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  • 1
    Electronic Resource
    Electronic Resource
    Using time domain reflectometry for monitoring mineralization of nitrogen from soil organic matter (2000)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 51 (2000), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The mineralization of nitrogen from soil organic matter is important when one tries to optimize nitrogen fertilization and assess risks of N losses to the environment, but its measurement is laborious and expensive. We have explored the possibilities for monitoring N mineralization directly using time domain reflectometry (TDR). Net N and S mineralization were monitored over a 101-day period in two layers (0–30 and 30–60 cm) of a loamy sand soil during aerobic incubation in a laboratory experiment. At the same time electrical conductivity of the bulk soil, σa, was measured by TDR. A series of calibration measurements with different amounts of KNO3 at different soil moisture contents was made with the topsoil to calculate the electrical conductivity, σw, of the soil solution from σa and θ. The actual σw was determined from the conductivity of 1:2 soil:water extracts (σ1:2) with a mass balance approach using measured NO3– concentrations, after correction for ions present prior to the addition of KNO3. The average N mineralization rate in the topsoil was small (0.12 mg N kg−1 day−1), and, as expected, very small in the subsoil (0.023 mg N kg−1 day−1). In the top layer NO3– concentrations calculated from σa determined by TDR slightly underestimated measured concentrations in the first 4 weeks, and in the second half of the incubation there was a significant overestimation of measured NO3–. Using the sum of both measured NO3– and SO42– reduced the overestimation. In the subsoil calculated NO3– concentrations strongly and consistently overestimated measured concentrations, although both followed the same trend. As S mineralization in the subsoil was very small, and initial SO42– concentrations were largely taken into account in the calibration relations, SO42– concentrations could not explain the overestimation. The very small NO3– and SO42– concentrations in the B layer, at the lower limit of the concentrations used in the calibrations, are a possible explanation for the discrepancies. A separate calibration for the subsoil could also be required to improve estimates of NO3– concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.2000.00306.x
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  • 2
    Electronic Resource
    Electronic Resource
    The influence of model type and incubation time on the estimation of stable organic carbon in organic materials (2005)
    Oxford, UK; Malden, USA : Blackwell Science Ltd
    European journal of soil science 56 (2005), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: There is a renewed interest in the stability and turnover of organic carbon (C) in organic materials added to soil, partly driven by concerns about global changes. We used mineralization data from laboratory incubations to determine the amount of stable organic C present. Four organic wastes were incubated with soil under controlled conditions and C mineralization was monitored, and four additional C mineralization experiments were selected from the literature. All data were rescaled to a common temperature, and we fitted five different models with biological significance to the C mineralization data, namely a first-order model (M1), a parallel first-order model (M11), a parallel first-zero-order model (M10), a second-order model (M2) and a Monod kinetic model (Monod). All models could describe the mineralization data satisfactorily. However, this does not automatically imply that the individual parameter values are realistic estimates of the underlying biological processes. All models were then fitted for progressively shorter incubation times and were used to extrapolate C mineralization to predict the amount of (measured) stable organic C. The M11 and Monod models performed best in estimating stable organic C, but they did not fit the short-term incubation data (〈 100 days) for some materials. The M2 model allowed stable organic C to be estimated within less than 3% of the true value for all materials based on an incubation time of less than 60 days. The M1 and M10 models systematically and strongly under- or overestimated stable organic C as the incubation time was shortened, and should not be used for extrapolation from short-term data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2389.2004.00685.x
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  • 3
    Electronic Resource
    Electronic Resource
    Temperature effects on N mineralization: changes in soil solution composition and determination of temperature coefficients by TDR (2003)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 54 (2003), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: We studied the changes in composition of the soil solution following mineralization of N at different temperatures, with a view to using TDR to calculate temperature coefficients for the mineralization of N. Mineralization from soil organic nitrogen was measured during aerobic incubation under controlled conditions at six temperatures ranging from 5.5 to 30°C, and at constant water content in a loamy sand soil. We also monitored during the incubation the concentrations of SO42–, Cl–, HCO3–, Ca2+, K+, Mg2+ and Na+, and the pH and the electrical conductivity in 1:2 soil:water extracts. Zero-order N mineralization rates ranged between 0.164 at 5.5°C and 0.865 mg N kg−1 soil day−1 at 30°C. There was a significant decrease in soil pH during incubation, of up to 0.6 pH units at the end of the incubation at 30°C. The electrical conductivity of the soil extracts increased significantly at all temperatures (the increase between the start and the end of the incubation was 4-fold at 30°C) and was strongly correlated with N mineralization. The ratio of bivalent to monovalent cations increased markedly during mineralization (from 2.2 to 5.9 at 30°C), and this increase influenced the evolution of the electrical conductivity of the soil solution through the differences in molar-limiting ion conductivity between mainly Ca2+ and K+. Zero-order mineralization rate constants, k, for NO3– concentrations calculated from TDR varied between 0.070 (at 5.5°C) and 0.734 mg N kg−1 soil day−1 (at 30°C), which were slightly smaller, but in the same range, as the measured rates. Underestimation of the measured N mineralization rates was due, at least in part, to differences in cation composition of the soil solution between calibration and mineralization experiments. A temperature-dependence model for N mineralization from soil organic matter was fitted to both the measured and the TDR-calculated mineralization rates, k and kTDR, respectively. There were no significant differences between the model parameters from the two. Our results are promising for further use of TDR to monitor soil organic N mineralization. However, the influence of changing cation ratios will also have to be taken into account when trying to predict N mineralization from measured electrical conductivities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.2003.00521.x
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of soil compaction on carbon and nitrogen mineralization of soil organic matter and crop residues (2000)
    Springer
    Biology and fertility of soils 30 (2000), S. 544-549 
    Details
    ISSN: 1432-0789
    Keywords: Key words Soil compaction ; Carbon mineralization ; Nitrogen mineralization ; Crop residues ; Soil organic matter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  We studied the influence of soil compaction in a loamy sand soil on C and N mineralization and nitrification of soil organic matter and added crop residues. Samples of unamended soil, and soil amended with leek residues, at six bulk densities ranging from 1.2 to 1.6 Mg m–3 and 75% field capacity, were incubated. In the unamended soil, bulk density within the range studied did not influence any measure of microbial activity significantly. A small (but insignificant) decrease in nitrification rate at the highest bulk density was the only evidence for possible effects of compaction on microbial activity. In the amended soil the amounts of mineralized N at the end of the incubation were equal at all bulk densities, but first-order N mineralization rates tended to increase with increasing compaction, although the increase was not significant. Nitrification in the amended soils was more affected by compaction, and NO3 –-N contents after 3 weeks of incubation at bulk densities of 1.5 and 1.6 Mg m–3 were significantly lower (by about 8% and 16% of total added N, respectively), than those of the less compacted treatments. The C mineralization rate was strongly depressed at a bulk density of 1.6 Mg m–3, compared with the other treatments. The depression of C mineralization in compacted soils can lead to higher organic matter accumulation. Since N mineralization was not affected by compaction (within the range used here) the accumulated organic matter would have had higher C : N ratios than in the uncompacted soils, and hence would have been of a lower quality. In general, increasing soil compaction in this soil, starting at a bulk density of 1.5 Mg m–3, will affect some microbially driven processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050034
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