Dry deposition velocity of atmospheric nitrogen in a typical red soil agro-ecosystem in Southeastern China

Atmospheric dry deposition is an important nitrogen (N) input to farmland ecosystems. The main nitrogen compounds in the atmosphere include gaseous N (NH₃, NO₂, HNO₃) and aerosol N (NH₄ ⁺/NO₃ ^?). With the knowledge of increasing agricultural effects by dry deposition of nitrogen, researchers have paid great attention to this topic. Based on the big-leaf resistance dry deposition model, dry N deposition velocities (V _d) in a typical red soil agro-ecosystem, Yingtan, Jiangxi, Southeastern China, were estimated with the data from an Auto-Meteorological Experiment Station during 2004–2007. The results show that hourly deposition velocities (V _dh) were in the range of 0.17–0.34, 0.05–0.24, 0.57–1.27, and 0.05–0.41 cm/s for NH₃, NO₂, HNO₃, and aerosol N, respectively, and the V _dh were much higher in daytime than in nighttime and had a peak value around noon. Monthly dry deposition velocities (V _dm) were in the range of 0.14–0.36, 0.06–0.18, and 0.07–0.25 cm/s for NH₃, NO₂, and aerosol N, respectively. Their minimum values appeared from June to August, while their maximum values occurred from February to March each year. The maximum value for HNO₃ deposition velocities appeared in July each year, and V _dm(HNO₃) ranged from 0.58 to 1.31 cm/s during the 4 years. As for seasonal deposition velocities (V _ds), V _ds(NH₃), V _ds(NO₂), and V _ds(aerosol N) in winter or spring were significantly higher than those in summer or autumn, while V _ds(HNO₃) in summer were higher than that in winter. In addition, there is no significant difference among all the annual means for deposition velocities (V _da). The average values for NH₃, NO₂, HNO₃, and aerosol N deposition velocities in the 4 years were 0.26, 0.12, 0.81, and 0.16 cm/s, respectively. The model is convenient and feasible to estimate dry deposition velocity of atmospheric nitrogen in the typical red soil agro-ecosystem.     

Controls on N Retention and Exports in a Forested Watershed

We conducted a 15N-tracer study in a fertilized, forested catchment at the Bear Brook Watersheds in Maine (BBWM), USA, in order to characterize N cycling processes, identify sinks for ammonium-N additions, and determine the contribution of the experimental ammonium additions to nitrate exports from the treated catchment. Distributions of 15N in plant tissues, soils, precipitation and streamwater collected before adding tracers showed that nitrate-N (the dominant form of inorganic N deposition at the site) inputs under ambient conditions were depleted in 15N relative to plants and that soil was enriched in 15N relative to plants. The 15N content of streamwater nitrate was within the range of 15N contents in natural plant tissues, suggesting that nitrate deposited from the atmosphere is reduced and assimilated into soil and plant N pools before being leached as nitrate from the catchment. Variations in 15N natural abundances also suggested that most N uptake by trees is from the forest floor and that nitrification occurs in soils at this catchment under ambient conditions. Changes in 15N contents of plant tissues, soils and streamwater after adding a 15N tracer to the ammonium sulfate fertilizer applied to the treated catchment showed that soils were the dominant sink for the labeled ammonium. Surface soils (Oca horizon plus any underlying mineral soil to 5cm depth) assimilated 19 to 31 percent of the 42 kg ha-1 of 15N-labelled ammonium-N during the tracer study. Aboveground biomass assimilated 8 to 17 percent of the labeled ammonium-N additions. Of the three forest types on the catchment, the soil:biomass assimilation ratio of labeled-N was highest in the spruce forest, intermediate in the beech-dominated hardwood forest and lowest in the mixed hardwood-spruce forest. Although ammonium sulfate additions led to increases in streamwater nitrate, only 2 of the 13 kg ha-1 of nitrate-N exported from the catchment during the 2 years of tracer additions was derived from the 42 kg ha-1 of labeled ammonium-N additions.     

