Effective nitrification inhibitors may improve fertilizer recovery in irrigated cotton

N fertilizer is often poorly recovered in irrigated cotton production, due to N loss through denitrification. We researched the ability of inhibitors to delay nitrition and reduce the availability of NO₃ ^- to denitrifying microorganisms and thus improve N fertilizer recovery, 2-Ethynylpyridine, etridiazole, and nitrapyrin proved highly effective nitrification inhibitors, although nitrification was evident several weeks after their application. CaC₂ was relatively ineffective, even when wax-coated to prolong the evolution of C₂H₂. Phenylacetylene and ethynylcyclohexanol were also ineffective, despite having a chemical structure similar to 2-ethynylpyridine. A strong association was identified between each compound's ability to inhibit nitrification and its capacity to improve N fertilizer recovery. In one experiment, N fertilizer recovery was increased by 50% with 2-ethynylpyridine, etridiazole, or nitrapyrin application, from 33% without inhibitors. The inhibitors had little effect on fertilizer recovery where N losses were relatively small. 3-Methyl pyrazole significantly increased N uptake and lint yield, but the nitrification inhibitors had no significant effect on N uptake or on yield in two of the three of the cotton crops. A laboratory study confirmed that nitrification inhibitor effectiveness declined in the order 2-ethynylpyridine>etridiazole>nitrapyrin>3-methyl pyrazole>phenylacetylene>CaC₂>ethynylcyclohexanolThis research was conducted at Australian Cotton Research Institute, CSIRO Division of Plant Industry, Locked Bag 59, Narrabri, NSW 2390, Australia     

Effects of nitrification inhibitors on germination of various seeds in soil

Summary The effects of 19 nitrificiation inhibitors on germination of seeds in soil were investigated. The nitrification inhibitors tested were sodium azide, potassium azide, potassium ethyl xanthate, nitrapyrin (N-Serve), etridiazole (Dwell), 3-mercapto-1,2,4-triazole (MT), 2-amino-4-chloro-6-methylpyrimidine (AM), 2,4-diamino-6-trichloromethyl-s-triazine, 2-mercaptobenzothiazole (MBT), 4-amino-1,2,4-triazole (ATC), sodium thiocarbonate (STC), guanylthiourea (ASU), thiourea (TU), dicyandiamide (DCD), sulfathiazole (STC), phenylacetylene, 2-ethynyl-pyridine, 3-methylpyrazole-l-carboxamide (MPC), and ammonium thiosulfate (ATS). Germination tests were performed with seeds of alfalfa (Medicago sativa L.), wheat (Triticum aestivum L.), rye (Secale cereale L.), barley (Hordeum vulgare L.), sorghum [Sorghum bicolor (L.) Moench], oats (Avena sativa L.), and corn (Zea mays). Only 2 of the 19 nitrification inhibitors studied (potassium azide and sodium azide) reduced germination of the seeds tested when applied at the rate of 12.5 g g^–1. The other inhibitors studied had no effect on the germination of wheat, alfalfa, barley, corn, oat, rye, or sorghum seeds when they were applied at the rate of 125 g g^–1 soil, and most of them had no effect on seed germination when applied at the rate of 625 g g^–1 soil.     

Evaluation of 3-methylpyrazole-1-carboxamide as a soil nitrification inhibitor

Summary Laboratory studies to evaluate 3-methylpyrazole-1-carboxamide (MPC) as a soil nitrification inhibitor showed that it was comparable to nitrapyrin (N-Serve) for inhibiting nitrification of ammonium in soil, but was not as effective as etridiazole (Dwell) or 2-ethynylpyridine. They also showed that the effectiveness of MPC as a soil nitrification inhibitor is markedly affected by soil type and soil temperature, that MPC is more effective for inhibiting nitrification of ammonium-N than of urea-N, and that MPC has little, if any, effect on hydrolysis of urea or denitrification of nitrate in soil. These observations and other work discussed indicate that MPC is one of the most promising compounds so far proposed for inhibition of nitrification in soil.     

Potency of nitrification inhibitors following their repeated application to soil

Summary Nitrification inhibitors were applied to a field experiment on loamy sand soil each autumn for 4 years, immediately prior to sowing winter cereals. Laboratory experiments demonstrated that repeated application of the inhibitor dicyandiamide (DCD) to a soil had little effect either on the rate of DCD decomposition or the ability of DCD to inhibit nitrification. Repeated field application of the inhibitors DCD, nitrapyrin or etridiazole resulted in increased sensitivity of ammonium-oxidizing bacteria to nitrapyrin or etridiazole, but not to DCD. The rate of decomposition of etridiazole was unaffected by four annual applications of this inhibitor, but decomposition of nitrapyrin was somewhat slower in soil that had received nitrapyrin annually for 4 years than in soil that had never been treated with an inhibitor.     

