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1.
Soil microbes are frequently limited by carbon (C), but also have a high phosphorus (P) requirement. Little is known about the effect of P availability relative to the availability of C on soil microbial activity. In two separate experiments, we assessed the effect of P addition (20 mg P kg?1 soil) with and without glucose addition (500 mg C kg?1 soil) on gross nitrogen (N) mineralization (15N pool dilution method), microbial respiration, and nitrous oxide (N2O) emission in a grassland soil. In the first experiment, soils were incubated for 13 days at 90% water holding capacity (WHC) with addition of NO3? (99 mg N kg?1 soil) to support denitrification. Addition of C and P had no effect on gross N mineralization. Initially, N2O emission significantly increased with glucose, but it decreased at later stages of the incubation, suggesting a shift from C to NO3? limitation of denitrifiers. P addition increased the N2O/CO2 ratio without glucose but decreased it with glucose addition. Furthermore, the 15N recovery was lowest with glucose and without P addition, suggesting a glucose by P interaction on the denitrifying community. In the second experiment, soils were incubated for 2 days at 75% WHC without N addition. Glucose addition increased soil 15N recovery, but had no effect on gross N mineralization. Possibly, glucose addition increased short-term microbial N immobilization, thereby reducing N-substrates for nitrification and denitrification under more aerobic conditions. Our results indicate that both C and P affect N transformations in this grassland soil.  相似文献   

2.
The objective of this work was to provide evidence on the effects of faba bean (Vicia faba L.) and chickpea (Cicer arietinum L.) on the dynamics of soil N availability and yield parameters of wheat (Triticum turgidum L. var. durum) in a legume–wheat rotation in comparison with the effects of the more extensively studied common vetch (Vicia sativa L.). Soil samples were taken from field plots just before wheat sowing and incubated in the laboratory to assess N mineralization potential, soil respiration and N immobilization after incorporation of legume residues. Soil after vetch cultivation showed the highest residual N and mineralization potential (120 mg N kg?1 soil), the greatest CO2 release and the smallest N immobilization. Smaller mineral N release (80 mg N kg?1 soil) was shown by soil after faba bean cultivation, which, however, would be capable to support an average wheat production without fertilization. Soil after chickpea and wheat cultivation manifested no differences in residual N and mineralization or immobilization potential. Laboratory results were well correlated with grain yield and N uptake during the second season of rotation in the field. All legumes resulted in significant yield surpluses and provided N credit to the following unfertilized wheat.  相似文献   

3.
In a long‐term study of the effects on soil fertility and microbial activity of heavy metals contained in sewage sludges, metal‐amended liquid sludges each with elevated Zn, Cu or Cd concentrations were applied over a 3‐year period (1995–1997) to three sites in England. The experiments were sited adjacent to experimental plots receiving metal‐rich sludge cakes enabling comparisons to be made between the effects of heavy metal additions in metal‐amended liquid sludges and sludge cakes. The liquid sludge additions were regarded as ‘worst case’ treatments in terms of likely metal availability, akin to a long‐term situation following sewage sludge additions where organic matter levels had declined and stabilised. The aim was to establish individual Zn (50–425 mg kg?1), Cu (15–195 mg kg?1) and Cd (0.3–4.0 mg kg?1) metal dose–response treatments at each site, but with significantly smaller levels of organic matter addition than the corresponding sludge cake experiments. There were no differences (P > 0.05) in soil respiration rates, biomass carbon concentrations or most probable numbers of clover Rhizobium between the treatments at any of the sites at the end of the liquid sludge application programme. Soil heavy metal extractability differed between the metal‐amended liquid sludge and metal‐rich sludge cake treatments; Zn and Cd extractabilities were higher from the liquid sludge additions, whereas Cu extractability was higher from the sludge cake application. These differences in metal extractability in the treated soil samples reflected the contrasting NH4NO3 extractable metal contents of the metal‐amended liquid sludges and sludge cakes that were originally applied.  相似文献   

