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1.
Ratios between estimates of microbial biomass content and microbial activity in soils 总被引:10,自引:0,他引:10
The content levels and activities of the microbiota were estimated in topsoils and in one soil profile at agricultural and forest sites of the Bornhöved Lake district in northern Germany. Discrepancies between data achieved by fumigation-extraction (FE) and substrate-induced respiration (SIR), both used for the quantification of microbial biomass, were attributed to the composition of the microbial populations in the soils. In the topsoils, the active, glucose-responsive (SIR) versus the total, chloroform-sensitive microbial (FE) biomass decreased in the order; field maize monoculture (field-MM)>field crop rotation (field-CR) and dry grassland>beech forest. This ratio decreased within the soil profile of the beech forest from the litter horizon down to the topsoil. Differences between microbial biomass and activities suggested varying biomass-specific transformation intensities in the soils. The metabolic quotient (qCO2), defined as the respiration rate per unit of biomass, indicates the efficiency in acquiring organic C and the intensity of C mineralization, while biomass-specific arginine-ammonification (arginine-ammonification rate related to microbial biomass content) seems to be dependent on N availability. The qCO2, calculated on the basis of the total microbial biomass, decreased for the topsoils in the same order as did the ratio between the active, glucose-responsive microbial biomass to the total, chloroform-sensitive microbial biomass, in contrast to qCO2 values based on the glucose-responsive microbial biomass, which did not. There was no difference between the levels of biomass-specific arginine-ammonification in topsoils of the fertilized field-CR, fertilized field-MM, fertilized dry grassland and eutric alder forest, but levels were lower in the beech forest, dystric alder forest, and unfertilized wet grassland topsoils. Ratios between values of different microbiological features are suggested to be more useful than microbiological features related to soil weight when evaluating microbial populations and microbially mediated processes in soils. 相似文献
2.
The significance of microbial biomass sulphur in soil 总被引:2,自引:0,他引:2
The soil microbial biomass S fraction of total organic S in soil is considered to be relatively labile and the most active S pool for S turnover in soil. Its significance has been demonstrated in studies of S deficiency in agronomic situations and in those of S pollution from high atmospheric inputs. The utility of the CHCl3 fumigation-extraction technique for the measurement of microbial S has been proved for a range of soils and conditions. The various methodologies currently available are discussed, including the need for determination of the conversion (K
s) factor. Microbial S values, summarized from the available literature, ranged from 3 to 300 g S g-1 dry weight soil. They were generally greater in grassland than in arable systems, though the greatest values were obtained in the few examples from forest and peatland soil systems. Microbial S values showed direct relationships with both microbial C and with total soil organic S. Again, there were significant differences between arable and grassland systems. The effect of factors such as organic and inorganic inputs as well as soil physical conditions on microbial S are described. Microbial S turnover rates were estimated from seasonal, 35S-labelling and modelling studies. These rates varied between an approximately annual turnover rate in undisturbed soils up to 80 year-1 following the addition of readily available substrates. Prospective future research areas are also outlined. 相似文献
3.
Conservation tillage, and especially no-tillage, induce changes in the distribution of organic pools in the soil profile.
In long-term field experiments, marked stratification of the total soil microbial biomass and its activity have been observed
as consequence of the application of no-tillage to previously tilled soils. Our objective was to study the evolution of the
total and active soil microbial biomass and mineralized C in vitro during the first crop after the introduction of no-tillage
to an agricultural soil. The experiment was performed on a Typic Hapludoll from the Argentinean Pampa. Remaining plant residues,
total and active microbial biomass and mineralized C were determined at 0–5 cm and 5–15 cm depths, at three sampling times:
wheat tilling, silking and maturity. The introduction of no-tillage produced an accumulation of plant residues in the soil
surface layer (0–5 cm), showing stratification with depth at all sampling dates. Active microbial biomass and C mineralization
were higher under no-tillage than under conventional tillage in the top 5 cm of the profile. The total soil microbial biomass
did not differ between treatments. The active soil biomass was highly and positive correlated with plant residues (r
2=0.617;P<0.01) and with mineralized C (r
2=0.732;P<0.01). Consequently, the active microbial biomass and mineralized C reflected immediately the changes in residue management,
whereas the total microbial biomass seemed not to be an early indicator of the introduction of a new form of soil management
in our experiment.
