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1.
Mineralization of carbon and nitrogen,and nitrification in Scots pine forest soil treated with fast- and slow-release nitrogen fertilizers 总被引:5,自引:0,他引:5
We studied the effects of fast- and slow-release organic N fertilizers (urea and urea-formaldehyde, Nitroform) on mineralization, nitrification, and N leaching in an acid, poor forest soil. We also studied the effects of a nitrification inhibitor (dicyandiamide) applied together with urea. Net nitrification, mineralization of N and C were determined by aerobic laboratory incubation of soil samples taken one and three growing seasons after N application. Numbers of autotrophic nitrifiers were estimated by a most probable number method three growing seasons after the treatment. Urea increased the CO2 production immediately after application, but after three growing seasons, CO2 production was the lowest in the urea-treated soils. In the nitroform-treated soils, the concentration of exchangeable NH
inf4
sup+
after the first and third growing seasons was of the same magnitude, in contrast to the urea-treated soils, where hydrolysis took place immediately. Three growing seasons after application, the highest amount of NH
inf4
sup+
accumulated during the laboratory incubation was in the nitro-form-treated soils. Unlike urea, nitroform did not increase the production of NO
inf3
sup-
or the number of NH
inf4
sup+
oxidizers. In the urea+dicyandiamide-treated soils there was less NO
inf3
sup-
and a lower number of nitrifiers than in the urea-treated soils. The results showed that a slow-release N fertilizer, such as nitroform, increases the availability of mineral N in acid forest soils without increasing nitrification and hence the risk of NO
inf3
sup-
leaching. 相似文献
2.
We observed that soil cores collected in the field containing relatively high NH
inf4
sup+
and C substrate levels produced relatively large quantities of N2O. A series of laboratory experiments confirmed that the addition of NH
inf4
sup+
and glucose to soil increase N2O production under aerobic conditions. Denitrifying enzyme activity was also increased by the addition of NH
inf4
sup+
and glucose. Furthermore, NH
inf4
sup+
and glocose additions increased the production of N2O in the presence of C2H2. Therefore, we concluded that denitrification was the most likely source of N2O production. Denitrification was not, however, directly affected by NH
inf4
sup+
in anaerobic soil slurries, although the use of C substrate increased. In the presence of a high substrate C concentration, N2O production by denitrifiers may be affected by NO
inf3
sup-
supplied from NH
inf4
sup+
through nitrification. Alternatively, N2O may be produced during mixotrophic and heterotrophic growth of nitrifiers. The results indicated that the NH
inf4
sup+
concentration, in addition to NO
inf3
sup-
, C substrate, and O2 concentrations, is important for predicting N2O production and denitrification under field conditions. 相似文献
3.
Summary Three Illinois Mollisols were incubated for 2 weeks at 25°C after treatment with different amounts of glucose and/or 15N-labelled (NH4)2SO4 or 15N-labelled KNO3. The objectives were: (1) to compare the immobilization and interaction of NH
inf4
sup+
–N and NO
inf3
sup-
–N with the native soil N, and (2) to study the relationship between immobilization of applied N and the added N interaction. As determined, immobilized N refers to forms not extractable with 2 MKCl (immobilized 15N+clay-fixed 15NH
inf4
sup+
). In all cases, both NH
inf4
sup+
–N and NO
inf3
sup-
–N were actively immobilized and transformed into organic forms in the presence of glucose. In the absence of glucose, a higher proportion of NH
inf4
sup+
than NO
inf3
sup-
was recovered in organic forms. Although the three soils differed considerably in the amounts of applied N immobilized, similar trends in N immobilization were observed. A positive added N interaction occurred with all soils, the magnitude increasing with the rate of N addition. In the absence of glucose, higher added N interactions were obtained for NH
inf4
sup+
than NO
inf3
sup-
, whereas there was very little difference between NH
inf4
sup+
and NO
inf3
sup-
in the presence of glucose. The results indicate that under conditions of rapid immobilization (e.g., in the presence of glucose), NH
inf4
sup+
and NO
inf3
sup-
will show comparable interaction with the native soil N, whereas in unamended soil, the extent of this interaction will be greater with NH
inf4
sup+
than with NO
inf3
sup-
. Significant correlations were observed between applied N immobilized and the added N interaction only in one soil having a high initial mineral N content. 相似文献
4.
