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Article

Oil-Coated Ammonium Sulfate Improves Maize Nutrient Uptake and Regulates Nitrogen Leaching Rates in Sandy Soil

by
Shuangdui Yan
1,
Xinyu Dong
1,
Huishu Jiang
1,
Yu Liu
1,
Ying Han
1,
Tanwen Guo
1,
Yanhui Zhang
1,
Juan Li
2,* and
Qiuyan Yan
3
1
College of Resources and Environment, Shanxi Agricultural University, Taigu, Jinzhong 030801, China
2
State Key Laboratory of Efficient Utilization of Arid and Semi-Arid Arable Land in Northern China, Key Laboratory of Plant Nutrition and Fertilizer, Ministry of Agriculture and Rural Affairs, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China
3
Institute of Wheat Research, Shanxi Agricultural University, Linfen 041000, China
*
Author to whom correspondence should be addressed.
Agronomy 2024, 14(7), 1463; https://doi.org/10.3390/agronomy14071463
Submission received: 15 April 2024 / Revised: 21 June 2024 / Accepted: 3 July 2024 / Published: 5 July 2024
(This article belongs to the Special Issue Innovative Controlled Release Fertilizer Technologies in Agriculture)
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Abstract

:
Ammonium sulfate (AS) has been utilized in agriculture; however, there is a dearth of research on its application in maize cultivation subsequent to the implementation of nitrification inhibitors or coating treatments. This study aimed to analyze the impacts of various combinations of AS fertilizers on soil nutrients, plant nutrient uptake, yield, and fertilizer utilization efficiency in maize cultivation to establish an optimal and stabilized disposal method for AS. A completely randomized design was employed with five treatments (AU, the control using urea; AS, treatment using ammonium sulfate; ASN, treatment using ammonium sulfate with a nitrification inhibitor; ASG, treatment using oil-coated ammonium sulfate; and ASD, treatment using oil–humic acid-coated ammonium sulfate). The results show the following: (1) Compared with AU and AS, ASN, ASG, and ASD decreased the leaching rates of total nitrogen (TN), ammonium nitrogen (NH4+-N), and nitrate nitrogen (NO3−-N), and more residual N had accumulated in the soil. The first-order kinetic equation Nt = N0(1 − e−kt) could better fit the process of N accumulation and release, and the N-release rate constant was in the order of AU > CK > AS > ASG > ASN > ASD. (2) Compared with the AU and AS treatments, the plant dry weight, grain dry weight, spike width, spike length, and yields of maize increased by 8.85–11.08%, 12.98–14.15%, 2.95–3.52%, 5.50–5.65%, and 43.21–51.10%, respectively, under the ASG treatment. A path analysis revealed the main decision coefficient of the effective spike number on the maize yield. Furthermore, the accumulation levels of N, P, and K within above-ground plants significantly increased under the ASG treatment compared with those under the AU and AS treatments. N, P, and K partial factor productivity under the ASG treatment increased by 47.12%, 47.15%, and 73.40% on average, while grain N, P, and K balance increased by 50.45%, 47.10%, 55.61% on average, compared with the AU and AS treatments. Therefore, the ASG treatment exhibited the optimal slow-release effect on nutrients and achieved excellent performance in enhancing the production and efficiency of maize.

1. Introduction

Slow-/controlled-release nitrogen (N) can be utilized to effectively regulate the dissolution and release rate of N, facilitating its migration through various regulatory mechanisms to meet the nutrient demands of crops throughout their entire growth cycle [1,2,3]. Slow-release N exhibits a significantly reduced nutrient release rate compared to quick-release fertilizers upon application in soil, resulting in stable yields, prolonged nutrient availability, high fertilizer utilization efficiency, and minimal environmental pollution [4,5]. In the seedling stage, the application of slow-/controlled-release N fertilizers is recommended for inhibiting N transformation, minimizing losses, and delaying the peak occurrence time to fulfill the low nitrogen requirements during this stage while meeting the rapidly increasing demand during the flowering stage in maize cultivation, thereby promoting maize growth and ensuring optimal nutrient absorption [6,7,8]. Consequently, incorporating slow-/controlled-release N fertilizers into agricultural practices can effectively enhance fertilizer efficiency and crop yield.
Ammonium sulfate (AS) contains not only essential N nutrients for crops but also sulfur nutrients that promote crop development and metabolism [9]. For example, sulfur can promote the accumulation of starch and sugar in corn, increase fruit quality, and improve the nutritional value of maize [10]. After application in soil, AS immediately dissociates into available NH4+ and SO42−, which can be absorbed and used by crops; therefore, it has been widely applied in agriculture [11,12,13]. However, AS accounts for less than 1% of the total composition of N fertilizer varieties in China, which is far lower than the proportion of AS used in developed countries [14]. Therefore, in China, the industrial byproduct AS has great prospects for application and can promote the transformation and upgrading of traditional fertilizers in green agricultural development. Nevertheless, due to the quick-acting properties of AS, one-time basal application will lead to a large N supply in the crop seedling stage, whereas insufficient soil N supply during the later stages is likely to cause N deficiency in the later stages of plant growth. Therefore, it is necessary to carry out slow- and controlled-release measures for AS to prolong the release of fertilizer nutrients, meet the needs of crop growth, and achieve the high-efficiency utilization of AS.
In 2020, the maize planting area in China reached 41,264 thousand hectares, taking up 42.12% of the total grain planting area; moreover, the maize yield was 260,665 million tons, occupying 38.93% of the total grain yield [15]. The development of maize production plays a critical role in China’s agricultural economy. The screening of slow-/controlled-release nitrogen fertilizers suitable for maize growth can provide technical support and a theoretical foundation for the development of high-quality and high-yield maize, and new slow-/controlled-release fertilizers. Currently, the majority of studies investigating the effects of slow-/controlled-release nitrogen fertilizers have primarily focused on urea [16,17,18]. However, there is a lack of reports regarding the utilization of AS as the primary N source, and little is known about changes in soil nutrients, crop nutrients, fertilizer utilization rate, and yield following the application of AS combined with nitrification inhibitors and coating treatments.
Therefore, this study aimed to investigate the impact of AS on soil and maize under three different slow-/controlled-release measures. Additionally, correlation and path analyses were conducted to elucidate the roles played by each factor in maize production. These findings will contribute to establishing a scientific foundation for developing novel slow-/controlled-release AS fertilizers.

