Organic C

In order to classify the trophic state of detritus sink systems, instead of the conventional indicators based on inorganic nutrient availability and algal biomass and productivity in the water column, we used new biochemical descriptors based on the amount of sedimentary organic carbon (C) and nitrogen (N) potentially available to hetero-trophs. We investigated spatial and temporal changes in microphytobenthic biomass, organic matter biochemical com-position, and enzymatically hydrolyzable protein and carbohydrate pools along a northsouth transect in the Marsala lagoon (Mediterranean Sea, Italy) at three stations characterized by different hydrodynamic conditions and organic matter content in the sediment. In the Marsala lagoon water currents decreased from north to south and this pattern was reflected by organic matter distribution and composition. Sediment organic matter concentrations were among the highest reported in the literature and, in the central area where large meadows of the seagrass Posidonia oceanica were present, display a strong dominance of highly refractory carbohydrates. The protein to carbohydrate ratio was always , 1, indi-cating the dominance of aged organic detritus. Microphytobenthic biomass displays an increasing pattern southward, and its contribution to the biopolymeric C pools ranged from negligible in the central sector of the lagoon to 50% in its northern part, indicating that sources of sediment organic C also changed along the hydrodynamic gradient. The per-centage contribution of the enzymatically hydrolyzable fraction of proteins and carbohydrates was inversely related to total protein and total carbohydrate concentrations, respectively, suggesting that bioavailability of organic C and N in-creased with decreasing organic matter content in the sediment and with increasing hydrodynamic regime. Microphyto-benthic contribution to biopolymeric C (as a proxy of autotrophic organic C) and the ratio of the enzymatically digestible fraction to biopolymeric C (as an indicator of organic matter liability) were significantly correlated, suggesting that chlorophyll a sediment content might be used as an indicator of food promptly available to consumers. The present study also highlighted that the ratio of labile (i.e., enzymatically digestible) versus biopolymeric organic C in the sediments tends to decrease with increasing organic matter content, due to the increase of the refractory fraction of organic C.

Changes in oceanic primary production, linked to changes in the network of global biogeochemical cycles, have profoundly influenced the geochemistry of Earth for over 3 billion years. In the contemporary ocean, photosynthetic carbon fixation by marine phytoplankton leads to formation of ϳ45 gigatons of organic carbon per annum, of which 16 gigatons are exported to the ocean interior. Changes in the magnitude of total and export production can strongly influence atmospheric CO 2 levels (and hence climate) on geological time scales, as well as set upper bounds for sustainable fisheries harvest. The two fluxes are critically dependent on geophysical processes that determine mixed-layer depth, nutrient fluxes to and within the ocean, and food-web structure. Because the average turnover time of phytoplankton carbon in the ocean is on the order of a week or less, total and export production are extremely sensitive to external forcing and consequently are seldom in steady state. Elucidating the biogeochemical controls and feedbacks on primary production is essential to understanding how oceanic biota responded to and affected natural climatic variability in the geological past, and will respond to anthropogenically influenced changes in coming decades. One of the most crucial feedbacks results from changes in radiative forcing on the hydrological cycle, which influences the aeolian iron flux and, in turn, affects nitrogen fixation and primary production in the oceans. P. G.

Purpose: To evaluate uncertainties associated with treatment-planning computed tomography (CT) data obtained with the patient breathing freely. Methods and Materials: Patients with thoracic or abdominal tumors underwent a standard treatment-planning CT study while breathing quietly and freely, followed by CT scans while holding their breath at normal inhalation and normal exhalation. Identical treatment plans on all three CT data sets for each patient pointed out differences in: (a) radiation path lengths; (b) positions of the organs; (c) physical volumes of the lung, liver, and kidneys; (d) the interpretation of plan evaluation tools such as dose-volume histograms and normal tissue complication probability (NTCP) models; and (e) how well the planning CT data set represented the average of the inhalation and exhalation studies. Results: Inhalation and exhalation data differ in terms of radiation path length (nearly one quarter of the cases had path-length differences >l cm), although the free breathing and average path lengths do not exhibit large differences (O-9 mm). Liver and kidney movements averaged 2 cm, whereas differences between the free breathing and average positions averaged 0.6 cm. The physical volume of the liver between the free breathing and static studies varied by as much as 12%. The NTCP calculations on exhale and inhale studies varied from 3 to 43% for doses that resulted in a 15% NTCP on the free-breathing studies. Conclusion: Free-breathing CT studies may improperly estimate the position and volume of critical structures, and thus may mislead evaluation of plans based on such volume dependent criteria such as dose-volume histograms and NTCP calculations.

For various reasons, North American crop farmers are more likely to practice limited-duration no-till than continuous no-till (NT). Little is known about effects of short-term no-till (ST-NT) on organic C and total N relative to NT and conventional-till systems. A field experi- ment was initiated in 1980 to study the effects of NT, chisel plow (CP), and moldboard plow in

Nutrient and organic carbon (OC) losses are important components of the soil degradation processes produced by continuous agriculture. It was hypothesized that coarse textured soils will be more affected by cultivation than fine textured ones. The purpose of this study was to evaluate the status of OC, total nitrogen (Nt), and three phosphorous fractions (total inorganic, Pi; organic, Po; and available, Pa) in different textured virgin (under Prosopis caldenia forest) and cultivated soils of the semi-arid pampa of Argentina. Three virgin and non-fertilized cultivated soil pairs, representative from soils of the region, were selected for this study: two fine sandy loam Entic Haplustolls and a sandy Typic Ustipsamment. The element content of each soil was analysed from the (0)1-mm to 0)1}2-mm sized aggregates. Results indicated that cultivation decreased the OC, Po and Pi contents in fine aggregates of the fine textured soils, and in coarse aggregates of the coarse textured soil. Plant absorption and wind erosion were probably the main processes which decreased element contents in both textural soil types. It was speculated that in the sandy soil the elements lost from fine sized aggregates were restored by the break down of the weak coarse aggregates produced by tillage. The C/N ratios showed mostly small changes due to cultivation, indicating that no changes of organic matter quality occurred. Only the sandy soil showed C/N increases in the fine sized aggregates and decreases in the coarse sized aggregates. The C/Po quotients were not changed by cultivation, indicating that the qualitative composition of P organic compounds remained unchanged. Large OC decreases and Pa increases after cultivation detected in one of the fine textured soil were apparently linked to the occurrence of natural fires.

In this study, total heavy metal contents and their relationships with soil microbiological characteristics were investigated in agricultural soils which were with polluted heavy metals. Total heavy metal content of the soils varied from 0.95 to 3.20 μg Cd g –1 , 17.10 to 42.33 μg Co g –1 , 18.43 ...

