High Water Regime Can Reduce Ammonia Volatilization from Soils under Potato Production

Abstract

This research was conducted with Biscayne marl soil and Krome gravelly loam from Florida and Quincy fine sand and Warden silt loam from Washington to determine ammonia (NH₃) volatilization at various temperature and soil water regimes. Potassium nitrate (KNO₃), ammonium nitrate (NH₄NO₃), ammonium sulfate [(NH₄)₂SO₄], or urea were applied to the soil at a rate of 75 kg N ha^?1. Soil water regime was maintained at either 20% or 80% of field capacity (FC) and incubated at 11, 20, or 29°C, which represented the minimum, average, and maximum temperatures, respectively, during the potato growing season in Washington. Results indicated that the ammonia volatilization rate at 20% FC soil water regime was two‐ to three‐fold greater than that at 80% FC. The cumulative volatilization loss over 28 days was up to 25.7%. Results of this study demonstrated that ammonia volatilization was accelerated at low soil water regimes.     

Effects of Biochar and Biosolid on Adsorption of Nitrogen,Phosphorus, and Potassium in Two Soils

Increasing the retention of nutrients by agricultural soils is of great interest to minimize losses of nutrients by leaching and/or surface runoff. Soil amendments play a role in nutrient retention by increasing the surface area and/or other chemical processes. Biochar (BC) is high carbon-containing by-product of pyrolysis of carbon-rich feedstocks to produce bioenergy. Biosolid is a by-product of wastewater treatment plant. Use of these by-products as amendments to agricultural soils is beneficial to improve soil properties, soil quality, and nutrient retention and enhance carbon sequestration. In this study, the adsorption of NH₄-N, P, and K by a sandy soil (Quincy fine sand (QFS)) and a silty clay loam soil (Warden silty loam (WSL)) with BC (0, 22.4, and 44.8 mg ha^?1) and biosolid (0 and 22.4 mg ha^?1) amendments were investigated. Adsorption of NH₄-N by the QFS soil increased with BC application at lower NH₄-N concentrations in equilibrium solution. For the WSL soil, NH₄-N adsorption peaked at 22.4 mg ha^?1 BC rate. Biosolid application increased NH₄-N adsorption by the WSL soil while decreased that in the QFS soil. Adsorption of P was greater by the WSL soil as compared to that by the QFS soil. Biosolid amendment significantly increased P adsorption capacity in both soils, while BC amendment had no significant effects. BC and biosolid amendments decreased K adsorption capacity by the WSL soil but had no effects on that by the QFS soil. Ca release with increasing addition of K was greater by the WSL soil as compared to that by the QFS soil. In both the soils, Ca release was not influenced by BC amendment while it increased with addition of biosolid. The fit of adsorption data for NH₄-N, P, and K across all treatments and in two soils was better with the Freundlich model than that with the Langmuir model. The nutrients retained by BC or biosolid amended soils are easily released, therefore are readily available for the root uptake in cropped soils.     

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.     

Interactive effects of ammonium application rates and temperature on nitrous oxide emission from tropical agricultural soil

Emissions of nitrous oxide (N₂O), a potent greenhouse gas, from agricultural soil have been recognized to be affected by nitrogen (N) application and temperature. Most of the previous studies were carried out to determine effects of temperature on N₂O emissions at a fixed N application rate or those of N application rates at a specific temperature. Knowledge about the effects of different ammonium (NH₄⁺) application rates and temperatures on N₂O emissions from tropical agricultural soil and their interactions is limited. Five grams of air-dried sandy loam soil, collected in Central Vietnam, were adjusted to 0, 400, 800 and 1200 mg NH₄-N kg^–1 soil (abbreviated as 0 N, 400 N, 800 N and 1200 N, respectively) at 60% water holding capacity were aerobically incubated at 20°C, 25°C, 30°C or 35°C for 28 days. Mineral N contents and N₂O emission rates were determined on days 1, 3, 5, 7, 14, 21 and 28. Cumulative N₂O emissions for 28 days increased with increasing NH₄⁺ application rates from 0 to 800 mg N kg^–1 and then declined to 1200 mg N kg^–1. Cumulative N₂O emissions increased in the order of 35°C, 20°C, 30°C and 25°C. This lowest emission at 35°C occurred because N₂O production was derived only from autotrophic nitrification while other N₂O production processes, e.g., nitrifier denitrification and coupled nitrification-denitrification occurred at lower temperatures. More specifically, cumulative N₂O emissions peaked at 800 N and 25°C, and the lowest emissions occurred at 1200 N and 35°C. In conclusion, N₂O emissions were not exponentially correlated with NH₄⁺ application rates or temperatures. Higher NH₄⁺ application rates at higher temperatures suppressed N₂O emissions.     