4.
Two different biosolids were obtained composting anaerobic (A) and aerobic (B) municipal sewage sludge (SS) with rice husk. Higher amounts of SS (1:1 v/v) could be used in this composting process than in conventional ones. The two biosolids were characterized by chemical analysis and compared with a conventional green manure plus municipal solid waste and municipal SS compost. The effect of these products on soil functionality was studied in a 14-week incubation experiment by their addition to two different soils (silty clay—Ustic Endoaquert—and sandy loam—Aquic Xeropsamment). The total organic C ranged from 20 to 26 % and total N from 1.6 to 2.5 % in the two biosolids. The most relevant difference was due to dissolved organic C that was lower in the anaerobic biosolid (1 mg?C?kg?1) than in the other products (5–6 mg?C?kg?1). The total trace elements (Cd, Cr, Cu, Ni, Pb and Zn) contents were under the limits fixed by the European legislation for soil application of SS (EC Directive 86/278/EEC, 1986). The three biosolids did not show strong negative effects on soil functionality during the incubation experiment, although some significant differences were found. The aerobic biosolid B mainly increased cumulative N release, microbial activity, basal respiration rate, microbial biomass-C-to-total organic C ratio, β-glucosidase, alkaline phosphomonoesterase and aryl-sulphatase activities. The anaerobic one (B) decreased basal respiration rate, microbial biomass-C-to-total organic C ratio and aryl-sulphatase activity. DTPA soil bioavailable heavy metals were not affected by biosolids additions.  相似文献   

5.
Microbial adaptation to salinity can be achieved through synthesis of organic osmolytes,which requires high amounts of energy;however,a single addition of plant residues can only temporarily improve energy supply to soil microbes.Therefore,a laboratory incubation experiment was conducted to evaluate the responses of soil microbes to increasing salinity with repeated additions of plant residues using a loamy sand soil with an electrical conductivity in saturated paste extract（ECe） of 0.6 dS m-1.The soil was kept non-saline or salinized by adding different amounts of NaCl to achieve ECe of 12.5,25.0 and 50.0 dS m-1.The non-saline soil and the saline soils were amended with finely ground pea residues at two rates equivalent to 3.9 and 7.8 g C kg-1 soil on days 0,15 and29.The soils receiving no residues were included as a control.Cumulative respiration per g C added over 2 weeks after each residue addition was always greater at 3.9 than 7.8 g C kg-1 soil and higher in the non-saline soil than in the saline soils.In the saline soils,the cumulative respiration per g C added was higher after the second and third additions than after the first addition except with3.9 g C kg-1 at ECe of 50 dS m1.Though with the same amount of C added(7.8 g C kg-1),salinity reduced soil respiration to a lesser extent when 3.9 g C kg-1 was added twice compared to a single addition of 7.8 g C kg-1.After the third residue addition,the microbial biomass C concentration was significantly lower in the soils with ECe of 25 and 50 dS m1 than in the non-saline soil at3.9 g C kg-1,but only in the soil with ECe of 50 dS m-1 at 7.8 g C kg-1.We concluded that repeated residue additions increased the adaptation of soil microbial community to salinity,which was likely due to high C availability providing microbes with the energy needed for synthesis of organic osmolytes.  相似文献   

6.
The soils of the Antarctic dry valleys are exposed to extremely dry and cold conditions. Nevertheless, they contain small communities of micro-organisms that contribute to the biogeochemical transformations of the bioelements, albeit at slow rates. We have determined the dehydrogenase, β-glucosidase, acid and alkaline phosphatase and arylsulphatase activities and the rates of respiration (CO2 production) in laboratory assays of soils collected from a field experiment in an Antarctic dry valley. The objective of the field experiment was to test the responses of the soil microbial community to additions of C and N in simple (glucose and NH4Cl) and complex forms (glycine and lacustrine detritus from the adjacent lake comprising principally cyanobacterial necromass). The soil samples were taken 3 years after the experimental treatments had been applied. In unamended soil, all enzyme activities and respiration were detected indicating that the enzymatic capacity to mineralize organic C, P and S compounds existed in the soil, despite the very low organic matter content. Relative to the control (unamended soil), respiration was significantly increased by all the experimental additions of C and N except the smallest NH4Cl addition (1 mg N g−1 soil) and the smallest detritus addition (1.5 mg C g−1 soil and 0.13 mg N g−1 soil). The activities of all enzymes except dehydrogenase were increased by C and combined large C (10 mg C g−1 soil) and N additions, but either unchanged or diminished by addition of either N only or N (up to 10 mg N g−1 soil) with only small C (1 mg C g−1 soil) additions in the form of glucose and NH4Cl. This suggests that in the presence of a large amount of N, the C supply for enzyme biosynthesis was limited. When normalized with respect to soil respiration, only arylsulphatase per unit of respiration showed a significant increase with C and N additions as glucose and NH4Cl, consistent with S limitation when C and N limitations have been alleviated. Based on the positive responses of enzyme activity, detritus appeared to provide either conditions or resources which led to a larger biological response than a similar amount of C and more N added in the form of defined compounds (glucose, NH4Cl or glycine). Assessment of the soil microbial community by ester-linked fatty acid (ELFA) analysis provided no evidence of changes in the community structure as a result of the C and N supplementation treatments. Thus the respiration and enzyme activity responses to supplementation occurred in an apparently structurally stable or unresponsive microbial community.  相似文献   

