Effects of nitrogen input and grazing on methane fluxes of extensively and intensively managed grasslands in the Netherlands

 Generally, grasslands are considered as sinks for atmospheric CH₄, and N input as a factor which reduces CH₄ uptake by soils. We aimed to assess the short- and long-term effects of a wide range of N inputs, and of grazing versus mowing, on net CH₄ emissions of grasslands in the Netherlands. These grasslands are mostly intensively managed with a total N input via fertilisation and atmospheric deposition in the range of 300–500 kg N ha^–1 year^–1. Net CH₄ emissions were measured with vented, closed flux chambers at four contrasting sites, which were chosen to represent a range of N inputs. There were no significant effects of grazing versus mowing, stocking density, and withholding N fertilisation for 3–9 years, on net CH₄ emissions. When the ground-water level was close to the soil surface, the injection of cattle slurry resulted in a significant net CH₄ production. The highest atmospheric CH₄ uptake was found at the site with the lowest N input and the lowest ground-water level, with an annual CH₄ uptake of 1.1 kg CH₄ ha^–1 year^–1. This is assumed to be the upper limit of CH₄ uptake by grasslands in the Netherlands. We conclude that grasslands in the Netherlands are a net sink of CH₄, with an estimated CH₄ uptake of 0.5 Gg CH₄ year^–1. At the current rates of total N input, the overall effect of N fertilisation on net CH₄ emissions from grasslands is thought to be small or negligible. Received: 27 January 1998     

Impact of grazed grassland management on total N accumulation in soil receiving different levels of N inputs

Nitrogen balances and total N and C accumulation in soil were studied in reseeded grazed grassland swards receiving different fertilizer N inputs (100–500 kg N ha^?1 year^?1) from March 1989 to February 1999, at an experimental site in Northern Ireland. Soil N and C accumulated linearly at rates of 102–152 kg N ha^?1 year^?1 and 1125–1454 kg C ha^?1 year^?1, respectively, in the top 15 cm soil during the 10 year period. Fertilizer N had a highly significant effect on the rate of N and C accumulation. In the sward receiving 500 kg fertilizer N ha^?1 year^?1 the input (wet deposition + fertilizer N applied) minus output (drainflow + animal product) averaged 417 kg N ha^?1 year^?1. Total N accumulation in the top 15 cm of soil was 152 kg N ha^?1 year^?1. The predicted range in NH₃ emission from this sward was 36–95 kg N ha^?1 year^?1. Evidence suggested that the remaining large imbalance was either caused by denitrification and/or other unknown loss processes. In the sward receiving 100 kg fertilizer N ha^?1 year^?1, it was apparent that N accumulation in the top 15 cm soil was greater than the input minus output balance, even before allowing for gaseous emissions. This suggested that there was an additional input source, possibly resulting from a redistribution of N from lower down the soil profile. This is an important factor to take into account in constructing N balances, as not all the N accumulating in the top 15 cm soil may be directly caused by N input. N redistribution within the soil profile would exacerbate the N deficit in budget studies.     

Potassium leaching from cut grassland and from urine patches

In grassland farming, especially on coarse‐textured soils, K can be a critical element. On these soils, the actual K management as well as fertilizer history to a large extent determine the leaching of K. The effects of four fertilizer regimes on the nutrient balances and leaching of K from grassland grown on a sandy soil were investigated. The swards differed in the source and level of N input and K fertilizer: no fertilizer N + 166 kg K ha^?1 year^?1 (Control), 320 kg inorganic N ha^?1 + 300 kg K ha^?1 year^?1 (MIN 320), 320 kg N + 425 kg K ha^?1 year^?1 in form of cattle slurry (SLR 320) and a grass–clover sward + 166 kg K ha^?1 year^?1 (WCL 0) without any inorganic N input. In a second experimental phase, cores from these swards were used in a mini‐lysimeter study on the fate of K from urine patches. On cut grassland after 6 years K input minus removal in herbage resulted in average K surpluses per year of 47, 39, 56 and 159 kg K ha^?1 for the Control, MIN 320, WCL 0 and SLR 320, respectively. Related leaching losses per year averaged 7.5, 5, 15 and 25 kg K ha^?1. Losses of urinary‐K through leaching were 2.2–4.5 and 5.7–8.4% of the K supplied in summer and autumn applications, respectively. Plant and soil were the major sinks for K from fertilizer or urine. High levels of exchangeable K in the soil and/or large and late fertilizer or urine applications stimulated leaching of K.     

