Colonization of chemical factory wastes by soil nematodes

Soil nematodes were studied in 39- and 49-year-old “red” dumps mainly composed of Fe₂O₃ waste pyrite remnants from production of sulphuric and other acids, and in a 84-year-old “white” dump mainly composed of CaCO₃ material from soda production. The youngest stage of spontaneous biological succession contained moss–lichen patches which were mainly inhabited by bacterivorous nematodes (Acrobeloides nanus, Panagrolaimus rigidus, Rhabditis terricola, Bursilla monhystera) in very low abundance (about 50×10³ ind m⁻²). Invasion of grass resulted in increase of bacterivorous nematodes up to several millions  ind m⁻² but with considerable seasonal fluctuations. Nematode assemblages diversified in sites colonized by various deciduous trees and Paratylenchus straeleni was the dominant plant parasitic nematode. In site with stabilized grass carpet on the “white” dump dominant nematodes were Geocenamus quadrifer and Pungentus engadinensis. Eudorylaimus spp. first appeared in 49-year-old dump but their populations remained very low (1–9×10³ ind m⁻²). Some species found in control deciduous forests on natural soils (e.g. Xenocriconemella macrodora, Cephalenchus hexalineatus, Tylolaimophorus minor, Ogma menzeli, Hoplotylus femina) did not colonize deposits. Natural succession of nematodes on chemical waste materials was very slow and even after about 80 years their communities under deciduous trees showed many differences from those in nearby semi-natural mixed forests.     

Diversity and abundance of earthworms across an agricultural land-use intensity gradient

Understanding how communities of important soil invertebrates vary with land use may lead to the development of more sustainable land-use strategies. We assessed the abundance and species composition of earthworm communities across six replicated long-term experimental ecosystems that span a gradient in agricultural land-use intensity. The experimental systems include a conventional row-crop agricultural system, two lower-intensity row-crop systems (no-till and tilled organic input), an early successional old-field system, a 40–60 years old coniferous forest plantation, and an old-growth deciduous forest system. Earthworm populations varied among systems; they were lowest in the most intensively managed row-crop system (107 m⁻²) and coniferous forest (160 m⁻²); intermediate in the old-field (273 m⁻²), no-till (328 m⁻²) and tilled organic (344 m⁻²) cropping systems; and highest in the old-growth deciduous forest system (701 m⁻²). Juvenile Aporrectodea species were the most common earthworms encountered in intensively managed systems; other species made up a larger proportion of the community in less intensively managed systems. Earthworm community biomass and species richness also varied and were lowest in the conventional row-crop system and greatest in the old-growth forest system. These results suggest that both land-use intensity and land-use type are strong drivers of the abundance and composition of earthworm communities in agricultural ecosystems.     

High rates of forest clearance and fragmentation pre- and post-National Park establishment: The case of a Jamaican montane rainforest

The principal defense of tropical forests has been to designate them as protected areas, but few of these protected areas have been studied to determine their effectiveness at preventing forest clearance within their boundaries. We used remote sensing techniques to quantify three fundamental forest cover change processes: forest clearance, re-growth and fragmentation over a 19-year time period, in a National Park of Jamaica. Results show that forest clearance occurred at similar high levels prior and subsequent to the establishment of the area as a National Park in 1993: 1.50% yr⁻¹ (1983–1992) and 1.42% yr⁻¹ (1992–2002), respectively. Fragmentation continued post-establishment, and manifested itself in an increasing number of smaller more vulnerable fragments; the number of fragments increased by 60%, and the mean fragment size decreased by 40%. Core areas decreased with ensuing increases in edge lengths, and fragments became more isolated from one another. After designation as a National Park however, increased forest re-growth occurred, resulting in a 63% decline in the net deforestation rate from 0.80% yr⁻¹ (1983–1992) to 0.26% yr⁻¹ (1992–2002). Image classifications gave accuracies of 90–97% (Kappa 0.80–0.93). Although the decrease in net deforestation may indicate some level of success of this National Park, forest clearance and fragmentation, leading to species shifts and biodiversity loss were still present at pre-National Park levels. We then examined the preponderance of successful protected areas, and found that success may be an artifact of the most widely used method of assessment, which compares deforestation rates inside versus outside protected areas.     

Global warming affect Collembola community: A long-term study

Long-term (1992–2002) effects of climate changes on soil Collembola in Scots pine Pinus sylvestris forests in North Vidzeme Biosphere Reserve (northern Latvia) are investigated. The study was carried out in three forest stands of different age, young (30–40 years), middle aged (50–70 years), and old (150–200 years). One hundred soil samples were collected within each sampling site once a year in autumn over a period of 11 years. In total, 66 species of Collembola were found. Species richness varied between 47 and 56 and density of Collembola from 7300 to 8300 ind m⁻². A statistically significant increase in the sums of positive air temperatures (4 °C) was recorded during the period of investigation. Precipitation and thereby soil moisture showed considerable year-to-year fluctuations. Non-metric Multidimensional Scaling of the data yielded two axes explaining 48.6% and 38.6% of the variation. Axis 1 coincided with the trend of sums of positive air temperature (r=0.66). Axis 1 corresponded best with the negative impact of warming of climate on Collembola, mainly on the euedaphic species inhabiting the deeper layers of the organic soil horizon. Axis 2 was considered reflecting the effect of soil moisture fluctuations (correlation with moisture r=-0.62) on litter dwelling, mostly hemiedaphic Collembola. Species richness tended to decrease gradually in all forest sites during the study period from 29–36 to 13–26 species. Correlation between axes (r=0.455) indicated interaction effects between positive air temperatures and soil moisture. Forest age showed no substantial effect on the community structure, therefore the changes observed cannot be explained by ecological succession.     

