Effect of fertilizer,N rate and nitrapyrin on Ca and Mg nutrition of corn (zea hays,L.)

Abstract

Corn was grown with three rates (200, 400, 800 rng N/pot) of sewage sludge (Milorganite), KNO₃, or (NH₄)₂SO. application in the presence (10 ppm) or absence of nitrapyrin, a nitrification inhibitor. Bleached areas appeared on the lower leaves of plants at the lowest application of sludge when nitrapyrin was added. No other visible symptoms were noted.

Five‐week‐old seedlings were harvested, weighed and analyzed for Ca and Mg. Nitrapyrin restricted dry weight production of plants receiving sludge and increased growth in those receiving KNO₃. Concentrations of Ca and Mg were reduced in all plants receiving nitrapyrin except in those grown at the lowest rates of sludge application.     

Effects of nitrapyrin,terrazole, and simazine on soil nitrogen transformation and corn growth

Abstract

Nitrapyrin, terrazole and simazine were evaluated as chemical inhibitors of biological nitrification and denitrification. Corn (Zea mays L. cv. Hybrid Pioneer 3343) was grown in 60‐liter pots filled with a 50/50 (V/V) sand/Cecil clay mixture. Chemical treatments consisted of weekly applications of 0.25 ppm nitrapyrin, terrazole and/or simazine concurrently with 20 ppm N as either (NH₄)₂SO₄ or Ca(NO₃)₂ for 9 weeks. Thereafter, only N (20 ppm per pot) was applied to the media every three days for 4 weeks. Nitrapyrin, terrazole and simazine reduced nitrification resulting in both higher total plant N and residual soil NH₄ content relative to the control plants and soil. Plant growth was reduced by the inhibitory effects of the chemicals on nitrification and subsequent NH₄ accumulation in the medium. All chemicals reduced denitrification with terrazole being more effective than nitrapyrin as reflected by higher N contents of plants and residual soil NO₃‐N. Nitrapyrin and/or terrazole applied with Ca(NO₃)₂ increased plant biomass, but simazine, by inducing higher N0₂ concentration in the plant tissues, sharply reduced plant growth relative to the other treatments. When simazine was part of the chemical treatment, its effects on plant growth and total N contents generally outweighed or masked those of nitrapyrin or terrazole.     

Growth and mineral composition of tomato under various regimes of nitrogen nutrition 1

Five‐week‐old tomato plants were transplanted into pots containing 10 kg of potting compost which was amended with 0, 0.1, or 0.3 g of nitrapyrin and 4 g of N from KNO₃, (NH₄)₂SO₄ or sewage sludge and were grown in a greenhouse. After 2 to 3 weeks, leaves of the plants grown on any nitrapyrin x N source combination were curled with reduced laminae. Symptoms were most severe with the nitrapyrin x sludge regimes and least severe with the nitrapyrin x KNO₃ treatments. With (NH₄)₂SO₄ and sludge, growth was depressed linearly by nitrapyrin additions but was unaffected with KNO₃ fertilization. The concentrations of Ca and Mg in the shoots were lowered linearly or curvilinearly by nitrapyrin combination with any fertilizer whereas that of K was unaffected. Levels of Mn in leaves rose with nitrapyrin additions to the (NH₄)₂SO₄ or sludge treatment but were stable with any of the nitrapyrin x KNO₃ combinations. Cation antagonism among NH₄ ⁺, Ca⁺⁺, and Mg⁺⁺ is suggested as affecting the concentrations of these ions in tissues, whereas acidification of the medium and a restriction in dry matter production may account for the elevated levels of Mn in the tomato shoots grown in the presence of nitrapyrin.     

Influence of two “nitrogen regulators”; on soil n transformations and movement

Abstract

Experiments were conducted to assess the potential influence of a commercial product, EXTEND, on nitrogen transformations and movement in a sandy soil. Neither nitrapyrin (a commercially‐available nitrification inhibitor) nor EXTEND significantly affected the rate of NH₄ ⁺‐N or NO₃ ^‐‐N movement through a column of soil treated with urea‐ammonium nitrate liquid fertilizer. Nitrapyrin effectively inhibited nitrification, but the nitrification rate in the EXTEND treated systems were the same as control.     

