Extractable Nitrate Research Articles

Extractable nitrogen and microbial community structure respond to grassland restoration regardless of historical context and soil composition.

Grasslands have a long history of invasion by exotic annuals, which may alter microbial communities and nutrient cycling through changes in litter quality and biomass turnover rates. We compared plant community composition, soil chemical and microbial community composition, potential soil respiration and nitrogen (N) turnover rates between invaded and restored plots in inland and coastal grasslands. Restoration increased microbial biomass and fungal : bacterial (F : B) ratios, but sampling season had a greater influence on the F : B ratio than did restoration. Microbial community composition assessed by phospholipid fatty acid was altered by restoration, but also varied by season and by site. Total soil carbon (C) and N and potential soil respiration did not differ between treatments, but N mineralization decreased while extractable nitrate and nitrification and N immobilization rate increased in restored compared with unrestored sites. The differences in soil chemistry and microbial community composition between unrestored and restored sites indicate that these soils are responsive, and therefore not resistant to feedbacks caused by changes in vegetation type. The resilience, or recovery, of these soils is difficult to assess in the absence of uninvaded control grasslands. However, the rapid changes in microbial and N cycling characteristics following removal of invasives in both grassland sites suggest that the soils are resilient to invasion. The lack of change in total C and N pools may provide a buffer that promotes resilience of labile pools and microbial community structure.

Mobilization of selenium from the Mancos Shale and associated soils in the lower Uncompahgre River Basin, Colorado

This study investigates processes controlling mobilization of selenium in the lower part of the Uncompahgre River Basin in western Colorado. Selenium occurs naturally in the underlying Mancos Shale and is leached to groundwater and surface water by limited natural runoff, agricultural and domestic irrigation, and leakage from irrigation canals. Soil and sediment samples from the study area were tested using sequential extractions to identify the forms of selenium present in solid phases. Selenium speciation was characterized for nonirrigated and irrigated soils from an agricultural site and sediments from a wetland formed by a leaking canal. In nonirrigated areas, selenium was present in highly soluble sodium salts and gypsum. In irrigated soils, soluble forms of selenium were depleted and most selenium was associated with organic matter that was stable under near-surface weathering conditions. Laboratory leaching experiments and geochemical modeling confirm that selenium primarily is released to groundwater and surface water by dissolution of highly soluble selenium-bearing salts and gypsum present in soils and bedrock. Rates of selenium dissolution determined from column leachate experiments indicate that selenium is released most rapidly when water is applied to previously nonirrigated soils and sediment. High concentrations of extractable nitrate also were found in nonirrigated soils and bedrock that appear to be partially derived from weathered organic matter from the shale rather than from agricultural sources. Once selenium is mobilized, dissolved nitrate derived from natural sources appears to inhibit the reduction of dissolved selenium leading to elevated concentrations of selenium in groundwater. A conceptual model of selenium weathering is presented and used to explain seasonal variations in the surface-water chemistry of Loutzenhizer Arroyo, a major tributary contributor of selenium to the lower Uncompahgre River.

Soil freezing and N deposition: Transient vs. multi-year effects on extractable C and N, potential trace gas losses and microbial biomass

Decreased snow cover can increase soil freezing, potentially altering soil nitrogen (N) and carbon (C) availability and losses. However, it is unclear how increased soil freezing severity may interact with increased atmospheric N deposition, and to what extent these effects may extend over multiple growing seasons in herbaceous systems. We examined the interactive effects of increased soil freezing and N addition on extractable N and C pools, potential trace gas losses, and microbial biomass in a grass-dominated temperate old field. We used both a snow removal experiment and plant-soil mesocosms that were frozen under controlled conditions for one week and then returned to the field. For both experiments, the freezing treatments were only conducted over the first winter, with the legacy effects of freezing monitored over three subsequent years. As we predicted, soil freezing increased potential trace gas losses, soil extractable C and N and microbial biomass C and N during the first year, although these effects were transient. Nitrogen effects, when significant, generally did not interact with freezing. Legacy effects of snow removal were mostly absent in the second year, but the latter was very dry, and in the third year the legacy of snow removal resulted in increased extractable nitrate, potential N2O losses and microbial biomass N, and decreased fungal biomass and microbial biomass C. Overall, our results demonstrate that while the immediate soil N and C responses to freezing are mostly transient, legacy effects of soil freezing on soil N and C pools and microbial biomass can persist over multiple years, possibly as a result of changes to plant productivity and litter deposition.

