Nitrification in soils incubated with pig slurry or ammonium sulphate

The effects of temperature, moisture content and the addition of pig slurry on nitrification in two soils were studed. There was no accumulation of NO₂^?-N under the incubation conditions investigated and the accumulation of NO₃^?-N was linear for additions of 50–250 μg NH₄⁺-N g^? soil, either as ammonium sulphate or as pig slurry. Nitrate formation was treated as a single step, zero order process to enable a rate constant to be calculated. Nitrification rate increased with increasing moisture content up to the highest level tested, soil water potential ?8.0 kPa, corresponding to approximately 60% of water holding capacity in both soils. Measurable nitrification was found in both soils at the lowest moisture content (soil water potential ?1.5 MPa) and temperature (5° C) tested. The nitrification rate constant in soils treated with 50 μg NH₄⁺-N g^? soil was not significantly affected (P = 0.05) by the form of ammonium added. Addition of 250 μg NH₄⁺-N as ammonium sulphate caused a marked inhibition of nitrification at all moisture contents and temperatures. Addition of 250 μg NH₄⁺-N as pig slurry caused a marked increase in nitrification rate, the increase being greater at the higher temperatures and moisture contents.     

亚热带松林中强酸性土壤自养和异养硝化作用的研究

The occurrence of nitrification in some acidic forest soils is still a subject of debate. Identification of main nitrification pathways in acidic forest soils is still largely unknown. Acidic yellow soil (Oxisol) samples were selected to test whether nitrification can occur or not in acidic subtropical pine forest ecosystems. Relative contributions of autotrophs and heterotrophs to nitrification were studied by adding selective nitrification inhibitor nitrapyrin. Soil NH₄⁺-N concentrations decreased, but NO₃^--N concentrations increased significantly for the no-nitrapyrin control during the first week of incubation, indicating that nitrification did occur in the acidic subtropical soil. The calculated net nitrification rate was 0.49 mg N kg^-1 d^-1 for the no-nitrapyrin control during the first week of incubation. Nitrapyrin amendment resulted in a significant reduction of NO₃^--N concentration. Autotrophic nitrification rate averaged 0.28 mg N kg^-1 d^-1 and the heterotrophic nitrification rate was 0.21 mg N kg^-1 d^-1 in the first week. Ammonia-oxidizing bacteria (AOB) abundance increased slightly during incubation, but nitrapyrin amendment significantly decreased AOB amoA gene copy numbers by about 80%. However, the ammonia-oxidizing archaea (AOA) abundance showed significant increases only in the last 2 weeks of incubation and it was also decreased by nitrapyrin amendment. Our results indicated that nitrification did occur in the present acidic subtropical pine forest soil, and autotrophic nitrification was the main nitrification pathway. Both AOA and AOB were the active biotic agents responsible for autotrophic nitrification in the acidic subtropical pine forest soil.     

Nitrification in three soils amended with zinc sulfate

Zinc as ZnSO₄ was added to three soils at rates of 0, 10, 100 and 1000 μg Zn g^?1 soil. The soils were uniformly treated with 100 μg Ng^?1 as nh₄cl, incubated at 30°C and NH₄⁺-N and (NO₃^? + NO₂^?)-N determined weekly for 7 weeks. Nitrification in all three soils was totally inhibited by 1000 μg Zn g^?1. At the 100 μg Zn g^?1 rate, nitrification was significantly reduced in two of the three soils during some part of the incubation. This differential effect on nitrification at the 100 μg Zn g^?1 rate was related to differences in soil properties. These results imply that, with respect to nitrification, care should-be taken not to apply Zn-containing materials indiscriminately to soils.     

Numbers of autotrophic nitrifiers and nitrification in fertilized forest soil

The most probable number (MPN) method was used to estimate how numbers of autotrophic nitrifiers in Myrtillus-type and Calluna-type pine forest soils in southern Finland were affected by seven different fertilization treatments. No NH⁺₄ oxidizers and only a few hundred NO₂^?1 oxidizers g^?1 of soil were found in unfertilized organic (O) horizons. Ammonium nitrate and nitroform (ureaformaldehyde) had hardly any effect on the nitrifiers. Urea, alone or applied together with apatite + biotite or with apatite + biotite + micronutrients, increased numbers of NH₄⁺ and NO₂^? oxidizers. Wood ash, alone or with apatite, also had a stimulative effect. The effects of the stimulative fertilizers were less in the A₂ horizon than in the O horizon. The MPN counts were considerably affected by the duration of incubation: counts of NH₄⁺ oxidizers kept increasing for at least 8 weeks and counts of NO₂^? oxidizers for at least 15 weeks. These MPN counts were compared with earlier results from incubation experiments on the same soils to find out how they reflect changes in soil nitrification after fertilization.     

