Sources of N uptake by wheat (Triticum aestivum L.) and N transformations in soil treated with a nitrification inhibitor (nitrapyrin)

Rates of N uptake by spring wheat as ammonium and as nitrate, and rates of nitrification, gross N immobilization and gross N mineralization were measured in a pot experiment during 84 days of growth in a clay soil. Soil treatments included an unfertilized control and addition of ¹⁵NH₄NO₃ or NH₄ ¹⁵NO₃ in the absence and presence of N-serve 24E. Incorporation of ammonium into the soil organic N pool was considerably higher in the presence compared to the absence of nitrapyrin, but the processes contributing to this effect could not be positively identified. Both dry matter and grain yield as well as N uptake by wheat were enhanced in the presence of the inhibitor in N fertilized soil, despite the increased immobilization of N. On the other hand, inhibitor application had a detrimental effect on yield and N uptake by wheat in unfertilized soil. Both ammonium and nitrate forms of inorganic N were absorbed by wheat, but nitrate uptake was dominant in the absence of the inhibitor. The uptake of N as ammonium was higher and the uptake of N as nitrate was less, both in absolute and proportional terms, in the presence compared to the absence of inhibitor. In addition, the proportion of N taken up as ammonium was higher than the proportion of N as ammonium in the available N pool up to day 56 in the inhibitor treatment, which indicated a preference for ammonium uptake by wheat. Evidence was obtained which suggested that several factors may have contributed to the positive response of wheat to inhibitor application in N fertilized soil, including reduced N losses, higher gross N mineralization and a physiological response due to the proportional increase in uptake of inorganic N as ammonium.     

Control of nitrification of fertilizer nitrogen: Effect of inhibitors,banding and nesting

Laboratory incubation and field experiments were conducted to evaluate thiourea, ATC (4-amino-1, 2, 4 triazole hydrochloride) and N-Serve 24 E (2-chloro-6-trichloromethyl-pyridine) as inhibitors of nitrification of fertilizer N. In the incubation experiment, most of the added aqueous NH₃ or urea was nitrified at 14 days on both soils, but addition of the inhibitors to fertilizer N decreased the conversion of NH₄−N to NO₃−N markedly. There was less nitrification for ATC and thiourea but not for N-Serve 24 E when the fertilizers and the inhibitors were placed at a point as opposed to when mixed into soil. After 28 days, ATC and N-Serve 24 E were more effective in inhibiting nitrification than thiourea. ATC and N-Serve 24 E also inhibited release of mineral N (NH₄−N+NO₃−N) from native soil N. In the uncropped field experiment, which received N fertilizers in the fall, nitrification of fall-applied N placed in the 15-cm bands was almost complete by early May in the Malmo soil, but not in the Breton soil. When ATC or thiourea had been applied with urea, nitrification of fall-applied N was depressed by May and the recovery of applied N as NH₄−N was greater with increasing band spacing to 60 cm or placing N fertilizer in nests (a method of application where urea prills were placed at a point in the soil in the center of 60×60 cm area). In late June, the percentage recovery of fall-applied N in soil as NH₄−N or mineral N increased with wide band spacing, or nest placement, or by adding ATC to fertilizer N on both soils. These results indicate that placing ammonium-based N fertilizers in widely-spaced bands or in nests with low rates of inhibitors slows nitrification enough to prevent much of the losses from fall-applied N. Scientific Paper No. 552, Lacombe Research Station, Research Branch, Agric, Can.     

