Publikasjoner
NIBIOs ansatte publiserer flere hundre vitenskapelige artikler og forskningsrapporter hvert år. Her finner du referanser og lenker til publikasjoner og andre forsknings- og formidlingsaktiviteter. Samlingen oppdateres løpende med både nytt og historisk materiale. For mer informasjon om NIBIOs publikasjoner, besøk NIBIOs bibliotek.
1999
Forfattere
Per Ivar Våje Bal Ram Singh Rattan LalSammendrag
Nitrogen and water are both major limiting factors for agronomic production in Africa. The effect of erosion on the availability of N and water for plants is not known for major soils of the tropics. Therefore, a study was conducted to assess erosional effects on N- and water-balance on a Mollic Andosol of 9-17% slope at Lyamungu Agricultural Research and Training Institute (ARTI), Kilimanjaro region, Tanzania. Soil erosion phases were established on the bases of the topsoil depth (TSD) as an indicator of previous erosion: <1 cm; severely eroded, 16-25 cm; moderately eroded and 26-35 cm; slightly eroded. Fill-in lysimeters (80 cm diameter, 80 cm deep) and field runoff plots (4x10 m) were used to monitor evapotranspiration (ET) and seepage, and N losses through erosion, runoff leaching and plant uptake. Maize (Zea mays var. Kilima) was planted in lysimeters and runoff-plots over two cropping seasons (1995 and 1996). Rainfall and evaporation (E) were measured daily. Sediment samples from runoff plots were analysed for total N, P and C, and water samples from leachate, runoff, and
Forfattere
Anne-Grete Buseth BlankenbergSammendrag
Det er ikke registrert sammendrag
Forfattere
Trond Henriksen T.A BrelandSammendrag
Good predictions of plant litter carbon (C) and nitrogen (N) turnover in soil depends heavily on a reliable quantification of litter quality. In this work, eight common agricultural crop residues were described by their intrinsic chemical properties and incubated in a sandy soil (15°C and "0.01 MPa water potential). Measured C mineralization varied greatly between the plant materials and was well predicted by a simulation model in which litter C is subdivided into three pools according to the results of stepwise chemical digestion (Van Soest analysis). Nevertheless, there was a significant lack of fit for some of the materials. This was caused by differences in the specific decay rates of holocellulose-like substances (kSPM) as subsequently estimated for each plant material by fitting the model to data on remaining holocellulose. Even though the model takes account of microbial N deficiency, the optimized kSPM values were significantly correlated with initial N (r2 = 0.93) but not with lignin concentration. To test the predictive value in our model of indices and quantities thought to be related to litter degradability, we investigated whether they were correlated with the kinetically defined pool of readily decomposable plant constituents as estimated by fitting the model to measured C mineralization rates. Neutral detergent-soluble C (Van Soest analysis) was best correlated with the estimated pool (r2 = 0.78) followed by water-soluble C (r2 = 0.69) and C digestible in vitro in rumen fluid (r2 = 0.66). Measured C/N ratio in holocellulose-like substances was highly correlated with the overall C/N ratio of the plant materials (r2 = 0.96). In the model, we describe the degradability of litter N on the basis of the measured C/N ratios of the litter pools. The simulated microbial N requirement is governed by a successive replacement of rapidly growing organisms with a low C/N ratio by more slowly growing organisms with a slightly higher C/N ratio, reflecting the commonly observed increase along the decay continuum in the fungal contribution to microbial activity. This model feature was supported by a measured tendency to an increasing biomass C/N ratio. The model gave unbiased simulations of N mineralization and microbial biomass N. This indicates that the descriptions of litter N availability and microbial N requirement in the model were reasonable. However, significant discrepancies between simulated and measured values occurred for some of the plant materials during the first few days of decomposition, emphasizing the need for more accurate knowledge for this very dynamic phase. Our results suggest that an a priori characterization of litter degradability is possible in our model by the use of stepwise chemical digestion for subdivision of litter C and N combined with measurements of initial N to set the decay rate constant of holocellulose-like materials.
Forfattere
J Bligaard Richard Meadow O Nielsen A Percy-SmithSammendrag
The use of felt traps to estimate oviposition by the cabbage root fly, Delia radicum (L.), and turnip root fly, Delia floralis (Fall.), was compared with soil sampling at seven localities between 1992 and 1994 in Denmark and Norway. In all, 281 comparisons were made, based on 6800 samples. In 4.6% of these comparisons no eggs were found by either method. In 16% of the comparisons, 2.0±0.41 (±S.E.) eggs were found per soil sample and no eggs were found in felt traps, whereas in 0.7% of the comparisons 0.10±0.03 eggs were found per felt trap and no eggs in soil samples. When eggs were found using both methods, the ratio between soil sampling and felt traps varied from 13.1±3.2 when the egg laying rate was very low to 1.8±0.2 at high egg laying rates. Regression analysis showed significant correlation between felt trap catches and soil sampling (P
Sammendrag
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Forfattere
Arild SlettenSammendrag
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Forfattere
Trond MæhlumSammendrag
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Sammendrag
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Forfattere
O. Janne KjønaasSammendrag
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Forfattere
O. Janne KjønaasSammendrag
Mixtures of cation and anion exchange resins are used as part of the resin core technique to determine nitrogen transformation in forest soils as they adsorb the NH4-N and NO3-N from soil solution percolating through the incubated soil cores. In the field, the exchange resins may be subjected to a variety of conditions, involving drying, rehydration, freezing, and thawing. This paper examines how these processes affect adsorption of NH4-N and NO3-N and the stability of the resins. Lab tests were performed on the anion resin Amberlite IRA-93, the cationresin Amberlite IR-120, and a mixture of IRA-93 and IR-120, and the commercially-mixed bed resin Amberlite MB1. The background content of NO3-N and NH4-N on the resins was large and highly variable between different batches of resins in spite of a 2 M NaCl pre-rinse. The IR-120 cation resin that was subjected to 48 hours air-drying contained significantly less NH4-N than the most resins, while the drying of the IRA-93 anion resin caused a significant release of NO3-N from resins with no N addition. Although the variation was large, the mixed bed resin MB1 indicated a release of NH4-N, which supports results from long term in situ deployments. A reduced adsorption of NO3-N was found on the IRA-93 anion resins and the MB1 mixed bed resins that were dried prior to N addition while the dry IR-120 cation resins adsorbed significantly less NH4-N than the control resin. No effect of freezing the thawing efficiency was observed on resin stability or N adsorption efficiency. Sufficient blanks that have been subjected to similar moisture changes are necessary in N limited systems with low levels of avialable NH4-N and NO3-N.