Four soil profiles located near a copper smelter in Poland were investigated for the distribution and chemical fractions of Cu, Pb, and Zn and their mobility in relation to soil properties. Contamination with heavy metals was primarily restricted to surface horizons and the extent of contamination was 7‐ to 115‐fold for Cu, 30‐fold for Pb, and 6‐fold for Zn as compared with subsurface horizons. In the less‐contaminated fine‐textured soil, the metals were distributed in the order: residual >> Fe–Mn oxides occluded > organically complexed > exchangeable and specifically adsorbed, while the order for sandy soils was: residual > organically complexed > Fe–Mn oxides occluded > exchangeable and specifically adsorbed. The contaminated surface horizons of these profiles showed no consistent pattern of metal distribution. However, the common features of highly contaminated soils were very low percentage of residual fraction and the dominance of the NH4OAc extractable fraction. The sum of mobile metal fractions was generally <10% in subsurface horizons, while in the contaminated surface horizons these fractions made up 50% of the total metal contents. Soil properties contributed more to the relative distribution of the metal fractions in the studied profiles than did the distance and direction to the source of pollution. The amounts of metal extracted by 0.01 M CaCl2 accounted for only a small part of the same metals extracted by NH4OAc. The mobility indexes of metals correlated positively and significantly with the total content of metals and negatively with the clay content.

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Soil aggregation serves as storage and cycling of soil organic carbon (SOC) and total nitrogen (TN), which are essential for the functioning of terrestrial ecosystems. Thus, aggregate and particle associated SOC and TN in 0‐ to 10‐cm and 10‐ to 20‐cm layers were estimated for five land uses: rainfed cultivation (RF), agroforestry (AF), open pasture (OP), silvopasture (SP), and irrigation (IR) each with five replications within a watershed in Ethiopia. OP had the highest WSA > 2 mm (88·7%) and SOC associated with macroaggregates (20·0 g kg−1), which were significantly higher (P < 0·0001; P = 0·0017 for WSA and SOC, respectively) than that in other land uses in 0‐ to 10‐cm depth. SOC associated with both macroaggregates and microaggregates decreased with depth. Macroaggregates contained higher SOC than microaggregates in both layers under all land uses. AF had the highest SOC associated with microaggregates (2·6 g kg−1) followed by that in SP (2·3 g kg−1), indicating its potential to stabilize SOC more than other land uses. TN associated with macroaggregates followed a trend similar to that of SOC. OP had also significantly higher SOC (P = 0·0001) and TN (P = 0·0004) associated with sand particles than RF, AF, and IR. Sand‐associated SOC and TN were the highest in uncultivated systems. Moreover, the higher SOC concentrations associated with clay particles in soils under OP, SP, and AF showed that grass‐based and tree‐based systems are rich in stable SOC as clay‐associated SOC has higher residence time than that associated with sand or silt fractions. Copyright © 2013 John Wiley & Sons, Ltd.

Restoration of degraded soils is a development strategy to reduce desertification, soil erosion and environmental degradation, and alleviate chronic food shortages with great potential in sub-Saharan Africa (SSA). Further, it has the potential to provide terrestrial sinks of carbon (C) and reduce the rate of enrichment of atmospheric CO 2 . Soil organic carbon (SOC) contents decrease by 0 to 63 per cent following deforestation. There exists a high potential for increasing SOC through establishment of natural or improved fallow systems (agroforestry) with attainable rates of C sequestration in the range of 0Á1 to 5Á3 Mg C ha À1 yr À1. Biomass burning significantly reduces SOC in the upper few centimeters of soil, but has little impact below 10 to 20 cm depth. The timing of burning is also important, and periods with large amounts of biomass available generally have the largest losses of SOC. In cultivated areas, the addition of manure in combination with crop residues and notill show similar rates of attainable C sequestration (0 to 0Á36 Mg C ha À1 yr À1). Attainable rates of SOC sequestration on permanent cropland in SSA under improved cultivation systems (e.g. no-till) range from 0Á2 to 1Á5 Tg C yr À1 , while attainable rates under fallow systems are 0Á4 to 18Á5 Tg C yr À1 . Fallow systems generally have the highest potential for SOC sequestration in SSA with rates up to 28Á5 Tg C yr À1.