7.
In a long‐term study of the effects on soil fertility and microbial activity of heavy metals contained in sewage sludges, metal‐rich sludge cakes each with high Zn, Cu or Cd concentrations were applied annually for 4 years (1994–1997) to nine sites throughout Britain. These sites were selected to represent agricultural soils with a range of physical and chemical properties, typical of those likely to be amended with sewage sludge. The aim was to establish individual total Zn (approx. 60–450 mg kg?1), total Cu (approx. 15–200 mg kg?1) and total Cd (approx. 0.2–4 mg kg?1) metal dose–response treatments at each site. Sludges with low metal concentrations were added to all treatments to achieve as constant an addition of organic matter as possible. Across the nine sites, soil pH was the single most important factor controlling Zn (P < 0.001; r2 = 92%) and Cd extracted with 1 m NH4NO3 (P < 0.001; r2 = 72%), and total iron content the most important factor controlling Cu extracted with 1 m NH4NO3 (P < 0.001; r2 = 64%). There were also positive relationships (P < 0.001) between soil organic carbon (C) concentrations and soil biomass C and respiration rates across the nine sites. Oxidation of sludge C following land application resulted in approximately 45% of the digested sludge cake C and approximately 64% of the ‘raw’ sludge cake C being lost by the end of the 4‐year application period. The sludge cake applications generally increased soil microbial biomass C and soil respiration rates, whilst most probable numbers of clover Rhizobium were generally unchanged. Overall, there was no evidence that the metal applications were damaging soil microbial activity in the short term after the cessation of sludge cake addition.  相似文献   

8.
无机氮与蔬菜废弃物耦合对土壤氮矿化的影响   总被引：1，自引：0，他引：1  
为探明有机废弃物添加量与不同无机氮水平耦合对土壤氮矿化的影响,设计了3个甘蓝废弃叶添加量[B1:200 g.kg 1(土),B2:400 g.kg 1(土),B3:550 g.kg 1(土)]和4个无机氮水平[N0:0 mg.kg 1(土),N1:25mg.kg 1(土),N2:50 mg.kg 1(土),N3:100 mg.kg 1(土)]交互的控制培养试验(25℃,65%的田间持水量)。试验结果显示:各氮处理下土壤净累积氮矿化量是空白对照的4～5倍,N1水平下土壤净累积氮矿化量显著高于其他氮水平。各甘蓝废弃叶添加量处理下土壤净累积氮矿化量是空白对照的3～5倍,且B2添加量下土壤净累积氮矿化量显著高于B1和B3。统计分析表明,氮处理和甘蓝废弃叶添加量之间的交互效应不显著(P=0.275),甘蓝废弃叶的添加是影响氮矿化的主要因素(Eta2=0.16),而供氮水平为次要因素(Eta2=0.07)。B1添加量下,培养前期(0～20 d)土壤净累积矿化量逐渐升高,后期保持稳定水平;但B2和B3添加量下,培养前期(30 d)土壤呈现矿化、固持、再矿化现象,后期土壤净累积矿化量逐渐升高。氮矿化速率结果说明,甘蓝废弃叶添加后氮素矿化主要发生在培养前30 d。对培养期间土壤净累积氮矿化量随时间变化做一级动力方程模拟,拟合效果良好(R2=0.62～0.89)。  相似文献   

