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Article

Can Reduced Nitrogen Application of Slow/Controlled-Release Urea Enhance Maize Yield Stability and Mitigate Nitrate/Ammonium Nitrogen Leaching in Soil in North China?

by
Cong Zhao
1,2,3,4,
Meihua Ye
5,
Nana Li
1,2,3,4,*,
Xuefang Huang
1,2,3,4 and
Juanling Wang
1,2
1
Shanxi Institute of Organic Dryland Farming, Shanxi Agricultural University, Taiyuan 030031, China
2
Key Laboratory of Sustainable Dryland Agriculture (Co-Construction by Ministry of Agriculture and Rural Affairs and Shanxi Province), Jinzhong 030801, China
3
National Agricultural Environment Observation and Experimental Station in Jinzhong, Taiyuan 030031, China
4
Key Laboratory of Sustainable Dryland Agriculture of Shanxi Province, Taiyuan 030031, China
5
College of Agronomy, Shanxi Agricultural University, Jinzhong 030801, China
*
Author to whom correspondence should be addressed.
Agriculture 2025, 15(19), 2045; https://doi.org/10.3390/agriculture15192045
Submission received: 1 September 2025 / Revised: 22 September 2025 / Accepted: 28 September 2025 / Published: 29 September 2025
(This article belongs to the Section Crop Production)
Browse Figures
Versions Notes

Abstract

Reducing nitrogen (N) fertilizer input while sustaining maize yield and alleviating nitrogen leaching is a significant challenge due to economic and practical feasibility, as well as the environmental friendliness of this process. However, it remains unclear whether reducing nitrogen by using a blend of slow/controlled-release nitrogen fertilizer (SCRNF) with urea at an equal nitrogen rate can achieve the desired yield and mitigate nitrogen leaching. A field experiment consisting of four treatments (240 kg·N·hm−2, 100% urea, CK; 240 kg·N·hm−2, 50% N from urea and 50% N from SCRNF, N100%; 192 kg·N·hm−2, 50% N from urea and 50% N from SCRNF under 20% N reduction, NR20%; 144 kg·N·hm−2, 50% N from urea and 50% N from SCRNF under 40% N reduction, NR40%) was conducted in Shanxi from 2019 to 2021. In this study, we explored the effects of a mixture of SCRNF and urea on grain yield, yield components, main agronomic traits, nitrogen partial factor productivity, and content of nitrate/ammonium nitrogen in soil in maize under decreasing amounts of nitrogen fertilization. The results showed that the mixture of SCRNF and urea can improve spring maize yield under reduced nitrogen input, with its yield and yield component factors generally performing better than those of the control. The yield of the NR20% treatment was highest in 2020 and 2021, increasing by 8.8% and 11.7% over CK, respectively; the NR20% and NR40% treatments had no significant impact on the main agronomic traits of spring maize, such as plant height, leaf area, shoot biomass, and SPAD value of the ear leaf, compared with CK; the NR20% and NR40% treatments significantly (p < 0.05) enhanced nitrogen partial factor productivity but reduced nitrate and ammonium nitrogen in 0~200 cm soil over the three years compared with CK. Therefore, reducing nitrogen input by 20% with 50% N from urea and 50% N from biodegradable film-coated urea was an appropriate nitrogen fertilizer management measure for mitigating environmental risks without compromising maize yield in North China.