Nitrogen Volatilization from Arizona Irrigation Waters

A laboratory study was initiated to investigate the effects of temperature (25, 30, 35, and 40 °C) and water quality on the loss of fertilizer nitrogen (N) through volatilization out of irrigation waters collected from 10 different Arizona sources. A 300‐mL volume of each water source was placed in 450‐mL beakers open to the atmosphere in a constant‐temperature water bath with 10 mg of analytical‐grade ammonium sulfate [(NH₄)₂SO₄] dissolved into each sample. Small aliquots were drawn at specific time intervals over a 24‐h period and then analyzed for ammonium (NH₄ ⁺)‐N and nitrate (NO₃ ^?)‐N concentrations. Results showed potential losses from volatilization to be highly temperature dependent. Total losses (after 24 h) ranged from 30–48% at 25 °C to more than 90% at 40 °C. Volatilization loss of fertilizer N from irrigation waters was found to be significant and should be considered when making decisions regarding fertilizer N applications for crop production in Arizona particularly when using ammonia‐based fertilizers.     

Injury of leatherleaf fern and tomato from volatilized ammonia after fertilizer application

Abstract

A commercially blended 7–2–11 fertilizer containing 27 g ? kg^‐1 soluble ammoniacal nitrogen (NH₄‐N) was evaluated for ammonia (NH₃) volatilization and injury to leatherleaf fern (Rumohra adiantiformis) and an indicator plant, tomato (Lycopersicon esculentum). Closed system laboratory incubation studies on pH‐buffered sand medium indicated a very highly significant response (p≤0.001) of NH₃ volatilization to sand pH. The greatest risk from NH₃ emissions at pH 8.6 and 32°C appeared to be in the 5 to 70 hour period after fertilizer application. Gypsum (CaSO₄) did not affect NH₃ volatilization. Ammonium nitrate (NH₄NO₃) was identified as the main source of NH₃ volatilization from this fertilizer formulation, while on an equal mass basis, ammonium sulphate [(NH₄)₂SO₄] was more important. Both tomato and immature leatherleaf fern fronds were highly sensitive to volatilized NH₃ from the fertilizer. A critical phytotoxic NH₃(aq) concentration in sand solution of 0.14 mM was estimated for immature fern fronds. Mature fern fronds were significantly more tolerant of NH₃ emissions, which may explain their observed resistance to NH₃ injury in the field. Assessment of selected soil and irrigation water pH's from a leatherleaf fern growing area in Florida indicated a strong likelihood that volatilized NH₃ injury to foliage can occur under field conditions.     

Effects of cotton (Gossypium hirsutum L.) straw and its biochar application on NH3 volatilization and N use efficiency in a drip-irrigated cotton field

Reducing ammonia (NH₃) volatilization is a practical way to increase nitrogen (N) fertilizer use efficiency (NUE). In this field study, soil was amended once with either cotton (Gossypium hirsutum L.) straw (6 t ha^?1) or its biochar (3.7 t ha^?1) unfertilized (0 kg N ha^?1) or fertilized (450 kg N ha^?1), and then soil inorganic N concentration and distribution, NH₃ volatilization, cotton yield and NUE were measured during the next two growing seasons. In unfertilized plots, NH₃ volatilization losses in the straw-amended and biochar-amended treatments were 38–40% and 42–46%, respectively, less than that in control (i.e., unamended soil) during the two growing seasons. In the fertilized plots, NH₃ volatilization losses in the straw-amended and biochar-amended treatments were 30–39% and 43–54%, respectively, less than that in the control. Straw amendment increased inorganic N concentrations, cotton yield, cotton N uptake and NUE during the first cropping season after application, but not during the second. In contrast, biochar increased cotton N uptake and NUE during both the first and the second cropping seasons after application. Furthermore, the effects of biochar on cotton N uptake and NUE were greater in the second year than in the first year. These results indicate that cotton straw and cotton straw biochar can both reduce NH₃ volatilization and also increase cotton yield, N uptake and NUE. In addition, the positive effects of one application of cotton straw biochar were more long-lasting than those of cotton straw.     

