Effect of chromium and nitrogen form on photosynthesis and anti-oxidative system in barley

The effect of nitrogen forms on photosynthesis and anti-oxidative systems of barley plants under chromium stress was studied in a hydroponic experiment. The treatments comprised three chromium concentrations (0, 75, and 100 μM) and three N forms (NH₄)₂SO₄, urea, and Ca(NO₃)₂. In comparison with the urea or (NH₄)₂SO₄ fed plants, the Ca(NO₃)₂ fed plants had higher net photosynthetic rate, intercellular CO₂ concentration, stomatal conductance, transpiration rate, photosynthetically active radiation utilization efficiency, variable to maximum chlorophyll fluorescence ratio, and the content of chlorophylls and carotenoids. Cr toxicity caused oxidative stress in all plants but the Ca(NO₃)₂ fed plants had the least oxidative stress. Moreover, the Ca(NO₃)₂ fed plants had higher activities of anti-oxidative enzymes and content of non-enzymatic antioxidants than the urea or (NH₄)₂SO₄ fed plants. In addition, the Ca(NO₃)₂ fed plants had higher N and lower Cr content in all plant tissues than the urea or (NH₄)₂SO₄ fed plants. The current results indicate that the reasonable choice of N fertilizer is important for barley production on the Cr-contaminated soils.     

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.     

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.     

Effects of parathion and malathion on transformations of urea and ammonium sulfate nitrogen in soils

Summary A study of the effects of malathion and parathion applied at 10 and 50 g/g of soil on transformations of urea and (NH₄)₂SO₄–N in a sandy loam showed that the insecticides retarded urea hydrolysis as well as nitrification of urea and (NH₄)₂SO₄–N. At 50 parts/10⁶ rate of the insecticides, inhibition of urea hydrolysis ranged from 44 to 61% after 0.5 week and from 7 to 21% after 3 weeks of application. The insecticides inhibited the conversion of NH₄ ⁺ to NO₂ ^– without appreciably affecting the subsequent oxidation of NO₂ ^– to NO₃ ^– –N. This resulted in accumulation of higher amounts of NH₄ ⁺–N in soil samples treated with ammonium sulfate or urea N.The results suggest that transformations of urea and NH₄ ⁺ fertilizers in soils may be influenced by the amount of organophosphorus insecticide present and this may affect plant nutrition and fertilizer use.     

Application of nitrogen in NO 3 − form increases rhizosphere alkalisation in the subsurface soil layers in an acid soil

Leaching of NO ₃ ^? derived from ammoniacal fertilizers in the topsoil and subsequent uptake of NO ₃ ^? by plants from deeper layers may be used as a method of biological amelioration of subsurface soil acidity. This paper reports a glasshouse column experiment testing the above concept. Nitrogen with labelled ¹⁵N was supplied with and without lime to the surface soil (0–10 cm) as urea, (NH₄)₂SO₄ or Ca(NO₃)₂ at a rate equivalent to 120 kg N ha^?1. Soil columns were regularly watered from the top to facilitate NO ₃ ^? leaching. An aluminium-tolerant wheat genotype was grown for 38 days. The application of lime with nitrogen fertilizers increased growth of shoot and roots in all soil layers. The application of Ca(NO₃)₂ resulted in about 66% of recovery efficiency irrespective of whether lime was applied in the surface. This in turn resulted in about 0.2 units increase in rhizosphere pH in the subsurface (10–15 cm) soil layer compared to the same layer of the unlimed control. The supply of urea and (NH₄)₂SO₄ alone or with lime did not increase rhizosphere pH in the subsurface soil layers. Importantly, this study indicates that it is possible to exploit the process of nitrate uptake by wheat to increase pH in acidic subsurface soil.     

