Nitrapyrin Research Articles

Impact of nitrapyrin on urea‐based fertilizers in a Mediterranean calcareous soil: Nitrogen and microbial dynamics

AbstractNitrification inhibitors, such as nitrapyrin (NI), are increasingly co‐applied with nitrogen (N) fertilizers as part of sustainable agricultural practice. Several studies in temperate regions have documented the effectiveness of NI in retaining soil ammonium (NH4+), minimizing N loss and increasing crop yields. However, less is known about the effects of NI in Mediterranean regions, where agricultural production is challenging and requires intensive irrigation and fertilization. We investigated the short‐term impact of the nitrification inhibitor nitrapyrin (2‐chloro‐6‐(trichloromethyl)pyridine) in a two‐factor mesocosm experiment, using a typical Mediterranean soil, where NI was co‐applied with a selection of urea‐based fertilizers: urea (U), U with urease inhibitors (U + UI), methylene urea (MU) and zeolite‐coated urea (ZU). NI co‐applied with urea fertilizers resulted in higher availability of soil NH4+ and a concurrent increase in NH3 volatilization. Net cumulative soil NH4+ availability was 1.5–3.3 fold greater when NI was applied. Concurrently, net cumulative nitrate (NO3−) and nitrite (NO2−) availability was reduced by 10%–60%; this was found for all the tested fertilizer types except MU fertilizer, where the net cumulative soil NO3− and NO2− doubled. Nitrous oxide (N2O) emissions from urea fertilization were reduced by 40% with UI, 50% with NI and 66% with NI + UI. Interestingly, after 28 d, the composition of soil microbial communities was distinctly different, due to NI application. Specifically, NI application dramatically reduced the abundance of ammonia‐oxidizing and denitrifying bacterial functional groups. NI was effective in reducing N2O emissions in this calcareous soil; however, NH3 emissions were remarkably enhanced. These findings have important implications for the large‐scale adoption of inhibitor technologies in Mediterranean agroecosystems and for the reduction of greenhouse gas emissions.

Ammonia emission and nitrogen use efficiency with application of nitrification inhibitor and plant growth regulator in a calcareous soil (Karaj, Iran)

Ammonia volatilization (AV) is one of the main potential pathways of nitrogen (N) loss and re-deposited ammonia acts as an indirect source of N2O. The question arises how environmentally friendly inputs such as nitrification inhibitors (NI) and plant growth regulators (PGR) can affect AV in calcareous soils, while increasing nitrogen use efficiency (NUE) and crop yield. To answer this question, the effects of applying urea in combination with nitrapyrin (NP) as a NI and gibberellic acid (GA3) as a PGR on daily AV, winter wheat yield and NUE were evaluated. The treatments included a control treatment, urea and urea+NP + GA3 with five replications. Urea and urea coated with NP were applied in three equal split applications, and GA3 was foliar sprayed once. By using 15N-labeled urea and setting up three 15N microplots inside each plot, the nitrogen in the plant derived from fertilizer (Ndff) and the fate of N fertilizer were directly investigated. Ammonia emission factors and estimated values of indirect N2O-N produced from AV in urea and urea+NP + GA3 were 27% and 33%, and 0.38 and 0.45 kg N ha−1, respectively. The grain yield and 1000-grain weight in urea+NP + GA3 treatment were significantly increased by 15% and 13%, respectively, compared to urea. However, urea coated with NP increased AV and decreased Ndff by about 22% and 15%, respectively. The increase in AV caused by the addition of NP was relatively lower than amounts reported in previous studies. This could be due to the split application of N fertilizer on dry soil, the immediate incorporation and the ammonium fixation capacity of illite and vermiculite clay minerals presence in this soil and the reduction of readily available NH4+. The N difference method displayed 21% increase in NUE when urea was applied with NP and GA3 but tracking 15N showed that the combination of urea+NP + GA3 reduced NUE by about 8%. This suggests that NP may not be a viable option for increasing NUE in calcareous soils due to its ability to increase AV. Further research is needed to study the combination of other NIs with GA3 and investigate their effect on AV to simultaneously improve yield and NUE.

