Potential for Ammonia Volatilization from Urea in Dryland Kentucky Bluegrass Seed Production Systems

Urea replaced ammonium nitrate (AN) as a nitrogen (N) source for dryland Kentucky bluegrass seed production in the inland Pacific Northwest in the United States. This study assessed ammonia (NH₃) volatilization, N recovery, and seed yield from urea as compared to AN. Laboratory incubations indicate NH₃ volatilization is greater from soil covered by fresh residue than soil alone or covered by burned residue. Although pH of the fresh and burned residues exceeded 8.0, urease activity in burned residue was <15% of that in unburned residue or soil. Ammonia volatilization from dry urea and fluid urea AN was greater than AN at burned and unburned sites after a 5 October application. Ammonia volatilization was higher and N recovery and seed yield were lower for urea after a 15 November application at an unburned site. To reduce NH₃ volatilization, apply urea to fields with low urease activity or moisture content and/or immediately before a significant rain event.     

Calcium chloride and ammonium thiosulfate as ammonia volatilization inhibitors for urea fertilizers

Abstract

Surface‐applied urea fertilizers are susceptible to hydrolysis and loss of nitrogen (N) through ammonium (NH₃) volatilization when conditions favorable for these processes exist. Calcium chloride (CaCl₂) and ammonium thiosulfate (ATS) may inhibit urease activity and reduce NH₃ volatilization when mixed with urea fertilizers. The objective of this study was to evaluate the effectiveness of CaCl₂ and ATS as urea‐N loss inhibitors for contrasting soil types and varying environmental conditions. The proposed inhibitors were evaluated in the laboratory using a closed, dynamic air flow system to directly measure NH₃ volatilization. The initial effects of CaCl₂ on ammonia volatilization were more accentuated on an acid Lufkin fine sandy loam than a calcareous Ships clay, but during volatilization periods of ≥ 192 h, cumulative N loss was reduced more on the Ships soil than the Lufkin soil. Calcium chloride delayed the commencement of NH₃ volatilization following fertilizer application and reduced the maximum N loss rate. Ammonium thiosulfate was more effective on the Lufkin soil than the Ships soil. For the Lufkin soil, ATS reduced cumulative urea‐N loss by 11% after a volatilization period of 192 h. A 20% (v/v) addition of ATS to urea ammonium nitrate (UAN) was most effective on the coarse textured Lufkin soil whereas a 5% addition was more effective on the fine textured, Ships soil. Rapid soil drying following fertilizer application substantially reduced NH₃ volatilization from both soils and also increased the effectiveness of CaCl₂ but not ATS. Calcium chloride and ATS may function as limited NH₃ volatilization inhibitors, but their effectiveness is dependent on soil properties and environmental conditions.     

Volatilization of Ammonia Derived from Fertilizer and Its Reabsorption by Coffee Plants

Abstract

Volatilization of ammonia derived from nitrogen (N) fertilizers and its possible reabsorption by crops depend on specific soil, climate, and atmospheric conditions, as well as the method of fertilizer application and plant architecture. In an experiment carried out in Piracicaba, State of São Paulo, Brazil, the volatilization of ammonia derived from urea, ammonium sulfate, and natural soil were quantified using static semi‐open N‐ammonia (NH₃) collectors. Fertilizers were top‐dressed under the plant canopy on top of dead leaf mulch. In another experiment, the reabsorption of the volatilized ammonia by plants was quantified using ¹⁵N‐labeled urea. Results showed, as expected, that volatilization derived from urea was seven times more intense in relation to ammonium sulfate, whose volatilization was very low, and slightly more than the natural volatilization from soil at pH 5.3. The loss of ammonia from the ammonium sulfate was very low, little more than twice of that of the natural soil. Through isotopic labeling, it was verified that 43% of the volatilized N‐NH₃ was reabsorbed by coffee plants, which gives evidence that volatilization losses are greatly reversed through this process.     

