Anhydrous NH3 Research Articles

Spatiotemporal distribution of roots in a Maize-Kura clover living mulch system: Impact of tillage and fertilizer N source

Kura clover living mulch (KCLM) can be integrated into Midwestern row-crop production systems as a soil and water conservation tool. Rotary zone tillage is currently recommended to establish a clover-free zone for maize seeding in the living mulch, however, this practice is costly and presents a major barrier to producers. Banding anhydrous NH3 in a KCLM, due to its transient caustic impact, may damage clover roots and provide supplemental clover suppression. This experiment aimed to determine the effects of tillage intensity and fertilizer source on maize yield and clover root biomass. Maize was seeded into a KCLM prepared with rotary zone tillage (RZT) or shank strip tillage (ST) and fertilized with ammonium nitrate (NH4NO3) or NH3 banded under the tilled zone. Aboveground clover biomass, total root biomass, and soil N were sampled at eight times between tillage and the R4 maize physiological growth stage, and maize and clover roots were differentiated using their 13C isotope signatures. Results indicated that ST achieved adequate clover suppression and grain yields were not affected by tillage or fertilizer treatments. The RZT treatment reduced clover root biomass relative to ST, but fertilizer N source did not affect above or belowground clover biomass pools. Based on the results of this study, we conclude that ST can be used with any form of banded N fertilizer to successfully manage maize in KCLM while maintaining a greater level of clover root biomass than RZT.

Ammonia, methane and nitrous oxide emissions from furrow irrigated cotton crops from two nitrogen fertilisers and application methods

• Urea broadcast and fertigation were applied at a commercial irrigated cotton farm. • Gas emissions were measured by micrometeorological technique and OP-FTIR technique. • NH 3 flux from anhydrous NH 3 was 24% higher than broadcasting urea with irrigation. • Daily fluxes of CH 4 and N 2 O were both negative following both fertilisation events. Abstract Agricultural systems use nitrogen (N) fertilizers to improve crop nutrition and yield, but applied N can negatively impact the environment and human health due to the gases emitted during and after N application. There are few direct measurements of multiple gaseous emissions from N fertiliser applied to irrigated cotton farms. This study was conducted in a commercial cotton farm in NSW, Australia to measure gaseous emissions from two N fertilisation strategies (urea broadcast onto dry soil followed by irrigation, anhydrous ammonia injected into water at the main irrigation channel), with the N fertilizer rate of 27 kg N ha −1 for each application. Gas fluxes of ammonia (NH 3 ), methane (CH 4 ), and nitrous oxide (N 2 O) were measured simultaneously using an inverse-dispersion technique coupled with open-path Fourier transform infrared (OP-FTIR) spectroscopic technique, located 150 and 800 m from the input source of the irrigation water. We found that anhydrous ammonia injected into the irrigation water contributed to higher peak NH 3 emissions (0.79 ± 0.09 kg N ha −1 day −1 ) than broadcasting urea onto dry soil (-0.06 ± 0.02 kg N ha −1 day −1 ). When daily NH 3 fluxes were accumulated over 8 − 10 days, 24% of the applied N was lost as NH 3 during anhydrous ammonia application, but no N loss was detected over the course of measurement period from the broadcast urea followed by irrigation. The daily fluxes of CH 4 and N 2 O were both negative following both fertilisation events. Our study suggests that cotton farm managers should avoid the use of anhydrous NH 3 in irrigation water to mitigate the environmental impact, as well as low efficiency of N fertiliser use.

Extent and Variation of Nitrogen Losses from Non-legume Field Crops of Conterminous United States

Nitrogen (N) losses from field crops have raised environmental concerns. This manuscript accompanies a database of N loss studies from non-legume field crops conducted across the conterminous United States. Cumulative N losses through nitrous oxide-denitrification (CN2O), ammonia volatilization (CNH3), and nitrate leaching (CNO3−) during the growing season and associated crop, soil, and water management information were gathered to determine the extent and controls of these losses. This database consisted of 404, 26, and 358 observations of CN2O, CNH3, and CNO3− losses, respectively, from sixty-two peer-reviewed manuscripts. Corn (Zea mays) dominated the N loss studies. Losses ranged between −0.04 to 16.9, 2.50 to 50.9, and 0 to 257 kg N ha−1 for CN2O, CNH3 and CNO3−, respectively. Most CN2O and CNO3− observations were reported from Colorado (n = 100) and Iowa (n = 176), respectively. The highest values of CN2O, and CNO3− were reported from Illinois and Minnesota states, and corn and potato (Solanum tuberosum), respectively. The application of anhydrous NH3 had the highest value of CN2O loss, and ammonium nitrate had the highest CNO3− loss. Among the different placement methods, the injection of fertilizer-N had the highest CN2O loss, whereas the banding of fertilizer-N had the highest CNO3− loss. The maximum CNO3− loss was higher for chisel than no-tillage practice. Both CN2O and CNO3− were positively correlated with fertilizer N application rate and the amount of water input (irrigation and rainfall). Fertilizer-N management strategies to control N loss should consider the spatio-temporal variability of interactions among climate, crop-and soil types.