Assessment of Environmentally Harmful Nitrogen Surplus by 0.01 M Calcium Chloride Soil Extractant in Long-Term Experiments

Calcium chloride–extractable (1:10 soil/solution ratio, w/v) nitrate nitrogen (NO3-N), ammonium nitrogen (NH4-N), organic nitrogen (EON), and Ntotal fractions were measured in two long-term experiments. Both experiments are located in the Great Hungarian Plain. The first experiment was established on a Luvic Phaeozem soil and the second experiment was on a Calcic Chernozem soil. Researchers investigated the effects of long-term fertilization and irrigation on the amounts of nitrogen (N) fractions. Nitrogen rates caused significant increase in NO3-N and Ntotal fractions. These fractions were in close correlation (r = 0.87; r = 0.88) with nitrogen balance. The nitrate content of the 200-cm-deep soil layer of soils under different nitrogen- and water-supply conditions were also studied. As an effect of N overfertilization, the maximum nitrate accumulation on nonirrigated plots occurred in the 200-cm depth, whereas on irrigated plots a nitrate accumulation layer could not be observed in the 200-cm-deep soil layer.

Environmental effects on distributions of culturable soil oligotrophic bacteria along an elevational gradient in the Chihuahuan Desert

Oligotrophic bacteria have been isolated from many habitats, yet environmental regulation of their distributions in soil has not been elucidated. To address the issue of environmental influence upon oligotrophic distributions, Chihuahuan Desert soils were sampled from five sites along an elevational and vegetational gradient within Big Bend National Park during January and August of 2002 and 2003. Soils were diluted and plated on oligotrophic media, and plates were incubated at 15, 25, 35, 45 and 60 °C. Additionally, measurements of soil organic matter, pH, moisture, extractable nitrate, extractable ammonium and microbial biomass carbon were collected for each sample to relate oligotrophic bacterial distributions to soil nutrient and edaphic characteristics. Analysis of variance indicated significant site, season, incubation-temperature and interaction effects on total oligotroph numbers. Canonical correspondence analysis and multiple regressions indicated that all soil-chemistry variables significantly influenced discrete morphologies of oligotrophs. Oligotroph distributions were most congruent with soil-chemistry variation in three sites, whereas oligotrophic diversity in two sites did not adhere closely to measured environmental variables. While vegetation type may structure oligotroph communities at the two mid-elevational sites, abiotic constraints are drivers in low-desert sites.

When Wet Gets Wetter: Decoupling of Moisture, Redox Biogeochemistry, and Greenhouse Gas Fluxes in a Humid Tropical Forest Soil

Upland humid tropical forest soils are often characterized by fluctuating redox dynamics that vary temporally and spatially across the landscape. An increase in the frequency and intensity of rainfall events with climate change is likely to affect soil redox reactions that control the production and emissions of greenhouse gases. We used a 24-day rainfall manipulation experiment to evaluate temporal and spatial trends of surface soil (0‐20 cm) redox-active chemical species and greenhouse gas fluxes in the Luquillo Experimental Forest, Puerto Rico. Treatments consisted of a high rainfall simulation (60 mm day -1 ), afl uctuating rainfall regime, and a control. Water addition generated high temporal and spatial variation in soil moisture (0.3‐0.6 m 3 m -3 ), but had no significant effect on soil oxygen (O2) concentrations. Extractable nitrate (NO3 - ) concentrations decreased with daily water additions and reduced iron (Fe(II)) concentrations increased towards the end of the experiment. Overall, redox indicators displayed a weak, non-deterministic, nonlinear relationship with soil moisture. High concentrations of Fe(II) and manganese (Mn) were present even where moisture was relatively low, and net Mn reduction occurred in all plots including controls. Mean CO2 fluxes were best explained by soil C concentrations and a composite redox indicator, and not water addition. Several plots were CH4 sources irrespective of water addition, whereas other plots oscillated between weak CH4 sources and sinks. Fluxes of N2 Ow ere highest in control plots and were consistently low in water-addition plots. Together, these data suggest (1) a relative decoupling between soil moisture and redox processes at our spatial and temporal scales of measurement, (2) the co-occurrence of aerobic and anaerobic biogeochemical processes in well-drained surface soils, and (3) an absence of threshold effects from sustained precipitation on redox reactions over the scale of weeks. Our data suggest a need to re-evaluate representations of moisture in biogeochemical models.