Abstract

In a greenhouse, radish (Raphanus sativus L.), corn (Zea mays L.), soybean (Glycine max Merr), and wheat (Triticum aestivum L.) were grown in soil‐based medium with captan at 60 mg/kg and truban at 30 mg/kg and with different levels of N from (NH₄)₂SO₄ or NaNO₃. Growth of radish, soybean, and corn was restricted by NH₄‐N compared with NO₃‐N. Captan and truban stunted growth of radish and soybean. As NH₄‐N or NO₃‐N fertilizer increased, the concentration of Ca and Mg in all plants decreased, and the percentage of K in corn, soybean, and wheat increased. Application of captan and truban increased all cation concentrations in corn, wheat, and soybean but decreased Ca concentration in radish. The amount of residual NH₄‐N in the medium supplied with (NH₄)₂SO₄ was increased by application of captan or truban. Captan increased the residual NO₃‐N in the medium treated with NaNO₃. Chemical names used: captan, (N‐(trichloro)methylthio)‐4‐cyclo‐hexene‐l, 2‐dicarboximide); truban, (5‐ethoxy‐3‐trichloromethyl‐l, 2, 4,‐thiadiazole).     

Ammonium fixation from urea as influenced by nitrapyrin

Abstract

During the period 1977–1979, NaNO₃, urea, and urea plus 2% (wt/wt) nitrapyrin (2‐chloro‐6‐(trimethyl)pyridine) were compared on a Matapeake silt loam (fine silty mixed mesic Typic Hapludult) . Nitrogen sources were injected as solutions into the water system at 224 kg N ha^‐1yr^‐1used for subsurface trickle irrigation of corn (Zea maysL.). Nitrogen was withheld in 1980 in order to assess residual N effects. Grain yields in 1980 for the NaNO₃, urea, and urea plus Nitrapyrin treatments were 5.10, 4.56 and 6.52 Mg ha^‐1, respectively. Corresponding ear leaf N concentrations were 17.7, 16.7 and 19.2 g kg^‐1. Significantly higher grain yield and leaf N concentrations associated with the use of nitrapyrin as a nitrification inhibitor indicated greater soil N reserves for this treatment. Non‐exchangeable (fixed) NH₄ ⁺, in soil cores taken in November 1981 averaged 54, 59 and 74 ug N g^‐1for the respective N regimes. The concentration of fixed NH₄ ⁺increased with sampling depth, averaging 54, 61 and 72 ug N g^‐1for the 0–5, 30–35, and 60–65 cm profile depths, respectively. This trend is ascribed to increasing quantities of micaceous and vermiculitic clay (<2 um) with increasing profile depth.     

Nitrapyrin effect on corn N‐15 uptake efficiency,denitrification and nitrate leaching

Abstract

The effect of nitrapyrin on the fate of fertilizer nitrogen (N) applied to soil needs further investigation. Our objective was to determine the effect of nitrapyrin under two different leaching regimes on the fate of ammonium sulfate‐nitrogen [(NH₄)₂SO₄‐N] added to the soil, namely corn N uptake, denitrification, nitrate leaching and soil residual N. A Nunn sandy clay loam soil (fine, montmorillonitic, mesic, aridic, argiustoll), low in residual inorganic N was used. Nitrogen‐15 enriched (NH₄)₂SO₄ (5 atom% N‐15) was applied at five rates (0, 50, 100, 200, and 400 mg/kg), nitrapyrin at three rates 0, 1.3, and 2.6 μL/kg (0, 2.36, and 4.72 L/ha) and leaching at two rates (0 and 1000 mL over field capacity in two 500‐mL increments at 3 and 6 weeks after planting) in a complete factorial arrangement with three replications. Corn (Zea mays L.) seeds were planted in pots (2 kg soil/pot) and allowed to grow for 80 days in a greenhouse. The atom% N‐15 values were determined in plant tops, leachates and soil samples using a mass spectrometer. The results showed that N fertilizer increased dry matter production, plant N concentration, leaching of nitrates and denitrification significantly. The effect of nitrapyrin on yield was not statistically significant, but, it at a rate equivalent to 4.72 L/ha reduced denitrification and nitrate (NO₃) leaching and increased N uptake efficiency. Application of 4.72 L/ha of nitrapyrin versus control showed the following results respectively, N uptake: 46.3 versus 39.6%, denitrification: 26.3 versus 35.3% and NO₃ leaching: 2.7 vesus 6.7% of fertilizer N‐15. Nitrapyrin increased soil residual fertilizer N‐15 in organic matter and roots. The result of this study show that application of nitrapyrin at an adequate rate decreases denitrification and NO₃ leaching and increases N uptake efficiency.     

