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1.
Sandy soil samples collected from under a woody/grass savanna in the Lamto experimental area (6°13N, 5°20W; Côte dIvoire, West Africa), were fractionated according to particle size with the aim of measuring the natural abundance of 15N and determining the contents and composition of hydrolysable carbohydrates of soil organo-mineral particles for a better understanding of the contribution of each individual fraction to the soil function. The contributions of the fractions <20 m to the total pool of organic matter were 77% for C and 84% for N. Larger amounts of carbohydrates were found in the clay and silt fractions (3,784–6,043 g g–1 soil). The carbohydrate composition indicated that microbe-derived carbohydrates [e.g. galactose (Gal) and mannose (Man)] accumulated preferentially in the fine fractions while plant-derived sugars [e.g. arabinose (Ara) and xylose (Xyl)] were dominant in coarse fractions. A negative relationship was observed between C:N ratio and 15N natural abundance on the one hand, and on the other hand between C:N and (Gal+Man):(Ara+Xyl), Man:(Ara+Xyl) and Man:Xyl ratios, clearly indicating that the chemistry of the organic materials of the particle-size fractions reflects a change from soil chemistry dominated by plant materials to that dominated by microbial biomass and metabolites. The contribution of a given fraction to soil microbial activity is controlled by the quality or quantity of associated soil organic matter, its microbial biomass and also by the accumulation of microbial-derived carbohydrates which can be resynthesized or recycled. 相似文献
2.
Transformations of nitrogen-15-labelled urea in a flooded soil as affected by floodwater algae and green manure in a growth chamber 总被引:1,自引:0,他引:1
The effects of floodwater algae and green manure on transformations of 15N-urea were studied in columns of a sandy loam soil in a growth chamber. The columns were flooded and either kept in the light,
to allow algal growth, or in the dark (control) for 17 days before adding the labelled urea. Changes in urea-, NO3
–- and NH4
+-N levels and the pH of the floodwater were measured over the subsequent 41-day period, during which the control column remained
in the dark and those containing algae were maintained either in the dark to cause the death of the algae or in the light.
Volatilized NH3 was monitored, and on termination of the experiment the distribution of 15N between NO3
–, NH4
+ and organic forms was measured in the soil. Urea hydrolysis was most rapid in the presence of both living algae and green
manure, followed by dead algae, and was slowest in the control. The concentration of NH4
+-N in the floodwater was, however, reduced in the presence of algae due to assimilation and NH3 volatilization owing to the raised day-time pH in the floodwater. NH3 volatilization for the first 10 days was rather high in the columns kept in the light compared to those in the dark. Total
volatilization plus denitrification losses were greatest where dead algae were present, owing to the absence of live algae
which assimilated more than half of the applied N. Algal growth in floodwater increased the depth of the aerobic soil layer
present at the soil-water interface. Subsequently, under dark conditions, stimulated algal growth reduced the depth of the
aerobic layer causing less nitrification, which resulted in lower losses of N due to denitrification, i.e. 17% of the applied
urea-N as compared to 39% in the light treatments. Although the presence of green manure caused a marked increase in the rate
of hydrolysis, algal assimilation prevented excessive N losses via volatilization, indicating that the retention of higher
quantities of NH4
+-N may have increased fertilizer-N use efficiency.
Received: 22 January 1999 相似文献
3.
Effect of climate, soil type and earthworm activity on nitrogen transfer from a nitrogen-15-labelled decomposing material under field conditions 总被引:4,自引:0,他引:4
N transfer from 15N-labelled decomposing material into the microbial biomass and inorganic N forms was studied for more than 2 years at three
experimental sites differing in climatic conditions and earthworm abundance. The 15N-labelled decomposing material was mixed with low-elevation soil (LES), mid-elevation soil (MES) and high-elevation soil
(HES). The amended soils were put into two kinds of plastic cylinders closed on both sides with nets preventing (0.1 cm mesh)
and allowing (0.5 cm mesh) access by earthworms, and were buried in soil (20 cm depth) to monitor the transfer of N from the
15N-labelled decomposing material. Climate and soil type play an important role in the release of N from decomposing material.