Temporal and spatial variability of soil respiration in a boreal mixedwood forest

Temporal and spatial variability of soil respiration (R_s) was measured and analyzed in a 74-year-old, mixedwood, boreal forest in Ontario, Canada, over a period of 2 years (August 2003–July 2005). The ranges of R_s measured during the two study years were 0.5–6.9 μmol CO₂ m⁻² s⁻¹ for 2003–2004 (Year 1) and 0.4–6.8 μmol CO₂ m⁻² s⁻¹ for 2004–2005 (Year 2). Mean annual R_s for the stand was the same for both years, 2.7 μmol CO₂ m⁻² s⁻¹. Temporal variability of R_s was controlled mainly by soil temperature (T_s), but soil moisture had a confounding effect on T_s. Annual estimates of total soil CO₂ emissions at the site, calculated using a simple empirical R_s–T_s relationship, showed that R_s can account for about 88 ± 27% of total annual ecosystem respiration at the site. The majority of soil CO₂ emissions came from the upper 12 to 20 cm organic LFH (litter–fibric–humic) soil layer. The degree of spatial variability in R_s, along the measured transect, was seasonal and followed the seasonal trend of mean R_s: increasing through the growing season and converging to a minimum in winter (coefficient of variation (CV) ranged from 4 to 74% in Year 1 and 4 to 62% in Year 2). Spatial variability in R_s was found to be negatively related to spatial variability in the C:N ratio of the LHF layer at the site. Spatial variability in R_s was also found to depend on forest tree species composition within the stand. R_s was about 15% higher in a broadleaf deciduous tree patch compared to evergreen coniferous area. However, the difference was not always significant (at 95% CI). In general, R_s in the mixedwood patch, having both deciduous and coniferous species, was dominated by broadleaf trees, reflecting changing physiological controls on R_s with seasons. Our results highlight the importance of discerning soil CO₂ emissions at a variety of spatial and temporal scales. They also suggest including the LFH soil layer and allowing for seasonal variability in CO₂ production within that layer, when modeling soil respiration in forest ecosystems.     

Transpiration and early growth of tree plantations established on degraded cropland over shallow saline groundwater table in northwest Uzbekistan

This study examined the early growth and water use of tree plantations established on a marginalized irrigated cropland in northwest Uzbekistan, where salinization of agricultural soils is widespread due to shallow saline groundwater tables. During the first two growing seasons in 2003–2004, the tree stands consisting of Elaeagnus angustifolia L., Populus euphratica Oliv., and Ulmus pumila L. were irrigated with 80 mm year⁻¹, and, in 2005, were left to rely on the shallow (0.9–2.0 m deep) groundwater with a salinity of 1–5 dS m⁻¹. Soil salinity increased but remained within the range of moderate-to-strong (4–14 dS m⁻¹) during the three years. In the course of the growing season, plantations transpired 0.1–7 mm day⁻¹ in 2003 and 1–13 mm day⁻¹ in 2004–2005, as determined with the Penman–Monteith model. In the absence of irrigation, the annual stand transpiration averaged 1250, 1030, and 670 mm for E. angustifolia, P. euphratica and U. pumila, respectively. In 2005, the leaf area index of E. angustifolia ranged from 5 to 10, surpassing that of the other two species more than two-fold. Differences in canopy conductance and transpiration were significant among the tree species and the decoupling coefficient at no time exceeded 0.3, indicating strong physiological control of transpiration. The vigorous juvenile growth and high transpiration under deficit irrigation and after irrigation was terminated, suggested that afforestation with well-adapted tree species is a viable land use option for degraded cropland. The plantation responses to increasing soil salinity must be monitored to determine potential leaching demands in the long run.     

Fungal biomass changes during the decomposition of leaves of Michelia nilagirica and Semecarpus coriaceae in an upper montane rainforest in Sri Lanka

The agar-film method was used to assess fungal biomass and standing crop in several analogous decomposition stages of two leaf species (the fast decomposing Michelia nilagirica and the slow decomposing Semecarpus coriaceae), both from an upper montane rainforest in Sri Lanka. At all decomposition stages the fungal biomass on Michelia litter was significantly higher (P<0.001) than for Semecarpus and had developed much more rapidly (17.04 mg g⁻¹ at the first decomposition stage compared with 4.39 mg g⁻¹ for Semecarpus). These figures are considerably higher than those for a cool temperate deciduous forest, but when the data are given as fungal biomass per area the reverse is true. Data are given on the contribution of different hyphal types showing a trend for change (hyaline to dark hyphae) during the course of decomposition. The mass of dead hyphae is considerably lower than data from temperate forests. Data on immobilization of C and of plant nutrients (N, P, K, Ca, Mg and Na) are provided plus hyphal nutrient contents expressed as % of total contents in the leaf litter. These data are comparable to those from temperate forests.     

