Splitting nitrogen fertilization increases ammonia losses through volatilization in annual ryegrass pasture

ABSTRACT

Nitrogen (N) losses from soil through volatilization are influenced by multiple factors, including the amount and source of nitrogen fertilizer applied, crop type, intrinsic soil characteristics, and environmental conditions. The study aimed to quantify ammonia (N-NH₃) volatilization in relation to the method of nitrogen application, either split or single-rate, on annual ryegrass (Lolium multiflorum Lam.) pasture in an integrated crop-livestock system. The trial was conducted on a Humic Cambisol in Southern Brazil during the fall and winter seasons of 2022 and 2023. The treatments were: N-0 – no nitrogen fertilization; N-split – fertilization with 200 kg ha^-1 of N as urea split into four applications (50 kg ha^-1 at tillering and three subsequent applications of 50 kg ha^-1); and N-single – fertilization with 200 kg ha^-1 of N as urea applied in a single rate at the ryegrass tillering stage. Ammonia volatilization was assessed using static semi-open collectors and quantified by colorimetry. Losses due to volatilization were monitored for 14 days after each N application and summed over 56-day period. In both years, during the first evaluation, the N-single treatment caused the greatest losses but did not differ significantly from split fertilization (N-split). However, in the subsequent three evaluations, the highest volatilization losses were observed with N-split. Regarding the total accumulated losses of N-NH₃ over 56 days, the values in the first year were 375, 810, and 345 g ha^-1 for N-0, N-split, and N-single, respectively. In the second year, the losses were 808, 1963, and 900 g ha^-1 of N-NH₃ for N-0, N-split, and N-single. Splitting nitrogen fertilization resulted in greater N losses through volatilization than a single application at tilling; however, the losses remained below 1 % of the applied N. Despite these differences in volatilization, split nitrogen fertilization produced ryegrass forage yields equivalent to those obtained with the single-rate application. Split N fertilization increased NH₃ losses compared to single-dose application in ryegrass, yet yields were equivalent, and losses remained below 1 % of the applied N.

Keywords
nitrogen losses; urea; fertilization splitting; annual pasture

INTRODUCTION

Nitrogen (N) is an essential macronutrient for plant growth, participating in fundamental processes such as protein synthesis, chlorophyll formation, and N compound metabolism (Gastal et al., 2015; Perin et al., 2020). Among the sources, urea [CO(NH₂)₂] stands out as the most widely used fertilizer worldwide due to its high N content (≈46 %) and low cost per nutrient unit, being extensively applied in annual crops and pasture systems (Shan et al., 2015).

In annual ryegrass pastures, proper N management is crucial for tillering, biomass accumulation, and forage nutritive value (Pellegrini et al., 2010; Pavinato et al., 2014), especially in livestock production systems under subtropical conditions (Assmann et al., 2004). Traditional fertilization recommendations for ryegrass recommend splitting the total N rate, with applications at tillering and reapplications after cutting or grazing, aiming to synchronize N supply with plant demand and reduce potential losses (Sun et al., 2008). However, recent studies in integrated crop-livestock systems suggest that a single application of the entire N rate at tillering may result in similar productive performance compared with split applications, questioning the technical necessity of this practice under specific soil and climate conditions (Bernardon et al., 2021; Beltran-Barriga et al., 2022).

Regarding the recommended N rate, David et al. (2019) evaluated the application of 200 kg ha^-¹ of N in a cool-season pasture and observed nitrogen nutrition index (NNI) values close to one, indicating adequate N supply to plants and no significant nutritional limitation. Complementarily, Bernardon et al. (2021) suggested that applying 200 kg ha^-¹ of N at the beginning of tillering, as a single rate rather than split, is more than sufficient to meet the pasture requirements throughout the cycle, since the N concentration in the forage remained consistently above the standard reference curve.

After being applied to the soil, urea is rapidly hydrolyzed by the enzyme urease, forming ammonium (NH₄⁺) and hydroxide (OH^-) ions, which increase the pH in the microzone of reaction and favor the conversion of NH₄⁺ into ammonia (NH₃), thus raising volatilization potential (Hargrove, 1988; Rawluk et al., 2001). The intensity of urea hydrolysis and subsequent NH₃ losses by volatilization are determined by several soil and environmental factors. Soil moisture and temperature, pH, buffering capacity, texture, organic carbon and nitrogen contents, as well as the presence of crop residues on the surface, directly influence urease activity, pH increase in the hydrolysis zone, and NH₃ diffusion into the atmosphere (Timilsena et al., 2015; Cassimiro et al., 2023).

Ammonia volatilization is one of the main pathways of N loss in agricultural systems, reducing nitrogen use efficiency (NUE) and affecting its availability to plants. Additionally, it contributes to environmental impacts, including soil acidification, water body eutrophication, the formation of fine particulate matter, and the emission of reactive N compounds (Giannakis et al., 2019; Zhan et al., 2021; Dawar et al., 2024). Several studies have reported wide variation in ammonia losses depending on crop type, weather conditions, soil properties, and management practices. Perin et al. (2020) observed losses ranging from 0.3 to 29.6 % of applied N in wheat, while Turner et al. (2010) reported 9.5 % losses in winter wheat. For corn, Fontoura and Bayer (2010) reported losses of 1.3-3.0 %, whereas Dawar et al. (2024) found losses of 30-39 %. Even higher losses, up to 62 % of applied N, have been reported under different environmental and management conditions (Cassim et al., 2024). This evidence illustrates the high variability of the volatilization process, whose potential depends strongly on the interactions among soil properties, meteorological conditions, and fertilization management.