9.
Attempts to determine available carbon in soils   总被引：10，自引：0，他引：10  
Summary The size of the C pool that is readily available to microorganisms affects important N transformations that occur in soils, e.g., denitrification and N immobilization. In the present work, the C content of soil extracts, the C in water displaced from soil and biomass C were compared as indicators of available C. A comparison of C measured by the anthrone method and a total organic-C analysis of extracts indicated that only a small portion of C was in carbohydrates. The substrate-induced respiration method of measuring biomass in conjunction with the Wright-Hobbie model was used as an additional determination of available C. Total organic-C analysis of a 1 N H2SO4 extract gave the highest C values (500–1700 mg C kg-1 soil) and the substrate-induced respiration method gave the lowest (1–5 mg glucose equivalents kg-1 soil). The C values closest to the C turnover measured in long-term incubation studies were obtained by the substrate-induced respiration method using the Wright-Hobbie model.Contribution from the Soil-Microbial Systems Laboratory, NRI, USDA-ARS, Beltsville, MD 20705, USA  相似文献   

10.
Our aim was to study the effects of C (as glucose and artificial rhizodeposits) on S immobilization, in relation to microbial biomass‐S and soil arylsulphatase (ARS) activity, in contrasting soils (a calcareous and an acid brown soil). The glucose‐C and artificial rhizodeposit‐C with or without cysteine were added at six rates (0, 100, 200, 400, 600 and 800 mg kg?1 soil) to the two soils and then incubated with Na235SO4 for 1 week prior to analysis. The percentages of 35S immobilized increased when C as glucose and rhizodeposit (without cysteine) were added to both soils. With cysteine‐containing rhizodeposit, the percentages of 35S immobilized remained relatively stable (23.5% to 29.9%) in the calcareous soil, but decreased in the acid brown soil (52.7% to 31.5%). For both soils, cysteine‐containing rhizodeposit additions showed no significant correlation between immobilized‐35S and microbial biomass‐35S, suggesting that microorganisms immobilized cysteine‐S preferentially instead of 35S from the tracer (Na235SO4). In the calcareous soil, a positive and significant correlation was found between ARS activity and microbial biomass‐35S (r = 0.85, P < 0.05) when glucose was added. We also saw this correlation in the acid brown soil when rhizodeposit‐C without cysteine was added (r = 0.90, P < 0.05). Accordingly, the results showed the presence of extracellular arylsulphatase activity of 48.7 mg p‐nitrophenol kg?1 soil hour?1 in the calcareous soil and of 27.0 mg p‐nitrophenol kg?1 soil hour?1 in the acid brown soil.  相似文献   

11.
Abstract

A proportion of the nitrogen (N) applied to grasslands as organic or inorganic fertilizers can be lost to water courses as nitrate and to the atmosphere as nitrous and nitric oxides. Volcanic soils from Chile are not generally prone to leaching, possibly due to net immobilization of nitrate and/or ammonium, and/or due to inhibition of nitrification by either chemical or physical processes. In laboratory studies we found large mineralization potentials in soils from three different Chilean soils after 17 weeks of incubation, totalling 215 and 254 mg kg?1 dry soil for two Andisols and 127 mg kg?1 dry soil in an Ultisol. Nitrification occurred after a short period, and was lowest in the Ultisol. In addition, microbial analysis showed nitrifiers to be present in all three soils. Adsorption of ammonium was two-fold stronger than for nitrate, ranging from 29 to 180 kg N ha?1. The highest potential for N adsorption in the 0–60 cm soil profile was with the Ultisol (398 kg N ha?1), but was similar in both Andisols (193 and 172 kg N ha?1, respectively). The combination of ammonium retention together with delayed nitrification could account for the low leaching rates in these soils.  相似文献   

