Open AccessArticle

Pilot Study on a Liquid Mineral Foliar Fertilizer Mixed with Herbicides for Maize Protection and Nutrition

Camelia Hodoșan

¹,

Lucica Nistor

Paula Poşan

¹,

Sorin Iulius Bărbuică

Daniela Ianiţchi

¹,

Gabriela Luţă

^2,*

and

Lizica Szilagyi

^3,*

Faculty of Animal Productions Engineering and Management, University of Agronomic Sciences and Veterinary Medicine of Bucharest, 59 Marasti Blvd, District 1, 011464 Bucharest, Romania

Faculty of Biotechnologies, University of Agronomic Sciences and Veterinary Medicine of Bucharest, 59 Marasti Blvd, District 1, 011464 Bucharest, Romania

Faculty of Agriculture, University of Agronomic Sciences and Veterinary Medicine of Bucharest, 59 Marasti Blvd, District 1, 011464 Bucharest, Romania

Authors to whom correspondence should be addressed.

Agriculture 2024, 14(12), 2129; https://doi.org/10.3390/agriculture14122129

Submission received: 18 October 2024 / Revised: 14 November 2024 / Accepted: 22 November 2024 / Published: 24 November 2024

(This article belongs to the Section Crop Protection, Diseases, Pests and Weeds)

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Figure 1
Diagram of the laboratory installation used to make the complex composition of fertilizers (1—stand; 2—clamp; 3—gas bulb; 4—tripod; 5—balloon; 6—thermometer; 7—agitator; 8—refrigerant). "> Figure 2
Structural formulas of: (a) 2,4-D acid; (b) Dicamba. "> Figure 3
Temperatures (°C) recorded at the Moara Domneasca weather station, agricultural year 2020–2021. "> Figure 4
Precipitation (mm) recorded at the Moara Domneasca weather station, agricultural year 2020–2021. "> Figure 5
Temperatures (°C) recorded at the Moara Domneasca weather station, agricultural year 2021–2022. "> Figure 6
Precipitation (mm) recorded at the Moara Domneasca weather station, agricultural year 2021–2022. "> Figure 7
1H-NMR spectrum of 2,4-D acid. "> Figure 8
1H-NMR spectrum of Dicamba. "> Figure 9
The technological flow of manufacturing liquid foliar fertilizer. "> Figure 10
The new liquid foliar mineral fertilizer. ">

Versions Notes

Abstract

The purpose of this study was to develop a complex composition of a foliar liquid mineral fertilizer containing NPK macroelements and microelements including Fe, Mg, B, S, Zn, Cu, Mo, Ni, V, and Cr. This complex fertilizer aims to support the optimal development and maturation of maize crops, thereby enhancing both the quality and quantity of production. In our study, an original recipe was established for a complex composition of foliar liquid mineral fertilizer, and a technological process was developed in order to obtain the recipe at the laboratory level. The designed fertilizer was a complex mixture of fertilizers with herbicides with multiple purposes, which can be used in different pedo-climatic areas and which present, at the same time, low toxicity and minimal ecological impact. A wide-spectrum mixture DICOPUR TOP containing 2,4-D acid and Dicamba was chosen as a systemic herbicide which is absorbed by plants both in the root system and also on the leaves. For conditioning the complex mixture of fertilizers with herbicides, different types of polyvinyl alcohol with different degrees of hydrolysis were used. The liquid fertilizer mixture with DICOPUR TOP was applied over two years (2021 and 2022) to the Felix maize hybrid, demonstrating significant positive effects on grain yield while effectively controlling both dicotyledonous and monocotyledonous weeds.

Keywords:

macroelements; microelements; fertilizers; herbicides; polyvinyl alcohol; Zea mays L.

1. Introduction

In the current period, a diverse range of fertilizers with varying compositions of microelements is available in the global market [1]. While numerous fertilizer formulations have been researched, developed, and patented, they often contain only a fraction of the necessary microelements depending on their intended use [2].

It is recognized that a versatile fertilizer composition, applicable to cereals, vegetables, and fruit trees, should include both macro- and microelements [3,4,5]. To produce complex fertilizer compositions, a series of raw materials are necessary, which generate macroelements (NPK) and microelements (Fe, Mg, Cu, Zn, B, S, Mo, Ni, V, Cr, etc.), as well as other various substances such as surface-active agents, chelating agents, and complexing agents for the metal ions of microelements [6].

Nitrogen, phosphorus, and potassium serve as macroelement sources in mineral fertilizer compositions, while microelements are typically introduced into the system in the form of salts. To prevent the precipitation of metal ions, substances capable of forming complex combinations with transitional metal ions are used [7,8]. When using liquid foliar fertilizers, a very serious problem can arise, namely, the maintenance of the fertilizer in the form of drops on the leaves. This will lead, after the water evaporates, to a small area of macro- and microelements concentration, which will affect the leaves. To solve this issue, it is common practice to utilize a surfactant, specifically polyvinyl alcohol, with varying degrees of hydrolysis [4,9]. Polyvinyl alcohol finds extensive use in agriculture for conditioning fertilizers or fertilizer–pesticide mixtures, often to create gels or microcapsules for controlled substance release into the soil [10,11]. It also serves as an emulsifier for liquid fertilizers or pesticides, with low hydrolysis degree variants forming a protective film on plant surfaces to prolong pesticide action [12,13].

