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1.
The hydrolysis of the fluorescein diacetate (FDA), related to several soil hydrolases, has been utilised to estimate the potential microbial activity of soil freshly amended with a wide range of organic amendments and compared to the size and activity of soil microflora, measured by the microbial biomass C (B C) and CO2 evolution, respectively. Three different composting mixtures at different phases of the composting process were added to a semi-arid soil and incubated for 2 months under laboratory conditions. The addition of the organic amendment immediately increased B C and both measures of microbial activity (FDA and CO2 evolution). Highly significant correlations were found between FDA hydrolysis and B C for soil amended with the three composting mixtures (r = 0.81–0.96; P < 0.01), regardless of the origin, composition and degree of stability of the organic amendments. FDA hydrolysis, conversely to CO2 evolution, was unaffected by the disturbance caused by the soil amendment, indicating that the two parameters probably reflect different aspects of soil microbial activity. FDA hydrolysis could serve as an alternative estimation of the microbial biomass in freshly amended soils, despite the disturbance caused by the exogenous organic matter.  相似文献   

2.
Labile fractions of soil organic C (SOC) can respond rapidly to changes in C supply and are considered to be important indicators of soil quality. An attempt is made in this paper to investigate into the dynamics of total organic C (C tot), oxidisable organic C (C oc), very labile C (C frac 1), labile C (C frac 2), less labile C (C frac 3), non-labile C (C frac 4), microbial biomass C (C mic), mineralizable C (C min) and particulate organic C (C p) in relation to the system productivity of a 20-year-old rice (Oryza sativa L)–berseem (Trifolium alexandrium L) cropping system with different management strategies [no fertilization, only NPK and NPK + FYM (farmyard manure) applied in different seasons] in the hot humid, subtropics of India. Cultivation over the years caused a net decrease, while balanced fertilization with NPK maintained the SOC. About 62% of the C applied as FYM was stabilized into SOC. The passive pool (C frac 3 + C frac 4) constituted about 55% of the C tot. A larger proportion (63%) of applied C was stabilized in the passive pool of SOC. Of the analysed pools, C frac 1, C mic, C p and C min were influenced most by the treatments imposed and explained higher per cent variability in the yield of the crops.  相似文献   

3.
Secondary salinity effects on soil microbial biomass   总被引：2，自引：0，他引：2  
Secondary soil salinilization is a big problem in irrigated agriculture. We have studied the effects of irrigation-induced salinity on microbial biomass of soil under traditional cotton (Gossypium hirsutum L.) monoculture in Sayhunobod district of the Syr-Darya province of northwest Uzbekistan. Composite samples were randomly collected at 0–30 cm depth from weakly saline (2.3 ± 0.3 dS m−1), moderately saline (5.6 ± 0.6 dS m−1), and strongly saline (7.1 ± 0.6 dS m−1) replicated fields, 2-mm sieved, and analyzed for pH, electrical conductivity, total C, organic C (COrg), and extractable C, total N and P, and exchangeable ions (Ca2+, Mg2+, K+, Na+, Cl−, and CO32−), microbial biomass (Cmic). The Na+ and Cl− concentrations were 36-80% higher in strongly saline compared to weakly saline soil. The COrg concentration was decreased by 10% and CExt by 40% by increasing soil salinity, whereas decrease in Cmic ranged from 18-42% and the percentage of COrg present as Cmic from 8% to 26%. We conclude that irrigation-induced secondary salinity significantly affects soil chemical properties and the size of soil microflora.  相似文献   