1. Introduction

By 2050, it is estimated that food demand for the projected 9.6 billion global population will increase by 70% compared to the current requirements. Whether we can feed the future population depends greatly on how we explore and protect our soil resources and their valuable ecosystem services, as global agricultural production is facing a sustainability crisis due to intensive farming, land degradation, climate change, biodiversity loss, and environmental pollution [1,2]. Consequently, the development of sustainable agricultural practices is necessitated by the increasing global population and the corresponding rise in food demand [3,4].
Fertilizer application plays a critical role in sustainable agriculture. More than half of the increase in grain production is attributed to the application of chemical fertilizers [5]. Nitrogen fertilizer, an essential source of N required for crop growth, is crucial for ensuring global food security, contributing more than 60% to yield [6,7]. Urea, as the most popular nitrogen fertilizer applied worldwide to ensure the basic nitrogen supply for crops, statistically accounts for almost 77% of the total nitrogen demand of 107.4 million tonnes in global agriculture, and about 21% of this increase in demand has been recorded in the last decade [8]. However, due to its rapid release rate and short duration, the efficiency of urea use is currently very low, not only failing to meet the nutrient needs of crops at different growth stages but also leading to serious consequences for agricultural production and the ecological environment, such as heavy soil nitrate leaching, soil acidification, greenhouse gas emissions, and ammonium volatilization, ultimately resulting in groundwater and air pollution [9,10,11,12,13]. Hence, there is an urgent need for innovative approaches to promote soil health while maximizing nutrient availability to crops. One promising solution lies in the development and application of slow/controlled-release fertilizers, which can improve nutrient use efficiency and reduce the negative environmental impacts of agricultural practices [14,15,16].
Slow/controlled-release N fertilizers (SCRNFs), as a research hotspot for new fertilizers, are causing a revolution in fertilizer production and fertilization technology due to their advantages of longer nutrient release duration and less volatilization and leaching, thus reducing environmental pollution. They also offer new ways and ideas to solve the problem of low fertilizer utilization. Many studies have investigated the effects of SCRNF on crop yield and N utilization [17,18,19]. For instance, SCRNF was shown to increase rice yield by 7% in China, with the highest nitrogen use efficiency among various alternative fertilizers (slow/controlled-release fertilizer, organic fertilizer, green manure, etc.) [20]. Zhu et al. (2020) [21] found that SCRNF improved rice yield and N utilization, especially in infertile soils. These findings suggest that the application of SCRNF in paddies is an efficient strategy to ensure rice yield and to improve N utilization. Nevertheless, the nutrient release rate of SCRNF is greatly affected by the field environment. There are significant differences in dissolution rate and mode even in different media, not to mention in different types of soil [22,23].
In view of the excessive N input in local agricultural production at present and the few research reports on the application effect of SCRNF on spring maize under the arid and semi-arid climatic conditions of Shanxi, as well as its higher production cost than that of ordinary fertilizers, it is urgently necessary to explore an application mode that is suitable for the site conditions in Shanxi to meet the requirements of efficiency-enhancing and cost-saving agricultural development. Therefore, we tried to clarify the effects of SCRNF on spring maize yield, main agronomic traits, nitrogen partial factor productivity, and soil nitrate/ammonium in a 0~200 cm profile by reducing the N amount, to provide a basis for formulating reasonable nitrogen fertilizer management in arid areas. In this study, we aim to explore the following key questions: (1) Can SCRNF be used in reduced N amounts without compromising desired crop yield while mitigating soil nitrate/ammonium leaching in North China, since they can improve fertilizer utilization efficiency? (2) What is the most suitable N reduction amount and optimal SCRNF application for spring maize in Shanxi?

2. Materials and Methods

2.1. Site Description and Experimental Design

A three-year field experiment with maize was performed at the Dongyang Research Station of Shanxi Agricultural University, Jinzhong, Shanxi, China (37°56′ N, 112°69′ E; 800 m altitude), over 2019~2021. The test site is located in the Jinzhong Basin, which has a typical temperate continental monsoon climate. The average annual sunshine duration is 2639 h and the mean annual air temperature is 9.8 °C, with a mean minimum air temperature of −6.1 °C in the coldest month (January) and a mean maximum air temperature of 28.1 °C in the hottest month (July). The long-term mean annual rainfall is 430.2 mm and the average annual frost-free period is 154 days. The experimental site was characterized by low and erratic rainfall, with droughts occurring at different stages of maize growth. The long-term mean annual rainfall at the site was 430.2 mm and the mean annual evaporation was 1860.1 mm (Table S1). The study area is irrigated. The rainfall during the maize growth stage was 258, 420, and 334 mm, and the irrigation was performed at 225, 96, and 123 mm in each year from 2019 to 2021, respectively. The soil is fluvial soil and the surface soil texture is clay loam. Analyses of soil samples taken from the same experimental area in April 2019 showed that the top 20 cm of soil had a pH of 7.8, a soil organic matter of 14.4 g kg−1, total nitrogen of 1.1 g kg−1, total phosphorus of 0.21 g kg−1, total potassium of 55.7 g kg−1, and available nitrogen of 54.1 mg kg−1, available phosphorus of 10.0 mg kg−1, and available potassium of 131.9 mg kg−1.
The tested fertilizers were urea (N: 464 g kg−1, Wutaishan Chemical Co., Ltd., Wutai, Shanxi, China); SCRNF (N: 440 g kg−1, urea coated with biodegradable film fertilizer, Leading Bio-Agriculture Co., Ltd., Hebei, China); calcium superphosphate (P2O5: 120 g kg−1, Fengyi Phosphate Fertilizer Manufacturing Co., Ltd., Tongling, Anhui, China); and potassium chloride (K2O: 600 g kg−1, Sinochem Chemical Fertilizer Co., Ltd., Taiyuan, Shanxi, China).
The field experiment was performed in a 5 × 6 m plot using a completely randomized block design with four treatments and four replicates. The four treatments were as follows: (1) conventional fertilization: 240 kg·N·hm−2, 100% urea (CK); (2) equivalent nitrogen dosage to CK: 240 kg·N·hm−2, 50% N from urea + 50% N from SCRNF (N100%); (3) 20% reduction in N compared to CK: 192 kg·N·hm−2, 50% N from urea + 50% N from SCRNF (NR20%); (4) 40% reduction in N compared to CK: 144 kg·N·hm−2, 50% N from urea + 50% N from SCRNF (NR40%). Except for nitrogen fertilizer, the dosage of phosphorus and potassium fertilizer was the same for each treatment with P2O5 150 kg hm−2 and K2O 75 kg hm−2. All nitrogen, phosphorus, and potassium fertilizers were applied as base fertilizer in a single application before sowing. Rotary tillage was used before sowing. The maize variety used was Dafeng 30. In each experimental year, seeds were planted at a rate of approximately 49,500 plants hm−2 (33 cm × 60 cm) in late April or early May, and the crop was harvested in late September. Residues were harvested using a maize-harvesting machine. Weeds were managed using a herbicide. Other management measures are the same.