Effects of nitrification inhibitors on denitrification of nitrate in soil

Summary The influence of 28 nitrification inhibitors on denitrification of nitrate in soil was studied by determining the effects of different amounts of each inhibitor on the amounts of nitrate lost and the amounts of nitrite, N₂O and N₂ produced when soil samples were incubated anaerobically after treatment with nitrate or with nitrate and mannitol. The inhibitors used included nitrapyrin (N-Serve), etridiazole (Dwell), potassium azide, 2-amino-4-chloro-6-methylpyrimidine (AM), sulfathiazole (ST), 4-amino-1,2,4-triazole(ATC),2,4-diamino-6-trichloromethyl-s-triazine (CL-1580), potassium ethylxanthate, guanylthiourea (ASU), 4-nitrobenzotrichloride, 4-mesylbenzotrichloride, sodium thiocarbonate (STC), phenylmercuric acetate (PMA), and dicyandiamide (DCD).Only one of the nitrification inhibitors studied (potassium azide) retarded denitrification when applied at the rate of 10 g g^–1 soil, and only two (potassium azide and 2,4-diamino-6-trichloromethyl-s-triazine) inhibited denitrification when applied at the rate of 50 g g^–1 soil. The other inhibitors either had no appreciable effect on denitrification, or enhanced denitrification, when applied at the rate of 10 or 50 g g^–1 soil, enhancement being most marked with 3-mercapto-1,2,4-triazole. Seven of the inhibitors (potassium azide, sulfathiazole, potassium ethylxanthate, sodium isopropylxanthate, 4-nitrobenzotrichloride, sodium thiocarbonate, and phenylmercuric acetate) retarded denitrification when applied at the rate of 50 g g^–1 soil to soil that had been amended with mannitol to promote microbial activity.Reports that nitrapyrin (N-Serve) and etridiazole (Dwell) inhibit denitrification when applied at rates as low as 0.5 g g^–1 soil could not be confirmed. No inhibition of denitrification was observed when these compounds were applied at the rate of 10 g g^–1 soil, and enhancement of denitrification was observed when they were applied at the rate of 50 or 100 g g^–1 soil.     

Inhibition of nitrification in soil by gaseous hydrocarbons

Summary Recent work has shown that gaseous hydrocarbons such as methane, ethane, and ethylene are competitive inhibitors of the monooxygenase enzyme responsible for oxidation of ammonia by chemoautotrophic nitrifying microorganisms such as Nitrosomonas europaea. Because methane, ethane, and ethylene are produced by microbial activity in soil, we studied the possibility that they may inhibit oxidation of ammonia by the nitrifying soil microorganisms. We found that all three of these gaseous hydrocarbons inhibited nitrification in soil and that their ability to inhibit nitrification decreased in the order: ethylene > ethane > methane. Ethylene was much more effective than ethane or methane for inhibiting nitrification of ammonium in soil, but it was much less effective than acetylene, and it seems unlikely that the amounts of ethylene produced in soils will be sufficient to cause significant inhibition of nitrification by soil microorganisms.     

A method of selective inhibition to distinguish between nitrification and denitrification as sources of nitrous oxide in soil

Summary Nitrapyrin and C₂H₂ were evaluated as nitrification inhibitors in soil to determine the relative contributions of denitrification and nitrification to total N₂O production. In laboratory experiments nitrapyrin, or its solvent xylene, stimulated denitrification directly or indirectly and was therefore considered unsuitable. Low partial pressures of C₂H₂ (2.5–5.0 Pa) inhibited nitrification and had only a small effect on denitrification, which made it possible to estimate the contribution of denitrification. The contribution of nitrification was estimated by subtracting the denitrification value from total N₂O production (samples without C₂H₂). The critical C₂H₂ concentrations needed to achieve inhibition of nitrification, without affecting the N₂O reductase in denitrifiers, must be individually determined for each set of experimental conditions.     