Received: 23 February 1999 相似文献
4.
Soil organic carbon stocks, storage profile and microbial biomass under different crop management systems in a tropical agricultural ecosystem 总被引:3,自引:0,他引:3
We investigated the soil organic C and N stocks, storage profiles and microbial biomass as influenced by different crop management
systems in a tropical agricultural ecosystem. The different crop management systems significantly affected the C and N stocks
and microbial biomass C and N at different soil depths. Amongst the systems evaluated, the rice-wheat system maintained a
higher soil organic C content. Inclusion of legumes in the system improved the soil organic matter level and also soil microbial
biomass activity, vital for the nutrient turnover and long-term productivity of the soil. Irrespective of the cropping system,
approximately 58.4%, 25.7% and 15.9% of the C was distributed in 0–15, 15–30 and 30–60 cm depths, respectively.
Received: 10 October 1999 相似文献
5.
无机氮和葡萄糖添加对土壤微生物生物量和活性的影响 总被引:1,自引:0,他引:1
以黄淮海平原潮土为研究对象,通过室内恒温恒湿培养方法,比较研究了土壤中纤维素是否存在时,外源无机氮和葡萄糖添加对土壤微生物生物量及其活性的影响变化。实验设8个处理,包括不加任何物质的对照(CK)、添加无机氮(N)、葡萄糖(G)、纤维素(C)处理及葡萄糖和无机氮同时添加(G+N)处理,以及在纤维素存在基础上添加无机氮(C+N)、葡萄糖(C+G)、葡萄糖和无机氮同时添加(C+G+N)处理。在33天培养时间内,分别在不同的时间间隔内测定了土壤CO2累积释放量、微生物生物量碳(Cmic)、及脱氢酶(DHD)、β-葡萄糖苷酶(GLU)、过氧化氢酶(CAT)、碱性磷酸酶(APH)活性。结果表明,所有测定的微生物性质在CK与C处理间均没有显著性差异。与CK和C处理相比,其他所有处理的土壤CO2累积释放量均显著增加,其中C+G+N处理达最大值;G、G+N、C+G、C+G+N处理的土壤Cmic含量及DHD和APH活性显著提升,尤其在培养的前14天,而N和C+N处理则与CK处理相似,表示添加葡萄糖可显著增加上述处理生物活性水平,而添加无机氮则不能。添加无机氮和葡萄糖对GLU和CAT的影响不明显,大部分情况下它们在处理间没有表现出显著性差异。相关性分析表明,CO2释放速率始终与APH活性成显著正相关,但与Cmic和其他酶活性之间的相关关系则随着培养时间的不同而发生变化,这可能与不同培养时间的微生物组成或微生物利用底物的模式发生改变有关。聚类分析结果进一步表明,8个处理的土壤微生物活性水平可明显分成3组,其中活性水平最高的组只包含C+G+N处理,该结果提示在难分解纤维素存在时,无机氮和易利用有机碳的同时添加对提升土壤微生物活性的重要性。 相似文献
6.
Seasonal responses in microbial biomass carbon, phosphorus and sulphur in soils under pasture 总被引:28,自引:0,他引:28
The response of the soil microbial biomass to seasonal changes was investigated in the field under pastures. These studies
showed that over a 9-month period, microbial biomass carbon, phosphorus and sulphur (biomass C, P, S), and their ratios (C:P,
C:S, and P:S) responded differently to changes in soil moisture and to the input of fresh organic materials. From October
to December (1993), when plant residues were largely incorporated into the soils, biomass C and S increased by 150–210%. Biomass
P did not increase over this time, having decreased by 22–64% over the dry summer (July to September). There was no obvious
correlation between biomass C, P, and S and air temperature. The largest amounts of biomass C and P (2100–2300μg and 150–190μgg–1 soil, respectively) were found in those soils receiving farmyard manure (FYM or FYM+NPK) and P fertilizer, whereas the use
of ammonium sulphate decreased biomass C and P. The C:P, C:S, and P:S ratios of the biomass varied considerably (9–276:1;
50–149:1; and 0.3–14:1, respectively) with season and fertilizer regime. This reflected the potential for the biomass to release
(when ratios were narrow) or to immobilize (wide ratios) P and S at different times of the year. Thus, seasonal responses
in biomass C, P, and S are important in controlling the cycling of C, P, and S in pasture and ultimately in regulating plant
availability of P and S. The uptake of P in the pasture was well correlated with the sum of P in the biomass and soil available
pools. Thus, the simultaneous measurement of microbial biomass P and available P provide useful information on the potential
plant availability of P.