Among management factors, N rate and application method play a central role in determining loss magnitude. Ma et al. (2010) observed increased NH₃ losses with rising N rates (0, 30, 90, and 150 kg ha^-¹) in different soil types in Canada. However, Vale et al. (2014) demonstrated that higher N rates do not always result in proportional increases in losses, indicating strong dependence on soil characteristics and post-application climatic conditions.

Given this evidence, important knowledge gaps persist regarding NH₃ losses in pastures grown under subtropical conditions, particularly in medium-textured soils, where the interaction between climatic conditions and soil properties can significantly modulate volatilization. Therefore, the hypothesis formulated in this study was that, under subtropical conditions and in medium-textured soil, relative N–NH₃ losses by volatilization are low and similar between single urea application at tillering and split applications of the same total N rate, without affecting total forage production. Thus, N fertilization splitting might not be technically necessary for managing this forage species. This study aimed to quantify N–NH₃ volatilization losses as affected by two urea application strategies in an annual ryegrass (Lolium multiflorum Lam.) pasture: (i) a single application of 200 kg ha^-¹ of N at tillering, and (ii) four split applications of 50 kg ha^-¹ of N throughout the vegetative cycle under the soil and climate conditions of Southern Brazil.

MATERIALS AND METHODS

The study was conducted during the fall and winter seasons of 2022 and 2023 at the Santa Catarina Agricultural Research and Rural Extension Company (EPAGRI), Lages, Santa Catarina, Brazil (27°47’55” S, 50°19’25” W; 922 m a.s.l.). The climate is classified as Cfb according to Köppen classification system (Köppen, 1936). Climatic data (rainfall and temperature) recorded during the experimental period are presented in figure 1.

Figure 1
Precipitation and air temperatures during the experimental period of 2022 and 2023 in Lages (SC), Brazil. Source: EPAGRI/CIRAM.

Before the experiment was established, the area had been occupied by a perennial pasture of Giant missionary grass (Axonopus catharinensis) for several years. Before sowing annual ryegrass, the pasture was chemically desiccated, lime was applied, and soil preparation consisted of conventional tillage, including plowing and harrowing, to ensure adequate seedbed conditions.

The soil is classified as a Cambissolo Húmico Distrófico típico (Santos et al., 2018), which corresponds to a typical Humic Cambisols (IUSS, 2015), with medium texture and clay content below 30 % in the 0.00–0.20 m layer. Physical and chemical properties of the soil from 0 to 0.80 m depth at the beginning of the experiment (April 2022) are presented in table 1.

Table 1
Physical and chemical soil properties at a depth of 0 to 0.80 m prior to establishing annual ryegrass, soil analysis from April 2022. Lages, SC, 2022

Layer	Clay	K	P	OM	pH(H2O)	Sorption Complex
						H+Al	Ca2+	Mg2+	CECpH 7.0	Al	V
m	g kg-1	--- mg dm-3 ---		g dm-3		--- cmolc dm-3---				--- % ---
0.00-0.10	279.0	86.12	12.01	3.63	6.27	3.39	7.69	3.24	14.54	0.00	76.70
0.10-0.20	330.0	45.96	5.74	2.36	5.99	4.98	6.26	2.53	13.89	0.08	64.95
0.20-0.40	347.0	34.24	5.07	2.18	5.74	7.03	5.25	2.18	14.56	1.55	54.25
0.40-0.80	376.0	27.40	3.88	1.41	5.26	11.2	2.47	1.22	14,95	1.88	27.45

• K: Potassium; P: Phosphorus (Mehlich^-1); OM: organic matter; pH: potential of hydrogen; Ca²⁺: exchangeable calcium; Mg²⁺: exchangeable magnesium; CEC_{pH 7.0}: cation exchange capacity at pH 7.0; Al: aluminum; V%: base saturation.

Annual ryegrass (Lolium multiflorum L.) cultivar SCS316 CR Altovale was sown at a density of 30 kg ha^-1 with a row spacing of 0.17 m on April 25, 2022, and June 2, 2023. At sowing, phosphorus was applied at rates of 82 kg ha^-1 in 2022 and 115 kg ha^-1 in 2023 using triple superphosphate (42 % P₂O₅). Potassium was applied on the cover 30 days after sowing in 2022 and 45 days after sowing in 2023, at rates of 90 and 108 kg ha^-1 of K₂O, respectively, using potassium chloride (60 %). Fertilizer rates were determined based on soil nutrient levels obtained from soil analysis and following the regional recommendations (CQFS-RS/SC, 2016).

The experimental design consisted of a randomized complete block with three treatments (N-single, N-split, and N-0) and four replicates. Treatments consisted of N0 (control), without N application, N-single (total nitrogen applied at tillering - 200 kg ha^-1), and N-split (fractionated nitrogen applied in four rates of 50 kg ha^-1 each throughout the vegetative cycle). Nitrogen was applied as urea (44 % N). In 2022, applications for N-single occurred 31 days after sowing, and for N-split on May 26, July 4, July 25, and August 19. In 2023, N-single was applied on July 18, while N-split applications occurred on July 18, August 10, August 24, and September 14. The first application coincided with tillering, and the subsequent N-split applications followed after the first, second, and third grazing events.