4.
We investigated Cd, Zn, and Cd + Zn toxicity to soil microbial biomass and activity, and indigenous Rhizobium leguminosarum biovar trifolii, in two near neutral pH clay loam soils, under long-term arable and grassland management, in a 6-month laboratory incubation, with a view to determining the causative metal. Both soils were amended with Cd- or Zn-enriched sewage sludge, to produce soils with total Cd concentrations at four times (12 mg Cd g−1 soil), and total Zn concentrations (300 mg Zn kg−1 soil) at the EU upper permitted limit. The additive effects of Cd plus Zn at these soil concentrations were also investigated. There were no significant differences in microbial biomass C (B C), biomass ninhydrin N (B N), ATP, or microbial respiration between the different treatments. Microbial metabolic quotient (defined as qCO2 = units of CO2–C evolved unit−1 biomass C unit−1 time) also did not differ significantly between treatments. However, the microbial maintenance energy (in this study defined as qCO2-to-μ ratio value, where μ is the growth rate) indicated that more energy was required for microbial synthesis in metal-rich sludge-treated soils (especially Zn) than in control sludge-treated soils. Indigenous R. leguminosarum bv. trifolii numbers were not significantly different between untreated and sludge-treated grassland soils after 24 weeks regardless of metal or metal concentrations. However, rhizobial numbers in the arable soils treated with metal-contaminated sludges decreased significantly (P < 0.05) compared to the untreated control and uncontaminated sludge-treated soils after 24 weeks. The order of decreasing toxicity to rhizobia in the arable soils was Zn > Cd > Cd + Zn.  相似文献   

5.
 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   

6.
The objective of this study was to determine whether differences in canopy structure and litter composition affect soil characteristics and microbial activity in oak versus mixed fir-beech stands. Mean litter biomass was greater in mixed fir-beech stands (51.9t ha−1) compared to oak stands (15.7t ha−1). Canopy leaf area was also significantly larger in mixed stands (1.96m2 m−2) than in oak stands (1.73m2 m−2). Soil organic carbon (C org) and moisture were greater in mixed fir-beech stands, probably as a result of increased cover. Soil microbial biomass carbon (C mic), nitrogen (N mic), and total soil nitrogen (N tot) increased slightly in the mixed stand, although this difference was not significant. Overall, mixed stands showed a higher mean C org/N tot ratio (22.73) compared to oak stands (16.39), indicating relatively low rate of carbon mineralization. In addition, the percentage of organic C present as C mic in the surface soil decreased from 3.17% in the oak stand to 2.26% in the mixed stand, suggesting that fir-beech litter may be less suitable as a microbial substrate than oak litter.  相似文献   

7.
Soil microbial biomass carbon and nitrogen as affected by cropping systems   总被引：12，自引：0，他引：12  
 The impacts of crop rotations and N fertilization on microbial biomass C (Cmic) and N (Nmic) were studied in soils of two long-term field experiments initiated in 1978 at the Northeast Research Center (NERC) and in 1954 at the Clarion-Webster Research Center (CWRC), both in Iowa. Surface soil samples were taken in 1996 and 1997 from plots of corn (Zea mays L.), soybeans (Glycine max (L.) Merr.), oats (Avena sativa L.), or meadow (alfalfa) (Medicago sativa L.) that had received 0 or 180 kg N ha–1 before corn and an annual application of 20 kg P and 56 kg K ha–1. The Cmic and Nmic values were determined by the chloroform-fumigation-extraction method and the chloroform-fumigation-incubation method, respectively. The Cmic and Nmic values were significantly affected (P<0.05) by crop rotation and plant cover at time of sampling, but not by N fertilization. In general, the highest Cmic and Nmic contents were found in the multicropping systems (4-year rotations) taken in oats or meadow plots, and the lowest values were found in continuous corn and soybean systems. On average, Cmic made up about 1.0% of the organic C (Corg), and Nmic contributed about 2.4% of the total N (Ntot) in soils at both sites and years of sampling. The Cmic values were significantly correlated with Corg contents (r≥0.41**), whereas the relationship between Cmic and Ntot was significant (r≤0.53***) only for the samples taken in 1996 at the NERC site. The Cmic : Nmic ratios were, on average, 4.3 and 6.4 in 1996, and 7.6 and 11.4 in 1997 at the NERC and CWRC sites, respectively. Crop rotation significantly (P<0.05) affected this ratio only at the NERC site, and N fertilization showed no effect at either site. In general, multicropping systems resulted in greater Cmic : Corg (1.1%) and Nmic : Ntot (2.6%) ratios than monocropping systems (0.8% and 2.1%, respectively). Received: 9 February 1999  相似文献   

