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1.
The following six pig slurries obtained after acidification and/or solid/liquid separation were used in the research: original (S) and acidified (AS) pig slurry, nonacidified (LF) and acidified (ALF) pig slurry liquid fraction, and nonacidified (SF) and acidified (ASF) pig slurry solid fraction. Laboratory incubations were performed to assess the effect of the application of these slurries on N mineralization and CO2 and N2O emissions from a sandy soil. Acidification maintained higher NH4 +-N contents in soil particularly in the ALF-treated soil where NH4 +-N contents were two times higher than in LF-treated soil during the 55–171-day interval. At the end of the incubation (171 days), 32.9 and 24.2 mg N kg−1 dry soil were mineralized in the ASF- and SF-treated soils, respectively, but no mineralization occurred in LF- and S-treated soils, although acidification decreased N immobilization in ALF- (−25.3 mg N kg−1 soil) and AS- (−12.7 mg N kg−1 soil) compared to LF- (−34.4 mg N kg−1 soil) and S-treated (−18.6 mg N kg−1 soil) soils, respectively. Most of the dissolved CO2 was lost during the acidification process. More than 90% of the applied C in the LF-treated soil was lost during the incubation, indicating a high availability of the added organic compounds. Nitrous oxide emissions occurred only after day 12 and at a lower rate in soils treated with acidified than nonacidified slurries. However, during the first 61 days of incubation, 1,157 μg N kg−1 soil was lost as N2O in the AS-treated soil and only 937 in the S-treated soil.  相似文献   

2.
Crop residues with high C/N ratio immobilize N released during decomposition in soil, thus reducing N losses through leaching, denitrification, and nitrous oxide (N2O) emission. A laboratory incubation experiment was conducted for 84 days under controlled conditions (24°C and moisture content 55% of water-holding capacity) to study the influence of sugarcane, maize, sorghum, cotton and lucerne residues, and mineral N addition, on N mineralization–immobilization and N2O emission. Residues were added at the rate of 3 t C ha−1 to soil with, and without, 150 kg urea N ha−1. The addition of sugarcane, maize, and sorghum residues without N fertilizer resulted in a significant immobilization of soil N. Amended soil had significantly (P < 0.05) lower NO3−–N, which reached minimum values of 2.8 mg N kg−1 for sugarcane (at day 28), 10.3 mg N kg−1 for maize (day 7), and 5.9 mg N kg−1 for sorghum (day 7), compared to 22.7 mg N kg−1 for the unamended soil (day 7). During 84 days of incubation, the total mineral N in the residues + N treatments were decreased by 45 mg N kg−1 in sugarcane, 34 mg kg−1 in maize, 29 mg kg−1 in sorghum, and 16 mg kg−1 in cotton amended soil compared to soil + N fertilizer, although soil NO3−–N increased by 7 mg kg−1 in lucerne amended soil. The addition of residues also significantly increased amended soil microbial biomass C and N. Maximum emissions of N2O from crop residue amended soils occurred in the first 4–5 days of incubation. Overall, after 84 days of incubation, the cumulative N2O emission was 25% lower with cotton + N fertilizer, compared to soil + N fertilizer. The cumulative N2O emission was significantly and positively correlated with NO3−–N (r = 0.92, P < 0.01) and total mineral N (r = 0.93, P < 0.01) after 84 days of incubation, and had a weak but significant positive correlation with cumulative CO2 in the first 3 and 5 days of incubation (r = 0.59, P < 0.05).  相似文献   

3.
Laboratory incubation study showed that iron pyrites retarded nitrification of urea-derived ammonium (NH4 +), the effect being greatest at the highest level (10000 mg kg–1 soil). Nitrification inhibition with 10000 mg pyrite kg–1 soil, at the end of 30 days, was 40.3% compared to 55.9% for dicyandiamide (DCD). The inhibitory effect with lower rates of pyrite (100–500 mg kg–1) lasted only up to 9 days. Urea+pyrite treatment was also found to have higher exchangeable NH4 +-N compared to urea alone. DCD-amended soils had the highest NH4 +-N content throughout. Pyrite-treated soils had about 7–86% lower ammonia volatilization losses than urea alone. Total NH3 loss was the most with urea+DCD (7.9% of applied N), about 9% more than with urea alone. Received: 11 November 1995  相似文献   