2. Materials and Methods

2.1. Simulation Experiment Design

An experiment was carried out with a PVC pipe (25 cm × 5.70 cm) with a gauze covering the bottom; air-dried soil was passed through a 2 mm screen and packed into 10 cm according to a bulk weight of 1.30 g/cm3 in order to compact the lower soil (Figure 1), a modification of the method of Luo et al. [19]. The tested fertilizers were prepared with a disc granulating machine (1 m diameter, 45° dip angle, 13.6 r/min, Shandong, China) with ammonium sulfate fertilizer placed in the disc, and were sprayed with slow control materials (nitrification inhibitor, oil, and oil-humic acid) along with rotation. The nitrification inhibitor was 2-chloro-6-(trichloromethyl) pyridine, the oil was edible canola oil, and humic acid was coal-based humic acid. The tested fertilizer (Table 1) was mixed with the soil and packed into the 10 cm soil layer with an amount of N equal to 0.30 g/kg. Each fertilizer treatment was replicated three times. The top was covered with quartz sand to a depth of 1.00 cm, and a total of 663.46 g of soil was used. The edge effect of leaching was minimized by compacting the soil at the edge of the soil column. The PVC pipe was closed with a thin film with punctured holes after each soil column was saturated with water, and was cultured at 25 °C. Then, 150 mL of deionized water was added to induce leaching after 24 h, and the leaching solution was collected. The next leaching was induced after 4 days, and this was repeated 10 times for 40 days. The volume of each leaching solution was measured, and the concentrations of total nitrogen (TN), ammonium nitrogen (NH4+-N), and nitrate nitrogen (NO3−-N) were determined in each leaching solution.
The total nitrogen content in the leaching solution was determined via potassium persulfate oxidation and ultraviolet spectrophotometry, and the ammonium nitrogen and nitrate nitrogen contents were determined using a continuous-flow analyzer (Skalar San++, SKALAR, Holland) according to Bao et al. [20].
Nitrogen leaching amount (g) = Nitrogen concentration in each leaching solution (g/L) × Volume of leaching solution (L)
Nitrogen leaching rate per time (%) = (Nitrogen leaching amount per time/Nitrogen application amount) × 100
Cumulative nitrogen leaching rate (%) = Sum of nitrogen leaching rates from each leaching
The relationship between the nutrient release rate and time of different fertilizers was studied using the following first-order kinetic equation: Nt = N0(1 − e−kt).
In the equation, Nt is the release rate at time t; N0 is the maximum release rate; kt is the constant of the nutrient release rate (d−1); and t is time (d).
After the test was completed, the soil was mixed and collected from 0–10 and 10–20 cm soil layers to determine the total nitrogen, ammonium nitrogen, and nitrate nitrogen concentrations according to Bao et al. [20]. The total nitrogen content in the soil was determined using the Kjeldahl method, and the ammonium nitrogen and nitrate nitrogen contents were determined using a continuous-flow analyzer after leaching by potassium chloride.