Long‐term in‐season grain sorghum and soybean response to tillage and nitrogen management

AbstractInformation on tillage and N management is limited regarding in‐season N uptake by grain sorghum [Sorghum bicolor (L.) Moench] and growth of soybean [Glycine max (L.) Merr.] on claypan soils in the eastern Great Plains. The objective of this study was to determine the 20‐yr effects of tillage (conventional, reduced, and no‐till) and N fertilization (no‐N control; knifed anhydrous NH3; broadcast urea–ammonium nitrate solution, UAN; and broadcast dry urea) on grain sorghum N uptake and soybean biomass and their relationship to long‐term yields of those crops grown on a claypan soil. Nitrogen uptake at the boot stage during the first 10‐yr period was more than 20% greater with either conventional or reduced tillage compared with no‐till, and often greater with anhydrous NH3 and urea N sources than with UAN solution or the no‐N control. During the second 10‐yr period, N uptake was generally greater with conventional and reduced tillage than with no‐till at the 9‐leaf stage, but this response did not persist to the boot stage. Anhydrous NH3 often resulted in greater N uptake at both the 9‐leaf and boot stages compared with the other N sources. The relative yield increases with N uptake at the boot stage appeared due to increasing kernels head−1 but diminished as uptake exceeded 70−80 kg N ha−1. Although dry matter measured at the R2 growth stage of soybean rotationally grown in even‐numbered years was about 10% greater with tilled options than with no‐till, biomass was not related to yield increases.

System for Preparing and Applying 15N‐Labeled Anhydrous Ammonia in Field Plot Research

Core Ideas A manifold is described for preparing kilogram quantities of 15NH3. The 15NH3 is condensed into a collection tank that allows the use of a nitrification inhibitor. The collection tank connects to a tractor‐mounted toolbar for knifed applications to field plots. Although direct application of anhydrous ammonia (NH3) is a common practice for Midwestern corn (Zea mays L.) production in the USA, field studies utilizing 15N to quantify nitrogen (N) uptake efficiency have long been impeded by the difficulties and safety hazards inherent to a liquified gas that must be handled and applied under pressure. A manifold system is described for transferring known quantities of NH3 from labeled and unlabeled sources to obtain a desired 15N enrichment, and for collecting the mixture cryogenically in a tank specifically configured for knifed applications using a tractor‐mounted tool bar. Enrichments of 1.2 to 1.5 atom% 15N were obtained for 3 kg of NH3 prepared within a normal working day by a 15‐fold dilution with 10 atom% 15N as the starting label. A collection capacity of such magnitude represents a 3000% upscaling over systems previously described for this purpose, providing an essential prerequisite for field plot research to realistically assess the fate and fertilizer value of anhydrous NH3.

Laying hens behave differently in artificially and naturally sourced ammoniated environments