Ammonia volatilization was assessed using static semi-open collectors (Figure 2) (Lara-Cabezas and Trevelin, 1990), each comprising a transparent acrylic acetate chamber (Ø = 0.15 m and h = 0.35 m). Collectors were installed and fixed before fertilizer application. The N rate corresponding to each chamber base area was applied, after which the collectors were sealed. Fertilizer was then broadcast over the entire plot area (14 m²). Each collection chamber contained two circular low-density sponges (20 mm thick, 26 mm density) soaked in 50 mL of a sulfuric acid solution (H₂SO₄) 0.05 mol L^-1 + 2 % glycerin). The first sponge was placed at the bottom of the chamber, 0.12 m above the ground, to capture only ammonia volatilized inside the chambers. The second sponge was placed in the upper part of the chamber, 0.30 m above the ground, to prevent contamination of the lower sponge by external ammonia. Throughout the evaluation period, the chambers remained fixed in the same location.

Figure 2
Representation of a semi-open static ammonia (NH₃) collection cylinder.

Samplings were performed every 2 days following each N application for 14 days (2nd, 4th, 6th, 8th, 10th, 12th, and 14th days) to measure accumulated N-NH₃ losses. Ammonia content was quantified using the colorimetric method described by Miyazawa et al. (1992). Three reagent solutions were used for the determination: A, B, and C. Solution A consisted of 5 % salicylic acid + 5 % tribasic sodium citrate + 2.1 % sodium hydroxide (NaOH); solution B consisted of 0.1 % sodium nitroprusside; and solution C consisted of 0.15 % sodium hypochlorite (NaOCl). A test tube was filled with 6 mL of deionized water, 1 mL each of solutions A, B, and C, and 1 mL of the sample. Tube was shaken and left to stand for 1 h before being read in a spectrophotometer, with absorbance measured at a wavelength of 697 nm.

Grazing management and annual ryegrass forage production

Grazing was managed under an intermittent stocking system (Allen et al., 2011), in which a group of animals from each treatment grazed sequentially among the replicates corresponding to their treatment. Grazing commenced at a sward canopy height of 0.20 m and was terminated at 0.12 m. Grazing interruption criterion was defined as a 40 % reduction in pre-grazing sward canopy height. Each treatment maintained three “tester” animals, with additional “regulator” animals introduced as needed to achieve the target grazing intensity. Paddock areas were 1,800 m² for nitrogen-fertilized treatments (N-single and N-split) and 2,800 m² for the control without nitrogen application (N-0).

Total forage mass (TFM) was determined by taking five direct cuts under both pre- and post-grazing conditions using a circular frame with a 35.5 cm diameter. Samples were cut close to the soil surface and subsequently dried in a forced-air oven at 55 °C for 72 h to determine dry matter (DM) content. Pre- and post-grazing forage mass (kg ha^-1 DM) were calculated for each grazing cycle to estimate forage production throughout the experimental period. Total forage production was then calculated using equation 1.

Eq. 1 $TFM={MF}_{ent}+\left(M{F}_i-M{F}_{i-1}+\left(\left({\displaystyle \frac{M{F}_i-M{F}_{i-1}}{ND\left(P_i-P_{i-1}\right)}}\right)*\left(ND{P}_i\right)\right)+...n\right)+\left(M{F}_r-M{F}_s\right)$

in which: TFM is the total forage mass production (kg ha^-1 DM ); MF_ent is the forage mass at entry (pre-grazing) of the 1st grazing cycle (kg DM ha^-1); MFᵢ is the forage mass at entry (pre-grazing) of grazing cycle i (kg ha^-1 DM); MFᵢ₋₁ is the forage mass at exit (post-grazing) of the previous grazing cycle (i–1) (kg ha^-1 DM); ND(Pᵢ – Pᵢ₋₁) is the number of days between grazing cycles i and i–1; NDPᵢ is the number of grazing days in cycle i; MFᵣ is the residual forage mass, measured at the end of the last grazing cycle (kg ha^-1 DM); and MFₛ is the forage mass at exit (post-grazing) of the last grazing cycle (kg ha^-1 DM).

Statistics

Data analyses were conducted in R (R Development Core Team, 2023). Daily and cumulative N losses were modeled using linear mixed models with the lme4 package (Bates et al., 2015). Because treatments (chambers) were arranged in adjacent areas without full randomization due to land slope, a statistical model with aligned replications within treatments was applied. Data were analyzed separately by year. Means were compared using Tukey test (p<0.05). Forage DM yield data were tested for normality and homogeneity of variance and subjected to ANOVA, with means separated by Duncan test at the 5 % significance level (p<0.05).

RESULTS

The daily patterns of N–NH₃ loss following N application to the soil in 2022 are presented in figures 3a, 3b, 3c, and 3d, while the corresponding climatic conditions for each evaluation period are shown in figures 3e, 3f, 3g, and 3h. Each evaluation year comprised four monitoring periods of 14 days, corresponding to the four applications in the split nitrogen treatment (N-split).

In 2023, NH₃ losses during the first 15-day evaluation period, along with the associated climatic conditions, were previously described by Ciotta et al. (2025). The three subsequent evaluation periods of 2023 are presented in figures 4a, 4b, and 4c, with the corresponding climatic conditions shown in figures 4d, 4e, and 4f.

Figure 3
Ammonia volatilization (a, b, c, d) and climatic conditions (e, f, g, h) related to evaluating nitrogen fertilization methods at 200 kg ha^-1, respectively. Growth cycle of annual ryegrass pasture in 2022. Lages (SC), Brazil.

Figure 4
Ammonia volatilization (a, b, c) and climatic conditions(d, e, f) related to evaluating nitrogen fertilization methods at 200 kg ha^-1, respectively. Growth cycle of annual ryegrass pasture (2023), Lages (SC), Brazil. Values are means with standard error shown by vertical bars (n = 6). The data from the first evaluation period, along with the corresponding climatic conditions, are presented in Ciotta et al. (2025).

