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Article

Effects of Straw Return and Nitrogen Application Rates on Soil Ammonia Volatilization and Yield of Winter Wheat

by
Xuejie Wan
1,†,
Le Zhao
1,†,
Ziwei Wang
1,
Lin Che
1,
Yadong Xu
2,
Yubo Zhou
1,
Changhai Shi
1,
Lingyan Li
1 and
Yiguo Liu
1,*
1
College of Agronomy, Qingdao Agricultural University, Qingdao 266109, China
2
College of Agricultural Sciences, Zhengzhou University, Zhengzhou 450001, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Agronomy 2024, 14(7), 1469; https://doi.org/10.3390/agronomy14071469
Submission received: 10 May 2024 / Revised: 29 June 2024 / Accepted: 30 June 2024 / Published: 7 July 2024
(This article belongs to the Section Agroecology Innovation: Achieving System Resilience)
Browse Figures
Versions Notes

Abstract

:
This study investigates the impact of corn straw return and nitrogen application rates on ammonia volatilization and yield enhancement under field conditions, in order to reduce emissions while increasing crop yield. During the winter wheat season, a fissure area design was implemented, comprising three levels of straw return in the main area and three distinct nitrogen fertilizer levels in the subsidiary area, for a total of nine treatments. The results can be summarized as follows: (1) The ammonia emissions flux initially increased followed by a decrease, and was primarily concentrated within the first 14 days after fertilization, with a peak observed at 4–5 days before decreasing. Notably, nitrogen fertilizer significantly affected the cumulative ammonia emissions, ranging from 0.019 to 1.786 kg·hm−2·d−1 and 0.013 to 1.693 kg·hm−2·d−1 across the two seasons. (2) The soil with a higher nitrogen application rate exhibited elevated levels of inorganic nitrogen content and urease activity under the same straw return level. Maintaining a consistent nitrogen application level, the return of straw to the field increased the cumulative ammonia discharge, inorganic nitrogen content, and urease activity. (3) The interaction between straw return and nitrogen fertilizer substantially affected crop yield. Specifically, during the winter wheat season, the optimal combination for reducing ammonia emissions and enhancing yield was observed under straw return (both half or full) combined with 180 kg·hm−2 nitrogen application. Notably, the reduction of soil emissions and winter wheat yield augmentation were feasible through appropriate corn straw return in the preceding season.

1. Introduction

Wheat is one of China’s major cereal crops, and the rational use of nitrogen fertilizer is the key to ensuring high and stable wheat yield. But the excessive use of nitrogen fertilizer not only makes it difficult to achieve wheat yield, but also reduces the use of nitrogen fertilizer [1]. The mismanagement of nitrogen can cause substantial nitrogen loss [2,3,4].
Ammonia volatilization from agricultural fields constitutes a significant avenue for the gaseous loss of nitrogen fertilizer [5]. Ammonia volatilization losses can account for up to 25% of the nitrogen applied [6]. NH3 losses not only lead to resource waste but also causes environmental impacts, such as soil acidification, water eutrophication, and aerosol (PM2.5) formation in the atmosphere [7]. This phenomenon increases proportionally with the augmentation of N fertilizer application, exhibiting a rate of increase surpassing linearity [8]. However, excessive nitrogen application not only reduces crop yield and quality, but also causes resource waste and environmental contamination [9]. Optimal nitrogen fertilizer application can promote plant growth, notably enhancing root development and secretion production [10], thereby augmenting soil organic carbon storage.
China has abundant resources of crop residues. In 2017, the three major cereal crops—maize, rice, and wheat straw—accounted for 84.9% of the country’s total straw resources [11]. Upon returning their residues to the field, the nutrient resources permeate the soil, serving to fertilize it, increase organic matter content, and enhance soil quality. Numerous studies have explored the impact of straw return on soil ammonia volatilization. However, the response of soil ammonia volatilization to straw return varies due to differences in the climatic conditions, soil properties, straw characteristics, and other factors [12]. For instance, Wang et al. [13] have demonstrated a 20% increase in soil ammonia volatilization with wheat straw return combined with N fertilizer, compared to conventional N application. Similarly, Xu Cong’s [14] research on wheat–corn rotation systems revealed higher soil ammonia volatilization when using straw return combined with N fertilizer than with N fertilizer alone. Additionally, Wu et al. [15] suggested that reducing N fertilizer alongside straw return could enhance NH4+ fixation in dryland soils, suppress soil nitrification potential, decrease NO3− accumulation, and mitigate the risk of nitrate–nitrogen loss through leaching.
Urea applied to the soil is transformed by enzymes and micro-organisms in the soil. The decomposition of straw is affected by the quantity and quality of the straw, climate conditions (e.g., temperature and humidity), and soil properties [16]. The decomposition of urea is affected by rainfall, temperature, light, urease activity, soil pH, nitrogen application, and wind speed [17,18]. After urea is applied to the soil, it is hydrolyzed to ammonia by urease, thus affecting ammonia discharge in the field.
For these reasons, there is an urgent need to reduce agricultural ammonia volatilization to reduce the damage to agriculture, ecosystems, and human health. Research on the effects of nitrogen fertilizer and straw return on ammonia volatilization, and further studies on appropriate straw return and nitrogen fertilizer management measures to reduce ammonia volatilization losses from wheat fields, are important ways to achieve efficient and clean wheat production.

