Dynamics Of Inorganic Nitrogen Research Articles

Stabilized urea for maize grown on an Amazonian Cerrado soil

AbstractUrea splitting and the use of stabilized ureas in corn (Zea mays L.) crops are management strategies that increase urea efficiency and reduce nitrogen (N) losses by volatilization and leaching. This study aimed to evaluate the effects of urea stabilized with urease inhibitor (UI) and nitrification inhibitor (NI) compared to conventional urea applied at three different schedules, on corn grain yield and the dynamics of inorganic nitrogen on an Amazonian Cerrado soil, Brazil. Two experiments were carried out, one in 2019 and the other one in 2021, in a randomized block design with four replications. Treatments were arranged in a factorial scheme (3 × 3), with three types of urea (urea, U; UI; and NI) and three application schedules (100% at planting, 30% at planting and 70% as topdressing, and 30% at planting and two topdressings with 35% N). In 2019, compared to U and UI, NI increased corn yield when 100% of urea was applied at planting. Regardless of the splitting management, NI ensured the same yields. In 2021, urea splitting was required to improve corn yields, and UI promoted higher yield in all urea application schedule. In 2019 and 2021, both NI and UI, respectively, ensured higher inorganic N levels in the soil, especially after the first topdressing. These N contents are reflected in yield gains. Urea with nitrification or urease inhibitor may be a relevant option for managing nitrogen fertilization in corn crops in the Amazonian Cerrado.

Wetland nutrient assessment in lake Patzcuaro, Michoacan, Mexico

In the current project we have the opportunity to show a Wetland ecosystems are also located inside freshwater lakes as in Patzcuaro considered one of the most important natural lakes of Mexico due to its environmental, economic, cultural and social attributes. Extensive areas of this lake, its fauna, native flora and watershed are severely affected by sewage without treatment, fertilizers non-point runoff derived from agriculture, deforestation, and inadequate land use change. Within the most altered aquatic components from these processes is the wetland ecosystem which is the objective of this study because of its ecological and biogeochemical importance in Lake Patzcuaro. In this study the dynamics of total phosphorus and inorganic nitrogen inside the littoral wetland located in the southern shore of Patzcuaro where seven sites were established located inside the wetland, limnetic zone, and an underwater spring in a transect of 1,500 m long. The obtained values of dissolved total phosphorus and inorganic nitrogen indicated that these nutrients are retained when these components crossed the wetland ecosystem in 67.5% and 70.8% respectively. Hence, the wetland ecosystem is functioning as natural filter and the inputs from other pathways are deteriorating lake water quality.

Short Time‐Scale Variability of Ammonium, Nitrate, and Nitrogen Loss Dynamics During an Upwelling‐Induced Bloom at the Oregon Shelf

AbstractAmmonium, a key intermediate nutrient, is typically low to undetectable on the Oregon coast, particularly as active upwelling delivers high onshore flow of ammonium‐poor waters. However, during bloom and post‐bloom conditions large ammonium concentrations and uptake rates have been described. High‐frequency on board nitrate + nitrite and ammonium analysis synchronized with continuous data from a towed profiling vehicle (equipped with in situ temperature, salinity, dissolved oxygen, and beam attenuation sensors), allowed us to describe coupled high‐resolution physico‐chemical dynamics of inorganic nitrogen in seven cross‐shelf transects, over several days, during an active phytoplankton bloom following cessation of upwelling favorable winds. We present first‐of‐their‐kind high‐resolution cross‐sections showing a build‐up, both within a thin plume of onshore‐originated water, and in mid‐to‐bottom on‐shore water columns, from undetectable values to up to 8 µM of ammonium. The plume extended across the shelf at mid‐depth and was identified in all transects. We also detected a decrease of nitrate in distinct water masses close to the mid‐shelf seabed, associated with low dissolved oxygen, and identified and quantified the amount of nitrogen lost. We found that nitrogen loss was minimal on the first days of relaxation conditions, and increased up to 12 μM off Newport. Combining nitrogen fluxes from benthic incubation chambers and N loss calculated with the NO tracer, we estimated that denitrification in sediments could not account for all N loss, requiring 22%–86% to occur elsewhere. Close association of N loss with particle‐rich, low O2 waters suggests the possibility that particle‐aggregate micro‐environments could provide additional sites for water column denitrification.