An evaluation of a microbial inoculum in promoting organic C decomposition in a paddy soil following straw incorporation

Purpose

Impacts of a commercially available decay-facilitating microbial inoculum on carbon (C) and nitrogen (N) mineralization were evaluated during decomposition of rice straw in a paddy soil.

Materials and methods

Two incubation experiments were conducted for 105 days with a typical low-yield high-clay soil in central China to monitor effects of straw and the inoculum on CO₂ evolution, as well as dissolved organic C (DOC), NH₄ ⁺, NO₃ ^?, and pH under conditions of 15 °C 70 %, 25 °C 40 %, 25 °C 70 %, 25 °C 100 %, and 35 °C 70 % of water-holding capacity (WHC) with adequate N, supplied as urea or manure, respectively.

Results and discussion

Treatments of 25 °C 70 % WHC, 25 °C 100 % WHC, and 35 °C 70 % WHC generally achieved significant higher CO₂ evolution while treatment of 25 °C 40 % WHC had least. This was more evident with added manure compared to urea (P?<?0.05). The inoculum generally increased the decomposition of C inputs and the largest increases were in the initial 28 day in treatments 25 °C 70 % WHC, 25 °C 100 % WHC, and 35 °C 70 % WHC; only the 25 °C 40 % WHC actually immobilized C. The CO₂ release rates were positively correlated with DOC, but with different slopes within treatments. Despite equivalent N application rates, manure treatments had significantly less N (including NO₃ ^?, NH₄ ⁺, and total dissolved N) than those with urea. Incubation of 25 °C 40 % WHC decreased soil pH the least, probably due to relative low moisture causing delayed nitrification.

Conclusions

The results implied that the inoculum, especially fungi, would adjust to edaphic and N fertilization in regulating organic C mineralization, during which water potential would exhibit a great role in regulating substrate and nutrient availability.

     

Transformation of urea and ammonium nitrate in an entisol and a spodosol under citrus production

Abstract

Chemical transformations of ammonium nitrate (NH₄NO₃) and urea‐nitrogen (N), at different rates of application, were studied in a Candler (Typic Quartzipsamment) and Wabasso (sandy, Alfic Haplaquod) sand by incubating fertilized surface soil (from 0 to 15 cm depth) samples at 10% moisture content (by weight) in the laboratory at 25±1°C. During the 7 d incubation, the percentage of transformation of NH₄‐N into NO₃‐N was 33 to 41 and 37 to 41% in the Candler fine sand and Wabasso sand, respectively, at application rates of 1.00 g N kg¹. In a parallel experiment, 85 to 96% of urea applied (equivalent to 0.25 to 1.00 g N kg^‐1soil) was hydrolyzed to NH₄‐N within 4 d in the Candler soil, whereas it required 7 d to hydrolyze 90 to 95% of the urea applied in the Wabasso soil. No nitrification was evident for 30 days in the Candler fine sand which received urea application equivalent to ≥ 0.50 g N kg^‐1. In the urea‐amended Wabasso sand, the formation of NO₃ decreased as the rate of urea‐N increased. Possible loss of N from NH₃ volatilization or inhibition of activity of nitrifiers due to elevated soil pH (8.7 to 9.2) during the incubation of urea amended soils may have caused very low nitrification.     

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.     

