Influence of Calcium on the Development of Corn Plants Grown in Hydroponics

Abstract

This work aimed to evaluate the effect of calcium on the development of corn plants grown with the omission and excess of calcium in a nutrient solution. The experiment was conducted in a greenhouse from March to May 2012. Three concentrations of calcium (0, 200, and 600 mg Ca L⁻¹) were added to the nutrient solution, which was renewed weekly, for a total of 40 days. The following variables were measured weekly: the number of leaves, average stem diameter, dry weight of the plant shoots and roots, and visual leaf diagnosis. The results showed that when the plants were deprived of calcium, their root systems were significantly reduced, as determined by the Tukey test (p ≤ 0.05). The plants with calcium deprivation had shorter roots and a dark brown color and displayed initial symptoms of chlorosis in their young leaves, which eventually led to necrosis and tipping. Hydroponics is promising and has shown satisfactory production results, contributing to the improvement of the environment, job creation, and increased profit for rural producers.

1. Introduction

Brazil has the potential to become the world’s leading exporter of corn by 2030. Currently, the country ranks second in corn exports to the international market, following only the United States. Over the past five harvests, Brazilian corn exports have risen dramatically, increasing from 24.1 million tons in 2017/2018 to 45 million tons in 2021/2022, which represents an 85% increase [1]. The USDA estimates that the country’s corn exports will reach 47 million tons in 2022/2023, making Brazil responsible for 26% of the world’s corn market [2].

Corn (Zea mays L.) is the most widely cultivated cereal crop in Brazil, covering nearly 13 million hectares and producing around 33 million tons [3]. Although the state of Pará accounts for less than 2% of the country’s corn production [4], there is potential for a significant increase in both the area under cultivation and its productivity, as new land is being made available for corn cultivation. This growth in grain production is largely due to the adoption of advanced technologies and effective management practices developed specifically for Brazilian agriculture [5]. It is therefore important for farmers to acquire a deeper understanding of nutrient deficiencies and the correct application of nutrients so as to avoid toxicity.

Hydroponics has a highly competitive internal environment, primarily due to its effectiveness and production efficiency and the superior quality of its products. These factors enable it to adapt to more efficient production, logistics, and distribution systems [6]. The significant growth of hydroponics can be attributed to several factors, including the production of high-quality vegetables, the efficient use of physical space by allowing for multiple crops, lower incidence of pests and diseases, reduced use of phytosanitary treatments, better control of the nutrient medium used for plant growth, and better water and nutrient use, as well as the reduced contamination of groundwater with nitric nitrogen and other chemicals, as the nutrient solution is recirculated throughout the system [7].

Macro- and micronutrients are essential elements that perform specific functions for plant life [8,9]. Among the macronutrients, calcium is absorbed as a bivalent ion (Ca++) and is crucial for root development, as it is necessary for the translocation and storage of carbohydrates and proteins. Because it is immobile within the plant, a common symptom is interveinal chlorosis in younger leaves. Other symptoms such as flower drop and reduced root growth may also occur [10]. Calcium is one of the most important nutrient elements in plants, playing a crucial role in maintaining the stability of cell walls and membranes, as well as cell development [11].

The use of alternative calcium sources has been considered due to the limitations of limestone. For this reason, the use of silicate- and nitrate-based products has been suggested as a promising correction that could enhance biomass and grain production [12]. However, there are few studies on the use of calcium in corn, which highlights the need for further research on its impact on plant morphology [13]. Various studies have aimed to determine the effects of different calcium concentrations in hydroponic nutrient solutions on the growth and yield [11,14,15,16].

Evaluation of the physical properties, which are parameters of vegetative growth, is a potential solution for enhancing corn production at scale. These physical attributes, such as the plant dry mass, number of leaves, stem diameter, and plant size, provide insights into the influences of the cultivation system and cultivar interaction on productivity [17].

The growth phase of grasses exposed to nutritional deficiencies should be understood, as it is essential to assess the significance of each nutrient and its impacts on the quality and production potential of the crop. Thus, the objective of this study was to evaluate the effects of calcium on the development of corn plants grown under conditions of calcium deficiency and excess in nutrient solution.