Soil water conservation and yield of winter sorghum (Sorghum bicolor L. Moench) as influenced by tillage, organic materials and nitrogen fertilizer in semi-arid tropical India

Soil water and nutrients play an important role in increasing sorghum (Sorghum bicolor L. Moench) yields in the Vertisols of semi-arid tropics during post-rainy season. The effects of tillage practices, organic materials and nitrogen fertilizer on soil properties, water conservation and yield of sorghum were evaluated during winter seasons of 1994–1995 and 1995–1996 on deep Vertisols at Bijapur in the semi-arid tropics of Karnataka State (Zone 3) of south India. Conservation and availability of water and nutrients during different stages of crop growth were increased by deeper tillage resulting in increased grain yield of winter sorghum. Medium and deep tillage increased the grain yield by 23% (1509 kg ha⁻¹) and 57% (1919 kg ha⁻¹) during 1994–1995 and 14% (1562 kg ha⁻¹) and 34% (1835 kg ha⁻¹) during 1995–1996, respectively, over shallow tillage. Water use efficiency increased from shallow (4.90 kg ha⁻¹ mm⁻¹) to deep tillage (7.30 kg ha⁻¹ mm⁻¹). Greater water use efficiency during 1994–1995 as compared to 1995–1996 was attributed to lower consumptive use of water during 1994–1995. Among organic materials, application of Leucaena loppings conserved larger amounts of water and increased winter sorghum yield and water use efficiency. Application of Leucaena loppings increased the winter sorghum grain yield by 9% (mean of 1994–1995 and 1995–1996) as compared to vermicompost. Significantly (P < 0.05) higher water use efficiency of 6.32 kg ha⁻¹ mm⁻¹ was observed in Leucaena loppings incorporated plots compared to 5.72 kg ha⁻¹ mm⁻¹ from vermicompost. Grain yield increased by 245 kg ha⁻¹ with application of 25 kg N ha⁻¹ in 1994–1995, and a further increase in N application to 50 kg ha⁻¹ increased the grain yield by about 349 kg ha⁻¹ in 1995–1996. Deep tillage with application of 25 kg N ha⁻¹ resulted in significantly higher sorghum yield (2047 kg ha⁻¹) than control during 1994–1995. Deep tillage with integrated nutrient management (organic and inorganic N sources) conserved higher amount of soil water and resulted in increased sorghum yields especially during drought years.     

Management of a previously eroded tropical Alfisol with herbaceous legumes: Soil loss and physical properties under mound tillage

A study was carried out on a previously eroded Oxic Paleustalf in Ibadan, southwestern Nigeria to determine the extent of soil degradation under mound tillage with some herbaceous legumes and residue management methods. A series of factorial experiments was carried out on 12 existing runoff plots. The study commenced in 1996 after a 5-year natural fallow. Mound tillage was introduced in 1997 till 1999. The legumes – Vigna unguiculata (cowpea), Mucuna pruriens and Pueraria phaseoloides – were intercropped with maize in 1996 and 1998 while yam was planted alone in 1997 and 1999. This paper covers 1997–1999. At the end of each year, residues were either burned or mulched on respective plots. Soil loss, runoff, variations in mound height, bulk density, soil water retention and sorptivity were measured. Cumulative runoff was similar among interactions of legume and residue management in 1997 (57–151 mm) and 1999 (206–397 mm). However, in 1998, cumulative runoff of 95 mm observed for Mucuna-burned residue was significantly greater than the 46 mm observed for cowpea-burned residue and the 39–51 mm observed for mulched residues of cowpea, Mucuna and Pueraria. Cumulative soil loss of 7.6 Mg ha⁻¹ observed for Mucuna-burned residue in 1997 was significantly greater than those for Pueraria-mulched (0.9 Mg ha⁻¹) and Mucuna-mulched (1.4 Mg ha⁻¹) residues whereas in 1999 it was similar to soil loss from cowpea treatments and Pueraria-burned residue (2.3–5.3 Mg ha⁻¹). There were no significant differences in soil loss in 1998 (1–3.2 Mg ha⁻¹) whereas Mucuna-burned residue had a greater soil loss (28.6 Mg ha⁻¹) than mulched cowpea (6.9 Mg ha⁻¹) and Pueraria (5.4 Mg ha⁻¹). Mound heights (23 cm average) decreased non-linearly with cumulative rainfall. A cumulative rainfall of 500 mm removed 0.3–2.3 cm of soil from mounds in 1997, 3.5–6.9 cm in 1998 and 2.3–4.6 cm in 1999, indicating that (detached but less transported) soil from mounds was far higher than observed soil loss in each year. Soil water retention was improved at potentials ranging from −1 to −1500 kPa by Mucuna-mulched residue compared to the various burned-residue treatments. Also, mound sorptivity at −1 cm water head (14.3 cm h^−1/2) was higher than furrow sorptivity (8.5 cm h^−1/2), indicating differences in hydraulic characteristics between mound and furrow. Pueraria-mulched residues for mounds had the highest sorptivity of 17.24 cm h^−1/2, whereas the least value of 6.96 cm h^−1/2 was observed in furrow of Mucuna-burned residue. Pueraria phas eoloides was considered the best option for soil conservation on the previously eroded soil, cultivated with mound tillage.     