Soil properties affecting volatilization of ammonia from soils treated with urea

Abstract

The effects of various soil properties on ammonia (NH₃) volatilization from soils treated with urea were studied by measuring the NH₃ evolved when 20 soils selected to obtain a wide range in properties were incubated at ‐0.034 mPa soil moisture potential and 30°C for 10 days after treatment with urea. The nitrogen (N) volatilized as NH₃ from these soils represented from 0 to 65% of the urea‐N applied and averaged 14%. Simple correlation analyses showed that loss of NH₃ was negatively correlated (P<0.1%) with cation‐exchange capacity, silt content, and clay content and was positively correlated (P <0.1%) with sand content. Loss of NH₃ was also negatively correlated with total nitrogen content (P<1.0%), organic carbon content (P<1.0%), hydrogen ion buffering capacity (P<5.0%), and exchangeable acidity (P<5.0%), and was positively correlated with calcium carbonate equivalent (P <1.0%) and with soil pH after incubation with urea (P<1.0%), but was not significantly correlated with initial soil pH or soil urease activity. Multiple linear regression analyses indicated that the amount of urea N volatilized as NH₃ from the 20 soils studied increased with increase in sand content and decreased with increase in cation‐exchange capacity. They also indicated that soil texture and cation‐exchange capacity are better indicators of potential loss of urea N as NH₃ from soils fertilized with urea than are hydrogen ion buffering capacity or initial soil pH.     

Interaction of Changes in pH and Urease Activity Induced by Biochar Addition Affects Ammonia Volatilization on an Acid Paddy Soil Following Application of Urea

A pot experiment was conducted to test the hypothesis that the interaction of changes in pH and urease activity induced by biochar addition affects ammonia (NH₃) volatilization on acid soils following application of urea. The results showed that the difference in accumulative NH₃ volatilization between biochar addition rates of 20 and 0 Mg ha^–1 was not significant, while the biochar addition rate of 40 Mg ha^–1 had 42% higher accumulative NH₃ volatilization than the biochar addition rate of 0 Mg ha^–1. Soil pH significantly increased with increasing biochar addition rate. The soil urease activity was significantly reduced by biochar addition, but there was no significant difference between biochar addition rates of 20 and 40 Mg ha^–1. These results support our hypothesis and suggest that the biochar addition rate may need to be properly selected in order to minimize fertilizer-N loss through NH₃ volatilization on urea-fertilized acid paddy soils.     

Use of nitrogen process inhibitors for reducing gaseous nitrogen losses from land-applied farm effluents

Applications of dairy farm effluents to land may lead to ammonia (NH₃) volatilization and nitrous oxide (N₂O) emissions. Nitrogen (N) transformation process inhibitors, such as urease inhibitors (UIs) and nitrification inhibitors (NIs), have been used to reduce NH₃ and N₂O losses derived from agricultural N sources. The objective of this study was to examine the effects of amending dairy effluents with UI (N-(n-butyl) thiophosphoric triamide (NBTPT)) and NI (dicyandiamide (DCD)) on NH₃ and N₂O emissions. Treatments included either fresh or stored manure and either fresh or stored farm dairy effluent (FDE), with and without NBTPT (0.25 g kg^?1 N) or DCD (10 kg ha^?1), applied to a pasture on a free-draining volcanic parent material soil. The nutrient loading rate of FDE and manure, which had different dry matter contents (about 2 and 11 %, respectively) was 100 kg N ha^?1. Application of manure and FDE led to NH₃ volatilization (15, 1, 17 and 0.4 % of applied N in fresh manure, fresh FDE, stored manure and stored FDE, respectively). With UI (NBTPT), NH₃ volatilization from fresh manure was significantly (P?<?0.05) decreased to 8 % from 15 % of applied N, but the UI did not significantly reduce NH₃ volatilization from fresh FDE. The N₂O emission factors (amount of N₂O–N emitted as a percentage of applied N) for fresh manure, fresh FDE and stored FDE were 0.13?±?0.02, 0.14?±?0.03 and 0.03?±?0.01 %, respectively. The NI (DCD) was effective in decreasing N₂O emissions from stored FDE, fresh FDE and fresh manure by 90, 51 and 46 % (P?<?0.05), respectively. All types of effluent increased pasture production over the first 21 days after application (P?<?0.05). The addition of DCD resulted in an increase in pasture production at first harvest on day 21 (P?<?0.05). This study illustrates that UIs and NIs can be effective in mitigating NH₃ and N₂O emissions from land-applied dairy effluents.     