Toxic Effect of Cadmium on Rice as Affected by Nitrogen Fertilizer Form

A nutrient solution experiment was conducted to determine the influence of N forms on growth, oxidative stress, and Cd and N uptake in rice plants. The treatments were consisted of two Cd levels (0 and 1 μmol) and three N forms (NH₄)₂SO₄, NH₄NO₃ and Ca(NO₃)₂. The results indicated that without Cd addition in the culture solution, the N forms had no significant effect on all measured parameters, including plant growth, photosynthetic traits, malondialdehyde (MDA) concentration, superoxide dismutase (SOD) activity, and Cd and N concentration, while Cd addition in the medium resulted in significant differences in measured parameters among the three forms of N fertilizers. The least inhibition of growth was noted in (NH₄)₂SO₄-fed plants, and the largest in Ca(NO₃)₂-fed plants, when plants were exposed to Cd stress. The highest photosynthetic rate and chlorophyll content was also recorded in (NH₄)₂SO₄-fed plants. Addition of Cd caused a remarkable increase in SOD activity and MDA content in plants, and the extent of increase varied with N form, with (NH₄)₂SO₄-fed plants being smallest. In comparison with the control plants, the N concentration in roots and shoots was not significantly affected in (NH₄)₂SO₄-fed plants, but significant decrease in root N concentration was found for the NH₄NO₃ and Ca(NO₃)₂-fed plants under Cd stress. Moreover, the significant differences were also noted among the three N forms in both root and shoot Cd concentrations, with (NH₄)₂SO₄-fed plants being the lowest. The results indicated that the toxic effect of Cd on rice varied with the form of N fertilizer.     

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.     

Enhanced foliar 15N enrichment with increasing nitrogen addition rates: Role of plant species and nitrogen compounds

Determining the abundance of N isotope (δ¹⁵N) in natural environments is a simple but powerful method for providing integrated information on the N cycling dynamics and status in an ecosystem under exogenous N inputs. However, whether the input of different N compounds could differently impact plant growth and their ¹⁵N signatures remains unclear. Here, the response of ¹⁵N signatures and growth of three dominant plants (Leymus chinensis, Carex duriuscula, and Thermopsis lanceolata) to the addition of three N compounds (NH₄HCO₃, urea, and NH₄NO₃) at multiple N addition rates were assessed in a meadow steppe in Inner Mongolia. The three plants showed different initial foliar δ¹⁵N values because of differences in their N acquisition strategies. Particularly, T. lanceolata (N₂-fixing species) showed significantly lower ¹⁵N signatures than L. chinensis (associated with arbuscular mycorrhizal fungi [AMF]) and C. duriuscula (associated with AMF). Moreover, the foliar δ¹⁵N of all three species increased with increasing N addition rates, with a sharp increase above an N addition rate of ~10 g N m⁻² year⁻¹. Foliar δ¹⁵N values were significantly higher when NH₄HCO₃ and urea were added than when NH₄NO₃ was added, suggesting that adding weakly acidifying N compounds could result in a more open N cycle. Overall, our results imply that assessing the N transformation processes in the context of increasing global N deposition necessitates the consideration of N deposition rates, forms of the deposited N compounds, and N utilization strategies of the co-existing plant species in the ecosystem.     

Growth and ion uptake by wheat supplied nitrogen as nitrate,or ammonium,or both

Summary The effects of concentration and source (NH₄, NO₃, and NO₃ plus NH₄) of added N on the rate of growth, final yield, and content and rate of intake of N, P, K, Ca, Mg and S by wheat seedlings were evaluated. Rate of growth in dilute liquid cultures differed among the N sources giving yields relative to those of the all-NO₃ system of 92 per cent for the all-NH₄ system, and of 154 per cent for the NO₃ plus NH₄ system. At low rates of NH₄ intake in the all-NH₄ systems growth rates were equal to or slightly better than those of plants supplied equivalent concentrations of NO₃. Rates of NH₄ intake exceeding 100 mole g^–1 h^–1 resulted in reduced growth rates and incipient NH₄ toxicity. Yields at 95 per cent of maximum resulted with steady-state N concentrations of 80 M in all NO₃ systems, 30 M NH₄ in all-NH₄ systems, and in combined source systems when 200M NO₃ plus 30 M NH₄ were supplied. The rate of N intake and plant protein content, were maximal when both NO₃ and NH₄ were supplied. Increasing rates of NO₃ intake were associated with increases in the rates of Ca, Mg, and K intake; but with increasing rates of NH₄ absorption, intake of Ca and Mg decreased. The yield and growth rate enhancement observed from the addition of low concentrations of NH₄ to cultures supplying adequate NO₃ is suggested to result from the reduced energy requirement for utilization of NH₄, as compared to NO₃ in protein synthesis and from the increased photosynthetic capacity of the higher-protein NH₄-fed plants. In the all-NH₄ systems the maximum attainable growth rate was limited by NH₄ toxicity; whereas in the all-NO₃ systems the rate of NO₃ reduction was limiting.Contribution from the Department of Soils and Plant Nutrition, University of California, Davis, California 95616.     