There is greater biodiversity (in the senseof genetic distance among higher taxa) ofextant marine than of terrestrialO2-evolvers. In addition tocontributing the genes from one group ofalgae (Class Charophyceae, DivisionChlorophyta) to produce by evolution thedominant terrestrial plants (Embryophyta),the early marine O2-evolvers greatlymodified the atmosphere and hence the landsurface when the early terrestrialO2-evolvers grew. The earliestterrestrial phototrophs (from geochemicalevidence) occurred 1.2 Ga ago, over 0.7 Gabefore the Embryophyta evolved, but wellafter the earliest marine (cyanobacterial)O2 evolvers (3.45 Ga) and marineeukaryotic O2 evolvers (2.1 Ga). Evenby the time of evolution of the earliestterrestrial O2-evolvers the marineO2-evolvers had modified the atmosphereand land environment in at least thefollowing five ways. Once photosyntheticO2 paralleling organic C burial hadsatisfied marine (Fe2+, S2-reductants, atmospheric O2 built (1) upto a considerable fraction of the extantvalue (although some was consumed inoxidising terrestrial exposed Fe2+ and(2) provided stratospheric O3 and thusa UV-screen. (3) CO2 drawdown to∼20-30times the extant level is attributableto net production, and burial, of organic Cin the oceans (plus other geologicalprocesses). Furthermore, (4) theirproduction of volatile organic S compoundscould have helped to supply S to inland sitesbut also (5) delivered Cl and Br to thestratosphere thus lowering the O3 leveland the extent of UV screening.

The retention and mobility of hydrophobic organic contaminants (HOCs) in soil is mainly determined by hydrophobic partitioning to dissolved and particulate organic matter (DOM and POM, respectively). The aqueous phase, DOM, and POM fractions were extracted and separated from soils at three sites contaminated with technical chlorophenol formulations. Concentrations of chlorophenols (CP), polychlorinated phenoxyphenols (PCPP), polychlorinated diphenyl ethers (PCDE) and polychlorinated dibenzo-p-dioxins and furans (PCDD/F) were determined. The partitioning to POM, in relation to DOM, increased in all three soils with increasing hydrophobicity in the order CP < PCPP ~ PCDE ~ PCDF < PCDD. Differences in partitioning to DOM (logK(DOC)) and POM (logK(POC)) could not be explained by differences in gross organic C chemistry. Black carbon did not contribute significantly to the sorption of PCDDs, whereas >70% wood fibre in one soil resulted in a decrease of logK(POC) of 0.5 units for CPs and PCDDs. We conclude that logK(OC) for both DOM and POM need to be explicitly determined when the retention and mobility of HOCs is described and modelled in soils.

English broom (Cytisus scoparius) is an aggressive invasive shrub in native sclerophyll forests of South Australia. We studied its relative growth rate (RGR) and competitive ability in soils from invaded and uninvaded woodlands, in comparison to three native species it commonly displaces:Hakea rostrata, Acacia verniciflua, and A. myrtifolia. Hakea was the slowest growing species throughout the year. Both native species had their highest RGR during spring. The RGR of broom was higher than that of both hakea and acacia in the winter and spring. Despite losing its leaves in the summer, the RGR of broom through the year was higher than that of either of the native species. Soil from the invaded stands had higher organic C, N and soluble P than that from uninvaded sites. Broom and acacia grew better in the higher nutrient soil than in the lower nutrient soil. Competition did not decrease the final biomass of any of the species in low nutrient soil. In the higher nutrient soil the biomass of broom was reduced by competition with acacia, but not by competition with hakea. Competition by broom reduced the biomass of hakea but not that of acacia. Broom's earlier and higher RGR, high competitiveness in nutrient rich soils, and probably its ability to change nutrient availability could be important contributors to the mechanisms by which it invades native woodlands.

The present study was conducted to investigate the effects of different forms of soil acidities on microbial biomass C, ergosterol content, microbial metabolic quotient, microbial respiration quotient, and fluorescein diacetatehydrolyzing activity of some tea-growing soils of India. Total potential and exchangeable acidity and extractable and exchangeable aluminum were higher in Tripura followed by Jalpaiguri and Kharagpur soil. Different forms of acidity were significantly and positively correlated with each other. All the microbiological properties investigated were significantly and positively correlated with soil organic C content. The ratio of organic C with microbial parameters was significantly and negatively correlated with different forms of acidity. Principal component analysis indicated that the microbial activities were not directly affected by the extractable aluminum and total potential acidity. Although the tea soils had higher microbial biomass and activities because of higher organic matter content than other soils, the ratios of microbial parameters/organic carbon indicated that inhibition of microbial growth and activities had occurred because of acidity stress.

The aim of this work was to study the effect of different organic wastes, viz. cow dung, grass, aquatic weeds and municipal solid waste with lime and microbial inoculants on chemical and biochemical properties of vermicompost. Cow dung was the best substrate for vermicomposting. Application of lime (5 g/kg) and inoculation of microorganisms increased the nutrient content in vermicompost and also phosphatases and urease activities. Bacillus polymyxa, the free-living N-fixer, increased N-content of vermicompost significantly (p 6 0.01) as compared to other inoculants.

In the semi-arid Horqin Sandy Land of north China, Caragana microphylla , a leguminous shrub, is the dominant plant species and is widely used in vegetation reestablishment programs to stabilize shifting sand. We collected soil samples and investigated the invaded plant species in an age sequence of 0-, 5-, 13-, 21-, and 28-year-old C. microphylla plantations to assess the effects of the shrub on soil physicochemical properties and development of herbaceous species diversity. Soil samples were taken from two depths (0 Á/5 and 5 Á/20 cm) under the shrub canopy and in the mid-row location between shrubs. Results showed that shrub establishment and development improved soil water holding capacity (WHC), enhanced organic C and total N accumulation, and decreased pH and bulk density. Carbon and nitrogen concentrations increased significantly with increasing plantation age and had increased by 15.3 Á/20.5-fold and 11.1 Á/13.6-fold at 0 Á/5 cm depth at 28 years of plantation compared with non-vegetated dune, although incremental rates were faster in the early establishment stage (0 Á/13 year) than late successional stage (13 Á/28 year). It was found that C. microphylla contributed significant enrichment effects with higher C and N contents under their canopies as compared with alleys. With increased plantation age, the 'islands of fertility' expanded and enrichment ratios decreased. At the same time, C. microphylla facilitated the colonization and development of herbaceous species by ameliorating stressful environmental conditions. Species diversity increased with increasing plantation age. The simple, artificial vegetation system developed toward a complicated, artificial and natural ecosystem capable of reversing desertification. #

The behavior of As in the subsurface environment was examined along a transect of groundwater monitoring wells at a Superfund site, where enhanced reductive dechlorination (ERD) is being used for the remediation of groundwater contaminated with chlorinated solvents. The transect was installed parallel to the groundwater flow direction through the treatment area. The ERD technology involves the injection of organic C (OC) to stimulate in situ microbial dechlorination processes. A secondary effect of the ERD treatment at this site, however, is the mobilization of As, as well as Fe and Mn. The concentrations of these elements are low in groundwater collected upgradient of the ERD treatment area, indicating that, in the absence of the injected OC, the As that occurs naturally in the sediment is relatively immobile. Batch experiments conducted using sediments from the site inoculated with an Fe(III)-and As(V)-reducing bacterium and amended with lactate resulted in mobilization of As, Fe and Mn, suggesting that As mobilization in the field is due to microbial processes. In the areas of the transect downgradient of the ERD treatment area, however, the concentrations of OC, As, Fe and Mn in the groundwater are not elevated relative to background levels. The decrease in the dissolved concentration of OC can be attributed to mineralization by microorganisms. The losses of As, Fe and Mn from the dissolved phase must presumably be accompanied by their uptake onto aquifer solids, but chemical extractions provided evidence only for the enrichment of Fe(II). Nor could sorption of As(III) onto sediments be detected by X-ray absorption spectroscopy (XAS) against the background of native As in the sediments, which was present as As(V).

