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1.
An assessment of the contribution of net mineralization to N cycling in grass swards using a field incubation method 总被引:3,自引:0,他引:3
Measurements of net mineralization using a field incubation method were made over a full growing season (180 d). Soil cores, taken from cut swards which for many years had been previously grazed by cattle, were placed in jars in the field for successive incubation periods of 14 d. Acetylene was added to the incubation jars to inhibit nitrification in the soil cores and thereby prevent losses of N through denitrification. Net mineralization over 180 d amounted to 415, 321 and 310 kg N ha–1 under grass/clover, unfertilized grass and grass receiving 420 kg N ha–1 y–1, respectively. At the start of the growing season, an index of potentially mineralizable N in the soil was estimated by a chemical extraction method, but this index was <50% of the estimates obtained by field incubation. The amount of N in herbage harvested regularly from the swards also under-estimated the supply of N from the soil, with apparent recoveries of 53, 82 and 74% and total yields of N of 240, 263 and 538 (kg N ha–1) from grass/clover, unfertilized grass and fertilized grass, respectively. Mineralization rates varied significantly with seasonal soil temperature fluctuations, but the incubation method was apparently less sensitive in relation to changes in soil water content. Rates of N-turnover (as % of total soil N) were highest under grass/clover (9%), but similar under fertilized and unfertilized grass swards (approximately 5%). 相似文献
2.
A field incubation technique with acetylene to inhibit nitrification was used to estimate net N mineralization rates in some grassland soils through an annual cycle. Measurements were made on previously long-term grazed pastures on a silty clay loam soil in S.W. England which had background managements of +/– drainage and +/– fertilizer (200 kg N ha–1 yr–1). The effect of fertilizer addition on mineralization during the year of measurement was also determined. Small plots with animals excluded, and with herbage clipped and removed were used as treatment areas and measurements were made using an incubation period of 7 days at intervals of 7 or 14 days through the year. Soil temperature, moisture and mineral N contents were also determined. Mineralization rates fluctuated considerably in each treatment. Maximum daily rates ranged from 1.01 to 3.19 kg N ha–1, and there was substantial net release of N through the winter period (representing, on average, 27% of the annual release). Changes in temperature accounted for 35% of the variability but there was little significant effect of soil moisture. Annual net release of N ranged from 135 kg ha–1 (undrained soil, no previous or current fertilizer) to 376 (drained soil, +200 kg N ha–1 yr–1 previous and current fertilizer addition). Addition of fertilizer N to a previously unfertilized sward significantly increased the net release of N but there was no immediate effect of withholding fertilizer on mineralization during the year in which measurements were made. 相似文献
3.
D. S. Powlson 《Plant and Soil》1980,57(1):151-153
Summary The effect of cultivation (ploughing followed by rotavation) on the mineralization of soil nitrogen was measured at 2 sites on a silt loam soil. Both sites had a predominantly arable cropping history but one had been under grass for the previous 2 years and the other had carried wheat. Mineralization of N was slightly faster in cultivated soil but the difference was only significant at the site previously under grass. At this site cultivated soil contained 7 kg ha–1 more mineral N than uncultivated soil 2 weeks after treatment, and 9 kg ha–1 after 6 weeks. The corresponding figures for the site that had grown wheat were 4 and 6 kg N ha–1. 相似文献
4.
