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1.
Populations of plant parasitic nematodes and their effects on symbiotic nitrogen (N) fixation in herbaceous legumes and on
some selected characteristics of other plant species associated with such cover crops were studied. Two legume species [mucuna,
Mucuna pruriens (L) DC. var. utilis (Wright) Bruck and lablab, Lablab purpureus L. Sweet], one grass/weed species [imperata, Imperata cylindrica (L.) Rauschel] and a cereal (maize, Zea mays L.) were used. There were three soil treatments (fumigation, fumigation plus inoculation with Meloidogyne species, and an untreated control). Plant parasitic nematode populations in soil, roots and nodules were determined at 4,
8 and 12 weeks after planting. The response of the phytoparasitic nematodes to soil treatments varied according to the plant
species present. The predominant nematodes in soils, roots and nodules of legumes were of the genus Meloidogyne, whereas other genera of parasitic nematodes dominated the fauna in soils and roots of maize and imperata. Biomass yield
of mucuna was not significantly affected by either Meloidogyne spp. or the other genera of phytoparasitic nematodes. In contrast, the dry matter yield of lablab measured at 12 weeks was
reduced by 16% in inoculated compared with fumigated soils. Similarly, the biomass yields of maize and imperata were reduced
by 10% and 29%, respectively, in unfumigated rather than fumigated soils. The amounts of N accumulated in mucuna, maize and
imperata were not significantly affected by the two groups of plant parasitic nematodes. However, at 12 weeks, lablab grown
on inoculated soils accumulated only 69% of the N found in plants grown on fumigated soils. Inoculation of soil with Meloidogyne spp. significantly increased the number of nodules on lablab roots compared with the non-inoculated treatments, whereas nodulation
in mucuna was not affected by soil treatment. After 12 weeks, the quantity of N2 derived from symbiotic fixation in mucuna was not significantly affected by soil treatments whereas the amount of fixed N
in lablab was 32% lower in inoculated than in fumigated soils. Possible mechanisms for the non-suppressive effect of plant
parasitic nematodes on mucuna are discussed.
Received: 12 March 1999 相似文献
2.
Reliable estimates of symbiotically fixed N2 in herbaceous legumes are important in order to determine their role in maintaining or improving N levels in tropical low-external-input
farming systems. We have studied the effects of different management systems on the suitability of two non-N2-fixing reference crops, imperata [Imperata cylindrica (L.) Rauescel] and maize (Zea mays L.), for estimating N2 fixation in mucuna [Mucuna pruriens (L.) DC var. utilis (Wright) Bruck] and lablab [Lablab purpureus (L.) Sweet] in the field. The total-N-difference (TND) method of estimating N2 fixation was compared to the 15N-isotope-dilution (ID) technique. The two methods did not differ with respect to estimates of N2 fixation under in situ mulch (IM) systems. In contrast, under live-mulch (LM) systems the TND method underestimated N2 fixed in mucuna by 29% and in lablab by 40% compared to estimates made with the ID method. Irrespective of the treatment,
estimates of N derived from fixation in both herbaceous legumes were not influenced by either of the reference plants. Using
the ID technique, the proportion of N2 derived from fixation in mucuna and lablab at 12 weeks varied from 52% to 90% depending on whether the treatments were N
fertilized, inoculated or uninoculated, cover-crop systems. In view of the nature of cover-crop systems in the derived savanna
of West and Central Africa, where imperata is usually present as a weed or maize is grown in IM or LM systems, imperata or
maize could be used to estimate N2 fixation and N contributions of the legumes to soil fertility and subsequent crop improvements.
Received: 16 October 1999 相似文献
3.
Simple methods for the measurement of nitrogen (N) availability are needed to assess the effect of low-input, organically
based land management systems on the N supply of tropical soils. Our objectives were to determine the effect of contrasting
land-use systems (LUS) on soil N availability and to identify measures of N availability that correlated with maize (Zea mays L.) grain yield. The LUS at the two sites in Kenya involved growth of a maize crop following 17 months of either: (1) Sesbania sesban (L.) Merr. tree growth (sesbania fallow), (2) natural regrowth of vegetation without cultivation (natural fallow), (3) three
crops of unfertilized maize (maize monoculture), or (4) bare uncultivated soil (bare fallow). Soil was collected before the
post-fallow maize crop was sown. The LUS had no effect on total soil N or amount of N in the heavy fraction soil organic matter
(SOM) (>150 μm, >1.37 Mg m–3). Sesbania and natural fallows, as compared to maize monoculture, increased the N in light fraction SOM (>150 μm, <1.13Mgm–3), N in intermediate fraction SOM (>150 μm, 1.13 to 1.37 Mg m–3), ammonium-N and aerobic N mineralization at a depth of 0–15 cm. Maize yields were highest following the sesbania fallow.