Based on research on herbicide usage on both national and international levels, it has been observed that mixture herbicides (in synergistic effect) are commonly used to achieve a broad spectrum of action. Typically, these mixtures consist of herbicides with complementary actions, resulting in products with versatile applicability across multiple fields [14]. The utilization of herbicide mixtures offers significant technical and economic advantages: it substantially reduces the number of crop treatments required, thereby decreasing the need for machinery, labor force, and other resources, leading to notable reductions in energy consumption [15].

However, improper mixing or application of herbicide–fertilizer combinations can lead to phytotoxicity, resulting in damage to crop plants. The interaction between herbicides and fertilizers may exacerbate this risk, potentially causing reduced crop yields or even crop loss. Nevertheless, when utilized appropriately, herbicide–foliar fertilizer mixtures can effectively manage weeds and supply essential nutrients for plant growth. This can ultimately lead to increased crop yields and improved profitability for farmers.

Considering all of this, the possibility of making some compositions of fertilizers with mixtures of herbicides was studied in the present research. A broad-spectrum mixture, DICOPUR TOP 464 SL, comprising 2,4-D acid and Dicamba, was utilized as the herbicide. Its systemic action, absorbed through both leaves and roots [16], was examined against annual and perennial dicotyledonous and monocotyledonous weeds in maize crop. Adapted very well to Romanian climatic conditions, maize is a major crop, cultivated across an area exceeding 2 million hectares.

Weeds pose a significant threat to crop growth, as they compete with crops for essential resources such as light, water, and nutrients, particularly during the early stages of maize development. To ensure optimal crop performance in terms of both yield and quality, the application of herbicides is imperative [17]. Weed control in maize is essential, starting from pre-emergence until the 8–10 leaf stage to ensure optimal development.

Crucial factors for achieving high maize yields include hybrid selection, cultivation techniques, and fertilization. Maize’s nutrient-intensive nature, particularly its requirement for NPK, underscores the importance of proper fertilization, which includes foliar application of macro- and micronutrients.

The present research aims to develop a comprehensive foliar liquid mineral fertilizer and evaluate its effectiveness when combined with herbicide mixtures for weed control and maize yield assessment. This study is based on the premise that applying a liquid mineral foliar fertilizer mixed with herbicides will significantly enhance maize protection against common weeds while simultaneously improving nutritional uptake and overall plant health compared to traditional herbicide applications alone, which may induce a degree of toxicity.

2. Materials and Methods

The raw materials used to generate NPK macroelements were urea (CH₄N₂O), monoammonium phosphate MAP (NH₄H₂PO₄), and potassium nitrate (KNO₃), and the substances generating microelements were ferrous sulphate (FeSO₄), magnesium sulphate (MgSO₄), boric acid (H₃BO₃), zinc sulphate (ZnSO₄), copper sulphate (CuSO₄), ammonium paramolybdate ((NH₄)₆Mo₇O₂₄), nickel sulphate (NiSO₄), ammonium vanadate (NH₄VO₃), and sodium dichromate (Na₂Cr₂O₇). The microelements used are found in the form of metal ions, which are introduced in the system in the form of salts. In order to exclude the possibility of metal ion precipitation from the composition of the foliar fertilizer, there are substances capable of forming complex combinations with the ions of transition metals introduced into the system as microelements. As a complexing agent, we utilized EDTA (Ethylene-Diamine-Tetraacetic Acid—C₁₀H₁₆N₂O₈), and as a surfactant, we employed polyvinyl alcohol synthesized by us with varying degrees of hydrolysis. All materials used to generate NPK macroelements and microelements were procured from Haas-C-Impex SRL, Romania, Ploiesti.

The purities of the chemical substances used as generators of macro- and microelements were determined by analytical dosing methods. Briefly, by titration with appropriate reagents, each type of macroelement and microelement was quantitatively determined [18,19,20].

The process of obtaining the composition of liquid foliar mineral fertilizers was conducted in three phases:

(a): Preparation of the macroelements solution (N, P, K);
(b): Preparation of the microelements solution (Fe, Mg, B, Zn, Cu, Mo, Ni, V, Cr);
(c): Obtaining the composition of liquid foliar mineral fertilizers.

To conduct the experimental studies, a glass laboratory setup was utilized, comprising a 1.5 L round-bottom flask equipped with a mechanical stirrer with movable paddles, an ascending refrigerant with bubbles, a thermometer, and a dropping funnel (Figure 1). Heating was achieved using an electric stove, while cooling was facilitated with an ice bath. The preparation of the complex liquid foliar fertilizer composition was performed using the setup depicted in Figure 1, following a specific procedure. The composition of macroelements (containing the monoammoniacal phosphate solution, urea, and potassium nitrate) is introduced into the reaction flask and heated, with stirring, to 45–50 °C. Next, the microelement solution is added, in small portions, to the composition of macroelements. During the addition, the temperature of the contents of the reaction flask will be maintained at 45–50 °C.

After completing the addition of the microelement composition, the flask is filled with softened water to reach a total volume of 1 L. Subsequently, the contents of the flask are cooled to 5–7 °C using an ice bath and sodium chloride (NaCl). Once cooled, a homogeneous solution is achieved, free from suspended components. Next, 0.01 g of surfactant (polyvinyl alcohol) and 0.001 g of phenolphthalein are added to the solution while stirring, to prevent accidental transition to a basic medium. Finally, a homogeneous, clear, light green-blue solution is obtained, with a pH of 5.5–6.5 and a density of 1.1–1.15.

2.1. Obtaining the Solution of Macroelements (N, P, K)

Sixty liters of softened water was introduced into the reaction vessel, which was then heated and stirred to 45–50 °C. Subsequently, 93 kg of monoammonium phosphate was added to the heated water in the reactor in small portions under stirring, using a funnel for powdery materials.

