Blending of slow-release N fertilizer and urea improve rainfed maize yield, nitrogen use efficiency while reducing apparent N loss

doi:10.21203/rs.3.rs-4705852/v1

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Research Article

Blending of slow-release N fertilizer and urea improve rainfed maize yield, nitrogen use efficiency while reducing apparent N loss

https://doi.org/10.21203/rs.3.rs-4705852/v1

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Background and Aims

Effective nitrogen (N) management practices are essential for achieving efficient and sustainable agricultural production. The purpose of this study was to improve N use efficiency (NUE) and minimize N loss by optimizing the rate and type of N fertilizer application, while maintaining high yield of maize.

Methods

A two-year field experiment with U (urea), S (slow-release N fertilizer), and SU (Blending of S and U) under four N application levels (N1: 90 kg ha^-1, N2: 120 kg ha^-1, N3: 180 kg ha^-1, N4: 240 kg ha^-1) was conducted to investigate their effects on ammonia (NH₃) volatilization, residual soil nitrate N (NO₃⁻-N), yield, NUE, apparent N loss of rainfed maize.

Results

NH₃ volatilization in SU and S were 38.46% and 16.57% lower than that in U, respectively. SU and S were found to reduce the apparent N loss by 42.98% and 62.23%. SU decreased NO₃⁻-N leaching in deep soil, and increased NO₃⁻-N content in topsoil. Compared with U and S, SU significantly increased yield, plant N accumulation and NUE. SUN4 achieved the maximum maize yield and plant N accumulation, averaging 7968.36 kg ha^-1 and 166.45 kg ha^-1. In addition, mixing ratio of U and S was 53%-58%, which was the best ratio for high yield and NUE. Meanwhile, N fertilization with 150-220 kg ha^-1 can keep high yield and NUE.

Conclusion

The findings highlight SU effectively reduced N application rate and was an optimized N fertilization strategy for high yield and N efficient utilization of rainfed maize.

N fertilizer type

Grain yield

Apparent N loss

Ammonia volatilization

N use efficiency

Nitrogen (N) is a crucial nutrient for crop growth and yield (Savin et al., 2019; Qi et al., 2021). The application of N fertilizer has been reported to enhance crops yield by 30–50% (Li et al., 2021a). From 2010 to 2050, the global demand of human for food is projected to increase by 30%-62% (Dijk et al., 2021). The growing demand for food has in turn forced the large-scale use of N fertilizer in agricultural production. However, excessive N fertilization can lead to decreased nitrogen use efficiency (NUE) (Chen et al., 2020), and adversely affect soil, water, and atmosphere through pathways such as leaching and ammonia volatilization, resulting in agricultural non-point source pollution (Shi et al., 2023; Zhang et al., 2023).

Agricultural ammonia (NH₃) emissions account for 80%-90% of total anthropogenic NH₃ emissions (Li et al., 2018; Tian et al., 2021). A large amount of NH₃ volatilization can exacerbate soil acidification and surface water eutrophication, and lead to increased sedimentary N (Sun et al., 2020). Moreover, nitrate (NO₃⁻-N) leaching and runoff from agricultural fields can cause groundwater contamination and elevate nitrate contents in surface water, ultimately leading to serious water pollution (Wang and Li, 2019). Therefore, improving NUE, reducing N losses, and maintaining yield levels by optimizing N management practices are essential for achieving efficient and sustainable agricultural production.

Slow-release N fertilizers (S) have been applied in the production of maize, rice, and wheat as an alternative to urea for optimized N fertilizer management (Li et al., 2020d; Wang et al., 2023). Compared with urea, slow-release N fertilizer can improve maize yield and NUE, and reduce N losses such as NH₃ volatilization and residual soil NO₃⁻-N under the same N application rate (Tian et al., 2021; Zhang et al., 2021). However, slow-release N fertilizers were expensive and difficult to promote in large quantities (Suman et al., 2023). In addition, the release characteristics of slow-release N fertilizers were susceptible to environmental factors such as temperature and rainfall. Under dry or cool conditions, the release rate of N from slow-release N fertilizers was slower after fertilizer application (within 30 days), which cannot meet the demand of N at the early growth stage of crop (Guo et al., 2017). Nutrient deficiencies at the early growth stage will hinder vegetative growth of crops, and reduce the production of photosynthesis products, thus reducing crop yield (Xie et al., 2019). Therefore, some researchers have suggested blending slow-release N fertilizer with urea (SU) to reduce fertilizer costs, improve economic efficiency, and solve the problem of N slow release of S at the early growth stage of crops (Qu et al., 2020; Andrade et al., 2021). SU can minimize N losses while meeting the N demand of crops, thereby increasing crop N uptake and grain yield (Li et al., 2020b; Zhang et al., 2023). Meanwhile, SU can also increase NO₃⁻-N content in soil tillage and reduce NO₃⁻-N content in deeper soils, thus reducing the risk of N leaching (Garcia et al., 2018; Zhang et al., 2021). At the same time, SU can minimize the volatilization of soil NH₄⁺-N (Yuan et al., 2023; Zhang et al., 2023). In addition, SU can also reduce labor costs and fertilizer costs, save manpower and time compared with multiple topdressing of N fertilizer (Li et al., 2020b). Currently, SU was widely used in agricultural production in China and other countries (Guo et al., 2017; Ghafoor et al., 2021). Previous studies indicated that the optimal blending ratio of S and U in northern China was 70% when the N application rate was 180 kg ha^− 1 for maize cultivation (Garcia et al., 2018; Li et al., 2020a). However, the release characteristics of slow-release N fertilizer vary with the external environment. Currently, the precise range of SU and N application rate for rainfed maize in Northwest China is unclear. Therefore, it is very important to calculate the optimal blending ratio of SU, and N application rate by multivariate nonlinear regression analysis for the high yield and efficient N utilization of rainfed maize in Northwest China.

Rainfed farming is a typical farming practice in Northwest China (Li et al., 2020b), and blending slow-release N fertilizer with urea was a promising fertilization measure, which can replace the traditional one-time base application or multiple topdressing fertilizer to increase yield in Northwest China. However, few studies have explored the blending of slow-release N fertilizers with urea as a way to reduce N losses and increase yields. In addition, annual precipitation in this region is generally small and unevenly distributed, and there are few studies on the blending ratio range and N application rate for increasing grain yield and reducing N losses. Therefore, we conducted a two-year field experiment in the Guanzhong Plain of Northwest China to analyze the dynamics of NH₃ volatilization, NH₃ accumulation, distribution of NO₃⁻-N, apparent N loss in soil-plant systems, grain yield, and NUE under different N application rates and different blending ratios of S and U (S, U, and S: U = 7:3). The objectives of this study were to (1) investigate the effect on grain yield, NUE, and apparent N loss in rainfed maize fields in Northwest China under different N fertilizer types and different N application rates; (2) explore the precise blending ratio range of SU and N application rate for simultaneously increasing maize grain yield, reducing N loss in different ways and improving NUE; and (3) to achieve efficient, clean and sustainable production of rainfed maize in Northwest China, while ensuring China's food security.