Nitrogen isotopes reveal a particulate-matter-driven biogeochemical reactor in a temperate estuary

Abstract. Estuaries and rivers are important biogeochemical reactors that act to modify the loads and composition of nutrients in the coastal zone. In a case study during July 2013, we sampled an 80 km transect along the Elbe Estuary under low-oxygen conditions. To better elucidate specific mechanisms of estuarine nitrogen processing, we tracked the evolution of the stable isotopic composition of nitrate, nitrite, particulate matter, and ammonium through the water column. This approach allowed assessment of the in situ isotope effects of ammonium and nitrite oxidation and of remineralization at the reach scale. The isotope effects of nitrite oxidation and ammonium oxidation were consistent with pure-culture assessments. We found that the nitrogen budget of the Elbe Estuary is governed by settling, resuspension, and remineralization of particulate matter, and we further used our stable isotope data to evaluate sources and sinks of nitrogen in the Elbe Estuary via an isotope mass-balance approach. We find that the reactivity of particulate matter, through its remineralization in the estuary, is the main control on the isotope dynamics of inorganic nitrogen species. Moreover, while underscoring this role of particulate matter delivery and reactivity, the isotope mass balance also indicated additional sinks of reactive nitrogen, such as possible denitrification of water column nitrate in the intensively dredged and deep Hamburg Harbor region.

Spatial and Seasonal Dynamics of Inorganic Nitrogen and Phosphorous Compounds in an Orchard-Dominated Catchment with Anthropogenic Impacts

The influence of various types of agricultural activities on the dynamics of biogenic compounds of flowing water was broadly recognized in many spatial and temporal scales. However, relatively minor attention was paid to the hydrochemical functioning of horticultural catchments despite their importance and dominance in some regions of Europe. Thus, the current study investigated spatial and seasonal variations in inorganic nitrogen and phosphorous compounds in stream water in the Mogielanka River catchment, with 72% covered by apple orchards. Water samples were collected from fifteen sites distributed across the catchment in the monthly timescale from March 2020 to February 2021. Concentrations of NO3−, NO2−, NH4+, and PO43− were determined photometrically, while in situ water temperature, oxygen saturation, electrical conductivity, and pH, were measured with the use of portable devices. The impact of horticulture was mainly documented in the higher concentration of NO3− during the winter months; however, maximum values did not exceed 15 mg·dm−3 and were relatively low in comparison to catchments dominated by arable lands. The authors also found a clear impact of unstratified reservoirs and inflows from wastewater treatment plants on the dynamics of biogenic compounds. The correlations of PO43− with the sums of precipitation suggested, in turn, that increased PO43− concentration mainly results from poor sewage management. The results provided preliminary but unique and spatially extensive insight into the functioning of an orchard-dominated lowland catchment and allowed the researchers to point out the main recommendations for improving water quality in similar regions.

Dynamics of soil water extractable organic carbon and inorganic nitrogen and their environmental controls in mountain forest and meadow ecosystems in China

We investigated the differences among two types of forest (pine and oak forests) and a meadow in soil water extractable organic carbon (WEOC), ammonium (NH4+) and nitrate (NO3−) concentrations in the Qinling Mountains, China. Our results showed that soil WEOC, NH4+ and NO3− concentrations were higher in the meadow than in the forests, and they were higher in the pine forest than in the oak forest. The soil surface temperature and soil water content were positively correlated with WEOC and inorganic nitrogen concentrations (P < 0.01). In addition, there was a significantly negative correlation between soil WEOC concentration and pH (P < 0.01). Moreover, soil WEOC concentration was positively correlated with the inorganic nitrogen concentration (P < 0.01). Generally, soil WEOC concentration decreased in the forests, and increased in the meadow under warming condition. The effects of warming on soil WEOC and dissolved inorganic nitrogen (DIN) concentrations varied with time. We elucidated that warming had a significant influence on soil WEOC concentration in the pine forest, whereas soil DIN concentration was affected significantly by warming only in the meadow. Our findings indicate that soil WEOC and DIN show different responses to warming in the mountain forest and meadow ecosystems. This study could provide useful insights for the prediction of soil carbon and nitrogen cycling and their responses to climate change in the complex mountain ecosystem.

