Key findings:

The study found that using 6 g/L of humic acid and nitrogen individually or in combination produced the highest number of fruits, fruit weight, size, total soluble solids, and vitamin C content, indicating the optimal conditions for enhancing chickpea fruit yield and quality.

What is known and what is new?

Humic acid and nitrogen are essential for improving plant growth and yield. Previous studies have shown that both humic acid and nitrogen positively affect various quantitative and qualitative traits in different crops. This study specifically demonstrates the effects of different concentrations of humic acid and nitrogen on the yield and quality of chickpea fruits (Fragaria x ananassa Duch.). It reveals that the highest concentrations of humic acid (6 g/L) and nitrogen (6 g/L) individually and in combination significantly enhance fruit number, weight, size, total soluble solids, and vitamin C content.

What is the implication, and what should change now?

The study's findings suggest that applying higher concentrations of humic acid and nitrogen can significantly improve the yield and quality of chickpea fruits. This knowledge can help farmers and horticulturists enhance their chickpea production, leading to better crop performance and potentially higher economic returns. Agricultural practices should incorporate the use of 6 g/L humic acid and 6 g/L nitrogen in chickpea cultivation. Extension services should educate farmers about these findings to optimize their crop management practices.

Strawberry belongs to the small, important, and widespread fruit in the world. Shalik is a perennial herbaceous plant characterized by its beautiful shape, delicious taste, and high nutritional and therapeutic value. Its name is derived from the Latin word (fragrant or fragrance) and its English name is strawberry, and it is called strawberry in Turkey [1]. Where the origin of all commercial varieties of strawberry, which currently includes foreign varieties, is due to the hybridization between two types of endemic American varieties, namely F. Chiloensi and F. Virginiana. The original home of Shalik is Europe and North America, as well as spreading cultivation in Italy, Bologna, the Netherlands, France, and Bulgaria. Shalek is the fourth most consumed fruit after apples, oranges, and bananas [2]. Humic acid is one of the most important organic acids, and humic acid is one of the main products of the decomposition of organic matter (humus) that affects plant growth through its effect on the processes of photosynthesis and respiration (Dantas et al., 2007) [3], and works to increase plant tolerance to harsh conditions such as salinity, drought, and high temperatures [4,5]. Nitrogen is a necessary element in all the vital processes that take place inside the plant, as it greatly affects cell division, thus increasing the meristematic activity of the cells and expanding accordingly the surface area of the leaves. Increasing nitrogen will increase the chlorophyll pigment in the leaves and then increase the efficiency of photosynthesis. Nitrogen also encourages the growth of roots and increases the efficiency of the plant in absorbing water and nutrients from the soil, thus increasing the vegetative growth and the quantity and growth rate of the crop [6]. Also, nitrogen fertilizer increases the efficiency of the photosynthesis process and the manufacture of nutrients, in addition to that nitrogen fertilizer leads to an increase in the size of cells and the speed of their division [7].

The study was conducted at the Agricultural Research and Experiment Station belonging to the Department of Horticulture and Landscape Engineering / College of Agriculture / University of Kirkuk, located in the University Presidency in Al-Sayadah district in Kirkuk Governorate, during the year (2015-2016), the covered cultivation system (greenhouse) was used and the method of planting on terraces was used. This is to study the effect of spraying with concentrations of (0, 3, and 6) g/l of humic acid and (0, 3, and 6) g/l of nitrogen on some quantitative and qualitative traits of the fruits of humic. The plants were sprayed with humic acid and nitrogen until completely wet, using a little liquid soap as a dispersant. The seedlings were obtained from a private nursery in the Sulaymaniyah Governorate, where the seedlings were stored in refrigerated warehouses ready for cultivation and of a uniform size. After preparing and smoothing the soil and preparing it for planting, the experimental land was divided into three terraces, each with a length of 30 m, a width of 100 cm, and a height of 25 cm. The terraces were provided with a drip irrigation system. The terraces were covered with black nylon, and the distance between one plant and another was (30 cm). The seedlings were planted on November 1, 2015, and all agricultural operations recommended during the experimental period were carried out, including watering, weeding, and fertilization.

Studied traits:

1. Number of fruits: The number of fruits was calculated for each of the five plants selected for each experimental unit.