2.1. Experimental site description

The field experiments were conducted in 2019 and 2020 at the Water-saving Station of the Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas of the Ministry of Education, Northwest A&F University, Yangling, China (34° 20′ N, 108° 24′ E). The altitude of the test station is 524.7 m, the average temperature is 12.9℃, and the average annual rainfall is 632 mm, which is mainly concentrated in the months of July, August, and September (accounting for 55.5% of the whole year), the average annual evaporation is 1,500 mm, the average annual sunshine hours was 2,163.8 h, and the annual frost-free period is 221 d. This area is characterized by a warm temperate monsoon semi-humid climate, and it is a typical semi-humid drought-prone area. The soil texture in the 0–20 cm soil layer was medium loam (according to the United States Department of Agriculture Soil Classification). Soil properties were shown in Table 1. Automatic weather stations were used to record climatic variables for the two growing seasons of summer maize, 2019 and 2020 (Fig. 1).

Table 1

Basic soil properties of the 0–20 cm soil layer at the experimental site.
Soil property	Value
Bulk density	1.44 g cm^− 3
pH	8.14
Field capacity soil moisture	0.33 m³ m^− 3
Wilting point soil moisture(θ_w)	0.085
Soil organic carbon	12.02 g kg^− 1
Total nitrogen	0.93 g kg^− 1
Total phosphorus	0.84 g kg^− 1
Total potassium	20.33 g kg^− 1
Available phosphorus	21.42 mg kg^− 1
Available potassium	133.75 mg kg^− 1

2.2. Experimental design

The experiment was conducted in a two-factor completely randomized design with three types of N fertilizers (U: urea, S: slow-release N fertilizers, and SU: slow-release N fertilizers blended with urea at a ratio of 7:3) applied at four N application levels (N1: 90 kg ha^− 1, N2: 120 kg ha^− 1, N3: 180 kg ha^− 1, and N4: 240 kg ha^− 1). No N application (N0) was used as the control treatment (CK), a total of 13 treatments. Each treatment was replicated in three groups, arranged in randomized blocks (positioning design), and each plot was designed to cover an area of 21 m², including 5 rows, each 7 m long, with a 0.5 m wide isolation zone adjacent to the experimental area, and planted at a density of 55,000 plants ha^− 1, with a row spacing of 60 cm and a plant spacing of 30 cm. The maize variety for the experiment was the main variety (Zea mays L. cv. Zhengdan 958) of maize planted in Northwest China.

N fertilizers used in the experiment were urea (N ≥ 46%, 30% basal application, 70% topdressing at the jointing stage) and Stanley slow-release N fertilizer (N ≥ 29%, cumulative release period of three months, Fei Mu Ping Guo Commercial and Trading Co., Ltd., Shandong Province, China, pre-sowing basal application). SU and S were applied as basal fertilizer. For the U, 30% of the urea was applied before planting, while the remaining 70% was applied at the jointing stage. The phosphate fertilizer used in the experiment was calcium superphosphate (P₂O₅ ≥ 16%, Yunnan Yuxi Chemical Fertilizer Factory Co., Ltd.), and the potassium fertilizer was potassium sulfate (K₂O ≥ 50%, Russian Import Trading Company). The basal application rates of P₂O₅ and K₂O were 120 kg ha^− 1 and 100 kg ha^− 1, respectively. All treatments were planted in rainfed dry farming and crop management was consistent with local farm management practices.

2.3. Sampling and Measurements

2.3.1. NH₃ volatilization

The sponge absorption ventilation method was used as the measurement method (Xu et al., 2012). The measurement device was made of a polyvinyl chloride rigid plastic tube (inner diameter 15 cm, height 12 cm) and vertically inserted into the soil at a depth of 2 cm. During the measurement, two sponge pieces, each with a thickness of 2 cm and a diameter of 16 cm, uniformly soaked with 15 mL of glycerol phosphate solution (50 mL of phosphoric acid + 40 mL of glycerol, made up to 1000 mL with water), were placed inside plastic tubes. The lower sponge was 5 cm above the ground to absorb volatilized NH₃ from the soil, and the upper sponge was placed flush with the top of the tube to insulate it from the air. A top cover was placed over the top 30 cm of the device to avoid interference from rainfall. Three devices were placed at different locations in each plot.

From the first day after fertilization to the end of the experiment, the lower sponges were collected at 8:00 a.m. every day, numbered and sealed, and placed into 500 mL conical flasks, then 300 mL of 1.0 mol/L KCl solution was added until the sponges were completely immersed and oscillated for 1 h. NH₄⁺-N in the leachate was determined using a continuous flow analyzer (Seal AA3). Soil NH₃ volatilization was calculated as:

$$N{H_3} - N\left( {kg h{m^{ - 2}} {d^{ - 1}}} \right)={\raise0.7ex\hbox{$M$} \!\mathord{\left/ {\vphantom {M {A \times D}}}\right.\kern-0pt}\!\lower0.7ex\hbox{${A \times D}$}} \times {10^{ - 2}}$$

where M is the average amount of NH₃ per measurement from a single device (NH₃-N, mg); A is the cross-sectional area of the capture device (m²); and D is the time of each capture (d).

2.3.2. Soil nitrate nitrogen

After the harvest of summer maize each year, soil samples were collected at 20 cm intervals from a soil depth of 0-120 cm using a soil auger. A fresh soil sample of 5.0 g was weighed into a 150 mL conical flask, then 50 mL of 2 mol/L KCl solution was added, and the mixture was oscillated for 1 hour before being left to settle and filtered. The NO₃⁻-N content in the filtrate was determined using a flow analyzer (AutoAnalyzer-III, Bran + Luebbe, Germany). Residual soil NO₃⁻-N (kg ha^− 1) in the soil profile was considered to be the sum of the total storage in all sampled layers within the plot and was calculated using the following formula (Zheng et al., 2020):

$$NO_{3}^{ - } - N\left( {kg h{a^{ - 1}}} \right)=h \times {\rho _b} \times p \times 10/100$$

where h is the soil depth (cm), ρ_b is the soil bulk weight (g cm^− 3), and p is the soil NO₃⁻-N content (mg kg^− 1).

2.3.3. Plant dry matter and grain yield

Five representative plants from each treatment were selected for destructive sampling at the seedling, jointing, silking, filling, and maturity stage. The plant samples were placed in an oven at 105℃ for 30 min and then baked at 70℃ until constant weight. At the maturity stage of maize, all the maize in each plot was harvested for yield determination, then air-dried, threshed, and weighed to determine the standard yield of maize grain at 14% moisture content (Tsimba et al., 2013).