Received: 25 May 1996 相似文献
7.
R. J. Haynes 《Biology and Fertility of Soils》1999,30(3):210-216
The effects of 5 years of continuous grass/clover (Cont grass/clover) or grass (Cont grass) pasture or 5 years of annual
grass under conventional (Ann grass CT) or zero tillage (Ann grass ZT) were compared with that of 5 years of continuous barley
(LT arable) on a site which had previously been under arable crops for 11 years. For added comparison, a long-term grass/clover
pasture site (LT past) nearby was also sampled. Soil organic C (Corg) content followed the order LT arable=Ann grass CT<Ann grass ZT<Cont grass=Cont grass/clover<LTpast. Trends with treatment
for microbial biomass C (Cmic), basal respiration, flourescein diacetate (FDA) hydrolytic activity, arginine ammonification rate and the activities of
dehydrogenase, protease, histidase, acid phosphatase and arylsulphatase enzymes were broadly similar to those for Corg. For Cmic, FDA hydrolysis, arginine ammonification and the activities of histidase, acid phosphatase and arylsulphatase, the percentage
increase caused by 5 years of continuous pasture (in comparison with LT arable) was 100–180%, which was considerably greater
than that for organic C (i.e. 60%). The microbial metabolic quotient (qCO2) was higher for the two treatments which were mouldboard ploughed annually (LT arable and Ann grass CT) than for the undisturbed
sites. At the undisturbed sites, Corg declined markedly with depth (0–15 cm) and there was a similar stratification in the size and activity of Cmic and enzyme activity. The microbial quotient (Cmic/Corg) declined with depth whilst qCO2 tended to increase, reflecting a decrease in the proportion of readily available substrate with depth.
Received: 7 July 1998 相似文献
8.
Effect of soil CO2 concentration on microbial biomass 总被引:1,自引:0,他引:1
The effect of increasing soil CO2 concentration was studied in six different soils. The soils were incubated in ambient air (0.05 vol.% CO2) or in air enriched with CO2 (up to 5.0 vol.% CO2). Carbon dioxide evolution, microbial biomass, growth or death rate quotients and glucose decay rate were measured at 6,
12 and 24 h of CO2 exposure. The decrease in soil respiration ranged from 7% to 78% and was followed by a decrease in microbial biomass by 10–60%
in most cases. High CO2 treatments did not affect glucose decay rate but the portion of Cgluc mineralized to CO2 was lowered and a larger portion of Cgluc remained in soils. This carbon was not utilized by soil microorganisms.
Received: 30 August 1996 相似文献
9.
Phosphorus mineralization and microbial biomass in a Florida Spodosol: effects of water potential, temperature and fertilizer application 总被引:1,自引:0,他引:1
Phosphorus mineralization and microbial biomass were measured in the surface 5 cm of a Spodosol (sandy, siliceous hyperthermic
Ultic Alaquod) from north-central Florida. Soils from fertilized and unfertilized plantations of loblolly pine (Pinus taeda L.) were incubated at a range of water potentials (∼0, –3, –8, –10 and –1500 kPa) and temperatures (15 °C, 25 °C and 38 °C)
for 14 days and 42 days. Increasing water potential and temperature increased specific P mineralization (mineralization expressed
as a percentage of total P) regardless of fertilizer treatment. An increase in water potential from –10 kPa to –0.1 kPa resulted
in an increase of between 38% and 239% in the concentration of KCl-extractable inorganic P, depending on incubation temperature
and time. An increase in incubation temperature from 15 °C to 38 °C resulted in an increase of between 13% and 53% in KCl-extractable
inorganic P. Changes in specific P mineralization with change in water potential or temperature were not affected by fertilizer
application. This suggests that, although specific P mineralization was greater in the fertilized soils, environmental control
of P mineralization was the same for both treatments. Specific P mineralization was most sensitive when soils were at higher
water potentials, and decreased logarithmically to water potentials of between –3 kPa and –8 kPa. Specific P mineralization
was relatively insensitive to changes in water potential when water potential was lower than –8 kPa. Microbial biomass C showed
no consistent responses to changes of temperature or water potential and was not significantly correlated with specific P
mineralization. Our results suggest that field estimates of P mineralization in these Spodosols may be improved by accounting
for changes in soil water potential and temperature.