Nitrate-N, inorganic-N (ammonium plus nitrate) and anaerobic N mineralization correlated with maize grain yield at both sites.
The relationship between maize yield and pre-season nitrate-N improved when the depth of soil sampling was increased to 1 m
at one site (an Alfisol), but did not improve at the site with anion adsorption in the subsoil (an Oxisol). The sesbania fallow
was more effective than the natural fallow in increasing available soil N. Maize yield was better related to pre-season nitrate
than N in size-density fractions of SOM.
Received: 5 May 1997 相似文献
4.
P. F. A. M. Römkens Johannes van der Plicht Jan Hassink 《Biology and Fertility of Soils》1999,28(3):277-284
Conversion of arable land (maize) to pasture will affect the soil organic matter (SOM) content. Changes in the SOM content
were studied using a size- and density-fractionation method and 13C analysis. Twenty-six years of maize cropping had resulted in a depletion of carbon stored in the macro-organic fractions
(>150 μm) and an increase in the <20 μm fraction. Maize-derived carbon in the upper 20 cm increased from 10% in the finest
fraction (<20 μm) to 91% in the coarse (>250 μm), light (b.d. <1.13 g cm–3) fractions. Pasture installation resulted in a rapid recovery of the total SOM content. Up to 90% of the pasture-derived
carbon that was mineralized during maize cropping was replaced within 9 years. Especially the medium and coarse size (>150
μm) and light (b.d. <1.13 g cm–3) fractions were almost completely regenerated by input of root-derived SOM. The amount of medium-weight and heavy macro-organic
fractions (>150 μm; b.d. >1.13 g cm–3) in the 0- to 20-cm layer was still 40–50% lower than in the continuous pasture plots. Average half-life times calculated
from 13C analyses ranged from 7 years in the light fractions to 56 years in heavy fractions. Fractionation results and 13C data indicated that mechanical disturbance (plowing) during maize cropping had resulted in vertical displacement of dispersed
soil carbon from the 0- to 20-cm layer down to 60–80 cm. Conversion of arable land to pasture, therefore, not only causes
a regeneration of the soil carbon content, it also reduces the risk of contaminant transport by dispersed soil carbon.
Received: 10 March 1998 相似文献
5.
P. Houngnandan N. Sanginga P. Woomer B. Vanlauwe O. Van Cleemput 《Biology and Fertility of Soils》2000,30(5-6):558-565
Leguminous cover crops such as Mucuna pruriens (mucuna) have the potential to contribute to soil N and increase the yields of subsequent or associated cereal crops through
symbiotic N fixation. It has often been assumed that mucuna will freely nodulate, fix N2 and therefore contribute to soil N. However, results of recent work have indicated mucuna's failure to nodulate in some farmers'
fields in the derived savanna in Benin. One of the management practices that can help to improve mucuna establishment and
growth is the use of rhizobial inocula to ensure compatibility between the symbiotic partners. Experiments were conducted
in 1995 and 1996 on 15 farmers' fields located in three different villages (Eglimé, Zouzouvou and Tchi) in the derived savanna
in Benin. The aim was to determine the response of mucuna to inoculation and examine the factors affecting it when grown in
relay cropping with maize. The actual amount of N2 fixed by mucuna in the farmers' fields at 20 weeks after planting (WAP) averaged 60 kg N ha–1 (range: 41–76 kg N ha–1) representing 55% (range: 49–58%) of the plant total N. The result suggested that mucuna in these farmers' fields could not
meet its total N demand for growth and seed production only by N2 fixation. It was estimated that after grain removal mucuna led to a net N contribution ranging from –37 to 30 kg N ha–1. Shoot dry weight at 20 WAP varied between 1.5 and 8.7 t ha–1 and N accumulation ranged from 22 to 193 kg N ha–1. Inoculation increased shoot dry matter by an average of 28% above the uninoculated treatments, but the increase depended
on the field, location and year. For the combinations of inoculated treatments and farmers' fields, the response frequency
was higher in Eglimé and Tchi than in Zouzouvou. The response to inoculated treatments was dependent on the field and inversely
related to the numbers of rhizobia in the soil. Soil rhizobial populations ranged from 0 to >188 cells g–1 soil, and response to inoculation often occurred when numbers of indigenous rhizobia were <5 cells g–1 soil. In two farmers' fields at Zouzouvou where extractable P was below 10 μg g–1 soil, mucuna did not respond to rhizobial inoculation despite a higher population of rhizobia. Significant relationships
between mycorrhizal colonization, growth and nodulation of mucuna were observed, and inoculated plants with rhizobia had a
higher rate of colonization by arbuscular mycorrhizal fungi (%AMF) than uninoculated ones. Therefore, it was shown that mucuna
will establish and fix N2 effectively in those fields where farmer's management practices such as good crop rotation and rhizobial inoculation allow
a build up of AMF spores that might lead to a high degree of AMF infection and alleviate P deficiency.
