Effect of Environment on Wild Oat (Avena fatua) Control with Imazamethabenz or Fenoxaprop Tank-Mixed with Additives or MCPA

Greenhouse and growth chamber experiments were conducted to determine the effect of soil moisture and temperature on the phytotoxicity in wild oat of imazamethabenz or fenoxaprop tank-mixed with certain additives or MCPA. The surfactants Agral 90 at 0.5% and Enhance at 0.5% increased imazamethabenz phytotoxicity under both moist and drought conditions. These surfactants had no significant effect on fenoxaprop phytotoxicity regardless of the soil moisture regimes. Fenoxaprop activity was increased by ammonium sulfate [(NH₄)₂SO₄] at 1% but only under well watered conditions. Wild oat control with imazamethabenz was also slightly enhanced in a well watered regime by the addition of sodium bisulfate (NaHSO₄) at 0.13%. At high temperature (30/20°C) and low temperature (10/5°C), the phytotoxicity of imazamethabenz was increased when tank-mixed with Agral 90 at 0.25% or NaHSO₄ at 0.13% compared with that when imazamethabenz was applied alone, if soil moisture was adequate. There was no such increase under conditions of drought and high temperature. (NH₄)₂SO₄ at 1% did not significantly affect imazamethabenz performance irrespective of temperature/soil moisture conditions. The phytotoxicity to wild oat of imazamethabenz or fenoxaprop was not changed by tank-mixing with MCPA isooctyl ester at 300 g a.i./ha, regardless of soil moisture levels. The reduced fenoxaprop phytotoxicity in wild oat due to moisture stress was not readily alleviated by the inclusion of selected additives or MCPA in the tank mixture. Received May 10, 1996; accepted January 10, 1997     

Influence of nutrient supply and plant growth regulators on phytotoxicity of imazamethabenz in wild oat (Avena fatua L.)

The influences of nutrient supply and plant growth regulators on the phytotoxicity of imazamethabenz in wild oat (Avena fatua L.) were evaluated in the greenhouse. Wild oat plants supplied with half-strength rather than one-eighth-strength Hoagland solution were more susceptible to imazamethabenz, showing greater growth reduction in main shoot and tillers. The improved herbicide efficacy at higher nutrient levels appeared related to increased herbicide interception by the greater leaf surface available. Leaves developing at either nutrient level did not differ significantly in epicuticular wax, so differential absorption appeared unlikely. Wild oat plants supplemented with nutrient, switching from low to high levels at the time of herbicide application, were as susceptible to imazamethabenz or even more so than plants growing with a constant high level of nutrition. The wild oat pure-line Montana 73, a strongly tillering line, was more susceptible to imazamethabenz than the limited-tillering line, Crop Science 40. Both 2,4-D and GA₃ reduced imazamethabenz-induced tillering. Imazamethabenz efficacy was increased by GA₃ but not by 2,4-D. These results support the hypothesis that lowering apical dominance of wild oat increases imazamethabenz activity in tillers, and that increased tillering following sublethal doses of imazamethabenz treatment is associated with the release of apical dominance.     

Effect of decapitation on absorption,translocation, and phytotoxicity of imazamethabenz in wild oat (Avena fatua L.)

The release of apical dominance by the physical destruction in situ of the apical meristem and associated leaf primordia (decapitation) promoted the growth of tillers in non-herbicide-treated wild oat plants, as indicated by increased tiller lengths and fresh weights. At 96 h after [¹⁴C] herbicide treatment following decapitation, the absorption of [¹⁴C]imazamethabenz and total translocation of radioactivity were respectively increased by 28% and 49%. By 96 h after [¹⁴C]imazamethabenz application, the radioactivity detected in the roots of decapitated plants was 45% higher than that in the roots of nondecapitated plants while the radioactivity in tillers of decapitated plants was 2.6-fold that in tillers of intact plants. Decapitation together with foliar spraying of imazamethabenz at 200 g ha^–1 further reduced tiller fresh weight, greatly decreased the total tiller number, and thereafter significantly increased overall phytotoxicity by 32% as measured by total shoot fresh weight. The results of this study support the hypothesis that main shoot apical dominance limits translocation of applied imazamethabenz to lateral shoots, rendering tillers less susceptible to growth inhibition by the herbicide.     