Effects of ammonium and nitrate on mineralization of nitrogen from leguminous residues 总被引:2,自引:0,他引:2
A laboratory incubation experiment was conducted to compare the effects of NH
inf4
sup+
and NO
inf3
sup-
on mineralization of N from 15N-labelled vetch (Vicia villosa Rotn) in an Illinois Mollisol, and to determine the effect of a nitrification inhibitor (nitrapyrin) on mineralization of vetch N when used with NH
inf4
sup+
. The addition of either NH
inf4
sup+
or NO
inf3
sup-
(100 and 200 mg N kg-1 soil) significantly increased mineralization of vetch N during incubation for 40 days. The effect was greater with NH
inf4
sup+
than with NO
inf3
sup-
, and a further increase occurred in the presence of nitrapyrin (10 mg kg-1 soil). The addition of NO
inf3
sup-
retarded the nitrification of NH
inf4
sup+
-N derived from vetch. 相似文献
5.
Thiosulfate and CS2 inhibit nitrification. The effect of the addition of thiosulfate on the turnover of inorganic N compounds was tested in an Egyptian and a German arable soil under nitrifying and denitrifying conditions. For nitrification, the soils were amended with NH
inf4
sup+
and incubated under aerobic conditions. For denitrification, the soils were amended with NO
inf3
sup-
and incubated under anaerobic conditions. In both cases, the thiosulfate decreased with time while tetrathionate accumulated to an intermediate extent. Both compounds disappeared completely after <25 days. Production of CS2 was not observed. Carbonyl sulfide was produced only in the Egyptian soil, but production decreased with increasing amounts of added thiosulfate. Under nitrifying conditions, the addition of increasing amounts of thiosulfate (25, 50, and 100 g S g-1 dry weight) resulted in decreasing rates of NH
inf4
sup+
oxidation to NO
inf3
sup-
; it also resulted in an increasing intermediate accumulation of NO
inf2
sup-
and NO, and in an increasing production of N2O. Under denitrifying conditions, the addition of increasing amounts of thiosulfate did not significantly affect the rate of NO
inf3
sup-
reduction, and resulted in an increasing intermediate accumulation of NO
inf2
sup-
and of NO only in the German soil in which the production of N2O was slightly inhibited by thiosulfate. These results demonstrate that the nitrification of NH
inf4
sup+
and NO
inf2
sup-
was inhibited by increasing concentrations of thiosulfate and/or tetrathionate without involving the formation of volatile S compounds as potential nitrification inhibitors. Denitrification was not affected by the addition of thiosulfate. 相似文献
6.
Summary Recent developments in biotechnology industries produce increasing amounts of byproducts with potential uses in agriculture. The present research focused on the nitrification of NH
inf4
sup+
-N in biotechnology byproducts added to soils, and on the effects of 29 naturally occurring organic acids (19 aliphatic and 10 aromatic) on nitrification in soils. A 10-g soil sample was incubated for 10 days at 30°C with 2.0 mg NH
inf4
sup+
-N in a byproduct or with 10 or 50 mol organic acid and 2.0 mg reagent-grade NH
inf4
sup+
-N. In condensed molasses-fermentation solubles, produced during the microbial fermentation of sugar derived from corn (Zea mays L.) and molasses derived from beets (Beta sp.), in the production of lysine as a supplement in animal food, the nitrification of NH
inf4
sup+
-N was similar to that of byproduct or reagent-grade (NH4)2SO4. Nitrite accumulated when either of these materials was added to a calcareous Canisteo soil. The NH
inf4
sup+
-N in slops (produced during microbial fermentation processes occurring in the production of citric acid) was not nitrified in soils. Some organic acids inhibited, whereas others activated, nitrification in soils. Formic, acetic, and fumaric acids enhanced the production of NO
inf2
sup-
-N in a calcareous Canisteo soil, whereas all other aliphatic and aromatic acids studied decreased the accumulation of NO
inf2
sup-
-N. It is concluded that the addition or production of organic acids in soils affects the microbial dynamics, leading to significant changes in rates of nitrification and possibly in other N-transformation processes in soils. 相似文献
7.