Urea transformation in some tropical soils

The effects of incubation at 20°, 30° and 40°C and urea concentrations of 0, 50, 100 and 200 μg N/g soil on urea hydrolysis and nitrification were investigated in three Nigerian soils. At constant temperature urea hydrolysis and rate of NO₃^? accumulation increased with increasing rate of urea addition. Urea was rapidly hydrolyzed within 1 week of incubation. Nitrification in Apomu soil increased with increasing incubation temperature. Nitrification was slow in acid Nkpologu soil (pH 4.7). Texture, cation exchange capacity and C:N ratios of the soils were not related to urea hydrolysis or nitrification. Nitrite accumulation in these soils was insignificant. Soil pH was decreased by nitrification of hydrolyzed urea-N.     

Nitrification and ammonification in acid forest litter and humus as affected by peptone and ammonium-n amendment

Samples of strongly acid forest litter and humus from beneath Sitka spruce, heather, Scots pine and larch from two sites in north-east Scotland were incubated aerobically at 20°C in the laboratory. At the Glen Tanar site, spruce litter and larch humus showed significant nitrification and ammonification whereas spruce humus and Scots pine humus produced only NH₄⁺-N. Heather humus showed no net mineralization. At the Fetteresso site, application of fertilizer N, P and K to Sitka spruce up to 3 yr previously, significantly stimulated the production of NO₃⁻-N in both litter and humus.Amendment of the samples with organic N as peptone caused significant increases in NO₃⁻-N production in those samples that already showed nitrification. The increases in NO₃⁻-N generally represented a low proportion of the added peptone-N. Amendment with NH₄⁺-N as (NH₄)₂SO₄ either had no effect or significantly reduced NO₃⁻-N production (in larch humus). The results suggest the occurrence of heterotrophic nitrification in some of these forest samples.Net immobilization of NH₄⁺-N was typically greater in NH₄⁺-N amended than in peptone amended samples, except for heather humus which showed complete immobilization of both N sources.Total mineral N produced at the end of the aerobic incubation was correlated (P < 0.01) with NH₄⁺-N produced during a 30-day anaerobic incubation at 30°C. Net NO₃⁻-N production was greater in litter than in the corresponding humus samples and was correlated (P < 0.001) with initial organic N soluble in 1 m KCl.     

Soil NO3-N production and immobilization affected by NH4-N,glycine, and NO3-N addition in different forest types in Shikoku,southern Japan

The characteristics of production and immobilization of NO₃-N were evaluated for soils from four forest types in Kochi Prefecture, southern Japan. Net NO₃-N production during the laboratory incubation differed among the soils from the four forest types, being high under Japanese cedar (Cryptomeria japonica D. Don) and deciduous hardwood, and negligible under Japanese red pine (Pinus densiflora Sieb. et Zucc.) and hinoki cypress (Chamaecyparis obtusa Endlicher). Nitrification under Japanese cedar and hardwood was mainly autotrophic based on the fact that nitrification was inhibited by acetylene or nitrapyrin, and was not affected by cycloheximide. Net NO₃-N production in these soils increased by glycine addition, but did not increase appreciably by NH₄Cl addition. However, net NO₃-N production increased after the addition of CaCO₃ with NH₄Cl. These results indicate that the substrate of nitrification is NH₃ rather than NH₄ ⁺ and that the added NH₄ ⁺ is not utilized by nitrifiers at low pH values. With NO₃-N addition to soils under red pine and hinoki cypress, immobilization of NO₃-N was observed followed by rapid production of NH₄-N. These findings suggested that mobile NO₃-N can be converted to less mobile NH₄-N by the activities of soil microorganisms. This microbial process may play an important role in retaining nitrogen within forest ecosystems where the potential of N loss is high due to the high precipitation in the area.     