The contents of the reactor were stirred for an additional 30–35 min at a temperature of 45–50 °C. At this stage, the entire amount of monoammonium phosphate had dissolved. Next, 10 kg of urea was added to the reactor, in small portions, under stirring and maintaining the temperature at 45–50 °C. After adding the entire amount of urea, the content of the reactor was stirred at a temperature of 45–50 °C for another 30–35 min. At the end of the period, the entire amount of urea was dissolved.

After preparing the aqueous solution of ammonium phosphate and urea, 7.8 kg of potassium nitrate (KNO₃) was added to the reaction mixture. The addition of KNO₃ was also conducted at 45–50 °C, in small portions while stirring. Following the completion of adding KNO₃ to the reaction mixture, the contents of the reactor were stirred for an additional 30–35 min at a temperature of 45–50 °C. Subsequently, the contents of the reaction vessel were cooled to 15–20 °C.

Ultimately, a solution containing 87.1 kg of NPK macroelements was obtained.

2.2. Obtaining the Solution of Microelements (Fe, Mg, B, Cu, Zn, Mo, Ni, V, Cr)

Twenty liters of softened water was introduced into the reaction vessel, which was then heated and stirred to 55–60 °C. Initially, 0.95 kg of disodium salt of Ethylene-Diamine Tetraacetic Acid (EDTA) was added to the water in the reactor in small portions under stirring. Next, while maintaining the temperature at 55–60 °C and continuing to stir, chemical substances that generate microelements, as listed in Table 1, were added.

After adding all substances generating microelements, the contents of the reactor were stirred at a temperature of 55–60 °C for another 30–35 min. Subsequently, the contents of the flask were cooled to 15–20 °C. In the end, a total of 21.6684 kg of clear, homogeneous, blue-green solution was obtained. The stability constants of the complex combinations obtained were determined using the methods mentioned above.

2.3. Obtaining the Liquid Foliar Fertilizer

The composition containing the aqueous solution of the NPK macroelements (consisting of monoammonium phosphate, urea, and KNO₃) was introduced into the reactor and heated to 45–50 °C. Subsequently, the solution of microelements was gradually added to the solution of macroelements in small portions while stirring. The temperature in the reactor was maintained at 45–50 °C during the addition of the microelement solution. After the addition of the microelement solution, the contents of the reactor were cooled to 15–20 °C under stirring.

Next, 0.001 kg of surfactant (polyvinyl alcohol) and 0.0001 kg of phenolphthalein were added to the fertilizer solution. Finally, 100 L of liquid foliar fertilizer was obtained in the form of a homogeneous solution, green-blue in colour, having a pH = 5.5–6.5 and D = 1.1–1.115.

The foliar fertilizer obtained was combined with herbicides. Specifically, a broad-spectrum mixture containing 2,4-D acid (28%) and Dicamba (35%) was utilized. This mixture, commercially known as DICOPUR TOP and manufactured by NUFARM, consists of 2,4-D acid, which is the trade name for 2,4-dichlorophenoxyacetic acid, and Dicamba, the trade name for 2-methoxy-3,6-dichlorobenzoic acid (Figure 2a,b).

This systemic herbicide is absorbed by plants through both the root system and the leaves. The individual components were characterized using High-Resolution Nuclear Magnetic Resonance (1H-NMR) spectroscopy. For this purpose, the picoSpin 80 NMR spectrometer (Thermo Fisher Scientific company, Waltham, MA, USA) was utilized.

2.4. Field Studies

2.4.1. Experimental Site

The studies were conducted, during the 2021 and 2022 growing seasons, at the experimental field of Moara Domneasca Agronomic Research and Development Didactic Station, Ilfov County (44°49′ N, 26°26′ E), which is owned by the University of Agronomic Sciences and Veterinary Medicine of Bucharest.

The soil characteristics used in the experimental plots are presented in Table 2. It was characterized by moderately acidic pH, low humus content, middle class in terms of total nitrogen content, high levels of mobile phosphorus, and very high levels of mobile potassium. The analyses were carried out at the laboratories of National Institute of Research and Development for Pedology, Agrochemistry, and Environmental Protection (Bucharest, Romania).

From a climatic standpoint, the year 2021 can be characterized as favorable for maize crops, with an average temperature of 12.45 °C (Figure 3) and 551.6 mm of rainfall (Figure 4), 328.2 mm of which occurred between March and August.

In contrast, the year 2022 was characterized by warm and dry conditions, with an average temperature of 12.8 °C (Figure 5), the highest ever recorded, and 366.6 mm of rainfall (Figure 6).

2.4.2. Field Trial Set-Up

The hybrid maize was sown on 18 April 2021, and 14 April 2022, with a row spacing of 70 cm and a distance of 20 cm between plants, covering an elementary plot area of 25 m². The trial was performed by the randomized complete block design in four replications (RCBD). The previous crops were winter barley in 2021 and winter wheat in 2022. The fertilizers used for the previous crops, both wheat and barley, are presented in Table 3.

Since nitrogen application could lead to an increase in weed density in the same monoculture, crop rotation was applied [21]. The maize hybrid studied was Felix (FAO 460), developed at NARDI Fundulea, Romania. The main characteristics of this hybrid are described in Table 4 [22]. The experimental procedure involved the sowing of the maize hybrid on a well-prepared seed bed. At this stage, basal fertilization was applied using NPK fertilizer—15:15:15, at a dosage of 160 kg/ha. In the subsequent phase, at sowing, the fertilizer ammonium nitrate was applied at a rate of 120 kg/ha. The first irrigation event was initiated two weeks post-sowing, with subsequent irrigations administered as necessitated by the crop’s water requirements, only in the dry year of 2022. Standard agronomic practices were uniformly applied across all treatments throughout the crop’s growth cycle.

