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Article

Combining Depth and Rate of Selenium Fertilizer Basal Application to Improve Selenium Content and Yield in Sweet Maize

by
Zhiwei Peng
1,
Haoyuan Sun
2,
Yukun Guo
1,
Youtao Chen
2,3,4,* and
Xuebin Yin
1,3,4,*
1
College of Agriculture, Shanxi Agricultural University, Taiyuan 030031, China
2
College of Agriculture, Anhui Science and Technology University, Chuzhou 239000, China
3
Institute of Functional Agriculture (Food) Science and Technology at Yangtze River Delta, Anhui Science and Technology University, Chuzhou 239000, China
4
Anhui Province Key Laboratory of Functional Agriculture and Functional Food, Anhui Science and Technology University, Chuzhou 239000, China
*
Authors to whom correspondence should be addressed.
Agronomy 2025, 15(4), 775; https://doi.org/10.3390/agronomy15040775
Submission received: 1 March 2025 / Revised: 18 March 2025 / Accepted: 20 March 2025 / Published: 22 March 2025
(This article belongs to the Section Soil and Plant Nutrition)
Browse Figures
Versions Notes

Abstract

:
Selenium-enriched sweet maize is an important product to alleviate selenium deficiency in the human body. In this study, the effects of the basal application of selenium fertilizer on the selenium content and yield of maize were analyzed in a 2-year field trial using a two-factor, five-level, split-area experimental combination design with a different selenium fertilizer application rate (150–750 kg ha−1) and depth (1–20 cm). It was found that the selenium application rate and depth significantly affected dry matter mass, selenium content, and selenium accumulation in maize. In particular, the Se3D4 treatment combination (a selenium application rate of 450 kg ha−1 and depth of 15 cm) performed the best in increasing the selenium content and yield of the maize grain. The 2-year data showed that the selenium content of maize grain under Se3D4 treatment reached 3.59 mg kg−1 and 3.24 mg kg−1, which were 13.63 and 13.70 folds as the control, respectively, and the yield reached 6.28 t ha−1 and 6.07 t ha−1, which were 24.35% and 33.30% higher than the control, respectively. Therefore, by optimizing the application rate and depth of selenium fertilizer, the selenium content and yield of maize can be significantly increased. The results of this study provide a theoretical basis for the precise application of selenium fertilizer in the biofortification of sweet maize.

1. Introduction

Selenium (Se) is a trace nutrient essential for humans and animals [1]. It participates in the formation of a variety of enzymes, has antioxidant effects, can protect human cells from oxidative damage, and maintains the normal physiological functions of cells [2,3]. Therefore, selenium is essential for maintaining human health and promoting biological growth [4]. Selenium deficiency is harmful to human health and is closely related to diseases such as Keshan disease, Kaschin–Beck disease, liver disease, and various cancers [5,6,7,8]. In 2017, China Health and Family Planning Commission (now the National Health Commission) issued the health industry standard WS/T 578.3-2017 [9] “Dietary Nutrient Reference Intake for Chinese Residents Part 3: Trace Elements”, which stipulates that the reference intake of selenium for adults is 60 µg d⁻¹. However, the amount of selenium in people’s daily diet in most parts of China is only 26 µg, which is far from the recommended standard [10]. Consuming selenium-rich agricultural products is the best way to supplement this nutrient, especially selenium-rich staple foods, which play an important role in preventing and reducing selenium deficiency in the human body [11].
Maize (Zea mays L.), an important staple food crop [12], is listed as one of the three major cereal crops grown worldwide [13]. Considered a staple food in many parts of the world, it is rich in starch and antioxidant compounds such as phenolic compounds, carotenoids, and lutein [14], and it plays an important role in providing humans with their dietary intake of nutrients [15,16]. As research on maize continues to deepen, sweet maize has become popular among consumers due to its short growth cycle, unique taste, and high nutritional value [17]. The success of the Green Revolution led to the widespread cultivation of high-yield cereal crops and a significant increase in food production [18]. However, this trend has also led to a decrease in the concentration of micronutrients in food, creating an inadvertent “dilution effect” [19] and exacerbating the problem of “hidden hunger” [20]. Therefore, eating a certain amount of sweet maize rich in selenium can not only meet consumers’ demand for high-quality food but also effectively alleviate the problem of selenium deficiency.
At present, the artificial selenium enrichment technologies used for major crops include the soil application of selenium, the foliar spraying of selenium, and seed soaking or seed mixing with selenium solution [21,22,23,24,25,26,27]. Among them, foliar spraying has the advantages of effective targeting, fast absorption, low cost, and the use of small amounts of fertilizer, and it is widely used [28,29,30]. However, this method can easily lead to residual selenium fertilizer on the stems and grains, and it is greatly affected by the weather, posing a safety hazard. In contrast, the application of soil fertilizer usually involves applying the fertilizer at the roots via seed and fertilizer co-seeding technology, which is not labor-intensive, is low in cost, and has considerable promotion potential [31,32,33,34]. This technique requires a horizontal distance of 8 cm from the seeds during sowing to avoid burning the seedlings. The depth of fertilization can be changed by adjusting the machinery.
However, previous studies have primarily focused on the effects of different selenium concentrations on selenium-enriched maize [35,36]. In particular, research by Le Wang et al. demonstrated that when selenium application rates ranged between 150–225 g ha−1, it could enhance physiological characteristics, thereby improving both yield and selenium content [37]. Moreover, the influence of fertilization depth is equally crucial. Studies by Chen et al. revealed that a fertilization depth of 15 cm optimized root-shoot coordination, achieving optimal growth and distribution of underground roots along with superior above-ground photosynthetic performance, ultimately increasing grain yield and nitrogen-phosphorus fertilizer use efficiency [38]. A 2-year field study conducted in Northwest China further emphasized the critical importance of optimal nitrogen fertilization depth for improving growth, dry matter accumulation, and yield in hybrid seed maize. Compared with depths of 15 cm and 5 cm, fertilization at 25 cm depth significantly increased average plant height by 5.00% and 10.36%, respectively, enhanced dry matter accumulation by 2.65% and 3.39%, and improved total nutrient uptake rates by 19.17% and 7.11%. Additionally, the average grain nutrient uptake rate increased by 23.33% [39]. Nevertheless, research on the synergistic effects between application depth and rate of root-applied selenium fertilizer remains insufficient.
Therefore, this study hypothesizes that combining optimal selenium fertilizer rate with targeted root-zone placement depth will synergistically enhance selenium accumulation and yield in sweet maize by improving nutrient accessibility and minimizing losses. To test this hypothesis, a 2-year field experiment was conducted using a two-factor, five-level split-plot design to evaluate the effects of selenium rate (150–750 kg ha−1) and application depth (1–20 cm) on dry matter production, selenium enrichment, and yield components. The results aim to establish evidence-based guidelines for selenium fertilizer management, advancing both agronomic efficiency and human nutrition.