Interaction of salinity and enhanced ammonium and potassium nutrition in wheat

Wheat (Triticum aestivum L.) was grown to maturity in a pot experiment in a calcareous silty sand soil. N was applied at two levels as granulated N-P fertilizers, amended or not with nitrification inhibitors (1% and 5% DCD, 1% N-serve). Potassium as KCl was given at three levels of application. P was applied at a uniform rate. Two levels of salinity were obtained by using the soil as such (EC= 0.3 mmho/cm) and by adding NaCl to the same soil (EC=2.4 mmho/cm). 1% DCD and 1% N-serve treatments gave significantly higher wheat grain yields and N-uptake than the other ones. Nitrate content of leachates indicated a prevalent nitrate nutrition in the treatment without nitrification inhibitors. The 5% DCD treatment showed a yield depression. In the lower N level treatments, a significant yield increase, generated by 1% DCD and N-serve was found in the salinized soil as compared to the non-saline soil. Soil salinity reduced N-uptake when nitrification inhibitors were not present. In treatments having the inhibitors, N-uptake was equal or greater in the salinized than in the non saline soil. An enhanced ammonium nutrition increased the P uptake.     

Nitrogen leaching losses from conventional and new nitrogenous fertilizers in low-land rice culture

Summary A pot-culture experiment was conducted to assess the leaching losses of N from the conventional and new nitrogen fertilizers under low-land rice culture. Leaching losses of N were generally less than 20% of applied N with sources other than sodium nitrate and these could be reduced by blending urea with nitrification inhibitor N-Serve or coating withneem cake or by using urea super granules or slow-release N fertilizer sulphur coated urea. These new nitrogen fertilizers were more effective than urea for rice.     

Effect of ATC,N-Serve 24 E and thiourea nitrification inhibitors on yield and N uptake of barley fertilized with fall-applied N1

Solution urea and aqua NH₃ were injected in bands 9 cm deep and spaced 45 cm apart with and without nitrification inhibitors during October in 10 field experiments in north-central Alberta. ATC (4-amino-1,2,4-triazole hydrochloride), N-Serve 24 E (2-chloro-6-trichloromethyl-pyridine) and thiourea were used in two experiments, ATC only in another six experiments, and N-Serve 24 E only in another two experiments. Yield and apparent recovery of applied N in barley grain were determined. In the two experiments where fall treated plots were soil sampled in the following spring, 44% of the fall-applied N was recovered in the soil when inhibitors were not used. But where the inhibitors were added to the fall-applied N as NH₄−N in May was 4% and 31% without and with addition of inhibitors, respectively. Likewise, in experiments where three inhibitors were used, the treatments with inhibitors increased the yield and N recovery in grain by more than 50% compared to fall application without inhibitors. In the other experiments, fall-applied ATC or N-Serve 24 E did not always increase yield or N recovery in grain. Considering all experiments with ATC, the average recovery of applied N in barley grain was 28, 40 and 57% for fall banding, fall banding with ATC and spring application, respectively. In view of this and previous work in north-central Alberta, inhibitors injected in bands in the fall slowed nitrification and improved yield, but nests or large granules of urea were more effective. Scientific paper No 553, Lacomba Research Station, Research Branch, Agriculture Canada.     

Effect of calcium carbonate on ammonium and urea nutrition of young tea plants (Camellia sinensis L.) grown in sand culture

Summary When calcium carbonate incorporated nutrient solution containing ammonium sulphate was added to sand in pots marked nitrification of the added ammonium was noted. It resulted in improved growth of tea plants and the toxicity effects of ammonium ions were completely eliminated. Where urea was used as the form of N supply, moderate (50%) nitrification was observed to occur even in the absence of calcium carbonate, however it was very rapid in its presence.     

Relative efficiency of N fertilizers as influenced by N-serve in the potato crop

Summary Field experiments, on potato, were conducted in the alluvial soils of Ludhiana, in 1976–77 and 1980–81, to investigate the relative efficiency of N fertilizers as influenced by a nitrification inhibitor (N-serve). In the absence of N-serve, sulphate of ammonia (S/A) and calcium ammonium nitrate (CAN) proved superior to urea, on an equal N basis, in almost all the yield characters and yield, but urea treated with N-serve tended to equal S/A and proved better than CAN. The inhibitor increased the N-uptake and N-recovery from urea and decreased the optimum basal dose of the fertilizer, by 10.8kg N/ha in 1976–77 and by 40.5 kg N/ha in 1980–81, without reducing the tuber yield in any of the two years. S/A and CAN did not profit from the treatment with N-serve.     

