The Growth-Promoting Effect of Earthworm Vermiwash on House Tomato Plants

Abstract

Earthworm vermiwash, a by-product of the vermicomposting process and a light-brown-colored liquid rich in macro- and micronutrients that are essential for plant growth, has recently emerged as a potential tool for sustainable agriculture. It is expected to have antimicrobial, antipest, and soil-stabilizing effects. However, little is known about the optimal composition and dosage of vermiwashes, and the long-term stability is still unknown. Here, we investigated the long-term stability of vermiwash content and conducted a growth test on house tomatoes treated with different concentrations of vermiwash. The phosphate and potassium contents of the vermiwash were remarkably stable over time; however, if the initial ammonium content was high, the content changed with temperature, and nitrate-nitrogen was increased. Our results suggested that the vermiwash can be preserved at any temperature as both nitrogen components are helpful for plant growth. The vermiwash treatment outperformed the other two treatments in terms of plant height and fruit size. The threshold vermiwash nitrogen level was approximately 17.5–35 mg/L per week. Although an ideal ratio is advisable, earthworm vermiwash does not inhibit growth even at high concentrations. Thus, vermiwash is a sufficiently stable, beneficial liquid plant fertilizer.

1. Introduction

Continuous population growth has increased the demand for food consumption. To meet this growing demand, chemical fertilizers are widely used to increase crop production and have become inseparable from modern agriculture. Undoubtedly, this has helped reduce hunger and malnutrition in many parts of the world. However, the excessive and inappropriate use of fertilizers and pesticides pollutes waterways, hardens soil, decreases fertility, and increases greenhouse gases, causing hazards to human health and the environment, which is contrary to their initial purpose [1]. In recent years, it has become evident that chemical fertilizers pose serious challenges to sustainable growth [1]. Samadhiya et al. noted that chemical fertilizers also lead to the loss of soil microbiological diversity [2]. Accordingly, researchers are popularizing organic fertilizers, such as manure, guano, and bio-composts, to avoid soil pollution and consequent environmental threats. Vermiwash has emerged as a potential tool for combating multiple problems. Awadhpersad et al. emphasized that, in Suriname, vermiwash production is emerging as a method for generating effective liquid fertilizer [3].

Vermiwash is a liquid extract obtained from vermicomposting beds. It is a collection of excretory products and mucus secretions from earthworms, along with micro-and macronutrients. It contains necessary plant nutrients, plant growth-promoting hormones (auxin and gibberellins) [4], enzymes (protease, amylase, urease, and phosphatase that act as antimicrobic), and symbiotic microbes (nitrogen-fixing bacteria such as Azotobacter sp., Agrobacterium sp., and Rhizobium sp. and some phosphate-solubilizing bacteria) [5]. Furthermore, since vermiwash also contains antimicrobial peptides, it is expected to be able to inhibit pathogenic bacteria; consequently, it can be utilized to increase crop productivity [6]. Recently, it has been reported that vermiwash can also be employed in aquaponics [7]. Aquaponics is a class of hydroponics that has been recently garnering attention in which a nutrient solution is used to grow crops without soil. Aquaponics can be regarded as a system that synergistically integrates both hydrobiont (aquaculture) and vegetable (hydroponics) cultivation by establishing a symbiotic ecosystem of fish, microorganisms, and plants in a closed system [8,9]. Moreover, vermiwash is known to be nitrogen- and mineral-rich and can subsequently be utilized in the hydroponic cultivation of vegetables [7].

Vermiwash is also an excellent nutrient supplement, it enhances soil physicochemical properties and maintains long-term soil fertility [10]. Nayak et al. reported that vermiwash spray enhanced the growth (plant height and number of leaves) and yield (number of flowers and fruits per plant) of eggplant [10]. Nath et al. reported that vermiwash obtained from animal feces and agricultural and kitchen waste increased plant growth, flowering, and productivity [11]. However, little is known about the optimal composition of vermiwash and the range of uses for its components, including the minimum dose of vermiwash, desired nitrogen, phosphorus, and potassium (NPK) content ratio, its toxicity, growth-inhibiting side effects at high contents, and stability for long-term preservation.