Nitrogen mineralisation in the soil of indigenous oak and pine plantation forests in a Mediterranean environment

Nitrogen mineralisation in soils of various forest sites (pine plantation, natural and thinned oak) at Uluda? University campus in Bursa, Turkey was investigated continuously over a year by the field incubation method. Net nitrogen mineralisation and nitrification rates varied depending on sampling dates. Although nitrogen mineralisation and nitrification rates increased in the spring and summer months, there was no seasonal variation in the soils of the examined forests. Annual net nitrate (NO₃^?–N) accumulation in the upper soil layer (0–5 cm) was higher in Oak I and Oak II (14 kg ha y^?1 and 12 kg ha y^?1) than in the pine plantation (8 kg ha y^?1). While annual net NO₃^?–N accumulation (0–5 cm) varied between the oak forests (possibly due to forest management practices), annual net N_min values were similar in these forests. No significant correlation was found between the examined soil parameters and net nitrification and mineralisation rates in the soils (P > 0.05). These results indicate that tree species and forest management practices play important roles in N cycling in forest ecosystems.     

Nitrification,acidification, and nitrogen leaching from subtropical cropland soils as affected by rice straw-based biochar: laboratory incubation and column leaching studies

Purpose

Few studies have examined the effects of biochar on nitrification of ammonium-based fertilizer in acidic arable soils, which contributes to NO₃ ^? leaching and soil acidification.

Materials and methods

We conducted a 42-day aerobic incubation and a 119-day weekly leaching experiment to investigate nitrification, N leaching, and soil acidification in two subtropical soils to which 300 mg N kg^?1 ammonium sulfate or urea and 1 or 5 wt% rice straw biochar were applied.

Results and discussion

During aerobic incubation, NO₃ ^? accumulation was enhanced by applying biochar in increasing amounts from 1 to 5 wt%. As a result, pH decreased in the two soils from the original levels. Under leaching conditions, biochar did not increase NO₃ ^?, but 5 wt% biochar addition did reduce N leaching compared to that in soils treated with only N. Consistently, lower amounts of added N were recovered from the incubation (KCl-extractable N) and leaching (leaching plus KCl-extractable N) experiments following 5 wt% biochar application compared to soils treated with only N.

Conclusions

Incorporating biochar into acidic arable soils accelerates nitrification and thus weakens the liming effects of biochar. The enhanced nitrification does not necessarily increase NO₃ ^? leaching. Rather, biochar reduces overall N leaching due to both improved N adsorption and increased unaccounted-for N (immobilization and possible gaseous losses). Further studies are necessary to assess the effects of biochar (when used as an addition to soil) on N.     

Heterotrophic nitrification is the predominant NO3 − production pathway in acid coniferous forest soil in subtropical China

To date, occurrence and stimulation of different nitrification pathways in acidic soils remains unclear. Laboratory incubation experiments, using the acetylene inhibition and ¹⁵N tracing methods, were conducted to study the relative importance of heterotrophic and autotrophic nitrification in two acid soils (arable (AR) and coniferous forest) in subtropical China, and to verify the reliability of the ¹⁵N tracing model. The gross rate of autotrophic nitrification was 2.28 mg?kg^?1?day^?1, while that of the heterotrophic nitrification (0.01 mg?kg^?1?day^?1) was negligible in the AR soil. On the contrary, the gross rate of autotrophic nitrification was very low (0.05 mg?kg^?1?day^?1) and the heterotrophic nitrification (0.98 mg?kg^?1?day^?1) was the predominant NO₃ ^? production pathway accounting for more than 95 % of the total nitrification in the coniferous forest soil. Our results showed that the ¹⁵N tracing model was reliable when used to study soil N transformation in acid subtropical soils.     

Ammonia-oxidizing archaea are more important than ammonia-oxidizing bacteria in nitrification and NO3 −-N loss in acidic soil of sloped land

As part of a long-term sloped land use experiment established in 1995 at Taoyuan Agro-ecosystem Research Station (111°26′ E, 28°55′ N) in China, soil samples were collected from three land use types, including cropland (CL), natural forest, and tea plantation. Quantitative polymerase chain reaction and terminal restriction fragment length polymorphism were used to determine the abundance and community composition of amoA-containing bacteria (AOB) and archaea (AOA). The results indicate that land use type induced significant changes in soil potential nitrification rate and community composition, diversity, and abundance of AOB and AOA. Both AOB and AOA community compositions were generally similar between upper and lower slope positions (UP and LP), except within CL. The LP soils had significantly (p?<?0.05) higher diversity and abundance of both AOB and AOA than in the UP. Potential nitrification rate was significantly correlated (p?<?0.05) with diversity and abundance of AOA, but not with AOB. Among land use types, the NO₃ ^? and amoA-containing AOA runoff loss was greatest in CL. Nitrate-N runoff loss was significantly correlated (p?<?0.05) with the loss of AOA amoA copies in the runoff water. Furthermore, relationships between NO₃ ^?-N runoff loss and abundance of AOA but not of AOB at both slope positions were significantly correlated (p?<?0.05). These findings suggest that AOA are more important than AOB in nitrification and NO₃ ^?-N runoff loss in acidic soils across sloped land use types.     