Alexandra Maltas Marc Corbeels Eric Scopel Robert Oliver Jean-Marie Douzet Fernando Antonio Macena da Silva Jacques Wery 《Plant and Soil》2007,298(1-2):161-173
In the Cerrado region of Brazil conventional soybean monoculture is since the 1980s being replaced by direct seeding mulch-based
cropping (DMC) with two crops per year and absence of tillage practices. The objective of this study was to assess the long-term
impact of DMC on soil organic matter accumulation and nitrogen (N) mineralization. Measurements of soil organic carbon (C)
content, soil total N content and soil N mineralization, both under laboratory conditions using disturbed soil samples and
under field conditions using intact soil cores were conducted on a chronosequence of 2-, 6-, 9- and 14-year-old DMC fields
(DMC-2, DMC-6, DMC-9 and DMC-14, respectively). The average increase of organic C in the 0–30 cm topsoil layer under DMC was
1.91 Mg C ha−1 year−1. Soil total N increased with 103 kg N ha−1 year−1 (0–30 cm). The potential N mineralization rate under laboratory conditions (28°C, 75% of soil moisture at field capacity)
was 0.27, 0.28, 0.39 and 0.36 mg N kg soil−1 day−1 for, respectively, the DMC-2, DMC-6, DMC-9 and DMC-14 soils. The corresponding specific N mineralization rates were 0.16,
0.15, 0.22 and 0.17 mg N g N−1 day−1. There was no obvious explanation for the higher specific N mineralization rate of soils under DMC-9, given the similar soil
conditions and land-use history before DMC was introduced. Results from the in situ N incubation experiments were in good
agreement with those from the laboratory incubations. We estimated that soil N mineralization increases with about 2.0 kg
N ha−1 year−1 under DMC. The increase was mainly attributed to the larger soil total N content. These results indicate that even in the
medium term (10 years), continuous DMC cropping has limited implications for N fertilization recommendations, since the extra
soil N supply represents less than 20% of the common N fertilization dose for maize in the region. 相似文献
5.
The pattern between nitrogen mineralization and grazing intensities in an Inner Mongolian typical steppe 总被引:1,自引:0,他引:1
Ungulate grazing is known to play a crucial role in regulating energy flow and nutrient cycling in grassland ecosystems. However,
previous studies of the effect of grazing on soil N dynamics have showed controversial results. Some studies indicate that
grazing stimulates N mineralization while others report that grazing suppresses N mineralization. In order to reconcile these
contrasting results, we investigated the response pattern of nitrogen transformation to multiple grazing intensities in an
Inner Mongolian steppe. In our study, we measured net nitrogen mineralization rates and nitrification rates during a whole
growing season in a 17-year field experiment that had five grazing intensities (0.00, 1.33, 2.67, 4.00 and 5.33 sheep ha−1). Primarily because of changes in temperature and moisture conditions, net N mineralization rates varied substantially during
the growing season with higher values occurring in late July. No consistent differences in net N mineralization rates were
observed between grazing intensity treatments at the monthly time scale. Compared to mineralization rates, net nitrification
rates were generally low with slightly higher values occurring in late July and late August. Ungulate grazing stimulated the
cumulative net N transformations (mineralization, nitrification and ammonification) at the annual time scale, and the most
stimulation occurred at a moderate grazing intensity of 4.00 sheep ha−1, whereas the highest grazing intensity of 5.33 sheep ha−1 and the lighter grazing intensity of 1.33 sheep ha−1 stimulated less. The general response of net N mineralization to grazing intensity gradient is roughly in the form of a normal
distribution at the annual time scale. Our study demonstrated that grazing intensity in concert with soil moisture and temperature
conditions imposed significant controls on soil N transformation and availability in this Inner Mongolian steppe. 相似文献
6.
Kyung Won Seo Su Jin Heo Yowhan Son Nam Jin Noh Sue Kyoung Lee Chun Gyeong Yoon 《Landscape and Ecological Engineering》2011,7(1):93-99
This study was conducted to examine the influences of soil-moisture conditions on soil nitrogen (N) dynamics, including in
situ soil N mineralization, N availability, and denitrification in a pure Alnus japonica forest located in Seoul, central Korea. The soil N mineralization, N availability, and denitrification were determined using
the buried bag incubation method, ion exchange resin bag method, and acetylene block method, respectively. The annual net
N mineralization rate (kg N ha−1 year−1) and annual N availability (mg N bag−1) were 40.26 and 80.65 in the relatively dry site, −5.43 and 45.39 in the moist site, and 7.09 and 39.17 in the wet site,
respectively. The annual net N mineralization rate and annual N availability in the dry site were significantly higher than
those in the moist and wet sites, whereas there was no significant difference between the moist and wet sites. The annual
mean denitrification rate (kg N ha−1 year−1) in the dry, moist, and wet sites was 2.37, 2.76, and 1.59, respectively. However, there was no significant difference among
sites due to the high spatial and temporal variations. Our results indicate that soil-moisture condition influenced the in
situ N mineralization and resin bag N availability in an A. japonica forest, and treatments of proper drainage for poorly drained sites would increase soil N mineralization and N availability
and consequently be useful to conserve and manage the A. japonica forest. 相似文献
7.