Foliar applications of nitrogen to slash pine seedlings

Summary The absorption of N from foliar applications of various N sources by pine seedlings was studied under greenhouse conditions. Needles dipped into solutions of 4,000 ppm N from Ca(NO₃)₂ were burned slightly at the tips at two weeks. Although higher concentrations of (NH₂)₂CO and (NH₄)₂SO₄ could be used without plant damage, a uniform concentration of 3,000 ppm was used in all comparative tests of sources. The level of tissue N, brought about by soil fertilization 6 weeks previously, did not significantly influence absorption of foliarly applied N¹⁵. Soil moisture maintained at near 100, 60 to 70, and 25 to 35 per cent of water-holding capacity of the Leon fs did not significantly affect the absorption of tagged N. Greater quantities of N¹⁵ were absorbed as urea than as Ca(NO₃)₂ or (NH₄)₂SO₄. The use of a spreader-sticker increased the N¹⁵ uptake, regardless of the N compound used. However, the magnitude of the increased absorption associated with use as a sticker varied from 490 per cent with (NH₄)₂SO₄ to 260 per cent with urea. It was calculated that approximately 71, 45, and 39 per cent of foliar applied N was absorbed into needles within 24 hours from urea, Ca(NO₃)₂, and (NH₄)₂SO₄, respectively. Journal Paper No3588 of the Florida Agricultural Experiment Station, Gainesville, Florida.     

Toxicity of nitrapyrin to sunflower under different N nutrition regimes

Summary The purpose of this study was to investigate the phytotoxicity of nitrapyrin 2-chloro-6-(trichloromethyl)pyridine to sunflower (Helianthus annuus L.) under different N regimes and to see if N forms affect the phytotoxicity of nitrapyrin. Sunflower was grown in pot culture for 21 days and was fertilized with (NH₄)₂SO₄, NH₄NO₃ and NaNO₃ to provide 0, 100 and 200 ppm N and with nitrapyrin application of 0 and 20 ppm. All N-treated sunflower plants in all N regimes and regardless of titrapyrin treatment produced more root and shoot dry weights and contained a significantly higher N than untreated check. Nitrapyrin toxicity appeared as a curling of leaf margin and a tendril type of stem growth, the visible toxicity symptoms decreased in the order: (NH₄)₂SO₄>NH₄NO₃>NaNO₃. Furthermore nitrapyrin addition suppressed sunflower growth in each N regime, the suppressing effect being greater with (NH₄)₂SO₄ and NH₄NO₃ than as with NaNO₃. Although, shoot growth from plants receiving nitrapyrin was not significantly affected by any N regime, root growth of nitrapyrin-treated plants was somewhat restricted by NH₄ ⁺−N nutrition relative to NO₃ ⁻−N nutrition.     

Tillers Do Not Influence Phytotoxicity of Imazamethabenz in Wild Oat (Avena fatua)

The response of wild oat to imazamethabenz varies with the growth stage, but the role of tillers in this regard is unclear. Removal of tillers at the three-leaf stage before spraying with imazamethabenz did not significantly affect the total shoot fresh weight measured 3 weeks later. The leaf area and dry weight of intact plants at the three-leaf stage were 17–21% greater than for plants with coleoptilar and first leaf main shoot tillers (T0 and T1) removed. The greater leaf area may have increased herbicide interception per plant. Similar fresh weight reductions in main shoot, total tillers, and total shoots were found whether imazamethabenz was applied to the plant at the two-leaf without tillers or the three-leaf with two tillers stage. Imazamethabenz applied only to the main shoot reduced total shoot dry weight more than an equivalent amount of imazamethabenz applied only to tiller T1 or applied over the whole shoot. Imazamethabenz had the least inhibitory effect on whole plant growth when applied only to T1. When ¹⁴C-herbicide was applied to the first main shoot leaf of plants at the three-leaf stage with two tillers, the ¹⁴C translocated 38% to roots, 33% to the main shoot, and nearly 30% to all tillers. When ¹⁴C-herbicide was applied to the first leaf of T1 then the ¹⁴C translocated 50% to T1, 25% to the main shoot, 20% to roots, and 5% to all other tillers. The translocation pattern and fresh weight values suggested that the presence of early tillers during herbicide application neither increased nor decreased imazamethabenz efficacy in wild oat. Received June 4, 1997; accepted June 5, 1997     

