Optimization of dissolved organic nitrogen (DON) measurements in aqueous samples with high inorganic nitrogen concentrations.

Since dissolved organic nitrogen (DON) concentrations in aqueous samples can only be determined by the subtraction of three independently measured concentrations (total dissolved nitrogen (TDN), nitrate and ammonium), analytical errors are compounded in the calculation of DON concentration. Several methods were tested to increase the recovery and precision of the DON determinations in aqueous samples with high inorganic nitrogen concentrations. The first step was the objective selection of the most accurate TDN analysis method.

The influence of 10 years reduced tillage on the potential carbon mineralization of silt loam soils under a temperate climate.

The influence of 10 years reduced tillage (RT) on the potential carbon mineralization of the 0-5 cm layer of silt loam soils in Belgium under a temperate climate was investigated. Therefore, four fields at three locations under 10 years of RT and fields under conventional tillage (CT) with comparable crop rotation were selected. The higher % soil organic carbon in the upper layer resulted in a higher potential carbon mineralization of the RT fields.

Assessment of temporal and spatial variation of nitrate removal in riparian zones.

The aim of this study was to monitor long-term temporal and spatial groundwater NO(3) (-) removal efficiencies in different riparian zones via a limited number of sampling wells. Groundwater NO(3) (-) concentrations were measured fortnightly or monthly over a period of two years using transects of ground water sampling wells. Depending on the level of the NO(3) (-) load (up to 120mgNL(-1) at the input side of the riparian zone a distance of 10 to 30m was needed to remove NO(3) (-) from the groundwater below 11.

Quantification of the effect of fumigation on short- and long-term nitrogen mineralization and nitrification in different soils.

The effect of soil fumigation on N mineralization and nitrification needs to be better quantified to optimize N fertilizer advice and predict NO(-)(3) concentrations in crops and NO(-)(3) leaching risks. Seven soils representing a range in soil texture and organic matter contents were fumigated with Cyanamid DD 95 (a mixture of 1,3-dichloropropane and 1,3-dichloropropene). After removal of the fumigant, the fumigated soils and unfumigated controls were incubated for 20 wk and N mineralization and nitrification were monitored by destructive sampling.

Quantifying nitrate retention processes in a riparian buffer zone using the natural abundance of 15N in NO3-.

Quantifying the relative importance of denitrification and plant uptake to groundwater nitrate retention in riparian zones may lead to methods optimising the construction of riparian zones for water pollution control. The natural abundance of 15N in NO3- has been shown to be an interesting tool for providing insights into the NO3- retention processes occurring in riparian zones. In this study, 15N isotope fractionation (variation in delta15N of the residual NO3-) due to denitrification and due to plant uptake was measured in anaerobic soil slurries at different temperatures (5, 10 and 15 degrees C) and in hydroponic systems with different plant species (Lolium perenne L.

Relationship between soil organic C degradability and the evolution of the delta13C signature in profiles under permanent grassland.

The main objective of this research was to investigate to what extent the potential C dynamics of soil organic matter (SOM) are related to the degree of 13C enrichment with increasing depth in soil profiles under permanent grassland. The evolution of the C content and the 13C natural abundance (delta13C value) of SOM were investigated in three soil profiles (0-40 cm depth) under permanent grassland of varying texture (a loamy sand, a loam and a clay loam soil). The delta13C value of the SOM showed a gradual increase with increasing depth and decreasing C content in the profiles, ranging from 1.

Evolution of the delta13C signature related to total carbon contents and carbon decomposition rate constants in a soil profile under grassland.

Evolution of the total carbon (C) content and the (13)C enrichment (delta(13)C signature) of soil organic matter (SOM) with increasing depth in a soil profile under permanent grassland (C(3) vegetation) were investigated. The relationship between the total C content and the delta(13)C signature at different depths in the upper 30 cm of the soil profile could be well fitted by the Rayleigh equation (y = -29.8 - 2.

Characterization of soil organic matter fractions from grassland and cultivated soils via C content and delta13C signature.

Variations in (13)C natural abundance and distribution of total C among five size and density fractions of soil organic matter, water soluble organic C (WSOC) and microbial biomass C (MBC) were investigated in the upper layer (0-20 cm) of a continuous grassland soil (CG, C(3) vegetation), a C(3)-humus soil converted to continuous maize cultivation (CM, C(4) vegetation) and a C(3)-humus soil converted to a rotation of maize cultivation and grassland (R). The amounts of WSOC and MBC were both significantly larger in the CG than in the CM and the R. In the three soils, WSOC was depleted while MBC was enriched in (13)C as compared with whole soil C.