Rhizosphere soil microbial index of tree species in a coal mining ecosystem

Microbial characterization of the tree rhizosphere provides important information relating to the screening of tree species for re-vegetation of degraded land. Rhizosphere soil samples collected from a few predominant tree species growing in the coal mining ecosystem of Dhanbad, India, were analyzed for soil organic carbon (SOC), mineralizable N, microbial biomass carbon (MBC), active microbial biomass carbon (AMBC), basal soil respiration (BSR), and soil enzyme activities (dehydrogenase, urease, catalase, phenol oxidase, and peroxidase). Among the tree species studied, Aegle marmelos recorded the highest value for MBC (590 mg kg⁻¹), urease (190.5 μg NH₄⁺-N g⁻¹ h⁻¹), catalase (513 μg H₂O₂ g⁻¹ h⁻¹), dehydrogenase (92.3 μg TPF g⁻¹ h⁻¹), phenol oxidase (0.057 μM g⁻¹ h⁻¹) and BSR/AMBC (0.498 mg CO₂-C mg biomass⁻¹ day⁻¹); Tamarindus indica for mineralizable N (69.5 mg kg⁻¹); Morus alba for catalase (513 μg H₂O₂ g⁻¹ h⁻¹) and phenol oxidase (0.058 μM g⁻¹ h⁻¹); Tectona grandis for peroxidase (0.276 μM g⁻¹ h⁻¹), AMBC/MBC (99.4%), and BSR/MBC (0.108 mg CO₂-C mg biomass⁻¹ day⁻¹); Ficus religiosa for AMBC (128.4 mg kg⁻¹) and BSR (12.85 mg CO₂-C kg⁻¹ day⁻¹); Eugenia jambolana for MBC/SOC (8.03%); Butea monosoperma for AMBC/SOC (1.32%) and Azadirachta indica for BSR/AMBC (0.1134 mg CO₂-C mg biomass⁻¹ day⁻¹). Principal component analysis was employed to derive a rhizosphere soil microbial index (RSMI) and accordingly, dehydrogenase, BSR/MBC, MBC/SOC, EC, phenol oxidase and AMBC were found to be the most critical properties. The observed values for the above properties were converted into a unitless score (0–1.00) and the scores were integrated into RSMI. The tree species could be arranged in decreasing order of the RSMI as: A. marmelos (0.718), A. indica (0.715), Bauhinia bauhinia (0.693), B. monosperma (0.611), E. jambolana (0.601), Moringa oleifera (0.565), Dalbergia sissoo (0.498), T. indica (0.488), Morus alba (0.415), F. religiosa (0.291), Eucalyptus sp. (0.232) and T. grandis (0.181). It was concluded that tree species in coal mining areas had diverse effects on their respective rhizosphere microbial processes, which could directly or indirectly determine the survival and performance of the planted tree species in degraded coal mining areas. Tree species with higher RSMI values could be recommended for re-vegetation of degraded coal mining area.     

Modelling multi-year coupled carbon and water fluxes in a boreal aspen forest

In order to test two hypotheses: (i) that carbon (C) and energy exchanges between terrestrial ecosystems and the atmosphere are closely constrained by soil water availability, and (ii) that vegetation is able to optimize soil water uptake from different soil layers; two model simulations were conducted. The Boreal Ecosystem Productivity Simulator (BEPS) model was run to simulate an aspen forest in Saskatchewan, Canada during the period 1997–2004. In Simulation 1, the effect of soil water availability in different soil layers on stomatal conductance was weighted only by root fraction. In Simulation 2, the influence of soil water availability in different soil layers on stomatal conductance was weighted according to both the root fraction and soil water availability, in order to allow easier access of roots to soil layers containing more water.Comparison against measured fluxes showed that Simulation 2 was an improvement over Simulation 1 in predicting C, water and energy fluxes at different time scales in dry years. In Simulation 1, the daytime C and water fluxes were underestimated during the transition from adequate to insufficient soil water content in the upper layers. In this run, the model captured 92, 79 and 91% of the daily variances in gross primary productivity (GPP), net ecosystem productivity (NEP), and ecosystem respiration (R_e) during 1997–2004. In Simulation 2, the daily variances of GPP, NEP, and R_e explained by the model increased to 93, 82 and 92%, respectively. In Simulation 1, the annual NEP was considerably underestimated in the dry years and years with dry periods, with a root mean square error (RMSE) of 45 g C m⁻² year⁻¹ (n = 8) from 1997 to 2004. In Simulation 2, the RMSE value of simulated annual NEP was reduced to 14 g C m⁻² year⁻¹, a relatively small value compared with the average NEP of 157 g C m⁻² year⁻¹ during 1997–2004. This suggested that the ability of plant roots to extract water from deep soil layers is critical for the forest to maintain growth when surface layers dried out. Our model results showed that NEP was very sensitive to water conditions at this site. In wet years, heterotrophic respiration was enhanced and NEP was reduced.     