Understanding mulching influences on nitrogen (N) availability is important for developing N management strategies in plantations
at the upland sites of the southwestern China. Dynamics of biomass loss and nutrient release of mulching material, N availability
in the soil and N mineralization in situ were evaluated for the treatments with different mulch quantity in degraded agricultural
soil. The time taken for 95% decomposition of the initial biomass of Cogon grass (Imperata cylindrical L. Beauv. var. major) was 17 months with a half-life (t
1/2) of about 4.8 months. During the first 4 months about 55.2% of N was released, and after 1-year decomposition about 71.6%
of N was released from the mulch material. The fresh grass mulch increased the available N in the soil as they decomposed.
Compared to no mulch treatment, mulch treatments with 2.5, 5.0 and 7.5 kg m−2 mulching grass increased available N by about 13.1, 40.8 and 56.4% in the top soil (0–5 cm), and about 23.6, 78.0 and 139.3%
in the middle layer (5–20 cm), respectively. The mean annual net N mineralization in the mulched plots had 9.0–40.9% higher
cumulative rate than that in no-mulch plots, and the majority of the accumulated N in the incubated soils existed as NO3–N. There was a positive relationship between the rate of N mineralization and the available N in both the top soil and the
middle layer. Mulch improves soil nutrients and this improvement increased with increasing mulching quantity. The increment
of net N mineralization was approximately 69, 161 and 322 kg N ha−1 year−1 in the soil of 0–20 cm depth for the 2.5, 5.0 and 7.5 kg m−2 grass mulch treatments, respectively. The results from this study will provide a basis to optimize mulching techniques for
poplar plantations in degraded agricultural soils of southwestern China. 相似文献
8.
Nitrogen mineralization in high elevation forests of the Appalachians. I. Regional patterns in southern spruce-fir forests 总被引:4,自引:0,他引:4
Annual and seasonal rates of net nitrogen mineralization were determined for 19 sites in the spruce-fir forests of the Southern
Appalachian Mountains. These sites included high and low elevation stands of red spruce (Picea rubens Sarg.) and Fraser fir (Abies fraseri (Pursh.) Poir.) on east and west exposures on Whitetop Mountain, Virginia; Mt. Mitchell, North Carolina; and Clingman's Dome
in the Great Smoky Mountains National Park. Mineralization rates were determined using in situ soil incubations in PVC tubes
with ion exchange resin bags placed in the bottom of the tubes to collect leachate. Throughfall was collected in resin bags
placed in the top of the tubes. Average initial NH4-N + NO3-N ranged from 0.6 to 4.8 kg N/ha across all plots, and average mineralization rates ranged from 26 to 180 kg-N ha−1 yr−1. Throughfall ranged from 18 to 32 kg-N ha−1 yr−1 with NH4-N accounting for about two-thirds of the throughfall N across all sites. Throughfall and mineralization rates were not related
to elevation or exposure. The high rates of N mineralization and relatively high nitrate concentrations indicate that leaching
losses of nitrogen and associated cations could be substantial.
Requests for offprints 相似文献
9.
Summary Tillage has been shown to affect the uptake of phosphorus (P) and yield of soybeans, [Glycine max (L.) Merr.], but there is little information concerning the effects of P fertilization on nitrogen (N2) fixation in soybeans under no-tillage. Two field experiments were conducted in 1980 and 1981 to determine the effects of
soil P on N2 fixation under no-tillage and to study the interaction of P fertilization and tillage of N2 fixation, nutrient uptake, and yield of soybeans. In Exp. I, P was applied in 1977 at five rates up to 384 kg P ha−1 and the effects of residual soil P were evaluated in 1980 and 1981 under no-tillage management. Nitrogen fixation rates,
as measured by acetylene reduction assay, were significantly affected by soil P in Exp. I, but the assay proved to be a poor
technique for estimating total plant N in these tests. Acetylene reduction rates and plant P increased rapidly as soil P increased
from 2 to 20 mg kg−1, with little additional increase above 20 mg P kg−1.