Received: 14 June 1999 相似文献
6.
Long-term experiments on different crop management systems provide essential information about turnover of soil organic matter
and changes in microbial properties over a period of time. A long-term field site trial, which was established in 1967 near
Vienna, Austria, to document the fate of 14C-labelled manure (straw and farmyard) under different crop management systems (crop rotation, spring wheat and bare fallow),
was investigated. Soil samples were taken in 1997 and separated into size fractions (>250 μm, 250–63 μm, 63–2 μm, 2–0.1 μm
and <0.1 μm) after aggregate dispersion using low-energy sonication. Organic C, total N and 14C content were measured in the bulk soil and the size fractions and microbial properties were analysed in the bulk soil. Additionally,
C mineralization in bulk soil samples was monitored at 20 °C over a period of 28 days, and subsequently 14C-CO2 content was analysed. The distribution of organic C and N within the size fractions was similar between crop rotation and
spring wheat; the highest amounts of organic C and N were found in the clay-sized fraction. The amounts of C and N were significantly
smaller in the bare fallow, which was depleted of organic matter in the coarse-sized fractions. 14C distribution differed significantly from unlabelled C distribution, labelled C was accumulated in the silt-sized fraction,
indicating weak humification of the applied manure C. The highest rate of C mineralization was measured in the crop rotation
and spring wheat, whereas the emission rate of the bare fallow was about 40% lower. The higher 14C:C ratio of the bulk soil in comparison to the emitted CO2 indicated that labelled C compounds still remained mineralizable after a period of 30 years. Microbial properties showed
a great difference between crop management systems and bare fallow, particularly regarding urease and xylanase activity.
Received: 31 May 1999 相似文献
7.
R. Roscoe C. A. Vasconcellos A. E. Furtini-Neto G. A. A. Guedes L. A. Fernandes 《Biology and Fertility of Soils》2000,32(1):52-59
We studied the relationship between urease activity (UA) and soil organic matter (SOM), microbial biomass N (Nbiom) content, and urea-N fertilizer assimilation by maize in a Dark Red Latosol (Typic Haplustox) cultivated for 9 years under
no-tillage (NT), tillage with a disc plough (DP), and tillage with a moldboard plough (MP). Two soil depths were sampled (0–7.5 cm
and 7.5–15 cm) at 4 different times during the crop cycle. Urea was applied at four different rates, ranging from 0 to 240 kg
N ha–1. The levels of fertilizer N did not affect the UA, SOM content, and Nbiom content. No significant difference between the treatments (NT, DP, and MP) was observed for SOM during the experiment, probably
because the major part of the SOM was in recalcitrant pools, since the area was previously cultivated (conventional tillage)
for 20 years. The Nbiom content explained 97% and 69% of the variation in UA in the upper and deeper soil layer, respectively. UA and biomass N were
significantly higher in the NT system compared to the DP and MP systems. The highest maize productivity and urea-N recovery
was also observed for the NT system. We observed that the increase in urea-N losses under NT, possibly as a consequence of
a higher UA, was compensated for by the increase in N immobilized in the biomass.
Received: 2 July 1999 相似文献
8.