2. Materials and Methods

2.1. Experimental Location

The experimental site is located in the Functional Maize Experimental Base in Taoyuanbao Village, Taigu District, Jinzhong City, Shanxi Province, China. To eliminate the effects of Se fertilization on the plots, the experiment in the years 2023 and 2024 was conducted in different fields nearby. This place has a temperate continental climate with geographic coordinates of 37°25′ N 112°34′ E, an average annual temperature of 12.25 °C, and a frost-free period of about 180 days. The total precipitation from April to August in 2023 amounts to 151.1 mm with an average temperature of 20.5 °C, while the precipitation for the same period in 2024 amounts to 73.7 mm accompanied by a higher average temperature of 22.6 °C. The soil type is grayish-brown soil, and the specific physicochemical properties are detailed in Table 1.

2.2. Experimental Materials

The maize variety Fengnuo 168, provided by Anhui Science and Technology University, was used as the test material. It is a predominant cultivar in sweet maize, demonstrating broad adaptability to both northern and southern regions, along with high acceptance among farmers. This maize variety has successfully passed the uniformity trial for maize varieties in Northern China, demonstrating full compliance with the national maize variety approval standards established by China’s agricultural authorities. The average yield of this variety is 1.27 t ha−1 (fresh ear basis). The duration from seedling emergence to fresh ear harvesting is approximately 75.0 days. Key phenotypic characteristics include purple leaf sheaths at the seedling stage, light purple silks, green anthers, and green glumes. The plant exhibits a semi-compact architecture, with a plant height of 253 cm, an ear height of 103 cm, and 17 leaves per mature plant. It has spikes that are long cones, with a spike length of 18.6 cm and spike rows of 12–20 rows. The spikes have white rachis, with colored and sweet grain. A fresh 100-grain weighs 33.5 g. The compound fertilizer with the ratio N:P2O5:K2O of 26:10:15 was used as a basal application. Selenium fertilizer (SETEK-19BF-001) obtained from Suzhou SETEK Co. Ltd., Suzhou, China, containing a total selenium content of 1000 mg kg−1, was used in the study. The selenium fertilizer primarily comprised nano-selenium.

2.3. Experimental Design

The selenium fertilizer application rates were set at 150 kg ha−1, 300 kg ha−1, 450 kg ha−1, 600 kg ha−1, and 750 kg ha−1. Vertical depth of the fertilizer application was divided into five levels: 1 cm, 5 cm, 10 cm, 15 cm, and 20 cm. And horizontal distances of the fertilizers were all applied at 8 cm according to the local practice. Meanwhile, three replicates of untreated control groups (CK) were established, where the CK treatment groups received no selenium fertilizer application while maintaining identical other cultivation practices compared to the experimental groups. According to the two-factor, five-level split-zone experimental combination design, the specific combination design was detailed in Table 2, with 26 experimental treatments. The plot used for the experiment was 15 square meters (1.5 m by 10 m), and two rows were planted in each plot with 50 cm row spacing and 40 cm plant spacing, with 25 plants planted in each row. Three replications were set up in a randomized complete block design. The plots were provided with 1 m protection rows on the periphery and 0.5 m protection rows between the plots. Fertilizer was applied to all plots by root application. The compound fertilizer (N:P2O5:K2O of 26:10:15) was spread according to local requirements at a rate of 600 kg ha−1. On 10 May 2023, and 22 April 2024, fertilizer trenches were manually excavated, and a hole application method was used to test the 26 combinations designed in the protocol, where the selenium fertilizer was uniformly applied into the excavated holes and buried and filled in. Subsequently, seeding was carried out on 11 May 2023 and 23 April 2024. Flood irrigation was applied at 750 m3 ha−1 during three critical phenological stages of corn growth: at the jointing stage on 28 June 2023 and 19 June 2024, the tasseling stage on 29 July 2023 and 19 July 2024, and the filling stage on 7 August 2023 and 28 July 2024. Other field management practices, weeding was carried out routinely. Harvesting took place on 30 August 2023 and 20 August 2024, respectively (30 days after flowering).

2.4. Measurement Indicators and Methods

2.4.1. Sample Collection and Processing

At maize maturity, nine representative plants were randomly selected from each experimental plot [40]. First, these plants were rinsed three times using tap water to remove soil and other impurities from the surface, followed by three more rinses with distilled water and drained with filter paper. Then, the plant was divided into six parts: root, stem, leaf, staminate, bract, and ear for the next measurement and analysis.

2.4.2. Determination of Maize Agronomic Traits

The ear weight, length, and width were tested at first. Specifically, ear weight refers to the remaining weight of the ear after removing the husk, ear length refers to the length from the base to the top of the ear, and ear width refers to the diameter of the thickest part of the ear. Next, cob and grain divided from the ear, along with the other five parts mentioned above, were placed into an oven and subjected to a killing treatment at 105 °C for 30 min and then dried at 60 °C until constant weight. The dry matter mass of the seven parts of the plant was measured after cooling down, respectively. As for the yield, it was calculated based on the dry matter content of the grain at a moisture content of 14% [41].