2.2. Sampling, Analysis Methods, and Calculation

The plant height and leaf area of 10 plants were measured continuously in each plot during the tasseling stage of spring maize. Leaves at every position were measured to determine the maximum leaf width (W) and the leaf length (L). The leaf area (S) was then calculated as follows:
S = 0.75 × L × W
The aboveground biomass of 5 plants was measured. The ear leaves were measured using the SPAD-502 instrument (Japan). At maturity, ear number per square meter was determined in the field. Ears were harvested at the center of each plot (4 m2) to calculate the single ear weight and determine yield based on threshing. All plants harvested within the region formed a single biological replicate. Moreover, 20 samples, whose average ear weight was very close to that measured for yield estimation, were taken to measure ear characteristics in indoor testing. All the kernels were air-dried, and grain yield was calculated at 14% moisture, which is the standard in China for maize for storage or sale (GB/T 29890-2013).
Soil samples from the 0~200 cm layer were collected using a soil auger with a diameter of about 54 mm (made by the Institute of Soil and Water Conservation, Chinese Academy of Sciences) after maize harvest every year. Each 20 cm was considered a soil layer and sampled separately. Each sample contained five points in each plot; they were then mixed in equal amounts based on layer after removing impurities such as crop roots. Soil that adhered to the exterior of the drill bit needed to be thoroughly cleaned before each mixing operation to prevent cross-contamination between different sampling layers. Air-dried soil samples were treated with 1 mol L−1 of potassium chloride solution (the ratio of soil to liquid was 1:10) and extracted through shaking for 1 h. After filtration, nitrate and ammonium nitrogen were determined using a continuous flow analyzer (SAN++, Skalar Analytical B.V., Holland).
Nitrogen partial factor productivity is the ratio of maize grain yield and nitrogen input.
N partial factor productivity (kg kg−1) = grain yield/N input.

2.3. Statistical Analysis

All data were initially collated, processed, and subsequently, a chart was drawn using Microsoft Office Excel 2010 (Microsoft Inc., Washington, USA). The experimental results are shown as means ± standard error (n = 4). Statistical analyses were carried out using a one-way analysis of variance procedure in the IBM SPSS software version 22 (SPSS Inc., Chicago, IL, USA) to check the normal distribution and homoscedasticity, and Tukey’s honest significance test was used to assess the treatment means of the collected data for statistical significance at p < 0.05. The analysis of variance (ANOVA) was conducted following the general linear model procedure to evaluate single-factor effects and interaction effects. Two-way ANOVA was used to investigate the effects of fertilization and year on each index in this study.

3. Results

3.1. Yield of Spring Maize

Table 1 shows the yield of spring maize under different treatments and the effect of SCRNF application on increasing yield. Compared with CK, SCRNF promoted yield regardless of whether the amount of nitrogen fertilizer was reduced or not during the three years. The yield was highest in the NR40% treatment, followed by the NR20% treatment and N100% treatment in 2019, increasing by 6.6%, 4.5%, and 2.7%, respectively. However, the maize yield with NR20% was highest in both 2020 and 2021, increasing by 8.8% and 11.7% over CK, respectively, yet the ranking was different in the following two years: the yield order was NR40% > NR100% in 2020 but NR100% > NR40% in 2021. Although no significant differences were observed in yield, there were significant differences in the yield increase among the treatments of different N doses. The yield increases for NR20% and NR40% were significantly higher (p < 0.05) than that for N100% in 2019 and 2020, while the yield increases for NR20% and N100% were significantly higher (p < 0.05) than that for NR40% in 2021.