The Effects of Quinone Imine, a New Potent Nitrification Inhibitor, Dicyandiamide, and Nitrapyrin on Target and Off-Target Soil Microbiota.

ABSTRACTDicyandiamide (DCD) and nitrapyrin (NP) are nitrification inhibitors (NIs) used in agriculture for over 40 years. Recently, ethoxyquin (EQ) was proposed as a novel potential NI, acting through its derivative quinone imine (QI). Still, the specific activity of these NIs on the different groups of ammonia-oxidizing microorganisms (AOM), and mostly their effects on other soil microbiota remain unknown. We determined the impact of QI, and comparatively of DCD and NP, applied at two doses (regular versus high), on the function, diversity, and dynamics of target (AOM), functionally associated (nitrite-oxidizing bacteria-NOB), and off-target prokaryotic and fungal communities in two soils mainly differing in pH (5.4 versus 7.9). QI was equally effective to DCD but more effective than NP in inhibiting nitrification in the acidic soil, while in the alkaline soil QI was less efficient than DCD and NP. This was attributed to the higher activity of QI toward AOA prevailing in the acidic soil. All NIs induced significant effects on the composition of the AOB community in both soils, unlike AOA, which were less responsive. Beyond on-target effects, we noted an inhibitory effect of all NIs on the abundance of NOB in the alkaline soil, with Nitrobacter being more sensitive than Nitrospira. QI, unlike the other NIs, induced significant changes in the composition of the bacterial and fungal communities in both soils. Our findings have serious implications for the efficiency and future use of NIs on agriculture and provide unprecedented evidence for the potential off-target effects of NIs on soil microbiota.IMPORTANCE NIs could improve N use efficiency and decelerate N cycling. Still, we know little about their activity on the distinct AOM groups and about their effects on off-target soil microorganisms. Here, we studied the behavior of a new potent NI, QI, compared to established NIs. We show that (i) the variable efficacy of NIs across soils with different pH reflects differences in the inherent specific activity of the NIs to AOA and AOB; (ii) beyond AOM, NIs exhibit negative effects on other nitrifiers, like NOB; (iii) QI was the sole NI that significantly affected prokaryotic and fungal diversity. Our findings (i) highlight the need for novel NI strategies that consider the variable sensitivity of AOM groups to the different NIs (ii) identify QI as a potent AOA inhibitor, and (iii) stress the need for monitoring NIs’ impact on off-target soil microorganisms to ensure sustainable N fertilizers use and soil ecosystem functioning.

Facilitating Nitrification Inhibition through Green, Mechanochemical Synthesis of a Novel Nitrapyrin Complex

Nitrapyrin (NP) is applied to cultivated soils to inhibit the enzymatic activity of ammonia monooxygenase (AMO), but its poor aqueous solubility and high volatility severely limit its application. β-Cyclodextrin (β-CD) is commonly used to form inclusion complexes with hydrophobic molecules, improving water solubility and stability upon complexation. Here we report on the mechanochemical synthesis of the inclusion complex β-CD·NP, characterized via a combination of solid-state techniques, including ex-situ and in situ X-ray diffraction, Raman and NMR spectroscopies, transmission electron microscopy, and energy dispersive X-ray spectroscopy. The pure inhibitor NP was also structurally characterized. The β-CD·NP complex presents improved solubility and thermal stability, and still inhibits the enzymatic activity of AMO with high efficacy. All results indicate that the inclusion of NP into β-CD represents a viable route for the preparation of a novel class of inhibitors, with improved properties related to stability, water solubility, and good inhibition activity.

Comparison of Novel and Established Nitrification Inhibitors Relevant to Agriculture on Soil Ammonia- and Nitrite-Oxidizing Isolates.

