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Article

Effect of Dose and Date of Application of Vermicompost and Its Combination with N-Fertilizer on Maize Grain Yield

by
Peter Kováčik
1,*,
Vladimír Šimanský
1,*,
Mária Kmeťová
2,
Štefan Týr
3 and
Iwona Ledwożyw-Smoleń
4
1
Institute of Agrochemistry and Soil Sciences, Faculty of Agrobiology and Food Resources, Slovak University of Agriculture, 949 76 Nitra, Slovakia
2
Eurofins Food Testing Slovakia s.r.o., 940 02 Nové Zámky, Slovakia
3
Institute of Crop Production, Faculty of Agrobiology and Food Resources, Slovak University of Agriculture, 949 76 Nitra, Slovakia
4
Department of Plant Biology and Biotechnology, Faculty of Biotechnology and Horticulture, University of Agriculture in Krakow, 31-425 Krakow, Poland
*
Authors to whom correspondence should be addressed.
Agronomy 2026, 16(1), 118; https://doi.org/10.3390/agronomy16010118
Submission received: 1 December 2025 / Revised: 22 December 2025 / Accepted: 31 December 2025 / Published: 2 January 2026
(This article belongs to the Special Issue Innovations in Composting and Vermicomposting)
Versions Notes

Abstract

The European Union produces about 58 million tons of grain maize annually, and although Slovakia contributes only a small share, grain maize is an important crop occupying 10.6% of the country’s arable land. A two-year pot experiment was conducted to evaluate the effects of vermicompost (Vc) dose and application timing, applied alone or in combination with mineral nitrogen fertilizer, on maize grain yield and selected grain-quality parameters. The spring pre-sowing Vc application at 170 kg ha−1 total N proved appropriate.. Increasing the Vc dose from 170 to 340 kg ha−1 total N did not significantly influence grain yield, thousand kernel weight (TKW), or the contents of crude protein and starch. When soil was fertilized with Vc in autumn, the spring application of mineral N at 60 kg ha−1 resulted in higher grain yield compared with the spring application of Vc at 170 kg ha−1 total N. Application of Vc alone, regardless of dose or timing, did not affect starch content or TKW. The combined use of mineral and organic nitrogen sources appears to be the most effective strategy for maize nitrogen nutrition. Applying Vc in autumn or spring at 170 kg ha−1 total N, followed by 60 kg ha−1 mineral N in spring, created favorable conditions for achieving high grain yield and quality.