Received: 30 October 1997 相似文献
10.
Influence of soil properties on microbial populations, activity and biomass in humid subtropical mountainous ecosystems of India 总被引:1,自引:0,他引:1
Microbial populations, biomass, soil respiration and enzyme activities were determined in slightly acid organic soils of
major mountainous humid subtropical terrestrial ecosystems, along a soil fertility gradient, in order to evaluate the influence
of soil properties on microbial populations, activity and biomass and to understand the dynamics of the microbial biomass
in degraded ecosystems and mature forest. Although the population of fungi was highest in the undisturbed forest (Sacred Grove),
soil respiration was lowest in the 7-year-old regrowth and in natural grassland (approximately 373 μg g–1 h–1). Dehydrogenase and urease activities were high in "jhum" fallow, and among the forest stands they were highest in the 7-year-old
regrowth. Microbial biomass C (MBC) depended mainly on the organic C status of the soil. The MBC values were generally higher
in mature forest than in natural grassland, 1-year-old jhum fallow and the 4-year-old alder plantation. The MBC values obtained
by the chloroform-fumigation-incubation technique (330–1656 μg g–1) did not vary significantly from those obtained by the chloroform-fumigation-extraction technique (408–1684 μg g–1), however, the values correlated positively (P<0.001). The enzyme activities, soil respiration, bacterial and fungal populations and microbial biomass was greatly influenced
by several soil properties, particularly the levels of nutrients. The soil nutrient status, microbial populations, soil respiration
and dehydrogenase activity were greater in Sacred Grove, while urease activity was greater in grassland.
Received: 14 October 1998 相似文献
11.
Soil organic matter, microbial biomass and enzyme activities in a tropical agroforestry system 总被引:14,自引:0,他引:14
The effects of growing trees in combination with field crops on soil organic matter, microbial biomass C, basal respiration
and dehydrogenase and alkaline phosphatase activities were studied in soils under a 12-year-old Dalbergia sissoo (a N2-fixing tree) plantation intercropped with a wheat (Triticum aestivum) – cowpea (Vigna sinensis) cropping sequence. The inputs of organic matter through D. sissoo leaf litter increased and crop roots decreased with the increase in tree density. Higher organic C and total N, microbial
biomass C, basal soil respiration and activities of dehydrogenase and alkaline phosphatase were observed in treatments with
tree-crop combination than in the treatment without trees. Soil organic matter, microbial biomass C and soil enzyme activities
increased with the decrease in the spacing of the D. sissoo plantation. The results indicate that adoption of the agroforestry practices led to an improved organic matter status of
the soil, which is also reflected in the increased nutrient pool and microbial activities necessary for long-term productivity
of the soil. However, tree spacing should be properly maintained to minimize the effects of shading on the intercrops.
Received: 21 February 1997 相似文献
12.
Seasonal changes of microbial biomass carbon related to climatic factors in soils from karst areas of southwest China 总被引:7,自引:0,他引:7
The seasonal responses of soil microbial biomass C to changes in atmospheric temperature, soil moisture and soluble organic
C were studied in soils from the karst areas of southwest China. These soils are relatively weathered, leached and impoverished,
and have a low input of plant residues. Over 1 year, an inverse relationship between soil microbial biomass C and atmospheric
temperature was found. The highest microbial biomass C occurred in winter and the lowest in summer, and ranged from 231–723 μg
g–1 dry soil. Although there was no obvious relationship between microbial biomass C and soil moisture, a negative correlation
existed between microbial biomass C and soluble organic C. In the ecosystem studied, the marked changes in soil microbial
biomass C at above 20 °C were ascribed to fluctuations of soil moisture, which were controlled by climatic factors and geomorphic
conditions. The patterns of soluble organic C turnover were similar to those of soluble carbohydrate C, both of which were
controlled by soil drying-rewetting cycles. It was concluded that the lowest amounts of soil microbial biomass C, measured
in the summer, resulted in increases in soluble organic C due to higher turnover rates of the former at warmer air temperatures.