Nitrification inhibitors (NIs) applied to soil reduce nitrogen fertilizer losses from agro-ecosystems. NIs that are currently registered for use in agriculture appear to selectively inhibit ammonia-oxidizing bacteria (AOB), while their impact on other nitrifiers is limited or unknown. Ethoxyquin (EQ), a fruit preservative shown to inhibit ammonia-oxidizers (AO) in soil, is rapidly transformed to 2,6-dihydro-2,2,4-trimethyl-6-quinone imine (QI), and 2,4-dimethyl-6-ethoxy-quinoline (EQNL). We compared the inhibitory potential of EQ and its derivatives with that of dicyandiamide (DCD), nitrapyrin (NP), and 3,4-dimethylpyrazole-phosphate (DMPP), NIs that have been used in agricultural settings. The effect of each compound on the growth of AOB (Nitrosomonas europaea, Nitrosospira multiformis), ammonia-oxidizing archaea (AOA; “Candidatus Nitrosocosmicus franklandus,” “Candidatus Nitrosotalea sinensis”), and a nitrite-oxidizing bacterium (NOB; Nitrobacter sp. NHB1), all being soil isolates, were determined in liquid culture over a range of concentrations by measuring nitrite production or consumption and qPCR of amoA and nxrB genes, respectively. The degradation of NIs in the liquid cultures was also determined. In all cultures, EQ was transformed to the short-lived QI (major derivative) and the persistent EQNL (minor derivative). They all showed significantly higher inhibition activity of AOA compared to AOB and NOB isolates. QI was the most potent AOA inhibitor (EC50 = 0.3–0.7 μM) compared to EQ (EC50 = 1–1.4 μM) and EQNL (EC50 = 26.6–129.5 μM). The formation and concentration of QI in EQ-amended cultures correlated with the inhibition patterns for all isolates suggesting that it was primarily responsible for inhibition after application of EQ. DCD and DMPP showed greater inhibition of AOB compared to AOA or NOB, with DMPP being more potent (EC50 = 221.9–248.7 μM vs EC50 = 0.6–2.1 μM). NP was the only NI to which both AOA and AOB were equally sensitive with EC50s of 0.8–2.1 and 1.0–6.7 μM, respectively. Overall, EQ, QI, and NP were the most potent NIs against AOA, NP, and DMPP were the most effective against AOB, while NP, EQ and its derivatives showed the highest activity against the NOB isolate. Our findings benchmark the activity range of known and novel NIs with practical implications for their use in agriculture and the development of NIs with broad or complementary activity against all AO.

Nitrogen‐15 Evaluation of Fall‐Applied Anhydrous Ammonia: I. Efficiency of Nitrogen Uptake by Corn

Fall application of anhydrous ammonia (NH3) is a common practice for corn (Zea mays L.) production in the midwestern United States, but evaluations to date have relied entirely on yield comparisons that provide no means of distinguishing fertilizer from soil N uptake. To quantify fertilizer N uptake efficiency (FNUE) when using this practice, field trials using 15NH3 were conducted between 2016 and 2018 at four sites in a corn–soybean (Glycine max L. Merr.) rotation and at two sites under continuous corn. At each site, 224 kg N ha−1 was applied with and without the use of nitrapyrin (NP) to inhibit nitrification. Relative to grain yields without fertilizer N, response to fall N fertilization occurred at four of the six sites studied, averaging 53% (4.0 Mg ha−1) in two growing seasons with below‐normal rainfall. The use of NP was beneficial at only one site for increasing total N uptake, but resulted in a decrease at another, along with a significant reduction in grain yield. Isotopic estimates of FNUE (i.e., F15NUE) ranged from 12 to 34% (21% on average) for grain and from 16 to 42% (28% on average) for total aboveground biomass, and N derived from fertilizer ranged from 20 to 46% (32% on average). Both isotopic parameters were highest for the site lowest in native N availability, demonstrating the potential of site‐specific N management to improve fall NH3 fertilization by accounting for soil N mineralization.