Several selective dissolution methods were used to differentiate Al forms in 12 soils formed from volcanic materials (64 andic, vitric and organic horizons) in Iceland, Azores (Portugal), Tenerife (Spain) and Italy. The soils differ in many properties because of differences in parent materials, climatic conditions, soil age and history of land use. 'Inorganic' fractions of Al were characterized using pyrophosphate (Al p ), acid oxalate (Al o ) and cold NaOH (Al n ) extractions. The difference in Al o -Al p , and Si extracted using acid oxalate, shows important differences among soils from different sources: allophane is richer in alumina in the Andosols from Azores and Tenerife than in those from Iceland and Italy. Cold NaOH generally extracted the same quantity of Al as acid oxalate, but in the soils from Tenerife Al n exceeds Al o , indicating the presence of gibbsite or poorly ordered halloysite. To characterize the Al bonded to the organic matter fraction, extractions with pyrophosphate, CuCl 2 and LaCl 3 were used. Except in one soil from Tenerife (N10), CuCl 2 extracted less Al than pyrophosphate. In organic-rich mineral horizons, Al La , Al Cu and Al p increase with organic carbon content. Using unbuffered KCl and LaCl 3 , the amount of Al extracted increased with decreasing soil pH, but there was no similar relationship with unbuffered CuCl 2 . The general sequence of efficiency of the extractants was Al p >Al Cu >Al La z Al K in organic matter-rich horizons. Al Cu constituted 30% of Al p in all soils, indicating that CuCl 2 extracts a very specific Al fraction. Al p and Al Cu are positively related to organic C. in andic horizons also increase with organic C. Phosphate retention and pH in NaF were related to Al o and Al n . The soils of Iceland have larger P retention than the others, and vitric horizons from Tenerife have higher pH in NaF and smaller Al pools than the other soils. For many horizons, there is a strong relationship between Al Cu and components that determine soil CEC (organic matter and allophane), suggesting a possible action of CuCl 2 on noncrystalline 0341-8162/$ -see front matter D (E. García-Rodeja). www.elsevier.com/locate/catena Catena 56 (2004) 155 -183

The capacity of 36 Western Australian soils to adsorb phosphorus (P) was measured by three different methods: P retention index (PRI), P buffering capacity (PBC), and P adsorption (PA). The P adsorption values measured by all three methods varied markedly with soil type. When the P adsorption values were correlated with several soil properties, using simple and multiple linear regressions, PRI, PBC, or PA values were found to be significantly correlated with the aluminium oxide content of the soils. In addition, PBC and PRI was correlated with organic carbon content. The role of aluminium oxide (Al 2 O 3 ) in the soil was apparently more important in determining the P adsorption capacity of the soils than that of iron (Fe), even though the iron oxide (Fe 2 O 3 )content of all the soils studied was consistently higher than the aluminium oxide content. The relationship between P adsorption and the selected soil properties, as determined by multiple linear regression, explained 45-59% of the variation:

Lantana camara is a recognized weed of worldwide significance due to its extensive distribution and its impacts on primary industries and nature conservation. However, quantitative data on the impact of the weed on soil ecosystem properties are scanty, especially in SE Australia, despite the pervasive presence of the weed along its coastal and inland regions. Consequently, mineral soils for physicochemical analyses were collected beneath and away from L. camara infestations in four sites west of Brisbane, SE Australia. These sites (hoop pine plantation, cattle farm, and two eucalyptus forests with occasional grazing and a fire regime, respectively) vary in landscape and land-use types. Significant site effect was more frequently observed than effect due to invasion status. Nonetheless, after controlling for site differences,~50% of the 23 soil traits examined differed significantly between infested and non-infested soils. Moisture, pH, Ca, total and organic C, and total N (but not exchangeable N in form of NO 3 -) were significantly elevated, while sodium, chloride, copper, iron, sulfur, and manganese, many of which can be toxic to plant growth if present in excess levels, were present at lower levels in soils supporting L. camara compared to soils lacking the weed. These results indicate that L. camara can improve soil fertility and influence nutrient cycling, making the substratum ideal for its own growth and might explain the ability of the weed to outcompete other species, especially native ones.

A study was conducted from 2004 to 2006 to identify and prioritise indigenous species for soil fertility improvement, and to assess soil properties, nutrient concentration and other quality characteristics of green biomass of indigenous tree and shrub species. The most preferred species for soil fertility improvement in Galessa-Jeldu areas were Senecio gigas, Hagenia abyssinica, Dombeya torrida and Buddleja polystachya. The foliage and flower bud of S. gigas contained a higher P and K content. H. abyssinica had less lignin content in its foliage and flower bud. The variation among species for soluble phenolics in the foliage was from 10 to 169 mg g -1 and in the flower bud from 9 to 234 mg g -1 . The soil pH values under H. abyssinica and S. gigas were >6.34. The soil organic C content at 0-15cm depth was higher under H. abyssinica than under B. polystachya. Similarly, the soil under H. abyssinica and S. gigas had a high content of K at the 0-15cm depth. The contents of organic C...

Nitrogen (N) deposition exceeds the critical loads for this element in most parts of Switzerland apart from the Alps. At 17 sites (8 broadleaved stands, 8 coniferous stands, and 1 mixed stand) of the Swiss Long-term Forest Ecosystem Research network, we are investigating whether N deposition is associated with the N status of the forest ecosystems. N deposition, assessed from throughfall measurements, was related to the following indicators: (1) nitrate leaching below the rooting zone (measured on a subset of 9 sites); (2) the N nutrition of the forest stand based on foliar analyses (16 sites); and (3) crown defoliation, a non specific indicator of tree vitality (all 17 sites). Nitrate leaching ranging from about 2 to 16 kg N ha -1 a -1 was observed at sites subjected to moderate to high total N deposition ([10 kg ha -1 a -1 ). The C/N ratio of the soil organic layer, or, when it was not present, of the upper 5 cm of the mineral soil, together with the pool of organic carbon in the soil, played a critical role, as previous studies have also found. In addition, the humus type may need to be considered as well. For instance, little nitrate leaching (\2 kg N ha -1 a -1 ) was recorded at the Novaggio site, which is subjected to high total N deposition ([30 kg ha -1 a -1 ) but characterized by a C/N ratio of 24, large organic C stocks, and a moder humus type. Foliar N concentrations correlated with N deposition in both broadleaved and coniferous stands. In half of the coniferous stands, foliar N concentrations were in the deficiency range. Crown defoliation tended to be negatively correlated with N concentrations in the needles. In the majority of the broadleaved stands, foliar N concentrations were in the optimum nutritional range or, on one beech plot with high total N deposition ([25 kg ha -1 a -1 ), above the optimum values. There was no correlation between the crown defoliation of broadleaved trees and foliar concentrations.