3.2. Nitrogen Partial Factor Productivity

As shown in Table 2, the effects of N fertilizer were varied over the three experimental years. The increased yields per 1 kg fertilizer N for N100%, NR20%, and NR40% were 1.0, 2.1, and 4.1 kg kg−1, respectively. Compared with N100%, it improved significantly (p < 0.05) with the increase in nitrogen reduction in the application of SCRNF in 2019. There were different trends in 2020 and 2021. Notably, the NR20% treatment achieved the highest increased yield per 1 kg fertilizer N in both years. The second was the NR40% treatment in 2020, while the second was the N100% in 2021. The NR20% and NR40% treatments significantly (p < 0.05) increased yield per 1 kg fertilizer N compared to N100% in 2020, while no significant differences were observed between NR40% and N100% in 2021.
The results of nitrogen partial factor productivity with SCRNF were higher than those of the control. With the increase in the amount of N reduction in the tested years, N partial factor productivity increased gradually. The NR20% and NR40% treatments were significantly (p < 0.05) higher than the control and N100% throughout the study period, while no significant differences were observed between N100% and CK. When the reduced dose of N increased from 20% to 40%, the N partial factor productivity ranged between 48.9 kg kg−1 and 66.5 kg kg−1, and increased from 30.7% to 77.7% in 2019, respectively, which was the sharpest rise during the three years (Table 2).

3.3. Yield Components of Spring Maize

Figure 1 shows that the use of SCRNF in nitrogen reduction dosing did not, in general, significantly degrade the yield components of spring maize. Application of SCRNF slightly increased the ear length when treated with NR40% in 2021 (a 1.4% increase) than when treated with NR20% in 2019 (a 6.0% increase). Even with nitrogen reduction, there was still no significant difference compared with the control. With the extension of the experimental period, the variation in ear length decreased gradually to some extent, from 18.73~19.20 cm in 2019 to 16.57~17.56 cm in 2021 (Figure 1A). Despite no evident or regular change in ear diameter among the treatments and years, SCRNF application in terms of the nitrogen reduction did not significantly attenuate ear diameter (Figure 1B). The results of hundred-grain weight reflected a similar situation to that of ear length, with the exception of NR40%, which was lighter than CK in both 2019 and 2020 (Figure 1D). The grain number per ear significantly (p < 0.05) increased in the three treatments with SCRNF compared with the control in 2019 and 2021, except for the NR20% treatment in 2020. The number for the NR20% treatment was 675 in 2019, the highest during the experimental period, which increased by 24.8% over CK. A similar trend was found in 2021, with the number also peaking in the NR20% treatment, indicating that grain number per ear is reduced as the N dose decreases.

3.4. Main Agronomic Traits of Spring Maize

Figure 2 shows the effects of fertilization treatments on the plant height, leaf area, shoot biomass, and SPAD of ear leaves during the tasseling stage of spring maize. It can be seen that compared with the control, there was no significant difference in these agronomic traits, although the amount of N application decreased. The plant height was highest in the NR20% treatment in 2019 and lowest in CK in 2020, ranging from 220.1 cm to 290.3 cm. Application of SCRNF slightly favored plant height, except for the NR40% treatment in 2021, but plant height decreased more or less over N100% with the increase in nitrogen reduction rate. However, there is still only one exception, namely the NR20% treatment in 2019, which surpassed all the records of plant height during the experimental period (Figure 2A). Similar results can be found for leaf area. Nevertheless, the NR20% treatment peaked throughout the tested year; in particular, the value was largest in 2019 and increased by 12.8% compared with the control (Figure 2B). The trend in shoot biomass resembled that of plant height, with the maximum being reached for the NR20% treatment in 2019 and the minimum in CK in 2020 (Figure 2C). Though the SPAD value of ear leaves declined slightly as the nitrogen application rate decreased after treatment with SCRNF, there was no significant difference at this point (Figure 2D).