12.
Water quality of Lake Okeechobee has been a major environmental concern for many years. Transport of dissolved organic matter (DOM) in runoff water from watershed is critical to the increased inputs of nutrients (N and P) and metals (Cu and Zn). In this study, 124 soil samples were collected with varying soil types, land uses, and soil depths in Lake Okeechobee watershed and analyzed for water-extractable C, N, P, and metals to examine the relationship between dissolved organic carbon (DOC) and water soluble nutrients (N and P) and metals in the soils. DOC in the soils was in 27.64?C400 mg kg?1 (69.30 mg kg?1 in average) and varied with soil types, land uses, and soil depth. The highest water-extractable DOC was found in soils collected in sugar cane and field crops (277 and 244 mg kg?1 in average, respectively). Water soluble concentrations of N and P were in the range of 6.46?C129 and 0.02?C60.79 mg kg?1, respectively. The ratios of water-extractable C/N and C/P in soils were in 0.68?C12.52 (3.23 in average) and 3.19?C2,329 (216 in average), and varied with land uses. The lowest water-extractable C/N was observed in the soils from dairy (1.66), resident (1.79), and coniferous forest (4.49), whereas the lowest water-extractable C/P was with the land uses of dairy (13.1) and citrus (33.7). Therefore, N and P in the soils under these land uses may have high availability and leaching potential. The concentrations of water soluble Co, Cr, Cu, Ni, and Zn were in the ranges of?<?method detection limit (MDL)?C0.33, <MDL?C0.53, 0.04?C2.42, <MDL?C0.71, and 0.09?C1.13 mg kg?1, with corresponding mean values of 0.02, 0.01, 0.50, 0.07, and 0.37 mg kg?1, respectively. The highest water soluble Co (0.10 mg kg?1), Cr (0.26 mg kg?1), Ni (0.31 mg kg?1), and Zn (0.80 mg kg?1) were observed in soils under the land use of sugar cane, whereas the highest Cu (1.50 mg kg?1) was with field crop. The concentration of DOC was positively correlated with total organic carbon (TOC) (P <0.01), water soluble N (P <0.01), electrical conductivity (EC, P <0.01), and water soluble Co, Cr, Ni, and Zn (P <0.01), and Cu (P <0.05), whereas water soluble N was positively correlated with water soluble P, Cu, and Zn (P <0.01) in soils. These results indicate that the transport of DOC from land to water bodies may correlate with the loss of macro-nutrients (N, P), micro-nutrients (Cu, Zn, and Ni), and contaminants (Cr and Co) as well.  相似文献   

13.
Sludge derived from cow manure anaerobically digested to produce biogas (methane; CH4) was applied to maize (Zea mays L.) cultivated in a nutrient-low, alkaline, saline soil with electrolytic conductivity 9.4 dS m?1 and pH 9.3. Carbon dioxide (CO2) emission increased 3.1 times when sludge was applied to soil, 1.6 times when cultivated with maize and 3.5 times in sludge-amended maize cultivated soil compared to the unamended uncultivated soil (1.51 mg C kg?1 soil day?1). Nitrous oxide (N2O) emission from unamended soil was -0.0004 μg nitrogen (N) kg?1 soil day?1 and similar from soil cultivated with maize (0.27 μg N kg?1 soil day?1). Application of sludge increased the N2O emission to 4.59 μg N kg?1 soil day?1, but cultivating this soil reduced it to 2.42 μg N kg?1 soil day?1. It was found that application of anaerobic digested cow manure stimulated maize development in an alkaline saline soil and increased emissions of CO2 and N2O.  相似文献   

14.
An incubation experiment was conducted to determine the response of soil microbial biomass and activity to salinity when supplied with two different carbon forms. One nonsaline and three saline soils of similar texture (sandy clay loam) with electrical conductivities of the saturation extract (ECe) of 1, 11, 24 and 43 dS m?1 were used. Carbon was added at 2.5 and 5 g C kg?1 (2.5C, 5C) as glucose or cellulose; soluble N and P were added to achieve a C/N ratio of 20 and C/P ratio of 200. Soil microbial activity was assessed by measuring CO2 evolution continuously for 3 weeks; microbial biomass C and available N and P were determined on days 2, 7, 14 and 21. In all soils, cumulative respiration was higher with 5C than with 2.5C and higher with glucose than with cellulose. Cumulative respiration was highest in the nonsaline soil and decreased with increasing EC, whereas the decrease was gradual with glucose, there was a sharp drop in cumulative respiration with cellulose from the nonsaline soil to soil with EC11 with little further decrease at higher ECs. Microbial biomass C and available N and P concentrations were highest in the nonsaline soil but did not differ among the saline soils. Microbial biomass C was higher and available N was lower with 5C than with 2.5C. The C form affected the temporal changes of microbial biomass and available nutrients differentially. With glucose, microbial biomass was highest on day 2 and then decreased, whereas available N showed the opposite pattern, being lowest on day 2 and then increasing. With cellulose, microbial biomass C increased gradually over time, and available N decreased gradually. It is concluded that salinity reduced the ability of microbes to decompose cellulose more than that of glucose.  相似文献   