Influence of Drought on Graminicide Phytotoxicity in Wild Oat (Avena fatua) Grown under Different Temperature and Humidity Conditions

Controlled environmental experiments were carried out to determine the phytotoxicity of several graminicides on wild oat (Avena futua L.) as influenced by combination of drought and temperature stress or drought and low relative humidity. Compared with unstressed conditions (20/15°C plus adequate soil moisture), imazamethabenz phytotoxicity to wild oat was reduced significantly when plants were exposed to a combination of drought and high temperature (30/20°C) stress. Imazamethabenz phytotoxicity was reduced almost as much by high temperature stress alone as by a combined temperature and drought stress. When herbicides were applied to wild oat plants subjected to drought alone or to drought plus high temperature, the observed reduction in phytotoxicity from greatest to least was: fenoxaprop = diclofop > flamprop > imazamethabenz. Fenoxaprop performance was most inhibited by the combination of drought plus high temperature, although drought alone and to a lesser degree, high temperature alone, inhibited fenoxaprop action. High temperature had an adverse effect on the efficacy of fenoxaprop at lower application rates. Raising fenoxaprop application rates to 400 g ha⁻¹ overcame the inhibition caused by high temperature alone but only partially alleviated the effect of drought combined with high temperature. When plants were grown under a low temperature regimen the imposition of drought stress had little effect on imazamethabenz phytotoxicity but did reduce fenoxaprop phytotoxicity. At 25/15°C drought reduced the phytotoxicity of fenoxaprop and diclofop greatly but had no significant impact on the performance of any of the herbicides examined, regardless of soil moisture regimen. Received April 14, 1997; accepted September 22, 1997     

Influence of temperature and light intensity on absorption, translocation, and phytotoxicity of fenoxaprop-ethyl and imazamethabenz-methyl in Avena fatua

The absorption and translocation of fenoxaprop-ethyl and imazamethabenz-methyl were investigated in wild oat (Avena fatua L.) plants grown under different temperature and light intensity conditions by using ¹⁴C tracer techniques. The phytotoxicity of both herbicides, applied as individual droplets, was also determined under similar environments. The absorption of fenoxaprop-ethyl and imazamethabenz-methyl was increased by high temperature (30/20°C) and to a lesser extent by 70% shading; low temperature (10/5°C) had limited effect on the absorption. The basipetal translocation of fenoxaprop-ethyl was not affected by high temperature, and the increase in imazamethabenz-methyl translocation at high temperature was likely the result of the increased absorption. Low temperature decreased total translocation and translocation efficiency in both fenoxaprop-ethyl and imazamethabenz-methyl. Low light intensity tended to reduce the efficiency of basipetal translocation of both herbicides. Fenoxaprop-ethyl phytotoxicity was reduced by high temperature but not by low temperature. Temperature had little effect on imazamethabenz-methyl effectiveness. Under 70% shading, the phytotoxicity of both herbicides was enhanced.Abbreviation S.E.D. standard errors of difference     

Yield and nitrogen uptake of rapessed (Brassica campestris L.) with ammonium and nitrate

