| 1. |
- Lindberg, T., et al.
(författare)
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Distribution of15N in the soil-plant system during a four-year field lysimeter study with barley (Hordeum distichum L.) and perennial meadow fescue (Festuca pratensis Huds.)
- 1989
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Ingår i: Plant and Soil. - Dordrecht, Netherlands : Kluwer Academic Publishers. - 0032-079X .- 1573-5036. ; 119:1, s. 25-37
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Tidskriftsartikel (refereegranskat)abstract
- An annual cereal, barley, and a perennial grass ley, meadow fescue, were grown in field lysimeters in Sweden and fertilized with 12 and 20g Ca(NO3)2-N m-2 yr-1, respectively. Isotope-labeled (15N) fertilizer was added during year 1 of the study, whereafter similar amounts of unlabeled N were added during years 2 and 3. The grass ley lysimeters were ploughed after the growing season of year 3 and sown with barley during year 4. The barley harvest in year 1 removed 59% of the added fertilizer N, while the fertilizer N export by two meadow fescue harvests in year 1 was 65%. The labeled N export decreased rapidly after year 1, especially in the barley, but increased slightly after ploughing of the grass ley.The microbial biomass, measured with the chloroform fumigation method, incorporated a maximum of 1.4-1.7% of the labeled N during the first seven weeks after application. Later on, the incorporation stabilized at less than 1% in both cropping systems.The susceptibility of the residual labeled N to mineralization was evaluated three years after application by means of long-term laboratory incubations. The curves of cumulative mineralized N were described by a two-component first-order regression model that differentiated between an available and a more recalcitrant fraction of potentially mineralizable N. There was no difference in the amounts of potentially mineralizable N between the cropping systems. The labeled N comprised 5 and 2% of the amounts of potentially mineralizable N in the available and more recalcitrant fraction, respectively. The mineralization rate constants for the labeled N were almost twice as high as for the total potentially mineralizable N. The available fraction of the total potentially mineralizable N was 12%, while twice that proportion of the labeled N was available.It was concluded that the short-term ley did not differ from the annual crop with respect to the early disposition of the fertilizer N and the behaviour of the residual organic N.
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| 2. |
- Bååth, Erland, et al.
(författare)
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Effect of nitrogen and carbon supply on the development of soil organism populations and pine seedlings - microcosm experiment
- 1978
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Ingår i: Oikos. - 1600-0706. ; 31:2, s. 153-163
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Tidskriftsartikel (refereegranskat)abstract
- Series of pots containing Scots pine seedlings and a humus-sand mixture were watered twice weekly for 398 d with different nutrient solutions (control treatment with complete plant nutrient solution less nitrogen; glucose addition; nitrogen addition; glucose and nitrogen addition). Analyses were made of organic and nitrogen contents in the substrate, plant weights and nitrogen contents, nitrogen fixation and respiration rates, abundance, biomass and in some cases species composition of different soil organism populations. The growth rate of pine seedlings was lowest in series supplied with glucose, which is most easily explained by a deficiency of nitrogen due to microbial immobilization. The fungi and yeast were stimulated by addition of an easily available carbon source whereas the bacteria needed both nitrogen and carbon to maintain high biomass. A positive correlation between fungal feeding soil organisms and amount of fungal mycelium was found while a more complex situation prevailed with regard to bacterial numbers and bacterial feeding nematodes. The systems are evaluated in relation to the different treatments and compared with the field situation.
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| 3. |
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| 4. |
- Bååth, Erland, et al.
(författare)
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Impact of microbial-feeding animals on total soil activity and nitrogen dynamics - a soil microcosm experiment
- 1981
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Ingår i: Oikos. - 1600-0706. ; 37:3, s. 257-264
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedThe long-term impact of microbial-feeding animals on microbial populations was studied in microcosms containing pine seedlings growing in a gamma sterilized humus-sand mixture. Organism communities of diverse complexity were introduced into the microcosms. The two main experimental series contained microorganisms only and microorganisms and microorganism-feeding nematodes, respectively. After 18 months the following analyses were made: soil chemical characteristics, weight and nitrogen content of the seedlings, soil respiration, abundance, biomass, and in some cases, species composition of the different soil organism populations. During the incubation, leaching of nitrogen from the microcosms was measured continuously. The rate of nitrogen leaching from the microcosms increased during the first 6 months. During the remaining 12 months the leaching stabilized at a low rate. Initially, the series with microbial-feeding nematodes had a lower rate of nitrogen loss through leaching compared to the series with only microorganisms added. Towards the end of the experiment the situation was reversed. The pine seedlings showed a very poor growth in all series with no significant differences between the treatments. In the microcosms, bacteria appeared to be the most important microorganism group; fungi, algae and yeasts were present in low amounts. The presence of bacterial feeding nematodes reduced the number of bacteria but did not reduce the soil respiration rate. A significant correlation was obtained between the numbers of nematodes and the respiration rate of the microcosms, which is interpreted as an increased bacterial production rate due to the presence of bacterial-feeding animals.
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| 5. |
- Clarholm, M., et al.
(författare)
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Biological aspects of nitrogen mineralization in humus from a pine forest podsol incubated under different moisture and temperature conditions
- 1981
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Ingår i: Oikos. - 1600-0706. ; 37:2, s. 137-145
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedFluctuations of soil organism abundance, soil respiration and inorganic nitrogen werestudied in a laboratory experiment on material taken from the humus layer of a Scotspine forest and incubated under different moisture and temperature regimes. Theexperiment was run for 28 wk with samplings every 7 wk. At 28 wk, increases in"total movable N" (inorganic N + biomass N) were observed in samples incubated athigh temperature and/or high moisture content. Most of the N was found in biomassexcept in incubations at the highest temperatures and moistures. Under those conditions,high abundance of nematodes occurred together with drastically increasedamounts of inorganic N. Low values of inorganic N were recorded under conditionscommon in the field. No obvious relations could be detected between standing cropsof bacteria and temperature, moisture or respiration. The number of bacterial-feedingnematodes seemed to be a possible measure of previous bacterial productioncontributing more information than the standing crop measurements of the bacteria,which varied little despite the direct evidence of substantial bacterial production insome incubation conditions.
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| 6. |
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| 7. |
- Schnürer, Johan, 1957-, et al.
(författare)
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Fungi, bacteria and protozoa in soil from four arable cropping systems
- 1986
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Ingår i: Biology and Fertility of Soils. - New York : Springer. - 0178-2762 .- 1432-0789. ; 2:3, s. 119-126
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Tidskriftsartikel (refereegranskat)abstract
- The effects of four cropping systems on soil microorganisms were investigated during 3 years. The cropping systems were B0, barley without nitrogen fertilizers; B120, barley with 120 kg N ha-1 year-1; GL, grass ley receiving 200 kg N ha-1 year-1; and LL, lucerne ley without nitrogen fertilizer additions. At samplings in September during three consecutive years no differences were found between treatments. Total fungal lengths ranged between 0.7 and 2.0 × 103 m and bacterial numbers between 3.5 and 7.2 × 109 g-1 dry wt. soil.Twenty samplings over 3 years in B120 and in GL indicated higher numbers of bacteria and protozoa during the growing season, except for periods with moisture stress. No clear seasonal trends were found for the fungi. When comparing mean values for the 20 samplings, the grass ley contained significantly (P < 0.05) higher numbers of amoebae. Means of the bacterial numbers and biomass, total and FDA-active hyphal lengths were also higher or equal (FDA-active hyphae) but not significantly so.Seventy-nine per cent of the bacterial biomass and 73% of the total fungal lengths were found in the top soil, where also 85% of the oxygen was consumed.
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