3.5. Soil Nitrate Nitrogen Content and Distribution

Figure 3 shows the distribution of nitrate nitrogen content in the 0~200 cm soil profile from 2019 to 2021 under different fertilization treatments. The trend in nitrate nitrogen content in each treatment was basically the same with the deepening of the soil layer, exhibiting an S-type trend; that is, from top to bottom, there was a clear ‘valley–peak–valley’ pattern. In 2019, the content of nitrate nitrogen in the soil surface (20 cm) fluctuated between 17.5 mg kg−1 and 21.5 mg kg−1, with the ranking order N100% > NR20% > NR40% > CK. Near the 40 cm soil layer, it was slightly lower than that of the soil surface, which formed a small trough. The first accumulation peak appeared at the 40~100 cm soil layer, which was the smallest in the NR40% treatment, with a value of 18.6 mg kg−1, and the biggest in CK, whose value was up to 33.7 mg kg−1, nearly reaching double the former value. An evident low-value area was formed in the 120~160 cm soil layer, with nitrate nitrogen content ranging between 5.5 mg kg−1 and 12.2 mg kg−1; all nitrate nitrogen contents were below 10 mg kg−1, especially after application of SCRNF. From 180 cm to 200 cm, the deepest region detected in this experiment, the content of nitrate nitrogen began to rise gradually again, although the increase was very weak at this point. The NR40% treatment exhibited the lowest content of nitrate nitrogen. Based on the variation in nitrate nitrogen content, it can be inferred that the second accumulation peak may occur below 200 cm.
The most prominent distinction between 2020 and 2019 is that the first accumulation peak of CK in the 40~100 cm soil layer increased rapidly, and the corresponding nitrate nitrogen content was almost 40 mg kg−1, meaning a potential elevated risk. The content of nitrate nitrogen in the 80~100 cm soil layer exceeded that in 2019, surpassing 20 mg kg−1. SCRNF treatments did not produce such a large change. Furthermore, the maximum CK peak, approximately 40 mg kg−1, shifted downward and occurred in the 80 cm soil layer in 2021, whereas it was just within the 60 cm layer during 2019 and 2020. Moreover, in 2021, the nitrate nitrogen content of CK was almost double that in 2019 in the 100 cm soil layer. The curve shape remained basically unchanged after the application of SCRNF throughout the three years. Compared with the control, the NR20% and NR40% treatments significantly (p < 0.05) reduced the content of nitrate nitrogen in the 0~200 cm soil by 26.3% and 38.7% on average, respectively, over the three years (Figure 3).

3.6. Soil Ammonium Nitrogen Content and Distribution

Figure 4 presents the effects of different fertilization treatments on the content of ammonium nitrogen in the 0~200 cm soil profile during 2019, 2020, and 2021. Compared with nitrate nitrogen, the content of ammonium nitrogen in the 0~200 cm soil basically fluctuated within a narrow range of 1.2 to 9.4 mg kg−1, and more than 60% of the layers may be less than 5 mg kg−1 in the application of SCRNF. It changed very slowly with the increase in depth, showing a gradual decreasing trend. In general, the content of ammonium nitrogen in the treatment of reducing nitrogen fertilizer was also lower than that in the CK and N100% treatments in each layer of soil. Averaged over three years, the NR20% and NR40% treatments significantly (p < 0.05) decreased soil ammonium nitrogen by 33.1% and 40.4%, respectively, compared with the control.

3.7. Interaction Between Experimental Year and Fertilization

Only three parameters—length of ear, hundred-grain weight, and SPAD—were significantly affected by the experimental year but not by the interaction between year and fertilization (Table 3). This indicates that the impact of year on them was universal, while the other parameters were significantly affected by the interaction, showing that the effect of the fertilization treatment on most maize traits was dependent on the specific year. According to the monthly precipitation and monthly average temperature during the maize growing period (Table S1), the precipitation was highest (420 mm) in 2020 but lowest (258 mm) in 2019, despite the same average temperature in the three years, highlighting that there were significant differences in precipitation during the maize growing season among the three years.