2. Materials and Methods

The experiment was conducted in a greenhouse of the Soil Science Sector in the Istituto de Ciências Agrárias—ICA, Universidade Federal da Amazônia—UFRA, Belém, PA, from March to May 2021 (01°28/03″ S, 48°29/18″ W). The climate in the region where the experiment was conducted is hot and intense throughout the year. The temperature typically ranges from 24 °C to 32 °C and is rarely below 23 °C or above 33 °C. Rainfall occurs regularly in Belém, with the wettest month being March, which has an average of 369 mm of rainfall. During the months of April and May, when the experiment was conducted, the average precipitation is 362.0 mm and 246.6 mm, respectively. The daily average period of sunshine during the study period was 12.1 h. This information was obtained from Inmet [18].

The commercial seeds of corn (Zea mays L.) of the hybrid brand Yeldgard VT Pro TM were used in the study. The seeds were sown in sand trays, and after 5 days of germination, the seedlings were carefully removed and transplanted into 2 L polyethylene pots containing silica as a substrate. A flexible 3 mm-diameter hose was inserted into the bottom of each pot so as to allow the solution to drain by gravity.

During the experiment, the nutrient solution was applied in the morning between 7 and 8 am and drained at dusk, keeping the roots flooded with the solution for 9 to 10 h per day. For the remaining hours, the plants had their roots in the drained substrate and silica. This method allowed the corn plants to grow at night in a moist substrate and be submerged in the study solution during the rest of the day. This technique is called the “Hoagland solution” and was first developed in order to grow plants without soil or substrate. It is a hydroponic nutrient solution, as described in Hoagland and Arnon [19].

The amount of solution lost through evapotranspiration was replenished with the same nutrient solution every two days [20] in an appropriate and sufficient quantity for each container. The experimental design was completely randomized and followed a factorial scheme with six replicates. The three treatments consisted of increasing doses of calcium in the nutrient solution: the omission of calcium (0 mg/L), complete nutrient solution (200 mg/L), and excess calcium (600 mg/L) (as described in

Table 1. Chemical composition of nutrient solution stocks, in mol·L⁻¹, and treatments with Ca, in mL·L⁻¹, were used in the experiment.

Stock Solution	Concentration	Treatment (mL·L−1)
		Complete Solution (200 mg Ca L−1)	0 mg Ca L−1	600 mg Ca L−1
NaNO3	1 M	-	10	-
CaCl2	1 M	-	-	10
KH2BY4	1 M	1	1	1
KNO3	1 M	5	5	5
Ca(NO3)2·4H2O	1 M	5	-	5
MgSO4·7H2O	1 M	2	2	2
Micronutrients *	1 M	1	1	1
Sol. Fe-EDTA **	-	1	1	1

* Chemical composition of micronutrient solution: 2860 mg H₃BO₃; 1810 mg MnCl₂·4H₂O; 220 mg ZnSO₄·7H₂O; 80 mg CuSO₄·5H₂O; 20 mg H₂MoO₄·H₂O, per liter of solution. ** Fe-EDTA solution chemical composition: 26.1 g of Na₂-EDTA, 89.2 mL of NaOH M, and 24 g of FeSO₄·7H₂O.

) [21], administered over a period of 40 days. The calcium source used was calcium nitrate (Ca(NO₃)₂) p.a. and calcium chloride (CaCl₂) p.a. The nutrient solution was changed weekly, and its electrical conductivity and pH were monitored to maintain a value between 5.5 and 6.5.

During the 40-day experiment, the vegetative growth parameters were monitored weekly to keep track of the plant growth, namely:

• The plant height (with a 5 m metallic measuring tape);
• Number of leaves per plant (counting leaves with sheaths);
• Plant visual diagnosis (as monitoring nutrient sufficiency through foliar diagnosis is a useful tool for maximizing fertilizer efficiency).

At the end of the experiment, the following analyses were carried out:

• The mean stem diameter (300 mm Vonder metal caliper).
• Shoot and root dry weights, where the roots and shoots were collected, separated, and packed into paper bags. Afterward, they were left to dry in a forced-air circulation oven at 70 °C until reaching constant weight.

The data were subjected to analysis of variance, and the means were compared by the Tukey test (p < 0.05) using the SISVAR version 5.6 software [22].