LES transplanted to more humid sites (mid- and high-elevation sites) showed an increase in most of its biological activities
(N atom % excess, and microbial biomass C and N). Furthermore, LES was a sandy soil in which the 15N-labelled decomposing material was less bound than in MES and HES, which contained more silt and clay. This resulted in faster
organic matter turnover when climatic conditions were favourable. The presence of earthworms greatly increased the quantity
of inorganic N (mainly NH4
+) in the soils and enhanced the release of N from the 15N-labelled decomposing material and the native organic matter, compared to soil without earthworms.
Received: 21 January 1999 相似文献
4.
Transformations and recovery of residue and fertilizer nitrogen-15 in a sandy Lixisol of West Africa
The fate of 15N-labeled plant residues from different cover-cropping systems and labeled inorganic N fertilizer in the organic, soil mineral,
microbial biomass and soil organic matter (SOM) particle-size fractions was investigated in a sandy Lixisol. Plant residues
were from mucuna (legume), lablab (legume), imperata (grass), maize (cereal) and mixtures of mucuna or lablab with imperata
or maize, applied as a surface mulch. Inorganic N fertilizer was applied as 15N-(NH4)2SO4 at two rates (21 and 42 mg N kg–1 soil). Total N release from mucuna or lablab residues was 2–3 times higher than from the other residues, whereas imperata
immobilized N throughout the study period. In contrast, 15N was mineralized from all the plant residues irrespective of the mineralization–immobilization pattern observed for total
N. After 168 days, 69% of soil mineral N in mucuna- or lablab-mulched soils was derived from the added residues, representing
4–8% of residue N, whereas 9–30% of inorganic N was derived from imperata, maize and the mixed residues. At the end of the
study, 4–19% of microbial biomass N was derived from the added residue/fertilizer-N, accounting for 1–3% of added residue-N.
Averaged across treatments, particulate SOM fractions accounted for less than 1% of the total soil by weight but contained
20% of total soil C and 8% of soil N. Soils amended with mucuna or lablab incorporated more N in the 250–2000 μm SOM pool,
whereas soil amended with imperata or the mixed residues incorporated similar proportions of labeled N in the 250–2000 μm
and 53–250 μm fractions. In contrast, in soils receiving the maize or inorganic fertilizer-N treatments, higher proportions
of labeled N were incorporated into the 53–250 μm than the 250–2000 μm fractions. The relationship between these differences
in residue/fertilizer-N partitioning into different SOM particle-size fractions and soil productivity is discussed.
Received: 12 March 1999 相似文献
5.
The natural abundance of δ15N in disturbed and undisturbed pasture soils was examined. From the disturbed soil, the top 10 cm of the profile was examined
and the soil split into fractions based on particle size. Plant shoot and root material contained similar low enrichments
in 15N, whereas recently deposited shoot residues were highly enriched. Differences between the soil fractions in observed total
N did not reflect similar 15N variation. However, the enrichment of humic material extracted from the largest soil fraction was considerably lower in
15N relative to that from the smaller fractions. The complexity of the humic material from the larger fractions was less according
to the E
4
/E
6
ratio. Analysis of the profile from the undisturbed soil showed increasing 15N enrichment with depth which corresponded well with visible soil horizons and showed an inverse relationship with total soil
N. This 15N enrichment was mirrored by the enrichment in humic materials down the profile and also corresponded with an increasing chemical
complexity as shown by the E
4
/E
6
ratio.
Received: 15 March 1996 相似文献
6.