15.
Predicting nitrogen (N) and sulfur (S) mineralization of crop residues from the preceding crop might be a useful tool for forecasting soil N and S availability. Two soils from eastern North Dakota and three crop residues – corn, spring wheat, and soybean were used in an 8-week incubation study to estimate N and S mineralization from crop residues. The cumulative N and S mineralized were fit to a first-order kinetic model. Cumulative N mineralized ranged between 0.34 and 2.15 mg kg?1 and 0.45 to 3.41 mg kg?1 for the Glyndon and Fargo soils, respectively. Un-amended soils showed higher N mineralization than residue treated soils. For S, the highest mineralization occurred in un-amended Glyndon soil and in spring wheat-amended Fargo soil. This study indicates that crop residue additions can have a negative impact on plant available nutrients due to immobilization of N and S during the time when crops need the nutrients most.  相似文献   

16.
Wetland soils of the freshwater coastal deltaic regions of Louisiana have developed under decreasing influence from the Mississippi River, which has resulted in lower available nutrient conditions and sediment input relative to other coastal marshes. A laboratory soil respiration experiment was conducted to measure cumulative carbon dioxide (CO2) and methane (CH4) production in soils from a floating freshwater marsh in response to additions of added ammonium (N), phosphate (P), ammonium (N) + phosphate (P), and sulfate (S). CO2 respiration was significantly greater over a 28-day period than controls following ammonium N, phosphorus, and sulfate addition at 10 mg L?1. Nitrogen and phosphorus addition at 10 mg L?1 also increased methane production. The lower sulfate amendment (10 mg L?1) did not significantly increase CH4 production. In contrast, the greatest sulfate treatment (100 m l?1) significantly reduced total carbon (C) production by inhibiting CH4 production. The fact that soil C/N (20.2) and C/P (355) ratios were both relatively low may partially explain why both N and P colimited microbial activity and respiration. While microbial activity of freshwater floating marsh soils was stimulated over the short term with increased ammonium, nitrogen, phosphorus, and sulfate exposure, it is unclear whether the increase would be the same over extended periods or would increase in plant productivity from nutrient additions compensate for any loss in soil carbon.  相似文献   

17.
Summary A greenhouse study was conducted to examine the residual effects of sewage sludge on soybean Glycine max (L.) Merr., nodulation, and N fixation. Nodulating and nonnodulating isolines of Clark soybean were grown to the R2 stage in soils (Typic Paleudults) obtained from plots where heat-treated sludge had been applied in 1976 at rates equal to 0, 56,112, and 224 Mg ha–1 high (7.0) and low (6.2) soil pH regimes were established by CaCO3 additions. Sludge and soil pH treatments resulted in clearly defined differences in metal uptake by soybean shoots. Plant Zn, Cd, and Ni concentrations were greater on pH 6.2, sludge-amended soil than on the pH 7.0, amended soil. At low soil pH, soybean Zn and Cd concentrations, respectively, increased from 41 and 0.19 mg kg–1 (control) to 120 and 0.58 mg kg–1 at the 224 Mg hat sludge rate. At the high soil pH and 224 hg hat sludge rate, Zn and Cd concentrations were 45 and 0.15 mg kg–1, respectively.Symbiotic N fixation provided 90% of the total N accumulation. Total N accumulation, shoot N concentration, dry matter, and N fixation by nodulating soybeans exhibited a significant linear increase with sludge rate. Total N accumulation, dry matter, and N fixation were significantly greater at high soil pH. For high and low soil pH, respectively, N fixation increased from 422 and 382 mg N per plant (control) to 614 and 518 mg N per plant at the 224 Mg ha–1 sludge rate. While soybean nodulation also increased linearly on sludge-amended soil, a significant rate times pH interaction for nodule number indicated that nodulation was less strongly enhanced by sludge at low soil pH.  相似文献   