Characterizing nitrogen transfer from red clover populations to companion bluegrass under field conditions

Thilakarathna, R. M. M. S., Papadopoulos, Y. A., Rodd, A. V., Gunawardena, A. N., Fillmore, S. A. E. and Prithiviraj, B. 2012. Characterizing nitrogen transfer from red clover populations to companion bluegrass under field conditions. Can. J. Plant Sci. 92: 1163–1173. The ability of two red clover (Trifolium pratense L.) cultivars, AC Christie (diploid) and Tempus (tetraploid), to transfer fixed nitrogen (N) to companion bluegrass (Poa pratensis L.) was evaluated under field conditions. Plant samples were harvested three times during the 2009 growing season and N transfer from the red clover cultivars to bluegrass was determined using the natural abundance method for first harvest and 15N dilution techniques for second and third harvests. Soil and soil water samples were used to evaluate cultivar effects on soil N conditions. Both red clover cultivars derived more than 90% of their N from biological N fixation. The proportion of bluegrass N derived from interplant N transfer was 7, 11, and 26% for the first, second, and third harvests, respectively. Soil KCl extractable nitrate increased along the three cuts for Tempus in the 0 to 15-cm soil zone. Soil-water nitrate content increased periodically for AC Christie and remained constant for Tempus throughout the growing season. This result indicates that the two cultivars have distinctly different N cycling patterns.

Do legumes and non-legumes tree species affect soil properties in unmanaged forests and plantations in Costa Rican dry forests?

Legume tree species, which are abundant in tropical dry forests, may be a critical regulator of soil nutrient dynamics because of their high foliar nitrogen (N) and potential for symbiotic N fixation. We investigated whether three legume tree species (Acosmium panamense, Dalbergia retusa, and Gliricidia sepium) have distinct soil chemistry under their crowns compared to nearby non-legume species (Rehdera trinervis, Swietenia macrophylla, and Quercus oleoides) when grown in two habitats: a diverse secondary forest or in 18-yr old monoculture plantations in northwestern Costa Rica. We quantified soil moisture, pH, labile carbon (C), inorganic N (NH4+ and NO3−), net N mineralization rates, total C and N, δ15N signature and enzyme activity. We predicted that legumes would have higher soil nutrient availability under their crowns, but that this effect would be more pronounced in plantations, where tree species diversity is low. In the forest, soils under Dalbergia had the highest values of total C and N, and extractable nitrate, whereas soils under Acosmium the highest N mineralization rates. The activity of acid phosphatase enzymes varied among the soils under different species in both habitats, with the highest activity in the soils under the legume Acosmium at the forest site. In the plantations, Acosmium had the highest values for total soil C and N, labile C, and potential N mineralization rates. We conclude that 1) the legume species did not have consistent effects as a functional group, possibly due to different amounts of nodulation in individuals within species, and 2) as hypothesized, the magnitude of the species effect was more pronounced in the plantations than in the diverse secondary forest.

Selectivity Control in Synergistic Liquid–Liquid Anion Exchange of Univalent Anions via Structure-Specific Cooperativity between Quaternary Ammonium Cations and Anion Receptors

Two anion receptors enhance liquid-liquid anion exchange when added to quaternary alkylammonium chloride anion exchangers, but with a striking dependence on the structure of the alkylammonium cation that suggests a supramolecular cooperative effect. Two anion receptors were investigated, meso-octamethylcalix[4]pyrrole (C4P) and the bisthiourea tweezer 1,1'-(propane-1,3-diyl)bis(3-(4-sec-butylphenyl)thiourea (BTU). Whereas synergism is comparatively weak when either methyltri(C(8,10))alkylammonium chloride (Aliquat 336) or tetraheptylammonium chloride is used with the BTU receptor, synergism between C4P and Aliquat 336 is so pronounced that anion exchange prefers chloride over more extractable nitrate and trifluoroacetate, effectively overcoming the ubiquitous Hofmeister bias. A thermochemical analysis of synergistic anion exchange has been provided for the first time, resulting in the estimation of binding constants for C4P with the ion pairs of A336(+) with Cl(-), Br(-), OAc(F3)(-), NO(3)(-), and I(-).

