Effects of Sewage Sludge Compost and Vermicompost on Wheat Yield and Vitality

Abstract

This study investigates the effects of compost and vermicompost derived from sewage sludge and moulded pulp on wheat yield, nutrient uptake, photosynthetic activity, and drought resistance. Optimal weather conditions in March facilitated timely wheat sowing, contributing to ideal yields, while subsequent higher temperatures and rainfall influenced grain formation and weight. The experiment demonstrated that vermicompost significantly enhances plant physiological and yield parameters, including photosynthetic activity, chlorophyll content, and water use efficiency. Fertilized variants exhibited improved soil properties, leading to higher grain and straw yields compared to the control. Macronutrient uptake was notably higher in vermicompost-treated variants, with variant VI showing the highest values. Enhanced photosynthetic activity and drought resistance were observed in fertilized variants, attributed to better stomatal regulation and osmotic adjustment under stress conditions. The study underscores the role of vermicompost in promoting sustainable agriculture by improving nutrient availability, soil structure, and plant resilience. These findings suggest that compost and especially vermicompost applications can effectively enhance wheat productivity and resilience, offering a sustainable approach to improving crop performance under varying environmental conditions.

1. Introduction

Vermicomposting is a specific process of producing vermicompost using hybrid Californian earthworms, for example, Eisenia andrei. This type of composting yields material with a higher degree of decomposition compared to traditional composting methods. One unique characteristic of these earthworms is their ability to rapidly reproduce and double their biomass every 60 days. The process of vermicompost production involves generating a large quantity of waste materials, which are subsequently consumed by the earthworms and transformed into high-quality fertilizer. However, this process has its own conditions and limitations, such as optimal temperature, substrate moisture, and pH value. Disruption of these conditions can lead to the death of the earthworms. It is crucial to select suitable feed for the earthworms as they are highly sensitive to pesticides and high levels of nitrogen [1].

Vermicompost also contains a substantial amount of growth substances and phytohormones that promote plant growth and root system development, enrich the soil with beneficial microorganisms and bacteria, and enhance flowering efficiency by over 50% compared to traditional compost [2]. Sewage sludge contains nutrients beneficial for fertilization (nitrogen, potassium, phosphorus) and micronutrients such as iron, manganese, copper, molybdenum, and organic matter [3], which help increase crop yields and improve soil quality [4,5,6]. Additionally, it boosts microbial activity, improving nutrient cycling and soil health [7]. Most sludges also contain toxic metals, persistent organic compounds, pathogenic bacteria, and parasite eggs that can contaminate soil and groundwater [8]. Moulded pulp, made from recycled cardboard, is biodegradable and compostable, contributing to sustainable waste management and soil structure improvement [9]. Integrating these materials into composting systems enhances nutrient availability and promotes sustainable agriculture and environmental conservation. Vermicomposting sewage sludge with Eisenia spp. earthworms is an eco-friendly method of managing sewage sludge, where earthworms break down organic matter. The earthworms biologically, physically, and chemically modify sewage sludge, reducing the C:N ratio, increasing N and P content, decreasing pathogen load from various wastes, and producing quality soil fertilizer [10]. They reduce the presence of pathogens such as agens, Salmonella spp. bacteria, viruses, and parasitic worms like Ascaris spp. Lastly, they eliminate unpleasant odours [8].

According to Adhikary’s research [11], during vermicomposting, pathogens enter the earthworms’ trophic chain, leading to rapid waste sanitization and a 40–60% reduction in waste volume. One ton of vermicompost (biohumus) contains 35–40 kg of NPK (nitrogen, phosphorus, potassium), making it a high-quality organic fertilizer. The recommended amount of vermicompost for fertilizing annual crops is 0.2–0.3 kg·m⁻², 0.5–1.5 kg per tree or grapevine, and 3.5–5.0 t·ha⁻¹ for soil fertilization in greenhouses [12]. The high nutrient content in vermicompost can stimulate the growth of corn, Chinese cabbage, lettuce, spinach, and many other crops [13,14]. It promotes flower growth in chrysanthemums, calendula flowers, and petunias and encourages the development of eucalyptus, acacia, or pine trees [15].

The use of vermicompost can significantly positively affect the photosynthetic apparatus of plants, resulting in improved growth and yield parameters. Studies have shown that the application of vermicompost can increase the photosynthetic activity of plants, which may be due to the presence of bioactive compounds and microorganisms that promote plant health [16,17]. Nitrogen, phosphorus, and potassium are essential for chlorophyll formation, necessary for efficient photosynthesis [18]. Additionally, microbial activity in vermicompost improves soil structure and increases its ability to retain water, further promoting plant growth and photosynthetic capacity [19]. Other research suggests that the use of vermicompost can lead to increased plant resistance to stress conditions such as drought or excessive salinity, which can positively affect photosynthetic processes [20]. For example, plants grown on vermicompost-enriched substrates have been reported to have higher values of photosynthetic intensity with associated growth compared to plants grown on traditional substrates [16,17]. It can be said that the addition of vermicompost can improve the conditions for the photosynthetic apparatus of plants and thus promote their growth and yield. In this way, vermicompost becomes a valuable tool for sustainable agriculture and organic farming [21].

In addition to the mechanisms mentioned above, which improve soil fertility and reduce pathogen load, compost and especially vermicompost also contribute to increasing plant resistance to drought. The increase in organic matter content improves soil structure and its water retention capacity; this allows longer moisture retention in the root zone during dry periods [22,23]. At the same time, it stimulates soil microbial activity, which promotes the formation of stable soil agglomerates and the development of an extensive root system that enables plants to draw water from deeper layers [24]. In addition, vermicompost contains bioactive compounds and growth hormones that aid in the production of osmolytes such as proline and soluble sugars that help maintain cell turgor and cell stability during water deficit [25]. These mechanisms are further promoted by the modulation of hormonal responses, such as increased abscisic acid (ABA) production, which induces stomatal closure and reduces transpiration losses [26]. Together, these processes lead to increased water use efficiency and overall plant drought tolerance, all of which are key factors in sustainable agriculture [22,23].

Another important parameter that vermicompost can influence is the osmotic adjustment of plants, particularly under stress conditions such as salinity. Vermicompost application has been shown to effectively mitigate osmotic stress, which can otherwise impair the physiological parameters of plants [27,28]. Research indicates that vermicompost can enhance the levels of chlorophyll and other photosynthetic pigments, contributing to increased photosynthetic activity even in high-salinity conditions [29,30]. These enhancements are linked to higher stomatal conductance and more efficient CO₂ uptake mechanisms, which are vital for photosynthesis [31]. Additionally, vermicompost boosts the concentration of non-enzymatic antioxidants, such as proline and soluble sugars, which are crucial for the osmotic adjustment of plants [32]. These compounds help maintain cell turgor and stabilize cell membranes, essential for plant survival under osmotic stress [32,33].

This study builds on previous research that has shown that the application of compost and vermicompost can improve soil properties and promote crop growth [22]. In contrast to previous studies, which focused mainly on increasing yield and improving basic soil physico-chemical properties [22,34,35,36], our research combines the evaluation of yield parameters with detailed monitoring of plant physiological responses, particularly in relation to drought tolerance. Specifically, we focused on measuring parameters such as photosynthetic activity, water use efficiency (WUEi), and stomatal conductance to investigate how vermicompost application affects the ability of plants to adapt to water deficit. This comprehensive approach allowed us to identify synergistic effects between increased nutrient availability and modulation of plant hormonal balance (e.g., increased abscisic acid production) [37,38], which has not been adequately explored. Thus, the research gap identified by integrating physiological parameters with the assessment of soil properties in the context of drought tolerance represents the main contribution of our study and strengthens the rationale for its relevance to sustainable agriculture. These literature findings confirm that the use of compost, and vermicompost in particular, represents a more balanced approach to increasing soil fertility, improving water retention, and promoting hormonal responses. This is essential to enhance plant drought tolerance. Thus, our research not only confirms existing knowledge but also extends its framework by integrating physiological and hormonal parameters, providing a more comprehensive view of sustainable agriculture [39,40,41].