Erythrina poeppigiana, a woody tropical plant, was inoculated with vesicular-arbuscular mycorrhizal (VAM) fungiGlomus etunicatum Becker and Gerdeman,G. mosseae Nicol. and Gerd. Gerdeman and Trappe, orG. intraradices Schenk and Smith. Growth, N uptake, and nutrition were evaluated in VAM-inoculated plants and controls fertilized with two levels (3 or 6 mM) of either NH
inf4
sup+
-N or NO
inf3
sup-
-N. The response by the mycorrhizal plants to N fertilization, according to N source and/or level differed significantly from that of the control plants. In general, the growth of the mycorrhizal plants was similar to that of the non-mycorrhizal plants when N was provided as NH
inf4
sup+
. When the N source was NO
inf3
sup-
the control plants grew significantly less than the VAM plants. Inoculation with VAM fungi gave yield increases of 255 and 268% forG. etunicatum-colonized plants, 201 and 164% forG. mosseae-colonized plants and 286 and 218% forG. intraradices-colonized plants fertilized with 3 and 6 mM NO
inf3
sup-
-N, respectively. The increased growth and acquisition of nutrients by plants fertilized with NO
inf3
sup-
-N and inoculated with VAM shows that VAM mycelium has a capacity for NO
inf3
sup-
absorption. The results also showed thatE. poeppigiana seedlings preferred NH
inf4
sup+
as an N source.G. etunicatum was the most effective endophyte, not only increasing N, P, Ca, Mg, and Zn uptake in the presence of NO
inf3
sup-
fertilizer but also P and Mg in the presence of NH
inf4
sup+
applications. From these results we conclude that VAM symbiosis affects N metabolism inE. poeppigiana plants and that this species can overcome limitations on the use of NO
inf3
sup-
-N by the mediation of VAM fungi. 相似文献
8.
The effects of wheat straw and different forms of N on denitrification and N immobilization were studied in an anaerobic water-sediment system. The water-sediment system was supplemented with various combinations of wheat straw and 15N-labelled and unlabelled (NH4)2SO4 or KNO3, and incubated anaerobically at 30°C for 10 days. 15N-labelled and unlabelled NO
inf3
sup-
, NO
inf2
sup-
, NH
inf4
sup+
, and organic N were determined in the water-sediment system. The gases evolved (N2, CO2, N2O, and CH4) were analyzed by gas chromatography at regular intervals. Larger quantities of 15N2–N and organic 15N were formed in wheat straw-amended systems than in non-amended systems. Trends in CO2 production were similar to those of N2–N evolution. The evolution of N2O and CH4 was negligible. Denitrification processes accounted for about 22 and 71% of the added 15NO
inf3
sup-
–N in the absence and presence of wheat straw, respectively. The corresponding denitrification rates were 3.4 and 12.4 g 15Ng-1 dry sediment day-1. In systems amended with 15NO
inf3
sup-
–N and 15NO
inf3
sup-
+NH
inf4
sup+
–N without wheat straw, 1.82 and 1.58%, respectively, of the added 15NH
inf3
sup-
–N was immobilized. The corresponding figures for the same systems supplemented with wheat straw were 5.08 and 4.10%, respectively. Immobilization of 15NO
inf4
sup+
–N was higher than that of 15NO
inf3
sup-
–N. The presence of NO
inf3
sup-
–N did not stimulate NH
inf4
sup+
–N immobilization. 相似文献
9.