4.
The short-term effects of excessive NH4+-N on selected characteristics of soil unaffected (low annual N inputs) and affected (high annual N inputs) by cattle were investigated under laboratory conditions. The major hypothesis tested was that above a theoretical upper limit of NH4+ concentration, an excess of NH4+-N does not further increase NO3− formation rate in the soil, but only supports accumulation of NO2−-N and gaseous losses of N as N2O. Soils were amended with 10 to 500 μg NH4+-N g−1 soil. In both soils, addition of NH4+-N increased production of NO3−-N until some limit. This limit was higher in cattle-affected soil than in unaffected soil. Production of N2O increased in the whole range of amendments in both soils. At the highest level of NH4+-N addition, NO2−-N accumulated in cattle-affected soil while NO3−-N production decreased in cattle-unaffected soil. Despite being statistically significant, observed effects of high NH4+-N addition were relatively weak. Uptake of mineral N, stimulated by glucose amendment, decreased the mineral N content in both soils, but it also greatly increased production of N2O.  相似文献   

5.
Red lead (Pb3O4) has been used extensively in the past as an anti-corrosion paint for the protection of steel constructions. Prominent examples being some of the 200,000 high-voltage pylons in Germany which have been treated with red lead anti-corrosion paints until about 1970. Through weathering and maintenance work, paint compounds and particles are deposited on the soils beneath these constructions. In the present study, six such “pylon soils” were investigated in order to characterize the plant availability and plant uptake of Pb, Cd, and Zn. For comparison, three urban soils with similar levels of heavy metal contamination were included. One phase extractions with 1 M NH4NO3, sequential extractions (seven steps), and extractions at different soil pH were used to evaluate the heavy metal binding forms in the soil and availability to plants. Greenhouse experiments were conducted to determine heavy metal uptake by Lolium multiflorum and Lactuca sativa var. crispa in untreated and limed red lead paint contaminated soils. Concentrations of Pb and Zn in the pylon soils were elevated with maximum values of 783 mg Pb kg−1 and 635 Zn mg kg−1 while the soil Cd content was similar to nearby reference soils. The pylon soils were characterized by exceptionally high proportions of NH4NO3-extractable Pb reaching up to 17% of total Pb. Even if the relatively low pH of the soils is considered (pH 4.3–4.9), this appears to be a specific feature of the red lead contamination since similarly contaminated urban soils have to be acidified to pH 2.5 to achieve a similarly high Pb extractability. The Pb content in L. multiflorum shoots reached maximum values of 73 mg kg−1 after a cultivation time of 4 weeks in pylon soil. Lime amendment reduced the plant uptake of Pb and Zn significantly by up to 91%. But L. sativa var. crispa cultivated on soils limed to neutral pH still contained critical Pb concentrations (up to 0.6 mg kg−1 fresh weight). Possible mechanisms for the exceptionally high plant availability of soil Pb derived from red lead paint are discussed.  相似文献   

6.
Simple and rapid chemical indices of soil nitrogen (N)-supplying capacity are necessary for fertilizer recommendations. In this study, pot experiment involving rice, anaerobic incubation, and chemical analysis were conducted for paddy soils collected from nine locations in the Taihu Lake region of China. The paddy soils showed large variability in N-supplying capacity as indicated by the total N uptake (TNU) by rice plants in a pot experiment, which ranged from 639.7 to 1,046.2 mg N pot−1 at maturity stage, representing 5.8% of the total soil N on average. Anaerobic incubation for 3, 14, 28, and 112 days all resulted in a significant (P < 0.01) correlation between cumulative mineral NH4+-N and TNU, but generally better correlations were obtained with increasing incubation time. Soil organic C, total soil N, microbial C, and ultraviolet absorbance of NaHCO3 extract at 205 and 260 nm revealed no clear relationship with TNU or cumulative mineral NH4+-N. Soil C/N ratio, acid KMnO4-NH4+-N, alkaline KMnO4-NH4+-N, phosphate–borate buffer extractable NH4+-N (PB-NH4+-N), phosphate–borate buffer hydrolyzable NH4+-N (PBHYDR-NH4+-N) and hot KCl extractable NH4+-N (HKCl−NH4+-N) were all significantly (P < 0.05) related to TNU and cumulative mineral NH4+-N of long-term incubation (>28 days). However, the best chemical index of soil N-supplying capacity was the soil C/N ratio, which showed the highest correlation with TNU at maturity stage (R = −0.929, P < 0.001) and cumulative mineral NH4+-N (R = −0.971, P < 0.001). Acid KMnO4-NH4+-N plus native soil NH4+-N produced similar, but slightly worse predictions of soil N-supplying capacity than the soil C/N ratio.  相似文献   