1. Introduction

Maize (Zea mays L.) is the third most important cereal crop in the world after wheat and rice, with an annual production exceeding 1 billion tons [1]. The USA, China, and Brazil are the largest producers of this crop with average grain yields of 11, 7, and 6 t ha−1, respectively. In most developed countries of the world, including Slovakia, maize grain is used mainly for animal feed (85%), and the rest is used for food and industrial purposes [2].
According to two forecasting models, maize grain yields are expected to decline by 8.2% or 16.4% in the second half of the 21st century due to climate change, mainly due to soil water shortages [3]. One solution to alleviate the expected soil water shortage is to increase the organic matter content of agricultural soils, because organic matter reduces surface water runoff, i.e., increases water retention [4,5]. Achieving this goal requires increasing the use of organic fertilizers in plant cultivation. This is especially true for Slovak agriculture, which has a shortage of organic fertilizers. In China, the utilization rate of total organic fertilizer production in crop production is only about 40% [6]. This contrasts with the high rates of organic fertilizer application in some countries in Western Europe and North America [7].
Organic fertilizers have a positive impact not only on the water content of the soil, but also positively affect several chemical, physical, and biological parameters of the soil [8,9,10], which results in better nutrient uptake by cultivated plants and higher yields [11]. It is known that vermicomposts also positively affect soil reaction, soil sorption capacity, and soil air regime. They increase the stability of soil aggregates, reduce soil bulk density, and increase the number of bacteria of the genus Azotobacter chroococcum in the soil [12].
When it comes to organic fertilizers, in Slovak agriculture, the greatest trust is in manure and vermicompost. The reason is that farmers produce their own manure, which means they know its origin and composition, and the space and financial requirements for storing it are smaller than for storing slurry. Vermicomposts are a place for earthworms to live and reproduce, and their components serve as food for them. If the vermicompost contains ingredients unsuitable for their life, they will escape from the vermicompost or die. Vermicompost containing live earthworms indicates its suitability for agricultural purposes. Vermicomposts, unlike conventional composts, contain significantly larger amounts of macro and micronutrients, growth stimulants, and, after their use, nutrients remain in the soil in a mobile form for longer [12].
Unlike vermicompost, trust in conventional composts, and especially in composts made from municipal solid waste (MSW), is low in Slovakia, despite the knowledge that compost made from MSW has a comparable or even better effect on the yield of cultivated plants than manure [13]. This distrust stems from the fact that composts made from MSW can vary over a relatively wide range in terms of composted components.
Organic fertilizers have been widely used to improve soil fertility and crop productivity, but their optimal application strategies remain a major focus of research worldwide [14]. The effect of organic fertilizers on the height and quality of crops of all types of plants on the environment depends on several factors: the growing site, i.e., on the weather changes and soil parameters [15]; the cultivated crop [16]; the date and dose of the fertilizer used [17]; the type and state of fertilizer [18]; and the like. As a result of the above, not only their positive effects on plants, but also negative ones, are recorded after their use [12]. Their negative impacts on the environment have also been noted [18]. There is more knowledge about their positive impact on the height and quality of the crop than there is about their negative impact.
The positive impact of vermicompost on crop yields is mainly related to its positive impact on soil structure and nutrient availability [19]. The difference in the impact on soil and plants between vermicompost and other types of compost is due to the presence or absence of digestive tract secretions (earthworm casts). In the digestive tract, earthworms mix digested organic matter with minerals (soil), creating relatively water-stable aggregates. These aggregates are excreted, which have a positive effect on the physical, chemical, and biological parameters of the soil. In terms of physical parameters, they have a positive impact on the formation of soil aggregates, soil structure, and, consequently, on the soil’s ability to retain water, while also increasing soil resistance to erosion [20,21]. Earthworm castings are enriched in polysaccharides and lignin, which serve as cementing agents and contribute to increased stabilization and sequestration of carbon and nitrogen in the soil [22,23,24].
The reaction of individual plants to fertilizing with organic fertilizers is different. Maize is one of the crops that responds well to various organic fertilizers [25], which is why several organic fertilizers such as cattle manure [26], chicken manure [27], pig deep litter [28], poultry litter [29], pig slurry [30], biochar [31], meat-and-bone meal [32], and various types of composts [33] including vermicompost [34] are successfully used in its nutrition. It is recommended that the total mineral nitrogen requirement for maize nutrition be replaced by organic nitrogen in an amount of 40 to 60% [7].
The application of solid organic fertilizers (farmyard manure, composts) in the conditions of Slovakia is carried out mainly in autumn, and the application of suspension fertilizers (slurries, digestates) is realized before the sowing of crops, but also on post-harvest residues after harvesting cereals or oilseeds. The reason for this is the fact that in the conditions of Slovakia, the prevailing opinion among farmers is that it is inappropriate to apply Vc to the soil in the spring before sowing maize due to the short time elapsed between application of Vc and sowing of maize, which does not allow sufficient mineralization of the organic compounds contained in vermicompost.
In the European Union, in an effort to protect the environment from the potential negative effects of organic as well as mineral nitrogen fertilizers, the European Commission [35] adopted a measure limiting the maximum annual application of organic fertilizers to an amount equivalent to 170 kg ha–1 of N and, at the same time, it determines the doses and dates of application of mineral nitrogen fertilizers. The individual states of the Union have incorporated this legislation into national legislation, which in Slovak conditions means that the maximum one-time dose of N in the form of mineral fertilizers is determined at the level of 60 kg ha–1 of N. Such legislative regulations, as well as some others, with current technological procedures do not allow farmers to fully utilize the biological potential of plants. The result is often a decreasing efficiency of plant cultivation. Farmers, in an effort to maintain their ability to compete, are looking for different solutions. One of them is the cooperation with scientific and research institutions, with universities that verify and create such environmental systems of plant fertilization that have a positive impact on the height and quality of crops and on the economy of plant cultivation and do not burden the environment. For this reason, the aim of the present experiment was to determine the effect of separate autumn and spring applications of vermicompost and joint application with mineral N fertilizer in a dose respecting the regulation of the European Commission [35] and in an above-limit dose of Vc divided into two calendar years on the yield of maize grain and selected maize grain parameters. Since there is relatively lots of knowledge about the doses and timing of mineral N application to maize [36,37], but relatively little knowledge about the different timing of application of solid organic fertilizers (compost, manure), another aim of the study was to determine the size of the difference in maize grain yields between autumn and spring vermicompost application.