Soil erosion coupled with productivity decline is considered a major constraint to sustainable vegetable production in Southeast Asian steeplands, yet soil conservation technologies acceptable to vegetable growers have not been developed. Effectiveness of high-value contour hedgerows species [(Asparagus (Asparagus officinalis L.), pineapple (Ananas comosus (L.) Merr.), pigeon peas (Cajanus cajan (L.) Millsp.), lemon grass (Cymbopogon flexuosus (Nees ex Steud.) Wats.), and tea (Camellia sinensis (L.) O. Kuntze)] on control of steepland erosion was evaluated in a replicated researcher-managed field experiment, and 12 farmer-managed erosion-runoff plots from 1995 to 1998 across the landscape of the Manupali watershed in Mindanao, the Philippines. Annual soil loss from 42% slopes with superimposed researcher-managed high-value contour hedgerows treatment (45.4 Mg ha −1 ) was lower by 30% compared to the conventional practice of up-and-down cultivation (65.3 Mg ha −1 ). Annual soil loss measured in farmers' plots ranged from 1.4 Mg ha −1 to 52.5 Mg ha −1 on slopes ranging from 16 to 65%. Soil pH, organic C, total-N, and P downslope were greater by 7, 28, 13, and 10%, respectively, compared to upslope. Total-N, organic C, soil pH, Mg, and K measured at the end of the experiment in the researcher-managed contour hedgerows plots were lower by 45, 20, 30, 53, and 70%, respectively, compared to initial values. The Erosion-Productivity Impact Calculator (EPIC) model was used to assess the effects of annual cropping sequences under a contour hedgerow system on slopes ranging from 15 to 65%. The cabbage (Brassica oleracea var. capitata L.)-tomato (Lycopersicon esculentum Mill.)-cabbage sequence (the first crop planted in January) resulted in an average simulated annual soil loss of 28.1 Mg ha −1 across slope ranging from 15 to 65%, whereas tomato-cabbage-tomato resulted in an annual simulated soil loss of 98.3 Mg ha −1 . The cropping sequence of tomato-cabbage-tomato lost 3.0 Mg ha −1 more soil at 15% slope than did the cabbage-tomato-cabbage sequence, while at 65% slope, the tomato-cabbage-tomato sequence lost 181.2 Mg ha −1 more than the other sequence. On average, two-thirds of the total soil loss occurred during September-December. In order to reduce soil loss and increase productivity in steep sloping lands, high-value contour hedgerows with sequential cropping sequences that include either corn (Zea mays L.) or cabbage rather than tomato during the most erosive period of the year and variable fertility management strategies along the slope positions are suggested. The coincidence of predicted to actual soil loss from farmer-managed plots, based largely upon model development from researcher-managed plots, and the acute awareness : S 0 1 6 7 -8 8 0 9 ( 9 9 ) 0 0 1 5 0 -4 114 D. D. Poudel et al. / Agriculture, Ecosystems and Environment 79 (2000) 113-127 instilled amongst farmer cooperators of the magnitude of soil loss, strengthen the argument for farmer participatory research.

Residue retention and reduced tillage are both conservation agricultural management options that may enhance soil organic carbon (SOC) stabilization in tropical soils. Therefore, we evaluated the effects of long-term tillage and residue management on SOC dynamics in a Chromic Luvisol (red clay soil) and Areni-Gleyic Luvisol (sandy soil) in Zimbabwe. At the time of sampling the soils had been under conventional tillage (CT), mulch ripping (MR), clean ripping (CR) and tied ridging (TR) for 9 years. Soil was fully dispersed and separated into 212-2000 mm (coarse sand), 53-212 mm (fine sand), 20-53 mm (coarse silt), 5-20 mm (fine silt) and 0-5 mm (clay) size fractions. The whole soil and size fractions were analyzed for C content. Conventional tillage treatments had the least amount of SOC, with 14.9 mg C g À1 soil and 4.2 mg C g À1 soil for the red clay and sandy soils, respectively. The highest SOC content was 6.8 mg C g À1 soil in the sandy soil under MR, whereas for the red clay soil, TR had the highest SOC content of 20.4 mg C g À1 soil. Organic C in the size fractions increased with decreasing size of the fractions. In both soils, the smallest response to management was observed in the clay size fractions, confirming that this size fraction is the most stable. The coarse sand-size fraction was most responsive to management in the sandy soil where MR had 42% more organic C than CR, suggesting that SOC contents of this fraction are predominantly controlled by amounts of C input. In contrast, the fine sand fraction was the most responsive fraction in the red clay soil with a 66% greater C content in the TR than CT. This result suggests that tillage disturbance is the dominant factor reducing C stabilization in a clayey soil, probably by reducing C stabilization within microaggregates. In conclusion, developing viable conservation agriculture practices to optimize SOC contents and long-term agroecosystem sustainability should prioritize the maintenance of C inputs (e.g. residue retention) to coarse textured soils, but should focus on the reduction of SOC decomposition (e.g. through reduced tillage) in fine textured soils. #

Zooplankton biomass can be reliably estimated by a non-destructive method based on the statistical relationship between biovolume and the contents of carbon and nitrogen. Integrated zooplankton biovolume and the corresponding organic C and N contents were analysed in paired fresh and fixed (hexamine-buffered formalin) samples. Sample biovolume was estimated through the integration of individual volumes obtained by semi-automatic image analysis on fixed zooplankton samples. The corresponding C and N contents of paired fresh and preserved zooplankton were analysed with a Carlo-Erba C-H-N Analyser. The method allows simultaneous measurement of integrated and individual numbers and biomass (biovolume, C and N) spectrum. It is non-destructive and allows the minimization of errors and variability attributable to differences in the handling processes of samples and to the presence of particles other than zooplankton, like phytoplankton or detritus particulate matter.

We investigated whether long-term management of a Haplic Phaeocem (FAO) in¯uences organic C, microbial biomass and enzyme activities in the bulk soil and in particle size fractions. The following treatments were used: (1) no fertilization (control), (2) NPK, (3) 20 t FYM ha À 1 (farmyard manure), (4) 20 t FYM ha À 1 + NPK, (5) 30 t FYM ha À 1 and (6) 30 t FYM ha À 1 + NPK. The fertilizers were applied to plots of a crop rotation (sugar beet, potatoes, winter wheat, spring barley, alfalfa); inorganic fertilizers were applied every year, FYM was applied every second year. Particle size fractions were obtained by lowenergy sonication (0.25 kJ g À 1 ) and a combination of wet sieving and centrifugation, releasing the size fractions 2000±250, 250± 63, 63±2, 2±0.1 and <0.1 mm. FYM increased microbial biomass, N-mineralization, urease, arginine deaminase and alkaline phosphatase activity of the bulk soil, whereas the eect of additional NPK fertilization depended on the enzyme assayed. Xylanase activity of the bulk soil was mainly in¯uenced by the quality and quantity of the residues and by the amount of below-ground plant biomass. C and N contents (related to fraction dry weight) increased with diminishing particle size. The mean recoveries of C and N contents after the fractionation procedure were 96.8 and 97.1%, respectively. Organic amendments (20 vs 30 t FYM ha À 1 ) induced an equal increase of organic C and total N in all particle size fractions (2000±250, 250±63, 63± 2, 2±0.1 and <0.1 mm). Unfertilized soils were characterized by a higher C-to-N ratio of the particles (2000±250 and 250±63 mm) than the organically and inorganically fertilized soils. Microbial ninhydrin-reactive N was recovered to 73.6% after the fractionation procedure. Highest concentrations of ninhydrin-reactive N were found in the clay (2±0.1 mm) and silt fraction (63± 2 mm), lowest in the coarse sand fraction (2000±250 mm). The increased ninhydrin-reactive N in the bulk soil after long-term amendment with FYM is mainly attributed to an increase of ninhydrin-reactive N in the clay and silt fractions. Therefore, longterm organic amendments increased the capacity of the small-sized fractions to protect soil microorganisms. Urease activity was mainly located in the 63±2 and 2±0.1 mm fractions, whereas the coarse and ®ne sand particles accumulated disproportionately higher amounts of xylanase. The predominance of xylanase and urease in dierent particle size fractions depends apparently not only on the location of soil microorganisms and their substrates but also on the mechanisms of enzymes to adsorb and bind onto mineral and organic particles. #