In Exp. II, rates (0, 32, 64, and 128 kg P ha−1) and time (fall, spring and fall plus spring) of P application were compared under conventional tillage and no tillage. However,
plant P increased with increasing levels of applied P. Applied P had no affect on acetylene reduction rates but rates were
greater for no-tillage than conventional tillage at the V9 and R5 stages of growth in 1981. Plant uptake of P was more efficient
under no-tillage than under conventional tillage in 1980 and 1981. Application of 64 kg P ha−1 under no-tillage resulted in equivalent plant P levels as the 128 kg P ha−1 applied under conventional tillage. 相似文献
10.
Summary Previous investigations indicated some forage grass roots in Texas are heavily colonized with N2-fixing bacteria. The most numerous N2-fixing bacteria were in the genera Klebsiella and Enterobacter. In the present investigation inoculation experiments were
conducted using 18 isolates of these bacteria to determine if a N2-fixing association could be established between the bacteria and the grassesCynodon dactylon andPanicum coloratum. Plants were grown in soil for approximately 5 months in a greenhouse and were measured periodically for dry matter, nitrogen
accumulation, and acetylene reduction activity. Results of the investigation indicated that 25% of the plant-soil systems
were active in acetylene reduction and the activity was high enough to indicate agronomically significant quantities of N2 were being fixed (>8kg N ha−1). However, plant systems extrapolated to fix>8 kg N ha−1 contained less nitrogen and accumulated less dry matter than plants less active in acetylene reduction. Inocula could not
be re-isolated from healthy grass roots indicating that the N2-fixing activity may have not have been closely assiciated with plant roots. Future research is needed to determine factors
limiting colonization of grass roots. 相似文献
11.
To increase our insight into the above- and belowground N flows in grass and grass-clover swards relations between crop and soil parameters were studied in a cutting trial with perennial ryegrass (Lolium perenne) monocultures and ryegrass–white clover (Trifolium repens) mixtures. The effects of clover cultivar on herbage yield, the amount of clover-derived nitrogen, apparent N transfer to companion grass, dynamics of N and organic matter in the soil were estimated.The grass monocultures had very low DM yields (<2.1 t ha-1) and a low N concentration in the harvested herbage. During 1992–1995 the annual herbage DM yield in the mixtures ranged from 7.0 to 14.3 t ha-1, the white clover DM yield from 2.4 to 11.2 t ha-1 and the mean annual clover content in the herbage DM harvested from 34 to 78%. Mixtures with the large-leaved clover cv. Alice yielded significantly more herbage and clover DM and had a higher clover content than mixtures with small/medium-leaved cvs. Gwenda and Retor. Grass cultivar did not consistently affect yield, botanical composition or soil characteristics.The apparent N2 fixation was very high, ranging from 150 to 545 kg N ha-1 in the different mixtures. For each tonne of clover DM in the harvested herbage 49 to 63 kg N was harvested, while the apparent N transfer from clover to grass varied between 55 and 113 kg N ha-1 year-1.The net N mineralization rate was lower under monocultures than under mixtures. The C mineralization and the amounts of C and N in active soil organic matter fractions were similar for monocultures and mixtures, but the C:N ratio of the active soil organic matter fractions were higher under grass than under mixtures. This explains the lower N mineralization under grass. 相似文献
12.
Sources of Nitrogen to the Riparian Zone of a Desert Stream: Implications for Riparian Vegetation and Nitrogen Retention 总被引:5,自引:1,他引:4
John D. Schade Eugenia Marti Jill R. Welter Stuart G. Fisher Nancy B. Grimm 《Ecosystems》2002,5(1):68-79
Riparian zones effectively remove nitrogen (N) from water flowing through riparian soils, particularly in agricultural watersheds.