Decomposition rate of dicyandiamide and nitrification inhibition

Abstract

Degradation of dicyandiamide (DCD) was assayed in laboratory studies at 8, 15, and 22 C in a Decatur silt loam and in a Norfolk loamy sand. Dicyandiamide was very short lived at 22 C, with half‐lives of 7.4 and 14.7 days in the Decatur and Norfolk soils, respectively. In the Norfolk soil at 8 C, half‐life increased to 52.2 days. In a nitrificaton study of both soils at 22 C, 80 mg (NH₄)₂SO₄‐N kg^‐1 of soil was applied with 20 mg DCD‐N kg^‐1 of soil and 100 mg kg^‐1 (NH₄)₂S0₄‐N was added with 5% nitrapyrin. Distinct lag phases preceded zero order nitrification with the inhibitor treatments. Lag periods were 2 and 2.6 times the half life of DCD in the degradation study for Decatur and Norfolk soils, respectively. Like most nitrification inhibitors, the effectiveness of DCD decreases with increasing temperature. In the Norfolk loamy sand, nitrification inhibition by DCD was equal to nitrapyrin for up to 42 days, but in Decatur silt loam, DCD was less potent to nitrapyrin as a nitrification inhibitor.     

Polymers act as nitrogen carriers to fertilize greenhouse and field grown lettuce

Abstract

Two concentration levels for each of two polymer gels (polyacrylate and vinyl alcohol acrylic acid) were incorporated with urea, ammonium sulfate [(NH₄)₂SO₄], and potassium nitrate (KNO₃) fertilizer solutions and used as nitrogen (N) carriers to fertilize lettuce grown in a greenhouse and field study. Of the initial 1290 mg N applied, gel treatments contained up to 70 mg N after 43 days. The vinyl alcohol polymers retained significantly larger quantities of NO₃‐N from the (NH₄)₂SO₄ and KNO₃‐N sources than from the urea source. The N concentration in each gel treatment was an important factor and dependent on the polymer and fertilizer source. Both gels performed better when incorporated with (NH4)₂SO₄ and KNO₃ than with urea.     

Transformations of nitrogen fertilizers in soil

The effects of ¹⁵N-labelled urea, (NH₄)₂SO₄ and KNO₃ on immobilization, mineralization, nitrification and ammonium fixation were examined under aerobic conditions in an acid tropical soil (pH 4.0) and in a neutral temperate soil (pH 6.8). Urea, (NH₄)₂SO₄ and KNO₃ slightly increased net mineralization of soil organic nitrogen in both soils. There was also an apparent Added Nitrogen Interaction (ANI) i.e. added labelled NH₄-N stood proxy for unlabelled NH₄-N that would otherwise have been immobilized. So far as immobilization and nitrification were concerned, urea and (NH₄)₂SO₄ behaved very similarly in each soil. Immobilization of NO₃-N was negligible in both soils. Some of the added labelled NH₄-N was rapidly fixed, more by the temperate soil than by the tropical soil. This labelled fixed NH₄-N decreased during incubation, in contrast to labelled organic N, which did not decline.     

Nitrapyrin,terrazole, atrazine,and simazine influence on nitrification and corn growth

Most farming systems involving tilled crops require use of pesticides and nitrogen fertilizers in different combinations although most pesticides effects on soil N transformation are scantly documented. Studies were initiated to compare atrazine and simazine herbicides with two biological nitrification inhibitors (nitrapyrin and terrazole) for their effects on biological nitrification and corn (Zea mays L.) growth. In a laboratory study, inhibition of nitrification was less than 3% in a Tifton loamy sand incubated with 10 μg a.i g^‐1 soil atrazine or simazine but was more than 10% in soil amended with nitrapyrin or terrazole, applied separately or in combinations with either herbicide at the same rate. Similar trends were observed with soil treated with different combinations of 2.5 μg a.i. g^‐1 soil nitrapyrin or terrazole and 1.25 μg a.i. g^‐1 soil atrazine or simazine and incubated with and without corn plants under greenhouse conditions. The combination of either herbicide with nitrapyrin or terrazole significantly reduced the corn dry weights with substantial accumulation of Kjeldahl N and NO₃ ^‐ in tissues of plants, probably due to a concentration effect. However, these chemical combinations, applied at the rate of 1.2 kg a.i. ha^‐1 in conjunction with 35 kg ha^‐1 N as (NH₄)₂SO₄ in split banded applications (at planting and at the 6^th leaf stage), showed a nonsignificant trend towards increased corn ear yields in two‐year field studies. Generally, when atrazine or simazine was part of the chemical treatment, its effects on nitrification, plant growth and total N contents outweighed or masked those of nitrapyrin or terrazole.     