Growing agricultural crops under Millettia ferruginea (Hochst.) Baker, a tree that is endemic to Ethiopia, is an age-old practice in the country, but the beneficial effects of the tree on crops have not been scientifically quantified. To achieve this, four isolated and ...

This paper is a synthesis of the use of selected trace elements as proxies for reconstruction of paleoproductivity and paleoredox conditions. Many of the trace elements considered here show variations in oxidation state and solubility as a function of the redox status of the depositional environment. Redox-sensitive trace metals tend to be more soluble under oxidizing conditions and less soluble under reducing conditions, resulting in authigenic enrichments in oxygen-depleted sedimentary facies. This behavior makes U, V and Mo, and to a lesser extent certain other trace metals such as Cr and Co, useful as paleoredox proxies. Some redoxsensitive elements are delivered to the sediment mainly in association with organic matter (Ni, Cu, Zn, Cd) and they may be retained within the sediment in association with pyrite, after organic matter decay in reducing sediment. This particularity confers to Ni and Cu a good value as proxies for organic C sinking flux (frequently referred to as productivity). Elements with only one oxidation state such as Ba and P are classically used to assess paleoproductivity levels but they suffer from the fact that they are solubilized under reducing conditions and may be lost from oxygen-deprived sediments. The combined used of U, V and Mo enrichments may allow suboxic environments to be distinguished from anoxic-euxinic ones. Specifically, these elements tend to be much more strongly enriched in anoxic-euxinic environments and to exhibit weaker covariation with TOC than in suboxic environments.

This paper examines the impact of shrimp farming on rice ecosystem in a village in Southwestern Bangladesh. The village Damarpota has experienced transformation of 274 ha (79%) of its prime quality rice fields into shrimp farms during the period between 1985 and 2003. Prolonged shrimp farming for 5-, 10-, and 15-year period has increased soil salinity, acidity, and depleted soil Ca, K, Mg, and organic C content of all three types of soils in the villages to a variable degree and caused soil degradation that significantly affected the rice yield. Declined yield and acreage of rice jointly reduced the total production of rice and animal fodder. Soil degradation and loss of acreage under rice have threatened the sustainability of the village rice ecosystem. r

The climatic conditions of North East India are favorable for trees to produce biomass in the form of foliage and twigs that are very rich in essential plant nutrients. Effective recycling of this biomass would help meet the nutritional requirement of crops. Field experiment was conducted in kharif (June–November) seasons for consecutive 3 years (2003, 2004, and 2005) at a lowland farm, subtropical Meghalaya (950 m asl), India, to study the effect of incorporating N-fixing tree biomass (leaves and twigs) on productivity and economics of rice (Oryza sativa L.). Fresh biomass from five tree species including erythrina (Erythrina indica), acacia (Acacia auriculiformis), alder (Alnus nepalensis), tree bean (Parkia roxburghii), and cassia (Cassia siamea) were applied at a rate of 10 t/ha. A plot with recommended NPK rate (80:60:40 kg/ha) and a control plot were also maintained for comparison. Among the tree species used, the biomass of E. indica was superior in terms of N (3.2%), P (0.47%), K (1.5%), and organic C (18.8%) contents. In the first and second year, productivity of rice was high with recommended NPK rate (4.82 t/ha in 2003 and 5.08 t/ha in 2004) followed by rice with incorporation of E. indica biomass. In the third year of the experiment, effects of tree biomass incorporation on growth, yield and yield attributes surpassed those of the recommended NPK rate, with the exception of A. nepalensis biomass. In that year, the maximum grain yield was recorded under E. indica treatments, exceeding yields under the recommended NPK rate and control by 10.5 and 69.3%, respectively. Incorporation of tree biomass significantly improved (14–19% N and 62–83% P over control) the stocks of soil available N and P. Treatment with A. auriculiformis and E. indica biomass resulted in significantly higher soil organic C content which exceeded that under the recommended NPK rate by 10.3 and 9.2% and that under the control by 15.2 and 14%, respectively higher by species. The highest net return was recorded with the recommended NPK rate ($ 381/ha) followed by E. indica ($ 303/ha). Since the local farmers are resource poor and rarely use chemical fertilizers, application of plant biomass, particularly that of E. indica, to lowland rice is a recommendable option to improve productivity and income, and to sustain soil health.

The present study investigated the effect of cultivation with or without inorganic fertilization, and farmyard manure (FYM), paddy straw (PS), and green manure (GM) along with inorganic fertilizers on soil aggregation, array and accessibility of aggregate associated C, specially the micro-scale location or stability of soil organic C (SOC) at 0-0.15, 0.15-0.30 and 0.30-0.45 m depths on a silty clay soil of Inceptisol in the hot, humid subtropics of eastern India, with a long-term 21 year old rice (Oryza sativa L.)-wheat (Triticum aestivum L.) cropping system. In general, structural indices were found higher in the soil receiving organic amendments (NPK + FYM, NPK + PS and NPK + GM) than the minerally fertilized (NPK) soil or the control and in the surface than in depth. Among treatments including organic amendments, GM seems to be less efficient in increasing aggregate stability. The aggregated C decreased with increasing soil depth and was distributed as 'silt + clay' C (b 0.05 mm) N coarse macroaggregated C (CMacAC, N 2.0 mm) = mesoaggregated C (MesAC, 0.25-2.0 mm) N coarse microaggregated C (CMicAC, 0.05-0.25 mm). Within a size class, aggregated C concentrations of the organically amended treatments were in the order of FYM ≥ PS ≥ GM, limiting the negative effect of ploughing but not to the level of native soil. A significant positive linear relationship was found between the 'silt + clay' C and the silt and clay content of this soil. Out of the added organics, C from FYM was stabilized more than PS and GM, respectively, and C from GM was stabilized more in 'silt + clay' sized fraction than FYM and PS. This study represents a further step towards understanding the bio-chemical nature of organics and their array with mineral particles for C stabilization.

