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1.
Transformation of calcium cyanamide and its inhibitory effect on urea nitrification in some tropical soils 总被引:1,自引:0,他引:1
Transformation of calcium cyanamide and its inhibitory effect on urea nitrification was studied in some tropical soils. Three soils, from Onne, Mokwa and Samaru, representing different agro-climatological zones of Nigeria were incubated with calcium cyanamide, urea or a mixture of both for eight weeks at 30 °C and at field capacity moisture content. The recovery of inorganic N (NH
4
+
plus NO
2
-
plus NO
3
-
)from calcium cyanamide varied from 64% to 87% in different soils. Most of the inorganic N accumulated was in NH
4
+
form. Nitrification of the accumulated NH
4
+
in all the soils was slow.Urea (75 mg N kg–1 soil) was completely nitrified within a week in the Samaru and Mokwa soils whereas in the Onne soil the rate of nitrification was slow. Addition of CaCN2 at the rate of 10 mg N kg–1 soil generally delayed ammonification of urea and nitrification was severely inhibited in all the soils. Addition of CaCN2 at the rate of 20 mg N kg–1 soil further reduced the ammonification of urea and completely inhibited the nitrification. High recovery of inorganic N from calcium cyanamide and its effective reduction of nitrification of urea make it suitable source of N for plants in the tropics, provided it is managed to avoid phyto-toxicity. 相似文献
2.
Fredericka M. Deare N. Ahmad T. U. Ferguson 《Nutrient Cycling in Agroecosystems》1995,42(1-3):175-184
Three field trials were conducted in the early and late rainy season on a Piarco Series soil (Aquoxic Tropudults) in Central Trinidad to monitor downward movement of NH
4
+
-N and NO
3
-
-N under flat-tilled and ridge-tilled conditions as affected by mulch application. The first experiment was carried out in the early rainy season under bare-fallowed conditions, while okra (Abelmoschus esculentus) was the test crop used in the two remaining trials, which were conducted during the early and late rainy season periods. The plots were fertilized with urea seven days after crop emergence and 14 days after land preparation for the cropped and bare-fallowed experiments respectively. Soil samples were collected weekly after fertilizer application and analyzed for NH
4
+
-N, NO
3
-
-N and soil water.Urea application increased NH
4
+
-N levels in the soil and NH
4
+
-N was the dominant inorganic N form observed for the first four weeks after fertilization. Mulch application decreased NH
4
+
-N and NO
3
-
-N soil levels. Ridging the soil increased downward movement of NH
4
+
-N and NO
3
-
-N. Under bare-fallowed conditions, downward movement of NH
4
+
-N was noted in the 30 to 45 cm soil layer at seven days after fertilization, while under cropped conditions its movement was restricted to the 15 to 30 cm layer within the same period. In bare-fallowed soil, increased NO
3
-
-N and its downward movement was noted after four weeks of fertilization. In the cropped soil, downward movement of NO
3
-
-N was observed one week after fertilization in the early rainy season and three weeks after fertilization in the late rainy season. 相似文献
3.
Nitrogen movement and uptake by rice fertilized with urea supergranules in two contrasting Mollisols
In a glasshouse experiment, the periodic movement, loss and uptake of N by lowland rice fertilized with point-placed urea supergranule (USG) was studied in two soils differing in texture. Movement of urea-N, NH
4
+
-N and NO
3
-
-N was significantly faster in Patharchatta sandy loam (Typic Hapludoll) than in Beni silty clay loam (Aquic Hapludoll) and was mostly downward with peak concentration near the placement site.Nitrogen in leachate was higher in Patharchatta sandy loam than in Beni silty clay loam. About 60–70% of leaching of urea-N took place within 2 days of USG placement. The leaching of NH
4
+
-N and NO
3
-
-N increased till 14 and 21 days of USG placement in Patharchatta sandy loam and Beni silty clay loam, respectively. Nitrogen leached through urea, NH
4
+
and NO
3
-
forms was, respectively, 64, 25 and 25% higher from sandy loam. During 49 days, 49 and 32% of the applied N was recovered by rice plants from silty clay loam and sandy loam, respectively. 相似文献
4.