2.4.3. Herbicides and Foliar Fertilizer Application

When maize plants developed 4–6 leaves (14–16 BBCH) and the weeds were in the rosette phase (dicotyledonous weeds on 2–4 leaves), herbicides and foliar fertilizer were applied as a mixture. The herbicide–fertilizer mixture was sprayed using an electric-manual sprayer (Ruris RS 2000 2000RS19), which includes a spraying pump, atomizer, and a telescopic lance for spraying up to 3 m, at a dose of 5.0 L/ha (4:1) with 400 L of water/ha. As mentioned above, the herbicide used was DICOPUR TOP (2,4-D acid—28% and Dicamba—35%).

2.4.4. Parameters Studied

Maize hybrid response to herbicides and foliar fertilizer was evaluated by assessing the following parameters: (1) weed density (number of plants/m²), (2) efficiency (E%)—relative efficacy compared to the untreated control within a period of 2–4 weeks after treatment, and (3) grain yield, which was measured at the end of the growing seasons, with moisture content adjusted to 14%. The efficacy of the treatment was determined using the following formula:

Efficacy (%) = (Control weed count − Treatment weed count)/Control weed count) × 100,

where control weed count is the number of weeds in the control group (without treatment), and treatment weed count is the number of weeds in the group treated with the foliar fertilizer mixture with DICOPUR Top herbicide.

2.4.5. Statistical Analysis

The statistical processing of the obtained data was performed using Duncan’s method with the SPSS 19 program. The means were considered to be significantly different at p < 0.05.

3. Results and Discussion

3.1. Results Regarding the Developed Liquid Fertilizer

To complete a full life cycle, spanning from germination through vegetative and generative growth stages, plants rely on various inorganic micronutrients. These crucial micronutrients, including boron (B), chlorine (Cl), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), zinc (Zn), and molybdenum (Mo), are characterized by their concentrations in dry matter of tissue material (<1000 μg g⁻¹ dry matter (DM)) [23]. They play diverse functional roles in plant metabolism.

While the foliar fertilizer market offers numerous products with varying compositions tailored for fertilizing specific crops, our fertilizer also contains, in addition, vanadium and chromium, which play significant roles in plant metabolism. Vanadium can form complexes with enzymes involved in nitrogen fixation and nitrogen assimilation, essential processes for plant growth and development. Chromium enhances plant tolerance to environmental stresses such as drought, salinity, and heavy metal toxicity.

The purities of the chemicals used as macroelement generators (N, P, K) were determined to be between 97.0% and 98.5%, while those of the microelements (Fe, Mg, B, Zn, Cu, Mo, Ni, V, and Cr) ranged from 97.0% to 99.6% (Table 5).

The high purity levels observed in the chemicals used as macroelement and microelement generators contribute significantly to the effectiveness of the treatments applied, leading to enhanced plant development, increased productivity, and improved overall performance.

The stability of microelement complex combinations utilized in the foliar fertilizer composition was assessed to exclude the possibility of metal ion precipitation. EDTA (Ethylene-Diamine-Tetraacetic Acid) was employed as a complexing agent to form complex combinations with transitional metal ions introduced as microelements into the system. As demonstrated in Table 6, the utilized microelement complex combinations exhibited excellent stability.

The purity and composition of DICOPUR TOP components were assessed using 1H-NMR spectroscopy. Figure 7 and Table 7 illustrate the 1H-NMR spectrum for 2,4-D acid, showcasing the specific chemical characteristics observed in the analysis.

The analyzed samples used in the experimental determinations had an advanced purity (≥98.5%). Figure 8 displays the ¹H-NMR spectrum for Dicamba, providing insights into its chemical structure and characteristics. The analysis of the Dicamba spectrum revealed key characteristics, as summarized in Table 8.

The analyzed samples used in the experimental research exhibited advanced purity (≥98.5%). The complex composition of the liquid foliar fertilizer includes macro- and microelements, as detailed in Table 9. Furthermore, based on the obtained results, we developed an original technological process for producing 100 L of the complex composition of liquid foliar fertilizer.

Based on the results obtained at the laboratory level, a technological flow was established to produce the liquid foliar fertilizer. The main phases of the production process include obtaining solutions of macroelements (N, P, K) and microelements (Fe, Mg, B, Cu, Zn, Mo, Ni, V, Cr), followed by the production and packaging of the concentrated foliar liquid fertilizer. Figure 9 schematically presents the technological flow of manufacturing the liquid foliar fertilizer.

Table 10 provides a comprehensive breakdown of materials required for the production of 100 L of liquid foliar fertilizer, representing the concentrated product. This fertilizer exhibits broad versatility due to its compatibility for formulating liquid foliar compositions with various pesticides, including herbicides, insecticides, and fungicides.

Moreover, beyond its role in pesticide formulations, the fertilizer composition itself stands as a potent resource for agricultural, fruit growing, and vegetable growing applications. It is important to emphasize that prior to application, the composition necessitates dilution with water to achieve the desired concentration. This characteristic affords users flexibility in adjusting the application strength to suit specific agricultural contexts and crop requirements. The multifunctional nature of this fertilizer underscores its utility across diverse agricultural practices, contributing to enhanced plant health, yield, and biotic stress management strategies. Figure 10 shows a sample of the obtained fertilizer.