Changes in soil microbial biomass and aggregate stability under different land uses in the northeastern Turkey

The characteristics of three neighboring soils from the NE of Turkey were evaluated in order to elucidate the effect of different land-use management on the soil aggregate stability and microbial biomass in Galyan-Atasu dam watershed. Three experimental sites corresponding to three land uses were selected. The first site is a hazelnut orchard (agriculture), the second site is a forest dominated by mature coniferous trees, and the third site is grassland. Soil aggregate stability values for the 1–2-mm aggregates increased from forest (lowest) to agriculture (highest) in the current study. The percentage of clay was highest in agriculture soils with 33.57 %, and overall stability values increased according to soil clay content. The lower aggregate stability in the forest soils probably reflects the highly silty texture soils with 11.95 % compared to agriculture and grassland. However, in our study, there were no significant correlations between aggregate stability and organic C concentrations either in cultivated or forested soils. Aggregate stability depended more on the organic matter content when the organic matter content was greater than 50 or 60 mg g^?1. Below that threshold, aggregate stability may be mainly related to clay content. Furthermore, the results confirmed that higher percentages of Cmic/Corg in agricultural soils are the result of more labile organic substrates maintained in the soil, allowing a higher microbial biomass C per unit of soil organic C. This work gives a better understanding of the relationships between land-use type and soil aggregation and allows to know the soil response to different types of management in humid environments.     

Correlation between soil characteristics and lead and cadmium content in the aboveground biomass of Virginia tobacco

The study was conducted on alluvial-meadow, maroon-forest soils and vertisols with Virginia tobacco. The total content of lead and cadmium is measured through decomposition by HF, HClO₄, and HNO₃ acids. A solution of 0.005 M diethylentriaminepentaacetic acid + 0.1 M triethanolamine, pH 7.3 was used for extraction of the elements’ mobile forms from soils. The preparation of plant samples was made by means of dry ashing and dissolution in 3 M HCl. An atomic absorption spectrometer “Spektra AA 220” of the Australian company Varian was used for determination of Pb and Cd content in the soil and plant samples. Certified reference materials (three soils and tobacco leaves) were also analyzed for the verification of the accuracy of Pb and Cd determination. A correlation/regression analysis was conducted between pH, humus content, total and mobile forms of lead and cadmium in the soil, and the concentration of these elements in the aboveground biomass of Virginia tobacco. It was established that there are no statistically significant dependencies determined between soil pH and lead concentration in the plant organs of Virginia tobacco. Regressional dependencies of great significance were determined between the humus content, total and mobile lead and cadmium in the soil, and the element concentration in the leaves of the three harvesting zones.     

Pre-incubation in soil improves the nitrogen fertiliser value of hair waste

Global generation of human hair waste and its disposal at landfills could contribute to the leaching of nitrates into ground water. High concentrations of nitrogen (N) and other elements suggest that the waste could be a source of plant nutrients and differences in ethnic hair types could affect nutrient release and fertiliser value. The objective of this study was to determine the effects of hair type, as an N source, and pre-incubation time on dry-matter yield, nutrient uptake by spinach (Spinacia oleracea L.) and residual soil nutrients. Salons in Pietermaritzburg provided bulk African and Caucasian hair waste, without distinguishing age, sex, health status or livelihood of the individuals. The hair waste was analysed for elemental composition. A pot experiment was set up under glasshouse conditions. The hair waste was incorporated (400 kg N ha^?1) into a loamy oxisol and pre-incubated for 0, 28, 56 and 84 days before planting spinach. Potassium (K) and phosphorus (P) were corrected to the same level for all treatments. Spinach seedlings were then cultivated for 6 weeks. Shoot dry-matter and the uptake of all nutrients, except P, were increased by the pre-incubation of hair. African hair pre-incubated for 28 days resulted in greater dry-matter, N, K, Mn and S uptake than Caucasian hair. Increasing pre-incubation resulted in a decline in the residual soil pH and exchangeable K. The findings suggested that pre-incubation improves the N fertiliser value of hair and that African hair has greater value than Caucasian hair when pre-incubated for a short period.     