7.
One of the main environmental impacts of concentrated animal feeding operations is the soil degradation in vicinity with the livestock breeding facilities due to substances such as ammonia emitted from the various stages of the process. Owing to the high temperatures of the Mediterranean ecosystems, the evolution of gasses is more extensive and the soil degradation is consequently more severe than those obtained in northern Europe. In this research, the soil degradation effects of a large meat-producing, processing, and packaging unit have been investigated. The investigated intensive hog farming operation (IHFO) is located at a limestone soil coastal area with sea to the north and hills to the south. Soil samples of the upper mineral soil were taken in various distances and directions from the IHFO boundaries. Thirteen experimental cycles were carried out in the duration of 1.5 years starting in March 2009 until October 2010. The soil samples were analyzed on pH and electrical conductivity (EC) values as well as NH4 + and NO3 − concentrations. Significantly higher concentrations of the two nitrogen forms were observed on samples at increasing proximity downwind from the farm (south). Southern soil average NH4 + and NO3 − concentrations ranged between 0.4–118 μg NH4 +-N g−1 soil and 6.1–88.4 μg NO3 −-N g−1 soil, respectively. The variation of emitted gasses depositions was clearly reflected in the average pH and EC values. Average pH and EC values downwind from IHFO boundaries varied between 7.1–8.2 and 140–268 μS/cm, respectively.  相似文献   

8.
Changes in 15N abundance and amounts of biologically active soil nitrogen   总被引：1，自引：0，他引：1  
 Estimation of the capacity of soils to supply N for crop growth requires estimates of the complex interactions among organic and inorganic N components as a function of soil properties. Identification and measurement of active soil N forms could help to quantify estimates of N supply to crops. Isotopic dilution during incubation of soils with added 15NH4 + compounds could identify active N components. Dilution of 15N in KCl extracts of mineral and total N, non-exchangeable NH44 +, and N in K2SO4 extracts of fumigated and non-fumigated soil was measured during 7-week incubation. Samples from four soils varying in clay content from 60 to 710 g kg–1 were used. A constant level of 15N enrichment within KCl and K2SO4 extracted components was found at the end of the incubation period. Total N, microbial biomass C and non-exchangeable NH4 + contents of the soils were positively related to the clay contents. The mineralized N was positively related to the silt plus clay contents. The active soil N (ASN) contained 28–36% mineral N, 29–44% microbial biomass N, 0.3–5% non-exchangeable NH4 + with approximately one third of the ASN unidentified. Assuming that absolute amounts of active N are related to N availability, increasing clay content was related to increased N reserve for crop production but a slower turnover. Received: 7 July 1998  相似文献   

9.
 Wheat straw enclosed in mesh bags was buried for periods up to 1 year over two seasons in Scottish, Danish and Portuguese soils treated with 15NH4NO3 or NH4 15NO3. Scottish soils were: Terryvale, a poorly drained sandy loam; and Tipperty, an imperfectly drained brown forest soil with a higher clay content. The Danish soil (Foulum) was a freely drained sandy loam and the Portuguese soils were a sandy soil (Evora) and a clay soil (Beja). During the first month, 15N was being incorporated into the straw in the Tipperty, Terryvale and Foulum soils simultaneously as the total N content was decreasing. Subsequently, the straws began to show net immobilization and the total N content of the original straw was exceeded in Tipperty and Foulum soils after 4 months and 8 months, respectively. Net immobilization in Terryvale was detected only in the second season and did not occur in the first because of high soil moisture content. The rates of 15N incorporation were similar in the two Portuguese soils, and a loss of N was only detected after 8 months. After 1 month, in the two clay soils, Beja and Tipperty, 15NO3 – was incorporated into straw to a greater extent than 15NH4 + and this was attributed to 15NH4 + fixation by clay minerals. In contrast, 15NH4 + was more efficiently incorporated than 15NO3 – under waterlogged conditions (Terryvale) and NO3 – loss could be attributed to denitrification. The proportion of added 15N in the straw residue after 1 month varied between 6% and 18% for 15NH4 + and 2% and 23% for 15NO3 – and immobilization of N in the longer term tended to be greater in soils from northern Europe than from Portugal. Received: 19 January 1998  相似文献   