The growth and some physiological responses of rice to Cd toxicity as affected by nitrogen form

A hydroponic experiment was conducted to examine the effect of Cd stress on anti-oxidative enzyme activities at heading stage, yield components, root exudation and Cd and N uptake of rice plants grew in different N source i.e. (NH₄)₂SO₄, NH₄NO₃ and Ca(NO₃)₂. The results show that the effect of Cd stress on all measured parameters were N source dependent. Cd stress (1 μM) caused a remarkable reduction in grain yield and shoot biomass, an increase in root exudation, glutathione content, Cd concentration and catalase (CAT) and peroxidase (POD) activities of rice plants. In the plants under the control (without Cd addition) N source had no distinctive effect on the above measured parameters, but the differences among the three N forms in these parameters became significant when plants were exposed to Cd stress. Cd stress significantly increased POD and CAT activities, and gultathione content, with Ca(NO₃)₂-fed plants having the greatest POD and CAT activities and lowest glutathione content, and (NH₄)₂SO₄-fed plants being just opposite. Moreover, organic acid exudation varied also with N form for the Cd-stressed plants. In comparison with other two N forms, (NH₄)₂SO₄,-treated plants had higher grain yield, N concentration and lower Cd concentration in plants. The current results indicated that (NH₄)₂SO₄ is a better fertilizer for use in Cd contaminated soil.     

Evaluation of chemical methods for estimating available zinc and response of green gram (Phaseolus aureus roxb) to applied zinc in non-calcareous soils

Summary Studies were conducted in 22 non-calcareous soils (India) to evaluate various extractants,viz. (6N HCl, 0.1N HCl, EDTA (NH₄)₂CO₃, EDTA NH₄OAc, DTPA+CaCl₂ and 1M MgCl₂) to find critical levels of soil and plant Zn for green gram (Phaseolus aureus Roxb.). The order of extractability by the different extractants was 6N HCl>0.1N HCl>EDTA (NH₄)₂CO₃<EDTA NH₄OAc DTPA+CaCl₂>1M MgCl₂. Critical levels of 0.48 ppm DTPA × CaCl₂ extractable Zn, 0.80 ppm EDTA NH₄OAc extractable Zn, 0.70 ppm EDTA (NH₄)₂CO₃ extractable Zn, and 2.2 ppm 0.1N HCl extractable Zn were estimated for the soils tested. The critical Zn concentration in 6 weeks old plants was found to be 19 ppm. The 0.1N HCl method gave the best correlation (r=0.588^**) between extractable Zn and Bray's per cent yield, while with DTPA+CaCl₂, it was slightly low (r=0.542^**). The DTPA + CaCl₂ method gave significant (r=0.73^**) correlation with plant Zn concentration. The 0.1N HCl gave the higher correlation with Zn uptake (r=0.661^**) than DTPA (r=0.634^**) 6N HCl and 1M MgCl₂ method gave nonsignificant positive relationship with Bray's per cent yield. For noncalcareous soils apart from the common use of DTPA+CaCl₂, 0.1N HCl can also be used for predicting soil available Zn. The use of 0.1N HCl would be much cheaper than DTPA and other extractants used in the study.     

Effect of nitrogen source on ureides in soybean

In field-grown soybeans (Glycine max L. Merr. cv Harosoy), the percentage of N in the xylem as ureides increased with increasing N₂ fixation. During a 9-week collection period, the ureide content varied from 9.0 to 69.2% of the xylary N. Between 9 and 11 weeks (early pod fill), there was a good correlation (r = 0.93) between C₂H₂ reduction and the per cent N in xylem as ureides. The per cent N as ureides, however, does not always indicate the reliance of the plant on symbiotic N₂ fixation. This ureide content also depended on the level of NO₃⁻ available to the roots. Non-nodulated soybeans given from 0 to 200 kilogram N per hectare produced xylem sap which averaged from 31.8% to 9.0% N, respectively, in the xylem as ureides over the 9-week period.