2.4.3. Determination of Se Content for Different Organs in Maize

After weighing the dry matter for each part, the different organs were ground into powder and passed through an 80-mesh sieve for the preparation of Se content testing. A multi-element X-ray rapid analyzer was used to determine Se content, following the procedure outlined in LS/T6115-2016 [42,43]. The specific steps for selenium content analysis were as follows: 15 known concentration samples were used to construct a standard curve. Namely, the selenium content (mg kg−1) of root, stem, leaf, staminate, bract, cob, and grain ranges at 0.47–3.49, 0.16–3.69, 0.46–15.48, 0.25–10.50, 0.13–3.46, 0.11–2.63, and 0.24–4.27, respectively. The standard curve was validated using P44707B, a standard substance for maize flour component analysis. The relative standard deviation of the obtained measurement results was less than 5%, indicating that the method had good repeatability, the instrument operated stably, and the established model was accurate and reliable. Subsequently, the Se content for different organs in maize was analyzed by quantitative measurement mode, with the instrument automatically calculating and displaying the results. The grain selenium accumulation was calculated by multiplying the grain selenium content with the dry matter mass of the grain, and the whole plant selenium accumulation was obtained by summing the product of the selenium content of each organ of the plant and the dry matter weight of each organ.

2.5. Data Processing

Excel 2016 was used for data organization, SPSS 26.0 statistical analysis software was used for the analysis of the significance of differences (p < 0.05), and Origin 2021 software was used for the relevant graphics.

3. Results and Discussion

3.1. Effect of Selenium Application on Dry Matter

The two interactions of selenium rate and the rate and depth of selenium application had significant effects on the dry matter mass of the maize plants, while the depth of selenium application alone did not have a significant effect. The patterns were almost the same for the 2 years (Figure 1). At a selenium application rate of Se1, Se2, and Se3, the dry matter mass of the plants showed an increasing and then decreasing trend with the increase in the fertilizer depth, with the dry matter mass being the greatest under all D4 treatment conditions. When the selenium rate was located at Se4 and Se5, the dry matter mass of the plants showed a trend of decreasing and then increasing with the increase in the fertilizer depth, with the dry matter mass being the smallest under both D4 treatment conditions.
In 2023, under the Se2 treatment, the dry matter mass increased by 2.25%, 3.19%, 8.54%, 12.38%, and 9.10%, respectively, at different fertilizer depths compared to the CK. The dry matter mass of the plants under the Se3 treatment increased by 4.46%, 6.67%, 16.25%, 21.37%, and 12.84% compared to the CK at different fertilizer depths, respectively. It increased by 12.07% and 15.86% and decreased by 2.54%, 5.20%, and 0.57% under the Se4 treatment, respectively. In 2024, the plant dry matter mass increased by 4.44%, 6.66%, 16.28%, 21.39%, and 12.86% at the different fertilizer depths under the Se3 treatment compared to the CK, respectively, and it increased by 12.14% and 15.89% and decreased by 2.43%, 5.04%, and 0.44% under the Se4 treatment, respectively. In terms of reciprocal effects, the dry matter mass of the maize plants was lowest under the Se5D4 treatment and highest under the Se3D4 treatment. This was the optimal combination to improve the dry matter mass, which was 461.9 g and 416.7 g in both years, i.e., 21.37% and 21.39% higher than the control, respectively.
The selenium rate significantly affected the dry matter quality of the maize grains, while the application depth and rate and depth together did not. This pattern was generally the same for both years (Figure 2). At lower selenium rate (Se1, Se2, and Se3), the dry matter mass showed an increasing and then decreasing trend with increasing depth of fertilizer application, reaching the highest dry matter mass under the D4 treatment conditions. On the contrary, at higher selenium rate (Se4 and Se5), the dry matter mass showed a decreasing and then increasing trend with increasing depth of fertilization and was the smallest under both D4 treatment conditions.
In 2023, under the Se3 treatment, the dry matter quality of seeds at different fertilizer depths increased by 1.39%, 0.87%, 11.31%, 16.30%, and 8.04%, respectively, compared to the CK. Similarly, in 2024, the seed dry matter quality increased by 1.13%, 0.73%, 11.04%, 16.21%, and 7.72% at different fertilizer depths under the Se3 treatments compared to the CK, respectively. In terms of the combined effects of selenium rate and depth, the Se5D4 treatment resulted in the lowest seed dry matter mass of 77.90 g and 70.77 g in both years, which was 12.43% and 12.03% lower than the control, respectively. The Se3D4 treatment, on the other hand, achieved the highest seed dry matter mass of 103.5 g and 93.49 g in both years, which was an increase of 16.30% and 16.21%, respectively, compared to the control, indicating that this was the best fertilizer application combination to increase the dry matter content of the seeds.

3.2. Effects of Selenium Application on Selenium Enrichment

3.2.1. Effect of Selenium Application on Grain Selenium Content

The selenium rate, the depth of selenium application, and the interaction between the two had highly significant effects on the maize kernel selenium content, and the patterns were generally consistent across the 2 years (Figure 3). Under the same selenium rate, the selenium content of the maize grains increased and then decreased with the increase in the fertilizer depth in the order D4 > D3 > D5 > D2 > D1 > CK, and the selenium content of the maize grains was the highest in all treatments under D4. With the same depth of selenium application, the selenium content of the maize grains showed a gradual increase with increasing selenium rate, with the highest selenium content being found under all Se5 treatments. In terms of the interaction effect, the Se5D4 treatment combination resulted in the highest maize kernel selenium content in both years and was the best fertilization regimen for enhancing the selenium content, achieving 4.25 mg kg−1 (2023) and 3.83 mg kg−1 (2024), which were 16.12 and 16.18 folds as the control, respectively.