3.2. Response of Maize Plants to the Treatment with the Herbicide–Foliar Fertilizer Mixture

Weed species—Tests were carried out to evaluate the selectivity and efficacy of a post-emergence application of a liquid foliar fertilizer and DICOPUR TOP herbicide mixture, at a dose of 5.0 L ha⁻¹ (4:1), on maize crops. In 2021 and 2022, trials conducted in the experimental field revealed a high level of infestation by a wide range of annual and perennial monocotyledonous and dicotyledonous weeds, depending on the preceding crop and local soil and climatic conditions.

The results of the study showed an average infestation rate of 53% monocotyledonous and 47% dicotyledonous weeds over the two years (Table 11). The most representative weed species were Setaria viridis, Echinochloa crus-galli, Amaranthus retroflexus, Chenopodium album, and Polygonum convolvulus. The perennial weed species included Cirsium arvense, Convolvulus arvensis, and Sorghum halepense (Table 11).

Weed density—In the evaluations conducted in the experimental field, the selectivity rate (%) was assessed at 2- and 4-weeks post-application of a fertilizer and herbicide mixture in the maize experiment featuring the Felix hybrid.

Herbicides, particularly hormonal ones like DICOPUR TOP, often cause stress in maize plants. Cell growth and division are regulated by phytohormones, which are composed of proteins, and these proteins are, in turn, made up of amino acids. Phytotoxic effects were observed during the assessments, as indicated by a rating of 2 to 2.5 on the EWRS scale in the variant treated exclusively with the herbicide DICOPUR. A few days post-application, several key symptoms of phytotoxicity were noted in this variant. Specifically, the plants exhibited: (i) moderate leaf discolouration; (ii) deformed crown roots (“welded”); and (iii) at maturity, some cobs were missing grains. Additionally, some plants had two cobs forming at the same node, very close to the ground, which negatively affected production.

To support the plant during stressful conditions and to mitigate the negative effects of the herbicide’s active substances, we applied the foliar fertilizer described above alongside the herbicide. As a result, no significant phytotoxic effects were observed during the assessments, as indicated by a rating of 0 to 1.5 on the EWRS scale. The results obtained align with those previously reported by Milan Brankov et al. [16]. Their study demonstrated that under controlled conditions, the application of foliar fertilizer in conjunction with herbicides enhanced plant tolerance to the herbicides. Specifically, their findings indicate that plants exhibited increased resilience to herbicidal treatment when foliar fertilizer was included, suggesting that the presence of foliar fertilizer contributes to a higher level of herbicide tolerance.

According to the obtained data, both the treatment involving herbicide combined with foliar fertilizer and the treatment with herbicide alone significantly reduced weed density compared to the untreated control (Table 12). The herbicide and foliar fertilizer mixture proved to be the most effective, achieving a substantial reduction in overall weed populations. This combination notably decreased dicotyledonous weeds and also reduced monocotyledonous weeds, though to a lesser extent.

Herbicidal Efficacy—The herbicidal efficacy of the fertilizer–DICOPUR TOP mixture in controlling common weeds in maize crops over the two years of experimentation, compared to the untreated control, is presented in Table 13. The data analysis regarding the influence of herbicide and foliar fertilizer combinations on weed control demonstrates a consistent, unidirectional trend across both years. The mixed treatment of fertilizer and herbicide exhibited the highest effectiveness against dicotyledonous weeds, with efficacy rates ranging between 97.03% and 100%. In contrast, the effect on monocotyledonous weeds was significantly lower, with efficacy ranging from 42.56% to 44.64%.

These results indicate a notable disparity in the control of dicotyledonous versus monocotyledonous weeds, highlighting the need for further optimization of herbicide mixtures. Specifically, future formulations should aim to enhance the control of monocotyledonous weeds to achieve a more comprehensive weed management strategy in maize cultivation. The observed effectiveness of the fertilizer–herbicide combination on dicotyledons underscores the potential for integrating such treatments, though improvements in monocotyledon control are necessary to maximize overall efficacy.

Grain yield—Environmental factors such as temperature, precipitation, and soil moisture are critical to crop performance, and their influences can vary significantly from year to year. In our analysis, we observed that 2022 was marked by very dry conditions that had a substantial negative effect on maize yield, despite our efforts to implement irrigation practices. As shown in Table 14, grain production in 2022 was considerably lower than in 2021, a year characterized by more favorable growing conditions. This discrepancy underscores the significant impact that environmental variables can have on maize productivity.

From Table 14, it is evident that grain yield recorded significantly higher values in the variant where foliar fertilizer was applied in combination with DICOPUR TOP, compared to both the untreated control and the variant treated solely with herbicide. These findings suggest that the use of liquid fertilizer is particularly advantageous for maize, a crop with high nutrient demands that can benefit greatly from the additional nutrients provided by such fertilizers. The application of liquid fertilizer supports the plant’s overall health by helping to maintain green, healthy leaves, which are essential for maximizing photosynthesis. This, in turn, contributes to improved growth and a substantial increase in yield.

The positive effects of foliar fertilizers, combined with herbicide use, not only mitigate the potential stress caused by herbicides, but also enhance the plant’s ability to absorb and utilize essential nutrients during critical growth phases.

Similar findings were reported by Fageria et al. [24], who observed that combining foliar fertilization with post-emergence herbicides can not only increase the likelihood of a positive yield response, but also reduce the overall cost of application. By integrating these treatments, farmers can enhance nutrient availability during critical growth stages, while simultaneously managing weed competition more efficiently. This approach offers both agronomic and economic advantages, as it maximizes resource use and minimizes the need for separate applications, ultimately contributing to more cost-effective and sustainable crop management practices.