A laboratory incubation experiment was conducted to gain a better understanding of N transformations which occur near large urea granules in soil and the effects of dicyandiamide (DCD), nitrifier activity and liming. Soil cores containing a layer of urea were used to provide a one-dimensional approach and to facilitate sampling. A uniform layer of 2 g urea or urea + DCD was placed in the centre of a 20 cm-long soil core within PVC tubing. DCD was mixed with urea powder at 50 mg kg–1 urea and enrichment of soil with nitrifiers was accomplished by preincubating Conestogo silt loam with 50 mg NH
4
+
-N kg–1 soil. Brookston clay (pH 5.7) was limited with CaCO3 to increase the pH to 7.3. The cores were incubated at 15°C and, after periods of 10, 20, 35 and 45 days, were separated into 1-cm sections. The distribution of N species was similar on each side of the urea layer at each sampling. The pH and NH
4
+
(NH3) concentration were very high near the urea layer but decreased sharply with distance from it. DCD did not influence urea hydrolysis significantly. Liming of Brookston clay increased urea hydrolysis. The rate of urea hydrolysis was greater in Conestogo silt loam than limed Brookston clay. Nitrite accumulate was relatively small with all the treatments and occurred near the urea layer (0–4 cm) where pH and NH
4
+
(NH3) concentration were high. The nitrification occurred in the zone where NH
4
+
(NH3) concentration was below 1000µgN g–1 and soil pH was below 8.0 and 8.7 in Brookston and Conestogo soils, respectively. DCD reduced the nitrifier activity (NA) in soil thereby markedly inhibiting nitrification of NH
4
+
. Nitrification was increased significantly with liming of the Brookston soil or nitrifier enrichment of the Conestogo soil. There was a significant increase in NA during the nitrification of urea-N. The (NO
2
–
+ NO
3
–
)-N concentration peaks coincided with the NA peaks in the soil cores.A practical implication of this work is that large urea granules will not necessarily result in NO
2
–
phytotoxicity when applied near plants. A placement depth of about 5 cm below the soil surface may preclude NH3 loss from large urea granules. DCD is a potential nitrification inhibitor for use with large urea granules or small urea granules placed in nests. 相似文献
5.
Nitrogen uptake from non-exchangeable NH
4
+
byLolium multiflorum and availability of fertilizer NH
4
+
and fertilizer NO
3
-
were studied in pot experiments with three different soil types. The luvisol derived from loess released considerable amounts of non-exchangeable NH
4
+
when cropped. In this soil fertilizer NH
4
+
was only weakly fixed and was as available to the crop as fertilizer NO
3
-
. The recovery of fertilizer NH
4
+
was even higher than the recovery of fertilizer NO
3
-
. In the fluvisol (alluvial soil) and in the cambisol (brown earth from basalt) N recovery was higher from NO
3
-
fertilizer than from NH
4
+
fertilizer. In these soils NH
4
+
fertilizer was strongly fixed by 2:1 clay minerals and thus less available to the grass. Particularly in the basaltic soil the content of non-exchangeable NH
4
+
was low and so was the release of nonexchangeable NH
4
+
. At the same time this soil showed the strongest fixation of fertilizer NH
4
+
. Release and refixation of fertilizer NH
4
+
in the loess soil appears to be an important feature of this soil type with a beneficial effect on soil nitrogen turnover and availability. 相似文献
6.