4. Discussion

As a necessary nutrient element for crop growth, nitrogen plays a critical role in the sustainability and stability of farmland ecosystems [24]. Numerous studies have focused on its accumulation and utilization [25,26,27]. However, excessive application of N fertilizer is widespread in a large number of areas in China at present [28]. Consistent with this finding, we discovered that the yield following these treatments was higher than that of the control despite reduced nitrogen application. The yield of spring maize under 20% reduced nitrogen exhibited a consistent increase in this study for the three consecutive years compared with N100% (Table 1 and Table 3), which implies that the amount of nitrogen supplied by local farmers was relatively high, especially when using urea as the base fertilizer in a single application. Furthermore, after conventional chemical fertilizers are added to the soil, the nutrients are usually released very quickly. A considerable percentage of them cannot be absorbed and utilized by crops in time, and are subsequently leached with rainfall, not only wasting resources and energy but also polluting the agricultural and ecological environment [29].
Aside from this, a conventional chemical fertilizer such as urea can very easily cause an insufficient nitrogen supply and low seed-setting rate in the later stage. As shown in Figure 1, the grain number per ear was significantly (p < 0.05) reduced in the control compared with the three SCRNF treatments. Furthermore, the yield of CK decreased by 9.4% compared with the treatment of N100% in 2021, though their nitrogen supplies were equal (Table 1), which probably resulted from more N leaching in CK than in the SCRNF treatment (Figure 3, Table 3). N loss is equal to N deficiency to some extent. When the N supply is insufficient, the growth of crops will be suppressed due to the impairment of photosynthesis, protein synthesis, cell division, and root development, which further impacts the yield [30,31]. Similarly, Vitousek et al. (2009) [32] confirmed that inadequate amounts of N caused a reduction in crop yields in sub-Saharan Africa.
In most maize production systems, the application of nitrogen fertilizer is a rapid and direct measure to enhance crop yield [33]. However, there is a nonlinear link between crop yield and N application amount; excessive N fertilizer supply has been shown to degrade yield and quality [34]. In our experiment, the yield of the N100% treatment remained consistently below that of the NR20% treatment throughout the three-year study period, indicating that the extra 20% of N fertilizer did not prompt production and supporting the hypothesis that the conventional nitrogen application rate may be excessive to a certain degree. Therefore, it is necessary to explore the appropriate rate of nitrogen application and fertilization measures in the local area.
Considering the available reports on the effect of nitrogen reduction on crop yield, the results were contradictory owing to the different crop types, degrees of N reduction, soil texture, and environmental conditions [26,35]. Some researchers have shown that nitrogen reduction directly results in a decrease in crop yield [36]. Nevertheless, our study found that compared with the N100% treatment, there was no immediate decrease in the yield of spring maize, even after reducing the nitrogen input by 40%, during the first two years. The reason for this may be that there is a large amount of residual nitrogen in the soil (Figure 3, Table 3) due to long-term excessive fertilization, differences in soil texture [35], basic fertility, etc. It has also been demonstrated that maize yield would not decrease under a reduced nitrogen input by 20% in a wheat/maize rotation system under multiple cropping common vetch conditions [37]. However, Zhao et al. (2025) [26] found that when the ratio of reduced nitrogen was increased to 30%, the maize and wheat yield was significantly lower than that of the application of traditional nitrogen fertilizer without N reduction, which can be attributed to a much higher nitrogen reduction than the former.
Interestingly, the yield gap between CK and N100% widened annually in our research (Table 1 and Table 3). The yield of spring maize was higher than CK even under 40% reduced nitrogen but inferior to that of N100% just in the last test year, while the NR20% treatment surpassed CK and N100% steadily (Table 1). These results may be related to the application of slow/controlled-release nitrogen fertilizer. It has been well documented that SCRNF can effectively match the nutrient requirements of crops at different growth periods, consequently prompting the yield [38]. The reduction in nitrogen losses boosts the efficiency of N uptake from the coated urea [38] and offsets the negative effects of the application of smaller doses of N. As the experiment progressed, the yield of the NR20% treatment consistently surpassed that of N100%, while the yield-increasing effect of the NR40% treatment weakened, and even decreased below N100% in 2021 due to the decrease in soil N pool compared with the earlier two years (Figure 3), illustrating that there was a secure surplus of 20% to reduce nitrogen fertilizer dosage for the application of SCRNF on the premise of ensuring yield. Moreover, the application of SCRNF improved N partial factor productivity under reduced nitrogen input (Table 2), which demonstrated that more grains could be produced per unit of N fertilizer. It is noteworthy that the N reduction by 40% is likely to risk the production of spring maize over time since there have been cases where the yield was lower than that under no reduced nitrogen input; N reduction by 20% can be considered to be relatively reasonable given that it consistently achieved the highest yield increase per 1 kg N fertilizer (Table 2).
Our findings revealed that the application of SCRNF could increase the number of maize grains per ear without compromising the other yield component factors under a reduced N input (Figure 1, Table 3). This is because it can better align with the crop’s nutrient demand and favor the accumulation of nitrogen in seeds [38]. As there was generally no significant difference in plant height, leaf area, shoot biomass, and yield components among the different treatments (Figure 1 and Figure 2, and Table 3), SCRNF application could still ensure that maize received sufficient nutrient supply from the jointing and tasseling stages to the filling stage, even under reduced nitrogen conditions. This guaranteed that more nutrients were transferred from the source to the sink during the filling period, and the photosynthetic function of leaves was not affected by the reduced nitrogen input (Figure 2), resulting in a slight increase in the number of grains per ear and 100-grain weight (Figure 1), thus keeping the yield stable or even increasing it (Table 1 and Table 3).
In our case, the application of SCRNF could significantly decrease the content of nitrate and ammonium nitrogen in 0~200 cm soil under nitrogen reduction input, especially in the 0~120 cm soil layer (Figure 3 and Figure 4), due to the nutrient release pattern of SCRNF in synchronization with crop needs and the reduction in nitrogen leaching [38]. In addition, the absolute amount of pure nitrogen input was relatively small, although Zhao et al. (2025) [26] found the opposite phenomenon. The contradictory results were attributed to different treatments and soil depth. The latter only assayed the content of nitrate and ammonium nitrogen in 0~30 cm soil under a wheat/maize rotation system with multiple cropping green manure conditions. It should be noted that the peak value of nitrate accumulation in CK increased and shifted downward. Although residual fertilizer nitrogen plays a role in improving soil fertility and replenishing the soil nitrogen pool, the leaching loss of residual nitrogen under irrigation and rainfall conditions is an issue that deserves greater focus at present.
According to meteorological data during the maize growing period, the total rainfall and its distribution varied significantly despite similar temperature conditions during the three experimental years (Table S1). The precipitation during the maize growing season decreases in the order 2020 > 2021 > 2019. Since the experimental year is a composite variable, mainly including precipitation, temperature, interannual variation in soil background values, etc., rainfall and temperature are the meteorological elements that directly affected the growth of maize besides fertilization, especially in the arid and semi-arid regions like Shanxi, although irrigation could be added under severe drought conditions in the experiment. Nevertheless, irrigation was often not timely. Therefore, the experimental results were greatly influenced by year effects and climatic factors. Moreover, the irrigation, along with a large evaporation amount in the experimental site may impact the distribution of nitrate and ammonium in the soil profile.
Coated urea, prepared by enveloping the surface of urea granules with various organic and inorganic materials, is a kind of slow/controlled-release N fertilizer that can encourage the synchronization of crop uptake patterns throughout the entire growth period [38]. Thus, it provides a basis for improving fertilization practices to lower N loss and decrease N application dose without sacrificing crop yield. However, it has not been widely applied in the production of field crops due to its high price and production cost, especially in arid areas. Therefore, more attention should be paid to the optimal application ratio with urea, proper nitrogen reduction amount, timing, and split application of N fertilizer, suitable SCRNF varieties for the local climate, and appropriate plant density, besides the development of coating materials.