We measured the growth, nutrition, and N assimilation of arbuscular-mycorrhizal and non-mycorrhizal lettuce (Lactuca sativa L.) as affected by forms of N and drought. Moisture was maintained at 80% water-holding capacity, and N was applied as NO
inf3
sup-
, NH
inf4
sup+
, or NO
inf3
sup-
/NH
inf4
sup+
(3:1, 1:1, or 1:3). The growth of Glomus fasciculatum-colonized plants was comparable to that of uncolonized P-supplemented plants when N was provided as NH
inf4
sup+
or combined NO
inf3
sup-
/NH
inf4
sup+
. When N was supplied solely as NO
inf3
sup-
, G. fasciculatum-colonized plants produced a higher yield than P-fertilized plants, suggesting that the uptake and/or assimilation of NO
inf3
sup-
was particularly affected by mycorrhizal status in this water-limited situation. Nutrient availability, except Ca, was less limited for mycorrhizal plants than for P-fertilized plants. P fertilization increased the growth, glutamine synthetase activity, and protein content of lettuce to the same extent that G. fasciculatum colonization did when N was applied as NH
inf4
sup+
. With NO
inf3
sup-
-fertilization, G. fasciculatum-colonized plants showed increased growth, nitrate reductase activity, and protein content compared to P-fertilizer treatment. Plants colonized by G. mosseae showed increased photosynthetic activity and proline acumulation, and these mechanisms may be important in adaptation by the plant to drought conditions. The present results confirmed that under drought conditions, the uptake or metabolism of N forms is particularly affected in mycorrhizal fungi-colonized plants, depending on the mycorrhizal endophyte and the N source added. Thus the significance of arbuscular-mycorrhizal fungus selection for plant growth in drought conditions is a consideration for management strategy. 相似文献
10.
A field experiment was conducted to investigate the effects of 1,2,3,4,5,6-hexachlorocyclohexane (BHC), phorate, carbofuran, and fenvalerate, at their recommended doses, on some chemical and microbiological properties of the rhizosphere soil in relation to rice yields. In general, the insecticides had a beneficial effect on rhizosphere soil properties. Carbofuran strongly stimulated the mineralization of organic C. BHC and phorate led to the retention of less total N in the soil. BHC released more NH
inf4
sup+
-N than the other insecticides. Phorate, however, liberated the most NO
inf3
sup-
-N. Phorate and fenvalerate released more available P than BHC and carbofuran did. All the insecticides stimulated the proliferation of aerobic non-symbiotic N2-fixing and phosphate-solubilizing microorganisms, resulting in an overall increase in rice yield. BHC had the greatest effect on rice yields, followed by phorate. 相似文献
11.
Summary Gross rates of N mineralization, assimilation, nitrification, and NO
in3
sup-
reduction were determined in soil from a wet riparian fen by 1-day incubations of soil cores and slurries with 15N-labelled substrates. N mineralization transformed 0.1% of the total organic N pool daily in the soil cores, of which 25% was oxidized through autotrophic nitrification and 53%–70% was incorporated into microorganisms. N mineralization and nitrification were markedly inhibited below 5 cm in soil depth. At least 80% of the NO
in3
sup-
reduction in aerated cores occurred through dissimilatory processes. Dissimilatory reduction to NH
in4
sup+
(DNRA) occurred only below 5 cm in depth. The results show that NH
in4
sup+
oxidation was limited by available substrate and was itself a strong regulator of NO
in3
sup-
-reducing activity. NO
in3
sup-
reduction was significantly increased when the soil was suspended under anaerobiosis; adding glucose to the soil slurries increased NO
in3
sup-
reduction by 2.4–3.7 times. Between 3% and 9% (net) of the added NO
in3
sup-
was reduced through DNRA in the soil slurries. The highest percentage was observed in soil samples from deeper layers that were pre-incubated anaerobically. 相似文献
12.