Ammonia Volatilization from Soil,Dry-Matter Yield,and Nitrogen Levels of Italian Ryegrass

Nitrogen (N) loss by ammonia (NH₃) volatilization is the main factor for poor efficiency of urea fertilizer applied to the soil surface. Losses can be suppressed by addition of zeolite minerals to urea fertilizer. The objective of this study was to evaluate ammonia volatilization from soil and dry-matter yield and nitrogen levels of Italian ryegrass. A greenhouse experiment was carried out with the treatments of urea, urea incorporated into soil, urea + urease inhibitor, urea + zeolite, ammonium nitrate, and unfertilized treatment. Ammonia was captured by a foam absorber with a polytetrafluoroethylene tape. There were few differences between zeolite and urease inhibitor amendments concerning NH₃ volatilization from urea. Results indicate that zeolite minerals have the potential to improve the N-use efficiency and contributed to increasing N uptake. Zeolite and urea mixture reduced 50% the losses by volatilization observed with urea.     

Effects of Temperature and Soil Type on Ammonia Volatilization from Slow-Release Nitrogen Fertilizers

Ammonia (NH₃) volatilization is the major pathway for mineral nitrogen (N) loss from N sources applied to soils. The information on NH₃ volatilization from slow-release N fertilizers is limited. Ammonia volatilization, over a 78-d period, from four slow-release N fertilizers with different proportions of urea and urea polymer [Nitamin 30L (liquid) (L30), Nitamin RUAG 521G30 (liquid) (G30), Nitamin 42G (granular) (N42), and Nitroform (granular) (NF)] applied to a sandy loamy soil was evaluated. An increase in temperature from 20 to 30 °C increased cumulative NH₃ volatilization loss in the sandy soil by 1.4-, 1.7-, and 1.8-fold for N42, L30, and G30, respectively. Increasing the proportion of urea in the slow-release fertilizer increased NH₃ volatilization loss. At 30 °C, the cumulative NH₃ volatilization over 78 d from a sandy soil accounted for 45.6%, 43.9%, 22.4%, and <1% of total N applied as N42, L30, G30, and NF, respectively. The corresponding losses in a loamy soil were 9.2%, 3.1%, and 1.7%. There was a significantly positive correlation between NH₃ volatilization rate and concentration of NH₄-N released from all fertilizers, except for NF (n = 132; r = 0.359, P = 0.017 for N42; r = 0.410, P = 0.006 for L30; and r = 0.377, P < 0.012 for G30). Lower cumulative NH₃ volatilization from a loamy soil as compared to that from a sandy soil appeared to be related to rapid nitrification of NH₄-N in the former soil than that in the latter soil. These results indicate the composition of slow-release fertilizer, soil temperature, and soil type are main factors to dominate NH₃ volatilization from slow- release fertilizers.     

Control of ammonia volatilization with N‐(N‐butyl) thiophosphoric triamide in loamy sands

Abstract

In a laboratory study, ammonia (NH₃) was trapped from 10 g soil units treated with 10 mg urea‐N, 10 mg urea‐N plus 50 ug N‐(n‐butyl) thiophosphoric triamide (NBPT), or 10 mg urea‐N plus 50 ug phenyl‐phosphorodiamidate (PPD). The soil was a Dothan loamy sand with pH levels adjusted to 6.0, 6.5, and 6.9 prior to N application. After 12 days, NBPT reduced NH₃ volatilization 95 to 97%, while PPD reduced it 19 to 30%. Although NH₃ loss was positively related to initial soil pH, there was no interaction between pH and urease inhibitor. In a field study, NH₃ was trapped in semi‐closed chambers from 134 kg N/ha surface applied to corn (Zea mays L.) 6 weeks after planting. Nine days after N application, NH₃ losses were 20.5, 1.5, 1.5, and 0.2 kg N/ha from urea, urea plus 0.25% NBPT, urea plus 0.50% NBPT, and ammonium nitrate, respectively. Covariance analysis showed that percent organic matter was negatively related to NHL losses. The soil properties, initial pH, CEC, and percent sand, did not vary enough to affect NH₃ volatilization. In conclusion, in both the laboratory and the field, NBPT exhibited strong control of NH₃ volatilization, and could thereby prevent significant loss of surface‐applied urea‐N to crops.     