2.2. Field Experiment

2.2.1. Experimental Design

A field experiment was conducted at the Experimental Demonstration Base of the Wheat Research Institute, Hongbu Village, Wucun Town, Linfen City (111°33′07″ E, 36°13′02″ N) in Shanxi Province from 25 May 2021 to 13 September 2021. The previous crop was maize with one harvest a year. The site is rain-fed and belongs to a temperate monsoon climate, with an annual average temperature of 12.2 °C and annual precipitation of 486.5 mm. The soil type was calcareous cinnamon, and basic soil properties were 8.44 g/kg of organic matter, pH 8.57 (soil:water = 1:2.5), 1.39 g/kg of total nitrogen, 69.02 mg/kg of alkali-hydrolyzed nitrogen, 64.57 mg/kg of available potassium, and 4.66 mg/kg of available phosphorus.
Five fertilizer treatments (the same as in the simulated experiment) were compared in a completely random design with three replications. The area of each plot was 56.25 m2 (length 22.5 m × width 2.5 m), and 0.5 m protection rows were set up between the plots. Additionally, the fertilization amount of each plot was the same according to local conventional fertilization, including 160 N kg/ha, 90 P2O5 kg/ha, and 60 K2O kg/ha, separately, all of which were applied to the soil once as the basal fertilizer.

2.2.2. Soil Sampling and Measurements

Basic soil samples in the experimental area were collected before maize sowing, and basic physical and chemical indicators were determined. Moreover, soil samples at a 0–20 cm depth were also collected in the seedling, shooting, and maturity stages. After air drying, the Kjeldahl digestion approach was employed to determine the soil total N content; the alkali-hydrolyzed diffusion approach was applied to analyze the soil alkali-hydrolyzed N content; 0.5 mol/L NaHCO3 extraction and molybdenum–antimony resistance colorimetry were conducted to analyze the soil-available phosphorus content; 1 mol/L NH4Ac extraction flame photometry was performed to examine the soil-available potassium content, according to Bao et al. [20]; and soil urease activity was determined using the sodium phenol colorimetric method, according to Guan et al. [21].

2.2.3. Maize Plant Sampling and Determination

Plant samples were collected in the seedling, shooting, and maturity stages. After drying, the plant N content was determined using the concentrated H2SO4 digestion–H2O2–semi-trace Kjeldahl N method, the plant phosphorus content was measured using concentrated H2SO4 digestion–H2O2–vanadium molybdenum yellow colorimetry, and the plant potassium content was analyzed using concentrated H2SO4 digestion–H2O2–flame photometry according to Bao et al. [20]. An area of 2.5 m2 was randomly assigned in each experimental plot to harvest all maize spikes. After natural air-drying, the yield of 14% standard water content was determined, and the effective spike number, 1000-grain weight, and grain number per spike were determined. Meanwhile, five maize plants were selected to measure the plant biomass index. The same measurement was conducted three times in each experimental plot.

2.3. Data Analysis

Microsoft Excel 2016 and Origin 2021 were applied to obtain data statistics and charts, respectively. The SPSS 26.0 software (SPSS, Chicago, IL, USA) data analysis system was employed to test for significant differences (p < 0.05) and conduct a correlation analysis, principal component analysis, and path analysis between indicators. By calculating the path coefficient (β), the direct and indirect effects of every variable on the dependent variable could be analyzed by excluding the influence of the unit of measurement and the variation degree of independent variables [22,23]. The relevant indices were calculated using the following formulas modified by Meng et al. [24]:
Decision coefficient: D = 2rp − p2 (where r stands for the correlation coefficient, and p indicates the direct path coefficient).
Plant   N   ( P / K )   uptake   ( kg / h m 2 ) = Total   N   P / K %   in   plants 100 × Total   dry   matter   ( kg / h a )
N ( P / K )   partial   factor   productivity   ( kg / kg ) = Yield N ( P / K )   supplied
Grain   N   ( P / K )   balance   ( kg / kg ) = Grain   N   ( P / K )   content N   ( P / K )   supplied

3. Results

3.1. Simulation Experiment

3.1.1. N Leaching Rate

The accumulation leaching rate of TN and NH4+-N was in the order of AU > AS > ASD > ASN > ASG > CK across all collected times (Figure 2a,b). AS showed a higher NO3−-N leaching rate than AU, as well as a higher leaching rate than ASD, ASN, and ASG (Figure 2c). Overall, the lowest N leaching rates were obtained under the ASG treatment.
Regarding the N forms, NH4+-N accounted for 0.63%, 72.0%, 30.2%, 13.9%, 10.7%, and 25.5% (averages of 10 leaching times), and NO3−-N accounted for 0.27%, 0.83%, 0.91%, 0.39%, 0.33%, and 0.67% (averages of 10 leaching times) of the total N leaching in CK, AU, AS, ASN, ASG, and ASD, respectively. NH4+-N was the main leaching N form.
As shown in Table 2, the cumulative release dynamics of soil TN were fitted with the first-order dynamic equation Nt = N0(1 − e−kt) among all fertilizer treatments and showed a significant (p < 0.01) linear relationship with time. The k value of the N release rate of each treatment was in the order AU > CK > AS > ASD > ASN > ASG.