This experiment highlights the innovative use of vermicompost to enhance plant physiological and yield parameters under varying environmental conditions. The study uniquely combines the analysis of nutrient uptake, yield parameters, photosynthetic activity, chlorophyll content, water use efficiency, and osmotic potential, providing a comprehensive understanding of how vermicompost influences plant growth and stress resilience. Additionally, the experiment’s focus on different growth stages (BBCH 39, 55, and 75) and the impact of vermicompost on stomatal regulation and nutrient uptake offers new insights into optimizing agronomic practices for sustainable agriculture.

The main goals of this experiment are to assess how vermicompost application affects photosynthetic activity, chlorophyll content, and overall plant health across different growth stages; to determine the effectiveness of vermicompost in enhancing nutrient availability (N, P, K); to measure the impact of vermicompost on yield parameters such as grain yield, thousand-grain weight (TGW), and the number of grains per ear (NGE); and to explore the potential of vermicompost as a sustainable and eco-friendly alternative to chemical fertilizers, contributing to improved crop productivity and environmental health.

2. Materials and Methods

The experiment was conducted in the spring at the composting plant ZERS spol. s.r.o. in the village of Neškaredice near Kutná Hora (Czech Republic). The experiment utilized approximately 90 m² of soil located on the edge of a field. In terms of evaluating the soil’s ecological units, also known as BPEJ (Soil Ecological Evaluation Units) (3.02.00), it was classified as highly fertile soil (luvic chernozem). The designated area was divided into 15 smaller plots (3 plots for each variant), with each smaller plot measuring 3 × 2 m, 6 m² in total. The smaller plots were separated to prevent fertilizer contamination between them. The final division, with consecutive variants, included a control variant (O), vermicompost I (VI), compost I (CI), vermicompost II (VII), and compost II (CII) (Figure 1). Sludge I, used for compost and vermicompost production, originated from a wastewater treatment plant with a volume load exceeding 100,000 equivalent inhabitants, and sludge II came from a WWTP with a capacity between 10,000 and 100,000 equivalent inhabitants. The soil was sown with 240 kg·ha⁻¹ of the spring wheat variety Pexeso from Selgen. The expected germination rate of the sown spring wheat seeds out of the total amount was 4–5 million. The amount of fertilizer incorporated into the soil followed law No. 156/1998 Coll. about fertilizers, soil conditioners, plant biostimulants, substrates, and agricultural soil agrochemical testing (Fertilizer Act) [42]. With a 50% dry matter content of the fertilizer, the highest legal application rate was 40 t·ha⁻¹. The maximum application rate was 20 tons of dry matter per hectare over a 3-year period. With an average dry matter content of 32% in composts and vermicomposts, an application rate of 25 t·ha⁻¹ was applied. The control variant was not fertilized at all. During the growth of wheat, overgrown weeds were removed manually without the use of herbicides.

2.1. Composts and Vermicomposts Used

The composts and vermicomposts used were produced in a separate experiment at the ZERS spol. s.r.o. facility using the two previously mentioned sludges mixed with shredded cardboard (moulded pulp). Eisenia andrei earthworms were used for vermicomposting. To ensure suitable conditions for the worms, the compost was pre-composted for 14 days to reduce the ammonia content in the sewage sludge. The entire process took place in a covered hall with regular turning using a front-end loader. The initial temperature ranged from 25 to 40 °C, and the vermicompost’s moisture content was maintained at 80% throughout by watering. Detailed data from the process and parameters of composting and vermicomposting were published in the article by Hrčka et al. [43]. Mature composts (I and II) and vermicomposts (I and II) were subsequently used for fertilizing the field experiment. The content of pathogenic microorganisms in composts and vermicomposts is shown in

Table 1. Content of pathogenic microorganisms in composts and vermicomposts used.

	TCB [CFU·g−1 fw]	Escherichia coli [CFU·g−1 fw]	Enterococci [CFU·g−1 fw]	Salmonella spp. [-]
VI	899	711	723 × 102	negative
VII	388	439	136 × 10	negative
CI	83	128	751 × 102	negative
CII	160	283	175 × 10	negative

TCB—total coliform bacteria. Values are means (n = 18).

.

2.2. Temperature and Rainfall

Monthly rainfall totals and maximum and average air temperatures for the year 2022 are depicted in Figure 2. The Czech Republic had an overall average temperature of 9.2 °C in 2022, making 2022 a warmer year compared to the 1991–2020 period. Since 1996, the Czech Republic has experienced years with varying degrees of normal and above-average temperatures. With a total precipitation of 632 mm, the year 2022 fell within the normal range in terms of rainfall. The most precipitation-rich month was June, with an average of 101 mm (123% of the normal). In contrast, the least rainfall occurred in March, averaging 16 mm (35% of the normal). The average air temperature in the Central Bohemian region was 2.8 °C higher during the observed months compared to the long-term average (1991–2020). The total precipitation in the selected period from March to August 2022 was 379 mm, which was 18 mm more than the long-term average. June and August were abundant in rainfall, while March was not.

2.3. Sampling and Sample Preparation

The variants were sampled randomly, with sampling performed to ensure the greatest possible homogeneity and conclusiveness of the data obtained.

Soil samples were taken from all 5 differently fertilized plots in 3 replicates. These replicates were mixed to obtain 5 variants for representative sampling. After drying, soil samples were milled and sieved through a fine soil sieve (2 mm).

The harvest of mature spring wheat took place in August under ideal weather conditions to prevent devaluation by rain. Wheat samples were collected from each 1 m² of experimental plot. The wheat collection process followed traditional reaping methods using a sickle. Each sample was stored in pre-labelled bags. At the Czech University of Life Sciences in Prague laboratory, grain separation from straw was conducted, followed by subsequent laboratory analysis. For the grain, straw, and root samples of spring wheat, a Retsch SM 100 cutting mill was used. The sieve inserted into the mill had a slot size of 1 cm. A second grinding step was performed using a small mill with a 1 mm sieve to obtain finer sample material.

2.4. Physical, Chemical, and Biological Analyses

Soil moisture was determined gravimetrically based on the change in sample weight before and after drying at 35 °C. To determine soil pH, 8 g of material was weighed and mixed with 40 mL of demineralized water (1:5 ratio). The mixture was shaken in a laboratory shaker for 30 min, and the pH was measured using a WTW pH 340i instrument. A similar procedure was used to determine the active pH in soil samples by using calcium chloride (CaCl₂) in a 1:2.5 ratio. The soil samples were mixed with 2 g of soil and 5 mL of calcium chloride solution. The mixed samples were placed on a shaker for an hour to ensure thorough mixing. After shaking, the samples were left to stand quietly for 1 h and, after that, active pH was measured. Electrical conductivity (EC) measurements were performed on soil samples mixed with demineralized water in a 1:5 ratio. For each 8 g of soil sample, 40 mL of demineralized water was added. These mixtures were then placed in a laboratory shaker for 30 min. The samples were filtered, and EC was measured using a WTW cond 730 conductivity meter. Accessible nutrient content in soils (P, K, Mg) were determined using the Melich III extractant. For phosphorus extraction bound to aluminum, an acidic solution with ammonium fluoride was used to increase solubility. Ammonium nitrate aided in desorbing potassium, magnesium, and calcium. The solution’s acidity was adjusted using acetic acid and 65% nitric acid. The extraction was performed using the Mehlich III solution with an extraction solution containing 0.2 M CH₃COOH + 0.25 M NH₄NO₃ + 0.013 mol·L⁻¹ HNO₃ + 0.015 mol·L⁻¹ NH₄F + 0.001 mol·L⁻¹ EDTA, in a 1:10 ratio (3 g + 30 mL). The extraction process lasted 10 min [44].