The simultaneous impact of three successive crops of wheat (Triticum aestivum L.) and of the earthworm (Lumbricus terrestris L.) on the mineralisation of 15N-labelled organic compounds adsorbed to different soil size fractions (sand and organic residues >50 μm; silt 50–2 μm; coarse
clay 2–0.2 μm and fine clay <0.2 μm) was studied under controlled conditions in the greenhouse. Unplanted soils (UPS) were
used as controls. In planted soils without earthworm (PS) total plant biomass decreased with each cropping by up to 50%. However,
in planted soils with earthworms (PES) the total plant biomass loss was only 17%. This pattern was explained by the earthworm
effect. Compared to the unplanted soils, the planted soils had an increased (mean +37%) mineralisation of 15N adsorbed onto fine clays and a partial transfer of 15N to silt and coarse clay. The quantities of 15N mineralised and transferred were higher in the planted soils with earthworms, indicating an amplification of the phenomenon
in the presence of earthworms. The simultaneous effect of the rhizosphere and the drilosphere did not lead to increased mineralisation
of N adsorbed onto coarse clays and silts but instead a greater transfer of N associated with the fine fractions towards the
coarser fractions.
Received: 25 April 2000 相似文献
9.
B. Vanlauwe K. Aihou S. Aman B. K. Tossah J. Diels O. Lyasse S. Hauser N. Sanginga R. Merckx 《Biology and Fertility of Soils》2000,30(5-6):440-449
The impact of land use (unfertilized continuous maize cropping, unfertilized and fertilized alley cropping with maize, Gliricidia sepium tree fallow, natural fallow) on the soil organic matter (SOM) status and general soil fertility characteristics were investigated
for a series of soils representative for the West African moist savanna zone. Three soils from the humid forest zone were
also included. In an associated pot experiment, relationships between maize N and P uptake and SOM and general soil characteristics
were developed. Soils under natural fallow contained the highest amount of organic C (1.72%), total N (0.158%), and had the
highest effective cation exchange capacity (ECEC) [8.9 mEq 100 g–1 dry soil], while the Olsen P content was highest in the fertilized alley cropping plots (13.7 mg kg–1) and lowest under natural fallow (6.3 mg kg–1). The N concentration of the particulate organic matter (POM) was highest in the unfertilized alley cropping plots (2.4%),
while the total POM N content was highest under natural fallow (370 mg N kg–1) and lowest in continuously cropped plots (107 mg N kg–1). After addition of all nutrients except N, a highly significant linear relationship (R
2=0.91) was observed between the total N uptake in the shoots and roots of 7-week-old maize and the POM N content for the savanna
soils. POM in the humid forest soils was presumably protected from decomposition due to its higher silt and clay content.
After addition of all nutrients except P, the total maize P uptake was linearly related to the Olsen P content. R
2 increased from 0.56 to 0.67 in a multiple linear regression analysis including the Olsen P content and clay content (which
explained 11% of the variation in P uptake). Both the SOM status and N availability were shown to be improved in land-use
systems with organic matter additions, while only the addition of P fertilizer could improve P availability.
Received: 9 April 1999 相似文献
10.
Crop residues and fertilizer nitrogen influence residue decomposition and nitrous oxide emission from a Vertisol 总被引:2,自引:0,他引:2
Wisal Muhammad Sarah M. Vaughan Ram C. Dalal Neal W. Menzies 《Biology and Fertility of Soils》2011,47(1):15-23
Crop residues with high C/N ratio immobilize N released during decomposition in soil, thus reducing N losses through leaching,
denitrification, and nitrous oxide (N2O) emission. A laboratory incubation experiment was conducted for 84 days under controlled conditions (24°C and moisture content
55% of water-holding capacity) to study the influence of sugarcane, maize, sorghum, cotton and lucerne residues, and mineral
N addition, on N mineralization–immobilization and N2O emission. Residues were added at the rate of 3 t C ha−1 to soil with, and without, 150 kg urea N ha−1. The addition of sugarcane, maize, and sorghum residues without N fertilizer resulted in a significant immobilization of
soil N. Amended soil had significantly (P < 0.05) lower NO3−–N, which reached minimum values of 2.8 mg N kg−1 for sugarcane (at day 28), 10.3 mg N kg−1 for maize (day 7), and 5.9 mg N kg−1 for sorghum (day 7), compared to 22.7 mg N kg−1 for the unamended soil (day 7). During 84 days of incubation, the total mineral N in the residues + N treatments were decreased
by 45 mg N kg−1 in sugarcane, 34 mg kg−1 in maize, 29 mg kg−1 in sorghum, and 16 mg kg−1 in cotton amended soil compared to soil + N fertilizer, although soil NO3−–N increased by 7 mg kg−1 in lucerne amended soil. The addition of residues also significantly increased amended soil microbial biomass C and N. Maximum
emissions of N2O from crop residue amended soils occurred in the first 4–5 days of incubation. Overall, after 84 days of incubation, the
cumulative N2O emission was 25% lower with cotton + N fertilizer, compared to soil + N fertilizer. The cumulative N2O emission was significantly and positively correlated with NO3−–N (r = 0.92, P < 0.01) and total mineral N (r = 0.93, P < 0.01) after 84 days of incubation, and had a weak but significant positive correlation with cumulative CO2 in the first 3 and 5 days of incubation (r = 0.59, P < 0.05). 相似文献
11.