The mechanism of N removal is still unclear, especially the role of vegetation. Uptake and denitrification are the two most
commonly studied mechanisms. Retention of groundwater N by plant uptake is often inferred from measurements of N in net incremental
biomass. However, this assumes other sources of N are not contributing to the N demand of plants. The purpose of this work
was to investigate the relative importance of three sources of available N to riparian trees in a desert stream—input in stream
water during floods, input during baseflow, and mineralization of N from soil organic matter. Two approaches were used; a
mass balance approach in which the mass of available N from each source was estimated, and a correlational approach in which
indexes of each source were compared to leaf N for individual willow trees. Total N from all sources was 396 kg ha−1 y−1, with 172 kg ha−1 y−1 from mineralization, 214 kg ha−1 y−1 from the stream during baseflow, and 9.6 kg ha−1 y−1 from floods. Leaf N was significantly related to N mineralization rates and flood inputs; it was not related to baseflow
inputs. We conclude that mineralization is a major source of available N for willow trees, subsidized by input of N from floods.
Baseflow inputs are most likely removed by rapid denitrification at the stream–riparian edge, while higher rates of flood
supply exceed the capacity of this “filter.”
Received 18 January 2001; accepted 15 June 2001. 相似文献
13.
Jean-Michel Harmand Hector Ávila Etienne Dambrine Ute Skiba Sergio de Miguel Reina Vanessa Renderos Robert Oliver Francisco Jiménez John Beer 《Biogeochemistry》2007,85(2):125-139
Nitrogen fertilization is a key factor for coffee production but creates a risk of water contamination through nitrate (NO3−) leaching in heavily fertilized plantations under high rainfall. The inclusion of fast growing timber trees in these coffee
plantations may increase total biomass and reduce nutrient leaching. Potential controls of N loss were measured in an unshaded
coffee (Coffea arabica L.) plot and in an adjacent coffee plot shaded with the timber species Eucalyptus deglupta Blume (110 trees ha−1), established on an Acrisol that received 180 kg N ha−1 as ammonium-nitrate and 2,700 mm yr−1 rainfall. Results of the one year study showed that these trees had little effect on the N budget although some N fluxes
were modified. Soil N mineralization and nitrification rates in the 0–20 cm soil layer were similar in both systems (≈280 kg N ha−1 yr−1). N export in coffee harvest (2002) was 34 and 25 kg N ha−1 yr−1 in unshaded and shaded coffee, and N accumulation in permanent biomass and litter was 25 and 45 kg N ha−1 yr−1, respectively. The losses in surface runoff (≈0.8 kg mineral N ha−1 yr−1) and N2O emissions (1.9 kg N ha−1 yr−1) were low in both cases. Lysimeters located at 60, 120, and 200 cm depths in shaded coffee, detected average concentrations
of 12.9, 6.1 and 1.2 mg NO3−-N l−1, respectively. Drainage was slightly reduced in the coffee-timber plantation. NO3− leaching at 200 cm depth was about 27 ± 10 and 16 ± 7 kg N ha−1 yr−1 in unshaded and shaded coffee, respectively. In both plots, very low NO3− concentrations in soil solution at 200 cm depth (and in groundwater) were apparently due to NO3− adsorption in the subsoil but the duration of this process is not presently known. In these conventional coffee plantations,
fertilization and agroforestry practices must be refined to match plant needs and limit potential NO3− contamination of subsoil and shallow soil water. 相似文献
14.