3. Results

Table 2. Vegetative growth parameters of plants after 40 days of cultivation in nutrient solution with varying amounts of calcium.

Parameter	Treatment
	Ca Excess	Ca Omission	Nutritient Solution
Leaf number (unit)	5.67 ± 0.58 a	6.67 ± 3.21 a	6.67 ± 0.58 a
Stem diameter (cm)	1.67 ± 0.83 a	2.20 ± 0.89 a	2.30 ± 0.92 a
Shoot dry matter (g)	21.38 ± 0.77 a	15.81 ± 0.23 b	22.22 ± 1.29 a
Root dry matter (g)	9.78 ± 0.24 b	4.66 ± 0.30 c	20.90 ± 0.69 a

Distinct letters show significant differences by Tukey’s test (p < 0.05). Ca omission (0 mg Ca L⁻¹), Ca excess (600 mg Ca L⁻¹), and Nutrient Solution (200 mg Ca L⁻¹). Means followed by the same letter in a row do not differ from each other according to the Tukey test at 5% probability. Pcs. cm and g (grass).

displays the characteristics of plants grown for 40 days in a nutrient solution with varying amounts of calcium.

The number of leaves was not significantly different between the different amounts of calcium tested, as determined by the Tukey test (p ≤ 0.05). The values ranged from 5.67 to 6.67 units per plant.

Table 3. Average height of plants grown with different sources of calcium as a function of the cultivation time.

Cultivation (Days)	Plant Height (cm)
	Ca Excess	Ca Omission	Nutritient Solution
1	1.67 ± 0.83 a	2.20 ± 0.89 a	2.30 ± 0.92 a
8	9.57 ± 2.10 a	10.60 ± 0.80 a	10.27 ± 1.34 a
16	16.13 ± 2.14 a	16.53 ± 0.31 a	16.87 ± 0.70 a
24	25.00 ± 2.67 a	22.3 ± 3.39 a	23.37 ± 1.24 a
32	33.17 ± 0.76 a	32.00 ± 11.70 a	32.00 ± 0.87 a
40	46.17 ± 3.92 a	38.67 ± 20.77 a	45.70 ± 2.89 a

Distinct letters show significant differences by Tukey’s test (p < 0.05). Ca omission (0 mg Ca L⁻¹), Ca excess (600 mg Ca L⁻¹), and Nutrient Solution (200 mg Ca L⁻¹). Means followed by the same letter in a row do not differ from each other according to the Tukey test at 5% probability. cm (centimeters).

presents the average plant height during the 40 days of cultivation with varying amounts of calcium.

4. Discussion

The values obtained in this study, on average, were lower than those reported in Alves et al. [23] for vegetative growth and corn production 24 days after planting, in which the plants were cultivated in fertilized soil with various doses of wastewater from a treatment plant (8.9 units per plant on average). However, Macedo et al. [24] reported similar values (ranging from 5.50 to 7.50 units per plant) for the number of leaves on corn plants subjected to different treatments.

Our results indicated that calcium (Ca) treatment has significant impacts on the leaf number and greenness degree, as already pointed out by Gustiar et al. [14]. The same authors noted that the Ca content in plants can be increased using fertilizers or nutrient solutions with higher Ca concentrations. However, it is important to avoid excessive Ca application, as Ca can be toxic to plants. Baesso et al. [25] studied the effects of different dosages of calcium silicate on corn and found that using minimal doses reduces the risk of toxicity and can achieve results equal to or better than those obtained with high doses.

The average stem diameter is a parameter commonly used to assess plant productivity. We found an average diameter (2.20 cm) higher than those reported by Picazevicz et al. [26] (ranging from 1.09 to 1.30 cm) for corn plants in a study on corn growth in response to applications of Azospirillum brasilense, Rhizobium tropici, molybdenum, and nitrogen. Plants with larger stem diameters tend to store more reserves in these structures, which contributes to grain filling and provides support for the ears [27]. In contrast, reduced stem diameters have been observed in different corn cultivars when grown at higher densities due to increased competition among the plants, leading to an increased incidence of lodging [28].