Hyphal transport by a vesicular-arbuscular mycorrhizal fungus of N applied to the soil as ammonium or nitrate 总被引:6,自引:0,他引:6
Summary Transport of N by hyphae of a vesicular-arbuscular mycorrhizal fungus was studied under controlled experimental conditions. The N source was applied to the soil as 15NH
inf4
sup+
or 15NO
inf3
sup-
. Cucumis sativus was grown for 25 days, either alone or in symbiosis with Glomus intraradices, in containers with a hyphal compartment separated from the root compartment by a fine nylon mesh. Mineral N was then applied to the hyphal compartment as 15NH
inf4
sup+
or 15NO
inf3
sup-
at 5 cm distance from the root compartment. Soil samples were taken from the hyphal compartment at 1, 3 and 5 cm distance from the root compartment at 7 and 12 days after labelling, and the concentration of mineral N in the samples was measured from 2 M KCl extracts. Mycorrhizal colonization did not affect plant dry weight. The recovery of 15N in mycorrhizal plants was 38 or 40%, respectively, when 15NH
inf4
sup+
or 15NO
inf3
sup-
was applied. The corresponding values for non-mycorrhizal plants were 7 and 16%. The higher 15N recovery observed in mycorrhizal plants than in non-mycorrhizal plants suggests that hyphal transport of N from the applied 15N sources towards the host plant had occurred. The concentration of mineral N in the soil of hyphal compartments was considerably less in mycorrhizal treatments than in controls, indicating that the hyphae were able to deplete the soil for mineral N. 相似文献
13.
A pot experiment was conducted to compare the uptake and dry matter production potential of NH
inf4
sup+
and NO
inf3
sup-
and to study the effect of Baythroid, a contact poison for several insect pests of agricultural crops, on growth and N uptake of maize (Zea mays L.). Nitrogen was applied as (15NH4)2SO4, K15NO3, or 15NH4NO3 and in one treatment Baythroid was combined with 15NH4NO3. Source of N had, in general, a nonsignificant effect on dry matter and N yield, but uptake of NO
inf3
sup-
was significantly higher than that of NH
inf4
sup+
when both N sources were applied together. Substantial loss of N occurred from both the sources, with NH
inf4
sup+
showing greater losses. Baythroid was found to have a significant positive effect on dry matter yield of both root and shoot; N yield also increased significantly. Uptake of N from both the applied and native sources increased significantly in the presence of Baythroid and a substantial added nitrogen interaction (ANI) was determined. The positive effect of Baythroid was attributed to: (1) a prolonged availability of NH
inf4
sup+
due to inhibition of nitrification, (2) an increased availability of native soil N through enhanced mineralization, and (3) an enhanced root proliferation. 相似文献
14.
Summary In model experiments with a silty loam soil the effect of different C : NO
inf3
sup-
-N ratios on the reliability of C2H2 (1% v/v) in blocking N2O-reductase activity was examined. The soil was carefully mixed with different amounts of powdered lime leaves (Tilia vulgaris) to obtain organic C contents of about 1.8, 2.3, and 2.8%, and of NO
inf3
sup-
solution to give C : NO
inf3
sup-
-N ratios of 84, 107, 130, 156, 200, and 243. The soil samples were incubated in specially modified anaerobic jars (22 days, 25°C, 80% water-holding capacity, He atmosphere) and the atmosphere was analysed for N2, N2O, CO2, and C2H2 by gas chromatography at regular intervals. Destruction jars were used to analyse soil NO
inf3
sup-
, NH
4
+
and C. The results clearly showed that N2O-reductase activity was completely blocked by 1% (v/v) C2H2 only as long as NO
inf3
sup-
was present. In the presence of C2H2, NO
inf3
sup-
was apparently entirely converted into N2O. The C2H2 blockage of N2O-reductase activity ceased earlier in soils with a wide C : NO
inf3
sup-
-N ratio (156, 200, and 243) than in those with closer C : NO
inf3
sup-
-N ratios (84, 107, and 130). As soon as NO
inf3
sup-
was exhausted, N2O was reduced to N2 in spite of C2H2. The wider the C : NO
inf3
sup-
-N ratio, the earlier the production of N2 and the less the reliability of the C2H2 blockage. In the untreated control complete inhibition of N2O-reductase activity by C2H2 lasted for 7–12 days. In the field, estimates of total denitrification losses by the C2H2 inhibition technique should be considered reliable only as long as NO
inf3
sup-
is present. Consequently, NO
inf3
sup-
monitoring in the field is essential, particularly in soils supplied with easily decomposable organic matter. 相似文献
15.