Urea Nitrapyrin Placement Effects on Soil Nitrous Oxide Emissions in Claypan Soil.

Corn ( L.) production in poorly drained claypan soils in the US Midwest is a challenge due to low soil permeability, which may result in wetter soil conditions and relatively large amounts of soil NO emissions early in the growing season. The objectives of this study were to determine the effects of urea fertilizer placement with and without nitrapyrin (NI) on daily and cumulative soil NO emissions, and yield-scaled NO emissions in 2016 and 2017. Treatments included urea deep banded to a 20-cm depth (DB), urea deep banded to 20 cm plus NI (DB+NI), urea incorporated after a surface broadcast application to ∼8-cm depth (IA), urea broadcast on the soil surface (SA), and a nonfertilized control (NTC). Fertilizer was applied at 202 kg N ha. Surface soil NO efflux rates were generally lower (<50 g NO-N ha d) during the first 3 wk after N fertilization and latter parts of the growing seasons. When averaged across the 2016 and 2017 growing seasons, all fertilized treatments had significantly greater (2.33-5.60 kg NO-N ha, < 0.05) cumulative soil NO emissions than NTC. The DB+NI treatment had 54 and 55% lower cumulative soil NO emissions than IA and SA, respectively. In 2017, DB+NI had similar soil yield-scaled NO emissions to NTC. Percentage grain yield increase over NTC was highest for DB and DB+NI. Grain yield in 2016 was 14 to 18% higher for DB and DB+NI than SA. Results suggest that DB+NI is an effective management strategy for reducing cumulative soil NO emissions and increasing grain yields over the growing season.

Evaluation of Two Products Recently Introduced as Nitrification Inhibitors

ABSTRACTThis study compared the relative effectiveness of two products recently introduced as nitrification inhibitors with other materials used to inhibit nitrification. Four soils were treated with 0, 0.2, 1, 5, and 25 mg kg−1 of nitrapyrin (NP), a new microencapsulated nitrapyrin product (ENP), dicyandiamide (DCD), a new maleic-itaconic polymer product (MIP), and ammonium thiosulfate (ATS). The soils were also treated with 200 mg N kg−1 as urea, and percent inhibition of nitrification determined after 2 or 4 weeks of incubation. After 4 weeks, similar levels of nitrification inhibition were provided by 1 mg kg−1 of NP (72%), 5 mg kg−1 of ENP (79%), and 25 mg kg−1 of DCD (73%), averaged across soil. After 4 weeks with a sandy soil, the highest rate of MIP and ATS provided 15 and 36% inhibition, respectively. MIP and ATS were ineffective at inhibiting nitrification when added to the other three soils.Abbreviations: ATS: ammonium thiosulfate; DCD: dicyandiamide; ENP: encapsulated nitrapyrin; MIP: maleic-itaconic polymer; NP: nitrapyrin; UAN: urea-ammonium nitrate liquid fertilizer

Rice Grain Yield and Nitrogen Uptake as Affected by Urea Amendment and Rainfall Timing

Core Ideas Use of NBPT‐treated urea maximized N uptake and grain yield of rice regardless of soil moisture. Rainfall between urea application and flooding may be detrimental to rice grain yield. Dry soil conditions before and after urea application maximize fertilizer‐N recovery by rice. Nitrogen loss in the delayed‐flood method of rice (Oryza sativa L.) production is minimized by applying urea to a dry soil, use of a urease inhibitor, and immediate flooding. The time required to flood fields is often a factor limiting fertilizer‐N recovery. Our objectives were to compare the effects of simulated rainfall timing, N‐(n‐butyl) thiophosphoric triamide (NBPT) rate, and nitrapyrin (NP) rate on rice aboveground‐N content and grain yield. Field experiments evaluated rice growth as affected by NBPT rate (0 and 0.89 g NBPT kg−1 urea), NP rate (0 and 572 g NP ha−1), and three simulated rainfall timings (no simulated rainfall [NOSR], simulated rainfall before nitrogen [SRBN], and simulated rainfall after nitrogen [SRAN]). Yield was unaffected by simulated rainfall timing when rice was fertilized with NBPT‐treated urea (7904–8264 kg ha−1). When rice was fertilized with untreated urea, grain yields were greater with NOSR than with SRAN or SRBN. Within each simulated rainfall timing, rice yields were 6.9 to 21.3% greater when NBPT‐treated urea was applied. Nitrapyrin rate had no effect on yield in 2013, but, compared to untreated urea, NP‐treated urea decreased yield by 5.6% in 2014. Application of urea to moist soil followed by dry conditions or dry soil followed by rainfall are field environments that result in lower yields presumably to fertilizer N loss than when urea is applied to a dry soil that remains dry until rice is flooded. Use of urea amended with NBPT maximized grain yield in each simulated rainfall scenario.