Therefore, this study aimed to address these gaps in knowledge, and to achieve this, we conducted growth tests on house tomatoes using different concentrations of vermiwash at different frequencies. Plant growth, specifically the average plant height, was used as the outcome variable. We examined the differences in total yield (quantity and weight of tomato fruit), sugar content, and acidity of tomatoes from three separate plant groups (control, commercial fertilizer, and vermiwash-treated). Growth and fruit yield serve as highly suitable indicators for investigating the effects of fertilizer. Moreover, we examined the stability of vermiwash components over a prolonged period for preservation purposes. Due to the presence of diverse microorganisms in organic fertilizers, earthworm liquid fertilizer may undergo chemical composition alternations in nutrients, such as nitrogen, based on temperature variations. In addition, we investigated the stability of these components across various temperatures, considering their intended storage in outdoor environments for easy application. This work provides scientific data on the long-term stability and effectiveness of vermiwash for plant growth and fruit quality.

2. Materials and Methods

2.1. Materials

Earthworms (Eisenia andrei Sagami) were purchased from Sagami Joka Service, Inc. Ltd. (Kanagawa, Japan). Experimental earthworms were of different ages: non-clitellar and clitellar. Tomato seedlings (Frutika) were purchased from Soga Farm Co., Ltd., Niigata, Japan. Black soil was purchased from Kanuma City (Arclands Co., Ltd., Niigata, Japan). Organic vegetable soil (Hirota Shoten Y.K., Tochigi, Japan), Hyponex liquid fertilizer (HYPONeX Japan Corp., Ltd., Osaka, Japan), and Nissan tomato tone spray (Sumitomo Chemical Garden Products, Inc., Tokyo, Japan) were purchased from Arcland Co., Ltd., Niigata, Japan. Vermiwash reagents were purchased from Hanna Instruments Japan Co., Ltd. (Chiba, Japan).

2.2. Construction of Vermicomposting Beds and Production of Vermiwash

The earthworm breeding period was from 20 July 2018 to 16 October 2020, a total of 819 days. We obtained three different batches of vermiwash to be used in this experiment, the first of which was collected between the 628 and 684th (56 days) of breeding for stability testing, the second between the 684 and 720th (36 days), and the third between the 720 and 819th (99 days) for the tomato experiment.

The vermicomposting beds were constructed as follows: a 240 L plastic box was prepared and holed at the outer bottom side to fit a tap and regulate the water supply. The nonwoven fabric was attached to a tap to prevent earthworm desertion. The growth medium was prepared using wood chips. Boiled cabbage feed (250 g) was added 1–3 times per week. In addition, approximately 0.5 L of water was added 1–3 times per week after feeding. The unit was maintained moist. The first two weeks’ vermiwash was discarded as a low-nutrient liquid. Subsequently, the vermiwash was gradually collected in a 20 L polyethylene tank. The vermiwash collection tank was changed every 3 months (Figure S1).

2.3. Physico-Chemical Analysis

The temperature was measured using a thermosensor (DS18B20, Analog Devices Inc., Wilmington, MA, USA). pH was measured using a digital soil pH meter (Shinwa Rules Co., Ltd., Niigata, Japan). Ammonium (Nessler method), nitrite (EPA diazotization method), nitrate (cadmium reduction method), total phosphate (amino acid method), and total potassium (tetraphenylborate turbidimetric method) were measured according to the manufacturer’s instructions using a multi-item absorptiometer HI 83325 and reagent kits (Hanna Instruments).

2.4. Cultivation of Tomato Plants and Preparation of Experimental Sight

The first tomato cultivation experiment was held in a greenhouse from 7 June to 29 October 2021, a total of 144 d (Figure S2). The soil was prepared as follows: black soil from Kanuma city (three packages (16 L each) (Arclands, Niigata, Japan) for a total of 48 L) was mixed with one package (40 L) of organic vegetable soil (Hirota Shoten, Tochigi, Japan) and used for tomato cultivation. Nine pots were placed in the greenhouse for the experiments. Three tomato pots were filled with tap water, three with Hyponex liquid fertilizer (HYPONeX, Osaka, Japan), and three with earthworm vermiwash. Each pot was filled with mixed soil, and the seedlings were placed in pots and sorted by height and width to ensure that the three groups had similar seedlings. The second tomato cultivation experiment was held in a greenhouse between 31 May and 9 August 2022, a total of 70 days. The soil preparation was changed from the 2021 experiment as follows: organic vegetable soil (Hirota Shouten) was used for tomato cultivation.