5. Conclusions

The current grain yield increases have been caused by the high input and high consumption of agricultural resources in China. The blind and excessive application of chemical fertilizers in pursuit of high yields has led to problems such as an imbalance of soil nutrients, year-on-year declines in fertilizer use efficiency, and intensified agricultural non-point source pollution. We studied the effects of SCRNF application on the production of spring maize in a field and on the content of nitrate and ammonium nitrogen in soil under a reduced nitrogen input. The results showed that treatment with SCRNF could achieve a relatively high yield, even when the total nitrogen application amount was reduced. The maize yield was the highest in 2020 and 2021 following NR20% treatment, while the nitrate and ammonium nitrogen contents were significantly decreased in the 0~200 cm soil. Therefore, the application of SCRNF is an option that can both stabilize crop yield and protect the environment under reduced nitrogen input. Further long-term research should explore the expansion of production-scale fertilization programs and explore ways to reduce the costs of raw materials to reduce the overall costs of coated N fertilizers.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agriculture15192045/s1, Table S1. The monthly precipitation and monthly average temperature during the growing period of spring maize in 2019–2021.

Author Contributions

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

Funding

This research was supported by the Natural Science Foundation Program of Shanxi Province, China (No. 202403021222102); the Project of Shanxi Province Key Lab Construction (No. Z135050009017-1-6); the Science and Technology Major Project of Shanxi Province, China (No. 202101140601026); the National Key Research and Development Project of China (No. 2021YFD1901101-01).

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors.

Acknowledgments

We fully appreciate the editors and all anonymous reviewers for their constructive comments on this manuscript.

Conflicts of Interest

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

Abbreviations

The following abbreviations are used in this manuscript:
NNitrogen
SCRNFSlow/controlled-release nitrogen fertilizer