8.
In industrial areas, heavy metals may accumulate in forest soil organic horizons, affecting soil microorganisms and causing changes in the chemical composition of the accumulated organic matter. The objectives of this study were to test the ability of near-infrared spectroscopy (NIRS) to detect heavy metal effects on the chemical composition of forest soil O horizons and to test whether NIRS may be used to quantitatively determine total and exchangeable concentrations of Zn and Pb (Znt, Pbt, Znex, Pbex) and other chemical and microbial properties in forest soil O horizons polluted with heavy metals. The samples of O horizons (n = 79) were analyzed for organic C (Corg), total N and S (Nt, St), Znt, Pbt, Znex, Pbex, basal respiration (BR), microbial biomass (Cmic) and Cmic-to-Corg ratio. Spectra of the samples were recorded in the Vis-NIR range (400–2,500 nm). To detect heavy-metal-induced changes in the chemical composition of O horizons principal components (PC1–PC7) based on the spectral data were regressed against Znt + Pbt values. A modified partial least squares method was used to develop calibration models for prediction of various chemical and microbial properties of the samples from their spectra. Regression analysis revealed a significant relationship between PC3 and PC5 (r = −0.27 and −0.34, respectively) and Znt + Pbt values, indicating an effect of heavy metal pollution on the spectral properties of the O horizons and thus on their chemical composition. For quantitative estimations, the best calibration model was obtained for Corg-to-Nt ratio (r = 0.98). The models for Corg, Nt, and microbial properties were satisfactory but less accurate. NIRS failed to accurately predict St, Corg-to-St, Znt, Pbt, Znex, and Pbex.  相似文献   

9.
We manipulated Collembola Folsomia candida Willem density and observed the density effect on carbon and nitrogen mineralization and on nematodes in microcosms filled with mineral soil. Collembolan densities were 0 (control), 25 (low), 100 (medium), and 400 (high) individuals per microcosm. The Collembola enhanced soil respiration and nitrogen mineralization rate in a density-dependent manner (P < 0.05). The correlation between collembolan density and the metabolic quotient of microbes, qCO2, was weakly positive (r = 0.44, P < 0.05). Collembola did not affect microbial biomass. These results suggested that enhanced carbon and nitrogen mineralization was an indirect effect of Collembola mediated by increased microbial activity. Collembola changed the Cnema/Cmic ratio, but only when present at the low density. Thus, Collembola had both positive and negative effects on the nematode population. The positive impact probably depends on the enhancement of microbial activity due to Collembola grazing behavior, while the negative effect appears to result from predation of nematodes.  相似文献   

10.
The chemical and microbial properties of afforested mine soils are likely to depend on the species composition of the introduced vegetation. This study compared the chemical and microbial properties of organic horizons and the uppermost mineral layers in mine soils under pure pine (Pinus sylvestris), birch (Betula pendula), larch (Larix decidua), alder (Alnus glutinosa), and mixed pine–alder and birch–alder forest stands. The studied properties included soil pH, content of organic C (Corg) and total N (Nt), microbial biomass (Cmic), basal respiration, nitrogen mineralization rate (Min-N), and the activities of dehydrogenase, acid phosphomonoesterase, and urease. Near-infrared spectroscopy (NIR) was used to detect differences in the chemical composition of soil organic matter under the studied forest stands. There were significant differences in Corg and Nt contents between stands in both O and mineral soil horizons and also in the chemical composition of the accumulated organic matter, as indicated by NIR spectra differences. Alder was associated with the largest Corg and Nt accumulation but also with a significant decrease of pH in the mineral soil. Microbial biomass, respiration, the percentage of Corg present as Cmic, Min-N, and dehydrogenase activity were the highest under the birch stand, indicating a positive effect of birch on soil microflora. Admixture of alder to coniferous stand increased basal respiration, Min-N, and activities of dehydrogenase and acid phosphomonoesterase as compared with the pure pine stand. In the O horizon, soil pH and Nt content had the most important effects on all microbial properties. In this horizon, the activities of urease and acid phosphomonoesterase did not depend on microbial biomass. In the mineral layer, however, the amount of accumulated C and microbial biomass were of primary importance for the enzyme activities.  相似文献   