10.
Enchytraeids are involved both directly and indirectly in decomposition processes and nitrogen mineralization in soil. Their influence is especially important in nitrogen poor ecosystems such as heathland where the enchytraeid species, Cognettia sphagnetorum, is often abundant and playing a significant role in the N-cycling. The objective of this study was to quantify NH4+-N excretion of C. sphagnetorum at different temperatures. The results were combined with investigations of population dynamics during one year to estimate annual NH4+-N excretion of the population of C. sphagnetorum in a dry Danish heath soil. C. sphagnetorum significantly increased its NH4+-N excretion rate with increasing temperature. At 5 °C about 0.5 μg NH4+-N mg dry weight−1 day−1 was excreted increasing to about 3.3 μg NH4+-N mg dry weight−1 day−1 at 20 °C. Average enchytraeid biomass in the field was 2.5-3.5 g dry weight m−2 during cool and wet periods. Dry and warm conditions in May and June, 2008, had a drastic and long-term negative impact on the enchytraeid community. The excretion of NH4+-N by enchytraeids was therefore highest during the cool and moist months despite low temperatures (October 2007-May 2008) and amounted to about 2 mg NH4+-N m−2 day−1 during this period. The estimated annual NH4+-N excretion of the enchytraeid community was approximately 0.3 g N m−2 year−1. The results of the present study and the method described for estimation of N-excretion can increase our understanding of enchytraeids’ role in nitrogen mineralization.  相似文献   

11.
This work aims to identify and characterize heavy metal contamination in a fluvial system from Cartagena–La Unión mining district (SE Spain). In order to assess the dynamics of transport and the accumulation of heavy metals, sediments, surface water and vegetation, samples along “El Avenque” stream were collected. The former direct dumps of wastes and the presence of tailing ponds adjacent to the watercourse have contributed to the total contamination of the stream. Total Cd (103 mg kg−1), Cu (259 mg kg−1), Pb (26,786 mg kg−1) and Zn (9,312 mg kg−1) in sediments were above the limits of European legislation, being highest where tailing ponds are located. Bioavailable metals were high (3.55 mg Cd kg−1, 6.45 mg Cu kg−1, 4,200 mg Pb kg−1 and 343 mg Zn kg−1) and followed the same trend than total contents. Metals in water were higher in sampling points close to ponds, exceeding World Health Organization guidelines for water quality. There is a direct effect of solubilisation of sediment metals in water with high contents of SO42−, product of the oxidation of original sulphides. The mobility of metals varied significantly with shifts in pH. Downstream, available and soluble metals concentrations decreased mainly due to precipitation by increments in pH. As a general pattern, no metal was bioaccumulated by any tested plant. Thus, native vegetation has adopted physiological mechanisms not to accumulate metals. This information allows the understanding of the effect of mining activities on stream contamination, enforcing the immediate intervention to reduce risks related to metals’ mobility.  相似文献   

12.
The effects on nitrification and acidification in three subtropical soils to which (NH4)2SO4 or urea had been added at rate of 250 mg N kg−1 was studied using laboratory-based incubations. The results indicated that NH4+ input did not stimulate nitrification in a red forest soil, nor was there any soil acidification. Unlike red forest soil, (NH4)2SO4 enhanced nitrification of an upland soil, whilst urea was more effective in stimulating nitrification, and here the soil was slightly acidified. For another upland soil, NH4+ input greatly enhanced nitrification and as a result, this soil was significantly acidified. We conclude that the effects of NH4+ addition on nitrification and acidification in cultivated soils would be quite different from in forest soils. During the incubation, N isotope fractionation was closely related to the nitrifying capacity of the soils.  相似文献   

