits studied in sorghum in the spring and fall seasons 2022 : significant at 0.05, the upper and lower values represent the spring and the fall seasons, respectively. *

Table 9 .
Effect of seeds stimulation with banana peel extract and citric acid, planting date and their interaction on dry weight per plant (g) after harvest in sorghum The treatment of soaking in banana peel extract + citric acid significantly exceeded this trait compared to the treatment of soaking in distilled water in both seasons (Fig1).The sowing date of April 15 th outperformed with 27.55 g m -2 day -1 , while the sowing date of March 1 st gave the lowest average (19.44 g m -2 day -1 ) in the spring season (Fig2).The combination of soaking seeds in distilled water and the sowing date of April 15 th gave the highest value of the interaction, reaching 28.07 g m -2 day -1 (Fig3), due to the superiority of the combination of soaking seeds in distilled water + sowing date of April 15 th at plant dry weight (Table LSD 0.05 , Least significant difference test at probability level of 0.05; N.S: Non-significant at P≤0.053.8.Crop growth rate (g m-2 day-1)