3.2.2. Effect of Selenium Application on Grain Selenium Accumulation

The selenium rate and depth of selenium application, as well as their interactions, had highly significant effects on selenium accumulation in the maize grains, and the patterns were generally consistent between the 2 years (Figure 4). When the selenium rate was applied consistently, the selenium accumulation in the maize grains showed an increasing and then decreasing trend with the increase in the fertilizer depth, in the order of D4 > D3 > D5 > D2 > D1 > CK, with the highest selenium accumulation observed under all D4 treatments. When the depth of selenium application was D1, D2, and D5, the selenium accumulation in the maize grains gradually increased with the increase in the fertilizer rate, and the highest selenium accumulation of 261.3 μg was recorded under the Se5D5 treatment. At the D3 and D4 fertilizer depths, the selenium accumulation increased and then decreased with the increase in the fertilizer rate, in the order of Se3 > Se4 > Se5 > Se2 > Se1 > CK. The highest selenium accumulation was found in all of the Se3 treatments and was the greatest under the treatment conditions of Se3D4. In terms of reciprocal effects, the Se3D4 treatment was the optimal combination for increasing the selenium accumulation in the maize grains, with accumulations of 371.0 μg and 303.5 μg in the 2 years, which were 14.87 and 14.99 folds as the control, respectively.

3.2.3. Effect of Selenium Application on Plant Selenium Accumulation

The selenium rate and depth of application, as well as their interaction, had highly significant effects on selenium accumulation in the maize grains, and the patterns were generally consistent between the 2 years (Figure 5). At the same rate, the selenium accumulation in maize plants showed a tendency of increasing and then decreasing with the increase in the fertilizer depth, in the order of D4 > D3 > D5 > D2 > D1 > CK, and was the greatest under the condition of D4. The selenium accumulation in the maize plants gradually increased with increasing selenium rate with application depths of D1, D2, D3, and D5, and was greatest under the Se5D3 treatment. When the application depth was D4, the selenium accumulation in the maize plants increased and then decreased with the increase in selenium rate in the order Se4 > Se3 > Se5 > Se2 > Se1 > CK, and the accumulation was the greatest under the Se4D4 treatment. In terms of reciprocal effects, the Se4D4 treatment was found to be the optimal combination to increase selenium accumulation, with 1889 μg and 1545 μg of selenium in the maize plants in both years, which were 14.54 and 14.52 folds as the control, respectively.

3.3. Effect of Selenium Application on Yield and Other Related Indicators

The differences between years had a highly significant effect on maize yield and its related indicators, but the pattern was essentially similar between years. The selenium rate had highly significant effects on fresh spike weight, spike weight, and seed yield, a significant effect on spike length, and no significant effect on spike thickness. The interaction between selenium rate and depth of application had highly significant effects on cob weight and kernel weight, but not on fresh cob weight, cob length, or cob thickness in maize. The depth of selenium application had no significant effect on maize yield and its related indicators (see Table 3). At selenium rate of Se1, Se2, and Se3, the maize yield and its related indicators increased and then decreased with increasing fertilizer depth, with the highest yield and its related indicators under the D4 treatment. In contrast, at selenium rate of Se4 and Se5, yield and its related indicators decreased and then increased with increasing fertilizer depth, with the worst performance being observed under the D4 treatment. In 2023, spike weight increased by 5.17%, 7.12%, 14.14%, 21.94%, and 8.99%, respectively, while seed yield increased by 5.47%, 8.35%, 16.71%, 24.35%, and 10.18%, respectively, compared to the CK at different fertilizer depths under Se3 treatment. Spike weight increased by 10.25% and 9.98% and decreased by 0.28%, 4.55%, and 5.23% at different fertilizer depths under the Se4 treatment compared to the CK, respectively. Seed yield increased by 12.16% and 11.16% and decreased by 0.23%, 4.12%, and 7.21% compared to the CK, respectively. Spike weight was 1.63% lower, 2.15% higher, 9.08% lower, 13.56% lower, and 0.96% lower than the CK at different fertilizer depths under the Se5 treatment, respectively. In 2024, spike weight increased by 5.26%, 8.54%, 24.54%, 27.90%, and 12.24%. Seed yield increased by 2.19%, 6.69%, 28.57%, 33.30%, and 10.87%. And spike length increased by 4.58%, respectively, compared to the CK at different fertilizer depths under the Se3 treatment. Spike weight increased by 18.51% and 14.08% and decreased by 0.02%, 0.84%, and 2.29%, respectively, and seed yield increased by 20.74%, 13.36%, 1.03%, and 2.06% and decreased by 2.29%, respectively, compared to the CK at different fertilizer depths under the Se4 treatment. Seed yield reduced by 0.56%, 2.10%, 5.49%, and 11.84% and increased by 2.06% compared to the CK at different fertilizer depths under the Se5 treatment. In terms of reciprocal effects, the minimum seed yield of the maize was recorded for the Se5D4 treatment at 3.96 t ha−1 and 3.45 t ha−1 in both years, which was 8.81% and 11.84% lower than the control, respectively. The maximum kernel yield was recorded for the Se3D4 treatment, which was the optimum combination, with the maize yields for the 2 years of 6.28 t ha−1 and 6.07 t ha−1, which were 24.35% and 33.30% higher than the control group, respectively.

4. Discussion

4.1. Effect of Selenium Application Rate and Depth on Dry Matter Quality of Fresh Sweet Maize

In modern agricultural practices, selenium fertilizer application has received attention for its potential impact on crop growth and yield. Our results revealed a significant interaction between selenium rate and application depth in influencing dry matter accumulation. The Se3D4 treatment (450 kg ha−1 Se at 15 cm depth) maximized plant and grain dry matter mass, achieving 461.9 g (plant) and 103.5 g (grain) in 2023, and 416.7 g (plant) and 93.49 g (grain) in 2024 (Figure 1 and Figure 2). However, the effect of selenium fertilization is not mono-linear, and its effect has been found to be significantly affected by the rate and depth of application, with a general trend of increasing and then decreasing with increasing selenium applications [37]. This is similar to the results of our series of studies. Selenium fertilizer has a double-edged sword effect: the moderate application of selenium is beneficial to maize growth, but excessive application may cause growth inhibition. Jiang et al., [44] found the same trend in another study in which the application of high doses of selenium significantly reduced the root and stem growth of maize plants. This phenomenon has been observed in other crops, such as ryegrass seedlings, whose growth was stimulated at low doses of selenium and inhibited at high doses [45]. However, selenium can also cause (eco)toxicity in high rate, as observed in soils in selenium-containing regions of the world [46]. High selenium levels are more detrimental to maize growth and physiological responses than low selenium levels, and the reduction in growth characteristics may be attributed to the high accumulation of selenium in the roots and the disturbance of gas exchange parameters [47].