2. Materials and Methods

2.1. Experimental Design and Field Management

The two-year pot experiment was performed in the vegetation cage located in the area of the Slovak University of Agriculture in Nitra (48°18′ N, 18°05′ E). The total number of treatments (tr.) was 8 (Table 1). Treatment 1 was a controlled, unfertilized treatment (soil without vermicompost). In treatments 2 to 8, vermicompost (Vc) was applied, either alone (tr. 2, 3, 5, and 7) in two different doses and terms or together with mineral nitrogen (tr. 4, 6, 8).
The experiment was set up according to the randomized arrangement of pots with five replications. In both years of the experiment, 22 kg of Haplic Fluvisol, taken from the 0.25 m topsoil horizon, was weighed in the autumn into 40 pots (8 treatments, with 5 repetitions). The selection of the Haplic Fluvisol as the soil type for this experiment was justified by both its broad geographical representation and its agronomic importance. Within the soil resources of the Slovak Republic, Fluvisols occupy approximately 309.7 thousand hectares, corresponding to 12.6% of the total agricultural land area [38]. Globally, Fluvisols cover roughly 350 million hectares [39], making them one of the more widespread soil groups utilized in both intensive and extensive agricultural systems. Fluvisols are characterized by a high degree of variability and dynamism in their soil properties, resulting from the continuous fluvio-dynamic deposition of sediments. These soils are commonly found in agriculturally important lowland regions and are distinguished by favorable nutrient status, relatively good water-holding conditions, and high agricultural productivity, which make them suitable for cultivating a wide range of crops, including maize.
Subsequently, Vc was added to 25 pots (five treatments) in two different doses: 340 kg ha–1 N (tr. 2) and 170 kg ha–1 N (tr. 3 to 6), and mixed with the soil. Spring application of the Vc was carried out the last week of March in the treatments 3, 4, 7, and 8 at a dose of 170 kg ha–1 N and mixed with the soil (Table 1). The dose of nitrogen in Vc at the level of 170 kg ha–1 N was determined in accordance with the regulation of European Commission [35]. In March, a mineral nitrogen fertilizer, ammonium nitrate with dolomite (AND—27% N), was applied simultaneously with Vc, at a dose of 60 kg ha–1 N (Table 1), to pots of treatments 4, 6, and 8. The dose of 60 kg ha–1 of N was chosen on the basis of the Nitrate Directive implemented in Slovak legislation [40]. The doses of Vc and AND calculated for the area of one hectare were converted to the weight of one container. When converting from area to weight, it was calculated with the information that the volumetric weight of field soils in Slovakia is 1.5 g cm−3.
The basic agrochemical parameters of the used soil and Vc are given in Table 2. The dry matter content in the used (applied) vermicompost was 82.5%, i.e., the water content was 17.5%. Vc was produced and supplied by the company VermiVital Ltd. (Záhorce, Slovakia), which used earthworms of the genus Eisenia fetida to produce it.
Sowing of maize (10 individuals per pot), variety of PR38V91 from Pioneer (FAO 310), was carried out on 30 April in the first experimental year and on 28 April in the second experimental year. Three weeks after emergence (BBCH 10), the plants were thinned to ensure equal numbers per pot (4 plants per pot). At BBCH 16 growth stage, the plants were thinned again to achieve a final 3 plants per pot.
During the entire period of maize vegetation, the experiment was checked daily and irrigated and weeded as needed. It was irrigated with stagnant drinking water containing a negligible amount of nutrients (N-2.15, P-0.19, K-0.46, Ca-2.44, Mg-0.42, and S-2.62 mg L–1). Pots with plants were shaded on days of intense radiation. At the end of the experiment, the weight of the grain, the content of crude protein and starch in the grain, and the thousand kernel weight were determined.

2.2. Analysis of Soil and Vermicompost

The following analytical methods were used for determining the agrochemical parameters of used soil and vermicompost. NH4+-N by Nessler’s colorimetric method and NO3--N by colorimetric method with phenol-2.4 disulfonic acid, where the extract from soil was achieved by using the water solution of 1% K2SO4 [41]. Inorganic nitrogen Nin was calculated as a sum of NH4+-N + NO3−-N (Nin = NH4+-N + NO3−-N). Both NH4+-N and NO3−-N were determined in a fresh soil sample.
The contents of available P, K, Ca, and Mg were determined in the dry soil sample by the Mehlich 3 extraction procedure [42]. The content of available P was estimated by the molybdenum-blue method, and available forms of K, Ca, and Mg were measured by flame atomic absorption spectrometry (Bodenseewerk Perkin-Elmer GmbH–Model 2100, Germany). Soil organic carbon (Cox) was determined using the wet combustion method, involving the oxidation of SOM by a mixture of 0.07 mol L−1 H2SO4 and K2Cr2O7, followed by titration using Mohr’s salt according to Tyurin [43], total nitrogen (Nt) content according to Kjeldahl [44], electrical conductivity (EC) by the method of specific electrical conductivity, and pHKCl (in solution of 1.0 mol dm−3 KCl, soil to solution ratio 1:2.5) potentiometrically.