Biogeochemical indicators of elevated nitrogen deposition in semiarid Mediterranean ecosystems

Nitrogen (N) deposition has doubled the natural N inputs received by ecosystems through biological N fixation and is currently a global problem that is affecting the Mediterranean regions. We evaluated the existing relationships between increased atmospheric N deposition and biogeochemical indicators related to soil chemical factors and cryptogam species across semiarid central, southern, and eastern Spain. The cryptogam species studied were the biocrust-forming species Pleurochaete squarrosa (moss) and Cladonia foliacea (lichen). Sampling sites were chosen in Quercus coccifera (kermes oak) shrublands and Pinus halepensis (Aleppo pine) forests to cover a range of inorganic N deposition representative of the levels found in the Iberian Peninsula (between 4.4 and 8.1 kg N ha^?1 year^?1). We extended the ambient N deposition gradient by including experimental plots to which N had been added for 3 years at rates of 10, 20, and 50 kg N ha^?1 year^?1. Overall, N deposition (extant plus simulated) increased soil inorganic N availability and caused soil acidification. Nitrogen deposition increased phosphomonoesterase (PME) enzyme activity and PME/nitrate reductase (NR) ratio in both species, whereas the NR activity was reduced only in the moss. Responses of PME and NR activities were attributed to an induced N to phosphorus imbalance and to N saturation, respectively. When only considering the ambient N deposition, soil organic C and N contents were positively related to N deposition, a response driven by pine forests. The PME/NR ratios of the moss were better predictors of N deposition rates than PME or NR activities alone in shrublands, whereas no correlation between N deposition and the lichen physiology was observed. We conclude that integrative physiological measurements, such as PME/NR ratios, measured on sensitive species such as P. squarrosa, can provide useful data for national-scale biomonitoring programs, whereas soil acidification and soil C and N storage could be useful as additional corroborating ecosystem indicators of chronic N pollution.     

Atmospheric inorganic nitrogen deposition to a typical red soil forestland in southeastern China

A 2-year monitoring study was conducted to estimate nitrogen deposition to a typical red soil forestland in southeastern China. The dry deposition velocities (V(d)) were estimated using big leaf resistance analogy model. Atmospheric nitrogen dry deposition was estimated by combing V(d) and nitrogen compounds concentrations, and the wet deposition was calculated via rainfall and nitrogen concentrations in rainwater. The total inorganic nitrogen deposition was 83.7 kg ha(-1) a(-1) in 2004 and 81.3 kg ha(-1) a(-1) in 2005, respectively. The dry deposition contributed 78.6% to total nitrogen deposition, in which ammonia was the predominant contributor that accounted for 86.1%. Reduced nitrogen compounds were the predominant contributors, accounting for 78.3% of total nitrogen deposition. The results suggested that atmospheric inorganic nitrogen could be attributed to intensive agricultural practices such as excessive nitrogen fertilization and livestock production. Therefore, impacts of atmospheric nitrogen originated from agriculture practices on nearby forest ecosystems should be evaluated.     

Spatial and seasonal distribution of nitrogen in marsh soils of a typical floodplain wetland in Northeast China