Ammonia Emission from a Young Larch Ecosystem Afforested after Clear-Cutting of a Pristine Forest in Northernmost Japan

The present study aimed to elucidate the atmosphere–forest exchange of ammoniacal nitrogen (NH_X-N) at a young larch ecosystem. NH_X-N exchanges were measured at a remote site in northernmost Japan where 4-year-old larches were growing after a pristine forest had been clear-cut and subsequent dense dwarf bamboo (Sasa) had been strip-cut. The site was a clean area for atmospheric ammonia with mean concentrations of 0.38 and 0.11 μg N m^?3 in snowless and snow seasons, respectively. However, there was a general net emission of NH_X-N. The annual estimated emission of NH_X-N of 4.8 kg N ha^?1 year^?1 exceeded the annual wet deposition of 2.4 kg N ha^?1 year^?1, but the weekly exchange fluxes may have been underestimated by 28–60%. The main cause of the ammonia loss from the young larch ecosystem was probably enhanced nitrogen supply stimulated by the cutting of the pristine forest and Sasa, in particular, the Sasa.     

Nitrogen Retention in Japanese Cedar Stands in Northern Honshu, with High Nitrogen Deposition

High nitrogen, especially ammonium, input has been observed in Schichinohe, Aomori Prefecture, northeastern Japan. A monitoring study on precipitation, throughfall, and stream water has been carried out to estimate the stage of nitrogen saturation since 1996. Fifty-two to 70% of nitrogen input in throughfall was retained in forest ecosystems. Nitrate concentration in stream water tended to decrease throughout the study. There was no symptom of nitrogen saturation at Japanese cedar stands in Shichinohe, although high nitrogen input in open bulk has been observed. Ammonium (NH₄ ⁺) was retained in the canopy. The ratio of NH₄ ⁺ input in throughfall to that by open bulk was 0.40 – 0.47. Total inorganic nitrogen input under the canopy amounted 0.68 – 0.72 kmolc ha^?1 yr^?1 (9.6 – 10.0 kg N ha^?1 yr^?1). Our results suggests that atmospheric nitrogen input has benefitted the three growth.     

No significant difference in N2O emission,fertilizer-induced N2O emission factor and CH4 absorption between anaerobically digested cattle slurry and chemical fertilizer applied timothy (Phleum pratense L.) sward in central Hokkaido,Japan