Preservation of nitrifying capacity and nitrate availability in waterlogged soils by radial oxygen loss from roots of wetland plants 总被引:4,自引:0,他引:4
W. M. H. G. Engelaar J. C. Symens H. J. Laanbroek C. W. P. M. Blom 《Biology and Fertility of Soils》1995,20(4):243-248
The effects of radial O2 loss from roots on nitrification and NO
inf3
sup-
availability were studied. Plants of the flooding-resistant species Rumex palustris and the flooding-sensitive species Rumex thyrsiflorus were grown on drained and waterlogged soils with an initially high nitrifying capacity. Nitrate reductase activity in the plant leaves was used as an indicator of NO
inf3
sup-
availability to the plants. In a separate experiment these species were shown to have higher levels of nitrate reductase activity when NO
inf3
sup-
was added to the soils compared to when only NH
inf4
sup+
was provided. In drained soils nitrification was maintained and both plant species showed relatively high nitrate reductase activities in their leaves. In the water-logged series planted with R. thyrsiflorus, nitrification was inhibited, NH
inf4
sup+
accumulated, and the plants grew less well compared to those on drained soils. In contrast, waterlogged soils planted with R. palustris had a redox potential high enough for O2 to be continuously replenished. Furthermore, the nitrifying capacity of these latter soils was maintained at a high level. R. palustris grew well and NO
inf3
sup-
must have been available to the plant, since a high level of nitrate reductase activity was observed in the leaves. 相似文献
16.
Summary Denitrification (using the acetylene block method) was determined in earthworm casts and soils from permanent, drained or undrained pasture plots fertilized with 0 or 200 kg N ha-1 year-1 as ammonium nitrate. Rates of N2O production from soil cores were about three times higher from the fertilized than from the unfertilized plots while drainage had a relatively small effect. Denitrification rates from casts were 3–5 times higher than those from soil irrespective of the drainage treatment. Casts generally had higher NO
inf3
sup-
, NH
inf4
sup+
, and moisture contents, and higher microbial respiration rates than soil. Rates of N2O production were determined primarily by NO
inf3
sup-
supply, secondarily by moisture; available C did not appear to limit denitrification in these pastures. Estimates of the potential contribution of casts to denitrification ranges from 10.1% of 29.3 kg ha-1 year-1 from the unfertilized, drained plot to 22% of 82.5 kg ha-1 year-1 from the fertilized undrained plot. 相似文献
17.
Effects of soil variables and season on the production and consumption of nitric oxide in oxic soils 总被引:2,自引:0,他引:2
Summary NO production rates, NO uptake rate constants, NO compensation points, and different soil variables were determined for various soil types and different soil horizons, and checked for mutual correlations. NO production was detected in all, and NO comsuption in most soils tested. Only soils in a very early state of soil genesis showed no NO consumption activity. NO consumption was positively correlated with soil water and NH
4
+
contents. NO production rates were not correlated with any soil variable. Both NO production and NO consumption tended to decrease from the upper organic to the deeper mineral horizons in different climax soils. The seasonal variation of NO production and NO consumption in a calcic cambisol and a luvisol showed highest rates in summer. The rates of NO production and NO consumption were correlated with a few of the soil variables, but showed no uniform, theoretically comprehensible pattern. However, NO production in samples of the calcic cambisol was stimulated by fertilization with NH
4
+
, but not with NO
3
–
and was inhibited by nitrapyrin, indicating that NO was produced by nitrification. NO production made up about 3% of the nitrification rates. In the luvisol, in contrast, NO production was not affected by the addition of NH
4
+
or NO
3
–
. Nitrification was also undetectable in this acidic soil, except for a few patches where NO production was also detected. 相似文献
18.