几种吡啶类化合物对土壤硝化的抑制作用比较

为了探明吡啶类化合物对土壤硝化作用的抑制效应,采用室内微宇宙试验,研究了2-氯-6(三氯甲基)硫酸盐、2-氯-6(三氯甲基)盐酸盐、吡啶混合物和吡啶X类化合物对潮土、红壤和水稻土中铵态氮硝化的抑制作用。结果表明,在35 d培养期内,吡啶类化合物处理土壤硝态氮含量明显低于对照(未添加吡啶类化合物),吡啶类化合物对土壤中铵态氮的硝化抑制率介于2.91%~91.92%,抑制强度先逐渐升高后降低,在培养21 d时抑制强度达到峰值。不同类型吡啶类化合物对土壤中铵态氮的硝化抑制效果存在差异,吡啶盐酸盐类化合物优于其他几类化合物;吡啶类化合物对土壤中铵态氮的硝化抑制作用与土壤类型有关,对3种土壤中铵态氮的硝化抑制作用表现为潮土>水稻土>红壤。就同一土壤而言,硝化抑制强度随着吡啶类化合物用量的增加而增加。     

Effects of ammonium and nitrate on mineralization of nitrogen from leguminous residues

A laboratory incubation experiment was conducted to compare the effects of NH _inf4 ^sup+ and NO _inf3 ^sup- on mineralization of N from ¹⁵N-labelled vetch (Vicia villosa Rotn) in an Illinois Mollisol, and to determine the effect of a nitrification inhibitor (nitrapyrin) on mineralization of vetch N when used with NH _inf4 ^sup+ . The addition of either NH _inf4 ^sup+ or NO _inf3 ^sup- (100 and 200 mg N kg^-1 soil) significantly increased mineralization of vetch N during incubation for 40 days. The effect was greater with NH _inf4 ^sup+ than with NO _inf3 ^sup- , and a further increase occurred in the presence of nitrapyrin (10 mg kg^-1 soil). The addition of NO _inf3 ^sup- retarded the nitrification of NH _inf4 ^sup+ -N derived from vetch.     

芳香族化合物对土壤硝化作用的抑制研究

Aromatic compounds (ACs) in soil can induce competitive inhibition for soil NH₃ oxidation, and nitrification inhibitors can be used to this end. A laboratory incubation experiment was performed with 12 nitroaromatic compounds (NACs), 15 amidoaromatic compounds (AACs) and 20 hydroxyaromatic compounds (HACs) to assess the inhibitory effects of ACs on soil nitrification. Based on these results, the critical and optimal concentrations of ACs were determined for better inhibitory effects. Most of the test ACs were able to inhibit soil nitrification; the effectiveness differed with soil type. Among the ACs, the NACs with m-nitryl, amino or hydroxyl and the AACs with a nitro group or a chlorine atom on aromatic ring or with a p-hydroxyl were more effective. 3-nitroaniline, 4-aminophenol and 3-nitrophenol showed the greatest potential as nitrification inhibitors. The critical concentration of these compounds in brown soil and cinnamon soil was found to be 0.5 mg kg^-1 soil. Due to the toxicity, carcinogenicity and mutagenicity of ACs, further toxicological and ecotoxicological research is necessary before ACs are used as nitrification inhibitors in agricultural and horticultural practices.     

Effects of preemergence and postemergence herbicides on urea hydrolysis and nitrification of urea nitrogen in soil

The influence of 5 and 50 mg active ingredient kg^-1 soil of nine preemergence and nine postemergence herbicides on transformations of urea N in soil was studied in samples of two coarse-textured and two fine-textured soils incubated aerobically at 20°C. The effects of each herbicide on soil urea transformations was measured by determining the amounts of urea hydrolyzed and the amounts of NO _inf3 ^sup- and NO _inf2 ^sup- produced at various times after treatment with urea. Applied at the rate of 5 mg active ingredient kg^-1 soil, none of the herbicides retarded urea hydrolysis in the four soils used, but four of the postemergence herbicides (acifluorfen, diclofop methyl, fenoxaprop ethyl) retarded urea hydrolysis in the two coarse-textured soils. All the herbicides tested except siduron retarded nitrification in the two coarse-textured soils when applied at 50 mg of urea N active ingredient kg^-1 soil, and fenoxaprop ethyl and tridiphane markedly retarded nitrification of urea N in all four of the soils when applied at this rate. One-way analysis of variance and correlation analyses indicated that the inhibitory effects of the 18 herbicides tested on nitrification of urea N in soil increased with a decrease in the organic-matter content and an increase in the sand content of the soil. Present address: Department of Soil and Environmental Sciences, University of California, Riverside, CA 92521, USA     