4.2. Effect of Selenium Application Rate and Depth on Selenium Content and Accumulation in Maize

Our series of studies showed that the rate and depth of selenium had a significant effect on the selenium content and accumulation in the maize grains and plants. In particular, the selenium content in maize grains was significantly higher under the Se3D4 treatment with a rate of 450 kg ha−1 and a fertilizer depth of 15 cm, which was more than 12-fold higher than that of the control group, a result that may be attributed to the use of the hole application method, which concentrates the nutrients on the roots of the crop, thereby increasing fertilizer utilization and reducing volatilization and loss of fertilizer [48,49]. This result has important implications for selenium deficiency on a global scale. At the same fertilization concentration, the selenium content of the plants showed an increasing and then decreasing trend with the depth of fertilization. The selenium content of the maize grains under the D4 treatment was about twice as much as that under the D1 treatment, which could be attributed to the shallower application of the fertilizer in the D1 treatment, resulting in more serious fertilizer loss during surface runoff [50,51]. It was also found that the soil application of selenium increased the selenium content of the maize grains [52], and this increased gradually with increasing selenium application, a trend similar to that observed in rice and soybean [53]. The intensity of selenium uptake by plants may depend on a number of factors, including the type and stage of vegetation, the selenium content of the soil and its bioavailability to the plant, physiological conditions (salinity and soil pH), the presence of other substances, the activity of membrane transporters, and the mechanism of plant transport, which collectively determine the distribution and accumulation of selenium in the plant [54,55]. Notably, while the highest rate (Se5: 750 kg ha−1) increased grain selenium content (4.25 mg kg−1 in 2023, 3.83 mg kg−1 in 2024), it reduced accumulation due to dry matter penalties (Figure 4). This trade-off mirrors findings in plants, where high selenium disrupted nutrient partitioning [56], and in maize, where excessive selenium accumulation in roots inhibited translocation to grains [57]. The Se3D4 treatment balanced these factors, in the maize grains, with selenium accumulations of 371.0 μg and 303.5 μg in the 2 years, highlighting the importance of synergistic rate-depth optimization. Furthermore, the fresh edible sweet maize produced under this experimental regime exhibited high yield, selenium content, and selenium accumulation, all exceeding the selenium-enriched maize standards. Based on the findings of this study, it is recommended that consuming one-sixth portion (approximately 70 g) of selenium-enriched corn cultivated under these experimental conditions daily can fulfill the adult’s average daily nutritional requirement for selenium (60 μg). Another significant implication of this research lies in the fact that selenium-enriched corn produced through this cultivation model can serve as raw material for food processing, enabling intensive production while providing a safer and more efficient manufacturing approach for selenium-fortified food products.

4.3. Effect of Selenium Application Rate and Depth on Maize Yield and Related Indicators

In terms of yield, significant effects of selenium rate and depth were also observed in our study. The maximum maize yield was achieved under the Se3D4 treatment, which was 24.35% and 33.30% higher than the control. This result further confirms the importance of appropriate selenium application strategies for improving crop yields. This may be related to the application of selenium fertilizer, which maintains plant water status, regulates osmoregulatory substance content [58], enhances antioxidant activity [13], increases pigment content, and regulates photosynthesis [59]. Not only does it increase the cellulose content of the stover, but it also enhances the stalk’s resistance to stumping, which is critical for maize growth, yield, quality, and mechanized harvesting. It has also been shown that exogenous selenium treatment improves anatomical characteristics, physiological characteristics, and the yield of wheat stems [60], which suggests that selenium fertilization has potential benefits for different crops. The superiority of Se3D4 likely stems from optimized root-zone accessibility. Shallow applications (D1, 1 cm) may have led to selenium loss via surface runoff or volatilization [50], whereas deeper placement (D4, 15 cm) ensured sustained nutrient availability to the root system, as observed in maize under similar fertilization strategies [48]. Conversely, higher rate (Se4-Se5: 600–750 kg ha−1) reduced yield under D4, possibly due to selenium-induced oxidative stress impairing photosynthesis and biomass allocation [44,47]. These findings contrast with wheat studies, where selenium had minimal yield impacts [61], highlighting crop-specific differences in selenium tolerance and assimilation pathways. In addition, exogenous selenium application in soil activates soil microorganisms and promotes their activity [62], suggesting that selenium fertilization may indirectly promote crop growth by affecting soil microbial communities. Further studies have also shown that deep fertilization is an effective agricultural management strategy that improves crop yield and fertilizer utilization [63]. Fertilizer application at a certain depth in the soil has been shown to increase yields, improve fertilizer utilization, and conserve fertilizer in agricultural fields for a wide range of crops such as rice [64], maize [65], wheat [66], and vegetables [67].

5. Conclusions

This study comprehensively explored the effect of soil selenium application on the selenium content and yield of maize, clearly finding that the rate and depth of selenium application are key affecting factors. After 2 years of field trials, we concluded that, by precisely controlling the rate and depth of selenium application, the selenium content of crops and their yield can be significantly increased. Based on this finding, we recommend that, when applying selenium fertilizer, a horizontal distance of 8 cm from the maize plant, a vertical depth of 15 cm from the soil surface, and a selenium fertilizer rate of 450 kg ha−1 should be selected to achieve the best fertilization effect. The selenium accumulation amounted to 371.0 μg and 303.5 μg, respectively, both exceeding the standard for selenium-enriched maize. Concurrently, the grain yield achieved 6.28 t ha⁻¹ and 6.06 t ha⁻¹, surpassing the control group. These results demonstrate the superiority of this treatment combination in enhancing selenium content, selenium accumulation, and yield in maize. The data provide scientific support and rate references for the precise application of selenium in maize cultivation. In summary, this study provides a scientific basis for precision agriculture practice, which helps provide guidance for farmers to apply selenium fertilizer rationally in order to increase the nutritional and economic value of crops and improve the selenium nutritional status of the human body.

