A review of the impacts of degradation threats on soil properties in the UK

National governments are becoming increasingly aware of the importance of their soil resources and are shaping strategies accordingly. Implicit in any such strategy is that degradation threats and their potential effect on important soil properties and functions are defined and understood. In this paper, we aimed to review the principal degradation threats on important soil properties in the UK, seeking quantitative data where possible. Soil erosion results in the removal of important topsoil and, with it, nutrients, C and porosity. A decline in soil organic matter principally affects soil biological and microbiological properties, but also impacts on soil physical properties because of the link with soil structure. Soil contamination affects soil chemical properties, affecting nutrient availability and degrading microbial properties, whilst soil compaction degrades the soil pore network. Soil sealing removes the link between the soil and most of the ‘spheres’, significantly affecting hydrological and microbial functions, and soils on re-developed brownfield sites are typically degraded in most soil properties. Having synthesized the literature on the impact on soil properties, we discuss potential subsequent impacts on the important soil functions, including food and fibre production, storage of water and C, support for biodiversity, and protection of cultural and archaeological heritage. Looking forward, we suggest a twin approach of field-based monitoring supported by controlled laboratory experimentation to improve our mechanistic understanding of soils. This would enable us to better predict future impacts of degradation processes, including climate change, on soil properties and functions so that we may manage soil resources sustainably

Long-term management impacts on soil C, N and physical fertility, Part II: Bad Lauchstadt static and extreme FYM experiments

Manure is a source of plant nutrients and can make a valuable contribution to soil organic matter (SOM). Two experimental sites were studied on a Halpic Phaeozem soil near Bad Lauchstadt in Germany. The first experiment, called the static experiment, commenced in 1902. The impact of fresh farmyard manure (FYM) (0, 20 and 30 t ha⁻¹ 2 year⁻¹) combined with P, K and N fertiliser application on total organic C (CT), labile C (CL), non-labile C (CNL), total N (NT), mean weight diameter (MWD) and unsaturated hydraulic conductivity (Kunsat) was investigated. The second experiment commenced in 1984 and investigated the effect of extreme rates of fresh FYM applications (0, 50, 100 and 200 t ha⁻¹ year⁻¹) and cropping, or a continuous tilled fallow on the same soil properties. At both sites a nearby grassland site served as a reference. On the static experiment, FYM application increased all C fractions, particularly CL, where application of 30 t ha⁻¹ 2 year⁻¹ increased CL by 70% compared with no FYM application. Fertiliser additions to the static experiment had a positive influence on C fractions while NT increased from both FYM and fertiliser application. MWD increased as a result of FYM application, but did not reach that of the grassland site. Both fertiliser and FYM application increased Kunsat (10 mm tension) on the static experiment. In the second experiment application of 200 t ha⁻¹ year⁻¹ of FYM increased concentrations of CL by 173% and of CNL by 80%, compared with no FYM application to make them equivalent to, or greater than the grassland site. A continuously tilled fallow resulted in significant decreases in all C fractions, NT and MWD compared with the cropped site, while Kunsat (10 mm tension) was increased on the 0 and 50 t ha⁻¹ year⁻¹ treatments as a result of a recent tillage. There was no difference in Kunsat between the cropped and the continuous tilled fallow at FYM applications of 100 and 200 t ha⁻¹ year⁻¹. There were similar significant positive correlations of all C fractions and NT with MWD on both experimental sites but the relationships were much stronger on the extreme FYM experiment. Weaker relationships of C fractions and NT with Kunsat (10 mm tension) occurred for the static experimental site but these were not significant for the extreme FYM experimental site. The strongest relationship between C fractions and Kunsat was with CL. This research has shown that applications of FYM can increase SOM and improve soil physical fertility. However, the potential risk of very high rates of FYM on the environment need to be taken into consideration, especially since the application of organic materials to soils is likely to increase in the future

Simulating trends in soil organic carbon in long-term experiments using the CANDY model

CANDY (CArbon and Nitrogen DYnamics) is a simulation system based on long-term experiments of organic matter turnover and nitrogen dynamics at Bad Lauchstadt, Germany. Key driving variables are soil physical properties, meteorological data and management information. The main application of the CANDY model is the calculation of short-term dynamics of nitrogen transformation and long-term dynamics of organic matter turnover in arable soils. This paper concentrates on the evaluation of the model in simulating carbon dynamics in long-term experiments representing different land uses and very different geographical sites. The experimental data came from data sets that were made available to modellers at a workshop held at Rothamsted in 1995. In this paper we describe how the different data sets were modelled and provide a qualitative assessment of model performance. The performance of several models, including CANDY, are compared quantitatively in Smith et al. (1997). Our results show that the mathematical basis of the model, its consideration of a biological time base and its calculation of the 'reproducing carbon' are applicable over a wide range of sites and land-use scenarios. Most of the standard parameters can be used for other sites and land-use systems.</p

Simulating trends in soil organic carbon in long-term experiments using the DNDC model

Simulations of long-term (\u3e 20 year) soil organic carbon (SOC) dynamics by the DNDC model were compared with field observations at 11 plots in 5 field stations in Europe and Australia. The exercise was part of a NATO-sponsored workshop on long-term monitoring and modeling of soil organic matter. Eight of the eleven plots were cultivated cropland and three were grassland (harvested for hay). There were a range of fertilizer and manure treatments, as well as crop rotation sequences. Significant loss in SOC was observed at two plots in Australia where a grassland had been converted to cultivated cropland in 1925. Both field data and model simulations showed the plots reaching a new SOC equilibrium at about 44% of the 1925 levels. Equilibrium levels depended on crop rotation sequence, with higher SOC for the plot with less frequent fallowing. At one permanent grassland site at Rothamsted, UK, a large decline and recovery in SOC was observed in the field, but not in the model simulation. For all other cases, both field and model data showed relatively small changes in SOC, though field data tended to be more variable, perhaps due to variability in both crop and weed yield, and in residue management. Mean percent differences between simulated and measured SOC were 0.07% or less (as percent by weight, kilogram SOC/kilogram soil) for all but one of the plots simulated

Simulating trends of soil organic carbon in seven long-term experiments using the SOMM model of the humus types

Using the SOMM model of the humus types (Mor, Moder, Mull), simulations of SOM dynamics at seven long-term experiments were attempted as a part of a model evaluation exercise. The model comprises three compartments (undecomposed litter, partially humified litter, humus of mineral topsoil) and considers six processes of mineralization and humification as influenced by litter nitrogen and ash contents, soil C/N ratio, temperature and moisture. Results of simulations performed without any site-specific calibration mostly underestimate soil organic matter (SOM). Despite this lack of precision, general trends in SOM over time were often captured. Success of simulation was limited by difficulties in obtaining direct information about soil moisture regime, litter quantity and litter quality (nitrogen and ash content). Inadequacies in the model, such as no consideration of soil properties, may also account for some of the errors. Despite the limited success of the evaluation, it is encouraging that the model conceived for forested ecosystems, with additional development, may be applicable to non-forested systems. The exercise underlines the necessity of constant direct contact between modeller and data holder for a success of an evaluation.</p