Invertebrate control of soil organic matter stability 总被引:17,自引:0,他引:17
V. Wolters 《Biology and Fertility of Soils》2000,31(1):1-19
The control of soil organic matter (SOM) stability by soil invertebrates is evaluated in terms of their impact on the inherent
recalcitrance, accessibility to microorganisms, and interaction with stabilizing substances of organic compounds. Present
knowledge on internal (ingestion and associated transformations) and external (defecation, constructions) control mechanisms
of soil invertebrates is also reviewed. Soil animals contribute to the stabilization and destabilization of SOM by simultaneously
affecting chemical, physical, and microbial processes over several orders of magnitude. A very important aspect of this is
that invertebrates at higher trophic levels create feedback mechanisms that modify the spatio-temporal framework in which
the micro-food web affects SOM stability. Quantification of non-trophic and indirect effects is thus essential in order to
understand the long-term effects of soil biota on SOM turnover. It is hypothesized that the activities of invertebrates which
lead to an increase in SOM stability partly evolved as an adaptation to the need for increasing the suitability of their soil
habitat. Several gaps in knowledge are identified: food selection and associated changes in C pools, differential effects
on SOM turnover, specific associations with microorganisms, effects on dissolution and desorption reactions, humus-forming
and humus-degrading processes in gut and faeces, and the modification of invertebrate effects by environmental variables.
Future studies must not be confined merely to a mechanistic analysis of invertebrate control of SOM stability, but also pay
considerable attention to the functional and evolutionary aspects of animal diversity in soil. This alone will allow an integration
of biological expertise in order to develop new strategies of soil management which can be applied under a variety of environmental
conditions.
Received: 6 April 1999 相似文献
7.
Availability of N from Casuarina residues and inorganic N to maize, using 15N isotope techniques 总被引:1,自引:0,他引:1
The contribution of N from Casuarina equisetifolia (casuarina) residues to maize with inorganic N (ammonium sulphate) supplementation was studied in a pot experiment using
15N labelling techniques. A single rate of N application of 100 mg N kg–1 soil was applied as N-ammonium sulphate in combination with casuarina residues in the proportions 100 : 0; 75 : 25; 50 : 50;
25 : 75 and 0 : 100, respectively. The directly 15N-labelled casuarina residue and indirect labelling (unlabelled casuarina + 15N soil) were compared to estimate the proportion and amount of N derived from the residue and fertilizer. The application
of ammonium sulphate at a high rate significantly affected shoot dry matter (P<0.05) and likewise reduced the contribution of soil-derived N compared to residues. Total recoveries by maize of residue
N and applied fertilizer N averaged 11% and 24%, respectively. Residue and fertilizer use efficiencies were not influenced
by the addition of different rates of fertilizer or residue. The estimation of the contribution of N from different sources
showed that direct measurement of the 15N-labelled organic source was more reliable.
Received: 10 September 1997 相似文献
8.
S. S. Alfaia G. Guiraud F. Jacquin T. Muraoka G. A. Ribeiro 《Biology and Fertility of Soils》2000,31(3-4):329-333
The objective of this study was to determine the efficiency of two N fertilizers, (NH4)2SO4 and urea, for rice (Oryza sativa L.) and rye-grass (Lolium multiflorum L.) cultivated in an Ultisol of central Amazonia using 15N as a tracer. Rice was cultivated in the field, while rye-grass was grown in a phytotron. Fertilization with (NH4)2SO4 caused a 16% increase in the yield of rice grains and urea a 36% increase. In both crops total N uptake and N use efficiency
of the fertilizers were higher for urea than for (NH4)2SO4. The low values for N derived from fertilizer showed that the fertilizers contributed little to the total N absorbed by the
plants. The "priming effect" or positive added N interaction (ANI) between the fertilizer N and soil organic N was observed,
especially with urea. Immobilization by soil microorganisms was greater in the presence of urea, while losses were always
higher with the (NH4)2SO4 treatments. These losses were significant, and their reduction should allow more efficient use of this N fertilizer. It is
possible that the N use efficiency was higher for urea due to a pH increase, caused by urea hydrolysis, which in turn may
have favoured the activity of nitrifying bacteria in this extremely acid soil.
Received: 6 April 1999 相似文献
9.