Water culture, growth chamber, greenhouse and field experiments were conducted to compare the effect of NH₄−N and NO₃−N on yield and N uptake of rapeseed (Brassica campestris L.). In water culture, the yields of 28-day old rapeseed plants grown at 14 μg N ml⁻¹ were double with NO₃ compared to NH₄, but N uptake was little affected. There was no such effect when concentration was reduced to 3.5 or 7 μg N ml⁻¹. The yield and N uptake of 26-day old rapeseed grown on six soils (pH 4.6 to 6.5) in pots in a growth chamber were much greater with NO₃ than with NH₄, although N concentration was more in the NH₄- than the NO₃-grown plants. In a greenhouse experiment with rapeseed grown on 12 potted soils, the N uptake of applied N was greater with NO₃ than with NH₄ on all soils. Averages were 63% with NH₄ and 78% with NO₃. However, NH₄-fixation capacities of the soils were only weakly correlated with yield from the two sources of N (r=0.48) and the relation was similar with N uptake. In contrast to the behavior of water culture, growth chamber and greenhouse experiments, the 33 field experiments did not show consistent difference in seed yield with NH₄ and NO₃ applied at time of seeding. In nine field experiments where band application was used for Ca(NO₃)₂, (NH₄)₂ SO₄, NH₄ NO₃, yield tended to be greatest for (NH₄)₂SO₄. However, in 19 experiments on acid soils with and without lime, yields in most cases were similar with (NH₄)₂SO₄ and NH₄ NO₃. Nitrification inhibitors were added to spring banded NH₄-based fertilizers in five experiments, but the yields were not influenced. Scientific Paper No. 558, Lacombe Research Station, Agriculture Canada.     

Yield and crop parameters of wetland rice as influenced by soil and fertilizer nitrogen

Summary The behavior of soil N, fertilizer N and plant N was studied in a greenhouse experiment with 2 plant densities of rice (IR 36) under flooded conditions. Increasing plant density from 25 hills m² to 50 hills m² increased tiller number and panicle number but had no influence on grain yield. The yield of grain was linearly related to N content of the above ground dry matter at harvest (r²=.96) and thus the effect of manipulating the N supply on yield was directly related to N uptake.Mixing of (NH₄)₂SO₄ with the soil volume before transplanting resulted in increases in N in the aboveground dry matter equal to 87% of the applied N. When (NH₄)₂SO₄ was broadcast into the flood water at 4 stages of growth beginning 25 DAT, the corresponding increase was 77% of the applied N. When (NH₄)₂SO₄ was split between shallow mixing before transplanting and a broadcast application of 32 DAT, the corresponding increase was 42%. Thus several applications of fertilizer N increased grain production per unit of applied N.Inorganic N extractable by KCl was a useful but not an infailible guide to the behavior of the soil and fertilizer inorganic N.     

Cyanobacterial inoculation and nitrogen fertilization in rice

During three rice-growing seasons in Uruguay, field experiments were conducted to study the contribution of cyanobacterial inoculation and chemical N fertilization to rice production. Neither grain yield nor fertilizer recovery by the plant were affected by inoculation with native cyanobacterial isolates. A low fertilizer use efficiency (around 20%) was observed when labelled (NH₄)₂SO₄ was applied at sowing. Recovery of applied ¹⁵N by the soil–plant system was 50%. Inoculation did not modify ¹⁵N uptake by the plant when the fertilizer was three-split applied either. The total N-fertilizer recovery was higher when the fertilizer was split than when applied in a single dose. Plant N-fertilizer uptake was higher when the fertilizer was applied at tillering. Uptake of ¹⁵N from cyanobacteria by rice was studied in a greenhouse pots experiment without chemical nitrogen addition. Recovery of ¹⁵N from labelled cyanobacteria by rice in greenhouse growth conditions was similar to that of partial recovery of (NH₄)₂SO₄ applied at sowing in the field. Cyanobacterial N mineralization under controlled conditions was fast as cyanobacterial N was detected in plants after 25 days. Moreover 40 days after inoculation non-planted and inoculated soil had more inorganic N than the non-inoculated one.     