Abstract

Nitrous oxide (N₂O) and methane (CH₄) fluxes from a fertilized timothy (Phleum pratense L.) sward on the northern island of Japan were measured over 2?years using a randomized block design in the field. The objectives of the present study were to obtain annual N₂O and CH₄ emission rates and to elucidate the effect of the applied material (control [no nitrogen], anaerobically digested cattle slurry [ADCS] or chemical fertilizer [CF]) and the application season (autumn or spring) on the annual N₂O emission, fertilizer-induced N₂O emission factor (EF) and the annual CH₄ absorption. Ammonium sulfate was applied to the CF plots at the same application rate of NH₄-N to the ADCS plots. A three-way ANOVA was used to examine the significance of the factors (the applied material, the application season and the year). The ANOVA for the annual N₂O emission rates showed a significant effect with regard to the applied material (P?=?0.042). The annual N₂O emission rate from the control plots (0.398?kg N₂O-N ha^?1?year^?1) was significantly lower than that from the ADCS plots (0.708?kg N₂O-N ha^?1?year^?1) and the CF plots (0.636?kg N₂O-N ha^?1?year^?1). There was no significant difference in the annual N₂O emission rate between the ADCS and CF plots. The ANOVA for the EFs showed insignificance of all factors (P?>?0.05). The total mean?±?standard error of the EFs (fertilizer-induced N₂O-N emission/total applied N) was 0.0024?±?0.0007 (kg N₂O-N [kg N]^?1), which is similar to the reported EF (0.0032?±?0.0013) for well-drained uplands in Japan. The CH₄ absorption rates differed significantly between years (P?=?0.014). The CH₄ absorption rate in the first year (3.28?kg CH₄?ha^?1?year^?1) was higher than that in the second year (2.31?kg CH₄?ha^?1?year^?1), probably as a result of lower precipitation in the first year. In conclusion, under the same application rate of NH₄-N, differences in the applied materials (ADCS or CF) and the application season (autumn or spring) led to no significant differences in N₂O emission, fertilizer-induced N₂O EF and CH₄ absorption.     

Does the potential ammonium fixation of soils have an impact on the optimum nitrogen fertilizer rate?

Field experiments were conducted to determine the effect of nitrogen (N) fertilizer forms and doses on wheat (Triticum aestivum L.) on three soils differing in their ammonium (NH₄) fixation capacity [high = 161 mg fixed NH₄-N kg^?1 soil, medium = 31.5 mg fixed NH₄-N kg^?1 soil and no = nearly no fixed NH₄-N kg^?1 soil]. On high NH₄⁺ fixing soil, 80 kg N ha^?1 Urea+ ammonium nitrate [NH₄NO₃] or 240 kg N ha^?1 ammonium sulfate [(NH₄)₂SO₄]+(NH₄)₂SO₄, was required to obtain the maximum yield. Urea + NH₄NO₃ generally showed the highest significance in respect to the agronomic efficiency of N fertilizers. In the non NH₄⁺ fixing soil, 80 kg N ha^?1 urea+NH₄NO₃ was enough to obtain high grain yield. The agronomic efficiency of N fertilizers was generally higher in the non NH₄⁺ fixing soil than in the others. Grain protein was highly affected by NH₄⁺ fixation capacities and N doses. Harvest index was affected by the NH₄⁺ fixation capacity at the 1% significance level.     

Microbial biomass and mineralization-immobilization of nitrogen in some agricultural soils

Summary The chloroform fumigation-incubation method (CFIM) was used to measure the microbial biomass of 17 agricultural soils from Punjab Pakistan which represented different agricultural soil series. The biomass C was used to calculate biomass N and the changes occurring in NH₄ ⁺-N and NO₃ ^–-N content of soils were studied during the turnover of microbial biomass or added C source. Mineral N released in fumigated-incubated soils and biomass N calculated from biomass C was correlated with some N availability indexes.The soils contained 427–1240 kg C as biomass which represented 1.2%–6.9% of the total organic C in the soils studied. Calculations based on biomass C showed that the soils contained 64–186 kg N ha^–1 as microbial biomass. Immobilization of NCO₃ ^–-N was observed in different soils during the turnover of microbial biomass and any net increase in mineral N content of fumigated incubated soils was attributed entirely to NH₄ ⁺-N.Biomass N calculated from biomass C showed non-significant correlation with different N availability indexes whereas mineral N accumulated in fumigated-incubated soils showed highly significant correlations with other indexes including N uptake by plants.     