Author Contributions

Conceptualization, Z.P.; methodology, Z.P.; software, Z.P.; validation, Z.P., H.S. and Y.G.; formal analysis, Z.P.; investigation, Z.P.; resources, Z.P.; data curation, Z.P.; writing—original draft preparation, Z.P.; writing—review and editing, Y.C.; visualization, Z.P.; supervision, Y.C. and X.Y.; project administration, X.Y.; funding acquisition, Y.C. and X.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Special Fund for Anhui Provincial Key Laboratory of Functional Agriculture and Functional Food (800013), Key Technology Research and Talent Introduction Project for Functional Agriculture (KYYJ202201) and Talent Introduction Project for Fingerprint of Functional Substances of Crops (NXYJ202301).

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 conflict of interest.

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Figure 1. Dry matter of maize plants. Note: Different lowercase letters in a table indicate significant (p < 0.05) differences between the dry matter mass of plants at different fertilizer depths for the same fertilizer rate factor. * indicates significant difference at the 0.05, and NS no significant difference. CK represents the control group without selenium fertilizer application, while other cultivation practices were maintained consistent with the experimental groups. Se1, Se2, Se3, Se4, and Se5 correspond to selenium fertilizer application rates of 150 kg ha−1, 300 kg ha−1, 450 kg ha−1, 600 kg ha−1, and 750 kg ha−1, respectively. D1, D2, D3, D4, and D5 represent fertilization depths of 1 cm, 5 cm, 10 cm, 15 cm, and 20 cm, respectively. The same notation applies hereafter.
Figure 1. Dry matter of maize plants. Note: Different lowercase letters in a table indicate significant (p < 0.05) differences between the dry matter mass of plants at different fertilizer depths for the same fertilizer rate factor. * indicates significant difference at the 0.05, and NS no significant difference. CK represents the control group without selenium fertilizer application, while other cultivation practices were maintained consistent with the experimental groups. Se1, Se2, Se3, Se4, and Se5 correspond to selenium fertilizer application rates of 150 kg ha−1, 300 kg ha−1, 450 kg ha−1, 600 kg ha−1, and 750 kg ha−1, respectively. D1, D2, D3, D4, and D5 represent fertilization depths of 1 cm, 5 cm, 10 cm, 15 cm, and 20 cm, respectively. The same notation applies hereafter.
Agronomy 15 00775 g001
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Figure 2. Dry matter of maize grain. Note: Different lowercase letters in a table indicate significant (p < 0.05) differences between the dry matter mass of plants at different fertilizer depths for the same fertilizer rate factor. * indicates significant difference at the 0.05, and NS no significant difference.
Figure 2. Dry matter of maize grain. Note: Different lowercase letters in a table indicate significant (p < 0.05) differences between the dry matter mass of plants at different fertilizer depths for the same fertilizer rate factor. * indicates significant difference at the 0.05, and NS no significant difference.
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Figure 3. Selenium content in maize grain. Note: Different lowercase letters in a table indicate significant (p < 0.05) differences between the dry matter mass of plants at different fertilizer depths for the same fertilizer rate factor. ** indicates significant difference at the 0.01.
Figure 3. Selenium content in maize grain. Note: Different lowercase letters in a table indicate significant (p < 0.05) differences between the dry matter mass of plants at different fertilizer depths for the same fertilizer rate factor. ** indicates significant difference at the 0.01.
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Figure 4. Selenium accumulation in maize grains. Note: Different lowercase letters in a table indicate significant (p < 0.05) differences between the dry matter mass of plants at different fertilizer depths for the same fertilizer rate factor. ** indicates significant difference at the 0.01.
Figure 4. Selenium accumulation in maize grains. Note: Different lowercase letters in a table indicate significant (p < 0.05) differences between the dry matter mass of plants at different fertilizer depths for the same fertilizer rate factor. ** indicates significant difference at the 0.01.
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Figure 5. Selenium accumulation in maize plants. Note: Different lowercase letters in a table indicate significant (p < 0.05) differences between the dry matter mass of plants at different fertilizer depths for the same fertilizer rate factor. ** indicates significant difference at the 0.01.
Figure 5. Selenium accumulation in maize plants. Note: Different lowercase letters in a table indicate significant (p < 0.05) differences between the dry matter mass of plants at different fertilizer depths for the same fertilizer rate factor. ** indicates significant difference at the 0.01.
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Table 1. The basic soil physicochemical properties of the field for 2023 and 2024.
Table 1. The basic soil physicochemical properties of the field for 2023 and 2024.
Year20232024
pH8.558.99
Organic matter content (g kg−1)31.0233.98
Total nitrogen content (g kg−1)1.461.31
Total phosphorus content (g kg−1)1.210.99
Total potassium content (g kg−1)16.9717.39
Alkaline nitrogen content (mg kg−1)84.97105.1
Available phosphorus content (mg kg−1)70.8570.69
Available potassium content (mg kg−1)105.491.66
Selenium content (mg kg−1)0.380.33
Table 2. Two-factor five-level experimental design.
Table 2. Two-factor five-level experimental design.
CombinationSelenium Fertilizer Rate (kg ha−1)Vertical Depth of Fertilizer Application (cm)CombinationSelenium Fertilizer Rate (kg ha−1)Vertical Depth of Fertilizer Application (cm)