Effect of the nitrification inhibitor nitrapyrin on the fate of nitrogen applied to a soil incubated under laboratory conditions

The aim of this study was to examine the effect of the nitrification inhibitor nitrapyrin on the fate and recovery of fertilizer nitrogen (N) and on N mineralization from soil organic sources. Intact soil cores were collected from a grassland field. Diammonium phosphate (DAP) and urea were applied as N sources. Cores were equilibrated at –5 kPa matric potential and incubated at 20 °C for 42 to 56 days. Changes in NH₄⁺‐N, accumulation of NO₃^–‐N, apparent recovery of applied N, and emission of N₂O (acetylene was used to block N₂O reductase) were examined during the study. A significant increase in NH₄⁺‐N released through mineralization was recorded when nitrapyrin was added to the control soil without N fertilizer application. In the soils to which N was added either as urea or DAP, 50–90 % of the applied N disappeared from the NH₄⁺‐N pool. Some of this N (8–16 %) accumulated as NO₃^–‐N, while a small proportion of N (1 %) escaped as N₂O. Addition of nitrapyrin resulted in a decrease and delay of NH₄⁺‐N disappearance, accumulation of much lower soil NO₃^–‐N contents, a substantial reduction in N₂O emissions, and a 30–40 % increase in the apparent recovery of added N. The study indicates that N recovery can be increased by using the nitrification inhibitor nitrapyrin in grassland soils at moisture condition close to field capacity.     

Effects of the nitrification inhibitor nitrapyrin and tillage practices on yield-scaled nitrous oxide emission from a maize field in Iran

Nitrification inhibitors can effectively decrease nitrification rates and nitrous oxide(N₂O)emission while increasing crop yield under certain conditions.However,there is no information available on the effects of nitrification inhibitors and tillage practices on N₂O emissions from maize cropping in Iran.To study how tillage practices and nitrapyrin(a nitrification inhibitor)affect N₂O emission,a split factorial experiment using a completely randomized block design with three replications was carried out in Northeast Iran,which has a cold semiarid climate.Two main plots were created with conventional tillage and minimum tillage levels,and two nitrogen(N)fertilizer(urea)management systems(with and without nitrapyrin application)were created as subplots.Tillage level did not have any significant effect on soil ammonium(NH₄⁺)and nitrate(NO₃^-)concentrations,cumulative amount and yield-scaled N₂O emission,and aboveground biomass of maize,whereas nitrapyrin application showed significant effect.Nitrapyrin application significantly reduced the cumulative amount of N₂O emission by 41%and 32%in conventional tillage and minimum tillage practices,respectively.A reduction in soil NO₃^-concentration by nitrapyrin was also observed.The average yield-scaled N₂O emission was 13.6 g N₂O-N kg^-1N uptake in both tillage systems without nitrapyrin application and was significantly reduced to 7.9 and 8.2 g N₂O-N kg^-1N uptake upon the application of nitrapyrin in minimum tillage and conventional tillage practices,respectively.Additionally,nitrapyrin application increased maize biomass yield by 4%and 13%in the minimum tillage and conventional tillage systems,respectively.Our results indicate that nitrapyrin has a potential role in reducing N₂O emission from agricultural systems where urea fertilizers are broadcasted,which is common in Iran due to the practice of traditional farming.     

Evaluation of polymers for controlled‐release properties when incorporated with nitrogen fertilizer solutions

Abstract

Three polymers (polyacrylate, vinyl‐alcohol, starch‐based) were evaluated for controlled‐release properties when expanded in urea, ammonium sulfate ((NH₄)₂SO₄), and potassium nitrate (KNO₃) solutions, at five nitrogen (N) concentrations (0,10,15, 20 g N/L, and saturation). The expansion capacity (mL solution absorbed/g dry polymer) of each polymer varied and was dependent on the type and concentration of fertilizer solution. On average, polymers incorporated with urea, (NH₄)₂SO₄, and KNO₃ fertilizer solutions had expansion capacities of 275, 24, and 30 mL/g, respectively. All three polymers reacted with ammonium ions in solution and resisted normal extraction procedures of ammonium with 2N KCl. To determine gel characteristics when applied to a soil medium, selected gel treatments were incubated in containers of loamy sand soil up to 28 days and then assessed for the quantity of gel recovered, N content, and N concentration. Although most gels released a large portion of N after only 7 days, some gels slowed diffusion better than the dry fertilizer controls up to 28 days.     