Effects of form of effluent,season and urease inhibitor on ammonia volatilization from dairy farm effluent applied to pasture

Purpose

With land application of farm effluents from cows during housing or milking as an accepted practice, there are increasing concerns over its effect on nitrogen (N) loss through ammonia (NH₃) volatilization. Understanding the relative extent and seasonal variation of NH₃ volatilization from dairy effluent is important for the development of management practices for reducing NH₃ losses. The objectives of this study were to determine potential NH₃ losses from application of different types of dairy effluent (including both liquid farm dairy effluent (FDE) and semi-solid dairy farm manure) to a pasture soil during several contrasting seasons and to evaluate the potential of the urease inhibitor (UI)—N-(n-butyl) thiophosphoric triamide (NBTPT, commercially named Agrotain^®) to reduce gaseous NH₃ losses.

Material and methods

Field plot trials were conducted in New Zealand on an established grazed pasture consisting of a mixed perennial ryegrass (Lolium perenne L.)/white clover (Trifolium repens L.) sward. An enclosure method, with continuous air flow, was used to compare the effects of treatments on potential NH₃ volatilization losses from plots on a free-draining volcanic parent material soil which received either 0 (control) or 100 kg N ha^?1 as FDE or manure (about 2 and 15 % of dry matter (DM) contents in FDE or manure, respectively) with or without NBTPT (0.25 g NBTPT kg^?1 effluent N). The experiment was conducted in the spring of 2012 and summer and autumn of 2013.

Results and discussion

Results showed that application of manure and FDE, both in fresh and stored forms, potentially led to NH₃ volatilization, ranging from 0.6 to 19 % of applied N. Difference in NH₃ losses depended on the season and effluent type. Higher NH₃ volatilization was observed from both fresh and stored manure, compared to fresh and stored FDE. The difference was mainly due to solid contents. The losses of NH₃ were closely related to NH₄ ⁺-N content in the two types of manure. However, there was no relationship between NH₃ losses and NH₄ ⁺-N content in either type of FDE. There was no consistent seasonal pattern, although lower NH₃ losses from fresh FDE and stored FDE applied in spring compared to summer were observed. Potential NH₃ losses from application of fresh FDE or manure were significantly (P?<?0.05) reduced by 27 to 58 % when NBTPT was added, but the UI did not significantly reduce potential NH₃ volatilization from stored FDE or manure.

Conclusions

This study demonstrated that NH₃ losses from application of FDE were lower than from manure and that UIs can be effective in mitigating NH₃ emissions from land application of fresh FDE and manure. Additionally, reducing the application of FDE in summer can also potentially reduce NH₃ volatilization from pasture soil.     

Anaerobic ammonium oxidation and denitrification in a paddy soil as affected by temperature,pH, organic carbon,and substrates

Anaerobic ammonium oxidation (anammox process) widely occurs in paddy soil and may substantially contribute to permanent N removal; however, little is known about the factors controlling this process. Here, effects of temperature, pH, organic C, and substrates on potential rate of anammox and the relative contribution of anammox to total N₂ production in a paddy soil were investigated via slurry incubation combined with ¹⁵N tracer technique. Anammox occurred over a temperature range from 5 to 35 °C with an optimum rate at 25 °C (1.7 nmol N g^?1 h^?1) and a pH range from 4.8 to 10.1 with an optimum rate at pH 7.3 (1.7 nmol N g^?1 h^?1). The presence of glucose and acetate (5–100 mg C L^?1) significantly inhibited anammox activities and the ratio of anammox to total N₂ production. The response of potential rates of anammox to ammonium concentrations fitted well with Michaelis-Menten relationship showing a maximum rate (V_max) of 4.4 nmol N g^?1 h^?1 and an affinity constant (K_m) of 6.3 mg NH₄⁺-N L^?1. Whereas, nitrate addition (5–15 mg ¹⁵NO₃^?-N L^?1) significantly inhibited anammox activities and the ratio of anammox to total N₂ production. Our results provide useful information on factors controlling anammox process and its contribution to N loss in the paddy soil.     