脲酶抑制剂/硝化抑制剂对植稻土壤中尿素N行为的影响

采用自制根盒试验,主要研究了脲酶抑制剂氢醌（HQ）,硝化抑制剂双氰胺（DCD）及二者组合对离水稻根际不同距离处NH4^--N和NO3^-N分布的影响,结果表明,DCD及其与HQ组合均能显著促进稻株地上部分生长,始终显著降低水稻根际与近根际土中NH4^ -N含量直至施肥后60d,施肥后20d时,DCD及其与HQ组合可使非根际土中NH4^ -N含量显著增加,随后,却出现相反现象,施肥后20d时,距根际不同距离的土壤中,配施DCD或DCD＋HQ处理均能显著降低NO3^-N含量,随后,近根际和非根际仍保持上述现象直至施肥后40d;同未施DCD处理相比,根际土壤却较早出现NO3^--N含量高峰,正好与水稻N营养需求时期相一致,因此,DCD及其与HQ组合可减少水稻根际环境下尿素N损失潜势,通过不种稻土壤和距根际3cm处的土壤中尿素无机氮形态分布的差异,充分显示了研究水稻根际土壤氮素转化及相关抑制剂对其影响时,以取离根际3cm外的土壤作为非根际明显优于不种稻土壤。     

Effect of trickle fertigation with three forms of nitrogen on soil pH,levels of extractable nutrients below the emitter and plant growth

The effects of application of nitrogen as calcium nitrate, urea or ammonium sulphate at two rates through the trickle irrigation system on pH and nutrient status of the wetted volume of soil below the emitters and on growth and nutrition of courgette (zucchini) plants (Cucurbita pepo L.) was investigated. Soil acidification, caused by nitrification, occurred to a large extent in the volume of soil immediately below the emitters in the urea and ammonium sulphate treatments. Acidification was greater at the high rate of N addition and more pronounced with ammonium sulphate than urea. A significant amount of applied urea appeared to move through the soil as urea and consequently, at the same rate of N addition, levels of ammonium were lower directly below the emitter and those of nitrate were higher further away from the emitters for the urea than ammonium sulphate treatments. Soil acidification below the emitters resulted in significant decreases in levels of exchangeable Ca, Mg and K and increases in levels of exchangeable Al, EDTA-extractable Fe, Mn, Zn and Cu and bicarbonate-extractable P. Vegetative growth and harvestable yields of courgettes were increased by both irrigation and nitrogen applications. Vegetative growth was generally greater at the low rate of N addition than at the high one and generally followed the order calcium nitrate > urea > ammonium sulphate. However, fruit yields followed the order urea > ammonium sulphate > calcium nitrate and were larger at the high rate of N for urea and ammonium sulphate treatments and unaffected by rate for the calcium nitrate treatments. It is suggested that with fertigation, the form of applied N can have significant physiological effects of plant growth and yields because N may be applied into the root zone on numerous occasions during the growing season.     

Measurement of in situ rates of nitrification in sediment

A method has been developed for the measurement of nitrification rates in intact sediment cores without disturbing the concentration gradients of oxygen and ammonium. N-serve (2-chloro-6-trichloromethyl-pyridine), a specific inhibitor of the autotrophic ammonium oxidation, was injected into a 0–2 cm surface layer of the sediment (20 ppm) and added to the water column of sediment cores (5 ppm). N-serve in these concentrations was sufficient to inhibit nitrification, but did not change the rate of ammonium production or incorporation in sediment suspensions, which were incubated aerobically and anaerobically. The ammonium accumulation in cores injected with N-serve was thus equal to the amount of ammonium which was oxidized to nitrate in the control cores. Nitrification rates were in the range of 0–3 mmol N m^{–2 –1}     