Feeding of ¹⁵N₂, ¹⁵NH₄, or ¹⁵NO₃ to greenhouse-grown soybeans indicated substantial differences in the initial distribution of N by the xylem stream, but the ultimate distribution of N between plant parts and grain did not vary with available N or percentage of xylary N as ureides. Amino acids, not ureides, were the major source of N in the phloem. The soybeans maintained a similar composition in phloem irrespective of the xylem sap constituents, with N derived from N₂, NH₄, or NO₃ being equally accessible to the phloem stream.

     

Ionic balance,proton efflux,nitrate reductase activity and growth ofHippophaë rhamnoides L. ssp.rhamnoides as influenced by combined-N nutrition or N2 fixation

Growth of 2-month-old nonnodulatedHippophaë rhamnoides seedlings supplied with combined N was compared with that of nodulated seedlings grown on zero N. Plant growth was significantly better with combined N than with N₂ fixation and, although not statistically significant for individual harvests, tended to be highest in the presence of NH ₄ ⁺ , a mixture of NH ₄ ⁺ and NO ₃ ^? producing the highest yields. Growth was severely reduced when solely dependent on N₂ fixation and, unlike the combined-N plants, shoot to root ratios had only slightly increased after an initial decrease. An apparently insufficient nodule mass (nodule weight ratio <5 per cent) during the greater part of the experimental period is suggested as the main cause of the growth reduction in N₂-fixing plants. Thein vivo nitrate reductase activity (NRA) of NO ₃ ^? dependent plants was almost entirely located in the roots. However, when grown with a combination of NO ₃ ^? and NH ₄ ⁺ , root NRA was decreased by approximately 85 per cent.H. rhamnoides demonstrated in the mixed supply a strong preference for uptake of N as NH ₄ ⁺ , NO ₃ ^? contributing only for approximately 20 per cent to the total N assimilation. Specific rates of N acquisition and ion uptake were generally highest in NO ₃ ^? +NH ₄ ⁺ plants. The generation of organic anions per unit total plant dry weight was approximately 40 per cent less in the NH ₄ ⁺ plants than in the NO ₃ ^? plants. Measured extrusions of H⁺ or OH^? (HCO ₃ ^? ) were generally in good agreement with calculated values on the basis of plant composition, and the acidity generated with N₂ fixation amounted to 0.45–0.55 meq H⁺. (mmol N_org)^?1. Without acidity control and in the presence of NH ₄ ⁺ , specific rates of ion uptake and carboxylate generation were strongly depressed and growth was reduced by 30–35 per cent. Growth of nonnodulatedH. rhamnoides plants ceased at the lower pH limit of 3.1–3.2 and deterioration set in; in the case of N₂-fixing plants the nutrient solution pH stabilized at a value of 3.8–3.9 without any apparent adverse effects upon plant performance. The chemical composition of experimental and field-growing plants is being compared and some comments are made on the nitrogen supply characteristics of their natural sites.     

Effect of different concentrations of some ammonium fertilizers on the germination ofPennisetum typhoides Stapf & Hubb. andSorghum vulgare Pers

Summary Germination experiments were carried out with varying but equivalent amounts of NH₄Cl, (NH₄)₂SO₄, and NH₄NO₃, while in one experiment urea was included. It could be stated that the inhibitory effect on germination was ionic in nature, the effect of urea being rather small, while it was safer to use NH₄Cl or (NH₄)₂SO₄ than NH₄NO₃, especially under dry conditions.     

Nitrogen dynamics at the sediment–water interface in shallow, sub-tropical Florida Bay: why denitrification efficiency may decrease with increased eutrophication