Structure and function of the soil microbial community in microhabitats of a heavy metal polluted soil 总被引:26,自引:0,他引:26
E. Kandeler D. Tscherko K. D. Bruce M. Stemmer P. J. Hobbs R. D. Bardgett W. Amelung 《Biology and Fertility of Soils》2000,32(5):390-400
Particle-size fractionation of a heavy metal polluted soil was performed to study the influence of environmental pollution
on microbial community structure, microbial biomass, microbial residues and enzyme activities in microhabitats of a Calcaric
Phaeocem. In 1987, the soil was experimentally contaminated with four heavy metal loads: (1) uncontaminated controls; (2)
light (300 ppm Zn, 100 ppm Cu, 50 ppm Ni, 50 ppm V and 3 ppm Cd); (3) medium; and (4) heavy pollution (two- and threefold
the light load, respectively). After 10 years of exposure, the highest concentrations of microbial ninhydrin-reactive nitrogen
were found in the clay (2–0.1 μm) and silt fractions (63–2 μm), and the lowest were found in the coarse sand fraction (2,000–250 μm).
The phospholipid fatty acid analyses (PLFA) and denaturing gradient gel electrophoresis (DGGE) separation of 16S rRNA gene
fragments revealed that the microbial biomass within the clay fraction was predominantly due to soil bacteria. In contrast,
a high percentage of fungal-derived PLFA 18 : 2ω6 was found in the coarse sand fraction. Bacterial residues such as muramic
acid accumulated in the finer fractions in relation to fungal residues. The fractions also differed with respect to substrate
utilization: Urease was located mainly in the <2 μm fraction, alkaline phosphatase and arylsulfatase in the 2–63 μm fraction,
and xylanase activity was equally distributed in all fractions. Heavy metal pollution significantly decreased the concentration
of ninhydrin-reactive nitrogen of soil microorganisms in the silt and clay fraction and thus in the bulk soil. Soil enzyme
activity was reduced significantly in all fractions subjected to heavy metal pollution in the order arylsulfatase >phosphatase
>urease >xylanase. Heavy metal pollution did not markedly change the similarity pattern of the DGGE profiles and amino sugar
concentrations. Therefore, microbial biomass and enzyme activities seem to be more sensitive than 16S rRNA gene fragments
and microbial amino-sugar-N to heavy metal treatment.
Received: 21 January 2000 相似文献
12.
The critical S concentration and S requirement of the soil microbial biomass of a granitic regosol was examined. S was applied
at the rate of 0, 5, 10, 20, 30 and 50 μg S as MgSO4·7H2O, together with either 3000 μg glucose-C or 3333 μg cellulose-C, 400 μg N, and 200 μg P g –1 soil and 200 μg K g–1 soil. Microbial biomass, inorganic SO4
2–-S, and CO2 emission were monitored over 30 days during incubation at 25 °C. Both glucose and cellulose decomposition rates responded
positively to the S made available for microbial cell synthesis. The amounts of microbial biomass C and S increased with the
level of applied S up to 10 μg S g–1 soil and 30 μg S g–1 soil in the glucose- and cellulose-amended soil, respectively, and then declined. Incorporated S was found to be concentrated
within the microbial biomass or partially transformed into soil organic matter. The concentration of S in the microbial biomass
was higher in the cellulose- (4.8–14.2 mg g–1) than in the glucose-amended soil (3.7–10.9 mg g–1). The microbial biomass C:S ratio was higher in the glucose- (46–142 : 1) than in the cellulose-amended soil (36–115 : 1).
The critical S concentration in the microbial biomass (defined as that required to achieve 80% of the maximum synthesis of
microbial biomass C) was estimated to be 5.1 mg g–1 in the glucose- and 10.9 mg g–1 in the cellulose-amended soil. The minimum requirement of SO4
2–-S for microbial biomass formation was estimated to be 11 μg S g–1 soil and 21 μg S g–1 soil for glucose- and cellulose-amended soil, respectively. The highest levels of activity of the microbial biomass were
observed at the SO4
2–-S concentrations of 14 μg S g–1 soil and 17 μg S g–1 soil, for the glucose and cellulose amendments, respectively, and were approximately 31–54% higher during glucose than cellulose
decomposition.