10 (CK)0 (CK)14450 (Se3)10 (D3)
2150 (Se1)1 (D1)15450 (Se3)15 (D4)
3150 (Se1)5 (D2)16450 (Se3)20 (D5)
4150 (Se1)10 (D3)17600 (Se4)1 (D1)
5150 (Se1)15 (D4)18600 (Se4)5 (D2)
6150 (Se1)20 (D5)19600 (Se4)10 (D3)
7300 (Se2)1 (D1)20600 (Se4)15 (D4)
8300 (Se2)5 (D2)21600 (Se4)20 (D5)
9300 (Se2)10 (D3)22750 (Se5)1 (D1)
10300 (Se2)15 (D4)23750 (Se5)5 (D2)
11300 (Se2)20 (D5)24750 (Se5)10 (D3)
12450 (Se3)1 (D1)25750 (Se5)15 (D4)
13450 (Se3)5 (D2)26750 (Se5)20 (D5)
Table 3. Maize yield and yield components.
Table 3. Maize yield and yield components.
YearFertilization Rate (kg ha−1)Fertilization Depth (cm)Fresh Ear Weight (g)Ear Weight (g)Grain Yield (kg ha−1)Maize Cob Length (cm)Maize Cob Diameter (cm)
2023–2024150 (Se1)0 (CK)390.0 ± 24.3 a129.1 ± 6.8 a5051 ± 311 a19.77 ± 1.08 a5.75 ± 0.32 a
1 (D1)390.4 ± 22.3 a132.7 ± 5.5 a5247 ± 311 a19.89 ± 1.24 a5.78 ± 0.39 a
5 (D2)391.6 ± 27.0 a133.7 ± 8.7 a5271 ± 210 a20 ± 1.04 a5.8 ± 0.52 a
10 (D3)399.4 ± 17.1 a135.0 ± 8.8 a5310 ± 403 a20.12 ± 0.95 a5.84 ± 0.47 a
15 (D4)402.3 ± 16.7 a138.5 ± 8.7 a5500 ± 351 a20.43 ± 1.17 a5.9 ± 0.37 a
20 (D5)394.9 ± 21.6 a133.7 ± 5.5 a5311 ± 410 a19.92 ± 0.91 a5.8 ± 0.47 a
300 (Se2)0 (CK)390.0 ± 24.3 a129.1 ± 6.8 a5051 ± 311 a19.77 ± 1.08 a5.75 ± 0.32 a
1 (D1)394.3 ± 23.6 a133.3 ± 6.7 a5266 ± 371 a19.9 ± 1 a5.81 ± 0.56 a
5 (D2)397.8 ± 12.0 a138.1 ± 8.5 a5500 ± 254 a20.14 ± 0.82 a5.85 ± 0.5 a
10 (D3)406.8 ± 19.3 a139.9 ± 6.4 a5553 ± 280 a20.54 ± 1.03 a5.93 ± 0.24 a
15 (D4)409.9 ± 15.6 a143.5 ± 4.8 a5730 ± 295 a20.83 ± 1.09 a5.96 ± 0.54 a
20 (D5)407.2 ± 18.8 a138.2 ± 6.0 a5427 ± 296 a20.19 ± 1.09 a5.87 ± 0.31 a
450 (Se3)0 (CK)390.0 ± 24.3 a129.1 ± 6.8b5051 ± 311 c19.77 ± 1.08 a5.75 ± 0.32 a
1 (D1)402.3 ± 30.8 a135.8 ± 7.3 ab5327 ± 232 bc19.92 ± 1.55 a5.82 ± 0.34 a
5 (D2)402.6 ± 23.5 a138.3 ± 6.6 ab5473 ± 396 bc20.34 ± 0.91 a5.83 ± 0.52 a
10 (D3)421.7 ± 15.0 a147.4 ± 10.0 ab5895 ± 216 ab20.79 ± 0.89 a5.98 ± 0.38 a
15 (D4)437.4 ± 19.9 a157.5 ± 12.3 a6280 ± 334 a21.02 ± 1.03 a6.05 ± 0.54 a
20 (D5)412.8 ± 25.9 a140.7 ± 10.6 ab5565 ± 231 abc20.69 ± 1.38 a5.91 ± 0.53 a
600 (Se4)0 (CK)390.0 ± 24.3 a129.1 ± 6.8 ab5051 ± 311 ab19.77 ± 1.08 a5.75 ± 0.32 a
1 (D1)407.8 ± 20.0 a142.4 ± 5.2 a5665 ± 310 a20.77 ± 0.72 a5.9 ± 0.5 a
5 (D2)416.4 ± 25.9 a142.0 ± 6.8 a5614 ± 266 a20.79 ± 0.7 a5.98 ± 0.43 a
10 (D3)373.5 ± 15.7 a128.8 ± 5.0 ab5039 ± 242 ab19.77 ± 1.14 a5.75 ± 0.3 a
15 (D4)371.9 ± 17.2 a123.3 ± 7.5 b4843 ± 240 b19.6 ± 0.69 a5.65 ± 0.34 a
20 (D5)379.9 ± 16.6 a122.4 ± 7.2 b4687 ± 241 b19.77 ± 0.97 a5.68 ± 0.51 a
750 (Se5)0 (CK)390.0 ± 24.3 a129.1 ± 6.8 ab5051 ± 311 a19.77 ± 1.08 a5.75 ± 0.32 a
1 (D1)389.7 ± 19.6 a127.0 ± 7.7 ab4930 ± 258 a19.91 ± 0.68 a5.7 ± 0.46 a
5 (D2)374.1 ± 23.1 a131.9 ± 6.3 a5138 ± 283 a19.88 ± 0.57 a5.77 ± 0.38 a
10 (D3)365.8 ± 23.2 a117.4 ± 8.1 ab4655 ± 234 a19.11 ± 0.83 a5.64 ± 0.47 a
15 (D4)363.2 ± 25.0 a111.6 ± 8.2 b4606 ± 239 a19.33 ± 0.92 a5.57 ± 0.35 a
20 (D5)373.0 ± 24.0 a127.9 ± 7.8 ab5009 ± 396 a19.62 ± 1.01 a5.67 ± 0.44 a
2024–2025150 (Se1)0 (CK)359.0 ± 18.2 a114.2 ± 8.2 a4552 ± 254 a17.45 ± 0.87 a5.05 ± 0.3 a
1 (D1)359.6 ± 19.6 a115.8 ± 7.6 a4536 ± 266 a17.68 ± 1.22 a5.07 ± 0.43 a
5 (D2)361.4 ± 25.2 a116.8 ± 5.4 a4571 ± 191 a18.26 ± 0.29 a5.1 ± 0.19 a
10 (D3)363.4 ± 14.6 a119.9 ± 5.4 a4658 ± 287 a18.27 ± 1.09 a5.2 ± 0.21 a
15 (D4)365.5 ± 25.8 a124.1 ± 6.3 a4863 ± 318 a18.75 ± 1.76 a5.23 ± 0.18 a
20 (D5)362.0 ± 26.6 a116.5 ± 8.2 a4670 ± 321 a18.22 ± 1.02 a5.1 ± 0.28 a
300 (Se2)0 (CK)359.0 ± 18.2 a114.2 ± 8.2 b4552 ± 254 b17.45 ± 0.87 a5.05 ± 0.3 a
1 (D1)361.8 ± 16.1 a116.1 ± 7.0 b4533 ± 325 b17.84 ± 0.59 a5.12 ± 0.25 a
5 (D2)362.6 ± 23.0 a120.4 ± 5.3 b4698 ± 183 b18.58 ± 1.21 a5.21 ± 0.23 a
10 (D3)369.6 ± 23.9 a124.2 ± 7.9 ab4863 ± 364 b18.78 ± 0.99 a5.29 ± 0.3 a
15 (D4)375.8 ± 16.5 a139.3 ± 8.4 a5703 ± 327 a19.2 ± 0.73 a5.3 ± 0.22 a
20 (D5)371.2 ± 14.3 a122.9 ± 6.1 ab4784 ± 193 b18.61 ± 0.61 a5.21 ± 0.21 a
450 (Se3)0 (CK)359.0 ± 18.2 a114.2 ± 8.2 c4552 ± 254 c17.45 ± 0.87b5.05 ± 0.3 a
1 (D1)365.2 ± 19.3 a120.2 ± 5.1 c4652 ± 264 c18.25 ± 0.77 ab5.13 ± 0.33 a
5 (D2)368.2 ± 27.0 a124.0 ± 5.5 bc4857 ± 293 c18.75 ± 0.45 ab5.15 ± 0.13 a
10 (D3)384.1 ± 21.4 a142.3 ± 6.2 ab5853 ± 230 ab19.12 ± 0.65 ab5.32 ± 0.36 a
15 (D4)392.6 ± 26.2 a146.1 ± 10.1 a6068 ± 412 a19.43 ± 0.51 a5.34 ± 0.24 a
20 (D5)377.3 ± 21.5 a128.2 ± 9.8 abc5047 ± 410 bc19.03 ± 0.77 ab5.25 ± 0.29 a
600 (Se4)0 (CK)359.0 ± 18.2 a114.2 ± 8.2 bc4552 ± 254 b17.45 ± 0.87 a5.05 ± 0.3 a
1 (D1)375.0 ± 21.5 a135.4 ± 8.1 a5497 ± 406 a19.07 ± 1.32 a5.24 ± 0.27 a
5 (D2)382.9 ± 15.6 a130.3 ± 7.1 ab5160 ± 311 ab19.19 ± 0.57 a5.31 ± 0.31 a
10 (D3)356.1 ± 19.0 a114.2 ± 7.7 bc4599 ± 278 b17.46 ± 0.66 a5.01 ± 0.1 a
15 (D4)343.8 ± 25.5 a113.3 ± 7.0 bc4646 ± 266 b17.28 ± 1.26 a4.88 ± 0.32 a
20 (D5)356.8 ± 13.1 a111.6 ± 4.8 c4448 ± 188 b17.5 ± 0.42 a4.97 ± 0.2 a
750 (Se5)0 (CK)359.0 ± 18.2 a114.2 ± 8.2 a4552 ± 254 a17.45 ± 0.87 a5.05 ± 0.3 a
1 (D1)358.2 ± 25.2 a113.8 ± 5.3 a4527 ± 252 a17.88 ± 0.77 a5 ± 0.19 a
5 (D2)356.4 ± 24.0 a115.1 ± 8.6 a4457 ± 312 a17.54 ± 1.11 a5.06 ± 0.19 a
10 (D3)349.9 ± 19.2 a106.8 ± 5.6 a4303 ± 183 a16.55 ± 1.60 a4.8 ± 0.32 a
15 (D4)334.3 ± 15.1 a99.58 ± 5.8 a4013 ± 273 a16.65 ± 0.48 a4.65 ± 0.25 a
20 (D5)350.7 ± 24.9 a113.9 ± 6.5 a4646 ± 250 a17.35 ± 1.19 a4.97 ± 0.26 a
Source of variationYear (Y)**********
Fertilization rate*******NS
Fertilization depthNSNS*NSNS
Fertilization rate × Fertilization depthNS****NSNS
Note: Different lowercase letters in the table indicate significant (p < 0.05) differences between the dry matter mass of plants at different fertilizer depths for the same fertilizer rate factor. * indicates a significance level of p < 0.01, ** indicates a significance level of p < 0.05, and NS indicates no significance.
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MDPI and ACS Style