Nitrapyrin effectiveness in reducing nitrous oxide emissions decreases at low doses of urea in an Andosol

In the tropics,frequent nitrogen(N)fertilization of grazing areas can potentially increase nitrous oxide(N₂O)emissions.The application of nitrification inhibitors has been reported as an effective management practice for potentially reducing N loss from the soil-plant system and improving N use efficiency(NUE).The aim of this study was to determine the effect of the co-application of nitrapyrin(a nitrification inhibitor,NI)and urea in a tropical Andosol on the behavior of N and the emissions of N₂O from autotrophic and heterotrophic nitrification.A greenhouse experiment was performed using a soil(pH 5.9,organic matter content 78 g kg^-1,and N 5.6 g kg^-1)sown with Cynodon nlemfuensis at 60%water-filled pore space to quantify total N₂O emissions,N₂O derived from fertilizer,soil ammonium(NH₄⁺)and nitrate(NO₃^-),and NUE.The study included treatments that received deionized water only(control,NI).No significant differences were observed in soil NH₄⁺content between the UR and UR+NI treatments,probably because of soil mineralization and NO₃^-produced by heterotrophic nitrification,which is not effectively inhibited by nitrapyrin.After 56 d,N₂O emissions in UR(0.51±0.12 mg N₂O-N concluded that the soil organic N mineralization and heterotrophic nitrification are the main processes of NH₄⁺and NO₃^-production.Additionally,it was found that N₂O emissions were partially a consequence of the direct oxidation of the soil's organic N via heterotrophic nitrification coupled to denitrification.Finally,the results suggest that nitrapyrin would likely exert significant mitigation on N₂O emissions only if a substantial N surplus exists in soils with high organic matter content.     

Rate of nitrapyrin and soil ph effects on nitrification of ammonium fertilizer and growth and composition of burley tobacco

Abstract

Laboratory and greenhouse experiments were conducted to determine the effects of rate of nitrapyrin and soil pH on nitrification of NH₄ ⁺ fertilizer in soil, and growth and chemical composition of burley tobacco (Nicotiana tabacum L. cv. ‘KY ‐14'). Such experiments were needed to develop information for increasing efficiency of N fertilizer use and to lessen the fertilizer‐induced soil acidity and salt effects on tobacco plants.

Results for laboratory and greenhouse incubations indicated that nitrification proceeeded slowly below pH 5.0 and the nitrapyrin necessary to delay nitrification increased with both increasing soil pH and length of incubation time. Generally, nitrification could be delayed 30 days by nitrapyrin rates of 0.25 or 0.5 μg g^‐1 regardless of soil pH. but rates of 1 μg g^‐1 nitrapyrin or higher were required for 60 days and longer incubation times, particularly at higher soil pH.

Growth and morphology of tobacco plants were either unaffected, or affected positively, by low rates of nitrapyrin (up to 2 μg g^‐1). However, rates of 4 μg g^‐1 and above reduced total plant dry weight, reducing sugars and contents of mineral elements. Concentrations and content of plant NO₃ ^‐ N and Mn were greatly decreased by application of nitrapyrin. Values for most parameters measured increased with increasing soil pH. The data show that low rates of nitrapyrin may be used to alter the ratio of NO₃ ^‐ to NH₄ ⁺ N absorbed by tobacco and possibly improve growth and safety of tobacco.     

Growth and elemental composition of tomato as affected by fungicides and nitrogen sources

Tomato (Lycopersicon esculentum Mill.) plant growth and elemental composition were evaluated using three NH₄‐N:NO₃‐N form ratios with or without the fungicide benomyl, captan, lime‐sulfur, nitrapyrin, or terrazole in a greenhouse soil culture study. Nitrogen was applied weekly for 5 weeks providing a total of 115 mg N/kg. Each fungicide was applied at 0.25 mg/kg 3 days before transplanting, followed by 3 weekly applications with each N treatment. The largest shoot and root dry weights were obtained with 1:1 N form ratio. With 1:1 N ratio treatment, all chemicals significantly increased plant growth resulting in lower element concentrations relative to the untreated control. However, growth of plants receiving either 1:0 or 0:1 N ratio treatment was not affected by nitrapyrin and terrazole, but was restricted by benomyl, captan, or lime‐sulfur. Overall, elemental concentrations in the tissues of plants receiving either N form was related to the fungicide treatment.     

