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Nutrient dynamics in wetland ecosystems are largely controlled by soil moisture content. Therefore, the influence of soil moisture content on N mineralization should be explicitly taken into account in hydro-ecological models. The aim of this research was to establish relationships between N mineralization and soil moisture content in loamy to silty textured soils of floodplain wetlands in central Belgium. Large undisturbed soil cores were taken, incubated for 3 months under various moisture contents, and zero order and first order N mineralization rates were calculated. We used the percentage water-filled pore space (WFPS) as an expression of soil moisture because it is a better index for aeration dependent biological processes than volumetric moisture content or water retention. The relationship between the N mineralization rate and %WFPS was described by a Gaussian model. The optimum WFPS for N mineralization ranged between 57% and 78%, with a mean of 65% +/- 6% WFPS. Expected annual net N mineralization rates at field temperature (9.7 degrees C) and at optimal moisture content varied between 30 and 186 kg N ha(-1) (0-15 cm depth) year(-1), with a mean of 110 +/- 42 kg N ha(-1) (0-15 cm) year(-1). The mean N turnover rate amounted to 2.3 +/- 1.1 g N 100 g(-1) N year(-1). Multiple linear regressions between N mineralization and general soil parameters showed that soil structure has an overriding impact on N mineralization in wetland ecosystems

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To restore species-rich terrestrial ecosystems on ex-agricultural land, establishing nutrient limitation for dominant plant growth is essential, because in nutrient-rich soils, fast-growing species often exclude target species. However N-limitation is easier to achieve than P-limitation (because of a difference in biogeochemical behavior), biodiversity is generally highest under P-limitation. Commonly-used restoration methods to achieve low soil P-concentrations are either very expensive or take a very long time. A promising restoration technique is P-mining, an adjusted agricultural technique that aims at depleting soil-P. High biomass production and hence high P-removal with biomass is obtained by fertilizing with nutrients other than P. A pot experiment was set up to study P-mining with Lolium perenne L. on sandy soils with varying P-concentrations: from an intensively-used agricultural soil to a soil near the soil P-target for species-rich Nardus grassland. All pots received N- and K-fertilization. The effects of biostimulants on P-uptake were also assessed by the addition of arbuscular mycorrhiza (Glomus spp.), humic substances or phosphate-solubilizing bacteria (Bacillus sp. and Pseudomonas spp.). In our P-rich soil (111 μg POlsen/g), P-removal rate was high but bioavailable soil-P did not decrease. At lower soil P-concentrations (64 and 36 μg POlsen/g), bioavailable soil-P had decreased but the P-removal rate had by then dropped 60% despite N- and K-fertilization and despite that the target (< 10 μg POlsen/g) was still far away. None of the biostimulants altered this trajectory. Therefore, restoration will still take decades when starting with ex-agricultural soils unless P-fertilization history was much lower than average

Problems of excessive soil phosphorus (P) levels as a result of intensive agriculture are found in many regions in Western Europe, USA, Canada and New Zealand. This may lead to phosphorus leaching in soils with low P binding capacity. However, little is known about the changes in P saturation degree (PSD) of such soils with time. Between 1995 and 2005, an intensive inventory of the PSD status of acid sandy soils in Flanders was conducted, the results of which were used to enforce strict rules on P fertilizer inputs on P saturated soils. A new smaller survey on a selection of these fields was undertaken in 2009 and 2010. Comparison of the survey results shows that the mean PSD increased significantly from 46 to 59% over this period. We found evidence for a strong shift of the PSD from the upper to lower layers. The PSD level in the top layer (0-30 cm) generally increased significantly (P < 0.01) from 83 to 91%. The average increase in the PSD level of the 30-60 and 60-90 cm layers was even greater, from 33 to 55% and from 14 to 25%, respectively (P < 0.01). Current limits on P fertilizer application have not yet resulted in P mining in these soils and will thus need to be further restricted. The very clear increase in PSD movement in deeper layers from both increased P ox , and reduced Fe ox concentrations show that these high PSD soils pose a very serious and direct threat to groundwater quality.