Thus, there was a marked seasonal change in soil microbial biomass C.
Received: 1 November 1998 相似文献
13.
Dynamics of soil microbial biomass and nitrogen availability in a flooded rice soil amended with different C and N sources 总被引:4,自引:0,他引:4
A greenhouse experiment was conducted to compare effects of different C and N sources applied to a flooded soil on soil microbial
biomass (SMB) C and N, extractable soil organic N (NORG), and NH4
+-N in relation to plant N accumulation of rice (Oryza sativa L.). In addition to a control without inputs (CON), four treatments were imposed receiving: prilled urea (PU), rice straw
(RS), RS and PU (RS+PU), or Sesbania rostrata as green manure (SES). Treatments were arranged according to a completely randomized design with four replicates and further
consisted of pots with and without transplanted rice. While plant effects on the SMB were relatively small, the application
of organic N sources resulted in a rapid increase in SMB until 10 days after transplanting (DAT) followed by a gradual decline
until 73 DAT. Plant N accumulation data in these treatments clearly indicated that the SMB underwent a transition from a sink
to a source of plant-available soil N during the period of crop growth. Seasonal variation of the SMB was small in treatments
without amendment of organic material (CON, PU) presumably due to a lack of available C as energy source. Extractable NORG was significantly affected by soil planting status and organic N source amendment, but represented only a small N pool with
little temporal variation despite an assumed rapid turnover. Among the three treatments receiving the same amount of N from
different sources, the recovery efficiency of applied N was 58% for PU and 28% for both RS+PU and SES treatments at 73 DAT.
The N uptake of rice, however, was not driven by N availability alone, as most evident in the RS+PU treatment. We assume that
root physiological functions were impeded after application of organic N sources.
Received: 1 June 1999 相似文献
14.
Water and N availability are the major limiting factors of primary production in desert ecosystems, and the response of soil
biota to these two factors is of great importance. We examined the immediate response of soil nematodes and the microbial
biomass to a single pulse of water amendment in N-treated plots in the Israeli Negev desert. Plots were treated with 0, 50
and 100 kg NH4NO3 ha–1 in December 1992, and at the end of the summer period (August 1993) the plots were exposed to a 15 mm water. Soil samples
from the 0–10 cm layer were collected daily and analysed soil moisture, total soluble N, nematode populations and microbial
biomass. Soil moisture increased to 8.5%, then gradually decreased to 2% during the 11 days of the study. Microbial biomass,
soil respiration and metabolic quotient values did not exhibit any significant correlation with soil N levels. Free-living
nematode population levels in the different plots were found to increase from a mean level of 45 500 to a mean level of 92 300
individuals m–2. N treatment was found to affect the patterns of free-living nematode population dynamics. The results of this study demonstrated
the importance of moisture availability levels and the ability to mobilize previous N inputs into available N which, occurring
in pulses, can affect the microbial ecophysiological status, nematode population dynamics and the interrelationship between
these two important components in the desert soil milieu.
Received: 5 November 1998 相似文献
15.