Controlled‐release urea decreased ammonia volatilization and increased nitrogen use efficiency of cotton

Excessive nitrogen (N) fertilizer input leads to higher N loss via ammonia (NH₃) volatilization. Controlled‐release urea (CRU) was expected to reduce emission losses of N. An incubation and a plant growth experiment with Gossypium hirsutum L. were conducted with urea and CRU (a fertilizer mixture of polymer‐coating sulfur‐coated urea and polymer‐coated urea with N ratios of 5 : 5) under six levels of N fertilization rates, which were 0% (0 mg N kg⁻¹ soil), 50% (110 mg N kg⁻¹ soil), 75% (165 mg N kg⁻¹ soil), 100% (220 mg N kg⁻¹ soil), 125% (275 mg N kg⁻¹ soil), and 150% (330 mg N kg⁻¹ soil) of the recommended N fertilizer rate. For each type of N fertilizer, the NH₃ volatilization, cotton yield, and N uptake increased with the rate of N application, while N use efficiency reached a threshold and decreased when N application rates of urea and CRU exceeded 238.7 and 209.3 mg N kg⁻¹ soil, respectively. Ammonia volatilization was reduced by 65–105% with CRU in comparison to urea treatments. The N release characteristic of CRU corresponded well to the N requirements of cotton growth. Soil inorganic N contents, leaf SPAD values, and net photosynthetic rates were increased by CRU application, particularly from the full bloom stage to the initial boll‐opening stage. As a result, CRU treatments achieved significantly higher lint yield by 7–30%, and the N use efficiency of CRU treatments was increased by 25–124% relative to that of urea treatments. These results suggest that the application of CRU could be widely used for cotton production with higher N use efficiency and lower NH₃ volatilization.     

Urea nitricphosphate for cool‐season grass production

Abstract

Significant losses of nitrogen (N) can occur via volatilization of ammonia (NH₃) when non‐incorporated broadcast applications of urea or urea‐containing fertilizers are made. This study was conducted to determine the efficacy of urea nitricphosphate (UNP) as an N and phosphorus (P) source for cool‐season grasses and to evaluate NH₃ volatilization potential of UNP as compared to urea under laboratory conditions. A three‐year field study compared UNP to ammonium nitrate (AN) and urea at 56 and 112 kg N/ha for tall fescue (Festuca arundinacea Schreb.) and smooth brome (Bromus inermis Leyss.). Brome yields were significantly higher from UNP as compared to urea for one of the three years. No such differences occurred with fescue. Nitrogen uptake was significantly higher from UNP as compared to urea for one year each for brome and fescue. Phosphorus uptake by brome was significantly higher from UNP as compared to urea for two years. Laboratory incubation studies showed significantly lower NH₃ volatilization from UNP than from urea after seven days, but no significant differences after 14 days. The delay in NH₃ volatilization was due to the diffusion and subsequent hydrolysis of urea immediately below the soil zone initially influenced by the UNP. The reduction in NH₃ volatilization at the early time could partially be attributed to an inhibition of urea hydrolysis and significantly lower soil pH values for UNP as compared to urea in the upper 30 mm of soil cores. The general conclusion from the field and laboratory work was that UNP is a suitable N source for cool‐season grasses, with the primary potential benefit being delayed NH₃ volatilization as compared to urea.     

Structural Characteristics and Oxygen Consumption of the Epipelic Biofilm in Three Lowland Streams Exposed to Different Land Uses