2. Materials and Methods

2.1. Overview of the Pilot Area

The experiment spanned from October 2021 to June 2023 in an experimental field in Yanghe Town (119°37′ E, 36°15′ N), Jiaozhou City, Qingdao City, Shandong Province. This region has a temperate continental climate characterized by tidal soil and a frost-free period of 251 d. The annual precipitation recorded from October 2021 to June 2022 was 128 mm, which increased to 172 mm from October 2022 to June 2023. The baseline soil condition within the 0–20 cm layer is detailed in Table 1, and the weather conditions throughout the winter wheat ammonia emissions monitoring period are depicted in Figure 1.

2.2. Experimental Design

The experiment followed a split-zone design, encompassing three levels of straw return in the main area (no straw returned, half of the amount returned, and full straw return), and three nitrogen fertilizer levels in the secondary area: 0 (no nitrogen application), 180 kg·hm−2 (20% reduction), and 225 kg/hm2 (conventional application), constituting nine treatments (Table 2). Each experimental plot measured 8 m × 10 m, with a 0.5 m separation between plots and 2 m buffer rows. Base fertilizers, including urea (180 kg/hm2 or 225 kg/hm2), calcium superphosphate (90 kg/hm2), and potassium chloride (90 kg/hm2), were applied to the soil. In the non-return treatment, all straw from the previous corn crop was manually removed from the plot. The half-return treatment involved removing straw from alternate rows, while the full-return treatment retained all straw within the plot. Stalks within the plots were crushed into 5–10 cm fragments using haymakers. The corn stalks were ploughed into the field at a depth of 20–30 cm. The seeding rate for both 2021–2022 and 2022–2023 was maintained at 225 kg/hm2, due to late sowing. The quantities of straw returned to the field varied: 0, 6000, or 12,000 kg/hm2. Other corn management practices in the preceding season mirrored those of the farmers’ standard procedures.

2.3. Measurement Items and Methods

2.3.1. Soil Ammonia Volatilization and Influencing Factors

Soil ammonia volatilization was determined using the aeration method [19]. Two sponges soaked in phosphoric acid (3 cm thick, 15 cm diameter) were placed in PVC pipes. After the application of nitrogen fertilizer, ammonia volatilized from the soil was captured by glycerol phosphate and ammonia volatilization fluxes were recorded at 1–2 day intervals for one week and then monitored at 3–7 day intervals until no ammonia was present. Upon retrieval to the laboratory, the sponge was placed inside a 500 mL wide-mouth plastic bottle. Subsequently, a 300 mL potassium chloride (KCl) solution (1 mol/L) was added to fully submerge the sponge. The plastic bottles were sealed and agitated for 1 h. The sponge was then removed and allowed to stand before analysis using the ammonia module of the AA3 flow analyzer (SEAL, Hamburg, Germany). In the event of rainfall, measurements could proceed unhindered with appropriate rainproofing equipment, and the sampling duration may be adapted based on prevailing conditions.
Ammonia emission flux (kg·hm−2·d−1) = M × 10−2/(A × T)
where M represents the average amount of ammonia (mg) measured in a single plastic tube using the ventilation method, A represents the cross-sectional area of the sponge (0.02 m2), and T denotes the time of each successive collection.
Cumulative ammonia emissions (kg·hm−2) = Σ (ammonia emission flux × time of each successive collection
Ammonia volatilization loss rate (%) = Ammonia cumulative emissions/chemical nitrogen fertilizer use × 100%
Ammonia emission factor (%) = (Cumulative ammonia emission from nitrogen application area Cumulative ammonia emission from non-nitrogen application area)/Nitrogen application × 100%
Ammonia volatilization emission intensity = total ammonia volatilization per unit area/wheat production per unit area
Simultaneously to ammonia volatilization measurement, samples of topsoil (0–40 cm) were collected. Soil moisture content was measured using the drying method. Soil ammonium nitrogen and nitrate nitrogen concentrations were extracted using potassium chloride solution and the supernatant was determined using an AA3 flow analyzer (SEAL, Hamburg, Germany). Soil urease activity was analyzed colorimetrically using an ultraviolet visible spectrophotometer (Cary 60, Santa Clara, CA, USA).

2.3.2. Winter Wheat Yield and Components

The number of panicles, number of grains per spike, 1000-grain weight, aboveground biomass, and yield were investigated at the maturity stage. Grain yield was determined from a central plot area of 2 m2 and reported at a standard moisture content of 12% fresh weight. Two rows of 0.5 m2 plants were sampled in the center of each plot. After calculating the total panicle number and determining the panicle number per m2, the plant samples were divided into leaves, stems, and panicles. The ears were threshed by hand. The number of grains per panicle and grain weight (mg) were determined after drying in an oven at 70 °C to a fixed weight. The above-ground biomass was then weighed.