Horizontal and profile distributions of nitrogen in marsh soils in different seasons were studied in a typical site within the Erbaifangzi wetland in Northeast China. Results showed that there was higher spatial heterogeneity for nitrate nitrogen (NO₃^--_{3}^{-}-N) and ammonium nitrogen (NH₄⁺_{4}^{+}–N), as well as available nitrogen (AN), in surface soils in July compared to that in September. Relative to July, the mean nitrogen contents in surface soils were slightly higher in September; however, in November, soils contained significantly lower NO₃^--_{3}^{-}-N and NH₄⁺_{4}^{+}–N, higher AN, organic nitrogen (Org-N), and total nitrogen (TN). Except for mineral nitrogen, no significant differences were observed between Org-N and TN contents in September and November. Nitrogen contents generally declined exponentially with depth along soil profiles in three sampling dates (July, September, and November), except for a significant accumulation peak of NO₃^--_{3}^{-}-N at the 20–30 cm depth in September. However, NH₄⁺_{4}^{+}–N contents showed a vertical alternation of “increasing and decreasing” in both July and September, while nearly kept constant with depth in November. The depth ranking of nitrogen showed the shallowest distribution for AN, followed by Org-N and TN, while deeper distributions for NO₃^--_{3}^{-}-N and NH₄⁺_{4}^{+}–N. TN, Org-N, and AN were significantly correlated with soil organic matter and total phosphorus. Soil pH values were significantly correlated with TN and AN contents in surface soils. Clay contents showed significant correlations with nitrogen contents except for NO₃^--_{3}^{-}-N in surface soils and NH₄⁺_{4}^{+}–N in profile soils. However, soil moisture was not significantly correlated with nitrogen contents among all soil samples.     

Nitrification,soil acidification and streamwater chemistry following deglaciation,glacier bay national park and preserve

A major tool used in the assessment of anthropic atmospheric effects on aquatic and terrestrial ecosystems is biogeochemical nutrient cycling and budgets. However, to be most effective such study should be done in an ecosystem context. Also some assessment of natural variation in factors affecting nutrient cycling must be in place before trends, often subtle and long-term, attributable to man can be statistically quantified. The input and output balance of chemical species in watershed ecosystems is considerably influenced by ecosystem succession. It is hypothesized that during primary ecosystem succession chemical element output is initially relatively high due to rapid acidification and lack of plant uptake. Outputs decline during the period of high ecosystem productivity and biomass accumulation, and they again rise during late successional stages to approximate inputs from precipitation weathering, and aerosol capture. Glacier Bay provides a unique opportunity to quantify many mechanisms responsible for variation in nutrient cycles without the need for site manipulation. This is especially true for quantifying the rate and magnitude of natural acidification in ecosystems. The park has a spectrum of watersheds differing in stage of primary and secondary succession following deglaciation. These sites are not now subjected to or altered by anthropic atmospheric inputs. The objectives of this research were (1) determine the rate of soil chemical change which occurs following deglaciation, (2) relate soil acidification to presence of organic matter, soil NO _inf3 ^sup- , and total N, (3) estimate the downward movement of ionic species within the soil profiles with increasing acidification from advancing plant succession, and (4) determine if such processes and ionic movements might be reflected in watershed stream ionic outputs. We studied five watersheds ranging from 40–350 years since deglaciation. Soil samples were collected and lysimeters installed in seven vegetation successional stages following deglaciation. An anion of ecological importance and a common air contaminant is NO _inf3 ^sup- , and its discharge in streamflow from early successional ecosystems was found to be high. The terrestrial biota in such systems was dominated by Alnus sinuata, a major nitrogen fixer. Stream discharge of NO _inf3 ^sup- suggested that early successional ecosystem N fixation exceeded biotic uptake. This was confirmed by examining NO _inf3 ^sup- in soil extractions and lysimeters. This process was particularly evident beneath >20-year old Alnus (forty years since deglaciation). concurrent with increased NO _inf3 ^sup- concentrations below the rooting zone was increased H⁺ which increased 100x during 25 years of primary succession. This natural acidification from a mobile NO _inf3 ^sup- ion resulted in an pronounced increase in soil base cation leaching and mobilization of aluminium in the soil profile. The magnitude and short time required for such acidification greatly exceeded anything projected or modeled for systems impacted by anthropic inputs. Stream SO _inf4 ^sup2- concentrations also were high relative to precipitation inputs suggesting mineralization of sulfur within the ecosystem and/or poor soil adsorption of SO _inf4 ^sup2- . This is an important finding in such ecosystems where cation nutrient ion levels are often very low. Should atmospheric inputs of SO _inf4 ^sup2- increase additional loss of cations appears imminent. These data suggest that most early successional ecosystems at Glacier Bay would be sensitive to anthropic inputs of both NO _inf3 ^sup- and SO _inf4 ^sup2- . This is unusual in other ecosystems where many conserve ionic NO _inf3 ^sup- inputs, and older systems have considerable SO _inf4 ^sup2- adsorption capacity. The effect of any increased atmospheric inputs of these ions would be accelerated cation leaching and ecosystem acidification.Contribution from Fourth World Wilderness Congress—Acid Rain Symposium, Denver (Estes Park), Colorado, September 11–18, 1987.     