Nitrous oxide can be produced during nitrification, denitrification, dissimilatory reduction of NO
3
-
to NH
4
+
and chemo-denitrification. Since soils are a mosaic of aerobic and anaerobic zones, it is likely that multiple processes are contributing simultaneously to N2O production in a soil profile. The N2O produced by all processes may mix to form one pool before being reduced to N2 by denitrification. Reliable methods are needed for measuring the fluxes of N2O and N2 simultaneously from agricultural soils. The C2H2 inhibition and 15N gas-flux methods are suitable for use in undisturbed soils in the field. The main disadvantage of C2H2 is that as well as blocking N2O reductase, it also blocks nitrification and dissimilatory reduction of NO
3
-
to NH
4
+
. Potentially the 15 N gas-flux method can give reliable measurements of the fluxes of N2O and N2 when all N transformation processes proceed naturally. The analysis of 15N in N2 and N2O is now fully automated by continuous-flow isotope-ratio mass spectrometry for 12-ml gas samples contained in septum-capped vials. Depending on the methodology, the limit of detection ranges from 4 to 11 g N ha-1day-1 for N2 and 4 to 15 g N ha-1day-1 for N2O. By measuring the 15N content and distribution of 15N atoms in the N2O molecules, information can also be obtained to help diagnose the sources of N2O and the processes producing it. Only a limited number of field studies have been done using the 15N gas-flux method on agricultural soils. The measured flux rates and mole fractions of N2O have been highly variable. In rain-fed agricultural soils, soil temperature and water-filled pore space change with the weather and so are difficult to modify. Soil organic C, NO
3
-
and pH should be amenable to more control. The effect of organic C depends on the degree of anaerobiosis generated as a result of its metabolism. If conditions for denitrification are not limiting, split applications of organic C will produce more N2O than a single application because of the time lag in the synthesis of N2O reductase. Increasing the NO
3
-
concentration above the K
m value for NO
3
-
reductase, or decreasing soil pH from 7 to 5, will have little effect on denitrification rate but will increase the mole fraction of N2O. The effect of NO
3
-
concentration on the mole fraction of N2O is enhanced at low pH. Manipulating the interaction between NO
3
-
supply and soil pH offers the best hope for minimising N2O and N2 fluxes. 相似文献
7.
The clearing of tropical rain forest in the Amazon basin has created large areas of cattle pasture that are now declining in productivity. Practices adopted by ranchers to restore productivity to degraded pastures have the potential to alter soil N availability and gaseous N losses from soils. We examined how soil inorganic N pools, net N mineralization and net nitrification rates, nitrification potential and NO and N2O emissions from soils of a degraded pasture responded to the following restoration treatments: (1) soil tillage followed by replanting of grass and fertilization, (2) no-till application of non-selective herbicide, planting of rice, harvest followed by no-till replanting of grass and fertilization, and (3) the same no-till sequence with soybeans instead of rice. Tillage increased soil NH4+ and NO3? pools but NH4+ and NO3? pools remained relatively constant in the control and no-till treatments. Cumulative rates of net N mineralization and net nitrification during the first 6 months after treatment varied widely but were hightest in the tilled treatment. Emissions of NO and N2O fluxes increased with tillage and with N fertilization. There were no clear relationships among rates of N fertilizer application, net N mineralization, net nitrification, NO, N2O and total N oxide emissions. Our results indicate that pasture restoration sequences involving tilling and fertilizing will increase emissions of N oxides, but the magnitude of the increase is likely to differ based on timing of fertilizer application relative to the presence of plants and the magnitude of plant N demand. Emissions of N oxides appear to be decreased by the use of restoration sequences that minimize reductions in pasture grass cover. 相似文献
8.
D. C. Ditsch M. M. Alley K. R. Kelley Y. Z. Lei 《Nutrient Cycling in Agroecosystems》1992,31(3):355-362
Use of15N-depleted fertilizer materials have been primarily limited to fertilizer recovery studies of short duration. The objective of this study was to determine if15N-depleted fertilizer N could be satisfactorily used as a tracer of residual fertilizer N in plant tissue and various soil N fractions through a corn (Zea mays L.) -winter rye (Secale cereale L.) crop rotation. Nitrogen as15N-depleted (NH4)2SO4 was applied at five rates (0, 84, 168, 252, and 336 kg N ha–1) to corn. Immediately following corn harvest a winter rye cover crop treatment was initiated. Residual fertilizer N was easily detected in the soil NO
3
-
-N fraction following corn harvest (140-d after application). Low levels of exchangeable NH
4
+
-N (<2.5 mg kg–1) did not permit accurate isotope-ratio analysis. Fertilizer-derived N recovered in the soil total N fraction following corn harvest was detectable in the 0 to 30-cm depth at each N rate and in the 30 to 60 and 60 to 90-cm depths at the 336 kg ha–1 N rate. Atom %15N concentrations in the nonexchangeable NH
4
+
-N fraction did not differ from the control at each N rate. Nitrogen recovery by the winter rye cover crop reduced residual soil NO
3
-
-N levels below the 10 kg ha–1 level needed for accurate isotope-ratio analysis. Atom %15N concentrations in the soil total N fraction (approximately one yr after application) were indistinguishable from the control plots below the 168, 252, and 336 kg ha–1 N rate at the 0 to 30, 30 to 60, and 60 to 90-cm depths, respectively. Recovery of residual fertilizer N by the winter rye cover crop was verified by measuring significant decreases in atom %15N concentrations in rye tissue with increasing N rates. The greatest limitation to the use of15N-depleted fertilizer N as a tracer of residual fertilizer N in a corn-rye crop rotation appears to be its detectibility from native soil N in the total N pool.Research partially supported by grants from the National Fertilizer and Environmental Research Center/TVA and the Virginia Division of Soil and Water Conservation. 相似文献
9.