2.3. Analysis to Determine Grain-Quality Parameters

Crude protein content was calculated according to the formula 6.25 × % N, where nitrogen content was determined by the distillation Kjeldahl method after mineralization in the medium of concentrated H2SO4. Starch was determined polarimetrically by Ewers method [45]. In the polarimetric (or Ewers) method, starch is released from the sample by boiling in dilute hydrochloric acid (HCl). It then hydrolyses to glucose. Glucose concentration is determined by measuring the angle of polarization or optical rotation. Determination of TKW was carried out using the traditional measurement method based on manual steps such as weighing and counting the kernels [46].

2.4. Statistical Analysis

Averages from two years of trials were used in the statistical analysis. Out of five repetitions, four repetitions were statistically evaluated. The repetitions that deviated the most from the average were always excluded from the evaluation. The acquired results were processed by the multifactorial analysis (the treatment factor and the repetition factor) of variance (ANOVA). The differences between the treatments were evaluated by Tukey test at the significance level α = 0.05 (p < 0.05). The Statgraphics Centurion XV⋅I software version 16.2. (Statpoint Technologies, Inc., Washington, DC, USA) was used for statistical analysis.

3. Results and Discussion

3.1. Grain Yield

Plant nutrition is an important intensification factor of plant production and therefore it is necessary to pay constant attention to it. In the Central European area, plant nutrition determines the yield of field crops on average at the level of about 20–25%, of garden crops at the level of about 30%, while in the conditions of Slovak agriculture it usually affects the yield of plants in the range of 6 to 70% [40].
The lowest maize grain yield (30.38 g pot−1) was found in unfertilized treatment 1 (Table 3). All applied fertilizations (tr. 2 to 8) increased the grain yield by 2.1 times on average, while the yield increases were statistically significant. Within the fertilized treatments (tr. 2 to 8), the lowest grain yield was recorded in tr. 7, in which only Vc was applied in the spring at a basic dose of 170 kg ha–1 N. Almost the same grain yield as in tr. 7 was recorded in the tr. 5 in which Vc was applied in an identical dose of N (170 kg ha–1) in the autumn. The detected minimal difference in yields between tr. 5 (application of Vc in autumn) and tr. 7 (application of Vc in spring) did not confirm the assumption that spring application of Vc due to the insufficient time required for the release of nutrients from organic bonds [47] does not provide the cultivated plants with a sufficient amount of accessible nutrients, as a result of which plants fertilized with Vc in the spring will give lower yields than those that were fertilized with Vc in the autumn. A significant proportion of the relatively good effect of the spring application of Vc on maize grain yield was due to the sufficient soil moisture ensured by regular watering and by the narrow C:N ratio (9.79:1) in the vermicompost. The observed effect of spring application of Vc at a dose of 170 kg ha–1 on maize grain yield creates a prerequisite for the use of composts in Slovak agricultural conditions, or in conditions of a temperate climate zone and at a time other than autumn, provided that Vc is used with a C:N ratio of less than 10:1 and that sufficient soil moisture is ensured for vegetation mineralization processes.
The average grain yield for treatments fertilized only with Vc (tr. 2, 3, 5, and 7) was 52.78 g pot−1 (Table 3). Application of Vc in the above treatments at doses of 170 and 340 kg ha–1 N increased the yield by an average of 1.7 times compared to the unfertilized control. Dividing the one-time dose of Vc (340 kg ha–1) applied in autumn (tr. 2) into spring (170 kg ha–1 of N) and autumn doses (170 kg ha–1 of N) resulted in an insignificant increase in grain yield (tr. 2 vs. tr. 3). Likewise, the differences in yields between the treatments in which 340 kg ha–1 N was applied (tr. 2 and 3) and the treatments in which 170 kg ha–1 N (tr. 5 and 7) was applied in the form of Vc were insignificant. The detected statistically insignificant differences pointed to the fact that the dose of Vc at the level of 340 kg ha–1 N compared to the dose of 170 kg ha–1 N was ineffective, regardless of whether it was applied once or in two terms (in autumn and spring). These findings confirm that at high application rates of N fertilizers (organic or inorganic), yield increases may be minimal or that fertilization may have a depressing effect [40].