R. J. Haynes 《Biology and Fertility of Soils》2000,30(4):270-275
The effects of sample pretreatment (field-moist, air-dried or tension rewetted) on aggregate stability measured by wet sieving
or turbidimetry were compared for a group of soil samples ranging in organic C content from 20 to 40 g C kg–1. Concentrations of total N, total and hot-water-extractable carbohydrate and microbial biomass C were linearly related to
those of organic C. Aggregate stability measured by wet sieving using air-dried or field-moist samples and that measured by
turbidimetry, regardless of sample pretreatment, increased curvilinearly with increasing soil organic C content. However,
when tension-rewetted samples were used for wet sieving, aggregate stability was essentially unaffected by soil organic C
content. Measurements of aggregate stability (apart from wet sieving using rewetted soils) were closely correlated with one
another and with organic C, total and extractable carbohydrate and microbial biomass C content of the soils. The short-term
effects of aggregate stability were also studied. Soils from under long-term arable management and those under long-term arable
followed by 1 or 3 years under pasture had similar organic C contents, but aggregate stability measured by turbidimetry and
by wet sieving using air-dried or field-moist samples increased with increasing years under pasture. Light fraction C, microbial
biomass and hot-water-extractable carbohydrate concentrations also increased. It was concluded that both total and labile
soil organic C content are important in relation to water-stable aggregation and that the use of tension-rewetted samples
to measure stability by wet sieving is unsatisfactory since little separation of values is achieved.
Received: 6 January 1999 相似文献
10.
The impact of a low humus level in arable soils on microbial properties, soil organic matter quality and crop yield 总被引:7,自引:0,他引:7
In arable soils in Schleswig-Holstein (Northwest Germany) nearly 30% of the total organic C (TOC) stored in former times
in the soil has been mineralized in the last 20 years. Microbial biomass, enzyme activities and the soil organic matter (SOM)
composition were investigated in order to elucidate if a low TOC level affects microbial parameters, SOM quality and crop
yield. Microbial biomass C (Cmic) and enzyme activities decreased in soils with a low TOC level compared to soils with a typical TOC level. The decrease in
the Cmic/TOC ratio suggested low-level, steady-state microbial activity. The SOM quality changed with respect to an enrichment of
initial litter compounds in the top soil layers with a low TOC level. Recent management of the soils had not maintained a
desirable level of humic compounds. However, we found no significant decrease in crop yield. We suggest that microbial biomass
and dehydrogenase and alkaline phosphatase activities are not necessarily indicators of soil fertility in soils with a high
fertilization level without forage production and manure application.
Received: 12 December 1997 相似文献
11.
Influence of soil compaction on carbon and nitrogen mineralization of soil organic matter and crop residues 总被引:18,自引:0,他引:18
We studied the influence of soil compaction in a loamy sand soil on C and N mineralization and nitrification of soil organic
matter and added crop residues. Samples of unamended soil, and soil amended with leek residues, at six bulk densities ranging
from 1.2 to 1.6 Mg m–3 and 75% field capacity, were incubated. In the unamended soil, bulk density within the range studied did not influence any
measure of microbial activity significantly. A small (but insignificant) decrease in nitrification rate at the highest bulk
density was the only evidence for possible effects of compaction on microbial activity. In the amended soil the amounts of
mineralized N at the end of the incubation were equal at all bulk densities, but first-order N mineralization rates tended
to increase with increasing compaction, although the increase was not significant. Nitrification in the amended soils was
more affected by compaction, and NO3
–-N contents after 3 weeks of incubation at bulk densities of 1.5 and 1.6 Mg m–3 were significantly lower (by about 8% and 16% of total added N, respectively), than those of the less compacted treatments.
The C mineralization rate was strongly depressed at a bulk density of 1.6 Mg m–3, compared with the other treatments. The depression of C mineralization in compacted soils can lead to higher organic matter
accumulation. Since N mineralization was not affected by compaction (within the range used here) the accumulated organic matter
would have had higher C : N ratios than in the uncompacted soils, and hence would have been of a lower quality. In general,
increasing soil compaction in this soil, starting at a bulk density of 1.5 Mg m–3, will affect some microbially driven processes.
Received: 10 June 1999 相似文献
12.