Nitrogen (N) dynamics at the sediment–water interface were examined in four regions of Florida Bay to provide mechanistic information on the fate and effects of increased N inputs to shallow, subtropical, coastal environments. Dissimilatory nitrate (NO₃ ^?) reduction to ammonium (DNRA) was hypothesized to be a significant mechanism retaining bioreactive N in this warm, saline coastal ecosystem. Nitrogen dynamics, phosphorus (P) fluxes, and sediment oxygen demand (SOD) were measured in north-central (Rankin Key; eutrophic), north-eastern (Duck Key; high N to P seston ratios), north-western (Murray Key; low N to P ratios), and central (Rabbit Key; typical central site) Florida Bay in August 2004, January 2005, and November 2006. Site water was passed over intact sediment cores, and changes in oxygen (O₂), phosphate (o-PO₄ ^3?), ammonium (NH₄ ⁺), NO₃ ^?, nitrite (NO₂ ^?), and N₂ concentrations were measured, without and with addition of excess ¹⁵NO₃ ^? or ¹⁵NH₄ ⁺ to inflow water. These incubations provided estimates of SOD, nutrient fluxes, N₂ production, and potential DNRA rates. Denitrification rates were lowest in summer, when SOD was highest. DNRA rates and NH₄ ⁺ fluxes were high in summer at the eutrophic Rankin site, when denitrification rates were low and almost no N₂ came from added ¹⁵NO₃ ^?. Highest ¹⁵NH₄ ⁺ accumulation, resulting from DNRA, occurred at Rabbit Key during a picocyanobacteria bloom in November. ¹⁵NH₄ ⁺ accumulation rates among the stations correlated with SOD in August and January, but not in November during the algal bloom. These mechanistic results help explain why bioreactive N supply rates are sometimes high in Florida Bay and why denitrification efficiency may decrease with increased NO₃ ^? inputs in sub-tropical coastal environments.     

Effects of N source on proton excretion,ionic balance and growth ofAlnus glutinosa (L.) Gaertner: comparison of N2 fixation with single and mixed sources of NO3 and NH4

Summary Non-nodulatedalnus glutinosa plants were grown for 6 weeks in nutrient solutions using 3 combined-N treatments (NO₃; NO₃/NH₄; and NH₄) at a total N level of 4 meq.l^–1, and growth was ccmpared with nodulated plants at zero N (N₂ fixation). Of the combined-N sources, 100 per cent NH₄ resulted in the highest dry matter yields when the solution pH was adjusted daily atc. 6. The dry matter yield was lowest with NO₃.During the first 3 weeks, the yield of the N₂-fixing plants was as high as that of the NH₄ plants, but fell relatively behind during the second 3-week period. These effects could be attributed to higher initial N contents and higher shoot:root ratios, respectively, in the N₂-fixing plants. Specific rates of N acquisition in the root were of a comparable order of magnitude for the combined-N and zero-N treatments.When NO₃ was taken up, it was almost completely reduced in the roots. Regardless of N source there was a large excess of cations (C) relative to inorganic anions (A) in the plants, which was presumed to be balanced by an equivalent amount of organic anions (C-A). The relatively small differences in generation of organic anions for the various modes of N supply indicated the relative importance of the proton pump when NH₄ or N₂ was the N source. Proton or hydroxyl-ion effluxes, calculated on the basis of plant analyses, were generally in good agreement with measured excretion values. The acidity generation with N₂ fixation amounted toc. 0.5 meq H⁺.mmol^–1 N_org, which was distinctly higher than the range of 0.1–0.2 mentioned by Raven and Smith⁴³ for dinitrogen-fixing plants.Without pH adjustment, specific rates of cation uptake and carboxylate generation were strongly depressed as the acidity increased, when NO₃/NH₄, NH₄ and N₂ were the N sources. Growth ofAlnus glutinosa appeared to be still normal at a pH ofc. 2.8. During the final 3 weeks, only the NH₄ plants ceased growing at a pH of 2.6.     

Evaluation of thiosulfate as a nitrification inhibitor for manures and fertilizers