3.1.2. Soil N Residual

The ASN, ASG, and ASH treatments improved TN accumulation in both the 0–10 and 10–20 cm soil layers compared with the AU and AS treatments. The 10–20 cm soil layer had a higher TN content than the 0–10 cm soil layer (Figure 3a). The NH4+-N contents in the 10–20 cm soil layer were approximately two-fold higher than those in the 0–10 cm soil layer across all treatments. The AS treatments (AS, ASN, ASG, and ASD), especially the ASN treatment, produced a higher soil NH4+-N content than the AU treatment (Figure 3b). Greater NO3−-N had accumulated in the 0–10 cm soil layer than in the 10–20 cm soil layer, except for under the ASN and ASG treatments (Figure 3c).

3.2. Maize Growth and Yield Components

Plant heights were improved under the ASN, ASD, and ASG treatments compared with those under the AU and AS treatments, with no significant difference (Table 3). Compared with the ASN treatment, the ASG and AU treatments significantly increased plant dry weight, while the AS and ASD treatments increased dry weight, but the difference was not significant. The grain dry weight per spike under the ASG treatment was significantly higher than that under the ASN treatment; that is, it was 1.28 times that under the ASN treatment. There were no significant differences in the grain dry weights among the AU, AS, and ASD treatments, and they were all significantly higher than those under the ASN treatment. The spike coarse and spike length of the maize under the coating treatment increased relative to those under the ASN treatment, and the spike diameter and spike length of the maize under the AU and AS treatments also dramatically increased relative to those under the ASN treatment (Table 3).
Moreover, the effective spike numbers of the ASN, ASG, and ASD treatments evidently increased relative to those under the AU and AS treatments, especially under the ASG treatment. The 1000-grain weight and grain number per spike showed no significant differences between the ASG and AU treatments, but they were still higher than those under the other treatments. Furthermore, the ASN treatment produced the lowest 1000-grain weight, indicating that ASN is not conducive to the dry matter accumulation of grains (Figure 4a–c). Compared with the AU, AS, and ASN treatments, the yield of the maize under the coating treatments significantly increased by 11.63–50.10% (Figure 4d).
The direct effects (β) on maize yield were in the following order: effective spike number (0.671) > grain dry weight (0.341) > 1000-grain weight (0.276) > spike length (−0.265) > grains per spike (0.209). Meanwhile, the decision coefficient (D) of the effective spike number (0.540) was higher than that of the other traits, indicating that it was the leading factor affecting maize yield, while spike length had a negative direct effect on maize yield (Figure 5).

3.3. Soil Nitrogen, Plant Nitrogen Accumulation, and Nitrogen Use Efficiency

The total soil N content showed an initial increasing and later decreasing trend, except for with the ASN treatment (Figure 6a). In the seedling stage, the soil total N content under the ASN treatment increased remarkably relative to that under the other treatments, and it reduced in a later growth stage. In the maturity stage, the total soil N content under the ASG and ASD treatments increased relative to that under the AU and AS treatments.
In the seedling and shooting stages, urease activity under the ASN treatment increased relative to that under the other treatments. Urease activity across all treatments reached its maximum in the shooting stage (Figure 6b).
The soil alkali-hydrolyzed N content decreased rapidly from the seedling stage to the shooting stage, with a much smaller decrease from the shooting stage to the maturity stage than that from the seedling stage to the shooting stage (Figure 6c). In the seedling stage, the soil alkali-hydrolyzed N contents under the AS and ASD treatments significantly increased relative to those under the other treatments. In the shooting stage, the soil alkali-hydrolyzed N content under the AS treatment decreased rapidly, being significantly lower than that under the ASN, ASG, and ASD treatments. In the maturity stage, soil alkali-hydrolyzed N under the ASD treatment increased markedly compared with that under the other treatments.
In the seedling stage, the ASD treatment exhibited a significant advantage in N accumulation. In the shooting stage, N accumulation under the three slow-/controlled-release fertilizer treatments dramatically increased compared with that under the AU and AS treatments. In the maturity stage, plant N accumulation under the ASG treatment was the highest, while it was the lowest under the ASN treatment. The difference was not significant between the ASD and AU treatments, yet their plant N accumulation increased evidently relative to that under the AS treatment (Figure 6d).
Compared with the other treatments, the ASG treatment markedly increased N partial factor productivity and grain N balance, which were 1.43 times that under the AU treatment and 1.51 times that under the AS treatment (Figure 6e,f). In addition, N partial factor productivity under the ASD treatment also remarkably increased compared with that under the AU, AS, and ASN treatments, while the grain N balance was not significantly different between the four treatments.