Effect of high ammonium levels on nitrification,soil acidification,and exchangeable cation dynamics

Abstract

In almond orchards which are fertilized and irrigated with drip systems, fertilizers are applied to a relatively small soil volumes several times during the growing season. Where NH₄‐based fertilizers are used, high NH₄ levels are anticipated in soil solution and on exchange sites. The effects of high NH₄ concentration on nitrification, soil acidification, and exchangeable cation dynamics were studied in an incubation experiment where 500 and 2000 mg N/kg soil were added as (NrL₄)₂SO₄. After incubation for 25 days with added (NH₄)₂SO₄, nitrifying bacteria were lower than the populations at the start of experiment. In the 2000 mg N/kg treatment, nitrification activity nearly ceased and soil acidification was reduced. Although nitrification activity was lower in the 500 mg N/kg treatment than in the control, after 10 days of incubation, nitrification activity lowered soil pH by 0.7 units. After the initial 10 days, soil pH was lowered to 4.8 and nitrification activity was depressed. Ammonium ions occupied about 20 and 36 % of the exchange capacity in the 500 and 2000 mg N/kg treatments respectively, and exchangeable Ca, Mg, and K were significantly lowered. Extractable acidity was less than 0.1 cmoiykg dry soil.     

Persistence of effects of nitrification inhibitors added to soils

Abstract

The persistence of the effects of four nitrification inhibitors (2‐ethynylpyridine, nitrapyrin, etridiazole, 3‐methylpyrazole‐l‐carboxamide) on nitrification in soil was assessed by measuring the ability of two soils to nitrify NH₄ ⁺ [added as (NH₄)₂SO₄] after they had been treated with 5 μg inhibitor g^‐1 soil and incubated at 10, 20, or 30°C for 0, 21, 42, 84, 126, or 168 days. The soils used differed markedly in organic‐matter content (1.2 and 4.2% organic C). The data obtained showed that the persistence of the effects of the inhibitors studied decreased markedly with increase in soil temperature from 10 to 30°C and that, whereas the initial inhibitory effects of the test compounds on nitrification were greatest with the soil having the lower organic‐matter content, the persistence of their effects at 20 or 30°C was greatest with the soil having the higher organic‐matter content. The inhibitory effects of 2‐ethynylpyridine and etridiazole on nitrification were considerably more persistent than those of nitrapyrin or 3‐methylpyrazole‐l‐carboxamide and were significant even after incubation of inhibitor‐treated soil at 20°C for 168 days.     

Influence of biocides on tomato nitrogen uptake and soil nitrification and denitirification

As a result of repeated applications, some fungicides may accumulate in the soil to levels high enough to have adverse effects on the activity of soil microorganisms and plant growth. Comparison of the effects of 10 mg kg^‐1 soil of the benlate, captan, and lime‐sulfur fungicides with the nitrification inhibitors (NI) nitrapyrin and terrazole on oxidation of NH₄ ⁺ in Tifton loamy sand (siliceous, thermic plinthic Typic Kandiudults) incubated at 30° C showed that benlate had no significant effects whereas captan inhibited nitrification 21% more than lime‐sulfur, but about 20% less than NI. Application of benlate enhanced NO₃ ^‐ reduction to N₂O and N₂ in liquid medium inoculated with soil whereas 50 and 100 mg L"¹ medium of captan and lime‐sulfur compared favorably with the NI in suppressing NO₃ ^‐ and NO₂ ^‐ reductions, but were less effective than the inhibitors when applied at the low rate of 10 mg L^‐1 medium. In a greenhouse study with tomato (Lycopersicon esculentum Mill. cv. ‘Better Boy'), weekly drench applications of 0.25 mg kg^‐1 soil of the test biocides for four weeks with three NH₄ ⁺‐N: NO₃ ^‐‐N ratios showed that benlate applied with 1: 0 N ratio and lime‐sulfur applied with 0: 1 N ratio restricted significantly the plant growth and N uptake. The largest root: shoot ratios, total plant dry weight, and N uptake were obtained with plants fertilized with 1: 1 N ratio in combination with the biocides.