The fate of labelled15N urea and ammonium nitrate applied to a winter wheat crop

Labelled urea or ammonium nitrate was applied to winter wheat growing on a loamy soil in Northern France. Two applications of fertilizer were given: 50 kg N ha^–1 at tillering (early March) and 110 kg N ha^–1 at the beginning of stem elongation (mid-April). The kinetics of urea hydrolysis, nitrification of ammonium and the disappearance of inorganic nitrogen were followed at frequent intervals. Inorganic nitrogen soon disappeared, mainly immobilized by soil microflora and absorbed by the crop. Net immobilization of fertilizer N occured at a very similar rate for urea and ammonium nitrate. Maximum immobilization (16 kg N ha¹) was found at harvest for the first dressing and at anthesis for the second dressing (23 kg N ha¹). During the nitrification period, the labelled ammonium pool was immobilized two to three times faster than the labelled nitrate pool. No significant net¹⁵N remineralization was found during the growth cycle.The actual denitrification and volatilization losses were probably more important than indicated from calculations made by extrapolation of fluxes measured over short intervals. However microbial immobilization was the most important of the processes which compete with plant uptake for nitrogen.     

Effects of N-serve on soybeans and soil nitrogen transformations

Summary Plant dry weight, total N, and total Ca was increased at 0.1 and 1 ppm N-serve. At greater 10 ppm the plants showed visual symptoms of a stunted growth, stem elongation, flowers, and pods failed to form or were aborted, young leaves were curled, and roots were club shaped with many branches. These symptoms were increasingly evident with increasing N-serve application rates. The reason was attributed to an auxin effect. Dry wt and total N in the plant was less than the control at the higher N-serve applications. There was little effect on nitrogenase activity at less than 10 ppm N-serve. Nodulation tended to increase at 0.1 and 1 ppm N-serve.Nitrification was inhibited up to 104 days at 20 ppm N-serve. The soil pH of the high N-serve rates was decreased at 104 days probably due to nitrification. Generally there were little detectable differences among treatments in soil organic N. The average soil organic N from 0 to 104 days decreased by 0.01%. Average increase in total N within each pot at harvest was equivalent to about 138 kg N/ha.     

Nitrate reductase activity and growth response of forest species to ammonium and nitrate sources of nitrogen

Summary Three tree species,Eucalyptus regnans (F. Muell.),E. obliqua (L'Herit.),Pinus radiata (D. Don) were grown in sand culture with different proportions of nitrate and ammonium. Nitrate Reductase Activity (NRA) was induced in root tissue of all species and in leaf tissue of the eucalypts. An increasing proportion of nitrate resulted in increasing NRA in all species and hence NRA alone is no indication of N-preference. The highest NRA was found withE. regnans, a result which has also been obtained in the mature forest. The growth ofE. regnans was least with NH₄ ⁺ alone, whereas that ofE. obliqua was least with NO₃ ^– alone. The soils of matureE. regnans forest have a high potential for nitrification while those ofE. obliqua forest show little nitrification. Thus the preference for particular N sources shown by seedlings in culture is supported by related properties of mature forests. It is postulated however, that the inducibility of a high level of RNA in seedlings is more likely a result of a preference for NO₃ ^– than a cause.     