2. Average fruit weight (g): Readings were taken from the five selected plants for each experimental unit, according to the following equation:

                                                                Total fruit weight of the selected plants for each experimental unit   

The average weight of the fruit (gm) = __________________________________
                                                                                                      The total number of fruits for the selected plants

3. Fruit size (cm): The fruit size was measured using the Vernia device.

4. Percentage of Total Dissolved Solids (%): The total dissolved solids were measured using a Hand Refractometer. Ten homogeneous ripe fruits were cut from each experimental unit into slices and placed in an electric mixer for (2-3) minutes, after which the juice was filtered with a cotton cloth, and the reading was taken to represent (TSS) in the juice.

5. Vitamin C content of fruits (mg.100ml-1.juice): Vitamin C was estimated in fruit juice for all experimental treatments according to the method mentioned by Sadasivam and Manickam (2005) [8], using oxalic acid at a concentration of 2% as a preservative solution and rinsing with (2,6-Dichlorophenol Indophenol) dye, as ascorbic acid alone is able to reduce this dye as it turns from Blue in the basal medium to pink in the acidic medium.

1. The number of fruits

It was found from Table (1) that the use of humic at a concentration of 6 g / liter was significantly superior to the other treatments, as it gave the highest rate of fruits, which amounted to 22.6900 fruits/plant, and the use of 6 g / liter of N gave the highest rate of the number of fruits, which amounted to 25.7656 fruits/plant, which was significantly superior to other treatments. As for the double overlap, it was found that the overlap of (3,6) g/l of N with 6 g/l of humic acid was superior to the other overlaps, which gave the highest average number of fruits.     

Table 1: Effect of spraying with humic acid and nitrogen on the number of fruits of chickpea (Fragaria X ananassa Duch.)   

There are no significant differences between the values that share the same letter within one factor or its overlaps according to Dunkin's multiple range test at the 5% probability level.

2. The weight of the fruit.

The results of Table (2) showed that the use of humic at a concentration of 6 g / liter significantly outweighed the other treatments, as it gave the highest weight of the fruit, which amounted to 17.9900 g, which was significantly superior to the other concentrations, and that the use of 6 g / liter of N gave the highest weight of the fruit, which amounted to 19.1711, which was significantly superior to the other treatments. As for the secondary interaction, it was found that the interaction of 6 g/L of N with 6 g/L of humic acid was significantly superior to the other interactions, which gave weight to the fruit, which amounted to 19.8200 g.

Table 2: Effect of spraying with humic acid and nitrogen on the weight of fruits of chickpea (Fragaria X ananassa Duch.)

3. Size of the fruit:

It was found from the results of Table (3) that the use of humic at a concentration of 6 g / liter was significantly superior to other treatments, as it gave the highest fruit size, which was significantly superior to other treatments, which amounted to 18.3067 cm. As for the double interaction, it was found that the interaction of 6 g/L of N with 6 g/L of humic acid was superior to the comparison treatment, which gave the highest fruit size, reaching 19.9733 cm.

Table 3: Effect of spraying with humic acid and nitrogen on fruit size of chickpeas (Fragaria X ananassa Duch)

4. Total Solutes Percentage (TSS):

The results of Table (4) showed that the use of 6 g/L of humic acid was significantly superior to other treatments as it gave the highest percentage of total dissolved solids (TSS), which amounted to 8.89444, and that the use of 6 g/L of N gave the highest percentage of TSS, which amounted to 9.48778, significantly superior to other concentrations. The binary interaction between 6 g/L of N with 6 g/L of humic acid gave the best result, reaching 9.8933 compared to other interactions.

Table 4: Effect of spraying with humic acid and nitrogen on TSS chickpeas (Fragaria X ananassa Duch)

5. Vitamin C

Table (5) showed that the use of 6 g/l of humic acid gave the best value for vitamin C, which amounted to 16.0800, which was significantly superior to other concentrations. And the use of 6 g / liter of N gave the highest percentage of vitamin C, which was significantly superior to other concentrations, which amounted to 16.8733, and the interaction between 6 g / liter of humic acid with 6 g / liter of N gave the best result, which amounted to 17.3633, significantly superior to other interactions.

Table 5: Effect of spraying with humic acid and nitrogen on Vitamin C chickpea (Fragaria X ananassa Duch)

The use of humic acid at a concentration of 6 g/L and nitrogen N at a concentration of 6 g/L and the interaction between them gave the best results in all the studied traits.

Conflict of Interest: The authors declare that they have no conflict of interest.

Funding: No funding sources 

Ethical approval: The study was approved by the Institutional Ethics Committee of Universitas Negeri Makassar

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