Abstract: In the semiarid Mulga Lands of southern Queensland soil nitrogen (N) levels have declined after clearance of the native mulga (Acacia aneura F. Muell. ex Benth.) and conversion to grazed buffel grass (Cenchrus ciliaris) pasture. At three mulga sites, declines in soil total N ranged from 14% to 28% in the surface 10 cm of soil. In situ net N mineralization from December 2003 until November 2004 in the surface 10 cm was 49.5 kg N ha?1 year?1 in the mulga woodland, 48.2 kg N ha?1 year?1 in the young (<5 years old) buffel pasture (previously sown to wheat (Triticum aestivum L.) and 34.6 kg N ha?1 year?1 in the old buffel pasture (>20 years). Ammonium‐N was the dominant N pool under mulga in the top 30 cm, while nitrate‐N was dominant under the buffel pastures. Although ammonium‐N under mulga was significantly different to that for 21‐year‐old buffel pasture at all depths, nitrification and net N mineralization were not different between the three land uses at any depth or in the entire 90 cm profile. The Soil Nitrogen Availability Predictor model was used to predict field N mineralization rates for the mulga woodland and 21‐year‐old buffel pasture by using a medium‐term (6‐week) laboratory incubation to establish basal rates of N mineralization. The Soil Nitrogen Availability Predictor overestimated annual net N mineralization in the 0–30 cm depth of mulga by 9% and underestimated it by 28% for the old buffel pasture. The Soil Nitrogen Availability Predictor could be modified further to accurately predict net N mineralization for the mulga woodlands. 相似文献
15.
Dinitrogen fixation in white clover (Trifolium repens L.) grown in pure stand and mixture with perennial ryegrass (Lolium
perenne L.) was determined in the field using 15N isotope dilution and harvest of the shoots. The apparent transfer of clover N to perennial ryegrass was simultaneously assessed.
The soil was labelled either by immobilizing 15N in organic matter prior to establishment of the sward or by using the conventional labelling procedure in which 15N fertilizer is added after sward establishment. Immobilization of 15N in the soil organic matter has not previously been used in studies of N2 fixation in grass/clover pastures. However, this approach was a successful means of labelling, since the 15N enrichment only declined at a very slow rate during the experiment. After the second production year only 10–16% of the
applied 15N was recovered in the harvested herbage. The two labelling methods gave, nonetheless, a similar estimate of the percentage
of clover N derived from N2 fixation. In pure stand clover, 75–94% of the N was derived from N2 fixation and in the mixture 85–97%. The dry matter yield of the clover in mixture as percentage of total dry matter yield
was relatively high and increased from 59% in the first to 65% in the second production year. The average daily N2 fixation rate in the mixture-grown clover varied from less than 0.5 kg N ha−1 day−1 in autumn to more than 2.6 kg N ha−1 day−1 in June. For clover in pure stand the average N2 fixation rate was greater and varied between 0.5 and 3.3 kg N ha−1 day−1, but with the same seasonal pattern as for clover in mixture. The amount of N fixed in the mixture was 23, 187 and 177 kg
N ha−1 in the seeding, first and second production year, respectively, whereas pure stand clover fixed 28, 262 and 211 kg N ha−1 in the three years. The apparent transfer of clover N to grass was negligible in the seeding year, but clover N deposited
in the rhizosphere or released by turnover of stolons, roots and nodules, contributed 19 and 28 kg N ha−1 to the grass in the first and second production year, respectively.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
16.
Canada bluejoint grass [Calamagrostis canadensis (Michx.) Beauv., referred to as bluejoint below] is a competitive understory species widely distributed in the boreal region
in North America and builds up a thick litter layer that alters the soil surface microclimate in heavily infested sites. This
study examined the effects of understory removal, N fertilization, and litter layer removal on litter decomposition, soil
microbial biomass N (MBN), and net N mineralization and nitrification rates in LFH (the sum of organic horizons of litter,
partially decomposed litter and humus on the soil surface) and mineral soil (0–10 cm) in a 13-year-old white spruce [Picea glauca (Moench.) Voss] plantation infested with bluejoint in Alberta, Canada. Removal of the understory vegetation and the litter
layer together significantly increased soil temperature at 10 cm below the mineral soil surface by 1.7 and 1.3°C in summer
2003 and 2004, respectively, resulting in increased net N mineralization (by 1.09 and 0.14 mg N kg−1 day−1 in LFH and mineral soil, respectively, in 2004) and net nitrification rates (by 0.10 and 0.20 mg N kg−1 day−1 in LFH and mineral soil, respectively, in 2004). When the understory vegetation was intact, nitrification might have been
limited by NH4
+ availability due to competition for N from bluejoint and other understory species. Litter layer removal increased litter
decomposition rate (percentage mass loss per month) from 2.6 to 3.0% after 15 months of incubation. Nitrogen fertilization
did not show consistent effects on soil MBN, but increased net N mineralization and nitrification rates as well as available
N concentrations in the soil. Clearly, understory removal combined with N fertilization was most effective in increasing rates
of litter decomposition, net N mineralization and nitrification, and soil N availability. The management of understory vegetation
dominated by bluejoint in the boreal region should consider the strong effects of understory competition and the accumulated
litter layer on soil N cycling and the implications for forest management. 相似文献
17.