4. Conclusions

The studies aiming at foliar fertilizers with a complex composition containing macroelements (N, P, K) and microelements (Fe, Mg, B, S, Zn, Cu, Mo, Ni, V, Cr) established an original recipe and developed a technological laboratory process for its realization.

The complex designed composition of foliar liquid mineral fertilizer was based on the latest data from the specialized literature, of the areas established regarding the use of fertilizer and the need for it to be compatible with pesticides. The designed liquid foliar mineral fertilizer can be mixed with herbicides without precipitation of metal ions from the foliar fertilizer composition.

The stimulating effects of the complex composition of foliar liquid fertilizer designed in the development of plants during the growing season were highlighted by an intense colouring of the leaves, which is proof of a stimulation of the photosynthesis process. The use of the complex composition of liquid foliar fertilizer led to an increased resistance of plants to drought.

The complex composition of the foliar liquid mineral fertilizer can be used with maximum effects for various purposes. The treatment of maize crops showed good results on grain yield. The foliar liquid mineral fertilizer mixture with DICOPUR TOP ensured adequate control of dicotyledonous and monocotyledonous weeds in maize crops.

The fertilizer composition can also be used as such, in agriculture, fruit growing, vegetable growing, etc., with the mention that it should be diluted with water to the desired concentration before use.

The good results obtained for the new complex mixture of fertilizers with herbicides allow us to consider its future testing in various pedo-climatic zones and for different types of cultures (sunflowers, tomatoes, eggplants, potatoes, etc.). At the same time, aspects of toxicity and ecological impact must be taken into account and tested.

Author Contributions

Conceptualization, C.H. and L.S.; methodology, C.H. and D.I.; validation, C.H. and L.N.; formal analysis, P.P. and L.N.; investigation, L.S., S.I.B. and G.L.; resources, C.H. and L.S.; data curation, L.S., S.I.B. and D.I.; writing—original draft preparation, C.H., L.S. and P.P.; writing—review and editing, L.N. and G.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article, further inquiries can be directed to the corresponding authors.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Diagram of the laboratory installation used to make the complex composition of fertilizers (1—stand; 2—clamp; 3—gas bulb; 4—tripod; 5—balloon; 6—thermometer; 7—agitator; 8—refrigerant).

Figure 2. Structural formulas of: (a) 2,4-D acid; (b) Dicamba.

Figure 3. Temperatures (°C) recorded at the Moara Domneasca weather station, agricultural year 2020–2021.

Figure 4. Precipitation (mm) recorded at the Moara Domneasca weather station, agricultural year 2020–2021.

Figure 5. Temperatures (°C) recorded at the Moara Domneasca weather station, agricultural year 2021–2022.

Figure 6. Precipitation (mm) recorded at the Moara Domneasca weather station, agricultural year 2021–2022.

Figure 7. ¹H-NMR spectrum of 2,4-D acid.

Figure 8. ¹H-NMR spectrum of Dicamba.

Figure 9. The technological flow of manufacturing liquid foliar fertilizer.

Figure 10. The new liquid foliar mineral fertilizer.

Table 1. The amounts of chemical substances generating microelements added to obtain the solution of microelements.

Chemical Substances	Quantity	Chemical Substances	Quantity
FeSO₄. 7H₂O	0.50 kg	NiSO₄	0.0005 kg
MgSO₄. 7 H₂O	0.10 kg	Na₂Cr₂O₇	0.00025 kg
ZnSO₄. 7 H₂O	0.031 kg	NH₄VO₃	0.00025 kg
CuSO₄. 5 H₂O	0.0004 kg	H₃BO₃	0.085 kg
(NH₄)₆Mo₇O₂₄. H₂O	0.0009 kg

Table 2. Soil characteristics at the study site.

Type	Reddish Preluvosol
Texture	Clay-Loam
pH	5.62
Humus content	1.77%
Total nitrogen	0.182%
Mobile phosphorus	P_AL = 62 mg/kg
Mobile potassium	K_AL = 337 mg/kg

Table 3. Fertilizers used for the previous crops.

Winter barley (2019–2020)/Winter wheat (2020–2021)

Fertilization scheme

BBCH-00; DAP 150 kg/ha⁻¹ (27% N, 69% P₂O₅)

BBCH-30 Urea; 125 kg/ha (57.5% N)

BBCH-37 Ammonium nitrate; 100 kg/ha (33.5% N)

DAP—Diammonium phosphate; BBCH-00—after the soil tilling operation—before sowing; BBCH-30—the start of stem elongation; BBCH-37—stem elongation—flag leaf just visible.

Table 4. Description of hybrid maize Felix.

Characteristics
Growing period of 127–130 days; plant tall, vigorous with an average height of 260–270 cm; very good resistance to lodging; weight of 1000 grains: 300–320 g; hectoliter weight: 71–73 kg/hL.
Drought and heat resistance; resistant to smut (Ustilago maydis); tolerance to helminthosporiosis (Helminthosporium turcicum Pass); loses moisture easily from the grain.
8.0–9.2% protein; 4.0–4.5% fat; 73.0–74.2% starch.
The production of grains obtained under the following conditions: non-irrigated: 9.0–10.5 t/ha; Irrigated: 10.5–14.0 t/ha.
Recommendations: Cultivation area: recommended for zones I and II for corn cultivation. Optimal density: for non-irrigated: 55,000–60,000 plants/ha; for irrigated: 65,000–70,000 plants/ha.