Enhanced Efficiency Nitrogen Products Influence Ammonia Volatilization and Nitrous Oxide Emission from Two Contrasting Soils

Core IdeasAmmonia volatilization and N2O emissions from N‐sources were assessed in two soils.The N‐(n‐butyl) thiophosphoric triamide reduced NH3volatilization losses from both sandy loam and silty clay soils.Nitrapyrin and SuperU reduced N2O emissions from sandy loam soil only.Polymer coated urea was effective in reducing both NH3and N2O emissions from sandy loam soil.Right N‐source could mitigate gaseous N losses from agroecosystems.Potentials of enhanced efficiency nitrogen (EEN) products to control N losses can vary with soil pH, cation exchange capacity, organic matter, water, temperature, and management. A laboratory experiment was conducted to quantify and compare ammonia (NH3) volatilization and nitrous oxide (N2O) losses with (i) control, (ii) urea, urea treated with (iii) urease inhibitor, NBPT [N‐(n‐butyl) thiophosphoric triamide], (iv) nitrification inhibitor, nitrapyrin (NP) [2‐chloro‐6‐trichloro methyl pyridine], (v) urea stabilized with NBPT and nitrification inhibitor dicyandiamide (SuperU), and (vi) slow release N fertilizer polymer coated urea (PCU) amendments from Ulen sandy loam and Fargo silty clay soils. Across N amendments, cumulative NH3–N losses from sandy loam soil ranged from 0.7 to 4.3% of applied N, and were higher than those from silty clay soil (0.1–0.4% of applied N). In sandy loam, compared to urea, NBPT and PCU reduced NH3–N volatilization by 32.3 and 84.2%, respectively, whereas NP and SuperU increased NH3–N losses by 98.7 and 20.3%, respectively. However, in silty clay soil, only NBPT exhibited significant reduction in NH3–N losses of 71.4%, relative to urea. Cumulative N2O emissions did not differ between soil textures and ranged from 3.7 to 7.4% of applied N across N sources. However, soil N2O emissions differed among N sources in sandy loam soil. In sandy loam soil, NP, SuperU, and PCU treatments significantly reduced N2O‐N emissions by 23.5, 43.8, and 51.1%, respectively, compared to urea. Applicability of using EEN products to mitigate NH3and N2O emission losses varies with soil texture.

Corn Production on a Subsurface‐Drained Mollisol as Affected by Fall versus Spring Application of Nitrogen and Nitrapyrin