Influences of Hemlock Woolly Adelgid–Induced Stand-Level Mortality on Nitrogen Cycling and Stream Water Nitrogen Concentrations in Southern Pennsylvania

Hemlock woolly adelgid, Adelges tsugae, is spreading throughout the northeastern United States, causing large-scale dieback of the eastern hemlock, Tsuga canadensis. This study examined soil nitrogen transformations and stream water nitrogen content at five hemlock-dominated stands in southern Pennsylvania, spanning a spectrum of hemlock mortality, from no mortality to total A. tsugae–induced mortality with subsequent regrowth. Organic content, extractable nitrate, and net nitrification and mineralization rates, as well as nitrate and ammonium movement through the soil were significantly higher at sites with high mortality. Our results suggest that stand-level hemlock mortality is leading to increased nitrogen inputs to stream water. Stream water nitrate concentrations were lowest at the site with little to no mortality (0.035 mg/L NO3−) and highest at the site with intermediate mortality (0.69 mg/L NO3−). In the sites with the longest time since infestation and highest mineralization and nitrification rates, regenerative seedling growth (Betula spp. in particular) is leading to increased uptake of nitrate, likely reducing nitrate leaching rates once substantial regeneration occurs. However, for a period of several years after infestation, hemlock dieback may be a significant source of nitrate in headwater streams, potentially altering headwater aquatic community composition and increasing downstream nutrient pollution.

Nutrient Loss Following Phragmites australis Removal in Controlled Soil Mesocosms

Mechanisms to remove Common reed (Phragmites australis) typically include a combination of herbicide applications and mechanical cutting or plowing of the soil. The objective of this study was to remove P. australis by various mechanisms and measure the subsequent short-term release of nutrients via simulated rain events. Three rain events of similar duration and intensity were conducted on a control subset and three treatments (above and belowground biomass removal, herbicide application, and basal cut) of soil mesocosms (n = 6) that were designed to export excess water as either surface runoff or leachate through the soil profile. The dominant pathway for soluble reactive phosphorus (p < 0.001) and ammonium (p < 0.001) export were surface runoff while nitrate (p < 0.001) was leached through the soil profile. More nitrate was exported in the vegetation removal treatments (i.e., biomass removal, herbicide, and basal cut) than the control (p < 0.001) while more soluble reactive phosphorus was exported in the herbicide and basal cut treatment compared to the control (p = 0.010). In regards to ammonium, a higher export was observed in the herbicide treatment compared to the control, biomass removal, and basal cut treatments (p < 0.001). We attribute the higher amount of ammonium export in the herbicide treatment to the fact that the glyphosate herbicide used was in an isopropylamine salt form. After examining pre- and postmanipulation soil cores, there was a larger decrease in extractable ammonium in the control and all treatments compared to soil extractable nitrate, which displayed a smaller decrease and in some treatments actually increased during the course of the experiment. Ultimately, in this study, we observed a strong potential for nitrogen biogeochemistry to occur and the removal of vegetation-enhanced nutrient export.

Abundance and productivity mediate invader effects on nitrogen dynamics in a California grassland