2.5. Weekly Treatment of Tomatoes

Control plants (n = 3) received 500 mL of extra tap water once a week without the addition of any fertilizer. Each Hyponex group plant (n = 3) received 500 mL of commercial Hyponex fertilizer diluted 500 times once a week, as stated in the instructions. Each treatment group received 500 mL of earthworm vermiwash initially once every fortnight; then, the frequency and concentration were gradually increased. To be careful about the possible growth inhibition effect in the first month, we added earthworm fertilizer diluted thrice and added once every fortnight. Considering the plant growth starting from the 29th day of cultivation, fertilizer dilution was changed to twice and applied weekly. Starting from the 60th day, it was ensured that the fertilizer had no growth inhibitory effect; therefore, it was administered without dilution three times per week. In the last month of the experiment, we administered vermiwash containing elevated levels of nitrogen, phosphorus, and potassium. The detailed composition of fertilizers is shown in

Table 1. Vermiwash and commercial liquid fertilizers’ components.

Fertilizer	Components (mg/L)						Applied Date	Frequency
	NH3-N Ammonia Nitrogen	NO2-N Nitrite-Nitrogen	NO3-N Nitrate- Nitrogen	Nitrogen N	Phosphorus P	Potassium K
Fert.2021_1-3	1.16 ± 0	0.40 ± 0	1.35 ± 0.08	2.92 ± 0.08	16.1 ± 0.1	134 ± 1	June	once a fortnight
Fert.2021_1-2	1.74 ± 0	0.61 ± 0	2.03 ± 0.12	4.38 ± 0.13	24.1 ± 0.1	201 ± 1	July	once a week
Fert.2021_1-0	3.48 ± 0.02	1.22 ± 0	4.06 ± 0.24	8.77 ± 0.25	48.2 ± 0.3	402 ± 2	August	twice a week
Fert.2021_2-0	4.60 ± 0.03	1.93 ± 0.14	57.8 ± 6.6	64.3 ± 6.8	87.4 ± 1.1	805 ± 23	September	3 times a week
Fert.2022-1-0	3.33 ± 0.11	3.86 ± 0.35	49.2 ± 1.6	56.4 ± 2.1	88.5 ± 0.9	767 ± 33	June	once a week
Fert.2022-2-7	15.4 ± 0.5	4.52 ± 0.41	15.2 ± 0.4	35.1 ± 0.5	119 ± 2	79.0 ± 1.8	July	twice a week
Fert.2022-3-5	6.50 ± 0.20	0.67 ± 1.15	31.3 ± 0.3	38.5 ± 1.4	147 ± 3	135 ± 4	August	twice a week
Hyponex	78.7 ± 0.7	N.D.	21.6 ± 2.5	100 ± 3	115 ± 2	80.0 ± 0	(2021) June–September (2021) June–August	(2021) once a week (2022) once or twice a week

“Fert.” means a vermiwash. Hyponex is a commercial liquid fertilizer. The first season (2021) was from Fert.201_1-3 to Fert.2021_2-0, and second season was from Fert.2022-1-0 to Fert.2022-3-5 (2022).

(The first season is from Fert.2021_1-3 to Fert.2021_2-0, and the second season is from Fert.2022-1-0 to Fert.2022-3-5). Any axillary bud and dead or dried leaves were removed, and the plants were monitored and appropriately cared for. At the time of flower bud formation, Nissan tomato tone spray (Sumitomo Chemical Garden Products Inc., Tokyo, Japan) was applied.

2.6. Stability of the Vermiwash Components

Corrected vermiwash was incubated at 4, 25, and 40 °C. The components were measured monthly using a multi-item absorptiometer HI 83325 and reagent kits (Hanna Instruments, Chiba, Japan).

2.7. Data Collection

To compare the heights of the three groups, the stems of each plant were measured weekly from the root to the end of the tallest branch. The tomatoes were harvested according to the color chart (Figure S3) when the fruits ripened. We measured the weight and sugar content using a PAL-Light sensor–3 Mini (ATAGO Co., Ltd., Tokyo, Japan) and acidity using PAL-BX ACID3 (ATAGO). If circumstances did not allow for measurement immediately after harvesting, the fruit was stored in a refrigerator.