3.4. Available P(K) in Soil, P(K) in Plants, and Effective Use of P(K)

The soil-available P contents under the coating and AU treatments increased markedly relative to those under the AS and ASN treatments (Figure 7a). Additionally, the soil-available K contents under the ASG and ASD treatments increased compared with those under the AU, AS, and ASN treatments, but the differences under the AU, AS, and ASN treatments were not significant (Figure 7b). The highest P and K contents were detected under the ASG treatment, while the lowest contents were measured under the AS treatment (Figure 7c,d). Further, P partial productivity under the ASG treatment was 1.43 times that under the AU treatment and 1.51 times that under the AS treatment (Figure 7e). The ASG treatment resulted in a significantly increased K partial productivity and grain P balance relative to those resulting from the other treatments (Figure 7f,g). Additionally, grain K balance under the AU and ASG treatments increased evidently compared with that under the AS, ASD, and ASN treatments, and that under the ASN treatment was the lowest (Figure 7h).

3.5. Principal Component Analysis (PCA)

The two principal components, PC1 and PC2, interpreted 80.4% of the eight indicators used to quantify soil and plant nutrient status. Overall, the soil and plant nutrient status under the oil coating treatment was better than that under the other treatments. Typically, the nutrient status under the ASD treatment was higher, while that under the AS treatment was lower. Plant nutrient accumulation showed a high correlation with soil-available phosphorus and soil-available potassium, a low correlation with soil total nitrogen and alkali-hydrolyzed nitrogen, and a negative correlation with urease activity (Figure 8).
The three principal components, PC1, PC3, and PC2, accounted for 76.12% of the 14 indicators used to quantify soil nutrient and maize growth status. The soil nutrient and maize growth conditions were better under the coating treatments; they were the best under the ASG treatment and the worst under the AS treatment. Urease activity was moderately correlated with 1000-grain weight, TN, and grain number per spike; AK was strongly correlated with grain number per spike; and AP was weakly correlated with plant height, effective spike number, and yield (Figure 9a).
The three principal components, PC1, PC3, and PC2, explained 80.4% of the 12 indicators used to quantify plant nutrient and maize growth status. Typically, the coating treatment had a good effect on plant nutrients and maize growth. The ASG treatment led to the best plant nutrient and growth status, while the AS treatment induced the worst effect. Plant nutrients were correlated with maize biomass and strongly correlated with maize yield (Figure 9b).

4. Discussion

4.1. Ammonium Sulfate (AS) Coupled with Coatings Could Inhibit N Leaching to Deeper Soil Layers

N loss is the main reason for low N utilization rates, and nitrogen leaching is one of the main means of N loss. However, studies on soil N leaching have mostly focused on the leaching of nitrate nitrogen (NO3−-N). The limited adsorption capacity of soil colloids for cations leads to reduced adsorption sites for NH4+ and subsequent leaching with water after a large amount of N fertilizer is applied to soil [24]. Urea is an amide nitrogen (an organic nitrogen fertilizer) and must be hydrolyzed by urease to form ammonium nitrogen (NH4+-N) in soil, while AS is a physiologically acidic fertilizer and directly dissolves to produce NH4+. The higher cumulative leaching rate of NO3−-N in AS fertilizers compared with urea may be explained by the predominance of NH4+-N as the main form of leached nitrate in urea-treated soils, resulting in lower levels of nitrification substrate than AS treatments [25].
Generally, AS coupled with coating (ASN, ASG, or ASD) effectively suppresses the conversion of NO3−-N to NH4+-N by inhibiting the activities of nitrification bacteria during the reaction process after fertilizer application to soil, thereby relatively reducing the NH4+-N content of the leaching solution. Consequently, it also mitigates the leaching of NO3−-N [25]. In addition, the acidic property of AS fertilizer leads to a decrease in soil pH; the nitrification activity of bacteria decreased significantly in acidic soil [10]. Furthermore, due to the presence of an oil-coated layer on the fertilizer surface, the ASG and ASD treatments effectively prevent contact between the soil and the fertilizer. This barrier effect helps to avoid rapid fertilizer release and the subsequent loss of nitrogen through leaching. Overall, oil-coated fertilizers can reduce the loss of N by slowing down the hydrolysis rate and nitrification from NH4+ to NO3− of N fertilizer [26]. The lower N leaching rate could also be explained by the high ability of N immobilization in soil [27].