Changes in soil organic carbon, nutrients and aggregation after conversion of native desert soil into irrigated arable land

This study aimed at investigating the effects of agricultural exploitation on desert soil organic C, N and P, and soil aggregation. Four land uses were assessed: (1) 5-year wheat (Triticum aestivum L.)/barley (Hordeum vulgare L.) + 5-year maize (Zea mays L.); (2) 5-year wheat/barley + 5-year alfalfa (Medicago sativa L.); (3) 6-year wheat/barley + 4-year acacia (Robinia pseudoacacia L.) and (4) uncultivated desert soil. The desert soil contained total organic C (TOC) of 3.1, 3.7 and 4.2 g kg⁻¹ and particulate organic C (POC) of 0.6, 0.7 and 0.8 g kg⁻¹ at 0–10, 10–20 and 20–30 cm depths, respectively. The soil TOC concentration was increased by 32–68% under wheat–maize rotation and by 27–136% under wheat–acacia at 0–20 cm depth, and by 48% under wheat–alfalfa only at 0–10 cm depth. This contrasted with an increase in the soil POC concentration by 143–167% at depth 0–20 cm under wheat–maize and by 217%, 550% at depth 0–10 cm under wheat–alfalfa and wheat–acacia, respectively. The desert soil had 13 Mg ha⁻¹ TOC stock and 2 Mg ha⁻¹ POC stock at depth 0–30 cm, whereas crop rotations increased the soil TOC stock by 30–65% and POC stock by 200–350%. Over the 10-year period, the rates of TOC accumulation were 0.6, 0.3, 0.8 Mg ha⁻¹ year⁻¹ and the rates of POC accumulation were 0.4, 0.4 and 0.7 Mg ha⁻¹ year⁻¹ under wheat–maize, wheat–alfalfa and wheat–acacia rotations, respectively. At 0–30 cm depth, total soil N was increased by 61–64% under wheat–maize and wheat–acacia, but total soil P was reduced by 38% under wheat–alfalfa. A significant improvement in clay stability but not in aggregate water-stability was observed in cultivated soils. The results showed a significant increase in soil organic C pool but unimproved macro-aggregation of the desert soil after 10 years of cultivation.     

Contribution of fine roots to ecosystem biomass and net primary production in black spruce, aspen, and jack pine forests in Saskatchewan

Fine root (<2 mm) processes contribute to and exhibit control over a large pool of labile carbon (C) in boreal forest ecosystems because of the high proportion of C allocated to fine root net primary production (NPP), and the rapid decomposition of fine roots relative to aboveground counterparts. The objective of this study was to determine the contribution of fine roots to ecosystem biomass and NPP in a mature black spruce (Picea mariana Mill.) (OBS), aspen (Populus tremuloides Michx.) (OA), and jack pine (Pinus banksiana Lamb.) (OJP) stand, and an 11-year-old harvested jack pine (HJP) stand in Saskatchewan. Estimates of fine root biomass and NPP were obtained from nine minirhizotron (MR) tubes at each of the four Boreal Ecosystem Research and Monitoring Sites (BERMS). Fine root data were collected once a month for May–September in 2003 and 2004. Additional C biomass and NPP data for various components of the forest stands were obtained from Gower et al. (1997) and Howard et al. (2004). Annual fine root biomass averaged 3.10 ± 0.89, 1.71 ± 0.49, 1.62 ± 0.32, and 2.96 ± 0.67 Mg C ha⁻¹ (means ± S.D.) at OBS, OA, OJP, and HJP, respectively, comprising between 1 and 6% of total stand biomass. Annual fine root NPP averaged 2.66 ± 0.97, 2.03 ± 0.43, 1.44 ± 0.43, and 2.16 ± 0.81 Mg C ha⁻¹ year⁻¹ (means ± S.D.) at OBS, OA, OJP, and HJP, respectively, constituting between 41 and 71% of total stand NPP. Results of this study indicate that fine roots produce a large amount of C in boreal forests. It is speculated that fine root NPP may control a large amount of labile C-cycling in boreal forests and that fine root responses to environmental and anthropogenic stress may be an early indicator of impaired ecosystem functioning.     