Nitrogen from poultry manure (PM) and ammoniacal fertilizers undergoes rapid nitrification upon addition to soils, making it highly susceptible to leaching and thus creating a potential for groundwater contamination by nitrate-N. Any management technique that could delay nitrification would be desirable. A laboratory incubation study was conducted to determine the effect of thiosulfate, a known nitrification inhibitor, on nitrification in a loamy sand soil amended with five N sources, including two poultry manures and three N fertilizers [(NH₄)₂SO₄, NH₄NO₃, CO(NH₂)₂]. The manures or fertilizers were added to a soil-sand mixture alone or in combination with Na₂S₂O at a rate of 100 mg N kg^-1 for the inorganic N sources and 147 mg N kg^-1 and 122 mg N kg^-1 for PM-1 and PM-2 respectively. All treatments were incubated for 12 weeks and analyzed periodically for NO₃-N and NH₄-N.Thiosulfate was most effective with NH₄NO₃, maintaining 100% inhibition of nitrification throughout the 12 week study, and with (NH₄)₂SO₄ (89% inhibition at 12 weeks). Thiosulfate also inhibited nitrification from urea and poultry manure, but the inhibitory effect diminished later in the incubation. Urea had 81% inhibition of nitrification after eight weeks, decreasing to 26% by week 12, while the manures averaged 89% inhibition after four weeks and 20% at week 12. Net mineralization of organic N from PM was also reduced by the use of thiosulfate, particularly for PM-1 where the percentage of organic N mineralized decreased from 42% after four weeks incubation to 3% at week 12. Therefore, while thiosulfate can reduce nitrification from manures, and thus the potential for nitrate leaching, the timing of manure application will influence the effect of thiosulfate on the availability of manure N for plant uptake or leaching.     

Foliar N application reduces soil NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack>-N leaching loss in apple orchards

A comparison of the effects of foliar and soil N application was made in field-grown mature fruiting Gala/M9 apple trees (Malus domestica Borkh) in 2001 and 2002 growing seasons under Pacific Northwest growing conditions in southern British Columbia, Canada. The trees, six years old at the start of the experiment, were treated: (1) with 5 g/l urea sprays supplied every two weeks (7 times) from mid May to mid August (total about 50 g N/tree/year), (2) with the same amount of N applied to the soil with the same timing and quantity as for the foliar treatment, and (3) with no N (control). Leaf color (as SPAD readings) and N concentrations (mg/g), and soil NH₄⁺-N and NO₃^–-N were measured periodically throughout the two seasons. Leached NO₃^–-N was monitored monthly via an anion exchange probe from June to October in 2001 and from May to November in 2002. Shoot length was measured in October and N concentration of one-year-old wood and roots was determined in December of each growing s eason. Soil N application significantly increased shoot length relative to control or foliar N application. Leaf color, leaf N, and N concentration of one-year-old wood and roots were similarly increased relative to control by both soil and foliar N application. These treatments also increased fruit yield relative to control. There was no significant difference in yield and fruit quality between soil and foliar N applications. Soil N application increased soil NH₄⁺-N and NO₃^–-N content in the root zone, and also increased the NO₃^– leaching loss below the root zone especially late in the growing season. Our results suggested that tree N status and yield and fruit quality could be maintained by multiple urea sprays during the growing season in apple orchards, and foliar N application will reduce the risk of soil NO₃^–-N leaching.     

Effect of ammonium sulfate on the phytotoxicity, foliar uptake, and translocation of imazamethabenz in wild oat

Experiments were conducted in greenhouse, growth chamber, and laboratory conditions to determine the effect of ammonium sulfate [(NH₄)₂SO₄] on the phytotoxicity, foliar uptake, and translocation of imazamethabenz on wild oat. Rates of (NH₄)₂SO₄ up to 5% (w/v) applied with a greenhouse sprayer did not affect the phytotoxicity of the herbicide when the mix was applied at the one- to two-leaf stage. However, inclusion of 1 and 2% (NH₄)₂SO₄ increased the phytotoxicity of the herbicide when the mix was sprayed at the two- to three-leaf, or the three- to four-leaf stage. At 10%, (NH₄)₂SO₄ decreased the phytotoxicity of the sublethal dosage of the herbicide. When the herbicide was applied as individual drops to the growth chamber-grown plants, inclusion of (NH₄)₂SO₄ at 1% did not affect phytotoxicity as measured by shoot growth. The presence of (NH₄)₂SO₄ did not affect the amount of imazamethabenz retained by wild oat foliage, but it decreased [¹⁴C]imazamethabenz absorption, slightly antagonized acropetal translocation, and increased the basipetal translocation of [¹⁴C]imazamethabenz. It was concluded that application methods greatly modify the effect of (NH₄)₂SO₄ on imazamethabenz phytotoxicity. Herbicide absorption and translocation as determined by one method do not necessarily represent the absorption and translocation patterns when different application methods are used. Absorption and translocation were not the factors that were responsible for the observed effect of (NH₄)₂SO₄ on the herbicide phytotoxicity.Abbreviations SC suspension concentrate     

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.