2.8. Statistical Analysis

To determine the effect of vermiwash, plant height, number of harvested fruits, weight, sugar content, and acidity, data were analyzed and compared with the other two groups using the statistical software BellCurve for Excel (Social Survey Research Information Co., Ltd., Tokyo, Japan). To find a correlation between plant growth and fertilizer components, we used ordinary least squares regression analysis and performed a two-sample Welch’s t-test with unequal variances to find any significant differences in fruit quality.

3. Results and Discussion

3.1. Earthworm Breeding Condition and Vermiwash Content

Starting in late April 2019, the outside temperature (the first season in 2021), soil temperature and moisture were measured. Earthworm breeding average soil temperature during the summer season was 21.4 °C, which was lower than the outside temperature of 24.3 °C. Unexpectedly, in the winter, the soil temperature was lower (7.3 °C) than the outside temperature (8.9 °C). This was associated with the watering procedures used in the earthworm breeding process. The summer temperature during the day was near the range of the optimal temperature of 25–30 °C for the growth of earthworms [12]. According to Edward and Bohlen, the ideal moisture content range is 70–90%, with an optimum moisture content of 85% [13]. In our study, the average soil moisture was 87%, which could be considered optimal. The pH was stable at ~7.0 during all our experimental terms. Several researchers have found that worms can survive in a pH range of 5–9 but prefer a pH of 7 or higher [14]. Zarei et al. reported that reduction in pH is a crucial factor for the maintenance of nitrogen as the nutrient volatilizes in the form of ammonia gas at an alkaline pH [15]. The color of the acquired liquid changed from light yellow to brown, which correlated with the maximum nutrient content of the vermiwash.

Vermiwash components nitrate, phosphate, and potassium were analyzed and compared to Hyponex (commercial liquid fertilizer), which was diluted 500 times, following the manufacturer’s recommendations (Table 1). The total nitrate content of vermiwash Fert.2-0 (non-diluted vermiwash) was approximately 2.6-times higher than that of Hyponex. Nitrate was the main component of vermiwash, whereas Hyponex contained the same amount of ammonium and nitrate. Thus, the nitrogen components of vermiwash may be more stable and toxic than those of Hyponex. Potassium, needed for plant root growth, was approximately ten times higher in vermiwash than in Hyponex.

3.2. Long-Term Stability of Vermiwash Content

Organic fertilizers have the potential to be used effectively. However, they are often discussed in terms of their stability. Here, we also investigated the long-term stability of nitrate, phosphate, and potassium contents in vermiwash over time in 4, 25, and 40 °C conditions (Figure 1 and Figure 2). The initial components of the vermiwash are listed in

Table 2. Liquid fertilizers’ components.

Vermiwash Sample Name	Collected Period	Content (mg/L)
		NH3-N Ammonia Nitrogen	NO2-N Nitrite-Nitrogen	NO3-N Nitrate- Nitrogen	Nitrogen N	Phosphorus P	Potassium K
2021 Palm fiber *	2020.4.08–6.03	2.90 ± 0.56	1.20 ± 0	60.6 ± 6.9	64.7 ± 6.9	144 ± 3	553 ± 9
2022 Palm fiber **	2020.7.21–10.29	139 ± 3	30.0 ± 10.0	N.D.	169 ± 8	523 ± 6	387 ± 12

* For Figure 1, ** for Figure 2.

. The results of the 6–8 monthly follow-up studies revealed that the nitrate, phosphate, and potassium contents of the vermiwash were remarkably stable over time under each condition (Figure 1a,e,f and Figure 2a,e,f). However, if the initial ammonium content was high, the content changed with temperature (Figure 2b). In particular, the rate of change was dramatic at 25 and 40 °C. In this case, nitrate content increased. It is well-known that numerous microorganisms can be found in earthworm vermiwash [16]. Thus, it is thought that nitrifying bacteria, such as Nitrosomonas sp., might be present in vermiwash. This hypothesis was supported by the optimal nitrification temperature being 28–29 °C [17]. Therefore, to ensure high ammonia nitrogen content, vermiwash should be preserved at 4 °C. However, a high content of nitrate-nitrogen remained in the vermiwash when preserved at room temperature (20–25 °C), and thus, the vermiwashes were easy to use.