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Agriculture 15 02045 g001
Figure 1. Effects of different fertilization treatments on yield component factors of spring maize. (A) length of ear; (B) diameter of ear; (C) number of grains per ear; (D) hundred-grain weight. Note: Different lowercase letters mean significant differences among different treatment in the same year at 0.05 level.
Figure 1. Effects of different fertilization treatments on yield component factors of spring maize. (A) length of ear; (B) diameter of ear; (C) number of grains per ear; (D) hundred-grain weight. Note: Different lowercase letters mean significant differences among different treatment in the same year at 0.05 level.
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Figure 2. Effects of different fertilization treatments on the main agronomic traits of spring maize. (A) plant height; (B) leaf area; (C) shoot biomass; (D) SPAD value of ear leaf. Note: Different lowercase letters mean significant differences among different treatment in the same year at 0.05 level.
Figure 2. Effects of different fertilization treatments on the main agronomic traits of spring maize. (A) plant height; (B) leaf area; (C) shoot biomass; (D) SPAD value of ear leaf. Note: Different lowercase letters mean significant differences among different treatment in the same year at 0.05 level.
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Figure 3. The effect of different fertilization treatments on the content of nitrate nitrogen in 0~200 cm soil profile during 2019, 2020, and 2021.
Figure 3. The effect of different fertilization treatments on the content of nitrate nitrogen in 0~200 cm soil profile during 2019, 2020, and 2021.
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Figure 4. The effect of different fertilization treatments on the content of ammonium nitrogen in 0~200 cm soil profile during 2019, 2020, and 2021.
Figure 4. The effect of different fertilization treatments on the content of ammonium nitrogen in 0~200 cm soil profile during 2019, 2020, and 2021.
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Table 1. Spring maize yield and increased effect of different treatments.
Table 1. Spring maize yield and increased effect of different treatments.
TreatmentYield
(kg hm−2)		Yield Increase
(kg hm−2)
201920202021201920202021
CK8976.5 ± 100.4 a9931.0 ± 162.6 a7621.2 ±106.6 a------
N100%9224.0 ± 52.8 a10,348.0 ± 75.1 a8407.7 ± 96.0 a247.5 ± 41.5 b417.0 ± 28.9 b786.5 ± 26.1 a
NR20%9384.5 ± 76.6 a10,807.1 ± 113.7 a8515.6 ± 65.9 a408.0 ± 65.6 a876.0 ± 30.1 a894.4 ± 50.1 a
NR40%9572.1 ± 64.3 a10,457.5 ± 90.8 a8018.4 ± 48.0 a595.6 ± 42.4 a526.5 ± 10.2 a397.2 ± 19.7 b
Note: Different lowercase letters mean significant differences among different treatment in the same year at 0.05 level.
Table 2. Nitrogen partial productivity under different treatments.
Table 2. Nitrogen partial productivity under different treatments.
TreatmentIncreased Yield per 1 kg Fertilizer N
(kg kg−1)		N Partial Factor Productivity
(kg kg−1)		Increase of N Partial Factor Productivity (%)
201920202021201920202021201920202021
CK------37.4 ± 1.0 b41.4 ± 0.7 b31.8± 0.5 b------
N100%1.0 ± 0.06 c1.7 ± 0.09 b3.3 ± 0.15 b38.4 ± 0.8 b43.1 ± 0.3 b35.0 ± 0.4 b2.7 4.1 10.1
NR20%2.1 ± 0.30 b4.6 ± 0.11 a4.7 ± 0.80 a48.9 ± 0.4 a56.3 ± 0.6 a44.4 ± 0.4 a30.7 36.0 39.6
NR40%4.1 ± 0.31 a3.7 ± 0.09 a2.8 ± 0.10 b66.5 ± 0.1 a72.6 ± 0.6 a55.7± 0.3 a77.8 75.4 75.2
Note: Different lowercase letters mean significant differences among different treatment in the same year at 0.05 level.
Table 3. The interaction between experimental year and fertilization treatment on yield and related parameters, main agronomy traits, and the content of nitrate and ammonium nitrogen in 0~200 cm soil profile.
Table 3. The interaction between experimental year and fertilization treatment on yield and related parameters, main agronomy traits, and the content of nitrate and ammonium nitrogen in 0~200 cm soil profile.
VariableYear (Y)Treatment (T)Y × T
Yield****
Length of Ear*NSNS
Diameter of Ear***
Number of Grains per Ear*****
Hundred-Grains Weight****NS
Plant Height*****
Leaf Area******
Shoot Biomass******
SPAD****NS
Nitrate Nitrogen Content****
Ammonium Nitrogen Content****
Note: the asterisks represent significant effects: NS, not significant, p > 0.05 (2-tailed). * Significant at the 0.05 probability level. ** Significant at the 0.01 probability level.
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Zhao, C.; Ye, M.; Li, N.; Huang, X.; Wang, J. Can Reduced Nitrogen Application of Slow/Controlled-Release Urea Enhance Maize Yield Stability and Mitigate Nitrate/Ammonium Nitrogen Leaching in Soil in North China? Agriculture 2025, 15, 2045. https://doi.org/10.3390/agriculture15192045

AMA Style

Zhao C, Ye M, Li N, Huang X, Wang J. Can Reduced Nitrogen Application of Slow/Controlled-Release Urea Enhance Maize Yield Stability and Mitigate Nitrate/Ammonium Nitrogen Leaching in Soil in North China? Agriculture. 2025; 15(19):2045. https://doi.org/10.3390/agriculture15192045

Chicago/Turabian Style

Zhao, Cong, Meihua Ye, Nana Li, Xuefang Huang, and Juanling Wang. 2025. "Can Reduced Nitrogen Application of Slow/Controlled-Release Urea Enhance Maize Yield Stability and Mitigate Nitrate/Ammonium Nitrogen Leaching in Soil in North China?" Agriculture 15, no. 19: 2045. https://doi.org/10.3390/agriculture15192045

APA Style

Zhao, C., Ye, M., Li, N., Huang, X., & Wang, J. (2025). Can Reduced Nitrogen Application of Slow/Controlled-Release Urea Enhance Maize Yield Stability and Mitigate Nitrate/Ammonium Nitrogen Leaching in Soil in North China? Agriculture, 15(19), 2045. https://doi.org/10.3390/agriculture15192045

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