2.3.3. Methods for the Determination of Soil Indicators

The methods used for the determination of total nitrogen, available N, available P, available K, organic matter, and pH in soils were the Kjeldahl nitrogen determination (Kjeltec 8400, Beijing, China), the diffusion method (Portable digital titrator, Shanghai, China), flame photometry (Flame Photometer, M410, Cambridge, UK), the volumetric method with potassium dichromate (Portable digital titrator, Shanghai, China) and potentiometric methods, respectively (pH meter, PHS-3C, Shanghai, China) [20].

2.4. Data Processing and Analysis

The data were organized and calculated using Excel 2016, and plotted using Origin 2022. Annual data were subjected to an analysis of variance (SPSS 25), in order to assess the effect of nitrogen application and straw return on all measured parameters. The mean values were compared using the least significant difference test (LSD 0.05).
The Pearson correlation analysis between NH3 emissions, soil water content from 0 to 40 cm, NH4+ content from 0 to 40 cm, NO3− content from 0 to 40 cm, and urease activity from 0 to 40 cm in soil were evaluated using SPSS 25, with Pearson’s two-tailed (p < 0.01) comparison.

3. Results

3.1. Effects of Straw Return and Nitrogen Application Rates on Ammonia Emissions Flux of Winter Wheat

Figure 2 depicts the variations in the ammonia emission fluxes observed during the monitoring period of winter wheat from 2021 to 2023. Across different years, a consistent pattern emerged, characterized by an initial increase followed by a subsequent decrease in ammonia emission fluxes. Soil ammonia emissions primarily occurred within 14 days of fertilizer application, with peak emissions typically between 4 and 5 days of fertilizer application, and thereafter gradually declining. Ammonia emission fluxes increased with increasing nitrogen application. They also increased with increasing straw return. The maximum ammonia volatilization flux in the first season was 1.786 kg·hm−2·d−1 for the S2N2 treatment, which was 2.55% and 7.07% higher than the S1N2 and S0N3 treatments, respectively. The maximum ammonia volatilization flux in the first two seasons was 1.693 kg·hm−2·d−1 for the S2N2 treatment, which was 2.96% and 6.31% higher than the S1N2 and S0N3 treatments, respectively. Ammonia emission fluxes were lower in 2021–2022 than in 2022–2023 for the no N application treatment. This was mainly due to higher soil moisture due to continuous rainfall in the pre-sowing period of fertilizer application in 2021–2022 and lower average daily temperatures, which reduced urea hydrolysis (Figure 1).

3.2. Effects of Straw Return and Nitrogen Application Rates on Cumulative Ammonia Emissions, Loss Rate, Ammonia Emissions Coefficient, and Emissions Intensity in Winter Wheat

The cumulative amount of ammonia volatilization during the winter wheat monitoring periods in 2021–2022 and 2022–2023 is shown in Table 3, from which it can be seen that the cumulative ammonia emissions increased with increasing nitrogen application at the same straw return level. At the same level of N application, the difference between half- and full-returned straw was small and significantly higher than that with straw not returned to the field. Differences between the no-N treatments were small, but straw return increased cumulative ammonia emissions. The ammonia volatilization loss rate and ammonia emission coefficient were positively correlated with N application. The ammonia volatilization loss rate was higher with straw return than with no return. S2N2 had the highest cumulative ammonia emissions (9.27 kg/t), ammonia loss rate (4.12%), and ammonia emissions coefficient (3.93%). S0N2 had the highest ammonia emissions intensity 1.07 kg/t. The cumulative ammonia emissions in 2022–2023 ranged from 0.49 to 9.51 kg/hm2, with the highest cumulative ammonia emissions observed for the S1N2 (9.51 kg/t) treatment, followed by S2N2 (9.46 kg/hm2), with small differences between the two but both significantly higher than the other treatments, as shown in Table 3. The changes in ammonia emissions coefficients were consistent with the performance of ammonia loss rates. The accumulation of ammonia volatilization and the intensity of ammonia emissions in the winter wheat fields were higher in the second year than in the first year. In the straw and nitrogen fertilizer intercropping, during the period of the ammonia volatilization of wheat in both seasons, nitrogen fertilizer had highly significant effects on ammonia cumulative emissions, ammonia loss rate, ammonia emissions coefficients, and ammonia emissions intensities.