3.3. Cultivation of Tomato Plants

3.3.1. Tomato Growing Condition

The average greenhouse temperature during the cultivation period was 23.1 °C, with a maximum day temperature of 42.3 °C during the hot season in August. The average soil temperature was 24.5 °C, with a maximum of 58.1 °C. The soil moisture was, on average, 90%; however, during hot periods, it decreased to 31.9%. The electroconductivity of the soil ranged from 0.07 to 0.79 mS/cm, with an average value of 0.17 mS/cm. The soil pH was, on average, 6.58, with a maximum value of 6.86 in the control group and a minimum of 5.7 in the Hyponex group. These results demonstrated that vermiwash treatments did not influence soil pH. Researchers have suggested that vermiwash and vermicompost applications positively affect the physical and chemical characteristics of soil [18,19]. In addition, vermiwash contains enzymes that break down organic matter in the soil to release nutrients, thereby rejuvenating the depleted soil fertility, increasing the water-holding capability, maintaining soil quality, and enriching the nutrient composition [14,20].

3.3.2. Growth Results

The 2021 growth of tomato plants under different fertilizer treatments is shown in Figure 3. The plants from the vermiwash treatment groups had the highest average height of 136.5 cm, followed by Hyponex (117.7 cm) and the control (74 cm). Accordingly, the average weekly growth rates were 6.1, 5.2, and 2.9 cm, respectively. The figure shows that increased vermiwash content led to higher plant growth. When diluted vermiwash was added (fert:2021_1-3 and fert:2021_1-2), the height of the plants was similar to that of the control plants. However, when we added vermiwash without dilution (fert:2021_1-3), the growth effect outperformed the water treatment and, with an increased concentration of vermiwash (fert:2021_2-0), surpassed that of Hyponex. We propose that the proper nitrogen level of vermiwash should be in the threshold range of 17.5–35 mg/L per week for future earthworm liquid fertilizers. According to Pathma and Sakthivel, a higher concentration of nitrogen improves rhizobial colonization of nodules, and sufficient availability of soluble nitrogen in vermiwash enhances plant growth and increases productivity [21]. However, excessive nitrogen can lead to immense elongation of plant stems, decreasing productivity and efficiency. The optimal range can vary depending on the settings. The average weekly growth fluctuated because of the presence of plant-bearing fruits. When the plant develops fruits, most of the nutrients are used for ripening the fruits; therefore, the plants do not grow in height. When the ripened fruits are harvested, the plants begin to grow again.

These results revealed that vermiwash is not toxic to tomato plants, even at high concentrations. However, a minimum threshold level of nitrogen is required for plant growth promotion. In addition, the higher potassium content did not impede plant growth.

We found that high concentrations of vermiwash were safe. The 2022 experiment also showed that the initial nutrient concentrations are important for tomato growth (Figure 4). Vermiwash was used to increase the initial nitrogen and phosphate contents. Subsequently, the plant growth was increased in the Hyponex and vermiwash samples until the end. In addition, the statistical analyses revealed that the vermiwash and Hyponex groups demonstrated higher height compared to the control (p < 0.1).

3.4. Vermiwash as a Foliar Spray

Initially, we used soil without additional nutrients to determine the sole effect of vermiwash. However, starting in late July, all soils were replaced with more nutrient-rich soils because of the lower vigorousness of plants. Moreover, during the hot season, the tomato plants became frail due to the high temperatures (above 40 °C) in the greenhouse; therefore, extra fertilizer sprinkling was applied thrice weekly. After these measures, the tomato plants were revigorated and continued to thrive, developing firmer stems and leaves. Consequently, it can be inferred that sprinkling fertilizer onto the plant stem and leaves is as effective as pouring it into the roots. These results corroborate the findings that vermiwash is the best organic manure for foliar spraying of different crops [22]. The foliar vermiwash spray provides the necessary nutrients for stem elongation, early flowering, and fruiting phases. Moreover, it was elucidated that the initial soil for planting the seedlings is vital for the firm and strong stems of the plant and, consequently, for further growth and yield.

3.5. Yield and Fruit Quality Results

When flower buds formed and bloomed, Nissan tomato tone spray (containing 4-chlorophenoxyacetic acid, which promotes fruiting) was sprinkled. The total yield and average tomato statistics are shown in

Table 3. Total yield, average weight, sugar content, and acidity of tomato fruits in 2022. Numbers in parentheses indicate non-ripe fruits.