Nitrogen regulation of gibberellin biosynthesis in Gibberella fujikuroi

Summary In Gibberella fujikuroi, ammonium (NH₄ ⁺) interfered with the production of gibberellic acid (GA₃). Optimal production occurred at 19 mm (NH₄)₂SO₄ and the synthesis of GA₃ was reduced threefold in a medium with 38 mm (NH₄)₂SO₄. Using a resting cell system with mycelia previously grown on two concentrations (19 mm and 38 mm) of (NH₄)₂SO₄, it was found that NH₄ ⁺ depressed synthesis of the gibberellin-synthesizing enzymes. Furthermore, addition of NH₄ ⁺ to a producing system shut off gibberellin formation, indicating that the negative effect of NH₄ ⁺ ions is also due to inhibition of one or more enzymes in the gibberellin biosynthesis pathway. The onset of gibberellin biosynthesis in media with high (38 mm) and low (19 mm) concentrations of (NH₄)₂SO₄ was studied by addition of cycloheximide to batch cultures of various ages. Offprint requests to: B. Brückner     

Liquid–liquid extraction of antimicrobial peptide P34 by aqueous two-phase and micellar systems

Antimicrobial peptide P34 is a promising biopreservative for utilization in the food industry. In this work, aqueous biphasic systems (ABS) and aqueous biphasic micellar systems (ABMS) were studied as prestep for purification of peptide P34. The ABS was prepared with polyethylene glycol (PEG) and inorganic salts and the ABMS with Triton X-114 was chosen as the phase-forming surfactant. Results indicate that peptide P34 partitions preferentially to PEG-rich phase and extraction with ammonium sulfate [(NH₄)₂SO₄], yielding a 75% recovery of the antimicrobial activity, specific activity of 1,530 antimicrobial units per mg of protein, and purification fold of 2.48. Protein partition coefficient and partition coefficient for the biological activity with (NH₄)₂SO₄ system were 0.48 and 64, respectively. Addition of sodium chloride did not affect recovery, but decreased protein amount in the PEG-rich phase, indicating a higher partition of biomolecules. ABMS did not yield good recovery of antimicrobial activity. Purification fold using PEG–(NH₄)₂SO₄ and 1.0?mol l^?1 sodium chloride was twice higher than that obtained by conventional protocol, indicating a successful utilization of ABS as a step for purification of peptide P34.     

Physicochemical properties of salt-soluble,unsheared chromatin

Salt-dependent structural changes of rat liver chromatin isolated by an extraction procedure not involving shear and exogeneous nucleases were investigated by sedimentation and light scattering methods. The effects observed are complex involving changes of the molecular weight and expansion. Between 0.1 M and 0.2 M (NH₄)₂SO₄ where histone H1 is released, a fragmentation into molecules of half molecular weight is found which is accompanied by an expansion into a more extended conformation gradually increasing to 0.4 M (NH₄)₂SO₄. The H1-free chromatin does not exhibit the reduction in molecular weight but undergoes this expansion. The original conformation is not reversible on re-decreasing the salt concentration to 0.1 M (NH₄)₂SO₄.     

Phytoextraction of Cadmium and Zinc By Sedum plumbizincicola Using Different Nitrogen Fertilizers,a Nitrification Inhibitor and a Urease Inhibitor