Seventeen strains of Rhizobium leguminosarum biovar viceae specific to the lentil (Lens culinaris L.) were screened, using the high-yielding lentil cultivar L 4076, for their tolerance to three levels of NO
inf3
sup-
: 0, 4, and 8 mM NO
inf3
sup-
. Preliminary screening of this symbiosis for nodulation and N fixation in the presence of NO
inf3
sup-
showed significant variations among the strains. The number of nodules decreased and nitrogenase activity was depressed in all strains in the presence of NO
inf3
sup-
. Strains L-1-87, L-27-89, L-33-89, and L-40-89 tolerated 8 mM NO
inf3
sup-
. Four strains, three tolerant of NO
inf3
sup-
(L-1-87, L-27-89, and L-33-89), and one sensitive (L-11-89) to NO
inf3
sup-
, were selected from preliminary screening and used in a pot experiment to assess the symbiosis in the presence of 6 mM NO
inf3
sup-
at three stages of plant growth, viz., 40 days, 60 days, and at the final harvest. In general, the weight of nodules and C2H2 reduction activity was significantly higher after 60 days than after 40 days. Inoculation with strain L-1-87 produced the maximum number of nodules, and root and shoot biomass both in the presence and the absence of NO
inf3
sup-
. Nitrate reductase activity in the tops and nodules was assayed only after 60 days and did not show significant variations among strains and NO
inf3
sup-
treatments. The grain yields for all strains except L-11-89 were significantly higher in the presence of NO
inf3
sup-
than in the absence of NO
inf3
sup-
, indicating that tolerant strains contributed symbiotically fixed N to the plant's N pool, resulting in an additive effect on yield. Inoculation with strain L-1-87 produced the maximum grain yield and this strain appears to have potential use as an inoculant in the presence of high levels of soil N. 相似文献
19.
Potential variation of nitrogen transformations in pinyon-juniper ecosystems resulting from burning 总被引:3,自引:0,他引:3
Summary Forest floor litter, duff, and underlying soils were assembled in laboratory microcosms representing pinyon, juniper, and interspace field conditions. Burning removed more than 95% of both N and C from the litter, with losses from the duff dependent on soil moisture conditions. No significant changes in total N or C were noted in the soil. Immediate increases were observed in soil NH
inf4
sup+
, decreasing with depth and related to soil heating. The greatest increases were noted in both the pinyon and juniper soils that were dry at the time of the burn, with interspace soils exhibiting the least changes. Soil NH
inf4
sup+
closely approximated the controls on day 90 after the burns in all treatments. Ninety days after the burn microbial biomass N was highest in the controls, followed by the wet and then the dry-burned soils, in both the pinyon and juniper microcosms. This was inversely related to the levels of accumulated NO
inf3
sup-
. Nitrifying bacteria populations were indirectly correlated to soil temperatures during the burn. Population levels 90 days after the burn showed increases in both the wet- and the dry-burn treatments, with those in the pinyon treatments exceeding those found in the nitial controls of pinyon soils.The use of trade and company names in this paper is for the benefit of the reader; such use does not constitute an official endorsement or approval of any service or product by the U.S. Department of Agriculture to the exclusion of others that may be suitable 相似文献
20.
To estimate the availability of nonexchangeable NH
inf4
sup+
–N for soil microorganisms four incubation experiments were conducted under controlled conditions. The following results were obtained: Incorporating glucose as a source of readily oxidizable organic material favored the release of nonexchangeable NH
inf4
sup+
–N. Mobilization of NH
inf4
sup+
from the interlayers of the clay minerals was decreased by the application of K++, while Ca2+, which is supposed to expand the lattice of the clay minerals, had no influence on the release of NH
inf4
sup+
. Soil temperature had no effect on microbiological mobilization of NH
inf4
sup+
. It is assumed that, generally, the influence of nitrifying bacteria on the mobilization of nonexchangeable NH
inf4
sup+
–N is negligible. However, in soils with abundant amounts of available carbon promoting the activity of heterotrophic soil microorganisms, the release of NH
inf4
sup+
from clay minerals is favored under fallow conditions. 相似文献