Group	Total Amount	Total Weight (g)	Mean Weight (g)	Mean Sugar (%)	Mean Acidity (%)
Control	12	155	12.9 ± 1.5	11.1 ± 1.4	0.79 ± 0.14
Vermiwash	28	333	11.9 ± 2.8	10.0 ± 1.5	0.68 ± 0.18
Hyponex	33	398	12.1 ± 4.4	9.0 ± 1.6	0.59 ± 0.15
Total	73	886

.

We harvested 73 tomatoes, totaling 888 g, from the nine experimental pots. The vermiwash and Hyponex groups had higher yields than the control (p < 0.05). To determine the significance of differences in fruit quality, we performed a two-sample Welch’s t-test. The acidities in the vermiwash and Hyponex groups were lower than in the control group (p < 0.05). On the contrary, although vermiwash sugar content was higher than that of the Hyponex group sugar content, the control group content was highest (Figure 5a). Although Saini et al. also recorded the maximum tomato fruit weight with the vermiwash treatment [23], the weight was not significantly different between all groups (Figure 5b). Awadhpersad et al. also reported a larger diameter and higher number of tomatoes following vermicompost and vermiwash application [3]. Our results were consistent with the reports.

3.6. Factors That Affect Growth

Ordinary least squares regression analysis was used to determine the correlation between plant growth and fertilizer components. The three groups of plants were evaluated over 21 (2021) and 10 (2022) weeks. The dependent variable was plant growth, measured as plant height in cm, and the independent variables were fertilizer application, NPK content, and cultivation day. Descriptions of the variables used in the analysis are shown in

Table 4. Description of variables used in the analysis.

Variables	Description
Growth	Height of tomato plants (cm)
Vermiwash	Binary variable indicating vermiwash fertilizer (treated = 1, not treated = 0)
Hyponex	Binary variable indicating Hyponex fertilizer (treated = 1, not treated = 0)
Day	Cultivation Time (d)
N content in fertilizers	Nitrogen content of the fertilizers (mg/L)
P content in fertilizers	Phosphorus content of the fertilizers (mg/L)
K content in fertilizers	Potassium content of fertilizers (mg/L)

.

The factors affecting the growth of tomato plants are listed in

Table 5. Factors affecting the growth of tomato plants.

Factor	Ordinary Least Squares Regression
	2021		2022
Vermiwash	29.88 ***	(4.58)	−1.59	(7.42)
Hyponex	23.75 ***	(4.97)	−1.51	(5.9)
Day	0.68 ***	(0.03)	0.7 ***	(0.08)
Nitrogen N	0.86 ***	(0.26)	0.07	(0.06)
Phosphorus P	−0.71 **	(0.23)	0	(0.04)
Potassium K	0 *	(0.01)	0.01	(0.01)
Observations		63		33

The standard errors are indicated in parentheses. * p < 0.10; ** p < 0.05; *** p < 0.01.

. The 2021 experiment limited the nutrients. On the contrary, the 2022 experiment used high-nutrient type vermiwash (please see Section 3.3.1). The results from 2021 indicate that when plants were treated with vermiwash and Hyponex, their heights were, on average, 29.88 and 23.75 cm higher (p < 0.01), respectively, compared to the control. Nitrogen content was positively correlated with plant height, whereas phosphorus content was negatively correlated with plant height. Specifically, when the nitrogen level increased by 10 mg/L, the plant grew 8.6 cm higher. In contrast, when the phosphorus level increased by 10 mg/L, the height decreased by 7.1 cm. These values were statistically significant at the 1 percent level (p < 0.01), and we did not find any correlation between potassium levels and growth. This suggests that as nitrogen accelerates the growth of branches and leaves, potassium strengthens the roots and stems, and phosphorus promotes the formation of flowers and fruits. When plants develop flowers and fruits, most nutrients are used for fruit ripening; thus, plant height remains constant until harvest. Considering these effects, we attempted to calculate the appropriate ratio of nitrogen, phosphorus, and potassium in the fertilizer. The threshold of vermiwash nitrogen content was approximately 17.5–35 mg/L per week, and the level of potassium was suggested to be two times higher than that of nitrogen (referring to the commercial fertilizer Hyponex ratio. For the above reasons, we changed to the vermiwash with high nutrient components for the 2022 experiments. The only variable was cultivation time. These results revealed that the initial nutrient concentration is very important for plant growth and that appropriate vermiwash with sufficient nutrients can effectively replace commercial fertilizer.