G. L. Velthof O. Oenema R. Postma M. L. Van Beusichem 《Nutrient Cycling in Agroecosystems》1996,46(3):257-267
Five field experiments and one greenhouse experiment were carried out to assess the effects of nitrogen (N) fertilizer type and the amount of applied N fertilizer on nitrous oxide (N2O) emission from grassland. During cold and dry conditions in early spring, emission of N2O from both ammonium (NH
4
+
) and nitrate (NO
3
–
) containing fertilizers applied to a clay soil were relatively small, i.e. less than 0.1% of the N applied. Emission of N2O and total denitrification losses from NO
3
–
containing fertilizers were large after application to a poorly drained sand soil during a wet spring. A total of 5–12% and 8–14% of the applied N was lost as N2O and via denitrification, respectively. Emissions of N2O and total denitrification losses from NH
4
+
fertilizers and cattle slurry were less than 2% of the N applied. Addition of the nitrification inhibitor dicyandiamide (DCD) reduced N2O fluxes from ammonium sulphate (AS). However, the effect of DCD to reduce total N2O emission from AS was much smaller than the effect of using NH
4
+
fertilizer instead of NO
3
–
fertilizer, during wet conditions. The greenhouse study showed that a high groundwater level favors production of N2O from NO
3
–
fertilizers but not from NH
4
+
fertilizers. Inereasing calcium ammonium nitrate (CAN) application increased the emitted N2O on grassland from 0.6% of the fertilizer application rate for a dressing of 50 kg N ha–1 to 3.1% for a dressing of 300 kg N ha–1. In another experiment, N2O emission increased proportionally with increasing N rate. The results indicate that there is scope for reducing N2O emission from grasslands by choosing the N fertilizer type depending on the soil moisture status. Avoiding excessive N application rates may also minimize N2O emission from intensively managed grasslands. 相似文献
10.
Nitrification inhibitors such a dicyandiamide (DCD) help to reduce leaching losses by retaining applied N in the ammoniacal form. Research objectives were to evaluate dicyandiamide added to ammonium sulphate-nitrate (ASN) as a nitrification inhibitor in cultivated soils (Xeropsamments) and its effect on N uptake by citrus (Citrus sinensis (L.) Osbeck). Under field conditions, fertilization of adult trees with ASN (600 g N tree–1) either with or without DCD (2% DCD-N) was compared (ASN+DCD and ASN, respectively). The NH
4
+
-N concentrations in plots fertilized with ASN+DCD were significantly higher than ASN plot in the 0-15 cm layer during 5–105 day period. Nitrification started immediately after N application in both treatments (ASN and ASN+DCD). In all three soil layers analyzed, NO–
3-N concentrations were higher in the ASN plots than in the ASN+DCD during the first 20 days. This indicates that nitrification of NH+
4 from ASN was more rapid in the absence of DCD. On the other hand, fertilization with ASN+DCD kept higher levels of NO–
3-N in soils than ASN during the rest of experience period (40–160 days). Addition of DCD to ASN showed a higher N concentration in the spring-flush leaves with respect to the trees fertilized with ASN, during the growth cycle. These results suggest that the use of a nitrification inhibitor permitted a more efficient utilization of fertilizer N by citrus trees. The plants treated with DCD added to ASN showed a higher yield in number of units per tree and a better fruit colour index than those treated with ASN alone. 相似文献
11.