Long-term nitrogen balance for pearl millet (Pennisetum glaucum L.) in an acid sandy soil of Niger

On acid sandy soils of Niger (West Africa) fertilizer N recovery by pearl millet (Pennisetum glaucum L.) is often more than 100 per cent in years with normal or above average rainfall. Biological nitrogen fixation (BNF) by N₂-fixing bacteria may contribute to the N supply in pearl millet cropping systems. For a long-term field experiment comprising treatments with and without mineral fertilizer (F) and with and without crop residue application (CR) a N balance sheet was calculated over a period of six years (1983-1988). After six years of successive millet cropping total N uptake (36-77 kg N ha^?1 yr^?1) was distinctly higher than the amount of fertilizer N applied (30 kg N ha^?1 yr^?1). The atmospheric input of NH₄-N and NO₃-N in the rainwater was about 2 kg N ha_?1 yr^?1, 70 % in the form of NH₄-N. Gaseous NH₃ losses from urea (broadcast, incorporated) were estimated from other experiments to amount to 36 % of the fertilizer N applied. Nitrogen losses by leaching (15 to > 25 kg N ha^?1 yr^?1) were dependent on the treatment and on the quantity and distribution of single rainfall events (>50 mm). Decline in total soil N content (0-60 cm) ranged from 15 to 48 kg N ha^?1 yr^?1. The long-term N balance (1983-1988) indicated an annual net gain between 6 (+CR-F) and 13 (+CR+F) kg N ha^?1 yr^?1. For the control (-CR-F) the long-term N balance was negative (10 kg N ha^?1 yr^?1). In the treatment with crop residues only, the N balance was mainly determined by leaching losses, whereas in treatments with mineral fertilizer application the N balance depended primarily on N removal by the millet crop. The annual net gain in the N balance increased from 7 kg ha^?1 with mineral fertilizer to 13 kg ha^?1 in the combination mineral fertilizer plus crop residues. In both the rhizosphere and the bulk soil (0-15 cm), between 9 and 45% of the total bacterial population were N₂-fixing (diazotrophic) bacteria. The increased N gain upon crop residue application was positively correlated with an increase in the number of diazotrophic and total bacteria. The data on bacterial numbers suggest that the gain of N in the longterm N balance is most likely due to an N input by biological nitrogen fixation. In addition, evidence exists from related studies that the proliferation of diazotrophs and total bacteria in the rhizosphere due to crop residue application stimulated root growth of pearl millet, and thus improved the phosphorus (P) acquisition in the P deficient soil.     

Effects of Land Use Conversion from Native Forests to Exotic Plantations on Nitrogen and Phosphorus Retention in Catchments of Southern Chile

In six small catchments located at the Cordillera de la Costa in southern Chile (40° S), concentrations and fluxes of NO₃-N, NH₄-N, organic-N, total-N and total-P in bulk precipitation and runoff water were measured. The main objective of this study was to compare nitrogen and phosphorus retention of catchments with varying land cover of native forest and exotic plantations, in order to evaluate possible effects of land use change. Nitrate-N was the dominant fraction (>50%) of nitrogen loss, especially in the catchments dominated by exotic plantations. In the catchment with native forests, NO₃ ^? only contributed with 34% of the nitrogen loss and DON was the main output with 55%. Annual NO₃ ^? export was lower in the catchment with native forest compared to the catchments with exotic plantations where the streamflow output exceed the precipitation input. Average inputs of total-N were 2.6 kg ha^?1 year^?1 (DIN?=?1.4 kg ha^?1 year^?1, DON?=?1.2 kg ha^?1 year^?1) and outputs were 1.7 kg ha^?1 year^?1 (DIN?=?1.2 kg ha^?1 year^?1, DON?=?0.5 kg ha^?1 year^?1). Annual retention of total nitrogen fluctuated between 61% in a catchment dominated by native forests to 15% in catchments dominated by exotic plantations of Eucalyptus sp. Nitrogen retention was positively related with native forest coverage. The N retention capacity of the catchments could be both attributed to consequences of clear cutting practices and differences in vegetation cover.     