Nitrogen transformation from three soil organic amendments in a sandy soil

Abstract

A sandy soil was amended with various rates (20 – 320 g air-dry weight basis of the amendments per kg of air-dry soil) of chicken manure (CM), sewage sludge (SS), and incinerated sewage sludge (ISS) and incubated for 100 days in a greenhouse at 15% (wt/wt) soil water content. At the beginning of incubation, NH₄-N concentrations varied from 50 – 280 mg kg^?1 in the CM amended soil with negligible amounts of NO₃-N. Subsequently, the concentration of NH₄-N decreased while that of NO₃-N increased rapidly. In soil amended with SS at 20 – 80 g kg^?1 rates, the NO₃-N concentration increased sharply during the first 20 days, followed by a slow rate of increase over the rest of the incubation period. However, at a 160 g kg^?1 SS rate, there were three distinct phases of NO₃-N release which lasted for160 days. In the ISS amended soil, the nitrification process was completed during the initial 30 days, and the concentrations of NH₄-N and NO₃-N were lower than those for the other treatments. The mineralized N across different rates accounted for 20 – 36%, 16 – 40%, and 26 – 50% of the total N applied as CM, SS, and ISS, respectively.     

Combined effects of nitrogen deposition and biochar application on emissions of N2O,CO2 and NH3 from agricultural and forest soils

Abstract

Both nitrogen (N) deposition and biochar can affect the emissions of nitrous oxide (N₂O), carbon dioxide (CO₂) and ammonia (NH₃) from different soils. Here, we have established a simulated wet N deposition experiment to investigate the effects of N deposition and biochar addition on N₂O and CO₂ emissions and NH₃ volatilization from agricultural and forest soils. Repacked soil columns were subjected to six N deposition events over a 1-year period. N was applied at rates of 0 (N0), 60 (N60), and 120 (N120) kg Nh a^?1 yr^?1 without or with biochar (0 and 30 t ha^?1 yr^?1). For agricultural soil, adding N increased cumulative N₂O emissions by 29.8% and 99.1% (p < 0.05) from the N60 and N120 treatments, respectively as compared to without N treatments, and N120 emitted 53.4% more (p < 0.05) N₂O than the N60 treatment; NH₃ volatilization increased by 33.6% and 91.9% (p < 0.05) from the N60 and N120 treatments, respectively, as compared to without N treatments, and N120 emitted 43.6% more (p < 0.05) NH₃ than N60; cumulative CO₂ emissions were not influenced by N addition. For forest soil, adding N significantly increased cumulative N₂O emissions by 141.2% (p < 0.05) and 323.0% (p < 0.05) from N60 and N120 treatments, respectively, as compared to without N treatments, and N120 emitted 75.4% more (p < 0.05) N₂O than N60; NH₃ volatilization increased by 39.0% (p < 0.05) and 56.1% (p < 0.05) from the N60 and N120 treatments, respectively, as compared to without N treatments, and there was no obvious difference between N120 and N60 treatments; cumulative CO₂ emissions were not influenced by N addition. Biochar amendment significantly (p < 0.05) decreased cumulative N₂O emissions by 20.2% and 25.5% from agricultural and forest soils, respectively, and increased CO₂ emissions slightly by 7.2% and NH₃ volatilization obviously by 21.0% in the agricultural soil, while significantly decreasing CO₂ emissions by 31.5% and NH₃ volatilization by 22.5% in the forest soil. These results suggest that N deposition would strengthen N₂O and NH₃ emissions and have no effect on CO₂ emissions in both soils, and treatments receiving the higher N rate at N120 emitted obviously more N₂O and NH₃ than the lower rate at N60. Under the simulated N deposition circumstances, biochar incorporation suppressed N₂O emissions in both soils, and produced contrasting effects on CO₂ and NH₃ emissions, being enhanced in the agricultural soil while suppressed in the forest soil.     