Christopher Neill Paul A. Steudler Diana C. Garcia-Montiel Jerry M. Melillo Brigitte J. Feigl Marisa C. Piccolo Carlos C. Cerri 《Nutrient Cycling in Agroecosystems》2005,71(1):1-15
Tropical soils are important sources of nitrous oxide (N2O) and nitric oxide (NO) emissions from the Earths terrestrial ecosystems. Clearing of tropical rainforest for pasture has the potential to alter N2O and NO emissions from soils by altering moisture, nitrogen supply or other factors that control N oxide production. In this review we report annual rates of N2O and NO emissions from forest and pastures of different ages in the western Brazilian Amazon state of Rondônia and examine how forest clearing alters the major controls of N oxide production. Forests had annual N2O emissions of 1.7 to 4.3 kg N ha-1 y-1 and annual NO emissions of 1.4 kg N ha-1 y-1. Young pastures of 1–3 years old had higher N2O emissions than the original forest (3.1–5.1 kg N ha-1 y-1) but older pastures of 6 years or more had lower emissions (0.1 to 0.4 kg N ha-1 y-1). Both soil moisture and indices of soil N cycling were relatively poor predictors of N2O, NO and combined N2O + NO emissions. In forest, high N2O emissions occurred at soil moistures above 30 water-filled pore space, while NO emissions occurred at all measured soil moistures (18–43). In pastures, low N availability led to low N2O and NO emissions across the entire range of soil moistures. Based on these patterns and results of field fertilization experiments, we concluded that: (1) nitrification was the source of NO from forest soils, (2) denitrification was not a major source of N2O production from forest soils or was not limited by NO- supply, (3) denitrification was a major source of N2O production from pasture soils but only when NO3- was available, and (4) nitrification was not a major source of 3 NO production in pasture soils. Pulse wettings after prolonged dry periods increased N2O and NO3- emissions for only short periods and not enough to appreciably affect annual emission rates. We project that Basin-wide, the effect of clearing for pasture in the future will be a small reduction in total N2O emissions if the extensive pastures of the Amazon continue to be managed in a way similar to current practices. In the future, both N2Oand NO fluxes could increase if uses of pastures change to include greater use of N fertilizers or N-fixing crops. Predicting the consequences of these changes for N oxide production will require an understanding of how the processes of nitrification and denitrification interact with soil type and regional moisture regimes to control N2O and NO production from these new anthropogenic N sources. 相似文献
12.
Zucong Cai 《Nutrient Cycling in Agroecosystems》2002,63(2-3):267-274
Coupled nitrification and denitrification is considered as one of the main pathways of nitrogen losses in paddy soils. The effect of NO3
– on NH4
+ transformation was investigated by using the 15N technique. The paddy soils were collected from Wuxi (soil pH 5.84) and Yingtan (soil pH 5.02), China. The soils were added with either urea (18.57 mol urea-N enriched with 60 atom% 15N excess) plus 2.14 mol KNO3-N (natural abundance) per gram soil (U+NO3) or urea alone (U). The KNO3 was added 6 days after urea addition. The incubation was carried out under flooded condition in either air or N2 gas headspace at 25°C. The results showed that in air headspace, 15NH4
+ oxidization was so fast that about 10% and 8% of added 15N in the treatment U could be oxidized during the incubation period of 73 hours after KNO3 addition in Wuxi and Yingtan soil, respectively. The addition of KNO3 significantly inhibited 15NH4
+ oxidation (p<0.01) in air headspace, while it stimulated 15NH4
+ oxidation in N2 gas headspace, although the oxidation was depressed by the N2 gas headspace itself. Therefore, the accumulation of NO3
– would inhibit further nitrification of NH4
+ at micro-aerobic sites in paddy soils, especially in paddy soils with a low denitrification rate. On the other hand, NO3
– would lead to oxidation of NH4
+in anaerobic bulk soils. 相似文献
13.