Available nutrient content in composts and vermicomposts (P, K, Mg) were determined using CAD extraction agent: 2 mM diethylenetriaminopentaacetic acid (DTPA) + CaCl₂∙2H₂O in demineralized water; 5 g of dried sample was added to 50 mL of CAD solution and shaken for 1 h in laboratory temperature. After that, the samples were filtered according to BS EN 13651 [45]. For determining the total nutrient content in grain, straw, and wheat root samples, 0.5 g were weighed into labelled beakers. The samples underwent dry combustion for 4 h on a hot plate. The combustion temperature was gradually increased every hour, starting at 160 °C, rising to 220 °C after the first hour, and reaching a final temperature of 350 °C. All beakers on the hot plate were securely covered with hourglasses to prevent harmful vapours. Upon reaching the desired temperature, the samples were transferred to an oven for 24 h. The following day, each beaker was removed from the oven, and 1 mL of nitric acid was added. The nitric acid was evaporated for 1 h at 120 °C according to the laboratory procedure. Finally, the samples were placed back into the oven for incineration at a preset temperature of 500 °C for 1 h. Following the previous treatment, solid samples were converted to liquid form using a 1.5% nitric acid (HNO₃) solution. The resulting solutions were transferred to 25 mL test tubes and supplemented with an acidic solution. Both total and available nutrient contents were subsequently measured using ICP-OES (Varian VistaPro). The N content was measured using a CHNS VarioMacro Cube analyser (Elementar Analysensysteme GmbH, Langenselbold, Germany), which burns approximately 0.0025 g of the dry sample in a catalytic furnace. Plant nutrient uptake was calculated using yield values and total nutrient content in a given part of the plant.

Groups of microorganisms (fungi, bacteria) were identified using phospholipid fatty acid (PLFA) analyses according to Hanč et al. [46]. The National Institute of Public Health (Czech Republic) conducted pathogenic microorganism analysis. For Escherichia coli, 10 g samples were mixed with phosphate buffer, processed with Colilert-18 reagent in Quanti-Tray/2000 plates, and incubated for 18 h at 44 ± 1 °C. Enterococcal samples were spread on Slanetz–Bartley agar plates and incubated for 24 h. For Salmonella spp., 50 g samples were incubated in peptone broth then cultured in RV soil and plated on XLT and BGA agar plates, with colonies counted after 24 h. XLT agar showed black colonies, while BGA agar turned from pink to red according to Hrčka et al. [43].

2.5. Analysis of Physiological Parameters

Five random ears were selected from each sample for length measurements. The ear length was measured from the base to the tip in centimetres. The average number of grains per ear (NGE) was determined concurrently with ear length measurements. From each variant, 5 random ears were chosen, and the total number of grains was tallied after measurement. The average number of grains for each variant was calculated from the sum of all 3 replicates for each variant. Thousand-grain weight (TGW) is a unit used to determine the weight of a specific quantity of plant grains. The TGW assessment was conducted using an electronic seed counter C 21, with 500 seeds from each sample poured into the counter in two replicates, as standardized by the ČSN 46 0610 [47].

Leaf samples for the determination of leaf water potential were placed into a 5 mL syringe, sealed with Parafilm, and frozen at −24 °C. Water potential was determined using PSYPRO in C-52 measuring chambers (WESCOR Inc., South Logan, UT, USA) by pressing 10 µL of solution from frozen leaves to discs of filter paper. The measurements were performed in three repetitions of the five plant samples.

The net CO₂ assimilation (A), stomatal conductance (gs), and transpiration rate (E) were measured on 3rd fully expanded leaves, using a portable gas exchange system LCpro (ADC BioScientific Ltd., Hoddesdon, UK). The gas exchange was measured from 9:00 to 12:00 a.m. The irradiance was 650 μmol·m⁻²·s⁻¹ of photosynthetically active radiation (PAR). With a normal concentration of CO₂, the temperature in the measurement chamber was 23 °C, and the duration of the measurement of each sample was about 15 min, after the establishment of steady-state conditions inside the measurement chamber. The measurements of these parameters took place on single leaves from three different plants. The minimum chlorophyll fluorescence (F0) and the maximum chlorophyll fluorescence (Fm) were measured in situ, with the portable fluorometer OS5p+ (ADC BioScientific Ltd., Hoddesdon, UK), with 1 s excitation pulse (660 nm) and a saturation intensity of 3000 μmol·m⁻²·s⁻¹ after 20 min of darkness adaptation of the 4th or 5th fully expanded leaves. The maximum quantum yield of PSII was calculated using the formula Fv/Fm = (Fm − F0)/Fm. These parameters were measured in five replicates of each experimental plot.

Pigment content (chlorophyl a and b and total—Chl a; Chl b; Chl tot; Car x + c) was determined according to the methodology of Porra et al. [48]. Targets of 1 cm² were taken from wheat leaves. Targets were placed in plastic vials and 1 mL of dimethylformamide (DMF; Merck KGaA, Darmstadt, Germany) was added. Within 24 h, the pigments were extracted in cold darkness under nonstop shaking. Twenty-four hours after collection, the samples were spectrophotometrically analyzed using a UV-Vis Evolution 2000 instrument (Thermo Fisher Scientific Inc., Waltham, MA, USA). As blank, pure dimethylformamide was used. The absorbance (A) measurements were obtained at wavelengths of 480; 648.8; 663.8; and 710 nm.

2.6. Statistical Analyses

The data were processed using the MS Excel 365 programme (MS Office 365, Microsoft, Redmond, CA, USA). A test of normality and homogeneity of data was used. Data were analyzed using analysis of variance (ANOVA) and then compared using Fisher’s LSD test at significance levels p ≤ 0.05 and p ≤ 0.01. All statistical calculations were performed using Statistica 12 software (StatSoft, Tulsa, OK, USA). This statistical approach allowed an accurate assessment of the differences between the variants.

3. Results and Discussion

High soil pH values can lead to a deficiency of accessible nutrients for plants, thus reducing the utilization of nitrogen, phosphorus, and potassium. Acidic soil with a low pH value can be too aggressive for some plants, potentially deteriorating their growth or yield. From the comparison, it is evident that the pH value of all soil samples taken during cultivation increased from an average value of around 7.8 to 8.1. The pH values generally ranged between 8.0 and 8.2. Variant VI showed the lowest-pH CaCl₂, indicating a lower content of metal ions. Electric conductivity expresses the level of salt content in the soil or substrate. It affects plants and the quantity and growth of microorganisms in the soil. The results in

Table 2. Moisture, pH, and EC content in the soil and fertilizers before establishing the experiment and after harvest.

	pH (H2O) [-]	pH (CaCl2) [-]	EC [µS·cm−1]	Moisture [%]
Soil	7.8 ± 0.0 a	7.1 ± 0.0	204.7 ± 9.6 a	9.9 ± 0.2 a
Vermicompost I.	7.0 ± 0.0 b	-	1713.7 ± 78.7 b	68.7 ± 0.3 b
Vermicompost II.	7.0 ± 0.0 b	-	1901.3 ± 44.8 c	72.7 ± 0.3 c
Compost I.	7.1 ± 0.0 c	-	1466.3 ± 51.3 d	65.6 ± 0.6 d
Compost II.	7.2 ± 0.0 d	-	1545.7 ± 83.5 d	64.9 ± 0.8 d
O	8.1 ± 0.0 a	7.1 ± 0.1 a	127.0 ± 7.3 a	10.1 ± 0.9 a
V I.	8.0 ± 0.1 a	7.2 ± 0.0 a	118.2 ± 2.6 a	15.4 ± 0.7 b
V II.	8.1 ± 0.1 a	7.3 ± 0.0 b	126.5 ± 8.8 ab	17.8 ± 0.5 c
C I.	8.1 ± 0.0 a	7.3 ± 0.0 b	125.8 ± 7.3 a	14.9 ± 0.8 bd
C II.	8.2 ± 0.1 a	7.3 ± 0.1 ab	148.5 ± 13.5 b	13.7 ± 0.4 d