Laying hens are chronically exposed to high levels of ammonia (NH3), one of the most abundant aerial pollutants in poultry houses. Tests for aversion to NH3 in laying hens have used artificially sourced NH3/air mixtures (i.e., from a gas cylinder) showing that birds prefer fresh air to NH3. However, artificially sourced NH3/air mixtures may not accurately reflect barn air conditions, where manure emits a variety of gases. Herein, we investigated whether laying hens differentiate between artificially and naturally sourced NH3/air mixtures and how exposure to NH3 affects foraging and aversive behavior. A total of 20 laying hens was exposed to artificially sourced [A] (from an anhydrous NH3 cylinder) and naturally sourced [N] (from conspecific laying hen excreta) gas mixtures. Hens were exposed to A and N mixtures with NH3 concentrations of 25 and 45 ppm, as well as fresh air [FA]. During the experiment, all birds were exposed to each treatment 3 times using a custom-built polycarbonate chamber, containing a foraging area (containing raisins, mealworms, and feed mix) and a gas delivery system. All testing sessions were video recorded, analyzed with INTERACT® software, and subjected to a GLIMMIX procedure in SAS. Our results showed that the laying hens spent less time foraging overall (P < 0.001) and were slower to commence foraging (P = 0.004) in ammoniated environments compared to the fresh air. Laying hens were more likely to forage for a longer time (with fewer interruptions) in N than in A treatments (P < 0.001). Laying hens also reacted with greater aversion towards treatment A compared to treatment N (P < 0.001). These findings suggest that the laying hens of our study preferred fresh to ammoniated air and that they behaved differently in artificially and naturally sourced NH3/air mixtures, possibly due to the presence of familiar stimuli from the excreta. These findings have implications for new developments in methodological approaches for behavioral testing and for recommendations regarding NH3 levels inside poultry barns.

Revealing humidity-enhanced NH3 sensing effect by using resonant microcantilever

High performance NH3 sensor is of great importance in various application fields such as environmental protection and early diagnosis of stomach cancer. Herein, carboxyl group functionalized mesoporous silica nanoparticles (C-MSNs) with ultrahigh specific surface area are developed as high performance mass-type sensing material for trace-level NH3 detection. By using inkjet printing technology, C-MSNs material is precisely loaded on our lab-made integrated resonant microcantilever to construct a mass-type gas sensor. Based on the specific acid-base interaction between Brønsted acidic C-MSNs material and basic NH3 molecules, our sensor exhibits satisfactory NH3 sensing performance. The experimentally observed detection limit of our sensor reaches parts per billion (ppb) level. Exposed to NH3 with identical concentration, our sensor outputs a higher response in wet air than that of in dry atmosphere. In real air, hydrate NH3 molecule (i.e. NH3·xH2O) has a larger molecular weight than anhydrous NH3 in absolute dry experimental atmosphere. Therefore, our gravimetric sensor exhibits a higher response in real air. In order to in-depth elucidate the humidity-enhanced sensing effect, the micro-gravimetric sensing data obtained in wet air and in dry experimental environment are compared together. Based on our quantitatively measurement data, the molecular formula of hydrate NH3·xH2O existing in wet air (with 50–80% relative humidity) can be obtained as NH3·2∼2.4H2O.

Twenty Years of Grain Sorghum and Soybean Yield Response to Tillage and N Fertilization of a Claypan Soil

Core Ideas Long‐term sorghum and soybean response to tillage and N on claypan soil is limited. Long‐term sorghum yields are often substantially less with no‐till on a claypan soil. Subsurface N may result in greater sorghum yield than with surface applications. Anhydrous NH3 applications to sorghum may partially ameliorate the no‐till yield penalty. Long‐term soybean yields are little affected by tillage on a claypan soil. Crops grown without tillage on claypan soils in the eastern Great Plains often yield less than with tillage, especially cereals that require careful management regarding N fertilization. The objective of this 20‐year study was to determine the response of grain sorghum [Sorghum bicolor (L.) Moench] and soybean [Glycine max (L.) Merr.] in rotation to tillage and N fertilization on a claypan soil in southeastern Kansas. Sorghum was affected by tillage, N fertilization, or their interaction, except in the first year. Sorghum yields averaged 22% lower, and were never greater, with no‐till than with conventional or reduced tillage. Nitrogen fertilization increased sorghum yield, largely because of the greater number of kernels per head. Yields with application of anhydrous NH3 averaged 12% more than with surface‐applied N sources. Yield in half of the crop years was affected by tillage × N fertilizer interactions, and the long‐term interaction suggests that in the lower‐yielding no‐till system, the response to anhydrous NH3 may be greater than in tilled systems. Soybean yield was little affected by tillage, the residual effect from N treatments, or their interaction. In 1986, conventional tillage resulted in greater yield than with no‐till, but the reverse was true in 2002, and there was no difference in yield among tillage systems in the other 8 years. Thus, the potential yield penalty for growing grain sorghum in a no‐till system may be partially ameliorated by subsurface anhydrous NH3 fertilization; however, tillage selection or N treatment residual may have little effect on long‐term soybean production on this claypan soil.

ChemInform Abstract: Crystal Structure of Ag2(μ‐SCN)2(NH3)4.