Table 5. The purity of the substances used.

No.	Substance	Chemical Formula	Purity (%)
1	Urea	CH₄N₂O	97.5–98.5
2	Monoammoniacal phosphate	NH₄H₂PO₄	97.0–98.5
3	Potassium nitrate	KNO₃	97.5–98.5
4	Ferrous sulphate	FeSO₄	98.5
5	Magnesium sulphate	MgSO₄	97–98.5
6	Boric acid	H₃BO₃	97–98.5
7	Zinc sulphate	ZnSO₄	97.5–98.5
8	Copper sulphate	CuSO₄	99.5
9	Ammonium paramolybdate	(NH₄)₆Mo₇O₂₄	98–98.5
10	Nickel sulphate	NiSO₄	99.5
11	Ammonium vanadate	(NH₄)VO₃	99.6
12	Sodium dichromate	Na₂Cr₂O₇	99.5

Table 6. The stability constants of the obtained complex combinations.

Cation	Stability Constant (K)	Cation	Stability Constant (K)
Cr³⁺	1.00 × 10²³	Ni²⁺	4.17 × 10¹⁸
Cu²⁺	6.310 × 10¹⁸	V³⁺	7.9 × 10²⁵
Fe²⁺	2.14 × 10¹⁴	Zn²⁺	3.16 × 10¹⁶
Mg²⁺	4.90 × 10⁸

Table 7. Chemical characteristics of 2,4-D acid.

Characteristics	Chemical Expression
A singlet at δ = 4.7 ppm generated by the two protons attached to the carbon atom from the methyl group to the ether oxygen and the carboxyl function.
A singlet at δ = 5.7 ppm of the proton in the structure of the carboxylic function.
An AB system between δ = 6.2–7.1 ppm, as well as a doublet with a reduced coupling constant, at δ = 7.3 ppm, which correspond to the three aromatic protons in the benzene nucleus in positions 3.5 and 3.6.
At deuteration of the sample, the signal δ = 5.7 ppm corresponding to the proton in the structure of the carboxylic function disappeared, which demonstrated that the signal initially assigned to the proton in this position was correct.

Table 8. Chemical characteristics of Dicamba.

Characteristics	Chemical Expression
A singlet at δ = 4.0 ppm, corresponding to the three hydrogen atoms from the methoxy group.
Two doublets at δ = 7.1 and δ = 7.3 ppm corresponding to the two aromatic protons (from the benzene nucleus, from positions 4 and 5).
A singlet at TM = 3.6 ppm, given by the proton from the carboxylic function.

Table 9. The concentrations of macro- and microelements in the composition of the foliar liquid fertilizer.

No.	Macroelements	Content (%)	Substances	Quantity Used to Obtain 1 L of Fertilizer
1	Total nitrogen	8.5 (±0.5)	Urea	100 g
2	Phosphorus calculated as P₂O₅	6.5 (±0.5)	Monoammoniacal phosphate H₄⁺NO⁻P(O)(OH)₂; the product also participates in the nitrogen balance through NH₄	93 g
3	Potassium calculated as K₂O	4.2 (±0.5)	Potassium nitrate KNO₃; the product also participates in the total nitrogen balance through NO₃	78 g
No.	Microelements	Content (g L⁻¹)	Substances	Quantity Used to Obtain 1 L of Fertilizer
1	Iron	1.0–1.1	FeSO₄ 7H₂O	4.9–5.0 g
2	Magnesium	0.1–0.15	MgSO₄ 7H₂O	1.0–1.01 g
3	Boron	0.15–0.17	H₃BO₄	0.85 g
4	Zinc	0.07–0.09	ZnSO₄ 7H₂O	0.31 g
5	Copper	0.01–0.015	CuSO₄ 7H₂O	0.04 g
6	Molybdenum	0.005–0.007	(NH₄)₆Mo₇O₂₄	0.09 g
7	Nickel	0.001–0.0015	NiSO₄	0.045 g
8	Vanadium	0.001–0.0015	NH₄VO₄	0.023 g
9	Chromium	0.0008–0.0001	Na₂Cr₂O₇	0.022 g

Table 10. The balance of materials for the production of 100 L liquid foliar fertilizer (concentrated product).

No.	Input Products/Solutions	Quantity	Outputs Products/Solutions	Quantity
(A) Aqueous solution of NPK macroelements
1	Softened water	60 L	Solution of NPK macroelements	87.1 kg
2	Monoammoniacal phosphate	9.3 kg
3	Urea	10 kg
4	Nitre	7.8 kg
(B) Solution of microelements (Fe, Mg, B, Zn, Cu, Mo, Ni, V, Cr)
1	Softened water	20 L	Solution of microelements: Fe, Mg, B, Zn, Cu, Mo, Ni, V, Cr	21.6684 kg
2	Na₂—EDTA	0.95 kg
3	FeSO₄. 7H₂O	0.5 kg
4	MgSO₄. 7H₂O	0.1 kg
5	ZnSO₄. 7H₂O	0.031 kg
6	CuSO₄. 5H₂O	0.0004 kg
7	(NH₄)₆ Mo₇O₂₄. 4H₂O	0.0009 kg
8	NiSO₄	0.0005 kg
9	Na₂Cr₂O₇	0.00025 kg
10	NH₄VO₃	0.00025 kg
11	H₃BO₃	0.85
(C) Liquid foliar fertilizer “CaLuPa”, concentrated product
1	Aqueous solution of NPK macroelements	87.1 kg	Liquid foliar fertilizer “CaLuPa”, concentrated product	112.2695 kg
2	Aqueous solution of microelements (Fe, Mg, Zn, Cu, Mo, Ni, Cr, V, B)	21.6684 kg		112.2695 kg
3	Polyvinyl alcohol	0.001 kg		100 L
4	Phenolphthalein	0.0001 kg
5	Softened water until the completion of 100 L final product	3.5 L
Total inputs		112.2695 kg	Total outputs	112.2695 kg

Table 11. Weed species observed in maize crops during both experimental years.