中国亚热带中部三峡库区不同土地利用方式下甲烷氧化潜力研究

To compare the CH4 oxidation potential among diferent land uses and seasons,and to observe its response to monsoon precipitation pattern and carbon and nitrogen parameters,a one-year study was conducted for diferent land uses (vegetable field,tilled and non-tilled orchard,upland crops and pine forest) in central subtropical China.Results showed significant diferences in CH4 oxidation potential among diferent land uses(ranging from 3.08 to 0.36 kg CH4 ha-1 year-1).Upland with corn-peanut-sweet potato rotation showed the highest CH4 emission,while pine forest showed the highest CH4 oxidation potential among all land uses.Non-tilled citrus orchard (0.72±0.08 kg CH4 ha-1 year-1)absorbed two times more CH4 than tilled citrus orchard(0.38±0.06kg CH4 ha-1 year-1).Irrespective of diferent vegetation,inorganic N fertilizer application significantly influenced CH4 fluxes across the sites (R2=0.86,P=0.002).Water-filled pore space,soil microbial biomass carbon,and dissolved nitrogen showed significant efects across diferent land uses (31% to 38% of variability)in one linear regression model.However,their cumulative interaction was significant for pine forest only,which might be attributed to undisturbed microbial communities legitimately responding to other variables,leading to net CH4 oxidation in the soil.These results suggested that i)natural soil condition tended to create win-win situation for CH4 oxidation,and agricultural activities could disrupt the oxidation potentials of the soils;and ii)specific management practices including but not limiting to efficient fertilizer application and utilization,water use efciency,and less soil disruption might be required to increase the CH4 uptake from the soil.     

Soil mineral nitrogen dynamics under bare fallow and wheat in vertisols of semi-arid Mediterranean Morocco

 The evoluion of NH₄ ⁺-N and NO₃ ^–-N was monitored during three growing seasons, 1992–1993, 1993–1994, 1994–1995 in the soil profile (0–60 or 0–90 cm) under bare fallow and wheat on a vertisol site of the Sais plateau, Morocco. The aim of this study was to relate the soil mineral N dynamics to crop N uptake and soil N transformation processes. The efficacy of the current N fertilisation rate (100 kg N ha^–1) for wheat production in the region was evaluated. The high level of residual mineral N in the soil profile resulted from a low N plant uptake relative to the soil N supply and N fertilisation, and masked the effect of N fertilisation on dry matter accumulation. NH₄ ⁺-N was present in considerable amounts, suggesting a low nitrification rate under the given pedo-climatic conditions. An artefact due to the sampling procedure was encountered shortly after the application of N fertiliser. Losses through leaching and denitrification occurred after heavy rainfall, but were limited. At least part of the exchangeable NH₄ ⁺-N seemed to be barely taken up by the crop. NO₃ ^–-N was therefore considered to be a better indicator of plant-available N than total mineral N for this type of soil. The low N fertiliser use efficiencies demonstrated clearly that the current fertilisation rate (100 kg N ha^–1) for wheat production in this region is unsustainable. The maximum N uptake ranged from 40 kg N ha^–1 to 180 kg N ha^–1. The estimation of the seasonal production potential is considered to be the main prerequisite for the determination of the best rates and timing of N fertiliser application in this region. Received: 9 December 1997     

Nitrogen budget and relationships with riverine nitrogen exports of a dairy cattle farming catchment in eastern Hokkaido,Japan