Ammonia (NH₃) emission from nitrogen (N) fertilizers used in agriculture decreases N uptake by the crop and negatively impacts air quality. In order to better understand the factors influencing NH₃ emission from agriculture, this research was conducted with four major soils used for potato production: Biscayne Marl Soil (BMS, pH 7.27), and Krome Gravelly Loam (KGL, pH 7.69) from Florida; and Quincy Fine Sand (QFS, pH 6.65), and Warden Silt Loam (WSL, pH 6.46) from Washington. Potassium nitrate (KNO₃), ammonium nitrate (NH₄NO₃), ammonium sulfate ((NH₄)₂SO₄) or urea ((NH)₂CO) sources were evaluated for ammonia volatilization at 75 kg N ha^?1 rate. The soil water regime was maintained at either 20 or 80% of field capacity (FC), and incubated at 11, 20 or 29°C. Results indicated that NH₃ volatilization rate at 20% FC was 2 to 3-fold greater than that at 80% FC. The cumulative volatilization loss over 28 days ranged from 0.21% of N applied as NH₄NO₃ to 25.7% as (NH₄)₂SO₄. Results of this study demonstrate that NH₃ volatilization was accelerated at the low soil water regime. Moisture quotient (Q) is defined as a ratio of NH₃ emission rate at 20% FC to that at 80% FC both at the same temperature. The peak Q values of NH₃ volatilization were up to 20.8 for the BMS soil at 20°C, 112.9 for the KGL soil at 29°C, 19.0 for the QFS soil at 20°C, and 74.1 for the WSL soil at 29°C, respectively. Thus, maintaining a suitable soil water regime is important to minimize N-loss via NH₃ volatilization and to improve N uptake efficiency and air quality.     

Nitrogen losses by volatilization in a corn crop with two tillage systems in the Argentine Pampa

Abstract

Ammonia volatilization from soils is a complex process generally associated with surface applied nitrogen (N) fertilizer. The effect of conventional tillage and no tillage on NH₃ volatilization was evaluated on cultivated corn (Zea maize L.) field in Pampa Húmeda, Argentina. The objectives of this study were a) to determine the amount of N loss by volatilization (NH₃) from urea fertilized soils under two different tillage systems (conventional and no tillage) and two different fertilizer application methods (surface and incorporated application) and b) to relate volatilization losses with environmental factors and biochemical and microbiological properties. This experiment was conducted on a Vertic Argiudoll with a silty clay loam texture in the Argentine Pampa. The site has been in natural grassland for 8 years prior was planted to corn. Following the fertilizer application for conventional tillage and no tillage systems, the daily volatilization loss of NH₃ on the fertilized plots was highest during the first three days. Higher losses of NH₃ occurred in the no‐tillage treatments, with 11.5% and 6.2% of N‐urea lost when the fertilizer was surface applied and incorporated, respectively. For conventional tillage, 8.6 % of the N was lost when the fertilizer was surface applied and 5.4% when the fertilizer was incorporated. Surface application of urea stimulated urease enzyme activity. An opposite effect was observed when the urea was incorporated. Environmental changes conditioned the availability of energy substrates for microorganisms, which resulted in different rates of intensity of biochemical reactions in the soil. Multiple regression equations showed differences between surface applied urea and incorporated urea treatments due to the latter avoiding the direct exposure of the fertilizer to atmospheric conditions.     

Does soil amended with biochar and hydrochar reduce ammonia emissions following the application of pig slurry?

Combining amendments to the soil made by biochar or hydrochar with nitrogen (N) fertilizer can modify soil N dynamics and availability. Such a response suggests that these amendments would affect ammonia (NH₃) emissions from slurry similarly, and potentially reduce volatilization of NH₃. This study measured the potential emissions of NH₃ following application of pig slurry to the surface of silt‐loam and loam soils amended with biochar and hydrochar (both derived from Miscanthus × giganteus (Greef et Deu)) at a rate of 3% soil dry weight (16 t ha^?1 soil area, on average) and 60% water‐filled pore space (WFPS). The experiment was carried out in a dynamic chamber connected to a photo‐acoustic trace gas analyser in a controlled climate (20°C) for 48 hours. Statistically significant differences (P < 0.05) in total emissions were observed between both treatment and soil types. Surprisingly, both amendments increased emissions of NH₃ compared with the control; cumulative NH₃ emissions averaged 38.7 and 23.5% of applied total ammonium nitrogen (TAN) for hydrochar and biochar, respectively, whereas it was 18.2% for the control. The larger emissions in hydrochar‐amended soil were attributed to the reduced ability to absorb NH₄⁺ associated with greater hydrophobicity and strong pH buffering of the slurry. Furthermore, final soil analyses with deionised water extracts showed significant differences (P < 0.05) in mineral N concentration between treatments. The smaller ammonium concentrations in biochar‐amended soil suggest that some NH₄⁺‐N was immobilized by adsorption on to biochar surfaces. This study observed that biochar and hydrochar properties, as well as soil characteristics, play important roles in controlling NH₃ emissions from surface slurry applications. The results obtained identified circumstances where these amendments even enhance volatilization, which provides new information on and insight into the extent and limitations of the potential of biochar and hydrochar for the mitigation of emissions.     