Weed Class	Weed Species	The Percentage of Weeds
Annual dicotyledonous	Amaranthus retroflexus, Chenopodium album, Polygonum convolvulus	47%
Perennial dicotyledonous	Cirsium arvense, Convolvulus arvensis	47%
Annual monocotyledonous	Setaria viridis, Echinochloa crus-galli	53%
Perennial monocotyledonous	Sorghum halepense	53%

Table 12. Effect on weed density of foliar fertilizer with DICOPUR TOP and of the standard DICOPUR TOP herbicide treatments in maize crop (hybrid Felix) for the years 2021 and 2022.

Product	Weed Density (Number of Plants/m²)
	After 2 Weeks from the Treatment						After 4 Weeks from the Treatment
	DC		MC		Mean		DC		MC		Mean
	2021	2022	2021	2022	DC	MC	2021	2022	2021	2022	DC	MC
Control (untreated)	74.5	76.7	84.2	88.0	75.6	86.1	75.1	77.3	87.2	89.6	76.2	88.4
Foliar Fertilizer + DICOPUR TOP 5 L/ha (4:1)	0	0	40.6	55.0	0	47.8	2.0	2.5	44.3	57.4	2.25	50.85
DICOPUR TOP (standard treatment) 1 L/ha	2.5	3.5	42.8	57.0	3.0	49.9	3.0	5.4	49.6	58.2	4.2	53.9

DC—Dicotyledonous sp.; MC—Monocotyledonous sp.

Table 13. The herbicidal efficacy of the foliar fertilizer–DICOPUR TOP mixture in maize crops (hybrid Felix) for the years 2021 and 2022, assessed at 2 and 4 weeks after treatment.

Product	Herbicidal Efficacy (%)
	After 2 Weeks from the Treatment						After 4 Weeks from the Treatment
	DC		MC		Mean		DC		MC		Mean
	2021	2022	2021	2022	DC	MC	2021	2022	2021	2022	DC	MC
Control (untreated)	-	-	-	-	-	-	-	-	-	-	-	-
Foliar Fertilizer + DICOPUR TOP 5 L/ha (4:1)	100	100	51.78	37.5	100	44.64	97.33	96.74	49.19	35.93	97.03	42.56
DICOPUR TOP (standard treatment) 1 L/ha	96.64	95.43	49.16	35.22	96.03	42.19	96.00	93.01	43.11	35.04	94.50	39.07

DC—Dicotyledonous sp.; MC—Monocotyledonous sp.

Table 14. Effect on grain yield (t ha⁻¹; %) of foliar fertilizer with DICOPUR TOP and the standard DICOPUR TOP herbicide treatment in maize crop (hybrid Felix) for the years 2021 and 2022.

Product	Grain Yield (t ha⁻¹)
	2021		2022		Mean 2021–2022
	t ha⁻¹	%	t ha⁻¹	%	t ha⁻¹	%
Control (untreated)	8.63c	100	6.51c	100	7.57c	100
Foliar Fertilizer + DICOPUR TOP 5 L/ha (4:1)	10.54b	114.56	7.50b	115.20	9.02a	119.15
DICOPUR TOP (standard treatment) 1 L/ha	10.15b	110.32	7.32b	112.44	8.73b	115.38

Figures labelled with different letters indicate statistically significant differences based on Duncan’s multiple range test (p < 0.05).

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Hodoșan, C.; Nistor, L.; Poşan, P.; Bărbuică, S.I.; Ianiţchi, D.; Luţă, G.; Szilagyi, L. Pilot Study on a Liquid Mineral Foliar Fertilizer Mixed with Herbicides for Maize Protection and Nutrition. Agriculture 2024, 14, 2129. https://doi.org/10.3390/agriculture14122129

AMA Style

Hodoșan C, Nistor L, Poşan P, Bărbuică SI, Ianiţchi D, Luţă G, Szilagyi L. Pilot Study on a Liquid Mineral Foliar Fertilizer Mixed with Herbicides for Maize Protection and Nutrition. Agriculture. 2024; 14(12):2129. https://doi.org/10.3390/agriculture14122129

Chicago/Turabian Style

Hodoșan, Camelia, Lucica Nistor, Paula Poşan, Sorin Iulius Bărbuică, Daniela Ianiţchi, Gabriela Luţă, and Lizica Szilagyi. 2024. "Pilot Study on a Liquid Mineral Foliar Fertilizer Mixed with Herbicides for Maize Protection and Nutrition" Agriculture 14, no. 12: 2129. https://doi.org/10.3390/agriculture14122129

APA Style

Hodoșan, C., Nistor, L., Poşan, P., Bărbuică, S. I., Ianiţchi, D., Luţă, G., & Szilagyi, L. (2024). Pilot Study on a Liquid Mineral Foliar Fertilizer Mixed with Herbicides for Maize Protection and Nutrition. Agriculture, 14(12), 2129. https://doi.org/10.3390/agriculture14122129

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