不同氮肥在石灰性潮土中的转化及ATS对尿素氮转化的调控效应

根据氮肥施入土壤后的转化特性进行氮肥的高效调控和管理是提高氮肥利用效率、缓解氮肥污染的重要措施。为探究不同氮肥在石灰性潮土中的转化特性差异及硫代硫酸铵（ammonium thiosulfate，ATS）作为氮肥调控剂对尿素氮转化的影响，该研究采用室内土壤培养（土壤水分含量为田间持水量的60%，温度25 ℃）试验方法，以尿素、硫酸铵、氯化铵和ATS作为供试肥料，比较4种氮肥施入石灰性潮土后的转化特性差异，并以ATS作为氮素调控剂，以单施尿素作为对照，探究尿素配施不同用量ATS对尿素氮转化的影响。结果表明，4种供试氮肥在石灰性潮土中的转化过程明显不同。尿素在石灰性潮土中的水解速率最快，硝化作用强度也最高，硫酸铵其次；氯化铵由于Cl^-的硝化抑制作用，土壤表观硝化率在7～21 d显著低于尿素和硫酸铵（P＜0.05）；ATS施入土壤后，NH₄⁺-N转化为NO₂^--N的速率最高，而NO₂^--N转化为NO₃^--N的速率最低，NH₄⁺-N在土壤中的存留时间最长，出现峰值之后也一直保持最高的含量，表观硝化率最低。将ATS作为氮素调控剂与尿素配合施用，当其用量在60 mg/kg（含S量）以上时，既表现出了明显的抑制尿素水解的作用效果，也表现出了显著的硝化抑制作用（ P <0.05），且随着ATS用量的增加，抑制效应明显增强。这对于减少氮素损失，提高氮肥利用效率具有积极意义。但供试4种氮肥施入土壤后均出现了亚硝酸盐的累积，其中ATS处理的累积量显著高于尿素、硫酸铵和氯化铵（P＜0.05），累积持续时间也最长。ATS作为氮素调控剂调控氮素转化，也出现了类似的结果，且随着ATS用量增加，亚硝酸盐在土壤中存留时间明显延长，含量和峰值明显提高，出现峰值的时间也明显延后。     

Effect of reforestation on turnover of 15N-labelled nitrate and ammonium in relation to changes in soil microflora

The effects of incubation time, vegetation type (represented by a pine plantation, a protected and a periodically burnt eucalypt forest), lime and finely ground pine needles on the transformation of (¹⁵NH₄)₂SO₄ and K¹⁵NO₃ were studied in incubation experiments with a sandy lateritic podzolic soil from south-east Queensland. Microorganisms were counted so as to relate N transformations to particular groups of microorganisms.The heterotrophic miroflora utilized NH⁺₄ as a source of N in preference to NO^?₃, and autotrophic nitrifiers seemed to be weak competitors for NH⁺₄. Lime caused a slight loss of NO^?₃ and this was accompanied by an increase in the population of denitrifying bacteria.Lime promoted immobilization of NH⁺₄ by heterotrophic bacteria and subsequent mineralization by nitrifying bacteria, but when pine needles were also added the nitrifiers were suppressed and immobilization by heterotrophic bacteria dominated. Pine needles alone stimulated fungi to immobilize NH⁺₄.While reforestation with exotic pines caused a loss of total-N there was evidence of increased turnover, i.e. more rapid immobilization and nitrification, in pine plantation soils. Prescribed burning also promoted nitrification while reducing total-N.     

Residual Soil Nitrate: A Comparison between Air-Dried and Field-Moist Soil Samples

In the framework of the European nitrate directive (91/676/EEG), losses of nitrate (NO₃)– nitrogen (N) to both surface and groundwater are limited to 50 mg/l. Because the residual NO₃-N in the soil profile after harvest is considered the main determinant of nitrate leaching during wintertime, the Flemish government imposed a limit value of 90 kg NO₃-N ha^?1 up to a soil depth of 90 cm between 1 October and 15 November. This study compared two different soil sample preparation methodologies. When samples were analyzed immediately upon arrival, no differences in NO₃-N concentration were observed. However, although field-moist samples are maintained at 4 °C, nitrification is not completely stopped, as indicated by the increased NO₃-N concentration in field-moist samples 10 days after storage at 4 °C . In contrast, nitrification in air-dried samples is stopped during the oven drying when 40 °C is reached. Moreover, the reproducibility was significantly greater in air-dried samples as compared to field-moist samples.     