Introduction of the Factor of Partitioning in the Lithogenic Enrichment Factors of Trace Element Bioaccumulation in Plant Tissues

Bioindicators are widely used in the study of trace elements inputs into the environment and great efforts have been conducted to separate atmospheric from soil borne inputs on biomass accumulation. Many monitoring studies of trace element pollution take into account the dust particles located in the plant surface plus the contents of the plant tissues. However, it is usually only the trace element content in the plant tissues that is relevant on plant health. Enrichment factor equations take into account the trace element enrichment of biomasses with respect soil or bedrocks by comparing the ratios of the trace element in question to a lithogenic element, usually Al. However, the enrichment equations currently in use are inadequate because they do not take into account the fact that Al (or whichever reference element) and the element in question may have different solubility-absorption-retention levels depending on the rock and soil types involved. This constrain will become critical when results from different sites are compared and so in this article we propose that the solubility factors of each element are taken into account in order to overcome this constrain. We analysed Sb, Co, Ni, Cr, Pb, Cd, Mn, V, Zn, Cu, As, Hg, and Al concentration in different zones of Catalonia (NE Spain) using the evergreen oak Quercus ilex and the moss Hypnum cupressiforme as target species. We compared the results obtained in rural and non industrial areas with those from the Barcelona Metropolitan Area. We observed differences in Al concentrations of soils and bedrocks at each different site, together with the differences in solubility between Al and the element in question, and a weak correlation between total soil content and water extract content through different sites for most trace elements. All these findings show the unsuitability of the current enrichment factors for calculating lithospheric and atmospheric contributions to trace element concentrations in biomass tissues. The trace element enrichment factors were calculated by subtracting the part predicted by substrate composition (deduced from water extracts from soils and bedrock) from total concentrations. Results showed that for most of the trace elements analysed, trace elements enrichment factors were higher inside the Barcelona Metropolitan Area than outside, a finding that indicates that greater atmospheric inputs occur in urban areas. The results show that the most useful and correct way of establishing a reference for lithospheric and atmospheric inputs into the plant tissues is, first, to analyse samples of the same plant species collected from a number of sites possessing similar environmental conditions (climate, vegetation type, soil type) and, second, to use this new enrichment factor obtained by subtracting from the total concentration in plant tissue the predicted contribution of soil or bedrock extracts instead of that of total soil or bedrock concentrations.     

Toxicity assessment for petroleum-contaminated soil using terrestrial invertebrates and plant bioassays

The assessment of soil quality after a chemical or oil spill and/or remediation effort may be measured by evaluating the toxicity of soil organisms. To enhance our understanding of the soil quality resulting from laboratory and oil field spill remediation, we assessed toxicity levels by using earthworms and springtails testing and plant growth experiments. Total petroleum hydrocarbons (TPH)-contaminated soil samples were collected from an oilfield in Sfax, Tunisia. Two types of bioassays were performed. The first assessed the toxicity of spiked crude oil (API gravity 32) in Organization for Economic Co-operation and Development artificial soil. The second evaluated the habitat function through the avoidance responses of earthworms and springtails and the ability of Avena sativa to grow in TPH-contaminated soils diluted with farmland soil. The EC₅₀ of petroleum-contaminated soil for earthworms was 644 mg of TPH/kg of soil at 14 days, with 67 % of the earthworms dying after 14 days when the TPH content reached 1,000 mg/kg. The average germination rate, calculated 8 days after sowing, varied between 64 and 74 % in low contaminated soils and less than 50 % in highly contaminated soils.     