13.
The objective of this study was to investigate the effects of adding different rates of diethylenetriamine pentaacetate (DTPA) at different concentrations (0, 0.5, 1, and 5 mmol kg−1) and ethylenediamine disuccinate (EDDS) at 0, 5, 7.5, and 10 mmol kg−1 on the capacity of Brussels sprouts plants to take up Se from soils contaminated with 0, 5, 10, and 15 mg kg−1 NaSeO4, under a greenhouse conditions. Results indicated that the application of DTPA and EDDS to Se-contaminated soils significantly affect plant Se concentration, Se uptake, and dry matter yield of plants. Se concentration in the plant leaves, stems, and roots increased with increase in DTPA and EDDS application doses, but total Se uptake increased from 0 to 1.0 and 7.5 mmol kg−1 DTPA and EDDS application doses, respectively, and decreased after those levels due to toxic Se concentration for plant. Most plant available fractions and the carbonate, metal oxide, and organic matter-bound fractions increased linearly with Se application. At all DTPA and EDDS application rates, the Se concentrations in the leaves were about two to three times higher than those in the roots and about three to four times higher than those in the stems. This study suggests that the above-ground organs like leaf and shoots of Brussels sprouts can effectively be used in the removal of Se from soils contaminated with Se. Under the conditions in this experiment, Brussels sprouts were capable of removing 0.9–1.8 mg Se pot−1 when harvested at maturity without any chelating agent take into consideration one growing season per year. Based on the data of present experiment, it would be necessary to approximately 57–67 growing seasons without EDDS and EDTA to remove all total Se from polluted soil. Selenium removal can be further increased 12- to 20-fold with 7.5 mmol kg−1 EDDS and 1.0 mmol kg−1 DTPA application, respectively.  相似文献   

14.
During the intensive flood in May–June 2010, the floodplains in Little Poland Vistula Gap, used mostly for agriculture, were waterlogged for a period of over 1 month. The aim of the study was to assess the effect of the flood on the level of contamination of the soils in this region. The analysis included basic physicochemical soil properties, contents of ten metals, and concentrations of 16 polycyclic aromatic hydrocarbons (PAHs). The studies cover two territories on opposite sites of the river Vistula (Wilkow and Janowiec) differing in their areas (70 and 4.6 km2) and time of water logging (30 and 10 days). Forty soil samples were collected from both areas immediately after the flood event from the upper (0–30 cm) soil layer together with four samples from the 30–60-cm depth layer. This was supplemented by eight samples from the flood-deposited sediment layer (thickness, 2 cm). The concentrations of identified metals (As, Ba, Cr, Sn, Zn, Cd, Co, Cu, Ni, Pb) at all the sampling points were below the Polish legal limits for the upper layer of soils for agriculture use. The same regarded the median contents of nine PAHs compounds specified in the Polish regulations. In both areas, the median contents of Σ16 PAHs (0.21–0.35 mg kg−1), Zn (10.3–10.6 mg kg−1), Pb (9.2–10.7 mg kg−1), and Cd (0.03 mg kg−1) were much below the mean concentrations of those contaminants in arable soils on the national and European levels. The results show that this severe flooding episode in “clean” agricultural area had no immediate negative impact on the soils as regards the basic physicochemical properties (organic matter content, acidity, nitrogen content) and did not result in excessive soil contamination.  相似文献   