Nitrification and sludge characteristics in a submerged membrane bioreactor on synthetic inorganic wastewater 总被引:2,自引:0,他引:2
A submerged membrane bioreactor (SMBR) treating ammonia-bearing synthetic inorganic wastewater withoutsludge purge was studied in respect to nitrification and microbial parameters over a period of 210 days. The reactor was operated at a hydraulic retention time (HRT) of 24 h, and the NH4-N volumetric loading rate increased from 0.18 to 1.30 kg NH4+-N m−3d−1 by increasing influent NH4+-N from 180 mg/l−1 to 1300 mg/l−1. With the exception of a short period after the failure of pH control, the NH4+-N+ removal rate, was constantly above 99%. Due to the influent characteristics and the interception of the membrane module, the mixed liquor suspended solids (MLSS) varied from 3000 to 5000 mg/l−1 and the nitrifying bacteria were dominant in the SMBR. The numbers of ammonia oxidizers and nitrite oxidizers in the mixed liquor increased from 0.9×108 ml−1 and 1.0×108 ml to 1.6×108 ml−1 and 9×108 ml−1 respectively, and the specific nitrification rate from 0.27 to 0.56 g NH4+-N g−1 SS−1 d−1. An increasing occurrence of extracellular polymeric substances (EPS) around microbial clusters with operation time was clearly observed on scanning electron micrographs (SEM). The pressure difference of the membrane module was not over 0.01 mPa over the whole operation period. Present results show that SMBR can be operated efficiently and stably as a high-rate nitrifying technology. 相似文献
14.
Iain P. McTaggart Hiroko Akiyama Haruo Tsuruta Bruce C. Ball 《Nutrient Cycling in Agroecosystems》2002,63(2-3):207-217
In Japan, upland soils are an important source of nitrous oxide (N2O) and nitric oxide (NO) gas emissions. This paper reports on an investigation of the effect of soil moisture near saturation on N2O and NO emission rates from four upland soils in Japan of contrasting texture. The aim was to relate these effects to soil physical properties. Intact cores of each soil type were incubated in the laboratory at different moisture tensions after fertilisation with NH4-N, NO3-N or zero N. Emissions of N2O and NO were measured regularly over a 16–20 day period. At the end of the incubation, soil cores were analysed for physical properties. Moisture and N fertiliser significantly affected rates of emissions of both N2O and NO with large differences between the soil types. Nitrous oxide emissions were greatest in the finer-textured soils, whereas NO emissions were greater in the coarser-textured soils. Emissions of N2O increased at higher moisture contents in all soils, but the magnitude of increase was much greater in finer-textured soils. Nitric oxide emissions were only significant in soils fertilised with NH4-N and were negatively correlated with soil moisture. Analysis of soil properties showed that there was a strong relationship between the magnitude of emissions and soil physical properties. The importance of soil wetness to gas emissions was mainly through its influence on soil air-filled porosity, which itself was related to gas diffusivity. From the results of this research, we can now estimate likely effects of soil texture on emissions through the influence of soil type on soil aeration and soil drainage. This is of particular value in modelling N2O and NO emissions from soil moisture status and land use inputs. 相似文献
15.
G. S. Francis R. J. Haynes G. P. Sparling D. J. Ross P. H. Williams 《Nutrient Cycling in Agroecosystems》1992,33(1):59-70
A field experiment was conducted to investigate the effect of timing and method of cultivation of a 3-year old ryegrass/white clover pasture on subsequent N mineralization, NO
3
-
-N leaching, and growth and N uptake of a wheat crop in the following season. The size of various N pools and decomposition of14C-labelled ryegrass material were also investigated. Cultivation method (mouldboard or chisel ploughing) generally had no significant effect on the accumulation of mineral N in the profile in the autumn or on the amount of NO
3
-
-N leached over winter.14C measurements suggested that initial decomposition rate of plant material was faster from May than March cultivation treatments. Despite this, overall net mineralization of organic N (of soil plus plant origin) increased with increasing fallow period between cultivation and leaching. The total amounts of mineral N accumulated in the soil profile before the start of leaching were 139, 119 and 22 kg N ha–1 for the March, May and July cultivated soils respectively. Cumulative leaching losses over the trial calculated from soil solution samples were 78, 40 and 5 kg N ha–1 for the March, May and July cultivated soils respectively. Differences in N mineralization over the season were generally not reflected by changes in amounts of potentially-mineralizable soil N (as measured by extraction or laboratory incubation) or levels of microbial biomass during the season. The amount of mineral N in the profile in spring increased with decreasing fallow period. This was reflected in an approximately 15% and 25% greater grain yield and N uptake respectively by the following wheat crop in plots cultivated in July rather than in March. 相似文献
16.