The average grain yield for treatments fertilized with Vc together with mineral nitrogen (tr. 4, 6, 8) was 80.76 g pot−1 (Table 3). Within the entire trial, the highest yields were achieved in these three treatments (4, 6, 8) and were 2.8, 2.7, and 2.6 times higher than in the control treatment. The findings confirm the rationality of the joint application of mineral and organic fertilizers, which has been noted by several authors [48,49,50]. Mineral nitrogen added to Vc (tr. 4, 6, 8) increased the grain yield by 1.5 times on average compared to treatments fertilized only with Vc (tr. 2, 3, 5, 7). Yield increases caused by the addition of mineral nitrogen to Vc between individual treatments were at the level of 44.85% (tr. 4 vs. tr. 3), 55.19% (tr. 6 vs. tr. 5), and 61.10% (tr. 8 vs. tr. 7). The smallest, a 44.85% increase in yield after adding mineral N to Vc, was found in treatment 4 versus 3, where Vc was applied in a double dose of N (340 kg h–1 N) compared to treatments 6 and 8. A higher dose of Vc meant a smaller effect of mineral N fertilizer. The largest (61.10%) increase in maize grain yield after adding mineral N was found in the treatment 8 versus 7 where Vc was applied in the spring before the maize was sown in a basic dose of 170 kg ha–1 N. The reason for the significant increase in yield after the addition of mineral N was the accelerating effect of mineral N fertilizer on the process of mineralization of organic compounds found in the applied Vc, on the process of making nutrients available to plants [51] and their subsequent use by plants. The findings pointed to the fact that the effect of 60 kg ha–1 N in mineral fertilizer on grain yield depended on the dose and timing of vermicompost application.
Mutual differences in grain yield between the three treatments with the highest grain yield (tr. 4 vs. tr. 8 vs. tr. 6) were insignificant, despite the fact that different amounts of Vc were applied in them at different dates at the same dose of N in the form of mineral fertilizer, which confirms that nitrogen supplied in mineral fertilizer has a more significant impact on the yield of cultivated plants compared to nitrogen supplied in organic fertilizer [49].
The common feature of the treatments 4, 6, and 8, in which the largest harvest was achieved, was the spring pre-sowing application of mineral nitrogen fertilizer to the soil fertilized with vermicompost. The findings confirmed the knowledge that the formation of phytomass of cultivated plants is significantly influenced by fertilizers containing easily available, inorganic nitrogen, because nitrogen is a fundamental element of plant nutrition [52]. At the same time, it confirmed the knowledge known for decades about the justification (rationality) of using organic and mineral fertilizers together [53,54].
A comparison of the effect of spring application of mineral nitrogen at a dose of 60 kg ha–1 N (tr. 6) and spring application of Vc at a dose of 170 kg ha–1 N (tr. 3) to soils in which Vc was applied in autumn shows that the spring dose of mineral N at the level of 60 kg ha–1 increased the yield more significantly than the spring dose of Vc at the level of 170 kg ha–1 N. From the aspect of maize grain yield, the applied 170 kg ha–1 of N in the spring dose of Vc was not equal to the applied 60 kg ha−1 of N in the mineral fertilizer AND. The smaller effect of 170 kg of N dose in Vc compared to 60 kg of N in mineral fertilizer is a consequence of the fact that from the point of view of plant nutrition, the total amount of applied nitrogen is not essential, but is essential to the amount of mineral or easily mineralizing nitrogen. The reason is that the nitrogen received in the first half of the vegetation of the plant mainly affects its yield, and the nitrogen received in the second half of the vegetation mainly affects its qualitative parameters. For this reason, the impact of 170 kg of total nitrogen supplied by vermicompost (in which most of the nitrogen is bound in organic bonds) has a different impact on the yield of cultivated plants than 60 kg of nitrogen supplied in mineral form. Of the 170 kg of nitrogen supplied by vermicompost, only about 25 kg of nitrogen is in inorganic form and the rest is in organic form, from which the inorganic nitrogen is gradually released in the process of mineralization [55].