In 2022, during the first evaluation period (Figure 3a), the treatment with a total application of 200 kg ha^-1 at tillering (N-single) showed higher accumulated volatilization losses compared to the N-split, although both rates did not exceed 200 g ha^-1, which is considered low (Table 2). In the N-split treatment, losses peaked on the sixth day after application, then declined and stabilized. In the N-single treatment, the highest daily losses occurred on the sixth and tenth days. Climatic conditions, with 163 mm of total rainfall and average temperatures of 12 °C during the evaluated period (Figure 3e), likely contributed to the reduction in ammonia losses.

During the second evaluation period (Figure 3b), the greatest losses were recorded for the N-split treatment, while N-single had the lowest losses, even lower than the treatment without nitrogen fertilization (N-0). During this period, between the fourth and sixth days after application, the highest losses were observed for N-split, followed by stabilization. Weather conditions, with an average temperature of 13 °C and 57 mm of accumulated rainfall (Figure 3f), may have contributed to the increased losses in N-split.

In the third evaluation period (Figure 3c), the greatest losses occurred at the beginning of the evaluation, stabilizing by the eighth day. This trend was likely due to the 9 mm of rainfall between July 28 and 29 and mild temperatures (13 °C) (Figure 3g). The accumulated losses were 297, 124, and 91 g ha^-1 of N-NH₃ for N-split, N-0, and N-single, respectively (Table 2). In the fourth evaluation period (Figure 3d), accumulated losses were 227, 87.8, and 40.9 g ha^-1 for N-split, N-0, and N-single. The low temperatures and frequent rainfall maintained soil moisture, thereby mitigating losses due to volatilization.

Table 2
Average values of accumulated N-NH₃ losses (g ha^-1) during the annual ryegrass cycle. Lages, SC, 2022 and 2023

Fertilization methods	Evaluation time points				Accumulated	Losses
	1st Application	2nd Application	3rd Application	4th Application
	---g ha-1---				g ha-1 / 56 days	%
Year 2022
N-0	57 b	106 a	124 b	88 b	375 b	0
N-split	128a	157 a	297 a	228 a	810 a	0.40
N-single	174 a	39 b	91 c	41 b	345 b	-
Year 2023
N-0	144 b	251 b	174 b	239 b	808 b	0
N-split	396 a	552 a	386 a	629 a	1963 a	0.98
N-single	385 a	199 b	122 b	194 b	900 b	0.045

• ^*
  Means followed by the same lowercase letters in the vertical direction do not differ statistically according to the Tukey test, at a 5 % probability of error. Treatments: N-0: no nitrogen fertilization; N-split: 200 kg ha^-1 of N applied as urea split into four applications (50 kg ha^-1 each); N-single: 200 kg ha^-1 of N applied as a single rate at tillering.

In 2023, as reported by Ciotta et al. (2025), during the first evaluation period, ammonia losses were initially similar between the N-single and N-split treatment. However, the N-split treatment showed increased volatilization in the subsequent sampling events, resulting in greater cumulative losses and exceeding those of the N-single treatment from the fifth sampling onward. In the second (Figure 4a) and third evaluation periods (Figure 4b), N-split followed a similar pattern, with the highest losses occurring in the first collection, two days after application, followed by a decrease until the fourth collection (8 days), at which point losses stabilized. During both periods, the average temperature was 14 °C. In the second period, accumulated rainfall was 74 mm (Figure 4d), whereas in the third period, accumulated rainfall was 102 mm (Figure 4e).

During the final evaluation period (Figure 4c), N-split showed the highest accumulated losses (629 g ha^-1 N-NH₃) compared to N-single (194 g ha^-1) and N-0 (239 g ha^-1) (Table 2). The evaluation period recorded an accumulated rainfall of 123 mm and average temperatures of 17 °C. The increase in temperature likely contributed to the higher ammonia losses observed in this final application compared to previous applications this year. The accumulated N-NH₃ losses during the cool-season period (56 days) were up to 800 g ha^-1 in 2022 and 1963 g ha^-1 in 2023 for the N-split treatment (Table 2). In the first year, these losses represented 0.40 % of the applied rate, whereas in the second year, they represented 0.98 %.

Regarding ryegrass forage yield, nitrogen fertilization increased forage production in both evaluation years (Figure 5). However, the nitrogen application method, whether single or split, did not affect ryegrass total dry matter yield, which averaged above 9 Mg ha^-1 in both years.

Figure 5
Total forage yield of annual ryegrass cv. Alto Vale. Experimental Station of Lages, 2022 and 2023, Lages (SC), Brazil. Treatments: N-single: 200 kg ha^-1 of N applied as a single rate at tillering; N-split: 200 kg ha^-1 of N applied as urea split into four applications (50 kg ha^-1 each); N-0: no nitrogen fertilization.

DISCUSSION

The temporal dynamics of ammonia volatilization observed in this study corroborate previous findings that the majority of N losses occur shortly after fertilization, with a sharp peak followed by a rapid decline and stabilization. Although the duration of this critical emission window remains debated, with reports ranging from 3 to 6 days (Watson et al., 1990; Costa et al., 2003; Tasca et al., 2011; Rojas et al., 2012; Suter et al., 2013), our results are consistent with the conclusion by Dawar et al. (2024) that 80–85 % of volatilization occurs within the first week. The extended monitoring period adopted here (14 days) showed negligible residual emissions (≤40 g ha^-¹ N–NH₃), which have little agronomic significance.