AbstractColorless crystals of the title compound are obtained by reacting solid AgSCN with anhydrous liquid NH3 (237 K, 2 weeks).

In-field fuel use and load states of agricultural field machinery

The ability to define in-field tractor load states offers the potential to better specify and characterize fuel consumption rate for various field operations. For the same field operation, the tractor experiences diverse load demands and corresponding fuel use rates as it maneuvers through straight passes, turns, suspended operation for adjustments, repair and maintenance, and biomass or other material transfer operations. It is challenging to determine the actual fuel rate and load states of agricultural machinery using force prediction models, and hence, some form of in-field data acquisition capability is required. Controller Area Networks (CAN) available on the current model tractors provide engine performance data which can be used to determine tractor load states in field conditions. In this study, CAN message data containing fuel rate, engine speed and percent torque were logged from the tractor’s diagnostic port during anhydrous NH3 application, field cultivation and planting operations. Time series and frequency plots of fuel rate and percent torque were generated to evaluate tractor load states. Based on the percent torque, engine speed and rated engine power, actual load on the tractor was calculated in each tractor load state. Anhydrous NH3 application and field cultivation were characterized by three distinct tractor load states (TS-I, TS-II and TS-III) corresponding to idle states, parallel and headland passes, and turns, whereas corn planting was characterized by two load states (TS-I and TS-II): idle, and a combined state with parallel, headland passes and turns. For anhydrous NH3 application and field cultivation at ground speeds of 7.64kmh−1 and 8.68kmh−1, average tractor load per tool and fuel use rate per tool of the implement were found to be 7.21kWtool−1, 3.28Lh−1tool−1, and 1.31kWtool−1, 0.64Lh−1tool−1, respectively. For planting, average tractor load per row and fuel use rate per row were found to be 4.65kWrow−1 and 1.70Lh−1row−1 at a ground speed of 7.04kmh−1.

ChemInform Abstract: Ammine Calcium and Strontium Borohydrides: Syntheses, Structures, and Properties.

AbstractSr(NH3)4(BH4)2 (I) and Ca(NH3)6(BH4)2 (II) are prepared by passing anhydrous NH3 over Ca(BH4)2 and Sr(BH4)2 (‐5 °C, 1‐2 h) and subsequent vacuum drying.

Moving towards sustainable resources: Recovery and fractionation of nutrients from dairy manure digestate using membranes

The fractionation of nitrogen (as ammonia/ammonium) and phosphorus (as phosphate ions) present in the dairy manure digestate was investigated using a nanofiltration membrane NF270. The filtration and separation efficiencies were correlated to pH across the range 3 < pH < 11. Filtration at pH 11 enabled higher permeate flux of 125–150 LMH at 20 bar, however rejection of ammonia was high at 30–36% and phosphate was 96.4–97.2%. At pH 3 and pH 7, electrostatic charge effects led to higher permeation of ammonium and thus more efficient separation of nitrogen. The rejection of phosphorus was relatively constant at any given pH and determined as 83% at pH 3, 97% at pH 7 and 95% at pH 11. The fractionation of nitrogen and phosphorus from complex aqueous solutions was demonstrated to be highly dependent on the charge of the membrane and ionic speciation. Solutions rich in nitrogen (as ammonia/ammonium) were obtained with almost no phosphorus present (<1ppm) whilst the purification of the PO4–P was achieved by series of diafiltration (DF) operations which further separated the nitrogen. The separation of nutrients benefited from an advantageous membrane process with potential added value for a wide range of industries. The analysis of the process economics for a membrane based plant illustrates that the recovery of nutrients, particularly NH3–N, may be commercially feasible when compared to manufactured anhydrous NH3.

Use of Controller Area Network (CAN) Data To Determine Field Efficiencies of Agricultural Machinery

Abstract. Controller Area Network (CAN) bus is used on current agricultural equipment for in-vehicle communication among multiple microcontrollers. In this study, CAN data was collected from the tractor diagnostic port during three field operations: anhydrous ammonia (NH3) application, field cultivation, and planting. Specifically, CAN messages corresponding to engine fuel use rate were filtered, decoded, and analyzed. High fuel use rates were recorded from the tractor when implements were engaged in the soil compared to when the implements were lifted out of the ground at the end of the passes or, when the tractor was turning and idling. Threshold fuel rates (TFR) in liter per hour per tool for each operation were established based on the draft force requirements of the implements to distinguish between working and dwell periods. Using the calculated TFRs of 2.58 to 2.64 Lh-1tool-1, 0.41 to 0.50 Lh-1tool-1 and 1.46 to 1.65 Lh-1row-1, average field efficiencies (FE) of anhydrous NH3 application, field cultivation and planting were determined to be 71%, 71% and 68%, respectively. It was found that FE values for the planting operation were highly sensitive to variation in TFR when contrasted with anhydrous NH3 application and field cultivation operations.