3.2. Crude Protein and Starch in Grain

The content of crude protein (CP) in maize grain was the lowest in the controlled, unfertilized treatment 1 (Table 3). All tested fertilization treatments (tr. 2 to 8) affected it in a significant way. They increased its content. This finding is in accordance with the knowledge about the positive influence of fertilizers containing N on the content of crude protein in the grains of cultivated plants [56,57] regardless of the fertilizer in which the N is supplied [58,59,60].
Within the fertilized treatments (tr. 2 to 8), the smallest amounts of CP were formed in the grains of treatments 7 and 5, i.e., in the treatments in which only Vc was applied, in a basic dose of 170 kg ha–1 N, regardless of whether it was applied in spring or autumn.
A double dose of Vc (340 kg ha–1 N) compared to the basic dose (170 kg ha–1 N) did not affect the CP content significantly (tr. 2 and 3 vs. tr. 5 and 7), which points to the unreasonableness of such a dose of vermicompost, not only from the point of view of crude protein content, but also the height of the yield (Table 3). Similarly, the distribution of 340 kg ha−1 N dose of Vc into autumn and spring dose (tr. 3) compared to a one-time autumn dose of Vc (tr. 2) did not significantly affect the content of CP in maize grain. An insignificant difference between CP contents was also achieved between autumn and spring application of Vc at a dose of 170 kg ha−1 (tr. 5 vs. tr. 7). It follows from the above that the application of Vc increased the content of CP (tr. 2, 3, 5, and 7 vs. tr. 1), but the differences in the contents of CP between the treatments fertilized with different doses of Vc applied in different terms (tr. 2, 3, 5, and 7) were insignificant.
The highest CP contents were found in the treatments with Vc organic fertilizer applied together with AND mineral fertilizer (tr. 4, 6, 8), with the highest level (7.84%) found after the application of the largest dose of nitrogen (tr. 4). This finding is in accordance with the previous knowledge of Liang et al. [61] and Hammad et al. [62] stating that the application of nitrogen-containing fertilizers significantly increases the content of crude protein in plants. The rate of increase in CP content after application of N fertilizers depends on the dose of N [58].
The finding of the highest CP contents in the grains of treatments 4, 6, and 8 in the context of the already presented knowledge that the highest maize grain yields were achieved in the same treatments (Table 3) points to the high efficiency of adding mineral nitrogen to vermicompost and to the justification of the joint application of organic and mineral fertilizers in the cultivation of maize.
The amount of starch in plant seeds is genetically determined [57]. The highest starch content was found in maize grains grown in the unfertilized (control) treatment (60.8%) and the lowest one (56.97%) in the treatment 4 where the highest dose of N was applied (Table 4). The findings are in complete agreement with the knowledge of Kováčik and Ryant [40], stating that farmers farming in the territory of the former Czechoslovakia after applying fertilizers containing nitrogen in 80% of cases record a decrease in the starch content in plant seeds. Seebauer et al. [63] also found that maize grains grown without the use of N fertilizers had a higher starch content than maize grains that were grown with the use of N fertilizers. The starch content in maize grain is significantly determined by the application of fertilizers [64], while the most significant effect of fertilizers is the application of nitrogen fertilizers, which usually significantly negatively affects the starch content not only in maize grain, but also in cereal grains and tubers of root crops [65]. In an experiment by Rehman et al. [66], the starch content increased after the application of NPK fertilizers.

3.3. Thousend Kernel Weight

The parameter of thousand kernel weight was less significantly affected by experimental treatments than the parameter of grain yield size (Table 4). All fertilizations performed (tr. 2 to 8) increased TKW, although insignificantly in four of seven cases. The average increase in TKW due to the use of Vc alone and the joint application of Vc and mineral nitrogen (tr. 2 to 8) was only at the level of 5.9%. The parameter of thousand kernel weight has a high heritability [67] and is more dependent on genetic predispositions than on plant nutrition [40]. The smallest TKW was recorded in the unfertilized tr. 1 and the largest in tr. 4, in which the largest dose of nitrogen was applied to the soil. The smallest TKW on the non-nitrogen-fertilized treatment was also found by Ghaffari et al. [68]. Several authors [69,70] published the increase in TKW with increasing application rates of N fertilizers. On the contrary, the findings do not correspond to the knowledge of Bouacha et al. [71], who state that with increasing N dose, there is a decrease in TKW. If nitrogen fertilization increases the grain yield by up to 30%, then the increase in seed weight has a more significant effect on the yield increase than their number [72].
Non-significant increases occurred after application of Vc alone, whether at a rate of 170 kg ha–1 N applied in autumn or spring (tr. 2, 3) or in doses of 340 kg ha–1 N applied once or in two terms (tr. 5, 7). A significant change of an increase in TKW, in relation to the non-fertilized treatment (tr. 1), occurred only in the treatments where, in addition to Vc, mineral nitrogen was also applied (tr. 4, 6 and 8). From the above, it is clear that the interactive (joint) action of organic and mineral fertilizers had an impact on the change in TKW. The effect of the addition of mineral nitrogen to Vc (tr. 4 vs. tr. 3, tr. 6 vs. tr. 5, tr. 8 vs. tr. 7) was insignificant.
The difference in TKW values caused by the spring application of mineral nitrogen (60 kg ha–1 N) and the spring application of Vc (170 kg ha–1 N) to the soil fertilized with Vc in the autumn was also insignificant (tr. 6 vs. tr. 3), but the higher value of TKW was recorded for mineral N (333.94 g) than Vc (327.37 g). That confirms the observations obtained by Babulicova and Malovcova [73] of no differences in TKW of barley when comparing the effects of mineral and organic fertilization.