This paper reports the recycling of nutrients by vermicomposting of cow dung (CD), poultry droppings (PD) and food industry sludge (FIS) employing earthworms (Eisenia fetida). A total of six vermicomposting units were established and dynamics of chemical and biological parameters has been studied for 13 weeks. The waste mixture containing 50% CD + 25% PD + 25% FIS had better fertilizer value among studied waste combinations. At the end of experiment, vermicomposts showed decrease in pH and organic C, but increase in EC, total Kjeldhal N, total available P and total K contents. The C:N ratio of final vermicomposts also reduced to 10.7-12.7 from 22.8 to 56 in different waste combinations. The earthworms have good biomass gain and cocoon production in all vermicomposting units but CD alone and 50% CD + 25% PD + 25% FIS were better than other studied combinations.

Soil structure exerts important influences on the edaphic conditions and the environment. It is often expressed as the degree of stability of aggregates. Aggregation results from the rearrangement, flocculation and cementation of particles. It is mediated by soil organic carbon (SOC), biota, ionic bridging, clay and carbonates. The complex interactions of these aggregants can be synergistic or disruptive to aggregation. Clay-sized particles are commonly associated with aggregation by rearrangement and flocculation, although swelling clay can disrupt aggregates. Organo-metallic compounds and cations form bridges between particles. The SOC originates from plants, animals and microorganisms, and their exudates. It enhances aggregation through the bonding of primary soil particles. The effectiveness of SOC in forming stable aggregates is related to its decomposition rate, which in turn is influenced by its physical and chemical protection from microbial action. Soil inorganic carbon (SIC) increases aggregation in arid and semiarid environments, and the formation of secondary carbonates is influenced by the presence of SOC and Ca 2 + and Mg 2 +. Soil biota release CO 2 and form SOC which increase dissolution of primary carbonates while cations increase precipitation of secondary carbonates. The precipitation of (hydr)oxides, phosphates and carbonates enhances aggregation. Cations such as Si 4 + , Fe 3 + , Al 3 + and Ca 2 + stimulate the precipitation of compounds that act as bonding agents for primary particles. Roots and hyphae can enmesh particles together while realigning them and releasing organic compounds that hold particles together, a process with a positive impact on soil C sequestration. Soil structure can be significantly modified through management practices and environmental changes. Practices that increase productivity and decrease soil disruption enhance aggregation and structural development.

This paper reports the recycling of nutrients by vermicomposting of cow dung (CD), poultry droppings (PD) and food industry sludge (FIS) employing earthworms (Eisenia fetida). A total of six vermicomposting units were established and dynamics of chemical and biological parameters has been studied for 13 weeks. The waste mixture containing 50% CD + 25% PD + 25% FIS had better fertilizer value among studied waste combinations. At the end of experiment, vermicomposts showed decrease in pH and organic C, but increase in EC, total Kjeldhal N, total available P and total K contents. The C:N ratio of final vermicomposts also reduced to 10.7-12.7 from 22.8 to 56 in different waste combinations. The earthworms have good biomass gain and cocoon production in all vermicomposting units but CD alone and 50% CD + 25% PD + 25% FIS were better than other studied combinations.

Samples of 255 noncalcareous A, Ap, and AB horizons from se-CO 2 evolved from organic matter oxidized in a high lected major land resource areas (MLRA) in the north central USA were used to develop equations for predicting organic C content, as temperature furnace, is considered the most precise and determined with a Leco C analyzer, from weight loss-on-ignition accurate procedure today, but the high cost of dry com-(LOI). Organic C concentrations of the samples ranged from 1.09 to bustion instruments is a limitation to many laboratories. 114.6 g kg Ϫ1 . Within each MLRA, strong linear relationships were Additionally, the high temperature oxidation liberates observed between LOI and organic C measured by the Leco instru-C from carbonate minerals, so calcareous samples rement, with r 2 ranging from 0.94 to 0.98. Predictive equations develquire acid pretreatments or corrections for carbonate oped by least-squares regression were significantly different for indicontent. vidual MLRA's. Loss-on-ignition is a rapid, inexpensive, and accurate Wet chemical oxidation (Walkley and Black, 1934), method for estimating organic C concentration in soils of the north the Walkley-Black Procedure, was long the standard of central USA. We recommend that unique predictive equations be developed for individual soil-geographic regions.

Three pedons developed on basaltic parent materials on the Biu Plateau in the semi-arid region of Nigeria were characterized and classified. Soil pH values ranged from 6·0 to 6·6 and increased slightly with increase in profile depth. The clay content was generally above 40% and the slit fraction ranged from 20 to 34%. Exchangeable bases were high and values for exchangeable acidity did not exceed 0·20 cmol( + ) kg -1 . The NH 4 OAc-CEC, effective CEC, and base saturation (NH 4 OAc-CEC) were moderately high, while base saturation by effective CEC method was high with all values above 90%. Organic C content of the surface soils was medium, but the soils were deficient in N, P and S. The pedons were classified as Typic Haplustalfs (Haplic Alisol and Chromic Luvisol) and as Ustic Dystropept (Chromic Cambisol). The agricultural potentials of the soils were considered to be favourable, although constrained by N, P and S deficiencies.

Efforts were made to decompose herbal pharmaceutical industrial waste (HPIW) spiked with cow dung (CD) using Eisenia fetida. A total of five vermibeds: T 1 -HPIW (0% + CD 100%, control), T 2 -HPIW (25%), T 3 -HPIW (50%), T 4 -HPIW (75%) and T 5 -HPIW (100%) were used for vermicomposting. The changes in biology and chemistry of vermibeds were measured after ten days interval. E. fetida showed high growth and cocoon production rate in all vermibeds. The vermicomposted material contained great population of fungi 6.0-40.6 (CFU Â 10 5 g À1 ), bacteria 220-1276.0 (CFU Â 10 8 g À1 ) and actinomycetes 410.0-2962.0 (CFU Â 10 5 g À1 ) than initial material. Vermicomposted material was rich in plant-available forms of nutrients ðN-NO À 3 ; PO 3À 4 ; available K andSO À2 4 Þ. Results suggested that noxious industrial waste can be converted into valuable product for sustainable soil fertility programme.

Rice hulls and sawdust are two common C-rich wastes derived from rice and timber agro-industries in subtropical NE Argentina. An alternative to the current management of these wastes (from bedding to uncontrolled burning) is composting. However, given their C-rich nature and high C/N ratio, adequate composting requires mixing with a N-rich waste, such as poultry manure. The effect of different proportions of poultry manure, rice hulls and/or sawdust on composting efficiency and final compost quality was studied. Five piles were prepared with a 2:1 and 1:1 ratio of sawdust or rice hulls to poultry manure, and 1:1:1 of all three materials (V/V). Different indicators of compost stability and quality were measured. Thermophilic phase was shorter for piles with rice hulls than for piles with sawdust (60 days vs. 105 days). Time required for stability was similar for both C-rich wastes (about 180 days). Characteristics of final composts were: pH 5.8-7.2, electrical conductivity 2.5-3.3 mS/cm, organic C 20-26%, total N 2.2-2.9%, lignin 19-22%, total Ca 18-24 g/kg, and extractable P 6-8 g/kg, the latter representing 60% of total P. Nitrogen conservation was high in all piles, especially in the one containing both C-rich wastes. Piles with sawdust were characterized by high total and available N, while piles with only rice hulls had higher Si, K and pH. Extractable P was higher in 1:1 piles, and organic C in 2:1 piles.