11.
 The impacts of crop rotations and N fertilization on different pools of arylsulfatase activity (total, intracellular, and extracellular) were studied in soils of two long-term field experiments in Iowa to assess the contibution of the microbial biomass to the activity of this enzyme. Surface-soil samples were taken in 1996 and 1997 in corn, soybeans, oats, or meadow (alfalfa) plots that received 0 or 180 kg N ha–1 before corn, and an annual application of 20 kg P ha–1 and 56 kg K ha–1. The arylsulfatase activity in the soils was assayed at optimal pH (acetate buffer, pH 5.8) before and after chloroform fumigation; microbial biomass C (Cmic) and N (Nmic) were determined by chloroform-fumigation methods. All pools of arylsulfatase activity in soils were significantly affected by crop rotation and plant cover at sampling time, but not by N fertilization. Generally, the highest total, intracellular, and extracellular arylsulfatase activities were obtained in soils under cereal-meadow rotations, taken under oats or meadow, and the lowest under continuous cropping systems.Total, intracellular, and extracellular arylsulfatase activities were significantly correlated with Cmic (r>0.41, P<0.01) and Nmic (r>0.38, P<0.01) in soils. The averages of specific activity values, i.e., of arylsulfatase activity of the microbial biomass, expressed per milligram Cmic, ranged from 315 to 407 μg p-nitrophenol h–1. The total arylsulfatase activity was significantly correlated with the intracellular activity, with r values >0.79 (P<0.001). In general, about 45% of the total arylsulfatase activity was extracellular, and 55% was associated with the microbial biomass in soils, indicating the importance of the microflora as an enzyme source in soils. Received: 23 April 1998  相似文献   

12.
We investigated some aspects of soil quality and community-level physiological profiles (CLPP) of bacteria in soil under a long-term (37 years) trial with either exclusive inorganic fertilizers or fertilizers combined with farmyard manure cultivated with jute–rice–wheat system. The treatments consisted of 100% recommended dose (RD) of NPK, 150% RD of NPK, 100% RD of N, 100% RD of NPK + FYM (10 t ha−1 year−1), and untreated control. Long-term application of 150% RD of NPK lowered the soil pH considerably while the soils in the other treatments remained near neutral. The 100% RD of NPK + FYM treated plot showed significantly highest accumulation of organic carbon, total nitrogen, microbial biomass carbon, basal soil respiration, and fluorescein diacetate hydrolyzing activity among the treatments. CLPP analysis in Biolog Ecoplates revealed that utilization of carbohydrates was enhanced in all input treated regimes, while the same for polymers, carboxylic acids, amino acids, and amines/amides were similar or less than the untreated control. However, within these groups of carbon sources, heterogeneity of individual substrate utilization between treatments was also noted. Taken together, addition of organic supplements showed significantly increased microbial biomass carbon and microbial activity, but input of nutrient supplements, both inorganic and organic, only marginally affected the overall substrate utilization pattern of soil microorganisms.  相似文献   

13.
ABSTRACT

In the scheduling of nutrient supply programs, analysis of plant nutrient status has been found to be useful to prevent the deficiency or toxic effects of nutrients in any horticultural crop. So the present study was framed to assess the foliage nutrient content and vegetative growth under different irrigation and fertigation combination modules. Recently apple (Malus ×domestica) orchards in the state Himachal Pradesh of India have converted from the traditional royal delicious orchard at 6 × 6 m spacing with rainfed/basin irrigation to early spur varieties on dwarfing rootstock with drip irrigation, both with or without fertigation. An experimental field trial was started at the end of 2018 in a ‘Super Chief’/MM106 orchard at an experimental farm of the department of Soil Science & Water Management, Dr. YS Parmar University of Horticulture and Forestry, Nauni, Solan (HP). A factorial experiment with 16 treatment combinations of 4 irrigation levels viz. I1 – drip irrigation at 100% ETc, I2 – drip irrigation at 80% ETc, I3 – drip irrigation at 60% ETc, I4 – conventional irrigation, and four fertigation levels viz. F0 – No fertilizer application (absolute control), F1 – 100% of AD (NPK), F2 – 75% of AD (NPK) and F3 – 50% of AD (NPK) were replicated thrice with 3 plants in each replication. Vegetative growth parameters and leaf nutrient contents were affected by both fertilization and water rate. Irrigation and nutrient levels and their interactions exhibited significant effect on leaf N (3.10%), P (0.28%), K (1.77%), and S (0.44%) contents. Significantly maximum contents were observed in the irrigation level I1 (DI at 100% ETc). Among fertigation level, F1 [100% AD (NPK)] recorded highest contents of leaf N (3.17%), P (0.29%), K (1.80%), S (0.46%). Interaction I1F1 registered maximum leaf N (3.36%), P (0.36%), K (1.92%) and S (0.63%).