Values are means ± SD (n = 3). Different letters indicate significant differences between variants (Fisher’s LSD test, p ≤ 0.01).

show the pH and electrical conductivity (EC) values of soil, compost, and vermicompost samples before the experiment setup and after its completion. The EC values after the experiment varied between samples, but the values were relatively low, ranging from 118.2 to 148.5 µS·cm⁻¹. Compared to normal values, this is a medium or slightly high value, which was caused by the fertilization itself, as evident from the table, where both composts and vermicomposts had EC above 1400 µS·cm⁻¹. Overall, the pH and EC values were fairly similar and did not indicate significant differences between the variants. On the other hand, Aechra et al. [49] examined the effect of vermicompost on the physico-chemical properties of soil where wheat was grown. The experiment was conducted on the school grounds of a university in India over a period of 2 years. Vermicompost from a dairy farm was randomly applied in 3 repetitions at a rate of 4 t·ha⁻¹ and was incorporated into the field during sowing and the tillage phase. As a result, they found that the application of vermicompost to the soil reduced the pH and EC values. Similarly, Azarmi et al. [50] conducted an experiment to examine the impact of vermicompost on soil properties, where different amounts of vermicompost (0; 5; 10; and 15 t·ha⁻¹) were applied to a depth of 15 cm in the soil. Soil samples and property measurements were taken three months after the vermicompost application. The highest and lowest pH values were observed in the control variant without vermicompost (pH 8) and in the variant with 15 t·ha⁻¹ (pH 7.3). The application of vermicompost led to an increase in the content of available phosphorus, which likely contributed to the reduction in pH. This finding is further supported by the study of Atiyeh et al. [51], who found that the application of vermicompost in larger quantities led to a decrease in soil pH.

Yield components in crop production develop gradually and are interconnected. Spring wheat has a limited compensatory ability, meaning that in the event of a decrease in one yield component, it cannot sufficiently compensate for the levels of subsequent components. This ability is important for maintaining balance in the growth and development of the plant. If it is limited, it can lead to a reduction in yield and the quality of the harvest. There were only slight differences observed between the plots fertilized with vermicompost and those fertilized with compost. In variants fertilized with vermicompost, the average ear lengths were smaller than in variants fertilized with compost (

Table 3. Yield parameters of spring wheat.

	Harvest [kg·ha−1]	Straw Harvest [kg·ha−1]	Grain Harvest [kg·ha−1]	Ear Length [cm]	NGE [pcs]	TGW [g]
O	7996.7 ± 230.3 a	3676.7 ± 165.0 a	4320.0 ± 65.6 a	7.4 ± 0.5 a	27 ± 2 a	41.8 ± 0.5 ab
V I.	9320.0 ± 113.6 b	4233.3 ± 70.2 b	5086.7 ± 66.6 b	7.6 ± 0.3 a	27 ± 5 a	42.4 ± 1.7 b
V II.	9486.7 ± 470.4 b	4293.3 ± 246.8 b	5193.3 ± 223.7 b	7.1 ± 0.6 a	28 ± 4 a	42.3 ± 0.7 b
C I.	9220.0 ± 230.7 b	4236.7 ± 176.2 b	4983.3 ± 202.1 b	7.8 ± 0.4 a	29 ± 4 a	41.3 ± 1.1 ab
C II.	9150.0 ± 168.2 b	4140.0 ± 208.1 b	5010.0 ± 50.0 b	7.7 ± 0.2 a	30 ± 1 a	42.0 ± 1.3 ab

NGE—number of grains per ear; TGW—thousand grain weight. Values are means ± SD (n = 5). Different letters indicate significant differences between variants (Fisher’s LSD test, p ≤ 0.01).

). Variants C I and C II had an average ear length of 7.8 cm and 7.7 cm, respectively. V II had an average ear length of only 7.1 cm, compared to V I with 7.6 cm. It appears that the use of C II and C I increased the average ear length by 0.3–0.4 cm compared to the control variant. V II, on the other hand, did not lead to an increase in ear length and was slightly shorter compared to the control. However, given the number of measurements and the small difference between the results, it is not possible to show a definitive conclusion from this data set regarding the effectiveness of individual fertilizers on ear length. Variants C II (30 grains) and C I (29 grains) achieved the highest average number of grains per ear (NGE), while the lowest number of grains was counted in the control variant (O) and variant V I (27 grains). The grain yield was on average slightly higher with compost, but the grain size was larger in variants with vermicompost than in wheat fertilized with compost. Diviš et al. [52] reported that the potential productivity of spring wheat ear ranges from 100 to 150 grains, but the actual number of grains in ear at harvest is 15–45. The results of tests conducted by Petr and Lipavský [53] showed that modern varieties of spring wheat produce between 25 and 36 grains in each ear. In our experiment, we observed average to higher values according to the previous statements. Wheat grains of the Pexeso variety taken from all five variants measured in three repetitions showed different thousand-grain weights (TGWs). The average values ranged from 41.3 to 42.4 g. The highest average TGW was achieved from the plots fertilized with vermicompost I and II (Table 3). Diviš et al. [52] state that cereals usually have a thousand-grain weight between 30 and 50 g, which was confirmed in our experiment. In the experiments conducted by Petr and Lipavský [36], the average thousand-grain weight in new spring wheat varieties was 38 g. Researchers from UKZUZ (Central Institute for Supervising and Testing in Agriculture, Czech Republic) examined the utility values of the spring wheat harvest in 2022 [54]. For the Pexeso variety, they achieved a thousand-grain weight of 45.5 g, which was closest to our variant fertilized with vermicompost I. The high temperatures could have influenced the TGW values, with an average temperature of around 19 °C in May and June, but sufficient rainfall in June (132 mm) and early August (99 mm) supported the assimilation apparatus, preventing a sharp decrease in TGW. Overall, the highest yield was found in variant V II, while the lowest values were measured in the control variant, both for straw and grain.

From the comparison of data in

Table 4. Contents of available macronutrients in soils and fertilizers.

	P [mg·kg−1]	K [mg·kg−1]	Mg [mg·kg−1]
Soil	57.5 ± 9.1 a	397.7 ± 82.3 a	130.9 ± 19.7 a
Vermicompost I.	94.2 ± 7.8 b	1147.9 ± 61.6 b	994.3 ± 111.5 b
Vermicompost II.	87.2 ± 15.2 b	1938.6 ± 21.8 c	633.9 ± 7.9 c
Compost I.	88.2 ± 11.4 b	2054.3 ± 19.4 d	895.5 ± 5.6 b
Compost II.	59.3 ± 7.0 a	2312.7 ± 162.5 e	660.2 ± 29.1 c
O	43.5 ± 7.8 a	304.7 ± 21.8 a	122.9 ± 13.1 a
V I.	51.0 ± 7.8 ab	279.4 ± 40.5 a	120.2 ± 9.6 a
V II.	52.4 ± 10.9 ab	444.0 ± 105.0 b	149.6 ± 19.2 a
C I.	56.4 ± 12.3 ab	354.0 ± 66.6 ab	135.2 ± 10.7 a
C II.	61.1 ± 10.1 b	597.7 ± 395.9 ab	151.6 ± 34.7 a

Values are means ± SD (n = 3). Different letters indicate significant differences between variants (Fisher’s LSD test, p ≤ 0.01).