SummaryÐMicrobial C (C mic ) and N (N mic ), the C mic -to-organic C (C org ) and N mic -to-total N (N t ) ratios and the speci®c respiration of microbial biomass were investigated in a southern boreal mixed forest. The forest stands were 50 and 124 years old and consisted of trembling aspen, paper birch and mixed conifers comprising white spruce and balsam ®r. Stands were growing on soils derived either from clay (89% average clay content) or till (46% average clay content) deposits in the clay belt region of northern Quebec. In the forest¯oors the relative concentrations of microbial C and N and the C micto-C org and N mic -to-N t ratios, regarded as measures of organic matter quality, declined with stand age whereas the speci®c microbial respiration increased, indicating decreasing C assimilation eciency. In the mineral soils, in contrast, C mic -to-C org and N mic -to-N t ratios increased with stand age. The C mic -to-N mic ratio widened with stand age in both the forest¯oors and mineral soils, suggesting that the proportion of fungi had increased. Concentrations of microbial C and N were on average lower in forest¯oor beneath conifers (C mic -to-C org 1.9%, N mic -to-N t 7.5%) than beneath the deciduous species birch (C mic -to-C org 2.2%, N mic -to-N t 8.6%) and aspen (C mic -to-C org 2.4%, N mic -to-N t 9.2%). Average C mic -to-N mic ratios were only slightly dierent in the forest¯oors beneath the dierent tree species (C mic -to-N mic : conifers 8.9, birch 7.2, and aspen 8.3). In both forest¯oors and mineral soils, average concentrations of C mic and N mic were generally higher in the clay than in the till soils, but the C mic -to-C org ratios were similar in both soil types. The average N mic -to-N t ratios were lower in till than in clay soils only beneath conifers. The average speci®c microbial respiration (qCO 2 =mg CO 2 -C mg C mic À1 d À1

We assessed soil N and C dynamics in a decomposition experiment at microcosm scale with leaf litter of evergreen shrubs and perennial grasses of the Patagonian Monte. We hypothesised that eventual changes in leaf-litter quality in arid Patagonian ecosystems disturbed by grazing would lead to changes in C and N dynamics in decaying leaf litter and the associated soil. We constructed microcosms with local soil and litterbags containing leaf litter of three perennial grass and three evergreen shrub species. Microcosms were incubated at field capacity during 12, 42 and 84 days. We assessed N, C, phenolics and lignin concentrations in leaf litter before incubation, and N and C concentrations after incubation. We estimated inorganic and total N and organic C in soil before and after incubation. We calculated C and N budgets and the associated rates of C and N losses from leaf litter, microbial respiration, N immobilisation in litter and soil, and N mineralisation at microcosms of each species by inverse modelling techniques. Initial leaf-litter N concentration was significantly higher and C:N ratio lower in evergreen shrubs than in perennial grasses. Leaf litter of perennial grasses was very similar in initial chemical composition among species. In contrast, evergreen shrubs displayed a large variability in the concentration of secondary compounds among species. Accordingly, microcosms of perennial grasses showed similar rates of C and N processes while those of evergreen shrubs showed diverse patterns and rates of processes among them. Process rates in microcosms of one of the evergreen shrub species were closely related to those of perennial grasses. In contrast, process rates in microcosms of the two other evergreen shrub species were quite different between them and from those of perennial grasses. We conclude that (i) the replacement of perennial grasses by evergreen shrubs or the shifting of species within evergreen shrubs in ecosystems disturbed by grazing could have different effects on ecosystem processes depending on the species involved, and (ii) species rather than life forms should be used to predict leaf-litter decomposability and associated soil C and N dynamics particularly in evergreen shrubs.

We discuss how individualistic/collectivistic orientations of employees predict affective well-being at work, and how this relationship is moderated by the perceptions of spirit of camaraderie in organizations. The sample comprises 161 employees of 109 organizations operating in Portugal, a collectivistic culture. The findings suggest that: (a) collectivistic individuals show higher affective well-being than individualists; (b) this relationship is moderated by the employees' perceptions of the spirit of camaraderie in their organizations; (c) higher affective well being levels tend to be experienced by collectivists who find working in an organizational context to be rich in spirit of camaraderie, and lower levels of affective well being are expressed by individualists who perceive poor spirit of camaraderie in their working environments. The paper emphasizes that employee happiness can have different bases in different cultures and that individualism/collectivism orientations do not operate in the same way in different cultural and organizational contexts. Keywords Individualism/collectivism orientation Á Spirit of camaraderie Á Affective well-being at work 1 Introduction ''Happiness'' is a subjective experience, since people are happy to the extent that they believe themselves to be happy. Scholars have tended to treat ''happiness'' as psycho-We are very grateful to the three anonymous reviewers for their helpful comments and suggestions.

Biochar, a co-product of thermochemical conversion of lignocellulosic materials into advanced biofuels, may be used as a soil amendment to enhance the sustainability of biomass harvesting. We investigated the impact of biochar amendments (0, 5, 10, and 20 g-biochar kg − 1 soil) on the quality of a Clarion soil (Mesic Typic Hapludolls), collected (0-15 cm) in Boone County, Iowa. Repacked soil columns were incubated for 500 days at 25°C and 80% relative humidity. On week 12, 5 g of dried and ground swine manure was incorporated into the upper 3 cm of soil for half of the columns. Once each week, all columns were leached with 200 mL of 0.001 M CaCl 2 . Soil bulk density increased with time for all columns and was significantly lower for biochar amended soils relative to the un-amended soils. The biochar amended soils retained more water at gravity drained equilibrium (up to 15%), had greater water retention at − 1 and −5 bars soil water matric potential, (13 and 10% greater, respectively), larger specific surface areas (up to 18%), higher cation exchange capacities (up to 20%), and pH values (up to 1 pH unit) relative to the un-amended controls. No effect of biochar on saturated hydraulic conductivity was detected. The biochar amendments significantly increased total N (up to 7%), organic C (up to 69%), and Mehlich III extractable P, K, Mg and Ca but had no effect on Mehlich III extractable S, Cu, and Zn. The results indicate that biochar amendments have the potential to substantially improve the quality and fertility status of Midwestern agricultural soils.

The fate of carbon (C) in organisms, food webs, and ecosystems is to a major extent regulated by mass-balance principles and the availability of other key nutrient elements. In relative terms, nutrient limitation implies excess C, yet the fate of this C may be quite different in autotrophs and heterotrophs. For autotrophs nutrient limitation means less fixation of inorganic C or excretion of organic C, while for heterotrophs nutrient limitation means that more of ingested C will ''go to waste'' in the form of egestion or respiration. There is in general a mismatch between autotrophs and decomposers that have flexible but generally high C:element ratios, and consumers that have lower C:element ratios and tighter stoichiometric regulation. Thus, C-use efficiency in food webs may be governed by the element ratios in autotroph biomass and tend to increase when C:element ratios in food approach those of consumers. This tendency has a strong bearing on the sequestration of C in ecosystems, since more C will be diverted to detritus entering soils or sediments when C-use efficiency is low due to stoichiometric imbalance. There will be a strong evolutionary pressure to utilize such excess C for structural and metabolic purposes. This article explores how these basic principles may regulate C sequestration on different scales in aquatic and terrestrial ecosystems.