Cadmium (Cd) and zinc (Zn) phytoavailability and their phytoextraction by Sedum plumbizincicola using different nitrogen fertilizers, nitrification inhibitor (dicyandiamide, DCD) and urease inhibitor (N-(n-Butyl) thiophosphoric triamide, NBPT) were investigated in pot experiments where the soil was contaminated with 0.99 mg kg^?1 of Cd and 241 mg kg^?1 Zn. The soil solution pH varied between 7.30 and 8.25 during plant growth which was little affected by the type of N fertilizer. The (NH₄)₂SO₄+DCD treatment produced higher NH₄⁺?N concentrations in soil solution than the (NH₄)₂SO₄ and NaNO₃ treatment which indicated that DCD addition inhibited the nitrification process. Shoot Cd and Zn concentrations across all treatments showed ranges of 52.9–88.3 and 2691–4276 mg kg^?1, respectively. The (NH₄)₂SO₄+DCD treatment produced slightly higher but not significant Cd and Zn concentrations in the xylem sap than the NaNO₃ treatment. Plant shoots grown with NaNO₃ had higher Cd concentrations than (NH₄)₂SO₄+DCD treatment at 24.0 and 15.4 mg kg^?1, respectively. N fertilizer application had no significant effect on shoot dry biomass. Total Cd uptake in the urea+DCD treatment was higher than in the control, urea+NBPT, urea+NBPT+DCD, or urea treatments, by about 17.5, 23.3, 10.7, and 25.1%, respectively.     

Comparison of the efficiency of urea,aqueous ammonia and ammonium sulphate as nitrogen fertilizers

Summary Nitrogen-15 labelled urea, aqueous NH₃ and (NH₄)₂SO₄ were applied to soils contained in pots. The fertilizers were injected in 5 cm³ of solution, 3.5 cm below the soil surface, to simulate a fertilizer band in the field. Ryegrass (Lolium perenne) was planted, and several cuttings and roots were harvested. Efficiency was determined as the recovery of fertilizer-N in the plant tissues and soil.Total recovery varied from 94 to 100%. There was no significant difference between the total recovery of the 3 fertilizer forms, although recovery in the soil component was lower for (NH₄)₂SO₄ than for urea or NH₃. There was a significant difference in total recovery between soils due to the soil component. Only small amounts of¹⁵N were not recovered, whereas laboratory experiments reported elsewhere had demonstrated that substantial gaseous losses of N as N₂, N₂O and NO +NO₂ occurred in these soils during nitrification of added NH₃ fertilizer.     

Effects of ammonium ions on sporulation of Saccharomyces cerevisiae

The presence of low levels (2–4 mM) of (NH₄)₂SO₄ in sporulation medium results in a complete inhibition of ascus formation in Saccharomyces cerevisiae. Tests with other utilizable nitrogen sources and with the non-metabolizable ammonia analog, methylamine, indicate that the primary inhibitory effect is exerted by ammonium (NH₄⁺) and not a metabolite of NH₄⁺. Viability is also reduced but to a much lesser extent than sporulation. The levels of NH₄⁺ that repress sporulation do not affect the rate of oxygen utilization or ATP levels of cells in sporulation medium. The period during which the cells are sensitive to NH₄⁺ is relatively long, and they do not escape inhibition until the meiotic commitment stage. The most sensitive period is roughly coincident with the end of premeiotic DNA synthesis. NH₄⁺ does not inhibit the initiation of premeiotic DNA synthesis, but DNA replication is arrested after initiation and continued incubation in the presence of NH₄⁺ leads to massive DNA degradation. Commitment to recombination is not affected specifically by NH₄⁺. Preliminary experiments with an NH₄⁺-resistant mutant indicates that levels of NH₄⁺ sensitivity are under genetic control.     

Response of red-osier dogwood (Cornus stolonifera) seedlings to sodium sulphate salinity: effects of supplemental calcium

A greenhouse study was designed to test the effects of sodium sulphate (Na₂SO₄) on red-osier dogwood (Cornus stolonifera Michx) seedlings in the presence and absence of additional calcium (Ca²⁺). Changes in growth parameters, ion and carbohydrate accumulation and cell wall composition were examined. Calcium alleviated the effect of Na₂SO₄ on shoot height; however, it did not affect the reduction in shoot and root dry weights. An increased level of sodium (Na⁺) in roots of plant exposed to Na₂SO₄ was recorded in the presence of supplemental Ca²⁺ whereas there was no change in potassium (K⁺) and Ca²⁺ levels. In shoots of seedlings treated with Na₂SO₄, the addition of Ca²⁺ did not affect Na⁺, K⁺ and Ca²⁺ levels. The amount of soluble carbohydrates was increased in leaves of seedlings treated with Na₂SO₄ both in the absence and presence of supplemental Ca²⁺. The decrease in cell wall material in response to salt stress was alleviated by Ca²⁺ in stem tissues although Ca²⁺ did not alter the changes in hemicellulose and cellulose. Sugar composition of pectins and hemicellulose were modified in stems and leaves by Na₂SO₄ and/or Ca²⁺. The results of this study showed that calcium was able to alleviate the effects of salt stress on shoot height and cell wall content of red-osier dogwood stems. Furthermore, changes occurred in cell wall composition of red osier seedlings treated with Na₂SO₄.     