Received: 20 October 1999 相似文献
13.
Recovering decomposing plant residues from the particulate soil organic matter fraction: size versus density separation 总被引:2,自引:0,他引:2
A detailed size separation of particulate organic matter (POM) from soils amended with straw from Hordeum vulgare or Vicia sativa revealed that the loss of C during the first 56 days of incubation mainly occurred from particles >2,000 μm, without a concomitant
reduction in the size of these large particles. Preliminary studies of POM from non-amended soil had shown that the stable
heavy (>1.4 g cm–3) POM fraction was mainly (>80%) composed of particles <400 μm, whereas the light fraction was dominated by larger particles
(>80%). Therefore we decided to compare the POM <1.4 g cm3 with POM >400 μm. There was a very close relationship between POM>400 μm and POM <1.4 g cm–3 with regard to amounts of C and N, as well as the appearance of these fractions under the microscope. Similarly there was
a close relationship between changes in the C content of the POM fractions and the CO2 respired, and this was also the case when comparing changes in POM-N with net N mineralization. This indicated that the biological
activity during decomposition was actually localized in the POM. Due to the lighter workload and lower expenditure for reagents
in connection with size separation of POM, we recommend the size separation procedure in connection with studies of residue
decomposition in arable systems.
Received: 23 May 2000 相似文献
14.
We hypothesized that the integration of trees and shrubs in agricultural landscapes can reduce NO3
– leaching and increase utilization of subsoil N. A field survey was conducted on 14 farms on acid soils in the subhumid highlands
of Kenya, where there is little use of fertilizers, to determine the effect of vegetation types (VT) on soil NH4
+ and NO3
– to 4 m depth. The VT included maize (Zea mays) with poor growth and good growth, Markhamia lutea trees scattered in maize, natural weed fallow, banana (Musa spp.), hedgerow, and eucalyptus woodlot. The effect of VT on NH4
+ was small (<1 mg N kg–1). NO3
– within a VT was about constant with depth below 0.25 m, but subsoil NO3
– varied greatly among VT. Mean NO3
–-N concentrations at 0.5–4 m depth were low beneath hedgerow and woodlot (<0.2 mg kg–1), intermediate beneath weed fallow (0.2–0.7 mg kg–1), banana (0.5–1.0 mg kg–1) and markhamia (0.5–1.6 mg kg–1), and high beneath both poor (1.0–2.1 mg kg–1) and good (1.9–3.1 mg kg–1) maize. Subsoil NO3
– (0.5–4 m) was agronomically significant after maize harvest with 37 kg N ha–1 m–1 depth of subsoil beneath good maize and 27 kg N ha–1 m–1 depth beneath poor maize. In contrast, subsoil NO3
– was only 2 kg N ha–1 m–1 depth beneath woodlot and hedgerow. These results demonstrate that the integration of perennial vegetation and the rotation
of annual and perennial crops can tighten N cycling in agricultural landscapes.
Received: 8 July 1999 相似文献
15.
T. Mahmood R. Ali M. I. Sajjad M. B. Chaudhri G. R. Tahir F. Azam 《Biology and Fertility of Soils》2000,31(3-4):270-278
In a 2-year field study, denitrification loss was measured from an irrigated sandy-clay loam under cotton receiving urea-N
at 158–173 kg ha–1. An acetylene inhibition-soil core method was employed for the direct measurement of denitrification, considering also the
N2O entrapped in the soil. Taking into account the N2O evolved from soil cores and that entrapped in the soil, a total of 65.7 kg N ha–1 and 64.4 kg N ha–1 was lost due to denitrification during the 1995 and 1996 cotton-growing seasons, respectively. Most (>70%) of the denitrification
loss occurred during June–August, a period characterized by high soil temperatures and heavy monsoon rains. On average, 35%
of the denitrification-N2O was found entrapped in the soil and the amount of entrapped N2O was significantly correlated with head space N2O concentration and with water-filled pore space. 15N-balance during the 1996 growing season revealed a loss of 71.8 kg N ha–1. It was concluded that a substantial proportion of the fertilizer-N applied to irrigated cotton is lost under the semiarid
subtropical climatic conditions prevailing in the Central Punjab region of Pakistan and that denitrification is the major
N loss process under irrigated cotton in this region.
Received: 8 March 1999 相似文献
16.