Soil and climatic conditions proved to be key drivers of N loss dynamics. Suter et al. (2013), for instance, reported greater losses in autumn than in spring due to higher temperatures and increased urease activity. Similarly, in the present study, the mean temperature in 2023 (14.5 °C) was higher than in 2022 (12.2 °C), nearly doubling the total volatilization losses. This trend supports previous evidence showing that elevated temperature accelerates urea hydrolysis (Cameron et al., 2013) and enhances ammonia diffusion (Al-Kanani et al., 1991), thereby increasing N losses (Tasca et al., 2011; Sutton et al., 2013). Conversely, the relatively mild temperatures recorded during most of the experimental period contributed to low volatilization rates, reinforcing the recommendation to apply urea under moderate climatic conditions (Rawluk et al., 2001; Sutton et al., 2013).

In addition to temperature, precipitation plays a crucial role in reducing N losses. Even small rainfall events (4 mm within 24 h) are sufficient to dissolve urea granules and incorporate N into the soil, thereby reducing surface exposure and minimizing volatilization (Lara-Cabezas et al., 1997; Fontoura and Bayer, 2010; Suter et al., 2013). In this context, N volatilization is not determined by a single isolated factor, but rather results from the interaction among edaphoclimatic variables, such as temperature, rainfall regime, and soil properties, which regulate urease activity, the rate of urea hydrolysis, and ammonia diffusion within the soil–atmosphere system (Pan et al., 2016).

Soil and plant characteristics also influenced N utilization. The medium-textured soil (30 % clay; pH 6.1) exhibited lower susceptibility to volatilization than sandier soils, where lower retention capacity and greater fertilizer exposure tend to increase N losses (San Francisco et al., 2011). In addition, annual ryegrass is widely recognized for its high N use efficiency, which is associated with its strong tillering capacity and rapid regrowth (Varella et al., 2010; Gastal et al., 2015). This combination creates favorable conditions for a large proportion of the applied nutrient to be effectively incorporated into plant biomass (Pellegrini et al., 2010; Lemaire et al., 2014), rather than being lost to the atmosphere. In integrated crop–livestock systems, grazing further intensifies the N cycle by stimulating root growth, increasing plant nutrient demand, and promoting greater nutrient uptake and recycling within the system (Lemaire et al., 2014).

In this context, the volatilization losses observed in this study, below 1 % of the applied N in both years, are considered very low, especially when compared with losses commonly reported for summer crops such as corn under conventional nitrogen fertilization (Tasca et al., 2011; Suter et al., 2013; Sutton et al., 2013). It is also noteworthy that few studies have evaluated NH₃ losses in pastures under subtropical conditions, which limits direct comparisons with the existing literature. Therefore, the results presented here are innovative, providing novel data on the dynamics of NH₃ volatilization in annual ryegrass pastures managed under intermittent stocking in these edaphoclimatic conditions. The frequency of rainfall events, combined with mild temperatures, favored rapid urea incorporation into the soil, thereby reducing N losses, as reported by) Fontoura and Bayer (2010) and Tasca et al. (2011).

Regarding productive performance, biomass production exceeding 9 Mg ha^-1 DM in both years indicates that ryegrass efficiently converted available N, even in the presence of low volatilization losses. Studies on annual ryegrass have shown that N fertilization increases daily herbage accumulation rate, tiller density, and the duration of high-production periods, resulting in near-linear dry-matter responses up to certain N rates (Varella et al., 2010; Gastal et al., 2015). In the present study, the combination of adequate N supply and grazing management under intermittent stocking, with a 40 % reduction in sward height, allowed the crop growth potential to be fully exploited, maintaining a canopy with high light interception and intense leaf turnover, features typical of systems with adequate N availability.

The association between low NH₃ losses and high yield also indicates a high apparent N use efficiency in the system. In well-managed pastures, N recycling via feces and urine, together with grazing-induced stimulation of root growth and nutrient uptake, increases the fraction of N that returns to the soil–plant system and is reutilized by grasses (Lemaire et al., 2014). Thus, even though part of the applied N may be lost through volatilization or other pathways, the high dry matter production observed indicates that most of the supplied N was effectively utilized by the crop, which is consistent with the well-known high N use efficiency of annual ryegrass pasture (Varella et al., 2010; Gastal et al., 2015).

Although split N application resulted in slightly higher cumulative losses than a single application, these differences were agronomically negligible (<1 %) and did not compromise biomass production, which exceeded 9 Mg ha^-1 DM in both years. Similar results were reported by Lima (2018), who also observed low NH₃ losses in ryegrass pastures under conditions of high soil moisture and adequate water availability. Thus, the initial hypothesis of this study is confirmed: under subtropical conditions and in medium-textured soils, NH₃ volatilization losses are low and similar between single- and split-N application strategies, with no effect on annual ryegrass productivity. Consequently, split nitrogen fertilization appears agronomically unnecessary in this context, and a single application at the tillering stage emerges as an efficient and operationally advantageous strategy for N management, reducing costs and labor requirements without increasing volatilization risk, while maintaining high pasture yield.

CONCLUSIONS

Ammonia volatilization losses were low under the subtropical conditions and soil characteristics of the study site, remaining below 1 % of the applied nitrogen. Nitrogen fertilization increased total dry matter production of annual ryegrass regardless of application method. A single application of the recommended rate at the tillering stage is an efficient strategy that achieves high forage yields while minimizing labor and operational requirements. These results suggest that split applications are not technically justified for managing annual ryegrass in similar environments.