Influence of inorganic fertilizers and organic amendments on soil organic matter and soil microbial properties under tropical conditions 总被引:33,自引:0,他引:33
Soil organic matter level, mineralizable C and N, microbial biomass C and dehydrogenase, urease and alkaline phosphatase
activities were studied in soils from a field experiment under a pearl millet-wheat cropping sequence receiving inorganic
fertilizers and a combination of inorganic fertilizers and organic amendments for the last 11 years. The amounts of soil organic
matter and mineralizable C and N increased with the application of inorganic fertilizers. However, there were greater increases
of these parameters when farmyard manure, wheat straw or Sesbania bispinosa green manure was applied along with inorganic fertilizers. Microbial biomass C increased from 147 mg kg–1 soil in unfertilized soil to 423 mg kg–1 soil in soil amended with wheat straw and inorganic fertilizers. The urease and alkaline phosphatase activities of soils
increased significantly with a combination of inorganic fertilizers and organic amendments. The results indicate that soil
organic matter level and soil microbial activities, vital for the nutrient turnover and long-term productivity of the soil,
are enhanced by use of organic amendments along with inorganic fertilizers.
Received: 6 May 1998 相似文献
13.
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
14.
A study was conducted to determine mineralization rates in the field and in different soil layers under three grassland managements
(viz. a reseeded sward, a permanent sward with a conventional N management, and a long-term grass sward with 0 N (0-N) input).
Potential mineralization rates of soil particles (sand, silt and clay) and macro-organic matter fractions of different sizes
(i.e. 0.2–0.5, 0.5–2.0 and >2 mm) were also determined in the laboratory. In the reseeded plots, net mineralization was unchanged
down to 40 cm depth. In the undisturbed conventional-N swards, mineralization rates were substantially higher in the top layer
(0–10 cm) than in the deeper layers. In plots which had received no fertilizer N, mineralization was consistently low in all
the layers. There was more macro-organic matter (MOM) in the 0-N plots (equivalent to 23 g kg–1 soil for 0–40 cm) than in the two fertilized plots (i.e. conventional-N and reseeded) which contained similar amounts (ca. 15 g kg–1 soil). C and N contents of separated soil particles did not differ amongst the treatments, but there were large differences
with depth. Potential mineralization in the bulk soil was greatest in the 0–10 cm layers and gradually decreased with depth
in all the treatments. Separated sand particles had negligible rates of potential mineralization and the clay component had
the highest rates in the subsurface layers (10–40 cm). MOMs had high potential rate of mineralization in the surface layer
and decreased with soil depth, but there was no clear pattern in the differences between different size fractions.
Received: 17 November 1997 相似文献
15.
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
16.
Effects of a cadmium-contaminated sewage sludge compost on dynamics of organic matter and microbial activity in an arid soil 总被引:3,自引:0,他引:3
An incubation experiment lasting 120 days was carried out to ascertain the effect on the soil microbial activity and organic
matter mineralization of adding a sewage sludge compost contaminated with two different levels of Cd to an arid soil. Two
composts, with a low (2 mg kg–1) and high (815 mg kg–1) Cd content, respectively, were used in this experiment. Both composts increased the total organic C, humic substance and
water-soluble C contents, the beneficial effects still being noticeable after 120 days of incubation. The most labile C fraction
(water-soluble C) was the most sensitive to the high Cd content. The high Cd concentration decreased soil microbial biomass
C and stimulated the metabolic activity of the microbial biomass, the metabolic quotient (qCO2) revealing itself to be a very sensitive index of the stress that the incorporation of a Cd-contaminated sewage sludge compost
causes in a soil. The effect of Cd contamination on enzyme activities (urease, protease that hydrolyse N-α-benzoil-l-arginamide, phosphatase, and β-glucosidase) depended on the enzyme studied.
Received: 10 September 1997 相似文献
17.