Nitrogen enrichment in runoff sediments as affected by soil texture in Beijing mountain area

Enrichment ratio (ER) is widely used in nonpoint source pollution models to estimate the nutrient loss associated with soil erosion. The objective of this study was to determine the ER of total nitrogen (ER_N) in the sediments eroded from the typical soils with varying soil textures in Beijing mountain area. Each of the four soils was packed into a 40 by 30 by 15 cm soil pan and received 40-min simulated rainfalls at the intensity of 90 mm h^?1 on five slopes. ER_N for most sediments were above unity, indicating the common occurrence of nitrogen enrichment accompanied with soil erosion in Beijing mountain area. Soil texture was not the only factor that influenced N enrichment in this experiment since the ER_N for the two fine-textured soils were not always lower. Soil properties such as soil structure might exert a more important influence in some circumstances. The selective erosion of clay particles was the main reason for N enrichment, as implied by the significant positive correlation between the ER of total nitrogen and clay fraction in eroded sediments. Significant regression equations between ER_N and sediment yield were obtained for two pairs of soils, which were artificially categorized by soil texture. The one for fine-textured soils had greater intercept and more negative slope. Thus, the initially higher ER_N would be lower than that for the other two soils with coarser texture once the sediment yield exceeded 629 kg ha^?1.     

Assessment of soil nitrogen and related enzymes as influenced by the incorporation time of field pea cultivated as a catch crop in Alfisol

The effect of the time of catch crop (field pea) incorporation [catch crop incorporated in the autumn (A) or in the spring (B) versus plots without a catch crop (C)] on the soil enzymes related to N transformation (urease – UR, protease – PRO, nitrate reductase – NR, arginine ammonification rate – AAR), the total N and mineral N as well as microbial biomass N (MBN) contents were investigated in a 3-year experiment. The catch crop was sown at the beginning of August and plowed in the autumn in 2008, 2009 and 2010 or left as mulch during the winter. Soil samples for microbial activity were taken from spring barley plots that were grown in 2009, 2010 and 2011 before sowing (March), during the tillering phase (May), shooting (June) and after the harvesting of spring barley (August). The use of catch crop significantly increased the soil mineral and MBN contents as well as the activities of PRO and NR as compared to the control soil. The spring incorporation of the field pea significantly increased the MBN content in contrast to the autumn application, while the activity of N-cycle enzymes were clearly unaffected (UR and AAR) regardless of the time of the incorporation of field pea or else the results were inconsistent (PRO and NR). When the catch crop was incorporated in the spring, a significantly higher content of mineral N as compared to autumn incorporation was noted on only two of the four sampling dates. The enzymatic activity (PRO and AAR) was about 1.3-2.8 times higher in May and June as compared with March and August. Both spring or autumn incorporation of catch crop can be a useful management practice to increase the soil mineral N content and enhance the soil biological activity.     

Occurrence, distribution, and source of polybrominated diphenyl ethers in soil and leaves from Shenzhen Special Economic Zone, China