With an increase in the water volume and an increasing dose of NPK, vegetative growth parameters, i.e., tree height, plant spread, tree volume, trunk girth, and annual extension growth were noted to increase proportionately. Treatment DI at 100% ETc (I1), increased the tree height by 9.41, plant spread (EW by 32.0, NS by 16.3), tree volume by 61.36, trunk girth by 8.05, and annual extension growth by 14.22% over conventional irrigation (I4). Drip fertigated trees with F1 [100% AD (NPK)] reported the highest growth parameters. The results of two years apple trial suggested a positive effect of fertigation on enhanced effectiveness of fertilization and improved foliage nutrient content and vegetative growth.  相似文献   

14.
We determined the size, activity, and affinity of the microbial community for glucose in soils from long-term experimental grassland plots. The plots had been treated annually with either farmyard manure, inorganic NPK fertilizers, farmyard manure+inorganic NPK fertilizers, (NH4)2SO4 only, or no experimental amendment sine 1897. The largest biomass and activity differences were between the (NH4)2SO4-treated soil, which was very acid, and the rest, which were nearer neutral. In the (NH4)2SO4-treated soil, the biomass C to organic C ratio was small, but overall the community had high respiratory activity per unit of biomass (qCO2) and high overall affinity for glucose (low K m). The effects of the manure treatment were a greater biomass C and a lower overall glucose affinity than in the control plot. In the presence farmyard manure, NPK led to smaller biomass and a lower biomass to organic C ratio while having no significant effect on either glucose K m or qCO2. In the absence of farmyard manure, NPK led to significantly greater glucose affinity but had no significant effect on the biomass, the biomass C to organic C ratio or qCO2.  相似文献   

15.
Cassava is an important subsidiary food in the tropics. In Tamil Nadu, India, microbial cultures were used to eradicate the tuberous root rot of cassava. Hence, an experiment was conducted for two consecutive years to test the effects of coinoculation of microbes on soil properties. The surface soil from the experimental site was analysed for soil available nutrients, soil enzyme activities and microbial biomass carbon. The treatment of Azospirillum with Trichoderma at the 50% recommended N:P2O5:K2O (NPK) rate (50:25:50 kg ha?1) significantly increased soil available nitrogen (142.81 kg ha?1) by 72.66% over uninoculated control. There was a significant increase in available phosphorus in soil by the inoculation of AM (arbuscular mycorrhizal) fungi with Trichoderma at the 50% recommended NPK rate (41.04 kg ha?1) compared to other treatments. The application of Pseudomonas fluorescens with Trichoderma at the 50% recommended NPK rate significantly increased available iron (19.34 µg g?1) in soil. The treatment of Azospirillum with Trichoderma increased urease enzyme activity at the recommended NPK rate (816.32 μg urea hydrolyzed g?1 soil h?1). Soil application of all cultures at the 50% recommended NPK rate significantly increased dehydrogenase activity (88.63 μg TPF g?1 soil) and β-glucosidase activity (48.82 μg PNP g?1 soil) in soil. Inoculation of Trichoderma alone at the 50% recommended NPK rate significantly increased microbial biomass carbon (3748.85 μg g?1 soil). Thus, the microbial inoculations significantly increased soil available nutrient contents, enzyme activities such as urease, dehydrogenase and β-glucosidase activity and microbial biomass carbon by reducing the amount of the required fertilizer.  相似文献   

16.
 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   

17.
 The impacts of crop rotations and N fertilization on different pools of urease activity were studied in soils of two long-term field experiments in Iowa; at the Northeast Research Center (NERC) and the Clarion-Webster Research Center (CWRC). Surface soil samples (0–15 cm) were taken in 1996 and 1997 in corn, soybeans, oats, or meadow (alfalfa) plots that received 0 or 180 kg N ha–1, applied as urea before corn and an annual application of 20 kg P and 56 kg K ha–1. The urease activity in the soils was assayed at optimal pH (THAM buffer, pH 9.0), with and without toluene treatment, in a chloroform-fumigated sample and its nonfumigated counterpart. The microbial biomass C (Cmic) and N (Nmic) were determined by chloroform fumigation methods. The total, intracellular, extracellular and specific urease activities in the soils of the NERC site were significantly affected by crop rotation, but not by N fertilization. Generally, the highest total urease activities were obtained in soils under 4-year oats–meadow rotations and the lowest under continuous corn. The higher total activities under multicropping systems were caused by a higher activity of both the intracellular and extracellular urease fractions. In contrast, the highest values for the specific urease activity, i.e. of urease activity of the microbial biomass, were found in soils under continuous soybean and the least under the 4-year rotations. Total and extracellular urease activities were significantly correlated with Cmic (r>0.30* and >0.40**) and Nmic (r>0.39** and >0.44**) in soils of the NERC and CWRC sites, respectively. Total urease activity was significantly correlated with the intracellular activity (r>0.73***). About 46% of the total urease activity of the soils was associated with the microbial biomass, and 54% was extracellular in nature. Received: 25 May 1999  相似文献   