Tejinder S. Khera Milkha S. Aulakh John W. Doran 《Nutrient Cycling in Agroecosystems》1999,54(3):209-213
The influence of different depths of repacked soil cores on changes in N transformation processes was studied with a subtropical semi-arid soil amended with 100 mg N kg-1 of Sesbania green manure (GM) or fertilizer (NH4)2SO4 for 35 days under flooded and nonflooded conditions. Shallow soil depth enhanced the rate of nitrification, particularly where aeration was impeded in flooded soils. However, the opposite occurred for denitrification as the relative predominance of underlying anoxic zone increased with increase in soil depth. Nitrate produced in the thin oxic surface soil layer and overlying water in flooded soils was subsequently lost via denitrification, more rapidly where carbon was supplied by added GM. Decomposition of GM was rapid and apparent recovery of applied 100 mg GM-N kg-1 soil as mineral N after 35 days in flooded soils was 8, 26, 30 and 38% in 1.25-, 2.5-, 5.0- and 7.5-cm deep soil cores, respectively. Soil ammonium-N declined rapidly after an initial rise during decomposition of GM in soil in the shallow soil depth. In contrast, no such decline in NH
4
+
-N was observed in deep soil cores. In conclusion, the use of shallow soil depths during laboratory incubations can lead to variable results under flooded conditions. To simulate field conditions for obtaining reliable and quantitative information regarding N transformations in soils under flooded conditions, soil depths of 7.5 cm or greater should be used for laboratory incubations and growth chamber studies. 相似文献
17.
L. E. Jackson L. J. Stivers B. T. Warden K. K. Tanji 《Nutrient Cycling in Agroecosystems》1994,37(2):93-105
Low N use efficiency and high nitrate (NO
3
-
) pollution potentials are problems in intensive vegetable production systems. The purpose of this study was to quantify N utilization by lettuce (Lactuca sativa L. cv Salinas), and identify periods of NO
3
-
loss in an on-farm study in the Salinas Valley in coastal California. During autumn and winter, surface moisture remained low, and NO
3
-
concentrations increased, reflecting high net mineralizable N, as determined by anaerobic incubation, and nitrification potential, as determined by the chlorate inhibition method. At the onset of a large winter storm, tracer levels of15NO
3
-
were injected in the top 5 mm of soil in 30 cm-deep cylinders. After two weeks, most of the15N was present as15NO
3
-
at 10–30 cm depth. By difference, losses to denitrification accounted for ~ 25% of the surface-applied15N. Leaching below 30 cm did not occur, since no15N enrichment of NO
3
-
-N was measured in anion-exchange resin membranes placed at the base of each cylinder. During the crop period, NO
3
-
losses were most pronounced after irrigation events. Uptake of N by two crops of lettuce (above- and belowground material) was approximately equal to fertilizer inputs, yet simulation of N fates by the Erosion/Productivity Impact Calculator (EPIC) model indicated losses of 14.6 g-N m–2 by leaching and 2.5 g-N m–2 by denitrification during the 6-month crop period. The large NO
3
-
losses can be attributed to accumulation of soil NO
3
-
during winter that was leached or denitrified during the irrigated crop period. 相似文献
18.