4.2. Oil-Coated Ammonium Sulfate (ASG) Improved Yield and Nutrient Uptake of Maize

Maize yield is mainly determined by grain number per unit area and grain weight [28]. Numerous studies have verified the stimulation effect of slow-release fertilizer on crop yield. For example, slow-release fertilizer significantly increased the yield and yield components of two varieties of spring maize by 8.1% and 6.2% compared to conventional fertilization [29]. According to Zhao et al. [30], compared with ordinary nitrogen fertilizer, sulfur-coated nitrogen fertilizer and resin-coated nitrogen fertilizer increased the yield of maize by 10.04% and 9.68%, respectively. Similarly, Sun et al. [31] reported that slow-release urea improved rice yield by 15% and 11% compared to conventional urea application practices. In the present study, maize yield showed significant improvements, ranging from 43.21% to 51.10% under the ASG treatment, as well as from 11.63% to 17.7% under the ASD treatment, compared with the AU and AS treatments. Among the yield components, effective spike number had the main direct effect on yield increase, the same as in studies on rice [32] and wheat [33].
Controlled-release urea releases N at the same rate as crop N absorption; this can supply the N nutrient requirements of rice throughout the reproductive period. Additionally, the milling quality of rice treated with controlled-release urea is better than that of rice treated with regular urea [34]. Sufficient N supply in a later growth stage of maize could increase the enzymatic activities involved in carbon–N metabolism, increase net photosynthesis and post-silking biomass accumulation, and result in a high grain yield [35]. Soil nutrient levels influence the root distribution of maize, and above-ground plant growth and dry matter accumulation depend heavily on root systems [36]. In addition, coating rates significantly affect the release characteristics of controlled-release fertilizers [37]. This could be further examined in a subsequent study.

4.3. Oil-Coated Ammonium Sulfate (ASG) Improved N Utilization of Soil

Castor oil has been rapidly developed as a bio-based coating material for controlled-release fertilizers [37]. A previous study found that oil-coated fertilizers changed the nutrient release characteristics, with nutrients being released following the trend of the solute gradient, and an extra step was needed for water molecules to cross the film and make contact with internal fertilizer particles [25]. Among various types of oils, vegetable oil showed easy degradation, water resistance, shock resistance, and a nutrient release curve in soil [38]. Thus, coated treatments effectively enhanced the slow-/controlled-release properties of fertilizer [39]. Xie et al. [40] reported that a superhydrophobic coating treatment increased the N release time of coated urea in water from 36.49 to 69.51 days at a 5% coating rate. Oil-coated fertilizers release nutrients based on crop-specific fertilizer characteristics during different growth stages, thereby improving the nutrient uptake and utilization efficiency of crops [25].
The efficiency of fertilizers is considered a crucial criterion for the sustainability of both agricultural development and the environment. Conventional fertilizers are associated with several drawbacks, including rapid volatilization, easy absorption and fixation by soil, and various pathways for nutrient loss [36]. In contrast, slow-/controlled-release fertilizers effectively enhance fertilizer utilization efficiency, while reducing nutrient losses [41]. In the present study, the oil-coated AS treatments (ASG and ASD) maintained higher total N and alkali-hydrolyzed N contents in the soil than the ASN treatment and the AU and AS treatments. This can be attributed to the fact that AS is an ammonium nitrogen fertilizer applied as NH4+-N, while the nitrification inhibitor effectively inhibits NH4+-N transformation into NO3−-N. This results in a soil nitrogen supply during the seedling stage that is higher than the maize’s demand for nitrogen, which leads to insufficient nitrogen supply for maize at later growth stages [42]. By contrast, humic acid application improves soil conditions, activates phosphorus and potassium nutrients in the soil, regulates nitrogen transformation, and enhances the soil nitrogen content [43]. Moreover, humic acids have demonstrated an antimutagenic/desmutagenic activity in horticultural plants [44,45], which is an important aspect towards the sustainable use of chemicals in agriculture.
Furthermore, Wang et al. [46] found that, relative to conventional fertilization, the use of slow-release fertilizers at a significantly reduced amount (31%) significantly increased nitrogen and phosphorus utilization rates by 15.8% and 9.6%, respectively. According to our findings, the partial productivity of nitrogen, phosphorus, and potassium fertilizers increased significantly under the coating treatments compared to under treatment with conventional fertilizers. Furthermore, the ASG treatment exhibited a remarkable increase in partial productivity compared to the ASD treatment. Additionally, the grain N, P, and K balance noticeably improved under the ASG treatment compared to under other treatments. A PCA analysis indicated that the ASG treatment optimized plant nutrients, maize growth conditions, and soil nutrients. The urease inhibitor urea delayed the hydrolysis of urea to ammonium N by inhibiting the activity of urease, thereby slowing the release of N.

5. Conclusions

Under the same N level, ammonium sulfate (AS) decreased the N leaching rate compared with urea (AU), and AS coupled with an aid (a nitrification inhibitor, oil coating, or oil–humic acid coating) reduced the leaching rate further. The maize yield, yield components, and N uptake greatly improved under the oil-coated treatments, especially under the ASG treatment. Effective spike number was the main factor that influenced the maize yield. A PCA analysis indicated that the ASG treatment optimized plant nutrients, maize growth conditions, and soil nutrients. In conclusion, the slow-release effect of ASG fertilizer exhibited optimal performance for enhancing the production and efficiency of summer maize.

Author Contributions

Conceptualization, X.D.; Methodology, T.G. and Y.Z.; Software, H.J. and Y.H.; Formal analysis, H.J. and Y.Z.; Investigation, S.Y., Y.L. and T.G.; Resources, Y.H.; Data curation, Y.L. and Y.Z.; Writing—original draft, S.Y.; Writing—review & editing, X.D., Y.H., J.L. and Q.Y.; Visualization, X.D., Y.L. and T.G.; Supervision, Q.Y.; Project administration, S.Y.; Funding acquisition, J.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the Shanxi Provincial Key R&D Program (201803D221003-2), the Shanxi Provincial Postgraduate Innovation Project (2021Y338), and the National Natural Science Foundation of China (32372819).