Like the average diameter, plant dry mass production is also a crucial factor for the plant yield. In this study, the shoot dry matter ranged from 15.81 to 22.22 g per plant after 40 days of cultivation in nutrient solutions with varying amounts of calcium. Macedo et al. [24] reported higher values (on average 16.17 and 65.15 g per plant) in a study on the initial growth of corn subjected to different fertilization management strategies. Therefore, these results highlight the efficacy of using nutrient solutions compared to soil in corn cultivation.

Pramanick et al. [29] reported that the application of increased seaweed extract to crops can improve growth attributes such as the plant height, dry matter accumulation, and leaf area index. The same authors attributed this result to the biostimulant properties of seaweed extract, which provides crops with essential macro- and micronutrients and high levels of cytokinins, auxins, and betaines, leading to increased chlorophyll production, improved photosynthesis, and enhanced vegetative development and growth.

The comparison of mean values of root dry matter production between various calcium applications to corn plants revealed a significant difference (p ≤ 0.05). The most notable change was seen in regard to calcium omission, resulting in a mere 4.66 g of dry matter. This is a direct consequence of calcium deficiency in plants, which reduces the root system. In a study conducted by Macedo et al. [24], values of 5.57 to 18.18 g of root dry matter were observed, which are similar to ours, ranging from 9.78 to 20.90 g.

Research on corn dry matter has received significant attention in the scientific community, as evidenced by several studies. Oliveira et al. [30], for instance, investigated the phosphorus effect on corn dry mass. Baup et al. [31], in turn, developed a simple algorithm to estimate daily changes in corn dry mass in the field based on a satellite-derived Green Area Index. Finally, Oliveira et al. [32] examined the effects of manganese and silicon on corn dry mass. These studies illustrate the importance of continued research in this area, as there is still much to be explored and understood about corn growth and productivity.

The height of corn plants during growth over 1, 8, 16, 24, 32, and 40 days showed no significant difference, according to the Tukey test (p ≤ 0.05), for different calcium sources and cultivation times (Table 3). Another study [26] found an average height of 44.68 to 59.97 cm related to the effects of Azospirillum brasilense, Rhizobium tropici, nitrogen, and molybdenum on millet growth, s finding which is comparable to our results (38.67, 45.70, and 46.17 cm). According to the study conducted by Sihotang and Sipayung [33], analysis of variance and observation data showed that applying two different sources of calcium nutrients to an ultisol, such as eggshell or dolomite, had no significant effect on the height of corn plants.

Shareef et al. [34] reported a significant difference in plant height between two types of calcium compounds, with one compound resulting in plants approximately 10% taller. This increased height is attributed to the higher availability of nitrogen and calcium, which promote cell division in plants.

According to a study conducted by Fernandes et al. [13], corn plant height was found to be 6% higher 35 days after emergence when only calcium silicate was used, indicating that the plants experienced faster development in this stage.

Other authors, including those of [35,36,37,38], also showed satisfactory results for corn in response to different levels of fertilization. These works and the other studies mentioned above corroborate the results of this research. They are strong indicators that demonstrate the importance of understanding different corn cultivation techniques. As an example, hydroponics is promising and has shown satisfactory production results, contributing to the improvement of the environment, job creation, and increased profit for rural producers.

It is worth noting that this study is based on one year of data, and that the results are “preliminary” and are based on maize plants grown over a 3 month period in one location and in one year. However, the results were very satisfactory.

Hydroponics has emerged as a superior alternative to traditional soil cultivation and is widely utilized in many Western countries [39]. This study aimed to examine the applications of hydroponics and to forecast its potential significance. The technique can be applied to a variety of terrestrial plants, including commercial crops such as wheat, tomato, spinach, mint, coriander, and many others.

5. Conclusions

After 40 days of growth, corn plants exposed to varying levels of calcium (0, 200, and 600 mg/L) in nutrient solution showed no significant differences in the number of leaves, average stem diameter, or height.

The analysis of shoot dry mass production revealed the efficacy of using nutrient solutions containing different amounts of calcium compared to soil cultivation. Conversely, the root dry mass production showed that calcium omission caused a significant reduction in root growth.

Plants subjected to calcium deficiency had shortened roots and dark brown coloration, along with initial signs of chlorosis in the young leaves. This evolved into necrosis, leading to plant death if the deficiency persisted.