Eight years of carbon dioxide exchange above a mixed forest at Borden, Ontario

This paper summarizes results from 8 years (1996–2003) of eddy covariance-based ecosystem CO₂ exchange measurements at the Borden Forest Research Station (44°19′N, 79°56′W). The site represents a mid-latitude, 100-year-old, mixed deciduous and coniferous forest dominated by red maple, aspen and white pine. The years 1996 and 1997 were relatively cold, had a late spring and received below average photosynthetic photon flux density (PPFD). This contrasts with an early spring, warmer soil and air temperatures during 1998–1999, and with distinctly wet year of 2000 and dry years of 2001–2003. The combination of early spring, warmer air and soil temperature and relatively high level of PPFD was associated with higher net ecosystem productivity (NEP) that peaked during 1999. Photosynthetic capacity was reduced and NEP showed a mid-growing season depression during the dry years of 2001–2003. Annual average ecosystem respiration (R) determined from a light response model was 30% less than R derived from a logistic respiration equation, relating night time CO₂ flux and soil temperature. However these independently determined R values were well correlated indicating that the site is unaffected by fetch and spatial heterogeneity problems. Based on the combined 8 years of growing season daytime data, an air temperature of 20–25 °C and a vapor pressure deficit (VPD) of 1.3 kPa were found to be the optimal conditions for CO₂ uptake by the canopy. Over the 1996–2003 period, the forest sequestered carbon at an average rate of 140 ± 111 gC m⁻² y⁻¹. The corresponding gross ecosystem photosynthesis (GEP) and R over this period were 1116 ± 93 gC m⁻² y⁻¹ and 976 ± 68 gC m⁻² y⁻¹, respectively. The annual carbon sequestration ranged from 19 gC m⁻² in 1996 to 281 gC m⁻² in 1999. However, these estimates were sensitive to frictional velocity threshold () used for screening data associated with poor turbulent mixing at night. Increasing from 0.2 m s⁻¹ (based on the inflection point in the nighttime CO₂ flux vs. u_* relationship) to 0.35 m s⁻¹ (determined using a selection algorithm based on change-point detection) modified the 8-year mean NEP estimate from 140 ± 111 gC m⁻² y⁻¹ to 65 ± 120 gC m⁻² y⁻¹. Both approaches show that the Borden forest was a low to moderate sink of carbon over the 8-year period.     

Improving rhizospheric environment and sugarcane ratoon yield through bioagents amended farm yard manure in udic ustochrept soil

A field experiment was conducted for two crop cycles during 2003–2005 and 2004–2006 at the Indian Institute of Sugarcane Research, Lucknow in subtropical India. Trichoderma viride and Gluconacetobacter diazotrophicus amended farm yard manure (FYM) increased organic carbon (19.44 Mg ha⁻¹) and available nitrogen (260 kg N ha⁻¹) content of soil from 14.78 Mg ha⁻¹ (OC) and 204 kg N ha⁻¹ observed under farmer's practice (sole N application). Application of bioagents amended FYM improved soil porosity and reduced compaction (bulk density—1.39 Mg m⁻³ over 1.48 Mg m⁻³ under farmer's practice). Sugarcane ratoon crop removed the highest amount of nitrogen (N—165.7 kg ha⁻¹), phosphorus (P—24.01 kg ha⁻¹) and potassium (K—200.5 kg ha⁻¹) in the plots receiving FYM with Trichoderma and Gluconacetobacter. Inoculation of FYM with bioagents improved population of ammonifying and nitrifying bacteria in the soil. Phosphorus and potassium uptake of the crop was greatest in the plots receiving FYM, Trichoderma and Gluconacetobacter. Bioagents (Trichoderma and Gluconacetobacter) amended FYM increased ratoon cane (70.2 Mg ha⁻¹) and sugar yields (7.93 Mg ha⁻¹) compared with control (62.3 and 7.06 Mg ha⁻¹ ratoon cane and sugar yields, respectively).     

Effects of forest management on carabid beetles in Belgium: implications for biodiversity conservation

We sampled the carabid beetles in 22 forests managed by six different silvicultural systems, defined by treatment and tree species composition: even-aged conifer, even-aged beech, even-aged oak, uneven-aged conifer, uneven-aged beech and group mixed (beech + conifer). In each of these forests, we placed pitfall traps in young, medium-aged and mature stands (3 stages). We evaluated the effect of treatment, tree species composition, silvicultural system, stage and habitat type (silvicultural system + stage) on indicators of community conservation value and ecological structure. The species composition and the ecological structure of carabid beetles of the managed stands were then compared to that of nine unmanaged stands (without tree exploitation). In the managed forests, species richness was highest in large young stands (3-10 years old) and in forests managed by even-aged systems (with large clear-cuts), mainly due to eurytopic and opportunist carabid species with high dispersal abilities. Oak and beech, uneven-aged, and mature stands were mainly inhabited by typical forest species, and even-aged conifer stands mainly by ubiquitous species. Several typical forest species recorded in unmanaged stands were lacking from the managed forests. Large scale clear-cutting allows open-habitat species to enter the forest, which increases the species richness at a landscape level but can disfavour typical forest species by competition. Long rotations should be implemented and more areas left unmanaged in Belgium, in order to help typical forest species to re-colonise managed forests.     