Peng, Z.; Sun, H.; Guo, Y.; Chen, Y.; Yin, X. Combining Depth and Rate of Selenium Fertilizer Basal Application to Improve Selenium Content and Yield in Sweet Maize. Agronomy 2025, 15, 775. https://doi.org/10.3390/agronomy15040775

AMA Style

Peng Z, Sun H, Guo Y, Chen Y, Yin X. Combining Depth and Rate of Selenium Fertilizer Basal Application to Improve Selenium Content and Yield in Sweet Maize. Agronomy. 2025; 15(4):775. https://doi.org/10.3390/agronomy15040775

Chicago/Turabian Style

Peng, Zhiwei, Haoyuan Sun, Yukun Guo, Youtao Chen, and Xuebin Yin. 2025. "Combining Depth and Rate of Selenium Fertilizer Basal Application to Improve Selenium Content and Yield in Sweet Maize" Agronomy 15, no. 4: 775. https://doi.org/10.3390/agronomy15040775

APA Style

Peng, Z., Sun, H., Guo, Y., Chen, Y., & Yin, X. (2025). Combining Depth and Rate of Selenium Fertilizer Basal Application to Improve Selenium Content and Yield in Sweet Maize. Agronomy, 15(4), 775. https://doi.org/10.3390/agronomy15040775

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