Slurry field management and ammonia emissions under Mediterranean conditions

In Spain, farmers are interested in applying pig (Sus scrofa domesticus) slurry (PS) to their fields throughout the year. During the spring and summer months, ammonia (NH₃) volatilization may be high. We studied the potential range of NH₃ losses under a warm and a hot period of the year, using available field practices, and two strategies: PS directly incorporated into the soil, in spring (I‐spring); and PS applied by splash‐plate, in summer time (SP‐summer), both to bare soil. Measurements were conducted, after PS application, using the micrometeorological mass balance integrated horizontal flux method. The cumulative NH₃‐N volatilization was 35% (I‐spring) and 60% (SP‐summer) of total ammonium nitrogen applied, and half of the total NH₃‐N losses happened by 17 h and 8 h, respectively, after application. Incorporation strategy was less effective in avoiding NH₃ losses than is described in the literature. This fact has important consequences for the implementation of NH₃ mitigation measures in Mediterranean agricultural systems.     

Ammonia volatilization from ammonium sulphate,ammonium nitrate,and urea surface applied to winter wheat on a calcareous soil

Abstract

Ammonia (NH₃) volatilization losses from surface‐applied ammonium sulphate (AS), ammonium nitrate (AN), and urea to winter wheat and the effects of the NBPT [N‐(n‐butyl) thiophosphoric triamide], PG (Phospho‐gypsum), and PR (byproduct‐Pyrite) were determined in a field experiment. Effects on grain yield and protein content of the grain were also measured. Total NH₃ losses from AS, AN, and urea varied from 13.6–19.5%, 4.4–6.4%, and 3.9–12.0% depending on the compounds and their levels added to nitrogen (N) fertilizers, respectively. The compounds added to AS and AN increased NH₃‐N losses with respect to unamended fertilizers (control). On the other hand, while urea treatments with two tons of PG/ha increased NH₃ losses, the other compounds decreased the losses. The highest reductions of NH₃ loss were observed with NBPT 0.50% and NBPT 0.25% by 63.4% and 52.8%, respectively. Although the effect of nitrogeneous fertilizers on total N losses and protein content of wheat grain was found statistically significant (p<0.01), as the compounds applied with N fertilizers have had no significant effect. Also, a negative and highly significant correlation (r = ‐0.69???) was found between total N loss and protein content of the grain.     

Effect of ammonium sulfate pretreatment on ammonia volatilization after urea fertilization

Abstract

Urea applications to soil are subject to loss by ammonia (NH₃) volatilization, unless incorporated. It has been proposed that this loss can be reduced by stimulating populations of soil nitrifiers by an ammonium sulfate [(NH₄)₂SO₄] pretreatment two to four weeks before urea application. The objective of this laboratory trial was to evaluate this concept with five diverse soils, two North American Mollisols and three South American Oxisols. The soils were incubated untreated for two weeks, followed by pretreatment with 0 or 5 kg nitrogen (N) ha^‐1 as (NH₄)₂SO₄, on a soil surface area basis. After another two weeks of incubation, the soils were treated with the equivalent of 0 or 50 kg N ha^‐1 as urea. Ammonia loss was estimated after trapping into phosphoric acid (H₃PO₄). Ammonium sulfate pretreatment reduced NH₃ loss with the two Mollisols and a sandy Oxisol and increased the recovery of the urea application as mineral [ammonium (NH₄ ⁺) + nitrate (NO₃ ^‐)] N in these soils. Little NH₃ loss was detected from the two clay Oxisols, and (NH₄)₂SO₄pretreatment did not influence NH₃ loss or recovery of urea as mineral N. An example of a cropping system where this concept may have utility is discussed.     