A 2-year study was conducted in three rainfall zones of Zimbabwe to explore opportunities for harnessing biological nitrogen fixation of non-cultivated herbaceous legumes, which hitherto have been regarded simply as weeds, in order to improve soil productivity on smallholder farms. The rainfall zones used ranged from sub-humid (800 mm annually) to semiarid (<650 mm). Nitrogen is the single most important crop nutrient under the predominantly leached sandy soils of southern Africa, and alternative N sources are lacking for smallholder farmers. Diversity and abundance of indigenous legume species were determined under different land uses using farmer participatory research techniques among other methods. Over 30 different legume species, mainly of the genera Crotalaria, Indigofera and Tephrosia, were identified across the three agroregions. With the participation of farmers, a simple technique, termed the gwezu smell technique, was developed which enabled participating farmers to distinguish between legumes and non-leguminous plants. Diversity was higher in areas with less than 20 years of cropping compared with old farming areas with over 70 years of cultivation, suggesting that prevailing management practices have over time rendered soil environments unfavourable for productivity and regeneration of these legumes.

In the boreal mixed forest, stand composition generally changes from deciduous to mixed to coniferous stands during postdisturbance succession. Our objective was to determine the in¯uence of forest composition on the quality of soil nitrogen and carbon as determined by C and N mineralization during the course of a long-term in vitro incubation (282 days). Three stand types (Populus tremuloides, Betula papyrifera, and conifers (mixture of Abies balsamea and Picea glauca )), of two ages (50 and 124 years since ®re) growing on two soil types (clay and till) were considered. Expressed on an organic C basis, our results showed a greater N mineralization for deciduous than coniferous stands, both in the mineral soil and the forest¯oor, a higher N mineralization in the mineral soil of older stands as compared with young ones, and in till than in clay soils. Mineralization of C was higher in the forest¯oor of clay soils as compared to till soils while the opposite was found in the mineral soil. It was also higher in both soil layers of older sites. The observed dierences in N and C mineralization among stand types, stand ages and deposits appeared to be due to dierences in the most labile fraction of soil organic matter because these dierences were observed within 100 days of incubation. The ratio of C mineralized±N mineralized was greater in coniferous than deciduous soils in both soil layers, indicating a lesser quality of organic matter under coniferous stands. Despite signi®cant dierences among the above-listed factors for N and C mineralization on an organic C basis, the pool size of mineralized (or mineralizable) N and C was generally not signi®cantly dierent between the dierent forest and soil types because of an inverse relationship between quality and quantity of soil organic matter. Correlation and multiple regression analysis indicated that clay content (negatively), C±N ratio (negatively), available P as well as exchangeable Mn were related to the mineralization of N. 7 : S 0 0 3 8 -0 7 1 7 ( 0 0 ) 0 0 0 1 7 -1

Large tracts of land in South American native forests have been converted to monoculture for livestock production which could negatively affect soils and environmental quality. A proposed management alternative is to use agroforestry systems, but little information is available on how they affect the soils. The objective was to assess the effect of a silvopastoral chronosequence in a tropical region of Colombia on soil microbiological and physico/chemical properties. The systems (three replications) were: monoculture grass conven-

The number of studies on priming effects (PE) in soil has strongly increased during the last years. The information regarding real versus apparent PE as well as their mechanisms remains controversial. Based on a meta-analysis of studies published since 1980, we evaluated the intensity, direction, and the reality of PE in dependence on the amount and quality of added primers, the microbial biomass and community structure, enzyme activities, soil pH, and aggregate size. The meta-analysis allowed revealing quantitative relationships between the amounts of added substrates as related to microbial biomass C and induced PE. Additions of easily available organic C up to 15% of microbial biomass C induce a linear increase of extra CO2. When the added amount of easily available organic C is higher than 50% of the microbial biomass C, an exponential decrease of the PE or even a switch to negative values is often observed. A new approach based on the assessment of changes in the production of extracellular enzymes is suggested to distinguish real and apparent PE. To distinguish real and apparent PE, we discuss approaches based on the C budget. The importance of fungi for long-term changes of SOM decomposition is underlined. Priming effects can be linked with microbial community structure only considering changes in functional diversity. We conclude that the PE involves not only one mechanism but a succession of processes partly connected with succession of microbial community and functions. An overview of the dynamics and intensity of these processes as related to microbial biomass changes and C and N availability is presented.

Coastal hypoxia (defined here as <1.42 ml L −1 ; 62.5 µM; 2 mg L −1 , approx. 30% oxygen saturation) develops seasonally in many estuaries, fjords, and along open coasts as a result of natural upwelling or from anthropogenic eutrophication induced by riverine nutrient inputs. Permanent hypoxia occurs naturally in some isolated seas and marine basins as well as in open slope oxygen minimum zones. Responses of benthos to hypoxia depend on the duration, predictability, and intensity of oxygen depletion and on whether H 2 S is formed. Under suboxic conditions, large mats of filamentous sulfide oxidizing bacteria cover the seabed and consume sulfide. They are hypothesized to provide a detoxified microhabitat for eukaryotic benthic communities. Calcareous foraminiferans and nematodes are particularly tolerant of low oxygen concentrations and may attain high densities and dominance, often in association with microbial mats. When oxygen is sufficient to support metazoans, small, soft-bodied invertebrates (typically annelids), often with short generation times and elaborate branchial structures, predominate. Large taxa are more sensitive than small taxa to hypoxia. Crustaceans and echinoderms are typically more sensitive to hypoxia, with lower oxygen thresholds, than annelids, sipunculans, molluscs and cnidarians.

Biosolids, mainly from textile industries and the rest from households, were vermicomposted with Eisenia fetida, cow manure and oat straw for 2 months at three different moisture contents (60%, 70% and 80% dry weight base) in triplicate to reduce pathogens and toxic organic compounds, and to find the best medium for growth of E. fetida. The vermicompost with the best stability and maturity and a weight loss of 18% was obtained with 1,800 g biosolid, no straw and 800 g manure at 70% water content. This vermicompost had the following rop erties: pH 7.9; organic C content of 163 g kg-?; a; electrolytic conductivity of 11 mS cm-'; a humic-to-fulvic acid ratio of 0.5 (FIARA); total N content of 9 g kgpl; water soluble C (C,) less than 0.5%; cation exchange capacity of 41 cmol, kgpl; a respiration rate of 188 mg CO Z -C kgP1 compost-C daypl; a N05/C02 ratio greater than 8; and a NH$NO; ratio lower than 0.16. The vermicompost gave a germination index for cress (Lepidium sativum) of 80% after 2 months while the earthworm production increased 1.2-fold and volatile solids decreased five times. In addition, the vermicompost contained less than 3 CFU g-l~almonella spp., no fecal coliforms and Shigella spp. and no eggs of helminths. Concentration of sodium was 152 mg kgP1 dry compost, while concentrations of chromium, copper, zinc and lead were below the limits established by the USEPA.