18.
Summary Potential P and C mineralization rates were determined in a 12-week laboratory incubation study on subarctic forest and agricultural soil samples with and without N fertilizer added. There was no significant difference in net inorganic P produced between N fertilized and unfertilized soils. The forest soil surface horizons had the highest net inorganic P mineralized, 32 mg P kg-1 soil for the Oie and 17 mg P kg-1 soil for the Oa. In the cropped soils net inorganic P immobilization started after 4 weeks and lasted through 12 weeks of incubation. Cumulative CO2–C evolution rates differed significantly among soils, and between fertilizer treatments, with the N-fertilized soils evolving lower rates of CO2–C than the unfertilized soils. Soils from the surface horizons in the forest evolved the highest rates of CO2–C (127.6 and 89.4 mg g-1 soil for the Oie and Oa horizons, respectively) followed by the cleared uncropped soil (42.8 mg g-1 soil C), and the cropped soils (25.4 and 29.0 mg g-1 soil C). In vitro soil respiration rates, or potential soil organic matter decomposition rates, decreased with increasing time after clearing and in accord with the degree of disturbance. Only soils with high potential C mineralization rates and high organic P to total P ratios, mineralized P by the end of the study. Mineralizable P appeared to be associated with readily mineralizable organic C.  相似文献   

19.
A laboratory incubation experiment was conducted to evaluate the effect of magnesium chloride–induced salinity on carbon dioxide (CO2) evolution and nitrogen (N) mineralization in a silty loam nonsaline alkaline soil. Magnesium chloride (MgCl2) salinity was induced at 0, 4, 8, 12, 16, 20, 30, and 40.0 dS m?1 and measured CO2 evolution and N mineralization during 30 days of incubation. Both CO2 evolution and N mineralization decreased significantly with increasing salinity. The cumulative CO2 evolution decreased from 235 mg kg?1 soil at electrical conductivity (EC) 0.65 dS m?1 to 11.9 mg kg?1 soil at 40 dS m?1 during 30 days of incubation. Similarly, N mineralization decreased from 185.4 mg kg?1 at EC 0.65 dS m?1 to 34.45 mg kg?1 at EC 40.0 dS m?1 during the same period. These results suggested that increasing magnesium chloride salinity from 4 dS m?1 adversely affect microbial activity in terms of carbon dioxide evolution and N mineralization.  相似文献   

20.
Abstract

In Iran, the recent spike in herbal medicines has led to a corresponding price increase. Therefore, these montane species are now widely field cultivated. Medicinal plant consumers strongly prefer organically grown plants, and farmers are responding to this market. However, the effects of organic amendments on medicinal plant nutrient content and yield have been poorly studied. Therefore, this study measured the effects of different organic treatments on the growth of fenugreek and goat pea. Plants were grown to compare the effects of composted municipal waste (CMW), vermicompost (VC), and urea nitrogen (N) to untreated field soil (C0). Germination percentage was significantly higher in urea N (76.5%), CMW (75.5%), and VC (51.6%) compared to C0 (36.3%). Fenugreek performed better in organic amendment treatments than goat pea. Urea N also increased fenugreek plant dry matter significantly compared to C0, but this increment was not as high as CMW or VC. Plants grown in VC had higher whole plant N content (3.2%) than those grown in CMW (2.8%) and plants grown in urea N (2.6%). Plants treated with CMW (8613?mg kg?1) and VC (8503?mg kg?1) had a significantly higher P content than those treated with N (7430?mg kg?1) or C0 control grown (7236?mg kg?1). Application of VC significantly increased plant K content (2483?mg kg?1) compared to CMW (1850?mg kg?1), N (1750?mg kg?1), and C0 control (1716?mg kg?1). Even without fertilization, both plant species contained a considerable amount of micronutrient elements.  相似文献   

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