Abstract

Dairy farming regions are important contributors of nitrogen (N) to surface waters. We evaluated the N budget and relationships to riverine N exports within the Shibetsu River catchment (SRC) of a dairy farming area in eastern Hokkaido, Japan. Five drainage basins with variable land-cover proportions within the SRC were also evaluated individually. We quantified the net N input (NNI) to the catchment from the difference between the input (atmospheric deposition, chemical fertilizers, N fixation by crops and imported food and feed) and the output (exported food and feed, ΔS _liv and ΔS _hu, which are the differences between input and output in livestock and human biomass, respectively) using statistical and measured data. Volatilized ammonia (NH₃) was assumed to be recycled within the catchment. The riverine export of N was quantified. Agricultural N was a dominant source of N to the SRC. Imported feed was the largest input (38.1?kg?N?ha^?1?year^?1), accounting for 44% of the total inputs, followed by chemical fertilizers (32.4?kg?N?ha^?1?year^?1) and N fixation by crops (13.4?kg?N?ha^?1?year^?1). The exported food and feed was 24.7?kg?N?ha^?1?year^?1 and the ΔS _liv and ΔS _hu values were 7.6 and 0.0?kg?N?ha^?1?year^?1, respectively. As a result, the NNI amounted to 54.6?kg?N?ha^?1?year^?1. The riverine export of total N from the five drainage basins correlated well with the NNI, accounting for 27% of the NNI. The fate of the missing NNI that was not measured as riverine export could possibly have been denitrified and/or retained within the SRC. A change in the estimate of the deposition rate of volatilized NH₃ from 100 to 0% redeposited would have decreased the NNI by 37%, although we believe that most NH₃ was likely to have been redeposited. The present study demonstrated that our focus should be on controlling agricultural N to reduce the impact of environmental pollution as well as on evaluating denitrification, N stocks in soil and the fate of NH₃ volatilization in the SRC.     

Nitrogen Availability from Compost in High Tunnel Tomato Production

High yield agricultural systems, such as high tunnel (HT) vegetable production, require a large supply of soil nutrients, especially nitrogen (N). Compost is a common amendment used by HT growers both to supply nutrients and to improve physical and biological soil properties. We examined commercially-available composts and their effects on soil N, plant N uptake, and tomato yield in HT cultivation. In addition, a laboratory study examined N and carbon (C) mineralization from the composts, and the usefulness of compost properties as predictors of compost N mineralization was assessed under field and laboratory conditions. The field study used a randomized complete block design with four replications to compare four compost treatments (all added at the rate of 300 kg total N ha^?1) with unamended soil and an inorganic N treatment (110 kg N ha^?1). Tomatoes were grown in Monmouth, Maine during the summers of 2013 and 2014. Compost NO₃^?-N and NH₄⁺-N application rates were significantly correlated with soil NO₃^?-N and NH₄⁺-N concentrations throughout the growing season. Marketable yield was positively correlated with compost total inorganic N and NO₃^?-N in both years, and with NH₄⁺-N in 2014. There were no significant differences among composts in percentage of organic N mineralized and no correlations were observed with any measured compost property. In the laboratory study, all compost-amended soils had relatively high rates of CO₂ release for the initial few days and then the rates declined. The compost-amended soils mineralized 4%–6% of the compost organic N. This study suggested compost inorganic N content controls N availability to plants in the first year after compost application.     

Nitrate leaching in forest soils: an analysis of long‐term monitoring sites in Germany

Elevated atmospheric inputs of NH₄⁺ and NO₃^– have caused N saturation of many forest ecosystems in Central Europe, but the fate of deposited N that is not bounded by trees remains largely unknown. It is expected that an increase of NO₃^– leaching from forest soils may harm the quality of groundwater in many regions. The objective of this study was to analyze the input and output of NH₄⁺ and NO₃^– at 57 sites with mature forest stands in Germany. These long‐term study sites are part of the European Level II program and comprise 17 beech, 14 spruce, 17 pine, and 9 oak stands. The chloride balance method was used to calculate seepage fluxes and inorganic N leaching below the rooting zone for the period from 1996 to 2001. Nitrogen input by throughfall was significantly different among most forest types, and was in the order: spruce > beech/oak > pine. These differences can be largely explained by the amount of precipitation and, thus, it mirrors the regional and climatic distribution of these forest types in Germany. Mean long‐term N output with seepage was log‐normal distributed, and ranged between 0 and 26.5 kg N ha^–1 yr^–1, whereby 29 % of the sites released more than 5 kg N ha^–1 yr ^–1. Leaching of inorganic N was only significantly lower in the pine stands (P < 0.05) compared with leaching rates of the spruce stands. Median N output : input ratio ranged between 0.04 and 0.11 for the beech, oak, and pine stands, while the input : output ratio of the spruce stands was 0.24, suggesting a higher risk of NO₃^– leaching in spruce forests. Following log‐transformation of the data, N input explained 38 % of the variance in N output. The stratification of the data by the C : N ratio of the O horizon or the top mineral soil revealed that forests soils with a C : N ratio < 25 released significantly more NO₃^– (median of 4.6 kg N ha^–1 yr^–1) than forests with a C : N ratio > 25 (median of 0.8 kg N ha^–1 yr^–1). The stratification improved the correlation between N input and N output for sites with C : N ratios < 25 (r² = 0.47) while the correlation for sites with C : N ratios > 25 was weaker (r = 0.21) compared with the complete data set. Our results suggest that NO₃^– leaching may increase in soils with wide C : N ratios when N deposition remains on a high level and that the potential to store inorganic N decreases with C : N ratios in the O horizons becoming more narrow.     