Mark S. Castro Keith N. Eshleman Louis F. Pitelka Geoff Frech Molly Ramsey William S. Currie Karen Kuers Jeffrey A. Simmons Bob R. Pohlad Carolyn L. Thomas David M. Johnson 《Biogeochemistry》2007,84(3):333-348
The objective of this study was to evaluate the nitrogen (N) biogeochemistry of an 18–22 year old forested watershed in western
Maryland. We hypothesized that this watershed should not exhibit symptoms of N saturation. This watershed was a strong source
of nitrate (NO3
−) to the stream in all years, with a mean annual export of 9.5 kg N ha−1 year−1 and a range of 4.4–18.4 kg N ha−1 year−1. During the 2001 and 2002 water years, wet deposition of inorganic N was 9.0 kg N ha−1 year−1 and 6.3 kg N ha−1 year−1, respectively. Watershed N export rates in 2001 and 2002 water years were 4.2 kg N ha−1 year−1 and 5.3 kg N ha−1 year−1, respectively. During the wetter water years of 2003 and 2004, the watershed exported 15.0 kg N ha−1 year−1 and 18.4 kg N ha−1 year−1, rates that exceeded annual wet deposition of N by a factor of two (7.5 kg N ha−1 year−1 in 2003) and three (5.5 kg N ha−1 year−1 in 2004). Consistent with the high rates of N export, were high concentrations (2.1–3.3%) of N in foliage, wood (0.3%) and
fine roots, low C:N ratios in the forest floor (17–24) and mineral soil (14), high percentages (83–96%) of the amount of mineralized
N that was nitrified and elevated N concentrations (up to 3 mg N l−1) in soil solution. Although this watershed contained a young aggrading forest, it exhibited several symptoms of N saturation
commonly observed in more mature forests. 相似文献
18.
Chris van Kessel 《Plant and Soil》1994,164(1):69-76
Although wheat (Triticum aestivum L.) is the dominant crop of the semi-arid plains of Canada and the western United States, lentil (Lens culinaris Medik.) has become an important alternative crop. Sources and seasonal accumulation of N must be understood in order to identify
parameters that can lead to increased N2-fixing activity and yield. Inoculated lentil was grown in a sandy-loam soil at an irrigated site in Saskatchewan, Canada.
Wheat was used as the reference crop to estimate N2 fixation by the A-value approach. Lentil and wheat received 10 and 100 kg N ha−1 of ammonium nitrate, respectively. Crops were harvested six times during the growing season and plant components analyzed.
During the first 71 days after planting the wheat had a higher daily dry matter and N accumulation compared to lentil. However,
during the latter part of the growing season, daily dry matter and N accumulation were greater for lentil. The maximum total
N accumulation for lentil at maturity was 149 kg ha−1. In contrast, wheat had a maximum N accumulation of 98 kg ha−1 in the Feekes 11.1 stage, or 86 days after planting. The maximum daily rates of N accumulation were 3.82 kg N ha−1 day−1 for lentil and 2.21 kg N ha−1 day−1 for wheat. The percentage of N derived from N2 fixation (% Ndfa) ranged from 0 at the first harvest to 92 % at final harvest. Generative plant components had higher values
for % Ndfa than the vegetative components which indicates that N in the reproductive plant parts was derived largely from
current N2 fixation and lentil continued to fix N until the end of the pod fill stage. At final harvest, lentil had derived 129 kg N
ha−1 from N2 fixation with maximum N2-fixing activity (4.4 kg N ha−1 day−1) occurring during the early stages of pod fill. Higher maximum rates of N2-fixing activity than net N accumulation (3.82 kg N ha−1 day−1) may have been caused by N losses like volatilization. In addition, lentil provided a net N contribution to the soil of 59
kg ha−1 following the removal of the grain. 相似文献
19.