3.3. Effects of Straw Return and Nitrogen Application Rates on Soil Moisture Content during Ammonia Emissions Monitoring Period in Winter Wheat

Figure 3 illustrates the soil water content during the ammonia emissions monitoring period for winter wheat for both 2021–2022 and 2022–2023. Throughout the ammonia volatilization monitoring phase, the soil moisture content was affected by rainfall, with treatment differences proving to be non-significant. Notably, in 2021–2022, soil moisture content fluctuated considerably due to varying weather conditions (Figure 1). Under the same N application level, straw return to the field increased soil water content, with a small difference between the semi-return and full–return methods, both surpassing the non-return treatment. In contrast, during 2022–2023, the soil moisture content exhibited more variability in the 0–20 cm layer than in the 20–40 cm layer. Moreover, rainfall was lower than that in the first season, accompanied by a more gradual temperature decline, thereby exerting less impact on the 20–40 cm soil layer. Soil moisture and air temperature have a major influence on ammonia volatilization. Straw returned to the field can act as a heat sink, and increased soil temperature can accelerate the water uptake of urea. In the first year, the peak ammonia emissions occurred one day later than in the second year, due to large fluctuations in warming and cooling temperatures and the influence of continuous rainfall before planting. In the second year, the ammonia emissions monitoring period was characterized by higher temperatures and a relatively gentle temperature drop, which accelerated the rate of urea hydrolysis and resulted in a greater change in ammonia emissions fluxes than in the first year.

3.4. Effects of Straw Return and Nitrogen Application Rate on 0–40 cm Soil Inorganic Nitrogen during the Ammonia Volatilization Period of Winter Wheat

Figure 4 illustrates the changes in soil inorganic nitrogen during the monitoring period of winter wheat ammonia emissions from 2021 to 2022. Both soil ammonium nitrogen and nitrate nitrogen initially increased, reaching peak levels one week after fertilization, followed by a gradual decline. Notably, higher nitrogen application rates under identical straw management levels corresponded to higher soil ammonium and nitrate nitrogen contents. Similarly, at the same nitrogen application level, straw return methods exhibited higher soil ammonium and nitrate nitrogen contents than non-returning methods, with small differences between semi-return and full-return approaches. Furthermore, the soil layer at the 20–40 cm depth demonstrated lower ammonium and nitrate nitrogen content than the 0–20 cm layer, with the changes showing a consistent trend.
Figure 5 displays the fluctuations in soil inorganic nitrogen during the monitoring period of winter wheat ammonia emission in 2022–2023. Ammonium nitrogen and nitrate nitrogen contents in the 0–20 cm and 20–40 cm soil layers changed in the same way, first increasing and then decreasing, and reached their maximum values one week after fertilizer application (30.30–38.34 mg kg−1 and 30.04–40.00 mg kg−1, respectively). Ammonium N content was higher in the 0–20 cm soil layer than in the 20–40 cm soil layer; furthermore, the differences were significant between different N applications at the same straw level, and smaller between different straw return levels at the same N application level. The differences between the fertilizer treatments on the 14th day were small, but significantly higher than those under the non-fertilizer treatments (S0N0, S1N0, and S2N0). At the same level of N application, the differences in nitrate N content in each soil layer between straw returns were small and, at the same level of straw return, the higher the N application, the higher the nitrate N content in the soil layer. The differences between treatments were significant.

3.5. Effects of Straw Return and Nitrogen Application Rates on Urease Activity in 0–40 cm Soil during the Ammonia Volatilization Period of Winter Wheat

Figure 6 presents the changes in soil urease activity during the monitoring periods of winter wheat ammonia emissions in 2021–2022 and 2022–2023. Throughout the ammonia emissions monitoring phase, the 0–20 cm soil layer exhibited higher urease activity than the 20–40 cm layer. In addition, straw return treatments demonstrated higher urease activity than non-returning treatments. Although nitrogen application enhanced urease activity, the impact of varying nitrogen applications on urease was minimal, without significant differences observed. The changes in urease activity in the two seasons were basically the same, and the urease activity in the 0–20 cm soil layer showed a trend of “increase–decrease–decrease–increase”, with the highest urease activity on the 7th day after fertilizer application. Fertilizer treatment was significantly higher than no fertilizer treatment. The straw return treatment was significantly higher than the treatment without straw return. Soil urease activity from 20–40 cm showed inconsistent trends in both seasons. Urease activity increased and then decreased in the first season. In the second season, urease activity showed a slow decreasing trend.

3.6. Correlation between Ammonia Volatile Emissions Fluxes and Environmental Factors during the Monitoring Period of Ammonia Emissions from Winter Wheat with Straw Return and Nitrogen Application Rate

Figure 7 illustrates the correlations between winter wheat ammonia emission fluxes and environmental factors in 2021–2022 and 2022–2023. Key factors affecting ammonia volatilization included soil water content, soil ammonium and nitrate nitrogen levels, and urease activity. From Figure 7 it can be seen that 0–40 cm soil ammonium nitrogen, nitrate nitrogen, and urease activity significantly affected ammonia volatilization and showed a significant positive correlation. Soil moisture content affects ammonia volatilization fluxes by influencing urease activity. Ammonia volatilization loss rates and emission factors were not significantly related to ammonia emission fluxes in 2021–2022 and were significantly and positively related in 2022–2023. This was mainly due to the large difference in weather conditions between the two years (Figure 1). The 2021–2022 ammonia volatilization monitoring period was characterized by high temperature variability, heavy rainfall, and continuous rainfall prior to fertilizer application, resulting in high soil water content. Meanwhile, the 2022–2023 ammonia volatilization monitoring period was characterized by higher average daily temperatures, slower temperature decline, and sunny weather prior to fertilizer application.