Effects of increasing periods under intensive arable vegetable production on biological, chemical and physical indices of soil quality 总被引:6,自引:0,他引:6
The effects on soil condition of increasing periods under intensive cultivation for vegetable production on a Typic Haplohumult
were compared with those of pastoral management using soil biological, physical and chemical indices of soil quality. The
majority of the soils studied had reasonably high pH, exchangeable cation and extractable P levels reflecting the high fertilizer
rates applied to dairy pasture and more particularly vegetable-producing soils. Soil organic C (Corg) content under long-term pasture (>60 years) was in the range of 55 g C kg–1 to 65 g C kg–1. With increasing periods under vegetable production soil organic matter declined until a new equilibrium level was attained
at about 15–20 g C kg–1 after 60–80 years. The loss of soil organic matter resulted in a linear decline in microbial biomass C (Cmic) and basal respiratory rate. The microbial quotient (Cmic/Corg) decreased from 2.3% to 1.1% as soil organic matter content declined from 65 g C kg–1 to 15 g C kg–1 but the microbial metabolic quotient (basal respiration/Cmic ratio) remained unaffected. With decreasing soil organic matter content, the decline in arginine ammonification rate, fluorescein
diacetate hydrolytic activity, earthworm numbers, soil aggregate stability and total clod porosity was curvilinear and little
affected until soil organic C content fell below about 45 g C kg–1. Soils with an organic C content above 45 g C kg–1 had been under pasture for at least 30 years. At the same Corg content, soil biological activity and soil physical conditions were markedly improved when soils were under grass rather
than vegetables. It was concluded that for soils under continuous vegetable production, practices that add organic residues
to the soil should be promoted and that extending routine soil testing procedures to include key physical and biological properties
will be an important future step in promoting sustainable management practices in the area.
Received: 18 November 1997 相似文献
18.
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
19.
Influence of stock camping behaviour on the soil microbiological and biochemical properties of grazed pastoral soils 总被引:3,自引:0,他引:3
The size and activity of the soil microbial biomass in grazed pastures was compared on the main grazing area and on stock
camp areas where animals congregate. Two sites were on hill country and three on gently sloping border-dyke irrigated land.
Due to the transfer of nutrients and organic matter to the camp areas via dung and urine there was an accumulation of soil
organic C, organic and inorganic P and S and soluble salts in the camp areas. Soil pH also tended to be higher in camp areas
due to transfer of alkalinity by the grazing animals. Water soluble organic C, microbial biomass C and basal respiration were
all higher in soils from camp areas but the proportion of organic C present as microbial C and the microbial respiratory quotient
were unaffected. Microbial activity as quantified by arginine ammonification rate and fluorescein diacetate (FDA) hydrolysis
was higher in camp than non-camp soils but dehydrogenase activity remained unaffected. Activities of protease, histidase,
urease, acid phosphatase and aryl-sulphatase were all higher in stock camp soils. The activities of both histidase and aryl-sulphatase
were also higher when expressed per unit of microbial biomass C, indicating that the increased activity was the result of
increased enzyme production by the microbial community. Prolonged regular applications of dairy shed effluent (diluted dung
and urine from cattle) to a field had a similar effect to stock camping in increasing soil organic matter content, nutrient
accumulation and soil biological activity. It was concluded that the stock camping activity of grazing animals results in
an increase in both the fertility and biological activity in soils from camp areas at the expense of these properties on the
main grazing areas.
Received: 20 October 1997 相似文献
20.
Soil organic matter quantity and quality in mountain soils of the Alay Range, Kyrgyzia, affected by land use change 总被引:4,自引:0,他引:4
Changes in soil management practices influence the amount, quality and turnover of soil organic matter (SOM). Our objective
was to study the effects of deforestation followed by pasture establishment on SOM quantity, quality and turnover in mountain
soils of the Sui Checti valley in the Alay Range, Kyrgyzia. This objective was approached by analysis of total organic C (TOC),
N, lignin-derived phenols, and neutral sugars in soil samples and primary particle-size soil fractions. Pasture installation
led to a loss of about 30% TOC compared with the native Juniperus turkestanica forests. The pasture soils accumulated about 20% N, due to inputs via animal excrement. A change in land use from forest
to pasture mainly affected the SOM bound to the silt fraction; there was more microbial decomposition in the pasture than
in the forest silt fraction, as indicated by lower yields of lignin and carbohydrates, and also by a more advanced oxidative
lignin side-chain oxidation and higher values of plant : microbial sugar ratios. The ratio of arabinose : xylose was indicative
of the removal of carbohydrates when the original forest was replaced by pasture, and we conclude that this can be used as
an indicator of deforestation. The accumulation of lignin and its low humification within the forest floor could be due to
the extremely cold winter and dry summer climate.
Received: 10 March 1999 相似文献