ACKNOWLEDGMENTS

We thank the Agricultural Research and Rural Extension Company (EPAGRI) and the Universidade Tecnológica Federal do Paraná (UTFPR) for the research support.

• How to cite:
  Zanella JB, Ciotta MN, Soares AB, Mendes SDC, Baldissera TC, Rech TD, Severo IK, Dambros PH. Splitting nitrogen fertilization increases ammonia losses through volatilization in annual ryegrass pasture. Rev Bras Cienc Solo. 2026;50:e0250160. https://doi.org/10.36783/18069657rbcs20250160
• FUNDING
  This research was supported by the Fundação de Amparo à Pesquisa e Inovação do Estado de Santa Catarina (FAPESC) under Grant Agreement No. 2021TR001353. This study was supported by the Programa de Bolsas Universitárias de Santa Catarina para Pós-Graduação do Fundo de Apoio à Manutenção e ao Desenvolvimento da Educação Superior (UNIEDU/FUMDES), linked to the Santa Catarina State Department of Education.

DATA AVAILABILITY

The data that support the findings of this study are available from the corresponding author upon reasonable request.

References

• Allen VG, Batello C, Berretta EJ, Hodgson J, Kothmann M, Li X, Sanderson M. An international terminology for grazing lands and grazing animals. Grass Forage Sci. 2011;66:2-28. https://doi.org/10.1111/j.1365-2494.2010.00780.x
  » https://doi.org/10.1111/j.1365-2494.2010.00780.x
• Assmann AL, Pelissari A, Moraes A, Assmann TS, Oliveira EB, Sandini I. Beef cattle production and dry matter accumulation in the crop-pasture rotation system in presence and absence of white clover and nitrogen. Rev Bras Zootec. 2004;33:37-44. https://doi.org/10.1590/S1516-35982004000100006
  » https://doi.org/10.1590/S1516-35982004000100006
• Al-Kanani T, Mackenzie AF, Barthakur NN. Soil water and ammonia volatilization relationships with surface-applied nitrogen fertilizer solutions. Soil Sci Soc Am J. 1991;55:1761-6. https://doi.org/10.2136/sssaj1991.03615995005500060043x
  » https://doi.org/10.2136/sssaj1991.03615995005500060043x
• Bates D, Mächler M, Bolker B, Walker S. Fitting linear mixed-effects models using lme4. J Stat Softw. 2015;67:1-48. https://doi.org/10.18637/jss.v067.i01
  » https://doi.org/10.18637/jss.v067.i01
• Beltran-Barriga PA, Lima RC, Befart-Aiolfi R, Brugnara-Soares A, Simioni-Assmann T, Canaza-Cayo AW. Production characteristics of ryegrass pasture under different intensities of grazing and nitrogen fertilization in integrated crop-livestock systems. Indian J Agric Res. 2022;56:672-6.
• Bernardon A, Assmann TS, Soares AB, Franzluebbers A, Maccari M, De Bortolli MA. Carryover of N-fertilization from corn to pasture in an integrated crop-livestock system. Arch Agron Soil Sci. 2021;67:687-702. https://doi.org/10.1080/03650340.2020.1749268
  » https://doi.org/10.1080/03650340.2020.1749268
• Cameron KC, Di HJ, Moir JL. Nitrogen losses from the soil/plant system: A review. Ann Appl Biol. 2013;162:145-73. https://doi.org/10.1111/aab.12014
  » https://doi.org/10.1111/aab.12014
• Cassim BMAR, Cordioli VR, Chilante GF, Mazzi FL, Muniz AS, Inoue TT, Batista MA. Effects of straw mulching, liming, and soil texture on ammonia volatilisation: A study of conventional and enhanced efficiency fertilisers. Soil Res. 2024;62:SR23164. https://doi.org/10.1071/SR23164
  » https://doi.org/10.1071/SR23164
• Cassimiro JB, Oliveira CLB, Boni ADS, Donato NDL, Mei-Relles GC, Silva JF, Ribeiro IV, Heinrichs R. Ammonia volatilization and Marandu grass production in response to enhanced-efficiency nitrogen fertilizers. Agronomy. 2023;13:837. https://doi.org/10.3390/agronomy13030837
  » https://doi.org/10.3390/agronomy13030837
• Ciotta MN, Zanella JB, Mendes SDC, Soares AB, Passos JFM, Figueiredo LV. Perdas de nitrogênio por volatilização de amônia em pastagem de azevém sob diferentes doses de ureia. Rev Latino Am Ambient Saúde. 2025;7:161-7.
• Comissão de Química e Fertilidade do Solo - CQFS-RS/SC. Manual de calagem e adubação paraos Estados do Rio Grande do Sul e de Santa Catarina. 11. ed. Porto Alegre: Sociedade Brasileira de Ciência do Solo - Núcleo Regional Sul; 2016.
• Costa MCG, Vitti GC, Cantarella H. N-NH₃ losses from nitrogen sources applied over unburned sugarcane straw. Rev Bras Cienc Solo. 2003;27:631-7. https://doi.org/10.1590/S0100-06832003000400007
  » https://doi.org/10.1590/S0100-06832003000400007
• David DB, Conterato IF, Martins JD, Amaral GA, Ferreira MM, Azevedo EB. Índices de nutrição nitrogenada como estratégia de fertilização em pastagens de azevém anual. Pesq Agropec Gaúcha. 2019;25:195-204. https://doi.org/10.36812/pag.2019253195-204