Mechanisms behind the stimulation of nitrification by N input in subtropical acid forest soil

Purpose

Input of N as NH₄ ⁺ is known to stimulate nitrification and to enhance the risk of N losses through NO₃ ^? leaching in humid subtropical soils. However, the mechanisms responsible for this stimulation effect have not been fully addressed.

Materials and methods

In this study, an acid subtropical forest soil amended with urea at rates of 0, 20, 50, 100 mg N kg^?1 was pre-incubated at 25 °C and 60 % water-holding capacity (WHC) for 60 days. Gross N transformation rates were then measured using a ¹⁵N tracing methodology.

Results and discussion

Gross rates of mineralization and nitrification of NH₄ ⁺-N increased (P?<?0.05), while gross rate of NO₃ ^? immobilization significantly decreased with increasing N input rates (P?<?0.001). A significant relationship was established between the gross nitrification rate of NH₄ ⁺ and the gross mineralization rate (R ²?=?0.991, P?<?0.01), so was between net nitrification rate of NH₄ ⁺ and the net mineralization rate (R ²?=?0.973, P?<?0.05).

Conclusions

Stimulation effect of N input on the gross rate of nitrification of NH₄ ⁺-N in the acid soil, partially, resulted from stimulation effect of N input on organic N mineralization, which provides pH-favorable microsites for the nitrification of NH₄ ⁺ in acid soils (De Boer et al., Soil Biol Biochem 20:845–850, 1988; Prosser, Advan Microb Physiol 30:125–181, 1989). The stimulated gross nitrification rate with the decreased gross NO₃ ^? immobilization rate under the elevated N inputs could lead to accumulation of NO₃ ^? and to enhance the risk of NO₃ ^? loss from humid forest soils.

     

Nitrification Inhibition in Iowa Soils Treated with Stay‐N 2000 as Affected by Temperature and Matric Potential

The effects of temperature and water potential on nitrification were investigated in two Iowa soils treated with Stay‐N 2000. The soils were incubated at 10, 20, and 30 °C after soil water potentials of ?1, ?10, or ?60 kPa were applied to each soil. A first‐order equation was used to calculate the maximum nitrification rate (K _max), duration of lag period (t′), period of maximum nitrification (Δt), and termination period of nitrification (t _s). The highest K _max were 18 and 24 mg kg^?1 d^?1 nitrate (NO₃ ^?)–nitrogen (N), respectively, at 30 °C and ?10 kPa in both the Nicollet (fine‐loamy, mixed, superactive, mesic Aquic Hapludoll) and Canisteo (fine‐loamy, mixed, superactive, calcareous, mesic Typic Endoaquoll) soils and reduced to 4 and 16 mg kg^?1 d^?1 NO₃ ^?‐N when Stay‐N 2000 was added. The extension of t′ due to the addition of Stay‐N 2000 was as high as 7 d in the Nicollet soil at 10 °C and ?1 kPa and as little as 2 d in the Canisteo soil at 20 °C and ?10 kPa.     

The potential of using 15N natural abundance in changing ammonium-N and nitrate-N pools for studying in situ soil N transformations

Purpose

This study examined the usefulness of ¹⁵N natural abundance (δ¹⁵N) with in situ core incubation to quantify the predominant N transformation processes in a natural suburban forest of subtropical Australia, which was subjected to prescribed burning.

Materials and methods

In situ core incubation for 3 days with 20 ml water, or 160.79 ml of 60 mg L^?1 NO₃^?-N surface application, and in situ core with 160.79 ml water but without incubation were set up in Toohey forest for sampling three times as before (once) and after (twice) a prescribed burning. The δ¹⁵N of NH₄⁺-N and NO₃^?-N in the top 5 cm soil before and after the incubation, and δ¹⁵N of NO₃^?-N in the 5–10 cm soil before incubation were compared with each other to examine the soil N mineralisation, nitrification, denitrification, and nitrate leaching processes.