Nitrogen management strategies that affect corn (Zea mays L.) production and loss of NO3–N to subsurface, tile drainage often include decisions of when to apply N (fall or spring) and whether to use a nitrification inhibitor. A field study was conducted from the fall of 1993 through 2000 on a tile‐drained Canisteo clay loam [fine‐loamy, mixed (calcareous), mesic Typic Endoaquolls] to determine the influence of fall vs. spring application of N and nitrapyrin [2‐chloro‐6‐(trichloromethyl) pyridine] on yield of corn and soybean [Glycine max (L.) Merr.] in rotation. Four anhydrous ammonia treatments [fall without nitrapyrin (NP), fall with NP, spring preplant without NP, and spring with NP] were replicated four times and applied at 134 kg N ha−1 (120 lb acre−1) for corn each year. Fall applications occurred between 20 October and 1 November when soil temperatures generally were ≤10°C. Six‐year average corn grain yields were least for fall N without NP [10.10 Mg ha−1 (161 bu acre−1)] and greatest for fall N with NP [10.72 Mg ha−1 (171 bu acre−1)], spring N without NP [10.82 Mg ha−1 (172 bu acre−1)], and spring N with NP treatment [11.03 Mg ha−1 (176 bu acre−1)]. Year‐to‐year variation in yield response to the treatments was great and was characterized by above‐normal May rainfall affecting the performance of the fall treatments while above‐normal June rainfall affected both fall and spring treatments. Apparent N recovery ranged from 47% for fall N without NP to 61% for spring N with NP. Annual economic return to fertilizer was greatest for spring N with or without NP. Based on the dominating effect of spring rainfall, this study suggests growers consider a spring preplant N strategy either with or without NP as an alternative to fall N for greatest economic return and least N loss to the environment on these Mollisols.

Corn Production on a Subsurface‐Drained Mollisol as Affected by Time of Nitrogen Application and Nitrapyrin

Time of N fertilizer application to corn (Zea mays L.) and use of a nitrification inhibitor are management strategies that can affect corn production and loss of NO3–N from the soil profile via subsurface, tile drainage. A field study was conducted from the fall of 1986 through 1994 on a tile‐drained Canisteo clay loam soil [fine‐loamy, mixed (calcareous), mesic Typic Endoaquolls] to determine the influence of time of N application and nitrapyrin [2‐chloro‐6‐(trichloromethyl) pyridine] on yield of corn and soybean [Glycine max (L.) Merr.] in rotation and N uptake of corn. Four anhydrous ammonia (AA) treatments [(fall without nitrapyrin (NP), fall with NP, spring preplant, and split (40% preplant and 60% sidedress at V8 stage)] were replicated four times and applied at 150 kg N ha−1 (135 lb N acre−1) for corn each year. Fall applications occurred between 19 and 28 October when soil temperatures generally were ≤10°C. Seven‐year average corn grain yields were least for fall N without NP (8.27 Mg ha−1, 131 bu acre−1), intermediate for fall N with NP and spring N (8.72 Mg ha−1, 139 bu acre−1), and greatest for the split N treatment (9.11 Mg ha−1, 145 bu acre−1). Corn N uptake was not different among treatments in drier years but was generally greatest for the spring and split treatments in wet years. Apparent N recovery ranged from 31% for fall N without NP to 44% for the split treatment. Economic return to fertilizer was greatest for the split treatment ($239.40 ha−1 yr−1) and lowest for fall N without NP ($166.70 ha−1 yr−1). Application time strategies for AA considered to be best management practices for these poorly drained Mollisols include fall N with NP, spring preplant, and split application.

Smut Disease and Yield Performance in Corn (Zea mays L.) as Influenced by Nitrapyrin, Urea and Zinc Applications in Coarse‐textured Soils