3.7. Effects of Straw Return and Nitrogen Application Rates on Winter Wheat Yield and Yield Composition

Table 4 presents the yield and yield components of winter wheat across different treatments for the years 2021–2022 and 2022–2023. Yield variation was consistent between the two seasons: The N–applied treatment was significantly higher than the non–N–applied treatment, but the difference between the N applications of 180 kg/hm2 and 225 kg/hm2 was not significant. This indicates that the 20% N reduction had no significant effect on yield. The highest grain yields were always achieved under S2N2 (9.78 t/hm2 and 8.07 t/hm2 in the first and second years, respectively), which was 13.39% and 3.35% higher than in the S0N2 treatment with no straw return in the two seasons, respectively. The higher grain yield was associated with a higher spike number, kernel number per spike, thousand grain weight, biological yield, and HI.

4. Discussion

Fertilizer application rate, fertilizer application temperature, soil moisture content, urease activity, and precipitation all affect ammonia emissions from farmlands [21,22,23]. The soil ammonium nitrogen content has been positively correlated with soil ammonia emissions [24,25]. The excessive use of nitrogen fertilizer not only significantly reduces the N fertilizer use rate, but also causes a number of environmental problems; therefore, effective nitrogen fertilizer management measures are urgently needed to reduce the volatilization of ammonia from the field and improve the N fertilizer use rate, as the amount of nitrogen applied is positively correlated with soil ammonia emissions [24]. In this study, as fertilizer application increased, soil ammonium nitrogen content, ammonia loss rate, the ammonia emissions rate, and cumulative ammonia emissions in the soil also increased, consistent with previous research findings [25,26,27]. Lv et al. [25] found that crop straw and organic residues can effectively increase ammonia volatilization. This is consistent with the conclusion of the present study that straw cultivation significantly increased ammonia emission from the soil without fertilizer application. Sun et al. [28] found that ammonia volatilization was enhanced by straw tillage at soil pH < 6, which is consistent with the results of the present study. Currently reported ammonia volatilization losses from straw return vary widely from 5 to 39% [29]. Under consistent levels of straw return and nitrogen application, there were variations in cumulative ammonia emissions between the two years. However, the observed difference was relatively minor, which could likely be attributed to fluctuations in air temperature, rainfall patterns, fertilizer application from the previous crop season, and variations in the soil’s physicochemical properties throughout the two-year monitoring period for ammonia volatilization. These factors contributed to the difference in the data between the two years.
Soil urease can catalyze the hydrolysis of urea to ammonium ions, promote the volatilization of ammonia in the soil, and promote the mineralization of nitrogen. A large number of studies have shown that the return of straw to the field in combination with the application of nitrogen fertilizer can increase the activity of urease in the soil layer [30]. The combination of an appropriate amount of nitrogen fertilizer and straw return measures had a significant effect on soil enzyme activity. This is because straw is rich in organic matter, which can provide a large amount of nutrients to soil micro-organisms, increase their number and activity and, consequently, induce the production and increase the number of soil microbial enzymes. This increase in soil enzyme activity can help promote the decomposition and transformation of soil organic matter and provide nutrients for plant growth. On the other hand, after straw is returned to the field, its fiber tissue can adsorb the water in the soil, which not only promotes the decomposition of the straw, but also makes it easier for it to be decomposed by micro-organisms. At the same time, for microbial activities to provide good conditions, nitrogen fertilizer can be added to supplement the nitrogen needed for microbial activities, thus promoting an increase in the number of micro-organisms and their activity, further promoting soil enzyme activity [31,32]. In this study, at the same level of N application, urease activity was highest at 0–20 cm two weeks after fertilizer application, with the 0–20 cm soil layer urease activity being higher than that of the 20–40 cm layer; the difference between half and full straw return treatments was small, and straw return increased the soil urease activity caused by the additional application of N fertilizer. At the same level of straw return, the urease activity under nitrogen application was significantly higher than that under no nitrogen application, and the difference in urease activity between the 180 kg/hm2 and 225 kg/hm2 application was smaller but significantly higher than that under no nitrogen application. These results indicate that the application of nitrogen fertilizer had a great influence on the urease activity, and straw returned to the field with the appropriate amount of nitrogen fertilizer could increase the urease activity to the optimum level.