Results and discussion

The significant decrease in δ¹⁵N of NH₄⁺-N after incubation under 20 ml water treatment was ascribed to soil N mineralisation, and the significant decrease in δ¹⁵N of NH₄⁺-N and significant increase in δ¹⁵N of NO₃^?-N after incubation with elevated water and nitrate inputs were associated with N mineralisation and nitrification, respectively, 2 months after the burning. The 160.79 ml water treatment also triggered nitrification in the baseline soil cores in both samplings after the burning. Water was crucial to stimulate soil N mineralisation and nitrification, but excessive water depleted labile N pools and reduced N mineralisation and nitrification. Burning effects were hard to separate from the seasonal impacts on soil N cycling processes.

Conclusions

The δ¹⁵N in soil mineral N pools was sensitive to indicate soil N mineralisation and nitrification processes. Soil water and labile N were determining factors for N transformations in the soil. It is suggested that δ¹⁵N combined with soil inorganic N concentrations and net N transformation rates could be used to identify primary N transformation processes. More frequent samplings would be needed to differentiate burning impacts from the seasonal impacts on soil N cycling processes.

     

Nitrification Inhibitor,Fertilizer Rate,and Temperature Effects on Nitrous Oxide Emission and Nitrogen Transformation in Loamy Sand Soil

An incubation study investigated the effects of nitrification inhibitors (NIs), dicyandiamide (DCD), and neem oil on the nitrification process in loamy sand soil under different temperatures and fertilizer rates. Results showed that NIs decreased soil nitrification by slowing the conversion of soil ammonium (NH₄⁺)-nitrogen (N) and maintaining soil NH₄⁺-N and nitrate (NO₃^?)-N throughout the incubation time. DCD and neem oil decreased soil nitrous oxide (N₂O) emission by up to 30.9 and 18.8%, respectively. The effectiveness of DCD on reducing cumulative soil N₂O emission and retaining soil NH₄⁺-N was inconsistently greater than that of neem oil, but the NI rate was less obvious than temperature. Fertilizer rate had a stronger positive effect on soil nitrification than temperature, indicating that adding N into low-fertility soil had a greater influence on soil nitrification. DCD and neem oil would be a potential tool for slowing N fertilizer loss in a low-fertility soil under warm to hot climatic conditions.     

Mineralization of carbon and nitrogen,and nitrification in Scots pine forest soil treated with fast- and slow-release nitrogen fertilizers

We studied the effects of fast- and slow-release organic N fertilizers (urea and urea-formaldehyde, Nitroform) on mineralization, nitrification, and N leaching in an acid, poor forest soil. We also studied the effects of a nitrification inhibitor (dicyandiamide) applied together with urea. Net nitrification, mineralization of N and C were determined by aerobic laboratory incubation of soil samples taken one and three growing seasons after N application. Numbers of autotrophic nitrifiers were estimated by a most probable number method three growing seasons after the treatment. Urea increased the CO₂ production immediately after application, but after three growing seasons, CO₂ production was the lowest in the urea-treated soils. In the nitroform-treated soils, the concentration of exchangeable NH _inf4 ^sup+ after the first and third growing seasons was of the same magnitude, in contrast to the urea-treated soils, where hydrolysis took place immediately. Three growing seasons after application, the highest amount of NH _inf4 ^sup+ accumulated during the laboratory incubation was in the nitro-form-treated soils. Unlike urea, nitroform did not increase the production of NO _inf3 ^sup- or the number of NH _inf4 ^sup+ oxidizers. In the urea+dicyandiamide-treated soils there was less NO _inf3 ^sup- and a lower number of nitrifiers than in the urea-treated soils. The results showed that a slow-release N fertilizer, such as nitroform, increases the availability of mineral N in acid forest soils without increasing nitrification and hence the risk of NO _inf3 ^sup- leaching.     

Effects of nickel addition on nitrogen mineralization,nitrification, and nitrogen leaching in some boreal forest soils

The effects of Ni additions on nitrification, N mineralization, and N leaching were examined in soils from boreal jack pine (Pinus banksiana Lamb.) forests. The results of a series of incubation experiments suggested that under certain conditions, Ni at 100 μg g^?1 soil can stimulate nitrification, and at 500 μg g^?1 can stimulate N mineralization. Nitrification rates were very low overall, but were higher in soils from the vicinity of the Sudbury, Ontario Ni-Cu smelters than in uncontaminated soils. The nitrifier populations, estimated by the most probable number method, were extremely low in uncontaminated soils, but also increased following some Ni additions. Increased leaching of NO_f3 ^p was observed in soil columns treated with Ni. Since N tends to be in low supply in boreal forests, and therefore tightly cycled, the observed disruptions caused by Ni inputs could have an effect on forest productivity.