An N:P ratio of approximately 1:2 is ideal for fruit plants. However, the composition can vary widely depending on the setting, and a higher level of potassium does not necessarily impede growth. For instance, non-fruit-bearing plants may not require a higher amount of phosphorus, as Keerthi et al. recorded the highest cob yield with the application of 180–75–60 kg nitrogen, phosphorus, and potassium ha⁻¹ ratio vermicompost [24]. In this study, our vermiwash fertilizer had a lower phosphorus content than the Hyponex fertilizer. Consequently, fewer flowers and fruits developed. The phosphorus content can be increased in vermiwash by changing the feed during the vermicomposting process, such as feeding earthworms with waste mushroom beds (

Table 6. Vermiwash contents produced with different earthworm feeds.

Sample	Collected Period	Content (mg/L)
		NH3-N Ammonia Nitrogen	NO2-N Nitrite-Nitrogen	NO3-N Nitrate- Nitrogen	Nitrogen N	Phosphorus P	Potassium K
Wood chips	2020.7.21–10.29	3.20 ± 0.26	N.D.	N.D.	3.20 ± 0.26	65.0 ± 5.2	478 ± 12
Wood chips (preserved for 1 year)	2020.7.21–10.29	7.29 ± 0.90	N.D.	8.54 ± 0.80	15.8 ± 1.3	48.5 ± 2.6	863 ± 65
Waste mushroom bed	2020.7.21–10.29	662 ± 10	335 ± 26	554 ± 48	1552 ± 40	3157 ± 150	953 ± 21
Palm fibre	2020.7.21–10.29	3.91 ± 0.30	0.20 ± 0.40	48.3 ± 5.5	52.4 ± 5.3	87.7 ± 6.4	358 ± 3

). Several studies have reported different nutritional values for vermiwash; the nutrient value depends on the organic feed used in the vermicomposting process [15,25]. If phosphorus-rich vermiwash is applied, a higher yield is expected.

4. Conclusions

This study clarified several aspects of vermiwash utilization for agricultural purposes. The vermiwash long-term stability test revealed that the phosphate and potassium contents of the vermiwash were remarkably stable over six months at different temperatures. However, if the initial ammonium content was high, it changed with temperature, and nitrate-nitrogen was increased at higher temperatures. These results suggested that vermiwash can be preserved at various temperatures for long-term durations as both forms of nitrogen are helpful for plant growth. Furthermore, vermiwash had no growth-inhibiting effect, was non-toxic, and had a significant growth-promoting effect even at high concentrations. The growth effect of the vermiwash fertilizer treatment surpassed that of the commercial fertilizer, with the highest height and weekly growth. Moreover, the vermiwash and Hyponex groups had higher yields than the control groups (p < 0.05). Although the sugar content of the vermiwash group was higher than that of the Hyponex group, the control group had the highest sugar content. The weight was not significantly different between the groups. It was believed to be due to the low phosphorus levels of the vermiwash from E. andrei Sagami fed with cabbage that was used for the experiments. Phosphorus-enriched vermiwash, obtained by altering the feed used in the vermicomposting process, may increase the amount, weight, and sugar content of fruits. Thus, we identified the threshold for vermiwash content to trigger a promoting effect. For tomato plants, this threshold was between 17.5 and 35 mg/L of nitrogen per week in vermiwash. In addition, an N:P ratio of approximately 1:2 is desirable for fruit plants. The phosphorus content increased significantly after feeding the earthworms waste mushroom beds.

In addition, considering the vigorousness and growth speed of the plants, we assumed that the initial soil composition for planting the seedlings was a determining factor for the firm and strong stems and, consequently, for growth and yield. At temperatures above 40 °C in the greenhouse, which might cause drought in the plant and eventually death, sprinkling fertilizers onto the plant stem and leaves was as effective for plant growth as pouring them into the root.

There is a great opportunity to substitute chemical fertilizers with more sustainable vermiwash fertilizers, which can result in greener and more sustainable agriculture, improving food security, and contributing to combatting hunger and environmental sustainability efforts of sustainable development goals.