Soil nitrogen (N) transformations have been shown to be influenced by plant community composition. Identifying species traits that control nitrogen dynamics is more straightforward when species dramatically differ in N input via litter (e.g., N-fixing invaders in a non-fixing community) or in litter carbon:N or lignin:N ratios. Cases where invaders and residents are more similar for such traits are more challenging to evaluate. In these settings, a species' relative abundance and its contribution to overall ecosystem productivity are likely to contribute significantly to the development of effects on N availability and cycling. We compared soil N dynamics in experimental grassland communities dominated by native perennial grasses (NP), exotic annual grasses (EA), and exotic perennial grasses (EP), as well as mixtures of the native perennial grasses with each exotic grass group (NP + EA and NP + EP). These groups differ from each other in subtle ways in traits likely to influence soil N cycling including annual productivity, allocation to roots versus shoots, litter production, litter chemistry, and degree of summertime activity. We found that ecosystem N dynamics were significantly different between the various species groups with the greatest differences occurring between EA plots and other community types: soils in EA plots had significantly lower rates of net N mineralization, net nitrification, and microbial biomass-N compared to either NP or NP + EA plots, and lower extractable nitrate in the spring compared to either NP or EP plots. The higher the proportion of productivity in a plot that derived from exotic species, particularly exotic annual species, the lower were the measured rates of net N mineralization. Stepwise regression analysis showed that vegetation productivity was the best predictor of N cycling metrics: the higher the productivity, the higher the rates of net mineralization and nitrification, and microbial biomass-N. We conclude that species' abundance and productivity were strong controlling factors in the development of differences in ecosystem N dynamics between our experimental treatments. Inclusion of relative proportion of productivity contributed by community members in models of the development of species effects will likely aid in predicting when and where invasive species will alter ecosystem N dynamics.

The impact of nitrogen deposition on acid grasslands in the Atlantic region of Europe

A survey of 153 acid grasslands from the Atlantic biogeographic region of Europe indicates that chronic nitrogen deposition is changing plant species composition and soil and plant-tissue chemistry. Across the deposition gradient (2–44 kg N ha−1 yr−1) grass richness as a proportion of total species richness increased whereas forb richness decreased. Soil C:N ratio increased, but soil extractable nitrate and ammonium concentrations did not show any relationship with nitrogen deposition. The above-ground tissue nitrogen contents of three plant species were examined: Agrostis capillaris (grass), Galium saxatile (forb) and Rhytidiadelphus squarrosus (bryophyte). The tissue nitrogen content of neither vascular plant species showed any relationship with nitrogen deposition, but there was a weak positive relationship between R. squarrosus nitrogen content and nitrogen deposition. None of the species showed strong relationships between above-ground tissue N:P or C:N and nitrogen deposition, indicating that they are not good indicators of deposition rate.

Nitrogen Mineralization and Leaching in the Early Stages of a Subtropical Reforestation in Southern China

Nitrogen cycling is a critical component in plantations, yet the spatial and temporal variations of N transformations in different stages of reforestation are often poorly known. Here we report the seasonal variation of soil in situ net N mineralization, net nitrification and N leaching in five young plantations (two monocultures of exotic species: Eucalyptus urophylla and Acacia crassicarpa; a native species monoculture; a 10‐species mixture and a 30‐species mixture) and a shrubland (without experimental planting) in subtropical southern China. Our results show that net N mineralization and nitrification rates in the E. urophylla monoculture (13.5 and 9.98 kg N ha−1 yr−1, respectively) were the lowest among six planting treatments, less than 1/3 of those in the 10‐species and 30‐species mixtures. Two exotic fast‐growing monocultures had 10–60% lower soil extractable nitrate concentrations than the native plantations and shrubland and had the lowest nitrogen leaching losses. The leguminous A. crassicarpa monoculture did not have higher soil N availability in comparison with non‐leguminous species. Both N mineralization and nitrification varied seasonally; soil moisture seemed to be important in controlling these temporal variations. This study highlights that in the early stages of reforestaion, a better understanding of plant species effects on soil N cycling would be beneficial to forest management decisions and could provide a critical foundation for advancing restoration practices.

Long-term Changes in Forest Carbon and Nitrogen Cycling Caused by an Introduced Pest/Pathogen Complex

Invasion of exotic forest pests and pathogens is a serious environmental problem for many forests throughout the world, and has been especially damaging to forests of eastern North America. We studied the impacts of an exotic pest/pathogen complex, the beech bark disease (BBD), in the Catskill Mountains of New York State, USA. In this region, BBD has caused a decline in the basal area of American beech (Fagus grandifolia Ehrh.) over the last 60 years and this decline has been accompanied by an increase in the basal area of sugar maple (Acer saccharum Marsh.). We studied the impacts of the BBD on carbon (C) and nitrogen (N) cycling using a series of stands that represented a sequence of disease impact and beech replacement by sugar maple. Our study showed that these long-term changes in tree species composition can lead to important changes in C and N cycling in the ecosystem, including an increase in litter decomposition, a decrease in soil C:N ratio, and an increase in extractable nitrate in the soil and nitrate in soil solution. Rates of potential net N mineralization and nitrification did not change across the BBD sequence, but the fraction of mineralized N that was nitrified increased significantly. Many of the observed changes in ecosystem function are larger in magnitude than those attributed to climate change or air pollution, suggesting that the impacts of invasive pests and pathogens on tree species composition could be one of the most important factors driving changes in C and N cycling in these forests in the coming decades.