, it is clear that at the end of the experiment, the average content of all monitored available nutrients in the unfertilized soil decreased. The most significant decrease was observed in available phosphorus content (from 57.5 mg·kg⁻¹ to 43.5 mg·kg⁻¹) and available potassium content (from 397.7 mg·kg⁻¹ to 304.7 mg·kg⁻¹), while the available magnesium content decreased significantly less. The decline in the average content of all monitored nutrients may be attributed to various factors, such as the depletion of soil reserves or changes in soil structure after the experiment concluded. The standard deviation indicates that the values of individual measurements were not significantly different. Compost typically provides soil with a range of nutrients, with a high proportion of phosphorus. The activity of soil microorganisms promotes the mobilization of more phosphorus bound in the soil, which contributes to a greater uptake of this nutrient by plants. However, high soil pH can limit phosphorus uptake by plants, as shown in studies [55]. The highest average available phosphorus content in our experiment was found in the soil of variant C II (61.1 mg·kg⁻¹) and the lowest in the soil of variant V I (51.0 mg·kg⁻¹). The average available phosphorus contents in samples V I and V II were similar. A study conducted by Arancon et al. [56] found that soils enriched with food waste vermicompost at a rate of 10 t·ha⁻¹ contained more phosphorus than control variants enriched only with mineral fertilizers. This observation suggests that phosphorus uptake from vermicompost into the soil occurred more slowly, likely due to the activity of soil microorganisms that gradually released nutrients from organic materials. Moreover, the nutrient release from vermicompost is facilitated by the action of earthworms and microorganisms, which convert organic matter into soluble forms that are readily available for plant uptake [57,58]. In particular, vermicompost has been shown to enhance the availability of essential nutrients such as nitrogen, phosphorus, and potassium, which are crucial for plant growth [59,60]. In our experiment, it was shown that different sources of sewage sludge used for the production of compost and vermicompost significantly affected the potassium content in the soil. The soil to which compost II and vermicompost II (C II and V II) were applied contained, on average, more available potassium (597.7 mg·kg⁻¹ and 444.0 mg·kg⁻¹) than the soil to which fertilizers C I and V I (354.0 mg·kg⁻¹ and 279.4 mg·kg⁻¹) were applied. These results may influence the development and growth of plants grown in these soils, as potassium is a key element for the proper function of plant cells and photosynthesis processes. Azarmi et al. [50] studied the effect of vermicompost on potassium content in the soil. The experiment was conducted on an experimental farm in Iran. Sheep manure was used as a raw material for the production of vermicompost, which was applied at a rate of 0 (control), 5, 10, and 15 t·ha⁻¹. The results showed that after the application of vermicompost, potassium content in the soil increased by 34%, 46%, and 58% in the test variants (5, 10, and 15 t·ha⁻¹) compared to the control variant. Thus, the greater the amount of vermicompost applied, the more potassium content in the soil increased. These results indicate that vermicompost is an effective source of potassium for the soil and can help improve its fertility and plant nutrition. The average magnesium concentration in our C II variant was the highest (151.6 mg·kg⁻¹), followed by V II (149.6 mg·kg⁻¹), C I (135.2 mg·kg⁻¹), and finally V I (120.2 mg·kg⁻¹). Manivannan et al. [61] conducted a field experiment aimed at comparing the effectiveness of vermicompost and inorganic NPK fertilizers on magnesium content in clayey, sandy, and red clayey soils. Samples were taken from a depth of 15 cm before fertilizer application and 75 days after application (after bean harvest). The results showed that the application of 100% vermicompost (5 t·ha⁻¹) and 50% vermicompost supplemented with 50% NPK led to an increase in magnesium content in both clayey and sandy soils.

As expected, a significantly higher total nitrogen content and uptake was measured in grain compared to the straw. The highest value of nitrogen uptake was shown by variant VI in total (118 kg·ha⁻¹ for grain plus 29 kg·ha⁻¹ for straw). For N uptake by straw, this variant was the only one that differed statistically significantly from the other variants. The total nitrogen content in the grain varied from 22,650 mg·kg⁻¹ (control unfertilized variant) to 23,450 mg·kg⁻¹ (C I variant). The highest N uptake by grain was measured for variant V II 120.8 kg·ha⁻¹; on the other hand, the lowest N uptake was shown by the control variant 97.9 kg·ha⁻¹ (Figure 3A). The low values of N uptake by the control variant correspond to the lowest total N content in unfertilized soil, which was around 2000 mg·kg⁻¹ (C I: 20,130 mg·kg⁻¹, C II: 22,597 mg·kg⁻¹, V I: 19,875 mg·kg⁻¹, V II: 18,350 mg·kg⁻¹). Phosphorus is an essential nutrient for wheat, influencing nitrogen intensity and assimilation throughout the entire vegetative growth phase. Particularly at the beginning of the vegetation period, it is necessary to ensure its sufficiency for the formation of a strong root system. Phosphorus positively affects the growth and development process, including vernalization, heading, flowering, fertilization, and grain formation [62]. If the plant suffers from a phosphorus deficiency, its growth is restricted, the leaves are smaller, the stems are weaker, and the plant produces fewer tillers [63]. The average total phosphorus content was the highest in the grain, followed by the roots, and the lowest content was measured in the straw. The high phosphorus content in wheat grain was due to its influence on plant growth and development. The highest average phosphorus concentration was measured in grain samples from variant V I (3046 mg·kg⁻¹), followed by variants V II and C II (2887 mg·kg⁻¹ and 2835 mg·kg⁻¹). Roots from the C II variant contained the most phosphorus (1589 mg·kg⁻¹), whereas roots from the O variant contained the lowest amount of total phosphorus (762 mg·kg⁻¹). In the straw, the total phosphorus content ranged from 275 mg·kg⁻¹ to 541 mg·kg⁻¹ depending on the plant part and fertilization variant. Regarding phosphorus uptake by the stand, a statistically significantly higher uptake by the grain was observed in the variants fertilized with vermicomposts. The statistically lowest uptake by both straw and grain was observed in the control variant compared to the fertilized variants (Figure 3B). Grain uptake was several times higher than straw uptake. The physiological effect of potassium in plant metabolism is crucial for spring wheat yield formation. Potassium generally influences the transport of assimilates within the plant, particularly to the roots and seeds, affecting root system development [64]. The potassium content in plants changes as tissues age, with older plants having lower potassium content. Cereals have limited potassium uptake in the second half of the growing season and may even release it back into the soil due to stress factors, especially drought [65]. Potassium deficiency causes greater susceptibility to lodging, increases the risk of fungal diseases, reduces grain starch content, and negatively affects protein synthesis [63]. The average total potassium content was the highest in the straw, followed by the roots, and the lowest values were measured in the grain. The difference may be due to the natural transport of nitrogen from the roots and leaves to the above-ground biomass. The highest average total potassium content was measured in straw samples from variant V I (18,275 mg·kg⁻¹), followed by variants O and C II (18,212 mg·kg⁻¹ and 16,933 mg·kg⁻¹). Roots from the O variant (5506 mg·kg⁻¹) contained the most total potassium, whereas roots from C I (4384 mg·kg⁻¹) contained the least. The total potassium content in the grain ranged from 3312 mg·kg⁻¹ to 3609 mg·kg⁻¹ depending on the plant part and fertilization variant. Grain and roots contained the least total potassium because only a small amount is transported to them during growth and development. Potassium uptake, like phosphorus, was overall highest in variant V I, where a statistically significant difference in potassium uptake by straw was found compared to all other variants. The overall lowest uptake was observed in variants C I and O (Figure 3C). Straw uptake was several times higher than grain uptake. Magnesium activates enzyme systems in plants; Mg is part of chlorophyll and influences the enzymatic reactions of photosynthesis. Its participation in the biochemical reactions of the Calvin cycle allows for the fixation of carbon dioxide and the formation of organic compounds, including glucose. Magnesium also plays a role in phosphorylation, nitrate reduction, and the synthesis of oxoacids with ammonium nitrogen [65]. A deficiency of magnesium, along with a deficiency of potassium, leads to a decrease in photosynthesis and protein content in the grain [63]. The average total magnesium content was the highest in the roots, followed by the grain, and the lowest content was measured in the straw. The highest average total magnesium content was measured in root samples from the C I variant (1601 mg·kg⁻¹), followed by variants V II and V I (1552 mg·kg⁻¹ and 1523 mg·kg⁻¹). Grain from the V I variant (1204 mg·kg⁻¹) contained the most total Mg, whereas grain from the O variant (1068 mg·kg⁻¹) contained the least. In the straw, the total magnesium content ranged from 595 mg·kg⁻¹ to 793 mg·kg⁻¹ depending on the fertilization variant. Magnesium uptake was highest in variant V I, which was statistically significant. On the other hand, the lowest uptake was observed in the control variant (O), which was also statistically significant (Figure 3D).