2.3.4. Plant N accumulation and use efficiency

Calculation of total N content by Kjeldahl method (Bremner and Mulvaney, 1983). At the maturity stage of summer maize, five plants were selected for destructive sampling in each treatment. The samples were put into an oven at 105°C for 30 minutes and then dried at 70°C to a constant weight. After grinding and sieving through a 0.5 mm mesh, the sieved samples were digested with an H₂SO₄-H₂O₂ solution to prepare the test liquid. The plant N content was determined by automatic Kjeldahl N apparatus (FOSS 2300). The calculation formulas for plant nitrogen use efficiency and nitrogen accumulation were as follows:

$$Plant{\text{ }}N{\text{ }}accumulation\left( {kg{\text{ }}h{a^{ - 1}}} \right)=N{\text{ }}uptake\left( {kg{\text{ }}h{a^{ - 1}}} \right)={D_m} \times C$$

$$NUE(kg k{g^{ - 1}})={{{\text{Grain yield}}} \mathord{\left/ {\vphantom {{{\text{Grain yield}}} {{\text{Total N uptake}}}}} \right. \kern-0pt} {{\text{Total N uptake}}}}$$

where D_m is the plant dry matter weight (kg ha^− 1) and C is the plant N content (%).

2.3.5. Apparent N loss

Apparent N loss is determined by the difference between N input and N output (Guo et al., 2017). The calculation formula for apparent N loss was as follows:

$${N_{{\text{mineralization}}}}={\text{soil }}{{\text{N}}_{{\text{min0}}}}{\text{(at harvest)+crop }}{{\text{N}}_{\text{0}}}{\text{ uptake-soil }}{{\text{N}}_{{\text{min}}}}{\text{(initial)}}$$

$$Apparent N loss={\text{soil }}{{\text{N}}_{{\text{min}}}}{\text{(initial)+}}{{\text{N}}_{{\text{mineralization}}}}{\text{+}}{{\text{N}}_{{\text{fer}}}}{\text{-soil }}{{\text{N}}_{{\text{min}}}}{\text{(at harvest)-crop N uptake}}$$

$$Apparent{\text{ }}N{\text{ }}loss efficiency={{{\text{Apparent N loss}}} \mathord{\left/ {\vphantom {{{\text{Apparent N loss}}} {{\text{Total N uptake}}}}} \right. \kern-0pt} {{\text{Total N uptake}}}}$$

where N_{mineralization} is the apparent N mineralization during the maize growing season in the 0-120 cm soil layer in the plots (kg ha^− 1), soil N_min (initial) is the initial soil N_min (NH₄⁺-N + NO₃⁻-N) in the 0-120 cm soil layer in the plots (kg ha^− 1), crop N0 uptake is the crop N uptake in the 0-120 cm soil layer in the 0 N control plots (kg ha^− 1), soil N_min0 (at harvest) is the residual soil N_min in the 0-120 cm soil layer in the 0 N control plots (kg ha^− 1), soil N_min (at harvest) is the residual soil N_min in the 0-120 cm soil layer in the plots (kg ha^− 1), N_fer is the N application level (kg ha^− 1).

2.4. Statistical analysis

ANOVA was conducted using the SPSS software for analysis of variance. The primary effects include year, type of N fertilizer, and rate of N fertilization with bi- and tri-variate interactions included. Least Significant Difference (LSD) was employed to examine the difference among all treatments at a significance level (p = 0.05). GAUSS2D and LORENTZ2D models were used to establish binary quadratic regression equations between yield and NUE with N application rates and blending ratios. MATLAB software and RStudio software were used to determine the optimum values of yield and NUE and the recommended ranges of N application rates and blending ratios of slow-release nitrogen fertilizer with urea. The Origin 2021 software was used to draw figures.

3.1. Dynamics of NH₃ volatilization

During summer maize growing seasons in both 2019 and 2020, NH₃ volatilization flux was significantly different under three N fertilizer types and four N application rates (Fig. 2a, b, c, d, e, f, g, h). Daily NH₃ volatilization fluxes in U peaked within three or five days after both basal fertilization and topdressing application, then subsequently decreased and remained low over the two growing seasons. Similarly, daily NH₃ volatilization fluxes in SU peaked three or five days after basal fertilization and at the jointing stage of summer maize both in 2019 and 2020, and then declined and remained at a low level. However, daily NH₃ volatilization fluxes in S showed a gradual increase after basal fertilization, and reached the peak values at the jointing stage, then declined and remained at the background levels during the two growing seasons. Daily NH₃ volatilization fluxes increased with increasing N application under all treatments. The maximum values of daily NH₃ volatilization fluxes in U, S, SU under N4 were increased by 34.87%-120.56%, 12.93%-127.52%, 46.87%-116.74% in 2019 and 49.05%-101.88%, 25.32%-78.15%, 36.08%-89.80% in 2020 compared with other N application rates, respectively. In 2020, the highest daily NH₃ volatilization fluxes in U and SU were 2.81%-13.00% and 17.28%-33.92% higher than that in 2019, respectively. However, the highest daily NH₃ volatilization fluxes in S in 2019 were 4.63%-48.28% higher than that in 2020. For various N fertilizer types, the peak values of daily NH₃ volatilization fluxes followed the order of U > SU > S after basal fertilization and followed the order of U > S > SU after topdressing application. Daily NH₃ volatilization fluxes in U reached the peak values were 1.64 kg ha^− 1 d^− 1 (2019) and 1.76 kg ha^− 1 d^− 1 (2020) after basal fertilization, which were 0.08%-29.64% (2019) and 7.07%-22.97% (2020) greater than that in SU and S. Moreover, daily NH₃ volatilization fluxes in U also reached the peak values were 5.77 kg ha^− 1 d^− 1 (2019) and 5.89 kg ha^− 1 d^− 1 (2020) after topdressing application in both 2019 and 2020, which were 68.75%-290.52% (2019) and 125.06%-188.73% (2020) greater than that in SU and S. Daily NH₃ volatilization fluxes in UN4 achieved the highest values were 8.31 kg ha^− 1 d^− 1 (2019) and 8.60 kg ha^− 1 d^− 1 (2020), which were 79.60%-238.00% (2019) and 148.20%-198.10% (2020) greater than that in other treatments, respectively.