Effects of cropping history and peat amendments on the quality of a silt soil cropped with strawberries

Long-term field experiments are invaluable sites for studying changes in soil quality due to management practices. We utilized a field experiment on silt soil with 18 years (1982–1999) of conventional and organic farming systems for studying long-term impacts of farming system on soil properties. During 2000–2002, strawberries were grown on the whole area. Some conventional and organic plots were amended with peat in 2000 prior to strawberry planting. Chemical, biological and physical soil properties were measured in 2000–2002 at the end of the growing season. Several chemical properties were lower in the organic than in the conventional farming system, including electrical conductivity (1.12 × 10 4 S cm −1 vs. 1.67 × 10 4 S cm −1) and amounts of extractable phosphorus (15.7 mg l −1 vs. 24.8 mg l −1 soil) and potassium (68.6 mg l −1 vs. 83.6 mg l −1 soil). In contrast, soil organic carbon was significantly higher in the organic than in the conventional system (2.5% vs. 3.0%) in 2001. Farming system had no impact on pH, extractable nitrate, calcium and magnesium. Microbial biomass carbon was 20–25% higher in the organic than in the conventional system each year and microbial biomass nitrogen 32 and 23% higher in 2000 and 2001, respectively. Farming system affected also earthworms positively by increasing their numbers from 64.9 earthworms m −2 soil in conventional to 134.9 in organic. The effectiveness of arbuscular mycorrhizal fungi was slightly elevated in organic as compared with conventional in 2001. In contrast, mycorrhizal spore numbers were lower in organic than in conventional (64.4 spores 100 ml −1 soil vs. 195.3 spores 100 ml −1 soil). Peat amendment increased soil organic carbon from 2.2 to 5.0% in 2000. In 2001, the corresponding values were 2.2 and 3.9%, indicating partial mineralization of added peat. Also water-holding capacity increased after peat amendment. In contrast, pH, electrical conductivity and amounts of extractable nitrate, phosphorus and calcium were lower in peat-amended plots. Most biological soil properties measured were also lower in peat-amended than in non-amended plots, including amounts of microbial biomass nitrogen (26.5 μg g −1 soil vs. 41.8 μg g −1 soil) and carbon (224.0 μg g −1 soil vs. 260.9 μg g −1 soil), AMF effectiveness (−18.5% vs. +4.2%) and arbuscular mycorrhizal spore numbers (59.9 spores 100 ml −1 soil vs. 168.6 spores 100 ml −1 soil) measured in 2000. Earthworms and nematodes were not affected by peat. It is concluded that management practice had a strong impact on soil quality, but more extensive studies are warranted for defining soil variables of major importance for crop yield.

Effect of cropping system and peat amendment on strawberry growth and yield

Comparative studies have usually shown higher yields in conventional cropping systems (CCS) than in organic cropping systems (OCS). By utilizing a long-term field experiment on silt soil with 18 years of cropping history (1982–1999), including three OCSs and one CCS, we studied if this is true also for strawberry. The strawberry experiment was conducted in 2000–2002. The experiment had one CCS (A) and three OCSs (B,C,D). The impact of pre-planting peat amendment was also studied. The degree of overwintering, fruit yields, yield components and some soil nutrients were determined. Total and marketable fruit yields were estimated using a peduncle analysis based on weights of fruits of different orders in the peduncle, numbers of healthy and injured fruits in the peduncle and the number of peduncles per plant. The shoot growth, total and marketable fruit yields, as well as all yield components estimated were significantly higher in the OCS rotation D than in the CCS rotation A. The peat amendment, but not the cropping system, decreased the percentage of strawberry plants suffering from or killed by winter damage. However, peat amendment did not affect yield. The cropping system had no impact on soil pH, or the amount of extractable calcium, magnesium and nitrate. Extractable phosphorus and potassium were higher and soil organic carbon (Corg) slightly higher in the OCS than in the CCS. The peat amendment increased Corg by 2%. The amounts of extractable nutrients in soil were not a limiting factor for strawberry growth and yield as they were of sufficient levels both in CCS and OCS. It remains unclear whether the higher yield in the OCS was due to a long-term cropping history or to a short-term effect of composted manure, or to a combination of these two. The importance of soil organic management in strawberry production is emphasized.;