Sulphur and nitrogen input to the Ratanica forested catchment (Carpathian Foothills,southern Poland)

The study covers 1991–1994 concentrations of SO₂ and NO₂ in the air, concentrations of sulphur and nitrogen in bulk precipitation, throughfall and stemflow as well as input of S and N to the Ratanica forested catchment (S. Poland), which is exposed to moderate anthropogenic pollution are presented. There was high input of sulphur (26 kg ha^?1) and nitrogen (24 kg ha^?1) to the catchment, mainly in NH4⁺ (18 kg ha^?1). The significant contribution of NH₄ ⁺ connected with intensive agriculture in surrounding fields has led to eutrophication of the ecosystem.     

Uptake,transport and assimilation of 15N-nitrate and 15N-ammonium in tea (Camellia sinensis L.) plants

¹⁵N studies were conducted using hydroponically grown tea (Camellia sinensis L.) plants to clarify the characteristics of uptake, transport and assimilation of nitrate and ammonium. From the culture solution containing 50 mg L^-1 N0₃-N and 50 mg L^-1 NH.-N, the uptake of NH₃-N after 24 h was twice as high as that of NO₃-N, while the uptake of N0₃-N from the culture solution containing 90 mg N0₃-N and 10 mg NH₃-N was twice that of NH₄-N. The presence of 0.4 mM Al had no significant effect on the N0₃-N and NH₄-N uptake from the culture solutions containing 50 mg L^-1 N0₃-N and 50 mg L^-1 NH₄-N, 90 mg L^-1 N0₃-N and 10 mg L^-1 NH₄-N or 99 mg L^-1 N0₃-N and 1 mg L^-1 NH₄-N. Transport of N0₃-derived N to young leaves was much more rapid than that of NH₄-derived NO₃ and NH₄-derived N was largely retained in the roots and lower stem. Young and mature shoots separated from the roots absorbed more N0₃-N than intact plants. Nitrate assimilation occurred in both, roots and young as well as mature leaves. Internal cycling of N0₃-derived Nand NH₄-derived N from one root part to another part was not appreciable after 28 h, suggesting that a longer of time is required for cycling in woody plants.     

Response of protozoan and microbial communities in various coniferous forest soils after transfer to forests with different levels of atmospheric pollution