Data Availability Statement

The original contributions presented in the study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Agronomy 14 01463 g001
Figure 1. Simulation device.
Figure 1. Simulation device.
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Figure 2. Cumulative leaching curve of soil N forms under different treatments. (a) Cumulative leached nitrogen; (b) cumulative leached ammonium nitrogen; (c) cumulative leached nitrate nitrogen.
Figure 2. Cumulative leaching curve of soil N forms under different treatments. (a) Cumulative leached nitrogen; (b) cumulative leached ammonium nitrogen; (c) cumulative leached nitrate nitrogen.
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Figure 3. Total soil nitrogen (TN) (a), ammonium nitrogen (NH4+-N) (b), and nitrate nitrogen (NO3−-N) (c) contents of different fertilization treatments in the 0–10 and 10–20 cm soil layers. Different lowercase letters indicate significant differences (p < 0.05) within treatments in the 0–10 cm soil layer, and different capital letters indicate significant differences (p < 0.05) within treatments in the 10–20 cm soil layer; the same as below.
Figure 3. Total soil nitrogen (TN) (a), ammonium nitrogen (NH4+-N) (b), and nitrate nitrogen (NO3−-N) (c) contents of different fertilization treatments in the 0–10 and 10–20 cm soil layers. Different lowercase letters indicate significant differences (p < 0.05) within treatments in the 0–10 cm soil layer, and different capital letters indicate significant differences (p < 0.05) within treatments in the 10–20 cm soil layer; the same as below.
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Figure 4. Impacts of various fertilization treatments on 1000-grain weight (a), effective spike number (b), grain number per spike (c), and yield of maize (d). Different letters indicate significant differences at the 0.05 level.
Figure 4. Impacts of various fertilization treatments on 1000-grain weight (a), effective spike number (b), grain number per spike (c), and yield of maize (d). Different letters indicate significant differences at the 0.05 level.
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Figure 5. Path analysis of influencing factors for maize yield.
Figure 5. Path analysis of influencing factors for maize yield.
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Figure 6. Impacts of various fertilizer treatments on soil total nitrogen (a), urease (b), alkali-hydrolyzed nitrogen (c), plant nitrogen accumulation (d), nitrogen partial factor productivity (e), and grain nitrogen balance (f). Different letters indicate significant differences at p < 0.05.
Figure 6. Impacts of various fertilizer treatments on soil total nitrogen (a), urease (b), alkali-hydrolyzed nitrogen (c), plant nitrogen accumulation (d), nitrogen partial factor productivity (e), and grain nitrogen balance (f). Different letters indicate significant differences at p < 0.05.
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Figure 7. Impacts of various fertilizer treatments on soil available P (a), soil available K (b), plant P accumulation (c), plant K accumulation (d), P partial factor productivity (e), K partial factor productivity (f), grain P balance (g) and grain K balance (h). Different letters between fertilizer treatments indicate significant differences at p < 0.05.
Figure 7. Impacts of various fertilizer treatments on soil available P (a), soil available K (b), plant P accumulation (c), plant K accumulation (d), P partial factor productivity (e), K partial factor productivity (f), grain P balance (g) and grain K balance (h). Different letters between fertilizer treatments indicate significant differences at p < 0.05.
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Figure 8. The principal component analysis of different slow-/controlled-release sulfuric acid treatments based on soil nutrient and plant nutrient accumulation. TN, soil total nitrogen; UR, urease; AN, soil alkaline-hydrolyzed nitrogen; AP, soil-available phosphorus; AK, soil-available potassium; PNA, plant nitrogen accumulation; PPA, plant phosphorus accumulation; and PKA, plant potassium accumulation.
Figure 8. The principal component analysis of different slow-/controlled-release sulfuric acid treatments based on soil nutrient and plant nutrient accumulation. TN, soil total nitrogen; UR, urease; AN, soil alkaline-hydrolyzed nitrogen; AP, soil-available phosphorus; AK, soil-available potassium; PNA, plant nitrogen accumulation; PPA, plant phosphorus accumulation; and PKA, plant potassium accumulation.
