Potential of temperate agricultural soils for carbon sequestration: A meta-analysis of land-use effects.

Restoring depleted soil organic carbon (SOC) stocks of arable land to remove carbon from the atmosphere and offset fossil fuel emissions is a promising strategy for the mitigation of climate change. In agroecosystems conservational tillage practices and the abandonment of formerly plowed fields (ex-arable land) are shown to have the highest potential to sequester SOC. Nevertheless reported sequestration rates vary and the effects of environmental site conditions remain poorly understood. Our results are based on a meta-analysis of 273 paired SOC estimates from 65 publications which included only mineral soils from the temperate zone. SOC stocks of ex-arable grasslands with an average of 14years since abandonment were 18% larger compared to the SOC of arable land. Likewise, SOC stocks of never-plowed grassland plots were 11% larger than the SOC stocks of abandoned fields. The average sequestration rate was 0.72t Cha(-1)yr(-1). Semi-arid and sub-humid climate as well as low initial SOC stocks positively affected proportional SOC gains suggesting that the recovery of carbon stocks is not limited by low primary production. Therefore, the northward shift of cultivation areas in the temperate zone will lead to the abandonment of soils with high SOC recovery potential. However, if native soils are opened up elsewhere to compensate for yield losses due to abandonment the surplus of SOC in ex-arable land can easily be overcompensated by cultivation losses.

Spatio-temporal analysis of agricultural land-use intensity across the Western Siberian grain belt.

The Western Siberian grain belt covers 1millionkm² in Asiatic Russia and is of global importance for agriculture. Massive land-use changes took place in that region after the dissolution of the Soviet Union and the collapse of the state farm system. Decreasing land-use intensity (LUI) in post-Soviet Western Siberia was observed on grassland due to declining livestock whilst on cropland trends of land abandonment reversed in the early 2000s. Recultivation of abandoned cropland as well as increasing fertilizer inputs and narrowing crop rotations led to increasing LUI on cropland during the last two decades. Beyond that general trend, no information is available about spatial distribution and magnitude but a crucial precondition for the development of strategies for sustainable land management. To quantify changes and patterns in LUI, we developed an intensity index that reflects the impacts of land-based agricultural production. Based on subnational yearly statistical data, we calculated two separate input-orientated indices for cropland and grassland, respectively. The indices were applied on two spatial scale: at seven provinces covering the Western Siberian grain belt (Altay Kray, Chelyabinsk, Kurgan, Novosibirsk, Omsk, Sverdlovsk and Tyumen) and at all districts of the central province Tyumen. The spatio-temporal analysis clearly showed opposite trends for the two land-use types: decreasing intensity on grassland (-0.015 LUI units per year) and intensification on cropland (+0.014 LUI units per year). Furthermore, a spatial concentration towards intensity centres occurred during transition from a planned to a market economy. A principal component analysis enabled the individual calculations of both land-use types to be combined and revealed a strong link between biophysical conditions and LUI. The findings clearly showed the need for having a different strategy for future sustainable land management for grassland (predominantly used by livestock of households) and cropland (predominantly managed by large agricultural enterprises), which have to be addressed specifically by the different land users. As all input data are publicly available, the approach described is readily transferable to other regions or countries of the former Soviet Union.

Potential of vetiver (vetiveria zizanioides (L.) Nash) for phytoremediation of petroleum hydrocarbon-contaminated soils in Venezuela.

Venezuela is one of the largest oil producers in the world. For the rehabilitation of oil-contaminated sites, phytoremediation represents a promising technology whereby plants are used to enhance biodegradation processes in soil. A greenhouse study was conducted to determine the tolerance of vetiver (Vetiveria zizanioides (L.) Nash) to a Venezuelan heavy crude oil in soil. Additionally, the plant's potential for stimulating the biodegradation processes of petroleum hydrocarbons was tested under the application of two fertilizer levels. In the presence of contaminants, biomass and plant height were significantly reduced. As for fertilization, the lower fertilizer level led to higher biomass production. The specific root surface area was reduced under the effects of petroleum. However, vetiver was found to tolerate crude-oil contamination in a concentration of 5% (w/w). Concerning total oil and grease content in soil, no significant decrease under the influence of vetiver was detected when compared to the unplanted control. Thus, there was no evidence of vetiver enhancing the biodegradation of crude oil in soil under the conditions of this trial. However, uses of vetiver grass in relation to petroleum-contaminated soils are promising for amelioration of slightly polluted sites, to allow other species to get established and for erosion control.

Pedological characterisation of sites along a transect from a primary cadmium/lead/zinc smelting works.

A pedological characterisation of seven sites along a transect from a smelter at Avonmouth, UK, was undertaken. Site locations comprised a mixture of both grassland (5 sites) and oak tree dominated (2 sites) areas. Geographically, sites were either low lying or on adjacent elevated ground. Across the transect, a severe gradient of metal concentrations was found with highest values for organic soil horizons from close to the factory. Comparisons with quality standards indicate that these metal levels are likely to be a major ecological stressor. In addition to the strong metal gradient, a number of other between site differences were also observed. These were firstly water regime, which at the low lying sites close to the smelter showed influence by both, groundwater and stagnant water, while at more distant sites indicated susceptibility to stagnant water only, and secondly soil pH, which showed large between site variations, although no consistent trend along the transect. Humus forms at sites more than 1.5 km from the smelter were characteristic for the soil conditions and land-use present, while those at sites within 1.5 km showed disturbed profiles. Indeed, the humus types present at these locations suggest that the activity of soil invertebrates may be inhibited. This is almost certainly due primarily to the high concentrations of metals that were present in mineral soil and organic horizons at the sites. However, the potential influences of water regime and pH could also be relevant factors influencing the results of any further studies conducted at these study sites.

Metal effects on soil invertebrate feeding: measurements using the bait lamina method.

Heightened concerns regarding the protection of terrestrial ecosystems at a national level has increased the need to develop a suite of indicators capable of assessing the quality, integrity and fertility of soils. Of the assays currently available, tests that measure aspects of soil function and associated parameters are among the most promising, since these integrate effects on soil quality at the highest level of organisation. In this study we describe results of the deployment of an indicator of soil functional integrity (the bait lamina test) that is designed to measure the feeding activity of soil invertebrates. Bait lamina was used at six grassland sites located along a transect from a smelter at Avonmouth (South-West England) used in the EU funded BIOPRINT II project. Results indicated highest bait removal (feeding) at sites furthest from the factory, intermediate feeding activity at intervening sites and extremely low activities at the two sites closest to the smelter. The strong decline in activity for the group of sites closest to the smelter corresponded with increasing metal concentrations suggesting a clear impact of metals on detritivorous invertebrate feeding. Comparisons of the results of the bait lamina study to previous invertebrate survey work suggested that the differences in observed bait removal can be attributed to direct effects of metals on the abundance and biodiversity of key decomposer groups such as earthworms, isopods, molluscs, myriapods, springtails and mites.