18.
 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   

19.
Organics, biological, and inorganic fertilizers play a crucial role for improving crop yield and soil properties. Accordingly, we assessed their impact on yield, microbial activities, and transformations of carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) in soils under a 12-year-old intensively cultivated rice (Oriza sativa L.), mustard (Brassica juncea L.), sesame (Sesamum indicum L.) system with sole inorganic (NPK); NPK + farmyard manure (NPKF); NPK + green manure (NPKG) (Sesbania sesban L.), and NPK + green manure + bio-fertilizer (NPKGB) (Azotobacter chroococcum+ pseudomonas putida) treatments in sub-tropical India. The system yield was much higher with NPKF (23%) and NPKGB (18%) than that with NPK. Organic supplementation had a favorable influence on soil microbial biomass C (Cmic), N (Nmic), and activities of extracellular enzymes. Results of principal component and multiple regression analyses showed significant influence of Cmic on system yield (R2 = 91, p = 0.001) and S availability (R2 = 62, p = 0.001). Similarly, mineralizable N and acid phosphatase could predict significantly soil available N (R2 = 85, p = 0.001) and P (R2 = 51; p = 0.001), respectively. Results thus indicated that integrated nutrient management (NPKF/G) improved system yield, nutrient accumulation, and microbial activities in soils.  相似文献   

20.
Soil microbial and extractable C and N after wildfire   总被引：12，自引：0，他引：12  
 The effect of wildfire on soil microbes and extractable C (Cext) and N (Next) changed with respect to the time from burning and soil depth. Initially, microbial biomass C (Cmic) and N (Nmic) were drastically reduced in the soil surface layer (0–5 cm) and reduced by 50% in the subsurface (5–10 cm), whereas Cext increased by 62% in the surface layer and did not significantly change in the subsurface. These parameters were affected for the following 4 years, during which the average reductions in the soil surface and subsurface layers were, respectively, 60% and 50% for Cmic, 70% and 45% for Nmic, 60% and 40% for the ratio Cmic: organic C (Corg) and 70% and 30% for the ratio Nmic: total N (Ntot), while for Cext the surface layer was the only zone consistently affected and Cext decreased by up to 59%. Immediately after a fire, the Cext : Corg ratio increased by 3.5-fold and 2-fold in the surface and subsurface layers, respectively; thereafter for 2 years, it decreased in the surface layer (by up to 45%) while the effect on the subsurface layer was not consistent. The effect of burning on Next lasted 1 year, in which Next increased by up to 7- and 3-fold in the surface and subsurface layers, respectively, while the average Next : Ntot ratio doubled in the surface layer and increased by 34% in the subsurface. During the time in which each parameter was affected by burning, the soil factor explained a high percentage of variance in the fluctuations of Cmic, Nmic, Cmic : Corg and Nmic : Ntot, while those of Next and Next : Ntot, but not those of Cext and Cext : Corg depended on both the soil and its depth. In the burned soils similar patterns of response were found between the following parameters listed in pairs: Cmic and Nmic; Cmic : Corg and Nmic : Ntot; Cext and Next; and Cext : Corg and Next : Ntot. However, after the fire relationships found previously between the parameters studied and many other soils properties were either no longer evident, or were inverted. Although the addition of cellulose to the burned soil favoured fungal mycelium development and increased Cmic and Cext contents, the negative effect of burning on the microbial biomass and the Cext was not counteracted even under incubation conditions suitable for both microbial growth and C mineralization. Received: 28 May 1997  相似文献   

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