Long-term crop and soil response to biosolids applications in dryland wheat.

Biosolids have the potential to improve degraded soils in grain-fallow rotations. Our objectives were to determine if repeated biosolids applications in wheat ( L.)-fallow could supply adequate but not excessive N for grain production and increase soil C without creating a high risk of P loss. A replicated on-farm experiment was established in 1994 in central Washington, comparing anaerobically digested biosolids with anhydrous NH and a zero-N control. Biosolids were applied at 5, 7, and 9 Mg ha every fourth year through 2010 and incorporated 10 cm deep, while anhydrous NH plots received 56 kg ha N every second year. Grain yield and protein were determined. Soil chemical, biological, and bulk density analyses were made in 2012. Medium and high biosolids rates significantly increased grain yield (3.63 vs. 3.13 Mg ha) and protein (103 vs. 85 g kg) compared with anhydrous NH averaged across all crops. The medium biosolids rate had significantly lower bulk density (1.05 vs. 1.22 g kg) and greater total C (0-10-cm depth) (16.9 vs. 9.4 g kg), mineralizable N (156 vs. 52 mg kg), and extractable P (114 vs. 16 mg kg) than anhydrous NH. The P index site vulnerability increased from low for anhydrous NH to medium for the biosolids treatments. Soil NO-N was nearly always <10 mg N kg soil (0-30-cm depth). Medium and high biosolids rates significantly increased bacteria/fungi ratios, Gram-negative bacteria, and anaerobic bacteria markers compared with anhydrous NH. Biosolids can be an agronomically and environmentally sound management practice in wheat-fallow systems.

ChemInform Abstract: Synchrotron Powder Study of Na3V(PO3)3N.

AbstractPolycrystalline Na3V(PO3)3N is prepared by thermal nitridation of a mixture of NaPO3 and V2O5 (alumina crucible, flowing anhydrous NH3, 1.

Evaluation of Sweet Sorghum Bagasse as an Alternative Livestock Feed

ABSTRACTRecently, sweet sorghum [Sorghum bicolor (L) Moench] has garnered renewed attention as a promising feedstock for ethanol production. A byproduct of this is bagasse, which is sweet sorghum stalks remaining after juice extraction. It is possible that sweet sorghum bagasse could provide a source of livestock feed and that its nutritive value could be increased by ammoniation. Ammoniation refers to the treatment of low‐quality forages with NH3 to improve crude protein concentration, digestibility, and animal intake. The main objective of this study was to evaluate sweet sorghum bagasse as a livestock feed and determine the effect of ammoniation on in vitro true digestibility (IVTD) and crude protein (CP) of sweet sorghum bagasse. In vitro true digestibility and CP were determined on bagasse of 12 sweet sorghum cultivars grown in three environments and treated with and without anhydrous NH3 (39.0 g kg−1). Across environments, ammoniation increased bagasse IVTD from a mean of 731 g kg−1 dry matter (DM) to a mean of 750 g kg−1 DM, but IVTD of bagasse from only two of three environments was increased. Crude protein averaged 117 g kg−1 DM for ammoniated samples compared to 26 g kg−1 DM for nontreated samples. Ammoniation increased CP in every cultivar and in every environment. Sweet sorghum bagasse IVTD and CP characteristics combined with large yields indicate that this byproduct could serve as livestock feed and merits further investigation.

Selective Catalytic Reduction Study with Alternative Reducing Agents

Abstract Diesel engine technology has been driven by increasingly stringent environmental legislation. To comply with these laws, emissions-control systems are being rapidly improved. Within this context, development of exhaust gas after-treatment systems undertakes a significant role. Among the techniques used is selective catalytic reduction (SCR), which converts nitrogen oxides (NOx) into diatomic nitrogen (N2) and water (H2O). A reducing agent containing ammonia (NH3) is added to the flow and absorbed by a catalyst. Different reducing agents are currently used, principally anhydrous NH3, aqueous NH3, and urea. This study analyzed behavior of different urea- and formamide-based agents to SCR. Results are compared to those obtained with Adblue. In relation to the SCR system as well as to NOx reduction, we concluded that urea-based mixtures are the most efficient, although they present higher values of NH3 slip. Formamide-based mixtures are significantly less efficient than urea-based mixtures, but the N...

