Markus Deurer

Carbon sequestration in urban landscapes: the example of a turfgrass system in New Zealand

Soil carbon sequestration was analysed in the topsoil (0–0.25 m) of putting greens of different ages (5, 9, 20, 30, 40 years) in a golf course in Palmerston North, New Zealand. The soil texture was the same for all putting greens and the intensive management guaranteed that the carbon (C) inputs to the soil were very similar for all ages. Significant and linear soil C sequestration rates occurred for 40 years. The soil C sequestration rate in 0–0.25 m depth was 69 ± 8 g/m2.year over a 40-year period totalling 28 t/ha over 40 years. The relative microbial activity (dehydrogenase activity/total soil C content) representing the bioavailability of soil C decreased by about 50% over 40 years. The C sequestration and decrease of bioavailability of soil C was much more pronounced in 0.1–0.25 m depth than in the top 0.1 m. In the top 0.1 m, very little C sequestration occurred, most probably due to the intensive soil management in this depth. We concluded that the C sequestration was mainly caused by the increasing humification of C in the undisturbed part of the soil (0.1–0.25 m depth) as was indicated by a significant decrease in the relative microbial activity. Turfgrass systems such as putting greens are well suited to sequester C in urban areas.

A New Method to Quantify the Impact of Soil Carbon Management on Biophysical Soil Properties: The Example of Two Apple Orchard Systems in New Zealand

A new method to diagnose the environmental sustainability of specific orchard management practices was derived and tested. As a significant factor for soil quality, the soil carbon (C) management in the topsoil of the tree-row of an integrated and organic apple orchard was selected and compared. Soil C management was defined as land management practices that maintain or increase soil C. We analyzed the impact of the soil C management on biological (microbial biomass C, basal respiration, dehydrogenase activity, respiratory quotient) and physical (aggregate stability, amount of plant-available water, conductive mean pore diameter near water saturation) soil properties. Soil in the alley acted as a reference for the managed soil in the tree row. The total and hot-water-extractable C amounts served as a combined proxy for the soil C management. The soil C management accounted for 0 to 81% of the degradation or enhancement of biophysical soil properties in the integrated and organic system. In the integrated system, soil C management led to a loss of C in the top 0.3 m of the tree row within 12 yr, causing a decrease in microbial activities. In the tree row of the organic orchard, C loss occurred in the top 0.1 m, and the decrease in microbial activities was small or not significant. Regarding physical soil properties, the C loss in the integrated system led to a decrease of the aggregate stability, whereas it increased in the organic system. Generally, the impact of soil C management was better correlated with soil microbial than with the physical properties. With respect to environmental soil functions that are sensitive to the decrease in microbial activity or aggregate stability, soil C management was sustainable in the organic system but not in the integrated system.

Soil assessment of apple orchards under conventional and organic management

To determine the effect of wheel traffic and two different management practices on soil compaction and its consequences on physical and chemical soil properties, we measured penetration resistance, water infiltration, bulk density, macroporosity, chemical mobility, air permeability, and soil strength in a conventional orchard (integrated fruit-production program) with bare (sprayed with herbicides) rows and an organic apple orchard with grassed rows. Resistance measurements were taken both within the tree row and the wheel track, down to a depth of 0.35 to 0.40 m. The results indicate that compaction is greater in the wheel tracks under both management methods. Compaction in the wheel track was higher under organic than conventional management. Organic management resulted in a higher macroporosity in both the row and the wheel-track than conventional management. The ‘close-to-saturation’ infiltration rate was significantly greater within the row of the organic orchard (0.06 m/h) compared with the row of the conventional orchard (0.02 m/h), and compared with the wheel tracks (0.01 m/h). The precompression stress value in the top 100 mm, a measure of the soil strength, was low on all sites. The chemical mobilities were 57 and 50% in the organic orchard, and 86 and 93% in the conventional orchard, respectively, for wheel track and row. Apart from the compaction in the wheel track of the organic orchard, physical and chemical soil characteristics were in a better condition compared with the conventional orchard.

Magnetic Resonance Imaging of Hydrodynamic Dispersion in a Saturated Porous Medium

By using nuclear magnetic resonance imaging (NMRI) we have been able to analyse dispersion at the microscopic scale during steady-state flow through water-saturated glass beads. The flow rate through the porous medium was chosen high enough in order to neglect the influence of molecular diffusion on dispersion. Velocity statistics were measured, by NMRI, within slices of increasing thickness perpendicular to the direction of flow. It took more than two bead diameters before a representative elementary volume (REV) for the mean velocity was reached. This was in a region in the middle of the column that was not influenced by the boundary conditions. There the velocity variance decreased exponentially as a function of the slice thickness, due we consider to the formation of an interconnecting streamline network. The exponential decrease in the velocity variance reflects the transition from a local pattern of stochastic–convective flow to a convective–dispersion regime at the scale of the REV. We found that the point-like preferential influx and efflux boundary condition increased velocity variances and thus enhanced longitudinal hydrodynamic dispersion. Using the transverse correlation length of longitudinal velocity variance, we derived a mean transverse dispersivity that agreed well with Saffman’s (1959) model. So we have been able to provide for the first time a direct observation verification of a part of Saffman’s (1959) conjectures. By NMRI we observed this value to be independent of the observation scale of the slice thickness.

Chapter 26 Contaminants in the rootzone: Bioavailability, uptake and transport, and their implications for remediation

Publisher Summary This chapter focuses on the mechanisms that control the bioavailability, transport, and plant uptake of both metals and inorganic contaminants in soil. Their implications for phytoremediation of contaminated sites using poplars and willows are discussed. The chapter presents the results from screening experiments that have identified a huge range in the ability of willow clones to extract cadmium from contaminated soil. Beyond these pot experiments with willow clones, the emphasis is on the entire soil–plant–atmosphere continuum so that the dynamics and ultimate fate of water and contaminants in the rootzone can be detailed. A field project and large-scale lysimeter experiments are described in the chapter, exploring the ability of poplars to both dewater and remove the boron from contaminated sawdust piles. Experiments and analyses that have determined the fate of Cu, which is mobilized from soil by ethylenediamine tetra-acetic acid (EDTA) in an effort to enhance phytoextraction, are presented in the chapter. The power of quantitative modeling for providing predictions of the fate of rootzone water and contaminants is also demonstrated in the chapter.