During the two growing seasons of summer maize, cumulative NH₃ volatilization was significantly increased with increasing N application rate (Fig. 2i, j). Cumulative NH₃ volatilization in U, S, SU under N4 was increased by 48.58%-110.38%, 36.25%-92.28%, 58.44%-142.94% in 2019 and 32.85%-98.82%, 27.52%-79.16%, 37.83%-101.21% in 2020 compared with other N application rates, respectively. In 2020, the cumulative NH₃ volatilization was 3.35%-24.95% greater than that in 2019. For various N fertilizer types, cumulative NH₃ volatilization followed the order of U > S > SU. The cumulative NH₃ volatilization under UN4 achieved the highest value was 45.62 kg ha^− 1 in 2019 and 47.15 kg ha^− 1 in 2020, which was 29.05%-273.17% and 25.77%-208.67% greater than that in other treatments. Compared with U and S, SU significantly reduced the cumulative NH₃ volatilization.

3.2. Residual soil NO₃⁻-N

The residual soil NO₃⁻-N in the soil profile (0-120 cm) after maize harvest increased with increasing N application rate (Fig. 3a, b). For various N application rates, residual soil NO₃⁻-N under N4 in U, S, SU was increased by 16.14%-52.90%, 17.40%-53.08%, 19.51%-35.60% in 2019 and 12.53%-52.51%, 13.86%-53.32%, 23.30%-52.07% in 2020 compared with other N application rates, respectively. The residual soil NO₃⁻-N under U in 2019 was 10.78%-14.68% higher than that in 2020. However, the residual soil NO₃⁻-N under S in 2019 was 7.37%-13.03% less than that in 2020. For the SU, the residual soil NO₃⁻-N in 2019 was 0.82%-9.59% higher than that in 2020 under N1, N2, and N3. However, the residual soil NO₃⁻-N under SUN4 in 2019 decreased by 2.28% compared with that in 2020. In 2019, the residual soil NO₃⁻-N followed the order of U > S > SU > CK under N1, N3, and N4, and S > U > SU > CK under N2 (Fig. 3a). In 2020, the residual soil NO₃⁻-N followed the order of S > U > SU > CK under N1, N2, N3, and N4 (Fig. 3b). Compared with U, the residual soil NO₃⁻-N in SU (124.93 kg ha^− 1 in 2019 and 121.83 kg ha^− 1 in 2020) was decreased by 11.74% and 3.59%, respectively. Additionally, the residual soil NO₃⁻-N in U was 0.63% greater than that under S in 2019, but 19.92% less than that under S in 2020. In 2019 the residual soil NO₃⁻-N achieved a maximum value of 175.09 kg ha^− 1 in UN4, which was 2.18%-60.03% higher than those in the other treatments. However, in 2020, the residual soil NO₃⁻-N achieved a maximum value of 191.07 kg ha^− 1 in SN4, which was 13.86%-91.39% higher than those in other treatments.

In both 2019 and 2020, the NO₃⁻-N content in the 0-120 cm soil layer first decreased and then increased with the increasing soil depth (Fig. 3c, d, e, f, g, h). The distribution of soil NO₃⁻-N in U was mainly concentrated in the 60–120 cm soil layer, while the distribution of soil NO₃⁻-N in S was mainly concentrated in the 0–40 cm soil layer. In the 0-120 cm soil layer, the change of soil NO₃⁻-N content in SU was relatively smooth. Under N1, N2, N3, and N4, the soil NO₃⁻-N content under SU in the 0–40 cm soil layer was decreased by 13.52%-26.36% (2019) and 11.02%-22.78% (2020) compared with S, and increased by 25.96%-33.34% (2019) and 18.21%-58.88 (2020) relative to those in U. In the 60–120 cm soil layer, the soil NO₃⁻-N content under U was increased by 22.92%-54.09% (2019) and 7.81%-22.25% (2020) compared with S, and increased by 23.27%-39.78% (2019) and 17.99%-31.51% (2020) relative to those in SU.

3.3. Dry matter accumulation

Nitrogen applications significantly promoted the increase of summer maize dry matter (Fig. 4). At the seeding stage, the dry matter accumulation of maize followed the order of SU > U > S > CK under various N fertilizer types, in 2020. At the jointing stage, dry matter accumulation in 2019 followed the order of U > SU > S under N1 and N2, and SU > U > S under N3 and N4. In 2020, the dry matter accumulation followed the order of U > SU > S among all N application rates. At the silking stage, dry matter accumulation followed the order of SU > S > U in both 2019 and 2020 among various N application types. At the filling and the maturity stage of summer maize in 2019 and 2020, the dry matter accumulation followed the order of SU > S > U. The dry matter accumulation of the N fertilization at the maturity stage of summer maize in 2019 and 2020 increased by 23.03% -64.41% (2019) and 16.05%-73.63% (2020) compared with CK. For various N application rates, dry matter accumulation consistently increased with the increasing N application rate in both 2019 and 2020. The dry matter accumulation at the maturity stage of summer maize in U, S, SU under N4 was increased by 21.59%-33.63%, 7.43%-16.80%, 8.96%-16.74% in 2019 and 5.15%-28.83%, 6.73%-28.83%, 5.96%-22.17% in 2020 compared with other N application rates, respectively. The dry matter accumulation at the maturity stage of summer maize under U in 2019 was 2.53%-14.30% greater than that in 2020. For the SU, the dry matter accumulation at the maturity stage of summer maize in 2019 was 0.07%-6.84% greater than that in 2020 under N1, N2, and N4. However, the dry matter accumulation in S at the maturity stage of summer maize in 2019 was 1.42%-3.06% less than that in 2020 under N2, N3, and N4. Dry matter accumulation in SUN4 reached the highest value of 17,375.66 kg ha^− 1 (2019) and 17,019.99 kg ha^− 1 (2020), which were 8.22%-25.17% (2019) and 5.62%-33.16% (2020) greater than that in other treatments, respectively.

3.4. Plant N accumulation

Plant N accumulation at the maturity stage of summer maize increased with increasing N application rate (Fig. 5). Plant N accumulation in U, S, SU under N4 was increased by 10.34%-41.45%, 8.83%-32.10%, 11.67%-33.29% in 2019 and 8.59%-51.51%, 8.38%-41.21%, 9.87%-39.90% in 2020 compared with other N application rates, respectively. Plant N accumulation of summer maize in 2019 was greater than that in 2020. The plant N accumulation of summer maize followed the order of SU > S > U > CK in both 2019 and 2020. Compared with S and U, the plant N accumulation in SU was increased by an average of 9.71% and 30.37% in 2019, and 10.95% and 36.16% in 2020, respectively. Plant N accumulation in SUN4 reached the maximum value of 164.60 kg ha^− 1 (2019) and 168.30 kg ha^− 1 (2020), which was 11.04% and 28.47% in 2019, and 11.17% and 34.53% in 2020 higher than that in SN4 and UN4, respectively.