Tillage and cropping sequence impacts on nitrogen cycling in dryland farming in eastern Montana, USA

Information on N cycling in dryland crops and soils as influenced by long-term tillage and cropping sequence is needed to quantify soil N sequestration, mineralization, and N balance to reduce N fertilization rate and N losses through soil processes. The 21-yr effects of the combinations of tillage and cropping sequences was evaluated on dryland crop grain and biomass (stems + leaves) N, soil surface residue N, soil N fractions, and N balance at the 0–20 cm depth in Dooley sandy loam (fine-loamy, mixed, frigid, Typic Argiboroll) in eastern Montana, USA. Treatments were no-tilled continuous spring wheat (Triticum aestivum L.) (NTCW), spring-tilled continuous spring wheat (STCW), fall- and spring-tilled continuous spring wheat (FSTCW), fall- and spring-tilled spring wheat–barley (Hordeum vulgare L.) (1984–1999) followed by spring wheat–pea (Pisum sativum L.) (2000–2004) (FSTW-B/P), and spring-tilled spring wheat–fallow (STW-F). Nitrogen fractions were soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), potential N mineralization (PNM), NH₄-N, and NO₃-N. Annualized crop grain and biomass N varied with treatments and years and mean grain and biomass N from 1984 to 2004 were 14.3–21.2 kg N ha⁻¹ greater in NTCW, STCW, FSTCW, and FSTW-B/P than in STW-F. Soil surface residue N was 9.1–15.2 kg N ha⁻¹ greater in other treatments than in STW-F in 2004. The STN at 0–20 cm was 0.39–0.96 Mg N ha⁻¹, PON 0.10–0.30 Mg N ha⁻¹, and PNM 4.6–9.4 kg N ha⁻¹ greater in other treatments than in STW-F. At 0–5 cm, STN, PON, and MBN were greater in STCW than in FSTW-B/P and STW-F. At 5–20 cm, STN and PON were greater in NTCW and STCW than in STW-F, PNM and MBN were greater in STCW than in NTCW and STW-F, and NO₃-N was greater in FSTW-B/P than in NTCW and FSTCW. Estimated N loss through leaching, volatilization, or denitrification at 0–20 cm depth increased with increasing tillage frequency or greater with fallow than with continuous cropping and ranged from 9 kg N ha⁻¹ yr⁻¹ in NTCW to 46 kg N ha⁻¹ yr⁻¹ in STW-F. Long-term no-till or spring till with continuous cropping increased dryland crop grain and biomass N, soil surface residue N, N storage, and potential N mineralization, and reduced N loss compared with the conventional system, such as STW-F, at the surface 20 cm layer. Greater tillage frequency, followed by pea inclusion in the last 5 out of 21 yr in FSTW-B/P, however, increased N availability at the subsurface layer in 2004.     

Dynamics of acetylcholinesterase activity recovery in two earthworm species following exposure to ethyl-parathion

In order for cholinesterase (ChE) activity to be used as an effective biomarker in earthworms, the time course of enzyme activity inhibition and recovery must be fully characterized. A laboratory experiment was carried out using parathion as a model organophosphorus pesticide at the recommended dose (1 mg kg⁻¹) and a 10 fold higher dose (10 mg kg⁻¹), on two earthworm species (Allolobophora chlorotica and Aporrectodea caliginosa). ChE activity and weight were measured every week for a 14 day period of exposure to parathion and then for 8 weeks in uncontaminated soil. After 3 days of exposure, the weight of both earthworm species had decreased by 10–15% compared to the control, regardless of the dose used. During the remainder of the exposure period, no differences were observed between the two doses for A. chlorotica; but A. caliginosa showed rapid weight recuperation for the lowest dose applied. After 28 days and over, the control and both exposed species of worms lost similar amounts of weight. ChE inhibition was measured during and after the exposure period. ChE inhibition followed a different time course for the two species investigated. A. chlorotica appeared less sensitive to parathion than A. caliginosa. In this latter species, ChE inhibition was rapid at close to 70% of the control after 3 days, for either dose, and reached 80–90% after 7 days exposure. While A. chlorotica exhibited the same pattern of inhibition for 10 mg kg⁻¹ of parathion, the inhibition process was slower for the recommended dose with 50% inhibition after 7 days of exposure and 70% after 14 days. ChE activity recovery, after transfer to uncontaminated soil, also followed a different pattern for the two species. After exposure to 1 mg kg⁻¹ parathion, ChE activity from A. chlorotica underwent a slow but constant recovery process to regain the control value after 8 weeks in unpolluted conditions. On the other hand, the ChE activity from A. caliginosa remained strongly inhibited. The differential susceptibility to parathion found in this study could be related to differences in the specificity of the total ChE activities between those two species.     