15.
Since swine wastewater is used by farmers for soil fertilization, evaluation of toxic compounds or micro-contaminants of separate streams is required. This paper uses the toxicity identification evaluation (TIE) procedure for the physicochemical and ecotoxicological characterization of swine wastewater. To distinguish the most important toxic compounds, a physicochemical characterization and phase I-TIE procedure were performed. The acute toxic effect of swine wastewater and treated fractions (phase II-TIE) were evaluated using Daphnia magna determining 48-h LC50. Results show a high level of conductivity (23.5 μS cm−1), which is explained as due to the concentration of ions, such as ammonium (NH4+–N 1.6 g L−1), sulfate (SO42− 397.3 mg L−1), and chlorine (Cl− 1,230.0 mg L−1). The acute toxicity of the swine wastewater was evaluated on D. magna (48-h LC50 = 3.4%). Results of the different water treatments indicate that anionic exchange treatments could reduce 22.5% of swine wastewater’s acute toxicity by reducing chlorine (to around 51%) and conductivity (8.5%). On the other hand, cationic exchange treatment increased acute toxicity on D. magna (% RT = −624.4%), by reducing NH4+–N (around 100%) and total nitrogen (95.5%). This finding suggests that part of the toxicity comes from anionic compounds, such as chlorine.  相似文献   

16.
Seasonal drought in tropical agroecosystems may affect C and N mineralization of organic residues. To understand this effect, C and N mineralization dynamics in three tropical soils (Af, An1, and An2) amended with haricot bean (HB; Phaseolus vulgaris L.) and pigeon pea (PP; Cajanus cajan L.) residues (each at 5 mg g−1 dry soil) at two contrasting soil moisture contents (pF2.5 and pF3.9) were investigated under laboratory incubation for 100–135 days. The legume residues markedly enhanced the net cumulative CO2–C flux and its rate throughout the incubation period. The cumulative CO2–C fluxes and their rates were lower at pF3.9 than at pF2.5 with control soils and also relatively lower with HB-treated than PP-treated soil samples. After 100 days of incubation, 32–42% of the amended C of residues was recovered as CO2–C. In one of the three soils (An1), the results revealed that the decomposition of the recalcitrant fraction was more inhibited by drought stress than easily degradable fraction, suggesting further studies of moisture stress and litter quality interactions. Significantly (p < 0.05) greater NH4+–N and NO3−–N were produced with PP-treated (C/N ratio, 20.4) than HB-treated (C/N ratio, 40.6) soil samples. Greater net N mineralization or lower immobilization was displayed at pF2.5 than at pF3.9 with all soil samples. Strikingly, N was immobilized equivocally in both NH4+–N and NO3−–N forms, challenging the paradigm that ammonium is the preferred N source for microorganisms. The results strongly exhibited altered C/N stoichiometry due to drought stress substantially affecting the active microbial functional groups, fungi being dominant over bacteria. Interestingly, the results showed that legume residues can be potential fertilizer sources for nutrient-depleted tropical soils. In addition, application of plant residue can help to counter the N loss caused by leaching. It can also synchronize crop N uptake and N release from soil by utilizing microbes as an ephemeral nutrient pool during the early crop growth period.  相似文献   

17.
Tillage systems influence soil properties and may influence the availability of applied and mineralized soil N. This laboratory study (20°C) compared N cycling in two soils, a Wooster (fine, loamy Typic Fragiudalf) and a Hoytville (fine, illitic Mollic Epiaqualf) under continuous corn (Zea mays) production since at least 1963 with no-tillage (NT), minimum (CT) and plow tillage (PT) management. Fertilizer was added at the rate of 100 mg 15N kg–1–1 soil as 99.9% 15N as NH4Cl or Ca(NO3)2 and the soils were incubated in leaching columns for 1 week at 34 kPa before being leached periodically with 0.05 M CaCl2 for 26 weeks. As expected, the majority of the 15NO3– additions were removed from both soils with the first leaching. The majority of applied 15NH4+ additions were recovered as 15NO3– by week 5, with the NT soils demonstrating faster nitrification rates compared with soils under other tillage practices. For the remaining 22 weeks, only low levels of 15NO3– were leached from the soils regardless of tillage management. In the coarser textured Wooster soils (150 g clay kg–1), mineralization of native soil N in the fertilized soils was related to the total N content (r2 0.99) and amino acid N (r2 0.99), but N mineralization in the finer textured Hoytville (400 g clay kg–1) was constant across tillage treatments and not significantly related to soil total N or amino acid N content. The release of native soil N was enhanced by NH4+ or NO3– addition compared to the values released by the unfertilized control and exceeded possible pool substitution. The results question the use of incubation N mineralization tests conducted with unfertilized soils as a means for predicting soil N availability for crop N needs.  相似文献   