Figure 5 Plant N accumulation of summer maize at the maturity stage of maize under different N application rates and N application types in 2019 and 2020. (a) Plant N accumulation at the maturity stage of maize in 2019. (b) Plant N accumulation at the maturity stage of maize in 2020. CK is no N application. U is urea. S is slow-release N fertilizer. SU is urea blended with slow-release N fertilizer at ratios of 3:7. Different letters indicate significance at the 5% level for the same year by LSD test. Error bars are ± 1 standard deviation of the mean (n = 3). Vertical bars indicate LSD values at the p = 0.05 level

3.5. Apparent N losses

The Apparent N loss of the various treatments was shown (Table 2). During the summer maize growing season, N_{mineralization} in 2020 was 41.12 kg ha^− 1, which was 18.91% greater than that in 2019. In both 2019 and 2020, N uptake and apparent N loss in the N fertilization treatments were significantly (p < 0.05) higher than those in CK. Crop N uptake varied with N application types and rates. Crop N uptake was increased by an average of 23.99% and 31.95% when N application rates were increased from N1 to N4 in 2019 and 2020, respectively. Crop N uptake under SU and S took up an average of 30.37% and 18.83% more than U in 2019, with 36.16% and 22.70% more than U in 2020. The amount of N loss in maize fields was 10.66 kg ha^− 1~90.39 kg ha^− 1 in 2019 and 5.45 kg ha^− 1~109.50 kg ha^− 1 in 2020, respectively. The N loss accounted for about 2.29%-28.27% of total N input. The apparent N loss increased with the increasing N application rate. Compared with other N application rates, N4 increased apparent N losses by 29.93%-653.34% in 2019 and 31.77%-723.05% in 2020, respectively. The apparent N losses under U in 2019 were 12.64%-29.46% less than that in 2020. However, the apparent N losses under S in 2019 were 65.13%-288.75% higher than that in 2020. For the SU, the apparent N loss in 2019 was 8.87%-21.79% higher than those in 2020 under N2, N3, and N4. Under the same N application rate, the apparent N loss followed the order of U > SU > S in both 2019 and 2020. Apparent N loss in UN4 obtained the highest value was 90.39 kg ha^− 1 in 2019 and 109.50 kg ha^− 1 in 2020, which were 12.08%-748.33% in 2019 and 43.33%-1911.02% in 2020 greater than that in other treatments.

The apparent N loss efficiency first decreased and then increased with the increase of N fertilizer application rate in both 2019 and 2020. The interannual trend in apparent N loss efficiency was the same as the interannual trend in apparent N loss. At the same N application rate, the apparent N loss efficiencies of the treatments followed the order of U > SU > S in both years, except for SN1 in 2019. As for apparent N loss efficiency, apparent N loss efficiency for all treatments was less than 30%.

Table 2

Apparent N loss under different N application rates and N application types in 2019 and 2020.
Nitrogen fertilizer types	N_fer (kg ha^− 1)	Soil N_min (at harvest) (kg ha^− 1)		Crop N uptake (kg ha^− 1)		Soil N_min (initial) (kg ha^− 1)		N_{minneralization} (kg ha^− 1)		Apparent N loss (kg ha^− 1)		Apparent N loss efficiency (%)
Nitrogen fertilizer types	N_fer (kg ha^− 1)	2019	2020	2019	2020	2019	2020	2019	2020	2019	2020	2019	2020
CK	0	81.92g	81.62h	71.68h	65.66h	119.02	106.15	34.58	41.12	0.00g	0.00f	0.00d	0.00gh
U	90	114.52ef	100.11g	90.58g	82.57g					38.51cdef	54.59cd	15.74ab	23.00b
	120	130.26cde	117.58ef	105.96f	104.88f					37.39def	44.81d	13.57abc	16.76c
	180	150.75b	135.67d	116.12e	115.21e					66.74abcd	76.40b	19.91a	23.33b
	240	175.09a	152.67c	128.13d	125.10d					90.39a	109.50a	22.88a	28.27a
S	90	111.94f	124.62e	112.22ef	107.21f					19.45efg	5.45ef	7.88bcd	2.29fg
	120	137.47bcd	148.41c	125.48d	124.51d					10.66fg	-5.65f	3.86cd	-2.10h
	180	145.95bc	167.80b	136.21c	139.68c					51.45bcde	19.79e	15.38ab	6.05ef
	240	171.36a	191.07a	148.24b	151.39b					74.01abc	44.82d	18.78a	11.58d
SU	90	109.41f	99.84g	123.49d	120.30de					10.71fg	17.14e	4.34cd	7.22e
	120	117.81ef	112.56f	137.47c	137.88c					18.33efg	16.84e	6.59bcd	6.30ef
	180	124.14def	123.12ef	147.40b	153.18b					62.07abcd	50.97d	18.53a	15.57cd
	240	148.36b	151.81c	164.60a	168.30a					80.65ab	67.16bc	20.42a	17.33c
Notes: CK is no N application. U is urea. S is slow-release N fertilizer. SU is urea blended with slow-release N fertilizer at ratios of 3:7. N_fer is the N application level (kg ha^− 1). Soil N_min (at harvest) is the residual soil N_min in the 0-120 cm soil layer in the plots (kg ha^− 1). Soil N_min (initial) is the initial soil N_min (NH₄⁺-N + NO₃⁻-N) in the 0-120 cm soil layer in the plots (kg ha^− 1). N_{mineralization} is the apparent N mineralization during the maize growing season in the 0-120 cm soil layer in the plots (kg ha^− 1). Different alphabets indicate the significance within the same year at 5% level by LSD test

3.6. Grain yield and NUE

Maize grain yield increased with increasing N application rate in both 2019 and 2020 (Fig. 6a, b). Grain yield in UN4, SN4, and SUN4 was 7.75%-31.68%, 7.45%-27.68%, and 8.98%-27.99% greater than that of other treatments in 2019, and was 5.92%-34.91%, 6.03%-29.64%, and 3.73%-28.98% greater than that of other treatments in 2020. Grain yield in 2019 was greater than that in 2020 among U, S, and SU. Grain yield ranged from 4488.47 kg ha^− 1 to 8118.72 kg ha^− 1 in 2019 and from 4042.23 kg ha^− 1 to 7818.00 kg ha^− 1 in 2020. Regarding various N fertilizer types, the grain yield followed the order of SU > S > U > CK in both 2019 and 2020. The grain yield under SUN4 reached the maximum values of 118.72 kg ha^− 1 in 2019 and 7818.00 kg ha^− 1 in 2020, which were 8.98%-80.88% and 3.73%-93.41% higher than that in other treatments, respectively.

