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.     

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 radish under different nitrification inhibitors and nitrogen sources

Abstract

Captan [N‐(trichloromethylthio)‐4‐cyclo‐hexene‐l, 2‐dicarboximide] and benomy¹[methyl 1‐(butylcarbamoyl)‐2‐benzimidazolecarbamate] were evaluated as nitrification inhibitors and compared with nitrapyrin [2‐chloro‐6‐(trichloromethyl)pyridine]. Nitrapyrin, captan, and benorayl were applied at 0, 20, 40, and 60 mg/kg with three nitrogen sources, KNO₃, (NH₄)₂SO₄, and urea, at 300 mg N/kg to ‘Cherry Belle’ radish (Raphanus sativusL). Nitrapyrin and captan inhibited nitrification effectively, but benomyl was not an effective inhibitor. Growth of radish roots and shoots was restricted with application of nitrapyrin and captan combined with (NH₄)₂SO₄or urea relative to the comparable KNO₃treatments. The concentrations of Ca, Mg, and NO₃‐N in plants, especially in shoots, fell, and the percentage of ? was increased with the addition of nitrapyrin and captan. Benomyl did not affect plant growth or composition     

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 rate of nitrapyrin and source of N on soil pH and response of burley tobacco

Abstract

A field experiment was conducted on Maury silt loam soil (Typic Paleudalf) during 2 years to determine the effects of rate of nitrapyrin and source of N fertilizer on soil pH and response of burley tobacco (Nicotiana tabacum L.cv.^xKy‐14'). All sources of N were applied at the rate of 280 kg N ha^‐1. The information was needed to increase the efficiency of N fertilizer use and improve the growth and safety of tobacco.

Results indicated that application of a NO₃ ^‐source of N fertilizer or low rates of nitrapyrin (0.56 to 2.24 kg ha^‐1) decreased surface soil acidification and the concentration of plant Mn, while plant dry weight early in the growing season was increased. The early growth benefits noted for .nitrapyrin did not lead to increased cured leaf yields or value. Cured leaf yield and value were highest in plots receiving Ca(NO₃)₂, followed by KH₄NO₃, then urea.

Concentration of protein N, total alkaloids, and total volatile nitrogenous bases of cured leaves increased and NO₃ ^‐‐N decreased as rate of nitrapyrin increased. Total N concentration of cured leaf, however, was not significantly affected by nitrapyrin application, indicating that the proportion of absorbed N as NH₄ ⁺increased as nitrapyrin rate increased.     

Kinetics of Nitrification in Selected Iowa Soils Treated with Stay‐N 2000

Abstract

The effectiveness of Stay‐N 2000 or reformulated nitrapyrin [2‐chloro‐6‐(tricholoromethyl) pyridine] was investigated in two Iowa soils representative of Clarion and Okoboji soils that differed in organic carbon, pH, and texture. A nonlinear regression was used to estimate kinetic parameters. The maximum nitrification rate (K _max) and the duration of lag period (t′) were derived from the equation to characterize the nitrification process in both soils. Stay‐N 2000 appeared to be a better inhibitor than nitrapyrin to extend t′ and as effective as nitrapyrin in reducing K _max. Stay‐N 2000 reduced K _max an appreciable amount in the Okoboji soil at the rate of 12 µg a.i. g^?1 soil or three times the recommended rate. Nitrification rates were affected by the rates of nitrogen (N) applied to both soils; the higher the N rates, the higher K_max, and the more the nitrate (NO₃ ^?)‐N accumulation.     

Nitrogen effect on yield and kernel protein content of sweet corn grown on sandy soils

Abstract

Early spring application of N to Iowa sandy, leachable soils results in reduced sweet corn yields and kernel protein content. Normally, split N applications are used to coincide with crop N demand. Our objectives were to determine if nitrapyrin, a nitrification inhibitor, applied with urea would provide high yields and kernel protein levels when applied at planting.

Nitrogen rate increased yield, ear leaf N concentration, and kernel protein content in 1976 and 1978, with the optimum rate dependent on the year and soil N residual. Urea, with or without nitrapyrin, significantly enhanced yield 13%, early leaf N concentration 17%, and kernel protein content 9% as compared with Ca(NO₃)₂ for both years. High leaching loss of NO₃‐N occurred with the Ca(NO₃)₂ source as compared with urea alone. Kernel protein concentration correlated well with ear leaf N concentration (r = .74) and yield (r = .61). Ear leaf K content was not affected by N rate or source, but Ca(NO₃)₂ enhanced uptake of Ca and Mg as compared with the urea sources. Urea, with nitrapyrin, decreased leaf Mg content in 1978, but not in 1976, as compared with urea alone.     

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.     

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.     

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.     