18.
Nutrient concentrations in the soil and crop uptake from incorporated green manure and urea in flooded rice was studied in field experiments. Release of plant-available nitrogen (NH4 +-N) from green manure was slightly delayed compared with that from prilled urea (PU) because Sesbania rostrata L. and Aeschynomene afraspera L. released the N gradually after their decomposition, whereas N became available immediately after PU application. Exchangeable NH4 +-N concentration in soil peaked at 163 mg kg–1 in the transplanted rice (TPR) and 198 mg kg—1 in broadcast-seeded rice (BSR) at 0 and 1 week after PU application. Broadcast-seeded rice depleted NH4 +-N faster than did TPR because of the crop‘s vigorous growth in the former during the early stage. Soil solution NH4 +-N followed a similar trend to that of soil NH4 +-N. Incorporation of S. rostrata and A. afraspera increased the concentration of P, K+, Fe2+ and Mn2+ in soil solution more than did the application of PU. However, zinc concentration decreased in all treatments. Both PU and green manure increased the N status of the rice plants and enhanced the uptake of P, K, Fe, Mn and Zn by the rice crop. This suggests that application of green manures improves the uptake of these nutrients by the crop. The highest apparent N recovery was obtained with PU followed by green manure. Received: 11 November 1996  相似文献   

19.
We compared, from 2004 through 2006, rates of soil–atmosphere CH4 exchange at permanently established sampling sites in a temperate forest exposed to ambient (control plots; ∼380 μL L−1) or elevated (ambient + 200 μL L−1) CO2 since August 1996. A total of 880 observations showed net atmospheric CH4 consumption (flux from the atmosphere to the soil) from all static chambers most of the time at rates varying from 0.02 mg m−2 day−1 to 4.5 mg m−2 day−1. However, we infrequently found net CH4 production (flux from the soil to the atmosphere) at lower rates, 0.01 mg m−2 day−1 to 0.08 mg m−2 day−1. For the entire study, the mean (±SEM) rate of net CH4 consumption in control plots was higher than the mean for CO2-enriched plots, 0.55 (0.03) versus 0.51 (0.03) mg m−2 day−1. Annual rates of 184, 196, and 197 mg m−2 for net CH4 consumption at control plots during the three calendar years of this study were 19, 10, and 8% higher than comparable values for CO2 enriched plots. Differences between treatments were significant in 2004 and 2005 and nearly significant in 2006. Volumetric soil water content was consistently higher at CO2-enriched sites and a mixed-effects model identified a significant soil moisture x CO2 interaction on net atmospheric CH4 consumption. Increased soil moisture at CO2-enriched sites likely increases diffusional resistance of surface soils and the frequency of anaerobic microsites supporting methanogenesis, resulting in reduced rates of net atmospheric CH4 consumption. Our study extends our observations of reduced net atmospheric CH4 consumption at CO2-enriched plots to nearly five continuous years, suggesting that this is likely a sustained negative feedback to increasing atmospheric CO2 at this site.  相似文献   

20.
Field experiments were conducted to determine the effect of nitrogen (N) fertilizer forms and doses on wheat (Triticum aestivum L.) on three soils differing in their ammonium (NH4) fixation capacity [high = 161 mg fixed NH4-N kg?1 soil, medium = 31.5 mg fixed NH4-N kg?1 soil and no = nearly no fixed NH4-N kg?1 soil]. On high NH4+ fixing soil, 80 kg N ha?1 Urea+ ammonium nitrate [NH4NO3] or 240 kg N ha?1 ammonium sulfate [(NH4)2SO4]+(NH4)2SO4, was required to obtain the maximum yield. Urea + NH4NO3 generally showed the highest significance in respect to the agronomic efficiency of N fertilizers. In the non NH4+ fixing soil, 80 kg N ha?1 urea+NH4NO3 was enough to obtain high grain yield. The agronomic efficiency of N fertilizers was generally higher in the non NH4+ fixing soil than in the others. Grain protein was highly affected by NH4+ fixation capacities and N doses. Harvest index was affected by the NH4+ fixation capacity at the 1% significance level.  相似文献   

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