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Figure 9. The principal component analysis of different slow-/controlled-release sulfuric acid treatments based on soil nutrients and biomass (a) and plant nutrients and biomass (b). TN, soil total nitrogen; UR, urease; AN, soil alkali-hydrolyzed nitrogen; AP, soil-available phosphorus; AK, soil-available potassium; PNA, plant nitrogen accumulation; PPA, plant phosphorus accumulation; PKA, plant potassium accumulation; PH, plant height; PDW, plant dry weight; GDW, grain dry weight; SC, spike coarse; SL, spike length; TW, 1000-grain weight; ESN, effective spike number; and GNS, grain number per spike.
Figure 9. The principal component analysis of different slow-/controlled-release sulfuric acid treatments based on soil nutrients and biomass (a) and plant nutrients and biomass (b). TN, soil total nitrogen; UR, urease; AN, soil alkali-hydrolyzed nitrogen; AP, soil-available phosphorus; AK, soil-available potassium; PNA, plant nitrogen accumulation; PPA, plant phosphorus accumulation; PKA, plant potassium accumulation; PH, plant height; PDW, plant dry weight; GDW, grain dry weight; SC, spike coarse; SL, spike length; TW, 1000-grain weight; ESN, effective spike number; and GNS, grain number per spike.
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Table 1. Experimental treatment design.
Table 1. Experimental treatment design.
Treatment Fertilizer TypesN Fertilizer Slow Control Material P FertilizerK Fertilizer
CK///(NH4)2HPO4KCl
AUUreaUrea + (NH4)2HPO4/(NH4)2HPO4KCl
ASAmmonium sulfateAmmonium sulfate + (NH4)2HPO4/(NH4)2HPO4KCl
ASNAmmonium sulfate + nitrification inhibitorAmmonium sulfate + (NH4)2HPO4Nitrification inhibitor (1% of pure N content)(NH4)2HPO4KCl
ASGOil-coated ammonium sulfate Ammonium sulfate + (NH4)2HPO4Oil-coated (9% of AS application)(NH4)2HPO4KCl
ASDOil–humic acid-coated ammonium sulfateAmmonium sulfate + (NH4)2HPO4Oil–humic acid-coated (0.9% of AS application)(NH4)2HPO4KCl
Table 2. First-order kinetic equation of cumulative N leaching rate.
Table 2. First-order kinetic equation of cumulative N leaching rate.
TreatmentNt = N0(1 − e−kt)R2Se
CKNt = 0.048(1 − e−0.458t)0.949 **0.071
AUNt = 0.830(1 − e−1.188t)0.954 **0.210
ASNt = 0.646(1 − e−0.176t)0.984 **0.024
ASNNt = 0.851(1 − e−0.049t)0.999 **0.006
ASGNt = 1.800(1 − e−0.017t)0.999 **0.004
ASDNt = 0.783(1 − e−0.065t)0.997 **0.010
Note: ** indicates significance at the 0.01 level.
Table 3. Effects of different fertilization treatments on maize growth parameters.
Table 3. Effects of different fertilization treatments on maize growth parameters.
TreatmentPlant Height
(cm)		Plant Dry
Weight (g)		Grain Dry
Weight (g/spike)		Spike Diameter
(cm)		Spike Length
(cm)
AU260.67 ± 12.77 ab333.93 ± 35.49 a204.71 ± 9.28 b16.27 ± 0.12 b21.11 ± 0.51 b
AS245.00 ± 7.64 b327.24 ± 13.10 ab202.61 ± 8.07 b16.18 ± 0.10 ab21.08 ± 0.32 b
ASN268.33 ± 8.33 ab259.13 ± 3.14 b180.36 ± 6.04 c15.91 ± 0.10 c19.81 ± 0.29 c
ASG269.67 ± 12.35 ab363.50 ± 25.14 a231.28 ± 4.71 a16.75 ± 0.10 a22.27 ± 0.16 a
ASD279.67 ± 2.91 a330.59 ± 18.23 ab205.50 ± 6.96 b16.20 ± 0.10 ab21.45 ± 0.27 ab
Note: Different letters after values within one column between fertilizer treatments indicate significant differences at the 0.05 level.
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Yan, S.; Dong, X.; Jiang, H.; Liu, Y.; Han, Y.; Guo, T.; Zhang, Y.; Li, J.; Yan, Q. Oil-Coated Ammonium Sulfate Improves Maize Nutrient Uptake and Regulates Nitrogen Leaching Rates in Sandy Soil. Agronomy 2024, 14, 1463. https://doi.org/10.3390/agronomy14071463

AMA Style

Yan S, Dong X, Jiang H, Liu Y, Han Y, Guo T, Zhang Y, Li J, Yan Q. Oil-Coated Ammonium Sulfate Improves Maize Nutrient Uptake and Regulates Nitrogen Leaching Rates in Sandy Soil. Agronomy. 2024; 14(7):1463. https://doi.org/10.3390/agronomy14071463

Chicago/Turabian Style

Yan, Shuangdui, Xinyu Dong, Huishu Jiang, Yu Liu, Ying Han, Tanwen Guo, Yanhui Zhang, Juan Li, and Qiuyan Yan. 2024. "Oil-Coated Ammonium Sulfate Improves Maize Nutrient Uptake and Regulates Nitrogen Leaching Rates in Sandy Soil" Agronomy 14, no. 7: 1463. https://doi.org/10.3390/agronomy14071463

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