Transformation and binding of 13C and 14C-labelled atrazine in relation to straw decomposition in soil

As a source of organic matter, crop residues affect the behaviour of pesticides in agricultural soils. The fate of [U‐ring‐¹³C] and [U‐ring‐¹⁴C] atrazine (6‐chloro‐N‐ethyl‐N‐isopropyl‐1,3,5‐triazine‐2,4‐diamine) was investigated during laboratory incubation under controlled conditions in a loamy soil amended with wheat straw at two different states of decomposition: no preliminary decomposition or 6 months’ preliminary decomposition. After 3 months, non‐extractable, so‐called ‘bound’, ¹³C‐atrazine residues were recovered in three particle‐size fractions (> 200, 50–200 and < 50 μm), and investigated with solid‐state ¹³C‐NMR spectroscopy. Parallel incubations with [U‐ring‐¹⁴C] atrazine were carried out to quantify the bound residues as well as the extractable and mineralized fractions. The effect of straw residues on atrazine behaviour depended on whether they had been previously decomposed or not. When straw was decomposed for 6 months prior to incubation, atrazine mineralization was enhanced to 50% of the initial ¹⁴C in contrast to 15% of the initial ¹⁴C in soil alone and soil amended with fresh straw. In parallel, atrazine bound residues were formed in greater amount representing up to 20% of the initial ¹⁴C. CP/MAS ¹³C‐NMR on soil size fractions of soil–straw mixtures after incubation with ¹³C‐atrazine showed that bound residues contained mostly triazinic C, corresponding to atrazine or primary metabolites. Non‐humified organic materials recovered in size fractions > 200 and 50–200 μm contained significant amounts of bound residues, especially when straw was added to the soil. CP/MAS ¹³C‐NMR analysis of humic acids obtained from < 50‐μm fractions was difficult due to overlapping of the native carboxyl ¹³C signal with the ¹³C‐atrazine signal.     

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.     

Growth and composition of cabbage as affected by nitrogen nutrition

Abstract

The effect of cultivar and rate of N application on nitrate accumulation in cabbage (Brassica oleracea capitata, L.) was investigated in a field study. At harvest, significant differences in nitrate accumulation among cultivars occurred, with the greatest differences occurring at the highest rate of N applied, 450 kg N/ha. Two of three straight‐leaved varieties, Market Prize and Market Victor, accumulated more nitrate than three savoy‐leaved varieties, Savoy Ace, Savoy King, and Chieftain Savoy. The third straight‐leaved variety studied, Harris Resistant Danish, accumulated the least nitrate. Pattern of nitrate accumulation was closely correlated with date of maturity, with the earliest‐maturing variety, Market Victor, accumulating the highest levels of nitrate, and the latest‐maturing variety, Harris Resistant Danish, accumulating the least nitrate. For all six varieties, outer wrapper‐leaf samples showed higher nitrate levels than head samples.

In a second study, the effect of cultivar, N source, and nitrapyrin on yield and nutritional status of cabbage was studied under greenhouse conditions. The six cabbage cultivars showed no significant differences in nitrate accumulation after 65 days. The presence of 10 ppm of nitrapyrin, 2‐chloro‐6‐(trichloromethyl) pyridine, resulted in a restriction in fresh and dry weight production in cabbage. No visual, foliar symptoms of nitrapyrin toxicity were evident. Calcium levels were reduced in the presence of nitrapyrin regardless of N source. Adding nitrapyrin had no sign:ficant effect on Mg concentration, and highest Mg levels occurred under ammonium nutrition. Potassium levels were increased in the presence of nitrapyrin when the soil was not supplemented with K, whereas differences in K content due to the inhibitor were insignificant when KNO₃ was supplied.     

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.     

Influence of 2-chloro-6 (trichloromethyl) pyridine and dicyandiamide on nitrous oxide emission under different soil conditions

Abstract

Two experiments were conducted to evaluate the inhibitory effects of 2-chloro-6 (trichloromethyl) pyridine (nitrapyrin) and dicyandiamide on nitrous oxide (N₂O), a greenhouse gas, emission from soils amended with ammonium sulfate. In the two experiments, samples of an Andosol and a Gray Lowland soil were kept in glass vessels sealed with a butyl rubber cap and incubated at 25°C. In the first experiment, nitrapyrin (1 µg g^?1 dry soil) and dicyandiamide (10 µg g^?1 dry soil) were applied to samples of a water-saturated Andosol and a Gray Lowland soil to which ammonium sulfate had been applied at a rate of 0.1 mg N g^?1 dry soil. Nitrapyrin decreased N₂O emissions from the Andosol and the Gray Lowland soil by 71% and 24%, respectively. Dicyandiamide decreased N₂O emissions from the Andosol and Gray Lowland soil by 31% and 18%, respectively. In the second experiment, nitrapyrin (1 µg g^?1 dry soil) was applied to samples of an Andosol at 51% water-filled pore space to which ammonium sulfate had been applied at rates of 0.01, 0.1 and 0.5 mg N g^?1 dry soil. Nitrapyrin decreased N₂O emissions by 62%, 83% and 74%, respectively. Changes in the NH⁺ ₄ and NO^? ₂ + NO^? ₃ concentrations in soil showed that nitrapyrin and dicyandiamide slowed down the nitrification process, but did not completely stop the process at any time. The results reveal the potential of nitrification inhibitors to decrease N₂O emission from fertilized soil in a wide range of moisture conditions and nitrogen levels.     