Effect of Baythroid on nitrogen transformations in soil

Laboratory incubation experiments were conducted in soil to study the influence of the insecticide Baythroid on immobilization-remineralization of added inorganic N, mineralization of organic N, and nitrification of added NH _inf4 ^su+ -N. Baythroid was applied at 0, 0.4, 0.8, 1.6, 3.2, and 6.4 g g^-1 soil (active ingredient basis). The treated soils were incubated at 30°C for different time intervals depending upon the experiment. The immobilization and mineralization of N were significantly increased in the presence of Baythroid, the effect being greater with higher doses of the insecticide. Conversely, nitrification was retarded at lower doses of Baythroid and significantly inhibited at higher doses. The results of these studies suggest that excessive amonts of insecticide residues affect different microbial populations differently, leading to changes in nutrient cycling.     

pH 升高对红壤硝化过程产生 N2O 的影响

对红壤添加NaOH培养获得不同pH系列的土壤.通过室内培养试验.研究了3种pH条件下土壤的N_2O排放和无机N的变化情况.结果表明:硝化活性随土壤pH升高而增强:pH升高增加了土壤N_2O的释放;纯化学过程对N_2O散发的贡献随pH的升高而降低;Nitrapyrin在pH 4.8和pH 6.0时表现山硝化抑制作用,在pH 8.5时抑制效果不明显,且提高了培养期间pH8.5土壤N_2O的释放量.     

Use of urea coated with natural products to inhibit urea hydrolysis and nitrification in soil

Laboratory incubation experiments were conducted with uncoated urea or urea coated with dementholized oil (DMO), pitch (the mint oil discard), terpenes (the products of menthol mint oil), or dicyandiamide (DCD) to study the retardation of urea hydrolysis and nitrification in soil. Two levels (0.5 and 1 %) of coating were tested. Urea was applied at a rate of 200 mg kg⁻¹ of dry weight of soil. The urea hydrolysis and nitrification processes were inhibited by all three natural products. All the three natural products viz., DMO, terpenes, and pitch significantly retarded urease activity of soil.     

Effect of the inhibitors nitrapyrin and sodium chlorate on nitrification and N2O formation in an acid forest soil

An acid forest soil from beech forest gaps, which were either limed or unlimed, and the undisturbed forest was investigated for the type of nitrifying populations and the process of N₂O evolution. To see whether nitrifiers were of heterotrophic or autotrophic origin, the nitrification inhibitors nitrapyrin and sodium chlorate were applied to disturbed soil samples which underwent laboratory incubations. Nitrapyrin inhibits autotrophic nitrification. In different studies, sodium chlorate has been identified as an inhibitor either of autotrophic or of heterotrophic nitrification. In the samples investigated only nitrapyrin inhibited the autotrophic nitrification occurring in the limed soil. Sodium chlorate effectively inhibited heterotrophic nitrification. In the limed forest floor samples, where most autotrophic nitrification occured, sodium chlorate showed no inhibitory effect. In another laboratory incubation experiment, N₂O evolution from undisturbed soil columns, to which the above inhibitors were applied, was investigated. In those samples, in which nitrification had been reduced, neither inhibitor significantly reduced N₂O evolution. Thus it was concluded that the contribution of nitrification to N₂O losses is negligible, and that N₂O evolution arises from the activity of denitrifying organisms. Microbial biomass and respiration measurements showed that the inhibitors did not affect microflora negatively.     

氮素浓度和水分对水稻土硝化作用和微生物特性的影响

为了明确不同氮素浓度和水分对土壤硝化作用和微生物特性的影响,特别是高氮素浓度下的响应特异性,以红壤水稻土为供试土壤,设置4个硫铵用量水平[0(CK)、120 mg(N).kg-1(A1)、600 mg(N).kg-1(A2)、1 200 mg(N).kg-1(A3)],调节土壤水分为饱和持水量(WHC)的40%、60%和80%,研究了短期内不同氮素浓度和不同水分条件下土壤硝化作用、微生物生物量碳和微生物功能多样性的变化。结果表明:在40%、60%和80%WHC水分条件时,硫铵A2、A3浓度处理土壤硝化率和硝化速率普遍较低,硫铵A1浓度处理硝化率和硝化速率随土壤含水量的升高而升高;同含水量时随硫铵用量的升高而显著降低。在40%、60%和80%WHC水分条件时,微生物生物量碳随硫铵浓度的升高而降低;同浓度硫铵用量水平时,微生物生物量碳的变化基本表现为:60%WHC80%WHC40%WHC。分析发现不同水分和硫铵处理之间存在交互作用。BIOLOG分析显示:不同氮素浓度和不同水分处理,60%WHC下A1处理的平均吸光值(AWCD)和Shannon、Simpson、McIntosh指数最大,其次为60%WHC的硫铵CK处理,而不同水分下硫铵A2、A3处理,其AWCD值和Shannon、Simpson、McIntosh多样性指数都较低,进一步说明过量施肥导致微生物活性降低。不同氮素浓度和水分条件下土壤微生物和生化性状不同,过量施用化肥后将有可能造成土壤微生物性状和生化功能衰减。     

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.     