On‐Farm Evaluations to Calibrate Tools for Estimating Late‐Season Nitrogen Status of Corn

Properly calibrated diagnostic tools are needed to evaluate the performance of different N management practices for corn (Zea mays L.). Until now, mostly controlled studies were used for such calibrations. We utilizedon‐farm evaluation studies to verify current and identify new N status categories using the corn stalk nitrate test (CSNT) andlate‐season digital aerial imagery of the corn canopy. From 2007 through 2010, producers conducted 125 trials across Iowa. Each trial had treatments of a producer's normal N rate alternated with a rate that was about one‐third lower or higher. Categorical yield response (YR), expressed as profitable and unprofitable, was related to green reflectance (GR), relative green reflectance (RGR), or CSNT sampled within nine areas in each trial. Multilevel binary logistic regressions were used to estimate the probability of receiving profitable YR for a range of CSNT, RGR, and GR values. Among the three diagnostics, RGR performed slightly better but required applying at least two N rates within producers' fields. For CSNT, the identified optimal category was almost the same as that currently recommended in Iowa (700–2000 mg NO3–N kg−1), even when corn and N prices deviated from their long‐term averages by 30%. Due to the uncertainty in N availability, however, the critical CSNT value for fall manure treatments was about 3000 mg NO3–N kg−1 higher than that for fall anhydrous NH3, spring urea–NH4NO3, or sidedress N. On‐farm studies can be used to calibratelate‐season N diagnostic tools for evaluating management practices that differ in rates, forms, and timing of N applications.

Retention and nitrification of injected anhydrous NH3 as affected by soil pH

Benke, M. B., Goh, T. B., Karamanos, R., Lupwayi, N. Z. and Hao, X. 2012. Retention and nitrification of injected anhydrous NH 3 as affected by soil pH. Can. J. Soil Sci. 92: 589-598. Anhydrous ammonia is an economical and extensively used fertilizer, yet loss after injection can reduce its agronomic efficiency. A laboratory experiment was conducted to examine how soil properties affect ammonia retention and nitrification following anhydrous NH3 injection using 10 different Canadian prairie soils. Soils were also injected with atmospheric air for comparison. Following injection, soils were incubated for up to 216 h at field capacity. Among the soil properties studied [pH (1:2 water), clay, total N, and organic C contents], only pH was negatively related (R 2=0.55, n=10, 24 h incubation) to percentage injected N retained by soil. The amount of N retained by soil 24 h following injection was 92±2% (mean±SEM) when pH 7.5. Rate of nitrification increased (P<0.001) about 48-96 h...

Retention and nitrification of injected anhydrous NH3as affected by soil pH

Benke, M. B., Goh, T. B., Karamanos, R., Lupwayi, N. Z. and Hao, X. 2012. Retention and nitrification of injected anhydrous NH3as affected by soil pH. Can. J. Soil Sci. 92: 589–598. Anhydrous ammonia is an economical and extensively used fertilizer, yet loss after injection can reduce its agronomic efficiency. A laboratory experiment was conducted to examine how soil properties affect ammonia retention and nitrification following anhydrous NH3injection using 10 different Canadian prairie soils. Soils were also injected with atmospheric air for comparison. Following injection, soils were incubated for up to 216 h at field capacity. Among the soil properties studied [pH (1:2 water), clay, total N, and organic C contents], only pH was negatively related (R2=0.55, n=10, 24 h incubation) to percentage injected N retained by soil. The amount of N retained by soil 24 h following injection was 92±2% (mean±SEM) when pH &lt;6, compared with 64±2% when pH&gt;7.5. Rate of nitrification increased (P&lt;0.001) about 48–96 h following injection and was greater in pH&gt;7.5 than pH&lt;6 soils. There was no difference (P&gt;0.05) in bacterial diversity between ammonia- and air-injected soils. The slower nitrification rates suggest that potential leaching and denitrification losses in acid soils could be smaller than in alkaline soils.