Suppression of peatland methane emission by cumulative sulfate deposition in simulated acid rain

This field manipulation study tested the effect of weekly pulses of solutions of NH₄NO₃ and (NH₄)₂SO₄ salts on the evolution of CH₄ and N₂O from peatland soils. Methane and nitrous oxide emission from a nutrient-poor fen in northern Minnesota USA was measured over a full growing season from plots receiving weekly additions of NH₄NO₃ or (NH₄)₂SO₄. At this relatively pristine site, natural additions of N and S in precipitation occur at 8 and 5 kg ha^–1 y^–1, respectively. Nine weekly additions of the dissolved salts were made to increase this to a total deposition of 31 kg N ha^–1 y^–1 on the NH₄NO₃-amended plots and 30 and 29 kg ha^–1 y^–1 of N and S, respectively, in the (NH₄)₂SO₄-amended plots. Methane flux was measured weekly from treatment and control plots and all data comparisons are made on plots measured on the same day.After the onset of the treatments, and over the course of the growing season, CH₄ emission from the (NH₄)₂SO₄-amended plots averaged 163 mg CH₄ m^–2 d^–1, significantly lower than the same-day control plot mean of 259 mg CH₄ m^–2 d^–1 (repeated measures ANOVA). Total CH₄ flux from (NH₄)₂SO₄ treatment plots was one third lower than from control plots, at 11.7 and 17.1 g CH₄ m^–2, respectively. Methane emission from the NH₄NO₃-amended plots (mean of 256 mg CH₄ m^–2 d^–1) was not significantly different from that of controls measured on the same day (mean of 225 mg CH₄ m^–2 d^–1). Total CH₄ flux from NH₄NO₃ treatment plots and same-day controls was 16.9 and 15.1 g CH₄ m^–2, respectively. In general, stable, relatively warm and wet periods followed by environmental `triggers' such as rainfall or changes in water table or atmospheric pressure, which produced a CH<sub>4</sub> `pulse' in the other plots, produced no observable peak in CH₄ emission from the (NH₄)₂SO₄-amended plots. Nitrous oxide emission from all of the plots was below the detection limit over the course of the experiment.     

Field assessment of efficacy of nitrogen salts to control the root-knot nematode (Meloidogyne javanica) on tomato

Influence of different nitrogen salts at electrical conductivity levels (EC2, 4 and 8?mmhos/cm) on tomato and root-knot nematode (Meloidogyne javanica) and their interactions was evaluated under field conditions. It was found that both diammonium phosphate ((NH₄)₂HPO₄) and ammonium sulphate ((NH₄)₂SO₄) were more effective than ammonium chloride (NH₄Cl) in causing an obvious suppression of M. javanica infection on tomato through reducing root galling and nematode reproduction and improving tomato growth and yield and their suppressive effect was similar to that of oxamyl or ethoprophos. At higher ECs, the tested nitrogen salts did not greatly affect pH, EC and salinity of rhizospheric soil except NH₄Cl at EC8 that caused higher EC and salinity over the untreated control which makes NH₄Cl less suitable candidate. Therefore, the use of (NH₄)₂HPO₄ and (NH₄)₂SO₄ alone or in combination with other control measures could control M. javanica and improve the growth and yield of tomato under field conditions.