A rapid chloroform-fumigation extraction method for measuring soil microbial biomass carbon and nitrogen in flooded rice soils 总被引:2,自引:0,他引:2
C. Witt J. L. Gaunt C. C. Galicia J. C. G. Ottow H.-U. Neue 《Biology and Fertility of Soils》2000,30(5-6):510-519
A chloroform-fumigation extraction method with fumigation at atmospheric pressure (CFAP, without vacuum) was developed for
measuring microbial biomass C (CBIO) and N (NBIO) in water-saturated rice soils. The method was tested in a series of laboratory experiments and compared with the standard
chloroform-fumigation extraction (CFE, with vacuum). For both methods, there was little interference from living rice roots
or changing soil water content (0.44–0.55 kg kg–1 wet soil). A comparison of the two techniques showed a highly significant correlation for both CBIO and NBIO (P<0.001) suggesting that the simple and rapid CFAP is a reliable alternative to the CFE. It appeared, however, that a small
and relatively constant fraction of well-protected microbial biomass may only be lysed during fumigation under vacuum. Determinations
of microbial C and N were highly reproducible for both methods, but neither fumigation technique generated NBIO values which were positively correlated with CBIO. The range of observed microbial C:N ratios of 4–15 was unexpectedly wide for anaerobic soil conditions. Evidence that this
was related to inconsistencies in the release, degradation, and extractability of NBIO rather than CBIO came from the observation that increasing the fumigation time from 4 h to 48 h significantly increased NBIO but not CBIO. The release pattern of CBIO indicated that the standard fumigation time of 24 h is applicable to water-saturated rice soils. To correct for the incomplete
recovery of CBIO, we suggest applying the k
C factor of 2.64, commonly used for aerobic soils (Vance et al. 1987), but caution is required when correcting NBIO data. Until differences in fumigation efficiencies among CFE and CFAP are confirmed for a wider range of rice soils, we suggest
applying the same correction factor for both methods.
Received: 1 June 1999 相似文献
16.
Soil sulphur status following long-term annual application of animal manure and mineral fertilizers 总被引:1,自引:0,他引:1
In agricultural systems with low S inputs, crops rely on the release of S from organic forms in the soil. In the Askov long-term
experiments, started in 1894 on both sandy and loamy soils, soil S status following long-term application of animal manure
and mineral fertilizers was investigated in the growing season of 1995. In a field trial with oil-seed rape (Brassica napus, L.) soil analysis, leaf tissue analysis, yield and S removal in plant material was used to characterize differences in availability
of soil S. One half of all plots received 63 kg S ha–1 as gypsum. Long-term fertilization with animal manure or NPK fertilizer increased the content of soil organic C in both soils
and of organic S in the sandy soil compared with unfertilized plots. Although dry matter yields were unaffected, the S uptake
in harvested crop parts increased considerably after S application. The amounts of N and S in harvested seeds and straw were
closely related, but the N : S ratio decreased when S was applied. Soil and plant analyses both indicated that critical levels
of S concentrations were reached, and that S application was capable of raising S concentrations well above the critical level.
Because no additional mineralization from residual organic S took place, it was concluded that the residual S effect from
long-term annual applications of animal manure or mineral fertilizers did not significantly increase the level of soil S available
for crops with a short growing season, such as oil-seed rape.
Received: 9 January 1998 相似文献
17.
Effects of long-term waste water irrigation on soil organic matter, soil microbial biomass and its activities in central Mexico 总被引:4,自引:0,他引:4
The effect of long-term waste water irrigation (up to 80 years) on soil organic matter, soil microbial biomass and its activities
was studied in two agricultural soils (Vertisols and Leptosols) irrigated for 25, 65 and 80 years respectively at Irrigation
District 03 in the Valley of Mezquital near Mexico City. In the Vertisols, where larger amounts of water have been applied
than in the Leptosols, total organic C (TOC) contents increased 2.5-fold after 80 years of irrigation. In the Leptosols, however,
the degradability of the organic matter tended to increase with irrigation time. It appears that soil organic matter accumulation
was not due to pollutants nor did microbial biomass:TOC ratios and qCO2 values indicate a pollutant effect. Increases in soil microbial biomass C and activities were presumably due to the larger
application of organic matter. However, changes in soil microbial communities occurred, as denitrification capacities increased
greatly and adenylate energy charge (AEC) ratios were reduced after long-term irrigation. These changes were supposed to be
due to the addition of surfactants, especially alkylbenzene sulfonates (effect on denitrification capacity) and the addition
of sodium and salts (effect on AEC) through waste water irrigation. Heavy metals contained in the sewage do not appear to
be affecting soil processes yet, due to their low availability. Detrimental effects on soil microbial communities can be expected,
however, from further increases in pollutant concentrations due to prolonged application of untreated waste water or an increase
in mobility due to higher mineralization rates.