Ammonium nitrogen and nitrate nitrogen contents were closely related, and soil ammonium nitrogen was positively correlated with ammonia emissions. In this study, with increasing nitrogen application, soil ammonium nitrogen and nitrate nitrogen contents increased, and the soil ammonia emissions flux, ammonia accumulation, ammonia loss rate, and ammonia emissions coefficient also increased, which is consistent with the results of previous studies [25,33,34]. Straw fixes part of the NO3–N and releases organic acids during its decomposition, which inhibits the conversion of NH4+–N to NO3–N. At the same level of N application, the two methods of straw return to the field (half and full) both increased the ammonium and nitrate nitrogen content in the soil, and the differences between the treatments were small, but all were higher than that in the treatment without straw return to the field. At the same level of straw return, the amount of nitrogen applied had a direct effect on the contents of ammonium nitrogen and nitrate nitrogen in the soil: the higher the nitrogen application level, the higher the content of ammonium nitrogen and nitrate nitrogen in the soil. In this study, the levels of ammonium nitrogen and nitrate nitrogen were lower than those reported in the study of Lv et al. [25], which may be due to the differences in soil and climatic conditions at the experimental sites, resulting in the differences in levels.
Numerous studies have indicated that incorporating straw return into the field alongside nitrogen fertilizer facilitates mitigating nitrogen competition from soil micro-organisms during the straw decomposition process. This practice also promotes dry matter accumulation during the middle and late stages of winter wheat growth [27,35], thereby enhancing crop yields [36]. Fertilizer application can be viable when straw is returned to the field. Nitrogen fertilization under these conditions enhances the green leaf area of wheat, facilitating the accumulation and utilization of photosynthetic products during the late reproductive stage. According to Li et al. [37], the combination of straw return and N application effectively promotes crop yield. Chen et al. [36] and Zhu et al. [38] observed that, although increased nitrogen application did not consistently enhance winter wheat yield under corn stover return conditions, incorporating a certain amount of nitrogen fertilizer alongside stover return promoted wheat productivity. Conversely, straw return has been reported to decrease wheat yields. Li et al. [39] highlighted that inadequate tillage practices during the straw returning process may reduce sowing quality, hinder seedling emergence, and decrease wheat seedling emergence rates, consequently impeding the overall enhancement of wheat yield. Li et al. [40] demonstrated that an appropriate amount of straw return promoted wheat yield and cautioned against excessive straw return, which could decrease wheat productivity. Overall, reasonable nitrogen fertilizer application contributes to enhanced crop yield. The combination of reducing N fertilizer and incorporating peanut straw into wheat fields demonstrated that a 20% reduction in N fertilizer alongside straw incorporation during the wheat season resulted in increased wheat yield, enhanced N fertilizer utilization, and reduced ammonia emissions [41]. This study indicated a significant interaction effect between straw application and N fertilizer, consistent with the findings of Xu et al. [42]. Specifically, when comparing a 20% reduction in nitrogen fertilizer with conventional fertilizer application under both full and half amounts of straw returned to the field, no significant difference in yield was observed. However, returning straw to the field significantly increased the seed yield of winter wheat. Additionally, the practice of straw return to the field increased the inorganic nitrogen content in the soil, consistent with the findings of Lv et al. [25] in the Guanzhong area. The inorganic nitrogen content was lower than that in other studies. This variance may be attributed to the variations in soil and climatic conditions among the experimental sites. Notably, winter wheat yields increased by 2.41–16.19% with straw return alongside N fertilizer application, corroborating findings reported by Chen et al. [36]. In this study, winter wheat yield increased by 2.41–16.19% under equivalent N application levels, surpassing the findings of Li et al. [40]. These differences may result from variations in wheat varieties, sowing densities, and soil conditions. Additionally, the combined application of N fertilizers and straw return demonstrated a propensity to enhance winter wheat yield, biomass, and harvest index. Notably, in this study, we observed increases in yield, effective spike count, 1000-kernel weight, spike kernel count, and aboveground biomass, in contrast with the results of Long et al. [43].
In this study, comparing fertilization treatments between the years 2021–2022 and 2022–2023, without straw return to the field and at application rates of 180 kg/hm2 versus 225 kg/hm2, cumulative ammonia emissions increased by 40.94% and 39.06%, respectively. Correspondingly, the yield increased by 0.83%. Under the condition of semi-returning straw to the field, the increases in cumulative ammonia emissions were 30.95% and 34.49%, with yield increases of 0.1% and 1.12%, respectively. When straw was fully returned to the field, cumulative ammonia emissions increased by 35.88% and 39.05%, whereas yields increased by 0.2% and 0.56%, respectively. Significant differences in cumulative ammonia emissions were observed; however, the impact on the yield increase was not significant.

5. Conclusions

Under the conditions of this study, the treatment with N application at 225 kg/hm2 increased soil ammonia volatilization by 26.63–31.59% when compared to 180 kg/hm2. Straw return to the field enhanced the ammonia volatilization process and increased it by about 7%, compared to the treatment without straw return. On the basis of conventional nitrogen application, a 20% reduction in nitrogen fertilizer (180 kg/hm2), paired with half or full straw return to the field, could supplement the nutrients required during the growth process of winter wheat, thus increasing the thousand grain weight, the number of spikelet, and the number of spikelet per hectare of winter wheat at maturity, ultimately increasing the yield. In this experiment, 20% nitrogen reduction during the winter wheat season combined with semi-straw return was determined as the optimal strategy for reducing ammonia emissions while increasing yield.