  » https://doi.org/10.36812/pag.2019253195-204
• Dawar K, Dawar A, Tariq M, Mian IA, Muhammad A, Farid L, Khan S, Khan K, Fahad S, Danish S, Al-Ghamdi AA, Elshikh MS, Tahzeeb-ul-Hassan M. Enhancing nitrogen use efficiency and yield of maize (Zea mays L.) through ammonia volatilization mitigation and nitrogen management approaches. BMC Plant Biol. 2024;24:74. https://doi.org/10.1186/s12870-024-04749-7
  » https://doi.org/10.1186/s12870-024-04749-7
• Fontoura SMV, Bayer C. Ammonia volatilization in no-till system in the south-central region of the State of Paraná, Brazil. Rev Bras Cienc Solo. 2010;34:1677-84. https://doi.org/10.1590/S0100-06832010000500020
  » https://doi.org/10.1590/S0100-06832010000500020
• Gastal F, Lemaire G, Durand J-L, Louarn G. Quantifying crop responses to nitrogen and avenues to improve nitrogen-use efficiency. In: Sadras VO, Calderini DF, editors. Crop Physiology. 2nd ed. London: Academic Press; 2015. p. 161-206. https://doi.org/10.1016/B978-0-12-417104-6.00008-X
  » https://doi.org/10.1016/B978-0-12-417104-6.00008-X
• Giannakis E, Kushta J, Bruggeman A, Lelieveld J. Costs and benefits of agricultural ammonia emission abatement options for compliance with European air quality regulations. Environ Sci Eur. 2019;31:93. https://doi.org/10.1186/s12302-019-0275-0
  » https://doi.org/10.1186/s12302-019-0275-0
• Hargrove WL. Soil, environmental, and management factors influencing ammonia volatilization under field conditions. In: Bock BR, Kissel DE, editors. Ammonia volatilization from urea fertilizers. Alabama: National Fertilizer Development Center; 1988. p. 17-36.
• IUSS Working Group WRB. 2015. World Reference Base for Soil Resources (WRB), sistema universal reconhecido pela International Union of Soil Science (IUSS) e FAO. Available from: http://www.fao.org/3/a-i3794e.pdf
  » http://www.fao.org/3/a-i3794e.pdf
• Köppen W, Geiger R. Das geographische System der Klimate. In: Köppen W, Geiger R, editors. Handbuch der Klimatologie. Berlin: Gebrüder Borntraeger; 1936. p. 1-44.
• Lara-Cabezas WAR, Trivelin PCO. Eficiência de um coletor semi-aberto estático na quantificação de N-NH₃ volatilizado da ureia aplicada ao solo. Rev Bras Cienc Solo. 1990;14:345-52.
• Lara-Cabezas WR, Korndörfer GH, Motta SA. Volatilização de N-NH₃ na cultura de milho: I. Efeito da irrigação e substituição parcial da ureia por sulfato de amônio. Rev Bras Cienc Solo. 1997;21:481-7. https://doi.org/10.1590/S0100-06831997000300018
  » https://doi.org/10.1590/S0100-06831997000300018
• Lemaire G, Franzluebbers A, Carvalho PCF, Dedieu B. Integrated crop–livestock systems: strategies to achieve synergy between agricultural production and environmental quality. Agric Ecosyst Environ. 2014;190:4-8. https://doi.org/10.1016/j.agee.2013.08.009
  » https://doi.org/10.1016/j.agee.2013.08.009
• Lima RC. Adubação de sistemas: volatilização de amônia em área de integração lavoura-pecuária em experimento de longa duração [dissertation]. Pato Branco: Universidade Tecnológica Federal do Paraná; 2018.
• Ma BL, Wu TY, Tremblay N, Deen W, McLaughlin NB, Morrison MJ, Stewart G. On-farm assessment of the amount and timing of nitrogen fertilizer on ammonia volatilization. Agron J. 2010;102:134-44. https://doi.org/10.2134/agronj2009.0021
  » https://doi.org/10.2134/agronj2009.0021
• Miyazawa M, Pavan MA, Bloch MDF. Análise química de tecido vegetal. Londrina: Instituto Agronômico do Paraná; 1992. (Circular, 74).
• Pan B, Lam SK, Mosier AR, Luo Y, Chen D. Ammonia volatilization from synthetic fertilizers and its mitigation strategies: a global synthesis. Agric Ecosyst Environ. 2016;232:283-9. https://doi.org/10.1016/j.agee.2016.08.019
  » https://doi.org/10.1016/j.agee.2016.08.019
• Pavinato PS, Restelatto R, Sartor LR, Paris W. Produção e valor nutritivo do azevém (cv. Barjumbo) sob fertilização nitrogenada. Rev Cienc Agron. 2014;45:230-7. https://doi.org/10.1590/S1806-66902014000200002
  » https://doi.org/10.1590/S1806-66902014000200002
• Pellegrini LGD, Monteiro ALG, Neumann M, Moraes A, Pellegrin ACRS, Lustosa SBC. Produção e qualidade de azevém-anual submetido a adubação nitrogenada sob pastejo por cordeiros. Rev Bras Zootec. 2010;39:1894-904. https://doi.org/10.1590/S1516-35982010000900006
  » https://doi.org/10.1590/S1516-35982010000900006
• Perin V, Santos EA, Lollato R, Ruiz-Diaz D, Kluitenberg GJ. Impacts of ammonia volatilization from broadcast urea on winter wheat production. Agron J. 2020;112:3758-71. https://doi.org/10.1002/agj2.20371
  » https://doi.org/10.1002/agj2.20371