Stellera chamaejasme L. increases soil N availability, turnover rates and microbial biomass in an alpine meadow ecosystem on the eastern Tibetan Plateau of China

Plant species have been shown to have significant effects on soil nutrient pools and dynamics. Stellera chamaejasme L., a toxic perennial weed, has established and is now abundant in the alpine meadow on the eastern Tibetan Plateau of China since the 1960s. We quantified the effects of Stellera on carbon and nitrogen cycling in two topographic habitats, a flat valley and a south-facing slope, where Stellera was favored to spread within the study area. Aboveground litter biomass and tissue chemistry of aboveground litter and root were measured to explain the likely effects of Stellera on soil carbon and nutrient cycling. The sizes of various soil pools, e.g. nitrate, ammonium, inorganic phosphorus, microbial biomass, soil respiration and turnover rates including net mineralization, gross nitrification and denitrification were determined. The results showed that Stellera produced more aboveground litter than each of the co-occurring species. Aboveground litter of Stellera had higher tissue N and lower lignin:N than the other species. Stellera significantly increased surface soil (0–15 cm) organic matter, whereas no significant differences were found for organic C and total P in subsoil (15–30 cm) within and between patches of Stellera. Soil extractable nitrate concentrations in Stellera surface soil were 113% and 90% higher on the flat valley and on the south-facing slope, respectively. Both microbial biomass C and N were significantly higher in Stellera surface soil. Gross nitrification and microbial respiration were significantly higher in Stellera surface soil both on the flat valley and on the south-facing slope, whereas significant differences of denitrification were found only on the flat valley. The differences in the quantity and quality of aboveground litter are a likely mechanism responsible for the changes of soil properties.

Extraction of zirconium with tributyl phosphate from nitric acid solutions

The extraction of zirconium with tributyl phosphate (TBP) in organic diluent was studied. The dependence of the distribution ratio of Zr on the TBP concentration in the organic phase and also the IR spectra of Zr-TBP extracts obtained at different concentrations of Zr and HNO3 in the aqueous phase show that at least two kinds of extractable zirconium nitrate solvates with TBP are formed in extraction with 30% TBP. The solvate formed at HNO3 concentration not exceeding 3 M contains water molecules. The extract-able species formed at higher nitric acid concentration in the aqueous phase is anhydrous zirconium nitrate disolvate with TBP.

Have repeated applications of nitrogen and phosphorus to a loblolly pine plantation changed stand productivity and soil nutrient supply?

To develop a nitrogen (N) and phosphorus (P) fertilization regime that produces long-term increases in stand productivity and soil nutrient supply in loblolly pine plantations, a series of N + P fertilizer studies were established in the Southeastern United States. One of these installations was examined partway through the study to determine if changes to stand productivity and soil nutrient supply had already been achieved. Stand growth and foliar nutrient concentrations were measured for 6 years, and during the third year, a seedling bioassay was conducted with soil collected from the highest fertilization and nonfertilized treatments. Annual stand growth was increased by 14%–27% in the fertilized plots suggesting that the fertilizer regime improved stand productivity. However, results from the seedling bioassay showed that only P fertilization had caused changes in soil nutrient supply. Seedling P contents in the fertilized treatments were 3.6 times larger than those in the nonfertilized treatments. In contrast, total system N contents were equivalent in the fertilized and nonfertilized systems, and extractable nitrate (NO3–), ammonium (NH4+), and biologically active N were higher in the nonfertilized soils. Future measurements and seedlings bioassay assessments should be conducted to determine when and if long-term changes in soil quality and stand productivity are achieved.