The analysis of available heavy metals in soils and fertilizers showed significant differences between treatments. Initial composts and vermicomposts had elevated concentrations of heavy metals compared to untreated soil, particularly Zn (523.6–675.4 mg·kg⁻¹), Cu (111.8–184.3 mg·kg⁻¹), and Pb (20.8–25.5 mg·kg⁻¹) (

Table 5. Contents of available heavy metals in soils and fertilizers.

	Cd [mg·kg−1]	Pb [mg·kg−1]	As [mg·kg−1]	Cr [mg·kg−1]	Cu [mg·kg−1]	Ni [mg·kg−1]	Zn [mg·kg−1]
Soil	0.1 ± 0.0 a	13.2 ± 2.9 a	2.1 ± 0.5 a	<DL a	4.2 ± 0.8 a	0.7 ± 0.2 a	8.1 ± 1.6 a
Vermicompost I.	0.7 ± 0.1 bc	22.9 ± 1.1 b	5.2 ± 0.7 b	27.4 ± 2.1 bd	184.3 ± 9.8 b	16.5 ± 1.5 b	581.0 ± 29.6 b
Vermicompost II.	0.8 ± 0.1 c	25.5 ± 1.5 b	68.2 ± 5.4 c	27.3 ± 1.6 b	118.4 ± 12.4 c	17.5 ± 1.3 b	675.4 ± 41.5 c
Compost I.	0.6 ± 0.0 b	20.8 ± 0.8 c	4.4 ± 0.6 b	23.2 ± 1.1 c	169.6 ± 4.9 b	16.7 ± 1.3 b	523.6 ± 12.8 d
Compost II.	0.7 ± 0.1 bc	22.6 ± 1.7 bc	74.5 ± 7.0 c	23.5 ± 2.0 cd	111.8 ± 5.7 c	19.3 ± 1.7 b	615.0 ± 39.1 bc
O	0.1 ± 0.0 a	11.6 ± 1.7 a	1.4 ± 0.5 a	<DL a	3.8 ± 0.4 ab	0.6 ± 0.0 a	7.5 ± 1.1 a
V I.	0.1 ± 0.0 a	11.3 ± 1.8 a	1.4 ± 0.4 a	<DL a	3.7 ± 0.3 a	0.5 ± 0.1 a	7.8 ± 0.9 a
V II.	0.2 ± 0.0 b	14.5 ± 3.1 a	1.5 ± 0.6 a	<DL a	4.8 ± 0.7 b	0.8 ± 0.1 b	11.4 ± 1.2 b
C I.	0.2 ± 0.0 b	12.8 ± 1.3 a	1.5 ± 0.3 a	<DL a	4.3 ± 0.2 b	0.7 ± 0.1 ab	9.5 ± 0.3 c
C II.	0.2 ± 0.0 b	13.2 ± 1.8 a	1.6 ± 0.4 a	<DL a	4.4 ± 0.3 b	0.6 ± 0.0 a	10.6 ± 2.4 abc

DL—detection limit. Values are means ± SD (n = 3). Different letters indicate significant differences between variants (Fisher’s LSD test, p ≤ 0.01).

). After wheat harvest, fertilized soils (V I, V II, C I, C II) exhibited only minor increases in heavy metal availability compared to the unfertilized control (O), suggesting limited mobility of these elements. The compost- and vermicompost-treated soils showed slightly higher Zn (7.8–11.4 mg·kg⁻¹) and Cu (3.7–4.8 mg·kg⁻¹) than the control (Zn: 7.5 mg·kg⁻¹, Cu: 3.8 mg·kg⁻¹), while As, Cr, and Pb remained at low levels across all post-harvest samples. Composting and vermicomposting of sewage sludge have been studied as sustainable methods for stabilizing heavy metals and improving nutrient availability. Research indicates that composting can reduce metal bioavailability by promoting organic matter complexation and pH stabilization [66,67]. Vermicomposting, through the activity of earthworms, further enhances stabilization by binding metals to humic substances [68]. However, the effectiveness of these processes depends on sludge composition, composting conditions, and soil properties post-application. Studies on sludge-based amendments confirm that while total heavy metal content may be high, plant-available fractions often remain low [69], aligning with the present findings that indicate minimal accumulation in fertilized soils.

Among the monitored heavy metals (cadmium—Cd; lead—Pb; arsenic—As; chromium—Cr; copper—Cu; nickel—Ni; zinc—Zn), measurable concentrations in straw were detected only for chromium, copper, nickel, and zinc, while the remaining heavy metals (Cd, Pb, As) were below the detection limit. The uptake of chromium by straw ranged from 0.003 kg·ha⁻¹ (variant V I) to 0.007 kg·ha⁻¹ (variants O and V II). Copper was detected in both straw and grain, with plant uptake values as follows: straw (kg·ha⁻¹): O: 0.007, V I: 0.006, V II: 0.005, C I: 0.006, C II: 0.004; grain (kg·ha⁻¹): O: 0.014, V I: 0.019, V II: 0.018, C I: 0.018, C II: 0.015. The highest copper uptake by straw was recorded in the control variant, whereas the highest uptake in grain was observed in variant V I. Nickel uptake by the plant was detected only in straw, ranging from 0.002 kg·ha⁻¹ (variants V I and C I) to 0.003 kg·ha⁻¹ (variants O, V II, and C II). Zinc uptake in straw was highest in variant V I (0.073 kg·ha⁻¹) and lowest in variant C I (0.052 kg·ha⁻¹). Zinc was also detected in grain, with uptake values ranging from 0.109 kg·ha⁻¹ (variant O), progressively increasing from variants C II–C I–V II to variant V I, where the highest value of 0.156 kg·ha⁻¹ was recorded. The remaining heavy metals (Cd, Pb, As, Cr, Ni) were not detected in grain.

The microbial biomass analysis showed significant differences between treatments in fungal and bacterial abundance, as well as the bacteria-to-fungi (B/F) ratio. The initial composts and vermicomposts used for soil fertilization exhibited the highest fungal and bacterial biomass, with composts I and II showing the highest values (fungi: 5.56–6.36 µg PLFA·g⁻¹ dw; bacteria: 121.57–130.47 µg PLFA·g⁻¹ dw;

Table 6. Contents of groups of microorganisms in soils and fertilizers before establishing the experiment and after harvest.