K Mengel HG Schon G Keerthisinghe SK De Datta 《Nutrient Cycling in Agroecosystems》1986,9(1-2):117-130
The release of non-exchangeable (fixed) NH
4
+
and the importance of exchangeable NH
4
+
at transplanting (initial exchangeable NH
4
+
) for rice (Oryza sativa L.) growth was studied in representative lowland rice soils of the Philippines.The experiments showed that initial exchangeable ammonium behaved like fertilizer N and thus may serve as a valuable guideline for nitrogen fertilizer application rates when calculated on a hectare basis. By using the15N tracer technique it was found that nonexchangeable ammonium in soil may contribute to the nitrogen supplying capacity of lowland rice soils. Fixation and release of NH
4
+
seem to be more dependent on the form of clay minerals than on clay content. In soils rich in vermiculite non-exchangeable ammonium should be considered together with other available N sources such as exchangeable ammonium for N fertilizer recommendations for lowland rice. 相似文献
19.
J. M. Bremner 《Nutrient Cycling in Agroecosystems》1995,42(1-3):321-329
Recent research on the NH3 volatilization, NO
2
-
accumulation, and phytotoxicity problems encountered in the use of urea fertilizer is reviewed. This research has shown that the adverse effects of urea fertilizers on seed germination and seedling growth in soil are due to NH3 produced through hydrolysis of urea by soil urease and can be eliminated by addition of a urease inhibitor to these fertilizers. It also has shown that the leaf burn commonly observed after foliar fertilization of soybean with urea results from accumulation of toxic amounts of urea in soybean leaves rather than formation of toxic amounts of NH3 through hydrolysis of urea by leaf urease. It further showed that this leaf burn is accordingly increased rather than decreased by addition of a urease inhibitor to the urea fertilizer applied. N-(n-butyl)thiophosphoric triamide (NBPT) is the most effective compound currently available for retarding hydrolysis of urea fertilizer in soil, decreasing NH3 volatilization and NO
2
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accumulation in soils treated with urea, and eliminating the adverse effects of urea fertilizer on seed germination and seedling growth in soil. NBPT is a poor inhibitor of plant or microbial urease, but it decomposes quite rapidly in soil with formation of its oxon analog N-(n-butyl) phosphoric triamide, which is a potent inhibitor of urease activity. It is not as effective as phenylphosphorodiamidate (PPD) for retarding urea hydrolysis and ammonia volatilization in soils under waterlogged conditions, presumably because these conditions retard formation of its oxon analog. PPD is a potent inhibitor of urease activity but it decomposes quite rapidly in soils with formation of phenol, which is a relatively weak inhibitor of urease activity. Recent studies of the effects of pesticides on transformations of urea N in soil indicate that fungicides have greater potential than herbicides or insecticides for retarding hydrolysis of urea and nitrification of urea N in soil. 相似文献
20.
The influence of controlled release fertilisers and the form of applied fertiliser nitrogen on nitrous oxide emissions from an andosol 总被引:1,自引:0,他引:1
A laboratory experiment was conducted to determine whether applying controlled release nitrogen fertilisers could reduce nitrous oxide emissions from an andosol maintained at different water contents, compared with applying standard nitrogen fertiliser. The effect of the form of N applied (NH4-N or NO3-N) was also investigated. Soil was collected from an arable field and sub-samples were treated with controlled release or standard fertiliser, applied at a rate of 200 g N g–1 dry soil either as NH4
+ or NO3
–. The soils were maintained at 40%, 55%, 70% or 85% water filled pore space (WFPS) and incubated at 25 °C for 50 days. Gas samples were collected and analysed every 3–4 days and soil samples were analysed on five occasions during the incubation. Emissions of N2O were much greater from ammonium sulphate than from calcium nitrate fertiliser, indicating that nitrification was the main source of the N2O. Emissions at 85% WFPS were greater than at the lower water contents in all treatments. The use of controlled release NH4-N fertilisers reduced and delayed the maximum peak of emissions, but at 55% and 70% WFPS this did not always result in lower total emissions. Emissions from the controlled release NO3-N fertiliser were very low, but only significantly lower than from standard NO3-N fertiliser at water contents below 85% WFPS. The results demonstrate that choosing the appropriate form of fertiliser in relation to expected soil moisture could significantly reduce N2O emissions. Applying the fertiliser in a controlled-release form could further reduce emissions by reducing the length of time that fertiliser nitrogen is present in the soil and available for nitrification or denitrification. 相似文献