Influences of organic fertilization and solarization in a greenhouse on particle-size fractions of a Mediterranean sandy soil 总被引:1,自引:0,他引:1
The effects of a composted organic amendment and solarization on the organic matter (OM) of a sandy soil were determined
by means of particle-size fractionation and analysis of carbon and nitrogen contents. After 2 years, total soil carbon increased
under organic fertilization but did not significantly change with solarization. As a consequence of the climatic conditions
in the greenhouse, the carbon concentrations (g kg–1 fraction) of the particle-size fractions were lower than those found for temperate soils and closer to those for tropical
soils. The carbon amounts (g kg–1 soil) and carbon:nitrogen ratios, which were highest in fractions >200 μm, reflected the short-term influence of the industrially
processed organic amendment, rich in composted coarse plant debris. In contrast, the characteristics of the OM associated
with each fraction were not significantly affected by solarization. In comparison with other coarse-textured temperate or
tropical soils, carbon concentrations in fine silt (2–20 μm) and clay (0–2 μm) fractions were very low. This suggests a "greenhouse
effect", together with a high rate of carbon mineralization affecting fine silt and clay fractions.
Received: 19 November 1999 相似文献
17.
Plant residues placed in soil in mesh bags do not mimic realistic decomposition conditions. Alternative techniques, e.g. combined
particle size and density methods, have been proposed to monitor in situ decomposition of plant residues, but are not appropriately
evaluated for their ability to quantitatively recover and characterise decomposing residues of a range of sizes mixed with
soil over long incubation times. For this study, we used canola residues of three different starting sizes (<1, 5–7 and 20–25 mm)
mixed in a soil and incubated for 6 months. The modified method presented here relied on initial size separation of soil and
organic particles into fractions of sizes <106 and >106-μm by wet sieving, and then by repeated floatation and decantation,
using water as a density agent, to recover and characterise decomposing canola residues from a mixture of >106-μm mineral
plus organic materials into >106-to-500 and >500-μm fractions. On day 0, across the three residue-size treatments, the >500-μm
fraction recovered 93–96% of canola residue-C, with water-soluble residue-C loss during the recovery process quantified as
representing further 4–5%. The rate of loss of residue-C in the >500-μm fraction was the largest, matching well the cumulative
respiration loss of residue-C. The recovery of canola residue-C in the >500-μm fraction, determined as percent of cumulative
CO2–C respired of added C, decreased to 72–76% by the end of incubation, likely due to progressive generation of finer-sized
residues and microbial/faunal metabolites. The increase of N in the >500-μm fraction accounted for ca. 40% of total soil N
immobilised in the residue-amended soil. The extent and patterns of changes in C, N and S contents, and C-to-N and C-to-S
ratios of separated fractions were similar among all the residue treatments during decomposition, except for the ground-residue
treatment. The combined size and density separation procedure can be used to study decomposition in situ of soil-mixed plant
residues of different sizes that are usually found in agro-ecosystems. 相似文献
18.
M. D. Serna J. Bañuls A. Quiñones E. Primo-Millo F. Legaz 《Biology and Fertility of Soils》2000,32(1):41-46
The objectives of this work were to evaluate the inhibitory action on nitrification of 3,4-dimethylpyrazole phosphate (DMPP)
added to ammonium sulphate nitrate [(NH4)2SO4 plus NH4NO3; ASN] in a Citrus-cultivated soil, and to study its effect on N uptake. In a greenhouse experiment, 2 g N as ASN either with or without 0.015 g
DMPP (1% DMPP relative to NH4
+-N) was applied 6 times at 20-day intervals to plants grown in 14-l pots filled with soil. Addition of DMPP to ASN resulted
in higher levels of NH4
+-N and lower levels of NO3
–-N in the soil during the whole experimental period. The NO3
–-N concentration in drainage water was lower in the ASN plus DMPP (ASN+DMPP)-treated pots. Also, DMPP supplementation resulted
in greater uptake of the fertilizer-N by citrus plants. In another experiment, 100 g N as ASN, either with or without 0.75 g
DMPP (1% DMPP relative to NH4
+-N) was applied to 6-year-old citrus plants grown individually outdoors in containers. Concentrations of NH4
+-N and NO3
–-N at different soil depths and N distribution in the soil profile after consecutive flood irrigations were monitored. In
the ASN-amended soil, nitrification was faster, whereas the addition of the inhibitor led to the maintenance of relatively
high levels of NH4
+-N and NO3
–-N in soil for longer than when ASN was added alone. At the end of the experiment (120 days) 68.5% and 53.1% of the applied
N was leached below 0.60 m in the ASN and ASN+DMPP treatments, respectively. Also, leaf N levels were higher in plants fertilized
with ASN+DMPP. Collectively, these results indicate that the DMPP nitrification inhibitor improved N fertilizer efficiency
and reduced NO3
– leaching losses by retaining the applied N in the ammoniacal form.