Received: 28 April 1999 相似文献
18.
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
19.
In a cropping systems experiment in southeastern Norway, ecological (ECO), integrated (INT) and conventional (CON) forage
(FORAGE) and arable (ARABLE) model farms were compared. After 5 experimental years, topsoil was sampled in spring from spring
grain plots and incubated for 449 days at controlled temperature (15 °C) and moisture content (50% water-holding capacity).
There were no detectable differences between model farms in terms of total soil C or N. For INT and CON, however, values of
microbial biomass C and N, microbial quotient (Cmic/Corg), and C and N mineralization were, or tended to be, higher for FORAGE than for ARABLE. For the ECO treatment, values were
similar for FORAGE and ARABLE and did not differ significantly from that of CON-FORAGE. For INT and CON, the metabolic quotient
(qCO2) was lower for FORAGE than for ARABLE. Again, for the ECO treatment, values were similar for FORAGE and ARABLE and did not
differ significantly from that of CON-FORAGE. We estimated the sizes of conceptual soil organic matter pools by fitting a
decomposition model to biomass and mineralization data. This resulted in a 48% larger estimate for CON-FORAGE than for CON-ARABLE
of physically protected biomass C. For physically protected organic C the difference was 42%. Moreover, the stability of soil
aggregates against artificial rainfall was substantially greater for CON-FORAGE than for CON-ARABLE. On this basis, we hypothesized
that the lower qCO2 values in the FORAGE soils were mainly caused by a smaller proportion of active biomass due to enclosure of microorganisms
within aggregates. Altogether, our results indicated a poorer inherent soil fertility in ARABLE than in FORAGE rotations,
but the difference was small or absent in the ECO system, probably owing to the use of animal and green manures and reduced
tillage intensity in the ECO-ARABLE rotation.
Received: 28 October 1998 相似文献
20.
Soil microbial biomass and nitrogen supply in an irrigated lowland rice soil as affected by crop rotation and residue management 总被引:5,自引:0,他引:5
C. Witt Kenneth G. Cassman Johannes C. G. Ottow Ulrich Biker 《Biology and Fertility of Soils》1998,28(1):71-80
Processes that govern the soil nitrogen (N) supply in irrigated lowland rice systems are poorly understood. The objectives
of this paper were to investigate the effects of crop rotation and management on soil N dynamics, microbial biomass C (CBIO) and microbial biomass N (NBIO) in relation to rice N uptake and yield. A maize-rice (M-R) rotation was compared with a rice-rice (R-R) double-cropping
system over a 2-year period with four cropping seasons. In the M-R system, maize (Zea mays L.) was grown in aerated soil during the dry season (DS) followed by rice (Oryza sativa L.) grown in flooded soil during the wet season (WS). In the R-R system, rice was grown in flooded soil in both the DS and
WS. Three fertilizer N rates (0, 50 or 100 kg urea-N ha–1 in WS) were assigned to subplots within the cropping system main plots. Early versus late crop residue incorporation following
DS maize or rice were established as additional treatments in sub-subplots in the second year. In the R-R system, the time
of residue incorporation had a large effect on NO3
–-N accumulation during the fallow period and also on extractable NH4
+-N, rice N uptake and yield in the subsequent cropping period. In contrast, time of residue incorporation had little influence
on extractable N in both the fallow and rice-cropping periods of the M-R system, and no detectable effects on rice N uptake
or yield. In both cropping systems, CBIO and NBIO were not sensitive to residue incorporation despite differences of 2- to 3-fold increase in the amount of incorporated residue
C and N, and were relatively insensitive to N fertilizer application. Extractable organic N was consistently greater after
mid-tillering in M-R compared to the R-R system across N rate and residue incorporation treatments, and much of this organic
N was α-amino N. We conclude that N mineralization-immobilization dynamics in lowland rice systems are sensitive to soil aeration
as influenced by residue management in the fallow period and crop rotation, and that these factors have agronomically significant
effects on rice N uptake and yield. Microbial biomass measurements, however, were a poor indicator of these dynamics.
Received: 31 October 1997 相似文献