Carbon and nitrogen distribution in water-stable aggregates under two tillage techniques in Fluvisols of Owerri area, southeastern Nigeria

Organic matter influences soil structure and compactibility by binding soil mineral particles, reducing aggregate wettability, and influencing the mechanical strength of soil aggregates, which is the measure of coherence of inter-particle bonds. This work was carried out to examine how differences in water-stable aggregates influence the distribution of soil organic carbon and soil organic nitrogen under two tillage techniques [minimum tillage (only planting holes were opened) and conventional tillage (raised beds, 30 cm high, prepared manually with traditional hoes)] in soils of a Fluvisol in Owerri, southeastern Nigeria. Three pedons were dug and studied for each of the tillage technique along a soil sequence. Soil organic carbon and soil organic nitrogen distribution in whole soil and in water-stable aggregates under minimum tillage and conventional tillage were determined for the soils. Soil organic carbon contents in water-stable aggregates (WSA) of the pedons varied according to method of tillage. The highest mean values of soil organic carbon were obtained from minimum tillage and in water-stable aggregates 4.75–2.00 mm (16.03 Mg C ha⁻¹), 1.00–0.50 mm (14.06 Mg C ha⁻¹) and water-stable aggregates 2.00–1.00 mm (13.99 Mg C ha⁻¹) whereas under conventional tillage, water-stable aggregates 1.00–0.50 mm with soil organic carbon of 24.6 Mg C ha⁻¹ had the highest soil organic carbon content. Soil organic carbon correlated significantly with mean weight diameter (r = 0.48; P = 0.05; n = 15), water-stable aggregates 4.75–2.00 mm (r = 0.73; P = 0.05; n = 15), water-stable aggregates 2.00–1.00 mm (r = 0.55; P = 0.05, n = 15), water-stable aggregates 1.00–0.50 mm (r = 0.44; P = 0.05; n = 15) whereas no relationship was found between soil organic carbon and water-stable aggregates 0.50–0.25 mm (r = 0.15; P = 0.05; n = 15) and water-stable aggregates <0.25 mm (r = 0.17; P = 0.05; n = 15) in soils under minimum tillage. There was a significant correlation (r = 0.45–0.58; P = 0.05; n = 14) between all water-stable aggregates classes studied and soil organic carbon in soils under conventional tillage. Mean values of soil organic nitrogen were higher in soils under minimum tillage with 4.75–2.00 mm and 2.00–1.00 mm aggregate classes having 1.64 Mg N ha⁻¹ and 1.57 Mg N ha⁻¹ soil organic nitrogen when compared to 1.01 Mg N ha⁻¹ and 1.00 Mg N ha⁻¹ in conventionally tilled soils of the same aggregate classes, respectively. Larger water-stable aggregate classes (4.75–2.00; 2.00–1.00) had slightly more soil organic nitrogen (22–26%) than smaller aggregate classes (1.00–0.50; 0.50–0.25; >0.25) with 14–24% soil organic nitrogen in minimum tilled soils. In soils under conventional tillage, 1.00–0.50 mm, 0.50–0.25 mm and <0.25 mm aggregate classes contributed more soil organic nitrogen (19.66–22.40%) to the soil whereas larger water-stable aggregate classes contributed 19.22% soil organic nitrogen. The proportion of soil organic carbon and total nitrogen retained in soils with higher percentage of water-stable aggregates are less likely to be lost through soil and wind erosion. The higher values of SOC in the whole soil and WSA classes less than 2.00 mm are indications of positive influence of SOC on the stability of these peds.     

Carbon sequestration and relationship between carbon addition and storage under rainfed soybean–wheat rotation in a sandy loam soil of the Indian Himalayas

Soil organic matter (SOM) contributes to the productivity and physical properties of soils. Although crop productivity is sustained mainly through the application of organic manure in the Indian Himalayas, no information is available on the effects of long-term manure addition along with mineral fertilizers on C sequestration and the contribution of total C input towards soil organic C (SOC) storage. We analyzed results of a long-term experiment, initiated in 1973 on a sandy loam soil under rainfed conditions to determine the influence of different combinations of NPK fertilizer and fertilizer + farmyard manure (FYM) at 10 Mg ha⁻¹ on SOC content and its changes in the 0–45 cm soil depth. Concentration of SOC increased 40 and 70% in the NPK + FYM-treated plots as compared to NPK (43.1 Mg C ha⁻¹) and unfertilized control plots (35.5 Mg C ha⁻¹), respectively. Average annual contribution of C input from soybean (Glycine max (L.) Merr.) was 29% and that from wheat (Triticum aestivum L. Emend. Flori and Paol) was 24% of the harvestable above-ground biomass yield. Annual gross C input and annual rate of total SOC enrichment were 4852 and 900 kg C ha⁻¹, respectively, for the plots under NPK + FYM. It was estimated that 19% of the gross C input contributed towards the increase in SOC content. C loss from native SOM during 30 years averaged 61 kg C ha⁻¹ yr⁻¹. The estimated quantity of biomass C required to maintain equilibrium SOM content was 321 kg ha⁻¹ yr⁻¹. The total annual C input by the soybean–wheat rotation in the plots under unfertilized control was 890 kg ha⁻¹ yr⁻¹. Thus, increase in SOC concentration under long-term (30 years) rainfed soybean–wheat cropping was due to the fact that annual C input by the system was higher than the required amount to maintaining equilibrium SOM content.