Rapid and slow modulation of nitrate reductase activity in the red macroalga <Emphasis Type="Italic">Gracilaria chilensis</Emphasis> (Gracilariales,Rhodophyta): influence of different nitrogen sources

Nitrate is one of the most important stimuli in nitrate reductase (NR) induction, while ammonium is usually an inhibitor. We evaluated the influence of nitrate, ammonium or urea as nitrogen sources on NR activity of the agarophyte Gracilaria chilensis. The addition of nitrate rapidly (2 min) induced NR activity, suggesting a fast post-translational regulation. In contrast, nitrate addition to starved algae stimulated rapid nitrate uptake without a concomitant induction of NR activity. These results show that in the absence of nitrate, NR activity is negatively affected, while the nitrate uptake system is active and ready to operate as soon as nitrate is available in the external medium, indicating that nitrate uptake and assimilation are differentially regulated. The addition of ammonium or urea as nitrogen sources stimulated NR activity after 24 h, different from that observed for other algae. However, a decrease in NR activity was observed after the third day under ammonium or urea. During the dark phase, G. chilensis NR activity was low when compared to the light phase. A light pulse of 15 min during the dark phase induced NR activity 1.5-fold suggesting also fast post-translational regulation. Nitrate reductase regulation by phosphorylation and dephosphorylation, and by protein synthesis and degradation, were evaluated using inhibitors. The results obtained for G. chilensis show a post-translational regulation as a rapid response mechanism by phosphorylation and dephosphorylation, and a slower mechanism by regulation of RNA synthesis coupled to de novo NR protein synthesis.     

Soil and fertilizer nitrogen transformations under alternate flooding and drying moisture regimes

Summary A study of changes in NH₄ ⁺ and NO₃ ^––N in Maahas clay amended with (NH₄)₂SO₄ and subjected to 4 water regimes in the presence and absence of the nitrification inhibitor N-Serve (Nitrapyrin) showed that the mineral N was well conserved in the continoous regimes of 50% and 200% (soil weight basis) but suffered heavy losses due to nitrification-denitrification under alternate drying and flooding. N-Serve was effective in minimizing these losses.Another incubation study with 3 soils showed that after 10 cycles of flooding and drying (either at 60°C or 25°C), the ammonification of soil N was enhanced. Nitrification of soil as well as fertilizer NH₄ ⁺ was completely inhibited upto 4 weeks by the treatments involving drying at high temperature. Flooding and air drying at 25°C, on the other hand, enhanced ammonification of soil N but retarded nitrification. These treatments, however, enhanced both ammonification and nitrification of the applied NH₄ ⁺ fertilizer N. Under flooded conditions rate of NH₄ ⁺ production was faster in soils that were dried at 60°C or 25°C and then flooded as compared to air dried soils.It is concluded that N losses by nitrification-denitrification and related N transformations may be considerably altered by alternating moisture regimes. Flooding and drying treatments seem to retard nitrification of soil N but conserve that of fertilizer NH₄ ⁺ applied after these treatments.     

Apparent and Measured Rates of Nitrification in the Hypolimnion of a Mesotrophic Lake

Three distinct phases were observed in the change of dissolved inorganic nitrogen concentrations in the hypolimnion of Grasmere. The second phase of decreasing ammonia and increasing nitrate concentrations was typical of the nitrification process. Observations on nitrate concentration gradients between surface sediments and the water column and experiments using the nitrification inhibitor N-Serve indicated the in situ activity of chemolithotrophic nitrifying organisms. Nitrification rates were estimated throughout the period of stratification by using the N-Serve and [¹⁴C]bicarbonate uptake method. Comparison of the field nitrate concentrations with the predicted nitrate concentrations (from estimates of the nitrification rate) indicated that the method underestimated the true rate of nitrification. Possible reasons for this are discussed.     

Nitrogen balance sheet of (NH4)2SO4-gypsum pellets and mixtures and ureaformaldehyde applied to corn in pots of sand