	Fungi [μg PLFA·g−1 dw]	Bacteria [μg PLFA·g−1 dw]	B/F Ratio
Soil	0.08 ± 0.05 a	1.19 ± 0.65 a	15.54 ± 2.60 a
Vermicompost I.	2.49 ± 0.63 b	58.92 ± 21.22 b	23.28 ± 3.49 b
Vermicompost II.	3.85 ± 2.01 bc	84.35 ± 47.65 bc	21.92 ± 2.95 b
Compost I.	5.56 ± 0.44 c	130.47 ± 29.03 c	23.64 ± 4.54 b
Compost II.	6.36 ± 1.52 c	121.57 ± 21.02 c	19.68 ± 4.44 ab
O	0.05 ± 0.02 a	1.07 ± 0.52 a	21.87 ± 5.53 a
V I.	0.08 ± 0.01 a	1.71 ± 0.07 b	22.70 ± 3.04 a
V II.	0.11 ± 0.01 b	2.39 ± 0.54 c	22.52 ± 3.93 a
C I.	0.08 ± 0.02 ab	2.21 ± 1.41 abc	25.53 ± 9.32 a
C II.	0.22 ± 0.19 ab	2.44 ± 0.32 c	17.50 ± 11.14 a

Values are means ± SD (n = 3). Different letters indicate significant differences between variants (Fisher’s LSD test, p ≤ 0.01).

), followed by vermicomposts I and II. In contrast, the untreated soil had minimal microbial biomass (fungi: 0.08 ± 0.05; bacteria: 1.19 ± 0.65). After wheat harvest, fertilized soils (V I, V II, C I, C II) showed slightly increased microbial biomass compared to the unfertilized control (O), but overall values remained low. The B/F ratio varied between 17.50 and 25.53, with no significant differences among post-harvest treatments, suggesting that while organic amendments initially boosted microbial biomass, their long-term effects were limited.

The relationship between physiological parameters and yield parameters is crucial for understanding how various agronomic practices, such as the use of vermicompost, affect crop performance. In the analysis of variants VI and VII, which achieved the highest CO₂ assimilation rates (10.65 µmol CO₂·m⁻²·s⁻¹ and 10.75 µmol CO₂·m⁻²·s⁻¹), it is evident that they also exhibited the highest grain yields (5096.7 kg·ha⁻¹ and 5193.3 kg·ha⁻¹) [70]. This positive relationship may be related to the significant impact of vermicompost on the photosynthetic activity of plants, which is directly related to the yield. Similar conclusions have been confirmed in the literature, showing that increased atmospheric CO₂ concentration stimulates photosynthesis and boosts crop yields [71].

Furthermore, the relationship between physiological parameters and thousand-grain weight (TGW) is also significant. The highest TGW (42.4 g and 42.3 g) was shown in the vermicompost variants, indicating that better physiological activity contributed not only to higher yields but also to better grain quality [72]. The control variant (O) had lower TGW values (41.8 g) and also the lowest photosynthesis value, supporting the hypothesis of the positive effect of vermicompost on growth parameters. The literature states that higher photosynthetic capacity is crucial for ensuring sufficient assimilates for grain development [73]. Studies have also shown that improved photosynthesis and increased chlorophyll content lead to higher TGW and total yield [74]. These findings are consistent with the observation that physiological parameters, such as CO₂ assimilation, directly influence crop yield parameters. In the case of variants VI and VII, grown on plots amended with vermicompost, it appears that the combination of improved photosynthesis and an optimal nutritional regime can lead to significant improvements in yield parameters. In the analysis of the relationship between physiological and yield parameters, it is also important to consider the impact of various stress factors, such as drought or excessive heat, which can negatively affect photosynthesis and subsequently yields [75,76]. For example, under drought conditions, plants with higher assimilate reserves can respond to stress and maintain higher yields [77]. These findings confirm the importance of physiological parameters in the context of yield parameters and highlight the need to optimize conditions for plant growth. Additionally, studies show that improving photosynthesis and increasing assimilate content in plants can be achieved through proper management of nitrogen and other nutrients [78]. Proper fertilization can lead to higher photosynthetic activity, which subsequently translates into higher yields and better grain quality. Water use efficiency (WUEi), expressed as the ratio of photosynthetic rate (A) to stomatal conductance (gs), is a significant indicator of plant water management. In the analysis of variants VI and VII, the highest WUEi values were observed (102.7 µmol CO₂·mol⁻¹ H₂O and 106.3 µmol CO₂·mol⁻¹ H₂O;

Table 7. Parameters of gas exchange, chlorophyll florescence, and water balance.

	A [µmol CO2·m−2·s−1]	E [mmol H2O·m−2·s−1]	gs [mol H2O·m−2·s−1]	WUEi [μmol CO2·mol−1 H2O]	Fv/Fm	WP [MPa]
O	9.78 ± 0.55 ab	3.14 ± 0.11 a	0.19 ± 0.01 a	52.7 ± 17.2 c	0.818 ± 0.001 a	−1.69 ± 0.06 c
V I.	10.65 ± 0.22 a	2.24 ± 0.03 bc	0.10 ± 0 c	102.7 ± 6.1 a	0.818 ± 0.002 a	−1.97 ± 0.07 a
V II.	10.75 ± 0.22 a	2.20 ± 0.04 bc	0.10 ± 0 c	106.3 ± 8.2 a	0.813 ± 0.006 a	−1.88 ± 0.09 ab
C I.	9.38 ± 0.54 b	2.43 ± 0.13 b	0.13 ± 0.01 b	76.7 ± 30.9 b	0.810 ± 0.008 a	−1.83 ± 0.02 abc
C II.	9.80 ± 0.09 c	2.07 ± 0.04 c	0.09 ± 0 c	72.3 ± 6.4 b	0.809 ± 0.003 a	−1.76 ± 0.04 bc

A—assimilation of CO₂; E—transpiration of H₂O; gs—stomatal conductance; WUEi—water use efficiency (internal); Fv/Fm—fluorescence of chlorophyll; WP—water potential. Values are means ± SD. Different letters indicate significant differences between variants (Fisher’s LSD test, p ≤ 0.01).