During recent decades, forest ecosystems have been exposed to high levels of atmospheric pollution, and it has been argued that this affects the composition and activity of decomposer communities and, subsequently, ecosystem functioning. To investigate the effects of atmospheric pollution on protozoa and microflora, a new experimental design was used. Undisturbed soil columns, originating from six coniferous forests across Europe and representing different stages of soil acidification, were transferred to two Scots pine forests (Fontainebleau and Wekerom) with different levels of N and S deposition (NH₄ ⁺-N=4.90 and 42.50?kg ha^–1 year^–1; SO₄ ^–S=10.90 and 30.40?kg ha^–1 year^–1, respectively). The number of protozoa, microbial biomass C and microbial activity were estimated in the organic layer (Of) of the transferred soils at the two host sites after 21 months of incubation. The experiment aimed at answering two questions: (1) Do changes in environmental conditions, studied by transferring soils from one site to another, affect protozoa and microbial communities and, if so, (2) how important are changes in both N and S deposition in explaining the effects of soil transfer on protozoa and microbial communities? The interaction between protozoa and microbial communities was addressed with regard to these changes in environmental conditions. No effect of enhanced N or S deposition on protozoan numbers and microbial biomass C, basal respiration and caloric quotient was revealed. Reciprocal transfer of various soil columns resulted in lower abundance and activity of protozoa and microbes. This reduction could not be explained by differences in N and S deposition, but by differences in microclimate and adaptation. In some cases, protozoa correlated with pH, C/N ratio, P and S content and leached mineral N.     

A Single Law to Describe Atmospheric Nitrogen Bulk Deposition versus Rainfall Amount: Inputs at the Seine River Watershed Scale

Atmospheric nitrogen species (NH₄-N and (NO₃+NO₂)-N) were determined in weekly samples of atmospheric bulk deposition (dry plus wet), collected in France at seven sites over the course of a year. Rural, semi-rural and industrialised-urban sites were chosen in the Seine river watershed from the Seine estuary to upstream from Paris. Mean NH₄-N concentrations varied from 0.7 to 1.7 mg L^-1. Mean (NO₃+NO₂)-N concentrations were approximately 0.5 mg L^-1 for all sites except Paris (0.7 mg L^-1), which has a local impact on the fallout contamination from urban emissions. The relation between concentration and rainfall amount obeys a power law, in the form of y = ax ^b. When the nitrogen sources are very local, this relationship turns into a dilution law. Annual atmospheric nitrogen deposition (NH₄-N+(NO₃+NO₂)-N) was calculated and varied from 7.8 kg ha^-1 yr^-1 in the neighbourhood of a rural town to 17.3 kg ha^-1 yr^-1 in a very industrialised harbour. 58% of the atmospheric nitrogen deposition occurred during ‘spring + summer’ period. The total nitrogen atmospheric input to the Seine estuary, via direct deposition + indirect input via the watershed, was estimated to about 5% of the total nitrogen load within the Seine river basin.     

Ammonium Nitrogen Deposition as a Dominant Source of Nitrogen in a Forested Watershed Experiencing Acid Rain in Central Japan

To clarify nitrogen (N) sources, the overall N budget in a forested watershed in Kanagawa Prefecture, Central Japan was estimated by measuring dissolved inorganic N (DIN; NH₄ ⁺ + NO₃ ^– + NO₂ ^–) from Nov 2004 through Oct 2005. The estimated N budget (–1.43 kg N ha^–1 year^–1) showed that the N output rate (stream water N) was higher than the N input rate (bulk deposition N) in the watershed. The annual NO₂ ^– and NO₃ ^– input rates were 0.02 and 1.99 kg N ha^–1 year^–1, respectively. NH₄ ⁺ was the predominant source in this forested watershed, accounting for 71% (4.99 kg N ha^–1 year^–1) of DIN input rate. In addition, this study estimated rainfall pH, air temperature, and wind direction, which were considered as controlling factors related to the atmospheric deposition rate of NH₄ ⁺. This study showed that the rainfall NH₄ ⁺ was inversely proportional to the initial pH of the rainfall, which was calculated by adding the amount of H⁺ consumed by the dissociation process of NH_3(aq) to the measured rainfall pH. This result implies that acid rain can elevate the solubility of NH_3(g) and the dissociation capacity of NH₄ ⁺ throughout the process of precipitation. Also, this study provides strong evidence that the high NH₄ ⁺ deposition rate is mainly derived from NH_3(g) emitted from livestock wastes under the NH₃ transport condition of warm summer and favorable wind direction.