Summary A comparison of ammonium sulphate added to sand pots in different ways and ureaformaldehyde as sources of N to corn plants was carried out. The results showed that nitrogen utilization by plants from ammonium sulphategypsum pellets was greater than its utilization when ammonium sulphate was mixed with gypsum or when the pellets were ground or from ureaformaldehyde. The leached nitrogen from the pellets, ammonium sulphate applied in 3 portions and ureaformaldehyde was not significantly different and was lower than other ammonium sulphate treatments. The nitrogen remaining in pots fertilized by ureaformaldehyde was much greater than the corresponding amount in the case of all ammonium sulphate treatments. Gaseous loss of nitrogen took place in all nitrogen treatments with the loss from ammonium sulphate-gypsum pellets being the lowest.Incubation in sand of ureaformaldehyde, urea, and ammonium sulphate was carried out to understand better the growth conditions of corn fertilized by ureaformaldehyde. In the case of ureaformaldehyde- and urea-sand systems, the pH increased, NO₂ ^– accumulated and considerable loss of nitrogen took place. The pH, the NO₂ ^– accumulation and the loss of N tended to decrease with gypsum increments. re]19720801     

Clover and ryegrass are tolerant species to ammonium nutrition

The application of nitrification inhibitors (NIs) together with nitrogen fertilizers in grasslands is an effective alternative to reduce nitrate leaching and nitrogenous gases emissions to the atmosphere. Nevertheless, the use of NIs increases the amount of ammonium available for the plant that, due to its reported toxic effect in plants, can have a direct effect on crop production. Grassland species have traditionally suffered from intensive grazing and urea deposition and, therefore, a tolerance to ammonium nutrition could be expected in these species. Plants of Trifolium repens L. var. huia and Lolium perenne L. var. Herbus were grown under two nitrogen nutrition regimes (nitrate or ammonium) and three different nitrogen concentrations (0.5, 2.5 and 5 mmol/L). The effect of nitrogen form was determined on biomass production parameters, gas-exchange and water relations parameters as well as polyamine (PA) and ion tissue contents. Both grassland species showed tolerance to ammonium nutrition due to their capacity to adjust several metabolic processes in a species-specific way. Gas exchange measurements and biomass production (expressed as dry weight (DW)) were unaffected by the nitrogen form or dose in both species except for a decrease in root total DW in ryegrass plants grown under ammonium nutrition. Hydraulic conductance (L₀) increased in ryegrass with increasing ammonium doses but no change due to the nitrogen source was observed in water potential (Ψ_w) values. Both species, and specially ryegrass, accumulated free ammonium mainly in roots when grown under ammonium nutrition and its translocation to the shoot via xylem was also observed. A clear difference in cations and PAs pattern was observed in each species when comparing both nitrogen nutrition regimes.     

The roles of nitrate and ammonium in the regulation of the development of nitrate reductase in Chlamydomonas reinhardii

The regulation of the development of nitrate reductase (NR) activity in Chlamydomonas reinhardii has been compared in a wild-type strain and in a mutant (nit-A) which possesses a modified nitrate reductase enzyme that is non-functional in vivo. The modified enzyme cannot use NAD(P)H as an electron donor for nitrate reduction and it differs from wild-type enzyme in that NR activity is not inactivated in vitro by incubation with NAD(P)H and small quantities of cyanide; it is inactivated when reduced benzyl viologen or flavin mononucleotide is present. After short periods of nitrogen starvation mutant organisms contain much higher levels of terminal-NR activity than do similarly treated wild-type ones. Despite the inability of the mutant to utilize nitrate, no nitrate or nitrite was found in nitrogen-starved cultures; it is therefore concluded that the appearance of NR activity is not a consequence of nitrification. After prolonged nitrogen starvation (22 h) the NR level in the mutant is low. It increases rapidly if nitrate is then added and this increase in activity does not occur in the presence of ammonium, tungstate or cycloheximide. Disappearance of preformed NR activity is stimulated by addition of tungstate and even more by addition of ammonium. The results are interpreted as evidence for a continuous turnover of NR in cells of the mutant with ammonium both stimulating NR breakdown and stopping NR synthesis. Nitrate protects the enzyme from breakdown. Reversible inactivation of NR activity is thought to play an insignificant rôle in the mutant.Abbreviations NR nitrate reductase - BV benzyl viologen