Reactions of urea phosphate in calcareous and alkaline soils: I. Ammonia volatilization

Abstract

Nitrogen (N) loss in the form of volatilized ammonia (NH₃) is a considerable problem when ammonium (NH₄ ⁺⁾ forming fertilizers are applied to calcareous or alkaline soils. The volatilization of NH₃ from urea phosphate (UP) and urea (U) was studied on three selected soils (Hayhook SL, Laveen L, and Latene L) with the use of a laboratory aeration system. Urea phosphate and U were each applied at rates of 0, 50, 100, and 200 mg N kg^‐1 soil, either to the surface dry or in solution or mixed with the soil. The volatilized NH₃ was trapped in sulfuric acid, sampled periodically, and analyzed for N with the semi microkjeldahl distillation apparatus.

The highest N loss in the form of NH₃ occurred when U was applied to Hayhook soil (neutral to acidic, coarse textured, and low CaCO₃ content). However, UP applied to Hayhook soil resulted in the lowest NH₃‐N loss. Less NH₃‐N loss was found from U application to Laveen and Latene soils (fine textured with higher CaCO₃ content) than with Hayhook soil. The general trend was higher N loss when a surface application was made, either dry or in solution, than when the fertilizer was mixed with the soil. This trend showed an increase in the amount of volatilized NH₃ with increasing N application rates.

Generally, UP is a potential fertilizer for supplying N and phosphorus (P) as plant nutrients with a low potential for losses due to NH₃ volatilization.     

太湖地区水稻追肥的氨挥发损失和氮素平衡

采用密闭室通气法和¹⁵N 微区试验, 对太湖地区水稻不同生育期追施氮肥的氨挥发损失、水稻对氮肥的吸收利用和土壤氮素残留情况进行了研究。结果表明, 氨挥发损失主要发生在施肥后1 周内, 峰值出现在施肥后1~2 d, 氨挥发速率变化与田面水NH₄⁺-N 浓度变化规律一致, 分蘖肥和穗肥氨挥发损失率分别为16.7%和6.3%; 水稻分蘖肥的作物氮素利用率低于穗肥, 分别为36.7%和49.6%, 主要原因是穗肥的氨挥发损失较少,并且更易于向籽粒转移; 2 次追施氮肥的表观损失率分别为52.8%和40.7%; 在土壤中残留肥料氮为10.6%, 大都集中在0~20 cm 土壤中, 耕层以下较少。本结果表明, 在水稻孕穗时期施氮肥有利于提高氮肥利用效率、减少氮肥损失, 主要体现在穗肥拥有较低的氨挥发损失率和较高的籽粒利用率。     

Short‐term N2O,CO2, NH3 fluxes,and N/C transfers in a Danish grass‐clover pasture after simulated urine deposition in autumn

Urine patches are significant hot‐spots of C and N transformations. To investigate the effects of urine composition on C and N turnover and gaseous emissions from a Danish pasture soil, a field plot study was carried out in September 2001. Cattle urine was amended with two levels of ¹³C‐ and ¹⁵N‐labeled urea, corresponding to 5.58 and 9.54 g urea‐N l^–1, to reflect two levels of protein intake. Urine was then added to a sandy‐loam pasture soil equivalent to a rate of 23.3 or 39.8 g urea‐N m^–2. Pools and isotopic labeling of nitrous oxide (N₂O) and CO₂ emissions, extractable urea, ammonium (NH₄⁺), and nitrate (NO₃^–), and plant uptake were monitored during a 14 d period, while ammonia (NH₃) losses were estimated in separate plots amended with unlabeled urine. Ammonia volatilization was estimated to account for 14% and 12% of the urea‐N applied in the low (UL) and high (UH) urea treatment, respectively. The recovery of urea‐derived N as NH₄⁺ increased during the first several days, but isotopic dilution was significant, possibly as a result of stress‐induced microbial metabolism. After a 2 d lag phase, nitrification proceeded at similar rates in UL and UH despite a significant difference in NH₄⁺ availability. Nitrous oxide fluxes were low, but generally increased during the 14 d period, as did the proportion derived from urea‐N. On day 14, the contribution from urea was 23% (UL) and 13% (UH treatment), respectively. Cumulative total losses of N₂O during the 14 d period corresponded to 0.021% (UL) and 0.015% (UH) of applied urea‐N. Nitrification was probably the source of N₂O. Emission of urea‐derived C as CO₂ was only detectable within the first 24 h. Urea‐derived C and N in above‐ground plant material was only significant at the first sampling, indicating that uptake of urine‐C and N via the leaves was small. Urine composition did not influence the potential for N₂O emissions from urine patches under the experimental conditions, but the importance of site conditions and season should be investigated further.     