AbstractThe effects of nitrapyrin (NI), urea (U) and Zn rates on rhizosphere pH, smut incidence (S.I.), dry matter (D.M.), grain yield (G.Y.) and ear leaf N and Zn contents were studied in cemented plots, containing calcareous and non‐calcareous soils. Treatments were comprised of 3 U applications (46, 92 and 138 kg N acre−1), combined with 2 NI rates (0 and 0.22 kg acre‐1) and 2 levels of Zn (0 and 8 kg acre‐1). Corn seeds, cv ‘Amoun’ were planted in 1993 and 1994 and the seedlings were artificially infected with U. maydis‐spores at the 6 and 10 leaf growth stages. Results have shown that corn plants grown in calcareous soil imposed greater advantage in D.M. and G.Y., accompanied by a relatively low smut infection than those grown in non‐calcareous soil. Unlike the diversion effects of NI on soil pH and plant Zn content, its application was beneficial for improving yield and plant Zn content. Urea applications decreased the soil pH by 0.6 unit at the highest N rate and exerted stimulatory effects on ear leaf N and Zn contents. By increasing U rate to 138 kg N acre‐1, smut severity was increased by 6%. In contrast, by Zn fertilization, smut severity was decreased by 10.3%, accompanied by marked increases in G.Y. and leaf Zn content. Mixed results were detected on S.I. data, when NI was combined with U rates. In the presence of Zn, smut severity was dropped to 20.1% at 138 kg N acre‐1. The results also showed that in the absence of Zn supply, S.I. was dominated in NI‐treated plants and the reverse was true when Zn was included. Satisfactory results were achieved when 92 kg N acre‐1 were combined with 0.22 and 8 kg acre‐1 of NI and Zn, respectively.

Nitrification inhibitors ‐ Interaction with applied ammonium concentration

Abstract Soil samples of 50 g clay, clay loam and sandy loam were amended with ammonium sulphate giving 25, 50, 100, 200, and 400 mg nitrogen (N)/kg and with two nitrification inhibitors, Dicyandiamide (DCD) and N‐Serve (N‐S) each at two levels calculated relative to the N applied, 1 and 5%, and 0.5 and 1%, respectively. Water was added to moisture field capacity and the samples were incubated at 30°C for 7, 14, 28, and 56 days, each treatment and timing in three replicates. The lower level of application of nitrification inhibitors was not effective. Nitrate‐N (NO3‐N) recovery peaked at 28 days and did not change appreciably later, except the 1% N‐S treatments where a flush of NO3 appeared at the 56th sampling day. The nitrification inhibitory effects of the two inhibitors were enhanced at the 200 and 400 mg/kg ammonium‐N (NH4‐N) application in all three soils. Nitrification inhibition was not related to salt concentrations as measured by electrical conductivity.

Degradation of trichloroethylene by the ammonia-oxidizing bacterium Nitrosomonas europaea

Suspensions of Nitrosomonas europaea are shown to cause the complete disappearance of 10 μM trichloroethylene at rates of 1 μM mg protein −1. The reaction continues at nearly this rate for many hours. Fresh cells catalyze the reaction in the absence of added ammonium (presumably utilizing endogenous ammonia or stored reductant). In older cells, trichloroethylene degradation depends on the addition of ammonia. Acetylene, 2-chloro 6-trichloromethylpyridine and αα′-dipyridyl, which inhibit the oxidation of ammonia by cells, inhibit the degradation of trichloroethylene. Thus degradation of trichloroethylene is dependent on- and possibly catalyzed by the ammonia oxidizing enzyme.

Effect of Nitrapyrin on Mineralization of Urea and Isobutylidene Diurea in a Highly Organic Medium

Abstract Mineralization of nitrogen fertilizers was determined in an organic medium composed of 6 pine bark : 3 sand : 1 soil (by volume). Nitrification was evident by day 7 following treatment with urea and isobutylidene diurea (IBDU) and increased rapidly after day 14. Nitrification was not evident until day 56 in medium treated with urea + nitrapyrin (NI). Medium treated with urea or IBDU were depleted of NH4+ within 1 month, which corresponded to a peak in NO2– + NO3– accumulation. Only a small amount of NH4+ was not accounted for by nitrification and was assumed to be adsorbed by bark particles. Chemical names used: 2-chloro-6-(trichloromethyl)pyridine (nitrapyrin), 1,1-diureido isobutane (IBDU).