Author Contributions

Conceptualization, X.W., Y.X., C.S. and Y.L.; methodology, X.W. and Y.X.; formal analysis, L.Z.; investigation, Z.W. and Y.Z.; data curation, L.Z.; data collection: Y.Z. and L.L.; writing—original draft preparation, X.W., L.Z., Z.W., L.C. and L.L.; supervision, C.S.; funding acquisition, L.L. and Y.L.; final revision of the manuscript, C.S. and Y.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by “Shandong Province Natural Science Foundation Youth Project” (ZR2022QC081), the “Natural science Foundation of Shandong Province” (ZR2022MC148), “Shandong Provincial Key Research and Development Project” (2021LZGC013-6), and “Qingdao industry cultivation plan science and technology benefit the people special” (22-1-3-2-zyyd-nsh).

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 01469 g001
Figure 1. Average daily temperature and rainfall during the ammonia volatilization monitoring period.
Figure 1. Average daily temperature and rainfall during the ammonia volatilization monitoring period.
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Figure 2. Ammonia emissions flux changes in winter wheat from 2021 to 2023 under various straw return and nitrogen application rate treatments. Error bars represent the standard error.
Figure 2. Ammonia emissions flux changes in winter wheat from 2021 to 2023 under various straw return and nitrogen application rate treatments. Error bars represent the standard error.
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Figure 3. Soil water content during the ammonia volatilization periods in 2021–2022 and 2022–2023. Error bars represent the standard error.
Figure 3. Soil water content during the ammonia volatilization periods in 2021–2022 and 2022–2023. Error bars represent the standard error.
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Figure 4. Soil ammonium nitrogen and nitrate nitrogen changes during the ammonia volatilization period in 2021–2022. Error bars represent the standard error.
Figure 4. Soil ammonium nitrogen and nitrate nitrogen changes during the ammonia volatilization period in 2021–2022. Error bars represent the standard error.
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Figure 5. Soil ammonium nitrogen and nitrate nitrogen changes during ammonia volatilization in 2022–2023. Error bars represent the standard error.
Figure 5. Soil ammonium nitrogen and nitrate nitrogen changes during ammonia volatilization in 2022–2023. Error bars represent the standard error.
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Figure 6. Urease activity during ammonia volatilization in 2021–2022 and 2022–2023. Error bars represent the standard error. Different small letters represent significant differences between different treatments (p < 0.05).
Figure 6. Urease activity during ammonia volatilization in 2021–2022 and 2022–2023. Error bars represent the standard error. Different small letters represent significant differences between different treatments (p < 0.05).
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Figure 7. Correlation between ammonia volatilization emissions flux and environmental factors during the ammonia emissions monitoring periods in 2021–2022 and 2022–2023.
Figure 7. Correlation between ammonia volatilization emissions flux and environmental factors during the ammonia emissions monitoring periods in 2021–2022 and 2022–2023.
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Table 1. Basic physicochemical traits of the 0–20 cm soil layer.
Table 1. Basic physicochemical traits of the 0–20 cm soil layer.
TimeTotal N
(g/kg)		Available N
(mg/kg)		Available P
(mg/kg)		Available K
(mg/kg)		Organic Matter
(g/kg)		pH
2021–20221.1896.5832.01148.0113.415.32
2022–20231.3597.4532.18153.714.035.26
Table 2. Experimental treatments of straw return and nitrogen application rates.
Table 2. Experimental treatments of straw return and nitrogen application rates.
AbbreviationsTreatments
S0N0Straw not returned to the field + no N application
S0N1Straw not returned to field + 180 kg N/hm2
S0N2Straw not returned to field + 225 kg N/hm2
S1N0Half of the amount of straw returned to the field + no N application
S1N1Half of the amount of straw returned to the field + 180 kg N/hm2
S1N2Half of the amount of straw returned to the field + 225 kg N/hm2