The influence of nitrogen on atrazine and 2,4-dichlorophenoxyacetic acid mineralization in grassland soils

The influence of fertilizer N on the mineralization of atrazine [2-chloro-4(ethylamino)-6(isopropylamino)-s-triazine] and 2,4-D (2,4-dichlorophenoxyacetic acid) in soils was assessed in microcosms using radiometric techniques. N equivalent to 0, 250, and 500 kg N as NH₄NO₃ ha^-1 was added to three grassland soils. Compared to the control, the 250- and 500-kg treatments suppressed mineralization of atrazine by 75 and 54%, respectively, and inhibited mineralization of 2,4-D by 89 and 30%, respectively. Active fungal biomass responded to the N treatments in an opposite manner to herbicide mineralization. Compared to the control, the 250- and 500-kg treatments increased the active fungal biomass by more than 300 and 30%, respectively. These results agree with other observations that N can suppress the decomposition of resistant compounds but stimulate the primary growth of fungi. The degree of suppression was not related to the amount of N added nor to the inherent soil N levels before treatment. The interaction between the N additions and the active fungal biomass in affecting herbicide mineralization suggests that N may alter microbial processes and their use of C sources and thus influence rates of herbicide degradation in the field.     

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).     

Effect of nitrate addition on efficient use of ammonium sulfate fertilizer on corn under saline conditions. I. Pot experiment

Abstract

Plant growth in saline soils is regulated by the availability of nitrogen (N). High soil nitrate (NO₃)‐N can lead to poor water quality. Many workers think that NO₃‐N as a source for N can contribute to better plant growth in saline soils. The purpose of this work was to determine the necessity of NO₃‐N and the ratio of NO₃/ammonium (NH₄) in the N fertilizer which gives higher productivity of the biomass yield of corn. Corn (Zea mays L.) plants (Var. LG11) were grown under saline soil conditions (8.5 dS m^‐1), soils taken from the Euphrates valley (ACSAO Research Station) at Deir‐Ez‐Zor, east of Syria, from the surface layer of soil (0–25 cm). Five levels of N were applied in two forms, ammonium sulfate [¹⁵(NH₄)₂SO₄] with enrichment (1.5% a) as the NH₄‐N form and calcium nitrate [Ca(NO₃)₂] as the NO₃‐N form, besides fixed amounts of phosphorus (P) and potassium (K) for all N treatments. The corn plants were harvested at the flowering stage (56 days old), oven dried, weighed, and analyzed for total N and ¹⁵N recovery. The results indicated that the dry matter weight for treatments which received a combination of NH₄‐N and NO₃‐N gave higher dry matter yield than a single treatment of one source of N. But, NO₃‐N was more effective in improving yield than NH₄‐N. Nitrogen recoveries on the basis of added and absorbed N derived from fertilizer were significantly more affected by NO₃‐N than NH₄‐N.     

Effect of flow rate on the adsorption and desorption of glyphosate,simazine and atrazine in columns of sandy soils

Adsorption and desorption of the herbicides glyphosate [N-phosphonomethyl-aminoaceticacid], simazine [6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine] and atrazine [6-chloro-N²-ethyl-N⁴-isopropyl-1,3,5-triazine-2,4-diamine] were studied in four sandy soils from Western Australia. Distribution coefficients (K_ds) were calculated from breakthrough curves (BTCs) resulting from leaching step changes in concentrations through small saturated columns of soil at flow rates ranging from 0.3 to 30 m day^–1. A comparison was made with K_ds obtained after batch equilibrating solutions of the herbicides with the same soils. The K_ds of herbicides in soils decreased with increasing flow rate and most strongly for glyphosate in soils rich in clay content. Resulting increases in mobility of about 40–50% were estimated for simazine and atrazine and > 50% for glyphosate at flow rates of 3 m day^–1. Adsorption and desorption rates were estimated by fitting numerically simulated BTCs to experimental BTCs. Best fits were obtained with a time-dependent Freundlich adsorption equation. The resulting coefficient for time dependency in the equation suggests that the rates of adsorption and desorption are controlled mainly by diffusion in an adsorbing layer on or in soil particles.     

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.