EFFECT OF NITRAPYRIN RATE ON NITRIFICATION IN SOILS HAVING DIFFERENT ORGANIC MATTER CONTENTS1

Due to possible large losses of nitrate N from the rooting zone, N fertilizer application for corn (Zea mays L.) is usually supplied as split applications in the south-eastern United States. Nitrapyrin (NI) is a nitrification inhibitor that has the potential of reducing nitrate N losses and possibly allowing all the N to be applied preplant. However, increasing soil organic matter content decreases the effectiveness of NI. We conducted experiments to determine the rate of NI required to inhibit nitrification of broadcast applications of 100 kg N/ha as urea in soils with different organic matter contents. Soils and their organic matter contents used in this research were a Roanoke loamy sand (clayey, mixed, thermic Typic Ochraquult) of 1.9 g kg-1 OM, Cape Fear loam (clayey, mixed, thermic, Typic Umbraquult) of 61 g kg-1 OM, and a Conaby muck (coarse, loamy, mixed, nonacid, thermic Histic Humaquept) of 163 g kg-1 OM. When NI was not included, nitrification of the applied N was complete by 14 d in the Roanoke and Cape Fear soils and at 21 d in the Conaby soil. To inhibit nitrification for 35 d, rates of 2.24 and 8.96 kg NI/ha were required on the Roanoke and Cape Fear soils, respectively. After 35 d with the Conaby soil, there was no effect on nitrification with rates up to 8.96 kg NI/ha. Nitrapyrin effectiveness is thought to be reduced due to its sorption by organic matter. These data suggest that higher NI rates are required to reduce nitrification of ammonical N as soil organic matter content increases.

Efecto de dos inhibidores de la nitrificación sobre la concentración de nitratos en pasto “elefante” Pennisetum purpureum, Schum.

Effect of two Nitrification Inhibitors on Nitrate Accumulation in grass “ Elefant” Pennisetum purpureum Schum. In the Mario Gonzalez Aranda farm, wich is a property of National University of Colombia (Palmira-Valle) was realireJ an experiment intended to quantify the pricess of conversion of ammonium into nitrate in the ground and the concentrations of this ion on the Elefante grass, Pennisetum purpureum Schum. It was compared the grade of inhibition of two inhibitors products of the nitrification (Sulfatiazol, N-Serve) and the tendencies on the studieJprocess depending on the source (Urea, Nitron 26) and the quantity of nitrogen (100, 200 Kg N/Ha) applied on the grass. It was found that the concentrations of nitrats on the grounds and the vegetal tissue stretched to intensity at the same time as were increase the levels of nitrogenious fertilization and in some cases for the present environment conditions.

Der Einfluß von 1-Carbamoyl-3(5)-methylpyrazol (CMP) auf die Nitrifikation und bodenbiologische Kennwerte im Vergleich zu Nitrapyrin (NP) und Dicyandiamid (DCD)

Summary A new compound that retards the microbially induced process of nitrification, 1-carbamoyl-3(5)-methyl-pyrazole (CMP), is described and its influence on soil organisms, in comparison with the well-known nitrification inhibitors dicyano diamide (DCD) and nitrapyrin (NP) is discussed. This examination was carried through (i) by testing pure cultures of microorganisms, (ii) in the laboratory using two different soils, and (iii) by field experiments in different locations.

The Influence of Nitrification on the Medium Solution and Growth of Holly, Azalea, and Juniper in a Pine Bark Medium

Abstract Three genera of woody plants were container-grown in a pine bark medium. Pine bark was amended or unamended with nitrapyrin (NI) and fertilized with an NH4-N fertilizer. Medium solution NH4-N concentrations of bark without NI decreased rapidly for the first 3 to 5 weeks with a concomitant increase in NO3-N concentrations. Medium solution pH at 0 NI decreased 0.8 unit during periods of rapid NO3-N accumulation. The low medium solution pH of the 0 NI treatment resulted in solution Ca, Mg, and Mn concentrations that were several times greater than at 82 μg of NI. Correspondingly, tissue concentrations of these ions were generally greater at the 0 NI treatment than at the 82 μg NI treatment. In general, there were no differences in shoot dry weight in response to NI treatment. Results indicate that nitrification is important in the nutrition of container-grown plants.