Effect of nitrate addition on efficient use of ammonium sulfate fertilizer on corn under saline conditions. I. Pot experiment

Abstract

Plant growth in saline soils is regulated by the availability of nitrogen (N). High soil nitrate (NO₃)‐N can lead to poor water quality. Many workers think that NO₃‐N as a source for N can contribute to better plant growth in saline soils. The purpose of this work was to determine the necessity of NO₃‐N and the ratio of NO₃/ammonium (NH₄) in the N fertilizer which gives higher productivity of the biomass yield of corn. Corn (Zea mays L.) plants (Var. LG11) were grown under saline soil conditions (8.5 dS m^‐1), soils taken from the Euphrates valley (ACSAO Research Station) at Deir‐Ez‐Zor, east of Syria, from the surface layer of soil (0–25 cm). Five levels of N were applied in two forms, ammonium sulfate [¹⁵(NH₄)₂SO₄] with enrichment (1.5% a) as the NH₄‐N form and calcium nitrate [Ca(NO₃)₂] as the NO₃‐N form, besides fixed amounts of phosphorus (P) and potassium (K) for all N treatments. The corn plants were harvested at the flowering stage (56 days old), oven dried, weighed, and analyzed for total N and ¹⁵N recovery. The results indicated that the dry matter weight for treatments which received a combination of NH₄‐N and NO₃‐N gave higher dry matter yield than a single treatment of one source of N. But, NO₃‐N was more effective in improving yield than NH₄‐N. Nitrogen recoveries on the basis of added and absorbed N derived from fertilizer were significantly more affected by NO₃‐N than NH₄‐N.     

镇江丘陵区稻田化肥氮的氨挥发及其影响因素

采用密闭室方法对镇江丘陵区典型稻麦轮作制度下的水稻插秧、分蘖和孕穗期施用尿素的氨挥发进行了测定，并对施肥后土壤pH的变化及其对氨挥发的影响进行了分析，结果表明稻田施用尿素有明显的氨挥发损失，氨挥发损失率在水稻不同生育期有很大的差异，分蘖肥的氨挥发显著高于基肥和孕穗肥，受温度、植株状况以及光照条件等因素的影响，氮挥发存在明显的年际差异。田面水的pH值在施肥后有明显的昼夜波动，而氨挥发损失受田面水pH值变化的显著影响。稻草对不同生育期施肥的氨挥发影响不同。     

华北山前平原农田生态系统氮通量与调控

针对华北太行山前平原冬小麦-夏玉米轮作农田, 研究农田常规施肥[400 kg(N)·hm^-2·a^-1]条件下作物氮素吸收与损失通量过程, 并根据各氮素输出通量特征开展管理调控。研究结果表明, 全年小麦-玉米轮作农田系统氮输入总量为561~580 kg(N)·hm^-2, 输出量468~494 kg(N)·hm^-2, 两季作物总盈余86~93 kg(N)·hm^-2, 其中有机氮为24~36 kg·hm^-2。氨挥发和NO₃^--N 淋溶损失是该区域农田氮素损失的主要途径, 是氮肥利用率低的重要原因。平均每年因氨挥发而造成的肥料氮损失量为60 kg(N)·hm^-2, NO₃^--N 淋溶损失量为47~84kg(N)·hm^-2, 两者占施肥总量的30%。每年因硝化-反硝化过程造成的肥料损失很小, 仅为5.0~8.7 kg(N)·hm^-2。通过施肥后适时灌水、合理调控灌水时间与用量, 以及利用秸秆还田与肥料混合施用等管理措施可改善氮素的迁移和转化规律, 有效减少氨挥发和NO₃^--N 淋溶损失, 并结合缓/控释肥与精准施肥技术, 充分利用土壤本身矿质氮素, 可有效提高养分利用效率和作物产量, 改善农田生态环境与促进农业持续和谐发展。