NUE decreased with increasing N application rate in both 2019 and 2020 (Fig. 6c, d). NUE in UN4, SN4, and SUN4 was 2.45%-4.63%, 1.09%-5.19%, 4.30%-6.14% in 2019 and 1.90%-9.07%, 1.98%-7.97%, 8.75%-11.72% in 2020 less than that of other N application rate. NUE under U, S, and SU in 2019 were 4.69%-10.42% (U), 6.51%-13.26% (S), and 2.79%-9.29% (SU) greater than that in 2020. For various N fertilizer types, NUE followed the order of SU > S > U > CK. Compared with S and U, NUE in SU increased by 15.66% and 24.48%in 2019, and 22.34% and 30.42% in 2020, respectively.

3.7. Relationships between N application rate, blending ratio of SU, and grain yield/NUE

The relationship between N application rates, blending ratio of SU with summer maize grain yield/NUE was shown in Fig. 7. The binary quadratic regression equation was established between N application rates, blending ratio of SU with grain yield/NUE (Table 3). The correlation coefficients (R²) between the N application rates, blending ratio of SU with grain/NUE were all above 0.95.

In 2019, when the N application rate was 240 kg ha^− 1 and the blending rate of SU was 58.35%, the grain yield of summer maize reached the highest value of 8123.59 kg ha^− 1. However, when the N application rate was 90 kg ha^− 1 and the blending ratio of SU was 55.56%, the NUE reached the highest value of 51.34 kg kg^− 1. In 2020, the maximum value of grain yield (7940.10 kg ha^− 1) was achieved under the N application rate was 235 kg ha^− 1 and the blending rate of SU was 57.58%, while the maximum value of NUE (51.70 kg kg^− 1) was obtained under the N application rate was 90 kg ha^− 1 and the blending rate of SU was 55.56%. The main purpose of this study was to achieve high yield and improve NUE concurrently under the same N fertilizer application rate and blending ratio of SU. Therefore, it was necessary to jointly solve the established regression equations to simultaneously maintain the grain yield and NUE above 90% of the maximum values. The results showed that the grain yield and NUE in 2019 could be maintained at more than 90% of those maximum values when the N application rate was 150–240 kg ha^− 1 and the blending ratio of SU was 51.00%-65.00%. In 2020, grain yield and NUE could be maintained at more than 90% of those maximum values, when the N fertilizer application rate was 140–220 kg ha^− 1, and the blending ratio of SU was 53.00%-58.00%. In conclusion, combining the results of the two-year experiment, the N fertilizer application rate was 150–220 kg ha^− 1 and the blending ratio of SU was 53.00%-58.00% could achieve high grain yield (7146.09 kg ha^− 1) of summer maize and improve NUE (46.20 kg kg^− 1) simultaneously, and to maintain their values above 90% of the maximum value under the conditions of this study (Fig. 7; Table 3).

Table 3

Regression equation of grain yield and NUE of summer maize in 2019 and 2020.
Output	Regression equation	R²	Recommended range x (kg ha^− 1) & y (%)
2019			150–240&51.00–65.00
Grain yield/Y₁	Y₁=-4156.52 + 12424.20exp(-0.5((x-297.53)/376.63)²-0.5*((y-0.58)/0.92)²)	0.98
NUE/Y₂	Y₂ = 26.71 + 24.64exp(-0.5((x-79.66)/319.76)²-0.5*((y-0.55)/0.50)²)	0.96
2020			140–220&53.00–58.00
Grain yield/Y₁	Y₁=-3854.42 + 11794.56exp(-0.5((x-234.79)/262.82)²-0.5*((y-0.58)/0.83)²)	0.99
NUE/Y₂	Y₂ = 27.53 + 26.04/((1+((x + 21.32)/399.58)²) *(1+((y-0.55)/0.45)²))	0.95
Notes: x is N application rate. y is blending ratio of slow-release N fertilizer with urea. Recommended range is the value that maintains the grain yield and NUE above 90% of the maximum value under the conditions of this study.

4.1. Effect of N fertilizer types and N application rates on NH₃ volatilization

Previous studies showed that N application rates and N fertilizer types could significantly affect NH₃ volatilization (Huang et al., 2016; Tian et al., 2021). In this study, the NH₃ fluxes and cumulative NH₃ volatilization increased with increasing N application rate, which was consistent with the results of previous studies (Yang et al., 2013a; Tian et al., 2021). This can be attributed to the excessive application of N fertilizer, which could lead to accelerated hydrolysis of N fertilizers (Zheng et al., 2018). Accelerated hydrolysis of N fertilizers can in turn cause N supply to exceed the capacity of crop N uptake, leading to the accumulation of NO₃⁻-N and NH₄⁺-N in soil, and further aggravating NH₃ volatilization and the decline of NUE (Liu et al., 2020a). Daily NH₃ volatilization fluxes under different treatments reached the peak value at 3 or 5 days after fertilization (Fig. 2). This may be due to the rapid increase of NH₄⁺-N content in soil caused by urea hydrolysis, and soil N supply exceeded crop N uptake (Shang et al., 2014; Li et al., 2017). Subsequently, the volatilization of NH₃ gradually decreased and remained at a low level due to N being adsorbed by the soil and continuous uptake by summer maize (Zhang et al., 2011; Shi et al., 2023).

In this study, both S and SU reduced cumulative NH₃ volatilization of summer maize compared with U. This may be due to the fact that urea in slow-release N fertilizer was encapsulated by membranes, which not only impeded the delivery of water needed to dissolve the urea, but also could not in direct contact with the urease in the soil (Liu et al., 2020b). Thus, S and SU had a slower release rate, and a longer period of NH₃ volatilization but less cumulative NH₃ volatilization compared with U (Torralbo et al., 2022). In addition, the N release rates of SU and S were synchronized with the N demand of summer maize, which not only reduced N loss and improved the NUE, but also reduced NH₃ volatilization (Liu et al., 2020a). Moreover, S and SU were applied as base fertilizers to the 15 cm soil layer at one time, which could minimize N loss caused by topdressing in the form of multiple applications on the soil surface. This was due to the fact that NH₄⁺-N produced by the hydrolysis of N fertilizers was more readily absorbed by the soil, thus slowing down the NH₃ volatilization. In this study, the cumulative NH₃ volatilization of SU was 15.98%-33.51% (2019) and 18.02%-29.03% (2020) lesser than that in S. The reason for this result was that SU provided sufficient N at the early growth season compared with S, which can better meet the N demand of maize during the whole growth period and improved crop N uptake and NUE (Guo et al., 2017; Li et al., 2020a). This explained the reason why NUE followed the order of SU > S > U, and NH₃ volatilization followed the order of U > S > SU in this study.