Kristell Hergoualc’h Ute Skiba Jean-Michel Harmand Catherine Hénault 《Biogeochemistry》2008,89(3):329-345
The objective of this study was to evaluate the effect of N fertilization and the presence of N2 fixing leguminous trees on soil fluxes of greenhouse gases. For a one year period, we measured soil fluxes of nitrous oxide
(N2O), carbon dioxide (CO2) and methane (CH4), related soil parameters (temperature, water-filled pore space, mineral nitrogen content, N mineralization potential) and
litterfall in two highly fertilized (250 kg N ha−1 year−1) coffee cultivation: a monoculture (CM) and a culture shaded by the N2 fixing legume species Inga densiflora (CIn). Nitrogen fertilizer addition significantly influenced N2O emissions with 84% of the annual N2O emitted during the post fertilization periods, and temporarily increased soil respiration and decreased CH4 uptakes. The higher annual N2O emissions from the shaded plantation (5.8 ± 0.3 kg N ha−1 year−1) when compared to that from the monoculture (4.3 ± 0.1 kg N ha−1 year−1) was related to the higher N input through litterfall (246 ± 16 kg N ha−1 year−1) and higher potential soil N mineralization rate (3.7 ± 0.2 mg N kg−1 d.w. d−1) in the shaded cultivation when compared to the monoculture (153 ± 6.8 kg N ha−1 year−1 and 2.2 ± 0.2 mg N kg−1 d.w. d−1). This confirms that the presence of N2 fixing shade trees can increase N2O emissions. Annual CO2 and CH4 fluxes of both systems were similar (8.4 ± 2.6 and 7.5 ± 2.3 t C-CO2 ha−1 year−1, −1.1 ± 1.5 and 3.3 ± 1.1 kg C-CH4 ha−1 year−1, respectively in the CIn and CM plantations) but, unexpectedly increased during the dry season. 相似文献
20.
Quanxiao Fang Qiang Yu Enli Wang Yuhai Chen Guoliang Zhang Jing Wang Longhui Li 《Plant and Soil》2006,284(1-2):335-350
There is a growing concern about excessive nitrogen (N) and water use in agricultural systems in North China due to the reduced
resource use efficiency and increased groundwater pollution. A two-year experiment with two soil moisture by four N treatments
was conducted to investigate the effects of N application rates and soil moisture on soil N dynamics, crop yield, N uptake
and use efficiency in an intensive wheat–maize double cropping system (wheat–maize rotation) in the North China Plain. Under
the experimental conditions, crop yield of both wheat and maize did␣not␣increase significantly at N rates above 200 kg N ha−1. Nitrogen application rates affected little on ammonium-N (NH4-N) content in the 0–100 cm soil profiles. Excess nitrate-N (NO3-N), ranging from 221 kg N ha−1 to 620 kg N ha−1, accumulated in the 0–100 cm soil profile at the end of second rotation in the treatments with N rates of 200 kg N ha−1 and 300 kg N ha−1. In general, maize crop has higher N use efficiency than wheat crop. Higher NO3-N leaching occurred in maize season than in wheat season due to more water leakage caused by the concentrated summer rainfall.
The results of this study indicate that the optimum N rate may be much lower than that used in many areas in the North China
Plain given the high level of N already in the soil, and there is great potential for reducing N inputs to increase N use
efficiency and to mitigate N leaching into the groundwater. Avoiding excess water leakage through controlled irrigation and
matching N application to crop N demand is the key to reduce NO3-N leaching and maintain crop yield. Such management requires knowledge of crop water and N demand and soil N dynamics as
they change with variable climate temporally and spatially. Simulation modeling can capture those interactions and is considered
as a powerful tool to assist in␣the␣future optimization of N and irrigation managements.
Section Editor: L. Wade 相似文献