Polybrominated diphenyl ethers (PBDEs) were measured in soil and three plant species samples taken at different land use areas in Shenzhen China. The concentrations of ??₇BDEs (BDE-28, BDE-47, BDE-99, BDE-100, BDE-153, BDE-154, and BDE-183) and BDE-209 in the surface soils ranged from 0.23 to 271 and 8.9 to 5,956 ng/g dry weight (dw), respectively. These figures are comparable to that in the soils of electronic waste dismantling sites. BDE-209 was the predominant congener (contributes 85?C99% of ??₈PBDEs (??₇PBDEs plus BDE-209)) in soils. The regression slopes of total organic carbon and individual BDE congeners were rather gentle, indicating that factors other than soil organic matter regulated the soil concentrations. Proximity to sources of deposition processes might be the major factors. In the plant leaves, ??₇BDEs and BDE-209 concentrations ranged from 1.29 to 5.91 and 5.49 to 28.2 ng/g dw, respectively. BDE-209 is also the dominant component, but the contribution was much lower compared with that in soils. Bauhinia purpurea Linn. and Michelia alba DC. show some similarities on the uptake of PBDEs, while Ficus microcarpa var. pusillifolia is different from them. The correlations between plant leaf concentrations and predicted gaseous concentrations were moderate, indicating that gaseous concentration did not influence the leaf concentration significantly.     

Spatial and temporal variation of moisture content in the soil profiles of two different agricultural fields of semi-arid region

Modeling spatio-temporal variation of soil moisture with depth in the soil profile plays an important role for semi-arid crop production from an agro-hydrological perspective. This study was performed in Guvenc Catchment. Two soil series that were called Tabyabayir (TaS) and Kervanpinari (KeS) and classified as Leptosol and Vertisol Soil Groups were used in this research. The TeS has a much shallower (0–34 cm) than the KeS (0–134 cm). At every sampling time, a total of geo-referenced 100 soil moisture samples were taken based on horizon depths. The results indicated that soil moisture content changed spatially and temporally with soil texture and profile depth significantly. In addition, land use was to be important factor when soil was shallow. When the soil conditions were towards to dry, higher values for the coefficient of variation (CV) were observed for TaS (58 and 43 % for A and C horizons, respectively); however, the profile CV values were rather stable at the KeS. Spatial variability range of TaS was always higher at both dry and wet soil conditions when compared to that of KeS. Excessive drying of soil prevented to describe any spatial model for surface horizon, additionally resulting in a high nugget variance in the subsurface horizon for the TaS. On the contrary to TaS, distribution maps were formed all horizons for the KeS at any measurement times. These maps, depicting both dry and wet soil conditions through the profile depth, are highly expected to reduce the uncertainty associated with spatially and temporally determining the hydraulic responses of the catchment soils.     

Non-target effect of organic insecticides: effect of two plant extracts on soil microbial biomass and enzymatic activities in soil

Efficacious botanical derivatives can provide an alternative to synthetic pesticides for organic farming systems. However, there is lack of information regarding the side effects of organic pesticides on key soil ecological processes. In this study, we investigated the effects of aqueous extracts from Urginea maritima and Euphorbia myrsinites exhibiting translaminar and systemic activity against pests on microbial biomass and enzymatic activities in soil. Two grams of plant material was extracted with 100 ml of water and then diluted 1:100, 2:100, and 4:100 with distilled water. Diluted plant extracts were applied around hypocotyl of tomato by soil drench. The effect of both plant extracts on microbial biomass C, amount of total N and organic C, and enzymatic activity in soil was significant. After the last application, the highest microbial biomass C was determined in the lowest U. maritima concentration (U 1:100). Soils treated with the highest concentration of U. maritima (U 4:100) had always lower SMBC content than control soil. All concentrations of E. myrsinites decreased microbial biomass C by 18% to 27% compared to the control. Total nitrogen and organic carbon decreased in soils without (control) and with treated U. maritima extract from first application to last application. Phosphatase, urease, and β-glucosidase activities were monitored in plant extract-treated soils. Except U. maritima 1:100 treatments of second and fourth applications, the other treatments of plant extracts negatively affected enzymatic activity in soil. U. maritima and E. myrsinites plant extracts exhibited different effects on soil microbial biomass and activity, probably because of their different chemical contents.     