NH₃ volatilization was significantly affected by meteorological conditions, particularly temperature and precipitation (Yang et al., 2013b; Tian et al., 2021; Torralbo et al., 2022). In 2020, the cumulative NH₃ volatilization was 3.35%-24.95% greater than that in 2019. This may be due to the higher precipitation in 2020, which increased the erosion rate of the coating material and accelerated the hydrolysis of N fertilizer, thereby promoting the release of NH₃ into the atmosphere (SanzCobena et al., 2011; Liu et al., 2020b). However, studies have shown that NH₃ volatilization could be limited by high precipitation or frequency and low temperatures (Li et al., 2021b; Li et al., 2017). This was attributed to rainfall accelerating the leakage of N to deep soils, where NH₃ can be reabsorbed before escaping to the atmosphere, thereby alleviating NH₃ volatilization (Espindula et al., 2020; Li et al., 2021b). However, this result was mainly for areas where rainfall was scarce (Li et al., 2021b; Shi et al., 2023). In general, seven days after fertilization was the key period to reduce NH₃ volatilization caused by fertilization (Tian et al., 2021). During this period, it was feasible for farmers to reduce NH₃ volatilization by irrigating after fertilization or applying fertilizer before rain adjacently, using slow-release N fertilizers or blending slow-release N fertilizers and urea, and deep application of fertilizers (Zheng et al., 2018; Zhong et al., 2021).

4.2. Effects of N fertilizer types and N application rates on residual soil NO₃⁻-N

Previous studies showed that excessive application N fertilizer or improper use of N fertilizer types could lead to a large amount of N leaching (Yang et al., 2015; Ma et al., 2023). In this study, residual NO₃⁻-N content in the 0-120 cm soil layer of U, SU, and S increased with increasing N application (Fig. 3), which was consistent with previous research (Wang et al., 2018; Tang et al., 2021). In addition, different N fertilizer types also had significant effects on soil residual NO₃⁻-N content (Ma et al., 2023). In this study, SU significantly reduced the residual soil NO₃⁻-N in the 0-120 cm soil layer compared with U in both 2019 and 2020. This may be attributed to the fact that slow N release rate of SU compared with urea, and avoid the disadvantage of the concentrated release of N in urea, thereby reducing the residual soil NO₃⁻-N (Guo et al., 2017; Wang et al., 2018). However, S only significantly reduced the residual soil NO₃⁻-N in the 0-120 cm soil layer compared with U under N1, N3, and N4 in 2019, which is not consistent with the study of Wang et al., (2021). This may be due to the fact that the easy hydrolysis of urea in S and the strong precipitation in summer, resulting in more soil NO₃⁻-N being leached to the deeper layer below 120 cm (Yu et al., 2019). In this study, under the same N application rate, soil NO₃⁻-N in U was mainly concentrated in the 60–120 cm soil layer, while soil NO₃⁻-N in S and SU was mainly distributed in the 0–40 cm soil layer. This result may be attributed to the N slow-release characteristics of S and SU. On the one hand, the slow release of N was more in line with crop N uptake, which could not cause a large amount of N to accumulate in the soil and increase the risk of leaching to the deep soils (Ghafoor et al., 2021). On the other hand, maize roots were mainly distributed in the 0–40 cm soil layer, and absorbed soil NO₃⁻-N in the 0–40 cm soil layer. S and SU were conducive to the growth and development of maize roots, and also reduced the migration of soil NO₃⁻-N to deep soils (Tian et al., 2018). These findings were consistent with the results of Shi et al. (2023), who reported that slow-release N fertilizer or blended slow-release N fertilizer with urea reduces the residual amount of NO₃⁻-N in the deep soil layer compared with traditional urea while increasing NO₃⁻-N content in 0–40 cm soil layer. In addition, the interannual variation of rainfall amount and distribution during the summer maize growth season has a great influence on soil NO₃⁻-N content (Guo et al., 2016). The soil NO₃⁻-N content in 2019 was lower than that in 2020. This may be due to rainfall in 2020 was more abundant than in 2019, leading to more adequate hydrolysis of N fertilizers and increased soil NO₃⁻-N content (Li et al., 2020a).

Reasonable application of N fertilizer can effectively regulate the contradiction between N loss and grain yield increase, which is an effective way to reduce N loss from the plant-soil system to the environment (Deng et al., 2014). In addition, the change in N fertilizer types and N application rates would also have a significant impact on soil N loss through diverse pathways (Ma et al., 2023). In this study, the crop N uptake and soil N_min (at harvest) increased with increasing N application rate, whereas there were no significant differences in apparent N losses between N1 and N2 among U, S, and SU, indicating that crop N uptake could be increased and apparent N loss could be maintained without causing more pollution by appropriately increasing the N application rate. Slow-release N fertilizer could effectively reduce NH₃ emissions and contribute to a significant reduction in N loss (Zhang et al., 2019). In this study, S and SU reduced the apparent N loss and apparent N loss efficiency compared with U in both 2019 and 2020. This may be due to the fact that S and SU optimized the rate of N fertilizer release to meet crop N requirements, increased N uptake by maize, and improved the relationship between N input and output, resulting in increased crop N uptake and decreased soil N_min (at harvest) (Ghafoor et al., 2021). In order to reduce agricultural non-point source pollution, it was recommended to control the apparent N loss below 80 kg ha^− 1 (Ding et al., 2021). In this study, both SU and S satisfied this condition, and the N uptake of summer maize under SU was higher. Therefore, the rational application of SU is an effective way to reduce N loss from the plant-soil system to the environment and regulate the contradiction between N loss and grain yield.

4.3. Effects of N fertilizer types and N application rates on grain yield and N use efficiency of summer maize

Crop yield and NUE were the key indicators to evaluate the rationality of fertilization (Ren et al., 2022). Aboveground N uptake was closely related to crop yield and aboveground biomass (Liu et al., 2018). Optimizing crop N management to synchronize N supply with crop N demand was crucial for increasing crop yield, improving NUE, and reducing agricultural non-point source pollution (Malhi et al., 2001). In this study, the dry matter accumulation and grain yield increased with increasing N application rate. However, the NUE decreased with increasing N application rate. This was consistent with the finding of Srivastava et al. (2018), who reported that increasing the N application rate could increase grain yield and dry matter accumulation, but would lead to a decrease in NUE. Grain yield and NUE performed differently caused by the increased N application rate, this due to N loss will be accelerated when N input exceeded the assimilation capacity of crop (Zhu et al., 2016). For various N fertilizer types, the grain yield, dry matter accumulation, and NUE followed the order of SU > S > U, which was agreed with previous studies (Li et al., 2020c). Maize was accompanied by vegetative growth and reproductive growth after the jointing stage, so it demand a large amount of N. Traditional urea one-time basal application was difficult to meet the demand for N at the later growth stages of maize (Guo et al., 2017). In addition, due to the pressure of labor and economic costs, it is generally not considered to use multiple topdressing fertilization methods at the later growth stage of maize. Moreover, the N release rate of S and SU was more in line with the N demand of maize compared with urea, and effectively promoted crop N uptake and utilization. The release mechanism of slow-release nitrogen fertilizer was that the urea in the membranes was hydrolyzed after contact with the water in the soil (Timilsena et al., 2015), and the urea in the membranes was transported out of the membranes under the action of the concentration difference formed by the solute inside and outside the membranes by crop absorption (Azeem et al., 2014). Therefore, the hydrolysis rate of S after fertilization was slow compared with urea. However, SU relied on urea hydrolysis after fertilization, and relied on slow-release N fertilizer to release N at the later growth stages of maize, thus meeting the maize N demand during the whole growth period (Zheng et al., 2016; Guo et al., 2017). This explains why SU was better than S in promoting N uptake by summer maize. In addition, due to the N release rate was easily affected by the soil moisture (Azeem et al., 2014), the precipitation in 2020 was more abundant than that in 2019, which led to an increase in N loss and was not conducive to the N uptake and utilization by maize. This explains why grain yield, dry matter accumulation, and NUE in 2020 were lower than that in 2019.