Ammonia volatilization from urea-treated pasture and tillage soils: effects of soil properties

Mean NH₃ losses after nine days incubation at 18°C and 60% FC were 3.1±2.9% and 7.6±6.0% of applied urea-N from the pasture and tillage counterparts of 10 soil series. These losses were highly correlated with buffered CEC and maximal pH values (pH_m) generated three days after urea application. NH₃ volatilization was apparently controlled by buffered CEC and initial pH (R²= 72–87%) and was related to variations in soil organic matter and texture (R²= 77–81%). Losses in the acid pasture soils were attributed largely to initial pH differences, and in the tillage soils to buffered CEC only. Evolution was greater from the tillage than from the pasture equivalent in eight series. This was attributed to differences in CEC, including buffered CEC and pH-dependent charge, caused by differences in OM content primarily but also in texture between the two soil groups. Differences in NH₃ evolution from urea in pasture and tillage soils, in general, are not related to pH differences.     

Ammonia volatilization following urea application at maize fields in the East African highlands with different soil properties

Use of nitrogen (N) fertilizer is underway to increase in Sub-Saharan Africa (SSA). The effect of increasing N rates on ammonia (NH₃) volatilization—a main pathway of applied-N loss in cropping systems—has not been evaluated in this region. In two soils (Alfisols, ALF; and Andisols, AND) with maize crop in the East African highlands, we measured NH₃ volatilization following urea broadcast at six rates (0–150 kg N ha^?1) for 17 days, using a semi-open static chamber method. Immediate irrigation and urea deep placement were tested as mitigation treatments. The underlying mechanism was assessed by monitoring soil pH and mineral N (NH₄⁺ and NO₃^?) concentrations. More cumulative NH₃-N was volatilized in ALF than in AND at the same urea-N rate. Generally, higher urea-N rates increased proportional NH₃-N loss (percent of applied N loss as NH₃-N). Based on well-fitted sigmoid models, simple surface urea application is not recommended for ALF, while up to 60 kg N ha^?1 could be adopted for AND soils. The susceptibility of ALF to NH₃ loss mainly resulted from its low pH buffering capacity, low cation exchange capacity, and high urease activity. Both mitigation treatments were effective. The inhibited rise of soil pH but not NH₄⁺ concentration was the main reason for the mitigated NH₃-N losses, although nitrification in the irrigation treatment might also have contributed. Our results showed that in acidic soils common to SSA croplands, proportional NH₃-N loss can be substantial even at a low urea-N rate; and that the design of mitigation treatments should consider the soil’s inherent capacity to buffer NH₃ loss.     

Gaseous losses of fertilizer nitrogen from a citrus orchard in the red soil hilly region of Southeast China

The gaseous losses of fertilizer nitrogen (N) applied to agroecosystems are a major contributor to a host of environmental problems, inefficient production systems, and decreased N-use efficiency. These losses lead to the wastage of resources, increasing the greenhouse effect and harming human health. The red soil hilly region of Southeast China houses the biggest orchard area of the world, and nitrogen fertilizers are usually heavily applied to the orchard systems in China. Therefore, this study aimed to measure the gaseous losses of the fertilizer N by ammonia (NH₃) volatilization and denitrification losses using the venting method and acetylene inhibition method respectively, and to assess the potential environmental risk of NH₃ and nitrous oxide (N₂O) emission from this orchard system based on the recent orchard management practices. An experiment was conducted in an Ougan citrus (Citrus reticulata Blanco ‘Suavissima’) orchard in the red soil hilly region of Southeast China. Three fertilization treatments, including the control (no N fertilizer, CK), poultry manure (at a rate of 6.3 t/ha, OM), and conventional fertilization (OM 6.3 t/ha + chemical fertilizer 393 kg N/ha, CF), were used. In all treatments, the fertilizers were incorporated into the soil after application. The test results, which were continuously determined within one year, indicated that the NH₃ volatilization losses accounted for 4.5% of the OM nitrogen (OM-N) and 2.9% of the CF nitrogen (CF-N), whereas the denitrification N losses accounted for 2.1% of the OM-N and 2.9% of the CF-N. Overall, the total gaseous N losses (including NH₃ volatilization losses and denitrification N losses) were 5.8% in the CF treatment. A relatively higher N₂O flux, accounting for 1.8% of the CF-N, emitted from the CF treatment.