S2N0Total return of straw to the field + no N application
S2N1Total return of straw to field + 180 kg N/hm2
S2N2Total return of straw to field + 225 kg N/hm2
Table 3. Cumulative ammonia emissions, loss rate, ammonia emissions coefficient, and emissions intensity of winter wheat under varying straw return and nitrogen application rates.
Table 3. Cumulative ammonia emissions, loss rate, ammonia emissions coefficient, and emissions intensity of winter wheat under varying straw return and nitrogen application rates.
TreatmentsCumulative Ammonia Emissions
(kg/hm2)		Loss
Ratio
(%)		Emissions Factor
(%)		Emissions Intensity
(kg/t)
2021–2022
S0N00.384 ± 0.12 d----0.049 e
S0N16.397 ± 0.105 c3.55 d3.34 c0.742 c
S0N29.016 ± 0.35 a4.01 ab3.84 a1.065 a
S1N00.428 ± 0.011 d----0.054 e
S1N16.885 ± 0.069 b3.83 bc3.59 b0.722 c
S1N29.609 ± 0.079 a4.03 a3.84 a0.951 b
S2N00.427 ± 0.01 d----0.053 e
S2N16.823 ± 0.128 b3.79 c3.55 b0.697 d
S2N29.271 ± 0.131 a4.12 a3.93 a0.948 b
strawnsnsns**
nitrogen
fertilization		********
straw × nitrogen fertilizationnsnsns**
2022–2023
S0N00.485 ± 0.04 e----0.07 c
S0N16.419 ± 0.09 d3.3 d3.57 c0.83 b
S0N28.926 ± 0.13 b3.75 b3.97 a1.15 a
S1N00.505 ± 0.03 e----0.07 c
S1N16.737 ± 0.17 cd3.46 c3.74 b0.85 b
S1N29.507 ± 0.22 a4 a4.23 a1.18 a
S2N00.509 ± 0.02 e----0.07 c
S2N16.806 ± 0.13 c3.5 c3.78 b0.85 b
S2N29.464 ± 0.05 a3.98 a4.21 a1.18 a
strawns**ns
nitrogen
fertilization		********
straw × nitrogen fertilizationns**ns
Note: Different lowercase letters represent significant differences between different treatments (p < 0.05); * represents p < 0.05 and ** represents p < 0.01 and indicates significant relationships. ns indicates no significant relationship. The same below.
Table 4. Production and yield composition of winter wheat for each treatment in 2021–2022 and 2022–2023.
Table 4. Production and yield composition of winter wheat for each treatment in 2021–2022 and 2022–2023.
TreatmentsGrain Yield
(t/hm2)		Yield ComponentBiological Yield
(t/hm2)		Harvest
Index
(HI)
(%)
Spike
Number
(×104/hm2)		Kernel Number per Spike1000-Grain Weight
(g)
2021–2022
S0N07.87 c593.36 d36.4 b38.11 a18.3 cd43.05 f
S0N18.40 b633.37 cd37.53 ab38.79 a18.51 bcd45.46 edf
S0N28.47 b673.37 c37.4 ab38.82 a18.16 d46.63 cde
S1N07.96 c695.59 c36.6 b38.14 a18.11 d43.94 df
S1N19.53 a783.00 ab38.4 ab39.48 a19.59 ab48.68 abc
S1N29.54 a797.08 a38.33 ab39.40 a19.95 a47.85 bcd
S2N08.04 c708.92 bc37.4 ab39.36 a18.69 bcd43.03 f
S2N19.76 a812.63 a39.73 a39.52 a19.15 abcd51.18 a
S2N29.78 a833.38 a39.57 a39.92 a19.37 abc50.49 ab
straw*****ns**
nitrogen fertilizer******ns***
straw × nitrogen fertilizer**nsnsnsnsns
2022–2023
S0N07.08 b477.80 c47.44 d38.03 b17.49 a40.53 c
S0N17.75 a558.55 b53.78 a38.48 b17.69 a43.80 a
S0N27.77 a560.33 b50.11 c38.50 b17.97 a43.26 ab
S1N07.26 b480.02 c47.78 d38.40 b17.77 a40.85 bc
S1N17.93 a588.18 a53.89 a40.50 a17.52 a45.29 a
S1N28.02 a582.99 a53.67 b39.18 b17.64 a45.49 a
S2N07.36 b482.25 c49.67 b38.67 b17.79 a41.34 bc
S2N18.00 a571.14 ab54.89 a41.34 a17.77 a45.04 a
S2N28.04 a589.66 a52.00 a41.52 a17.95 a44.85 a
straw*ns***nsns
nitrogen fertilizer************
straw× nitrogen fertilizernsnsns*nsns
Note: Different lowercase letters represent significant differences between different treatments (p < 0.05); * represents p < 0.05 and ** represents p < 0.01 and indicates significant relationships. ns indicates no significant relationship.
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Wan, X.; Zhao, L.; Wang, Z.; Che, L.; Xu, Y.; Zhou, Y.; Shi, C.; Li, L.; Liu, Y. Effects of Straw Return and Nitrogen Application Rates on Soil Ammonia Volatilization and Yield of Winter Wheat. Agronomy 2024, 14, 1469. https://doi.org/10.3390/agronomy14071469

AMA Style

Wan X, Zhao L, Wang Z, Che L, Xu Y, Zhou Y, Shi C, Li L, Liu Y. Effects of Straw Return and Nitrogen Application Rates on Soil Ammonia Volatilization and Yield of Winter Wheat. Agronomy. 2024; 14(7):1469. https://doi.org/10.3390/agronomy14071469

Chicago/Turabian Style

Wan, Xuejie, Le Zhao, Ziwei Wang, Lin Che, Yadong Xu, Yubo Zhou, Changhai Shi, Lingyan Li, and Yiguo Liu. 2024. "Effects of Straw Return and Nitrogen Application Rates on Soil Ammonia Volatilization and Yield of Winter Wheat" Agronomy 14, no. 7: 1469. https://doi.org/10.3390/agronomy14071469

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