The blending ratio of SU affected the effectiveness of matching the N release rate of SU with the N demand of maize. It has been shown that the high proportion of slow-release N fertilizer in SU would lead to insufficient N supply at the early growth stage, thus affecting the vegetative growth of maize plants (Garcia et al., 2018). In contrast, the high proportion of slow-release N fertilizer in SU was too low to meet maize N demand at the late growth stage, which limited the reproductive growth of maize (Liu et al., 2023). In this study, in order to determine the range of recommended N application rates and blending ratios of SU, GAUSS2D and LORENTZ2D models were used to establish binary quadratic regression equations between yield/NUE with N application rates/blending ratios of SU. The results found that the blended ratio of slow-release N fertilizer with urea in SU ranged from 53%-58%, and the N application rate was 150–220 kg ha^− 1 could maintain obtain grain yield (7146.09 kg ha^− 1) and NUE (46.20 kg kg^− 1) above 90% of the maximum values. Grain yield and NUE in SU were 42.84% and 31.29% (U), 19.57% and 22.48% (S) greater than those predicted according to binary quadratic regression equations, respectively. Those results are similar to the finding of Garcia et al (2018), who reported that when slow-release N fertilizer and urea were mixed at a ratio of 45.00%-75.00%, maize yield and NUE could be significantly increased, and N loss effectively reduced. In conclusion, the SU was an effective N management method, which could maximize NUE, increase yield, reduce labor and mitigate environmental pollution.

Conclusions

In this study, SU reduced NH₃ volatilization (34.90%-43.62%), residual soil NO₃⁻-N (0.28%-17.66%), and apparent N loss (7.00%-72.19%), while increased grain yield (35.83%-49.96%) and NUE (22.96%-38.10%) of summer maize under different N application rates. Compared with U, reducing the application rate of SU not only did not reduce the grain yield and N uptake of maize, but also significantly increased the NUE. In addition, the blending ratio of S and U of SU was the main factor affecting grain yield and NUE. For rainfed maize in Guanzhong Plain of Northwest China, it was recommended that the blending ratio of slow-release N fertilizer and urea in SU ranged from 53%-58%, and N application rate was 150–220 kg ha^− 1 as optimized fertilization practices. In future studies, further attention should be paid to the development of the blending ratio of SU in different regions and different crops to improve crop yield and NUE, while reducing N loss.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that might influence the work reported in this paper.

Funding

This study was jointly supported by Yunnan Fundamental Research Projects (grant NO. 202301BE070001-050, 202401AT070335), the National Natural Science Foundation of China (No. 52369006).

Acknowledgments

This research was funded by Yunnan Fundamental Research Projects (grant NO. 202301BE070001-050, 202401AT070335) and the National Natural Science Foundation of China (No. 52369006). The authors would like to thank Kunming University of Science and Technology for assistance with data collection and analysis to carry on, the Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas of the Ministry of Education, Northwest A&F University for assistance with the long-term field experiment.

Data availability

Data will be provided from the corresponding author on reasonable request.

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You are reading this latest preprint version

Blending of slow-release N fertilizer and urea improve rainfed maize yield, nitrogen use efficiency while reducing apparent N loss

Status:

Version 1

Abstract

Figures

1. Introduction

2. Materials and methods

2.1. Experimental site description

2.2. Experimental design

2.3. Sampling and Measurements

2.3.1. NH₃ volatilization

2.3.2. Soil nitrate nitrogen

2.3.3. Plant dry matter and grain yield

2.3.4. Plant N accumulation and use efficiency

2.3.5. Apparent N loss

2.4. Statistical analysis

3. Results

3.1. Dynamics of NH₃ volatilization

3.2. Residual soil NO₃⁻-N

3.3. Dry matter accumulation

3.4. Plant N accumulation

3.5. Apparent N losses

3.6. Grain yield and NUE

3.7. Relationships between N application rate, blending ratio of SU, and grain yield/NUE

4. Discussion

4.1. Effect of N fertilizer types and N application rates on NH₃ volatilization

4.2. Effects of N fertilizer types and N application rates on residual soil NO₃⁻-N

Declarations

Declaration of competing interest

Funding

Acknowledgments

Data availability

References

Supplementary Files

Status:

Version 1

Blending of slow-release N fertilizer and urea improve rainfed maize yield, nitrogen use efficiency while reducing apparent N loss

Status:

Version 1

Abstract

Figures

1. Introduction

2. Materials and methods

2.1. Experimental site description

2.2. Experimental design

2.3. Sampling and Measurements

2.3.1. NH3 volatilization

2.3.2. Soil nitrate nitrogen

2.3.3. Plant dry matter and grain yield

2.3.4. Plant N accumulation and use efficiency

2.3.5. Apparent N loss

2.4. Statistical analysis

3. Results

3.1. Dynamics of NH3 volatilization

3.2. Residual soil NO3−-N

3.3. Dry matter accumulation

3.4. Plant N accumulation

3.5. Apparent N losses

3.6. Grain yield and NUE

3.7. Relationships between N application rate, blending ratio of SU, and grain yield/NUE

4. Discussion

4.1. Effect of N fertilizer types and N application rates on NH3 volatilization

4.2. Effects of N fertilizer types and N application rates on residual soil NO3−-N

Declarations

Declaration of competing interest

Funding

Acknowledgments

Data availability

References

Supplementary Files

Status:

Version 1

2.3.1. NH₃ volatilization

3.1. Dynamics of NH₃ volatilization

3.2. Residual soil NO₃⁻-N

4.1. Effect of N fertilizer types and N application rates on NH₃ volatilization

4.2. Effects of N fertilizer types and N application rates on residual soil NO₃⁻-N