Acid soil indicators in forest soils of the Cherry River Watershed, West Virginia

Declining forest health has been observed during the past several decades in several areas of the eastern USA, and some of this decline is attributed to acid deposition. Decreases in soil pH and increases in soil acidity are indicators of potential impacts on tree growth due to acid inputs and Al toxicity. The Cherry River watershed, which lies within the Monongahela National Forest in West Virginia, has some of the highest rates of acid deposition in Appalachia. East and West areas within the watershed, which showed differences in precipitation, stream chemistry, and vegetation composition, were compared to evaluate soil acidity conditions and to assess their degree of risk on tree growth. Thirty-one soil pits in the West area and 36 pits in the East area were dug and described, and soil samples from each horizon were analyzed for chemical parameters. In A horizons, East area soils averaged 3.7 pH with 9.4 cmol_c kg^???1 of acidity compared to pH 4.0 and 6.2 cmol_c kg^???1 of acidity in West area soils. Extractable cations (Ca, Mg, and Al) were significantly higher in the A, transition, and upper B horizons of East versus West soils. However, even with differences in cation concentrations, Ca/Al molar ratios were similar for East and West soils. For both sites using the Ca/Al ratio, a 50% risk of impaired tree growth was found for A horizons, while a 75% risk was found for deeper horizons. Low concentrations of base cations and high extractable Al in these soils translate into a high degree of risk for forest regeneration and tree growth after conventional tree harvesting.     

Nitrogen mineralization in O horizon soils during 27 years of nitrogen enrichment at the Bear Brook Watershed in Maine,USA

Chronic elevated nitrogen (N) deposition has altered the N status of temperate forests, with significant implications for ecosystem function. The Bear Brook Watershed in Maine (BBWM) is a whole paired watershed manipulation experiment established to study the effects of N and sulfur (S) deposition on ecosystem function. N was added bimonthly as (NH₄)₂SO₄ to one watershed from 1989 to 2016, and research at the site has studied the evolution of ecosystem response to the treatment through time. Here, we synthesize results from 27 years of research at the site and describe the temporal trend of N availability and N mineralization at BBWM in response to chronic N deposition. Our findings suggest that there was a delayed response in soil N dynamics, since labile soil N concentrations did not show increases in the treated watershed (West Bear, WB) compared to the reference watershed (East Bear, EB) until after the first 4 years of treatment. Labile N became increasingly available in WB through time, and after 25 years of manipulations, treated soils had 10× more extractable ammonium than EB soils. The WB soils had 200× more extractable nitrate than EB soils, driven by both, high nitrate concentrations in WB and low nitrate concentrations in EB. Nitrification rates increased in WB soils and accounted for ~?50% of net N mineralization, compared to ~?5% in EB soils. The study provides evidence of the decadal evolution in soil function at BBWM and illustrates the importance of long-term data to capture ecosystem response to chronic disturbance.     

A method for assessing generalised nitrogen leaching estimates for agricultural land

The purpose of this study was to develop a method for assessing generalised N leaching estimates from large areas of agricultural land. The system developed was based on calculating a number of N leaching estimates for different typical cropping situations. The estimates were normalised with respect to varying weather conditions and crop production. The different cropping situations were described by setting up a matrix consisting of crucial factors influencing leaching such as soils, crops and climate. Nitrogen leaching was then estimated for a number of combinations of these factors. Calculations were made for three different regions where all the major crops were cultivated on soils with seven different textures and four different organic-N classes and two fertilisation regimes. The three regions are representative of climates and agricultural practices in some of the major agricultural areas in Sweden. The model used was the SOILN model. Leaching of nitrogen from the root zone showed large variations. The range was from 1 to 50 kg ha⁻¹ for different soils and crops when only fertiliser N was applied. Leaching varied both due to different climates and differences in cultivation practices between the regions. Leaching decreased in a south-north gradient. Leaching increased as a result of greater mineralisation when the organic matter content in the soils was increased, leaching was less from soils with a high clay content and was very small for the heavy clay soil. This revised version was published online in July 2006 with corrections to the Cover Date.