• R Development Core Team. R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing; 2023. Available from: http://www.R-project.org/
  » http://www.R-project.org/
• Rawluk CDL, Grant CA, Racz GJ. Ammonia volatilization from soils fertilized with urea and varying rates of urease inhibitor NBPT. Can J Soil Sci. 2001;81:239-46. https://doi.org/10.4141/S00-052
  » https://doi.org/10.4141/S00-052
• Rojas CAL, Bayer C, Fontoura SMV, Weber MA, Vieiro F. Ammonia volatilization from urea as affected by tillage systems and winter cover crops in the south-central region of Paraná. Rev Bras Cienc Solo. 2012;36:261-70. https://doi.org/10.1590/S0100-06832012000100027
  » https://doi.org/10.1590/S0100-06832012000100027
• San Francisco S, Urrutia O, Martin V, Peristeropoulos A, Garcia-Mina JM. Efficiency of urease and nitrification inhibitors in reducing ammonia volatilization from diverse nitrogen fertilizers applied to different soil types and wheat straw mulching. J Sci Food Agric. 2011;91:1569-75. https://doi.org/10.1002/jsfa.4349
  » https://doi.org/10.1002/jsfa.4349
• Santos HG, Jacomine PKT, Anjos LHC, Oliveira VA, Oliveira JB, Coelho MR, Lumbreras JF, Cunha TJF. Sistema brasileiro de classificação de solos. 3. ed. rev. ampl. Rio de Janeiro: Embrapa Solos; 2013.
• Shan L, He Y, Chen J, Huang Q, Wang H. Ammonia volatilization from a Chinese cabbage field under different nitrogen treatments in the Taihu Lake Basin, China. J Environ Sci. 2015;38:14-23. https://doi.org/10.1016/j.jes.2015.04.028
  » https://doi.org/10.1016/j.jes.2015.04.028
• Sun X, Longhurst B, Luo J, Luo N. Fertiliser nitrogen and factors affecting pasture responses. Open Agric J. 2008;2:35-42. https://doi.org/10.2174/1874331500802010035
  » https://doi.org/10.2174/1874331500802010035
• Suter H, Sultana H, Turner D, Davies R, Walker C, Chen D. Influence of urea fertiliser formulation, urease inhibitor and season on ammonia loss from ryegrass. Nutr Cycl Agroecosyst. 2013;95:175-85. https://doi.org/10.1007/s10705-013-9556-y
  » https://doi.org/10.1007/s10705-013-9556-y
• Sutton MA, Reis S, Riddick SN, Dragosits U, Nemitz E, Theobald MR, De Vries W. Towards a climate-dependent paradigm of ammonia emission and deposition. Philos Trans R Soc Lond B Biol Sci. 2013;368:20130166. https://doi.org/10.1098/rstb.2013.0166f
  » https://doi.org/10.1098/rstb.2013.0166f
• Tasca FA, Ernani PR, Rogeri DA, Gatiboni LC, Cassol PC. Ammonia volatilization following soil application of conventional urea or urea with urease inhibitor. Rev Bras Cienc Solo. 2011;35:493-502. https://doi.org/10.1590/S0100-06832011000200018
  » https://doi.org/10.1590/S0100-06832011000200018
• Timilsena YP, Adhikari R, Casey P, Muster T, Gilla H, Adhikaria B. Enhanced efficiency fertilisers: A review of formulation and nutrient release patterns. J Sci Food Agric. 2015;95:1131-42. https://doi.org/10.1002/jsfa.6812
  » https://doi.org/10.1002/jsfa.6812
• Turner DA, Edis RB, Chen D, Freney JR, Denmead OT, Christie R. Determination and mitigation of ammonia loss from urea applied to winter wheat with N-(n-butyl) thiophosphorictriamide. Agric Ecosyst Environ. 2010;137:261-6. https://doi.org/10.1016/j.agee.2010.02.011
  » https://doi.org/10.1016/j.agee.2010.02.011
• Vale MLC, Sousa RO, Scivittaro WB. Evaluation of ammonia volatilization losses by adjusted parameters of a logistic function. Rev Bras Cienc Solo. 2014;38:223-31. https://doi.org/10.1590/S0100-06832014000100022
  » https://doi.org/10.1590/S0100-06832014000100022
• Varella AC, Carassai IJ, Baldissera TC, Nabinger C, Lustosa SBC, Moraes A, Radin B. Annual ryegrass dry matter yield and nitrogen responses to fertilizer N applications in southern Brazil. Agron NZ. 2010;40:33-42.
• Watson CJ, Stevens RJ, Laughlin RJ. Effectiveness of the urease inhibitor NBPT (N-(n-butyl) thiophosphoric triamide) for improving the efficiency of urea for ryegrass production. Fertil Res. 1990;24:11-5. https://doi.org/10.1007/BF01073142
  » https://doi.org/10.1007/BF01073142
• Zhan X, Adalibieke W, Cui X, Winiwarter W, Reis S, Zhang L, Bai Z, Wang Q, Huang W, Zhou F. Improved estimates of ammonia emissions from global croplands. Environ Sci Technol. 2021;55:1329-38. https://doi.org/10.1021/acs.est.0c05149
  » https://doi.org/10.1021/acs.est.0c05149

Edited by

• Editor:
  José Miguel Reichert https://orcid.org/0000-0001-9943-2898 and Jeferson Dieckow https://orcid.org/0000-0002-3025-4402

Publication Dates

• Publication in this collection
  03 Aug 2026
• Date of issue
  2026

History

• Received
  03 Sept 2025
• Accepted
  10 Feb 2026