Received: 31 May 1999 相似文献
19.
The location of soil organic matter (SOM) within the soil matrix is considered a major factor determining its turnover, but quantitative information about the effects of land cover and land use on the distribution of SOM at the soil aggregate level is rare. We analyzed the effect of land cover/land use (spruce forest, grassland, wheat and maize) on the distribution of free particulate organic matter (POM) with a density <1.6 g cm−3 (free POM<1.6), occluded particulate organic matter with densities <1.6 g cm−3 (occluded POM<1.6) and 1.6-2.0 g cm−3 (occluded POM1.6-2.0) and mineral-associated SOM (>2.0 g cm−3) in size classes of slaking-resistant aggregates (53-250, 250-1000, 1000-2000, >2000 μm) and in the sieve fraction <53 μm from silty soils by applying a combined aggregate size and density fractionation procedure. We also determined the turnover time of soil organic carbon (SOC) fractions at the aggregate level in the soil of the maize site using the 13C/12C isotope ratio. SOM contents were higher in the grassland soil aggregates than in those of the arable soils mainly because of greater contents of mineral-associated SOM. The contribution of occluded POM to total SOC in the A horizon aggregates was greater in the spruce soil (23-44%) than in the grassland (11%) and arable soils (19%). The mass and carbon content of both the free and occluded POM fractions were greater in the forest soil than in the grassland and arable soils. In all soils, the C/N ratios of soil fractions within each aggregate size class decreased in the following order: free POM<1.6>occluded POM<1.6-2.0>mineral-associated SOM. The mean age of SOC associated with the <53 μm mineral fraction of water-stable aggregates in the Ap horizon of the maize site varied between 63 and 69 yr in aggregates >250 μm, 76 yr in the 53-250 μm aggregate class, and 102 yr in the sieve fraction <53 μm. The mean age of SOC in the occluded POM increased with decreasing aggregate size from 20 to 30 yr in aggregates >1000 μm to 66 yr in aggregates <53 μm. Free POM had the most rapid rates of C-turnover, with residence times ranging from 10 yr in the fraction >2000 μm to 42 yr in the fraction 53-250 μm. Results indicated that SOM in slaking-resistant aggregates was not a homogeneous pool, but consisted of size/density fractions exhibiting different composition and stability. The properties of these fractions were influenced by the aggregate size. Land cover/land use were important factors controlling the amount and composition of SOM fractions at the aggregate level. 相似文献
20.
Soil organic carbon stocks,distribution, and composition affected by historic land use changes on adjacent sites 总被引:1,自引:0,他引:1
Historic alterations in land use from forest to grassland and cropland to forest were used to determine impacts on carbon
(C) stocks and distribution and soil organic matter (SOM) characteristics on adjacent Cambisols in Eastern Germany. We investigated
a continuous Norway spruce forest (F-F), a former cropland afforested in 1930 (C-F), and a grassland deforested in 1953 (F-G).
For C and N stocks, we sampled the A and B horizons of nine soil pits per site. Additionally, we separated SOM fractions of
A and B horizons by physical means from one central soil pit per pedon. To unravel differences of SOM composition, we analyzed
SOM fractions by 13C-CPMAS NMR spectroscopy and radiocarbon analysis. For the mineral soils, differences in total C stocks between the sites
were low (F-F = 8.3 kg m−2; C-F = 7.3 kg m−2; F-G = 8.2 kg m−2). Larger total C stocks (+25%) were found under continuous forest compared with grassland, due to the C stored within the
organic horizons. Due to a faster turnover, the contents of free particulate organic matter (POM) were lower under grassland.
High alkyl C/O/N-alkyl C ratios of free POM fractions indicated higher decomposition stages under forest (1.16) in relation
to former cropland (0.48) and grassland (0.33). Historic management, such as burning of tree residues, was still identifiable
in the subsoils by the composition and 14C activity of occluded POM fractions. The high potential of longer lasting C sequestration within fractions of slower turnover
was indicated by the larger amounts of claybound C per square meter found under continuous forest in contrast to grassland. 相似文献