4. Conclusions

The findings of this study demonstrate that the autumn application of vermicompost (Vc) combined with a spring application of mineral nitrogen fertilizer (AND) at 60 kg ha−1 N resulted in a more pronounced increase in maize grain yield than the spring application of Vc at 170 kg ha−1 N. Although a total Vc dose of 340 kg ha−1 N also enhanced grain yield, its effect remained weaker compared with the combination of 170 kg ha−1 N from Vc with 60 kg ha−1 N from mineral fertilizer. Splitting the full Vc dose of 340 kg ha−1 N into equal autumn and spring applications produced only a slight and statistically insignificant improvement in yield. Across both Vc doses (170 and 340 kg ha−1 N), vermicompost did not influence the thousand-kernel weight, yet it consistently increased crude protein content in maize grain. The grain yield response to the 60 kg ha−1 N mineral fertilizer depended on the applied Vc dose, with higher Vc levels reducing the effectiveness of mineral nitrogen. Although Vc tended to increase crude protein concentration, differences among Vc doses and application timings were not statistically significant. The highest crude protein concentrations were observed in treatments receiving Vc together with mineral fertilizer AND, particularly in those with the greatest total nitrogen input. In contrast, starch content showed an inverse relationship to nitrogen availability: the highest values were detected in the unfertilized control, while the lowest occurred in the treatment with the highest nitrogen dose. The negative influence of Vc application on starch content was minimal and statistically insignificant, regardless of dose or timing. The small differences in yield between autumn and spring Vc application do not support the assumption that spring application of vermicompost is unsuitable under conditions of adequate soil moisture.

Author Contributions

Conceptualization, P.K.; methodology, P.K.; software, M.K. and Š.T.; validation, P.K., V.Š. and I.L.-S.; formal analysis, Š.T.; investigation, P.K. and M.K.; resources, P.K.; data curation, M.K.; writing—original draft preparation, P.K.; writing—review and editing, V.Š.; visualization, P.K., V.Š. and I.L.-S.; supervision, P.K. and V.Š.; project administration, P.K.; funding acquisition, P.K. All authors have read and agreed to the published version of the manuscript.

Funding

This article was supported by the National Scientific Granting Agency (VEGA) of the Ministry of Education of Slovak Republic via Research Project No. 1/0378/20.

Data Availability Statement

The datasets generated and analyzed during the current study are available from the authors upon a reasonable request.

Acknowledgments

The authors express their gratitude to the editor and the reviewers for their constructive comments.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or the interpretation of the data; in the writing of the manuscript; or in the decision to publish the results.