), which indicate that vermicompost improves water use for photosynthesis. On the other hand, the control variant showed the lowest efficiency (52.7 µmol CO₂·mol⁻¹ H₂O), indicating less effective water management [79]. Several factors may contribute to the higher WUEi in variants VI and VII, firstly, better soil structure and water retention due to higher organic matter content. The literature indicates that organic matter improves soil’s water-holding capacity, which is crucial for maintaining optimal plant growth conditions [80]. The higher microorganism content in the soil, supported by vermicompost, also enhances water uptake by the root system. Some studies showed that a healthy and well-developed root system can efficiently absorb water, contributing to higher WUEi [81]. Another factor that may have contributed to higher WUEi in the vermicompost variant was optimized stomatal regulation leading to reduced transpiration. Vermicompost use promotes the development of a healthy root system, which has a better ability to regulate stomatal opening and closing in response to water availability. This regulation is partly influenced by the presence of bioactive substances, such as hormones that promote stomatal closure during water stress, contributing to more efficient water use [82]. In the case of variants VI and VII, it is assumed that improved stomatal regulation contributed to lower transpiration and higher water use efficiency. Furthermore, some studies suggest that aquaporins, which regulate water flow in plants, may play an important role in water use efficiency. For example, aquaporins in roots and leaves affect overall transpiration and plant water management [81]. In the vermicompost variant, increased aquaporin activity could be associated with better transpiration regulation and higher WUEi. Furthermore, stomatal regulation is also influenced by abscisic acid (ABA), which plays a key role in plant response to water stress. The literature indicates that ABA can induce stomatal closure, reducing transpiration and increasing WUEi [83]. Stomatal conductance (gs) and water potential (WP) are key factors affecting CO₂ uptake and transpiration regulation. The lower stomatal conductance value in the vermicompost variants (0.10 mol H₂O·m⁻²·s⁻¹) indicates more efficient stomatal regulation, allowing better protection against water stress [84]. This regulation is crucial because stomatal conductance directly determines the plant’s ability to absorb CO₂ and lose water, which is essential for maintaining photosynthetic activity [85]. Water potential (WP) provides information about water availability in plants. The lowest WP values in variant VI (−1.97 MPa) may indicate higher transpiration losses during intensive growth, while the control variant (−1.69 MPa) shows less water use and lower growth activity [86]. The higher negative WP in variants grown with vermicompost suggests greater water stress but also higher photosynthetic activity and nutrient uptake, which may result from more efficient use of available water [87]. Stomatal regulation is also an important factor that can affect transpiration (E) and thus the overall water balance of plants. With lower transpiration and better stomatal regulation, plants can use water more efficiently, which is important for their growth and yields [88]. Bunce [89] indicates that stomatal conductance and water potential are closely linked to the overall physiological performance of plants, confirming the importance of optimizing these parameters to ensure healthy growth and crop yields. Based on the experimental results, which demonstrate that vermicompost-enriched variants exhibit higher water use efficiency (WUEi) and lower stomatal conductance (gs), it can be inferred that the enhancement in stress tolerance is not solely attributable to improved water availability. Vermicompost contains bioactive compounds and growth hormones that can modulate the synthesis of endogenous hormones, particularly abscisic acid (ABA) [34]. Elevated ABA levels, as indicated by our findings (lower gs values in variants VI and VII), induce stomatal closure, thereby reducing transpiration losses and enhancing plant water efficiency [22]. Additionally, the action of auxins and cytokinins promotes the development of a more extensive root system, facilitating more efficient water uptake from deeper soil layers [90]. These hormonal interactions synergistically enhance nutrient availability from vermicompost. Collectively, these factors contribute to an overall improvement in plant drought tolerance, which is crucial for sustainable agriculture [91]. Further research focusing on the modulation of endogenous hormone levels could provide deeper insights into the mechanisms underlying improved drought tolerance in wheat [35].

In this experiment, chlorophyll fluorescence was quantified, revealing that the plants in our study exhibited values ranging from 0.818 to 0.809, while the control plants maintained values around 0.818. These findings suggest a discrepancy in fluorescence between the experimental and control plants. Additionally, the literature indicates that a value of 0.800 is considered normal, implying that this method of measuring chlorophyll fluorescence may lack the sensitivity required to detect subtle physiological changes potentially induced by the application of experimental additives [92,93].

Experimental data showed that the vermicompost variants (VI, VII) had higher chlorophyll values, corresponding to the BBCH 39 and 55 stages, when plants maximize light uptake and photosynthesis (Figure 4). At BBCH 39, when the metering season begins, variant VII exhibited the highest chlorophyll values and lower transpiration, indicating improved stomatal regulation due to increased nutrient availability and better soil structure, which according to Croft et al. [94] allows more efficient water and mineral uptake by plants. This improved stomatal regulation contributes to more efficient water use and ensures optimal conditions for photosynthesis. Better nutrient supply from vermicompost supports leaf area development and photosynthetic capacity, corresponding to maximum biomass production and higher CO₂ assimilation rates (A) [95]. At BBCH 55, the beginning of flowering, there is a slight decrease in chlorophyll, associated with the redistribution of assimilates to the ears. During this phase, carotenoids increase, protecting leaves from oxidative stress, which is crucial for maintaining photosynthetic activity [96]. The reduction in stomatal conductance (gs) at this stage corresponds with experimental results, suggesting that plants adapt to changing conditions and optimize their water management. At BBCH 75, during senescence, a more pronounced decrease in chlorophyll is observed due to leaf senescence. However, vermicompost variants maintain a better chlorophyll-to-carotenoid ratio, resulting in delayed senescence and better protection of the photosynthetic apparatus during grain maturation [97]. The application of vermicompost led to better availability of nitrogen (N), phosphorus (P), and potassium (K), positively affecting chlorophyll formation and photosynthesis intensity. Higher N availability in the soil for variants VI and VII meant better chlorophyll synthesis, confirmed by higher photosynthetic activity and grain yields in these variants [95]. Carotenoids are important in protecting the photosynthetic apparatus against stress conditions such as high temperature and drought. At BBCH 75, carotenoid levels increased, corresponding to rising stress in the later growth stages. Vermicompost variants showed higher carotenoid levels, which may contribute to better protection against oxidative stress and maintaining plant productivity [98]. Additionally, carotenoids play a key role in neutralizing reactive oxygen species and help protect the photosynthetic apparatus from damage [99].

Our study showed that the application of compost and especially vermicompost led to a significant improvement in wheat yield, increased nutrient uptake, improved photosynthetic activity, and enhanced drought tolerance. These results are consistent with previous studies showing that organic amendments improve soil properties and overall plant performance [22,91]. Vermicompost has been shown to be particularly effective; its effectiveness can be attributed to its high content of bioactive compounds and growth hormones that promote nutrient availability and the development of an extensive root system [35,36]. When compared to biochar, it has been shown that although biochar improves soil structure and water-holding capacity, its nutrient and bioactive content tends to be lower than vermicompost [100]. On the other hand, manure, although rich in nutrients, may have the disadvantage of potential accumulation of heavy metals and other contaminants [101,102]. For these reasons, compost, and vermicompost in particular, represents a more balanced approach that not only increases soil fertility and water retention but also promotes plant hormonal responses, such as increased levels of abscisic acids; this contributes to improved stomatal regulation and reduced transpiration losses [103,104]. Based on these findings, it can be concluded that compost and vermicompost provide better results than other organic fertilizers, and this is also confirmed by other studies focusing on sustainable agriculture and wheat production [105,106].

4. Conclusions

During the experiment, optimal weather conditions in March ensured timely wheat sowing, contributing to ideal yields. However, higher temperatures in May and June and increased rainfall in June and August could have impacted grain formation and weight. Composts and vermicomposts improved soil properties, leading to higher grain and straw yields. Variants fertilized with composts and vermicomposts showed higher NGE and TGW, confirming their effectiveness in enhancing wheat yield. The use of vermicompost significantly enhanced the physiological and yield parameters of plants, improving photosynthetic activity, chlorophyll content, and water use efficiency. The plant’s uptake of macronutrients was highest in variant VI and lowest in the control variant. Vermicompost helped in osmotic adjustment under stress conditions, enhancing nutrient availability and soil structure, contributing to more efficient water and nutrient uptake, improved stomatal regulation, and increased resistance to oxidative stress. Overall, vermicompost proves to be a valuable tool for sustainable agriculture, promoting optimal plant growth and productivity.

On the basis of our results and general recommendations for the application of organic fertilizers, we recommend applying vermicompost to wheat at rates ranging from 0.2 to 0.3 kg·m⁻², which corresponds to approximately 2–3 t·ha⁻¹, but this only applies to vermicompost from sewage sludge with pulp. This rate helps to increase the organic matter content of the soil, thereby improving its water retention capacity and encouraging the development of a deeper and more extensive root system. This helps to increase the water efficiency of the plants and thus improve drought tolerance and overall yield. However, for successful application in the field, it is essential to take into account site-specific conditions such as soil structure, climatic conditions, and other agronomic factors. We therefore recommend that pilot tests be first carried out on a smaller area so that the dosage can be adjusted and optimized for specific conditions. This approach ensures that the application of vermicompost is not only effective in terms of increasing yield, but also sustainable in the long term and adapted to the specificities of local agriculture.