Phosphorus addition enhances loss of nitrogen in a phosphorus-poor soil

Plants and microbes have limited stoichiometric flexibility to take up and store nitrogen (N) and phosphorus (P). Variation in the relative availability of N and P to plants and microbes may therefore affect how strongly N and P are held in terrestrial ecosystems with important implications for net primary productivity and carbon sequestration. We hypothesized that an increase in P availability in a P-poor soil would increase N uptake by plants and microbes thereby reducing N loss. We grew mixtures of the C3 grass Phalaris aquatica L. and the legume Medicago sativa L. in mesocosms with soils low in P availability and then used a novel technique by adding a ¹⁵N tracer with and without 1 g P m⁻² to soil with different moisture and available N conditions, and measured the ¹⁵N recovery after 48 h in microbes, plants and soil. In contrast to our hypothesis, we found that P addition reduced ¹⁵N in microbes without water stress by 80% and also reduced total¹⁵N recovery, particularly without water stress. Water stress in combination with N addition further showed low total ¹⁵N recovery, possibly because of reduced plant uptake thereby leaving more ¹⁵N in the soil available for nitrification and denitrification. Our results suggest that P addition can result in large gaseous N loss in P-poor soils, most likely by directly stimulating nitrification and denitrification.     

Nitrogen starvation promotes biodegradation of N-heterocyclic compounds in soil

Mineralization studies were performed to examine the impact of N deprivation on microbial utilization of the N-heterocyclic herbicides, atrazine and cloransulam-methyl (C-M). Soil depleted by 130 years of cropping to Zea mays without fertilization was contrasted to soil from the same site regularly receiving fertilizers. Long-term N deprivation promoted rapid degradation of atrazine and the C-M pyrimidine ring, whereas no significant effect was observed on degradation of the C-M phenyl ring. When a sandy soil naturally low in N was used, addition of 5 or more μg NH₄-N/g soil suppressed mineralization of the C-M pyrimidine ring. These findings provide insight into organic N availability and suggest broad implications for the effect of exogenous N in degradation of heterocyclic herbicides.     

Nitrapyrin decreased nitrification of nitrogen released from soil organic matter but not amoA gene abundance at high soil temperature

Water pulses have a significant impact on nitrogen (N) cycling, making management of N challenging in agricultural soils that are exposed to episodic rainfall. In hot, dry environments, wetting of dry soil during summer fallow causes a rapid flush of organic matter mineralisation and subsequent nitrification, which may lead to N loss via nitrous oxide emission and nitrate leaching. Here we examined the potential for the nitrification inhibitor nitrapyrin to decrease gross nitrification at elevated temperature in soils with contrasting soil organic matter contents, and the consequent effects on ammonia oxidiser populations. Soil was collected during summer fallow while dry (water content 0.01 g g⁻¹ soil) from a research site with two management treatments (tilled soil and tilled soil with long-term additional crop residues) by three field replicates. The field dry soil (0–10 cm) was wet with or without nitrapyrin, and incubated (20 or 40 °C) at either constant soil water content or allowed to dry (to simulate summer drying after a rainfall event). Gross N transformation rates and inorganic N pools sizes were determined on six occasions during the 14 day incubation. Bacterial and archaeal amoA gene abundance was determined on days 0, 1, 7 and 14. Nitrapyrin increased ammonium retention and decreased gross nitrification rates even with soil drying at 40 °C. Nitrification was likely driven by bacterial ammonia oxidisers, as the archaeal amoA gene was below detection in the surface soil layer. Bacterial ammonia oxidiser gene abundances were not affected by nitrapyrin, despite the decrease in nitrifier activity. Increased soil organic matter from long-term additional crop residues diminished the effectiveness of nitrapyrin. The present study highlights the potential for nitrapyrin to decrease nitrification and the risk of N loss due to mineralisation of soil organic matter under summer fallow conditions.