References

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Table 1. Treatments of pot experiment.
Table 1. Treatments of pot experiment.
TreatmentDose of N Dose of Vc (dm/fm) ∗Dose of ANDTerm of Application
in Vcin ANDas Ntas Nin
n.Designationkg ha–1t ha–1kg ha–1VcAND
1So (control)000000--
2So + Vcaut34034003405.5116/19.40aut-
3So + Vcaut170 + Vcspr17034003405.5116/19.40aut+spr-
4So + Vcaut170 + Vcspr170 + Nspr603406040065.5116/19.4222aut+sprspr
5So + Vcaut17017001702.758/9,70aut-
6So + Vcaut170 + Nspr601706023062.758/9.7222autspr
7So + Vcspr17017001702.758/9.70spr-
8So + Vcspr170 + Nspr601706023062.758/9.7222sprspr
Vc—vermicompost, AND—ammonium nitrate with dolomite, Nt—total nitrogen, Nin—inorganic nitrogen, dm—dry matter, fm—fresh matter, ∗ amount of dry matter in vermicompost = 82.5%, n.—number, So—soil, aut—autumn, spr—spring.
Table 2. Parameters of soil and vermicompost used in the experiment (100% dry matter).
Table 2. Parameters of soil and vermicompost used in the experiment (100% dry matter).
Com.NinNH4+-NNO3−-NPKCaMgSNtCoxC:NECpHKCl
mg kg–1%mS cm–1
soil18.75.812.920.327736127544.10.262.088.000.246.04
Vc34428.5315.5377311,543801435805342.1218.478.713.457.17
Com.—component, Vc—vermicompost, Nin—inorganic nitrogen, Nt—total nitrogen, P, K, Ca, Mg, S—available forms of phosphorus, potassium, calcium, magnesium, and sulfur, EC—electrical conductivity.
Table 3. Effect of trial treatments on maize grain yield and on crude protein content in grain.
Table 3. Effect of trial treatments on maize grain yield and on crude protein content in grain.
TreatmentGrainCrude Protein
n.Designationg pot–1rel. %%rel. %
1So (control)30.38 ± 3.22 a100.00 6.43 ± 0.05 a100.00
2So + Vcaut34053.04 ± 3.11 b174.59100.00 7.10 ± 0.03 bc110.42100.00
3So + Vcaut170 + Vcspr17057.66 ± 3.04 b189.80108.71 7.00 ± 0.04 b108.8698.59
4So + Vcaut170 + Vcspr170 + Nspr6083.52± 2.92 c274.91157.47 7.84 ± 0.05 d121.93110.42
5So + Vcaut17050.32 ± 3.77 b165.6394.87100.006.93 ± 0.43 b107.7897.61100.00
6So + Vcaut170 + Nspr6078.09 ± 2.81 c257.04147.23155.97.48 ± 0.31 cd116.33105.35107.94
7So + Vcspr17050.08 ± 3.03 b164.8594.4299.526.91 ± 0.10 b107.4797.3299.71
8So + Vcspr170 + Nspr6080.68 ± 2.38 c265.57152.11160.337.21 ± 0.23 bc112,13101.55104.04
2–864.77213.20--7.21112.13--
2, 3, 5, 752.78173.73100.00-6.99108.71100.00-
4, 6, 880.76265.83153.01-7.51116.80107.44-
HSD0.05 7.696 0.469
n.—number, So—soil, Vc—vermicompost, aut—autumn, spr—spring, HSD0.05—honestly significant difference at the level α = 0.05; different letters behind a numerical value respond to the statistically significant difference at the level 95.0% (p < 0.05).
Table 4. Effect of trial treatments on starch content in maize grain and the thousand kernel weight.
Table 4. Effect of trial treatments on starch content in maize grain and the thousand kernel weight.
TreatmentStarch ContentThousand Kernel Weight
n.Designation%rel. %grel. %
1So (control)60.80 ± 0.84 b100.00 311.94 ± 10.64 a100,00
2So + Vcaut34059.58 ± 0.57 b97.99100.00 322.99 ± 5.97 ab103.54100,00
3So + Vcaut170 + Vcspr17059.33 ± 0.67 b97.5899.58 327.37 ± 4.57 abc104.95101.36
4So + Vcaut170 + Vcspr170 + Nspr6056.97 ± 0.38 a93.7095.62 345.45 ± 7.61 c110.74106.95
5So + Vcaut17060.18 ± 0.86 b98.98101.01100.00319.41 ± 7.57 ab102.3998.89100.00
6So + Vcaut170 + Nspr6060.05 ± 0.88 b98.77100.7999.78333.94 ± 7.86 bc107.05103.39104.55
7So + Vcspr17059.58 ± 0.42 b97.99100.0099.00325.68 ± 8.74 abc104.40100.83101.96
8So + Vcspr170 + Nspr6059.16 ± 0.84 b97.1499.1398.14337.87 ± 9.22 bc108.31104.70105.78
2–859.2697.47 330.39105.91
2, 3, 5, 759.6798.14100.00 323.86103.82100.00
4, 6, 858.7396.6098.42 339.09108.70104.70
HSD0.05 1.714 20.360
n.—number, So—soil, Vc—vermicompost, aut—autumn, spr—spring, HSD0.05—honestly significant difference at the level α = 0.05; different letters behind a numerical value respond to the statistically significant difference at the level 95.0% (p < 0.05).
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Kováčik, P.; Šimanský, V.; Kmeťová, M.; Týr, Š.; Ledwożyw-Smoleń, I. Effect of Dose and Date of Application of Vermicompost and Its Combination with N-Fertilizer on Maize Grain Yield. Agronomy 2026, 16, 118. https://doi.org/10.3390/agronomy16010118

AMA Style

Kováčik P, Šimanský V, Kmeťová M, Týr Š, Ledwożyw-Smoleń I. Effect of Dose and Date of Application of Vermicompost and Its Combination with N-Fertilizer on Maize Grain Yield. Agronomy. 2026; 16(1):118. https://doi.org/10.3390/agronomy16010118

Chicago/Turabian Style

Kováčik, Peter, Vladimír Šimanský, Mária Kmeťová, Štefan Týr, and Iwona Ledwożyw-Smoleń. 2026. "Effect of Dose and Date of Application of Vermicompost and Its Combination with N-Fertilizer on Maize Grain Yield" Agronomy 16, no. 1: 118. https://doi.org/10.3390/agronomy16010118

APA Style

Kováčik, P., Šimanský, V., Kmeťová, M., Týr, Š., & Ledwożyw-Smoleń, I. (2026). Effect of Dose and Date of Application of Vermicompost and Its Combination with N-Fertilizer on Maize Grain Yield. Agronomy, 16(1), 118. https://doi.org/10.3390/agronomy16010118

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