Impacts of Subsurface Tile Drainage on Age—Concentration Dynamics of Inorganic Nitrogen in Soil

AbstractWe explore the impacts of tile drains in agricultural fields on the coupled age and concentration dynamics of nitrate, immobile ammonium, mobile ammonia and ammonium, and nonreactive tracers such as chloride. We implement two mobile interacting pore domains to capture matrix and preferential flow paths in a coupled ecohydrology and biogeochemistry model, Dhara. We apply this model to an agricultural farm that utilizes a corn‐soybean rotation in the Midwestern United States located in the Intensively Managed Landscapes Critical Zone Observatory. In general, we observe both low concentration and age of nitrate in the areas that are classified as topographic depressions even with the presence of tile drains. Also, an increase in the age of mobile ammonia/ammonium is observed after installing tile drains. This is in contrast to the cases for nitrate, immobile ammonium, and nonreactive tracer. These results arise because the depletion of mobile ammonia/ammonium due to tile drainage causes a high mobility flux from immobile ammonium to mobile ammonia/ammonium, which also carries a considerable amount of relatively old age of nitrogen from immobile ammonium to mobile ammonia/ammonium. These results illustrate how storm event scale dynamics impact spatial heterogeneity and temporal variability of the efflux, which helps in disentangling the complexity of nitrogen dynamics in the soil. This understanding can contribute to precision agriculture for nitrogen applications to reduce environmental impacts.

Green manure effects on inorganic nitrogen dynamics in soil and its accumulation in grape must

The adoption of green manure practices in organic agriculture is increasingly spreading. This work aims to prove whether winter green manure—when compared to a traditional mineral fertilizer— alters the dynamics of inorganic nitrogen (NO3−and NH4+) availability in soil and the yeast assimilable nitrogen (YAN) in grape musts. During a two-year period, the soil nitrogen content was influenced by climatic trend and, especially, by rainfall. In fact, rainy periods reduced inorganic nitrogen availability in the soil. In both years, the green manure plot presented higher soil content of inorganic nitrogen at fruit-set, while different dynamics were shown over the following phenological phases. The must YAN concentration did not differ among treatments over the two-year experiment.

Dynamika dus�ka v p�de pod p�enicou letnou f. ozimnou (Triticum aestivum L.) v z�vislosti od sp�sobu obr�bania

The trial on an experimental basis of Slovak University of Agriculture in Nitra during the growing seasons 2011/2012 and 2012/2013 under winter wheat was conducted. The object of this study was to determine the effects of different tillage systems on the dynamics of inorganic nitrogen forms. Three tillage systems were used: B1 -> conventional soil cultivation – medium depth ploughing (to 0.25 m); B2 -> shallow soil cultivation (to 0.20 m); B3 -> minimalization soil tillage – disk tillage (to 0.15 m). Within each treatment was used of NPK fertilization according to its content in soil + plough down of post harvest residues. Concentration of nitrate nitrogen (1.29 mg*kg-1 – 29.68 mg*kg-1) and ammonium nitrogen (0.13 mg*kg-1 – 14.34 mg*kg-1) had significant dynamics over the whole research period. The highest content of Nin was in the autumn season (39.09 mg*kg-1), which provide sufficient nutrients for initial growth of the winter wheat. Tillage system had no statistically significant effect on dynamics of inorganic nitrogen in the soil. On the other hand, reduction of depth tillage has been associated with an increase content of inorganic nitrogen (B1 = 9.54 mg*kg-1; B2 = 9.89 mg*kg-1; B3 = 11.19 mg*kg-1). The results of experiment shown that dynamics of inorganic nitrogen was mainly influenced by the change of temperature and humidity parameters during the growing season.

Three‐reaction model for the anaerobic digestion of microalgae

Coupling an anaerobic digester to a microalgal culture has received increasing attention as an alternative process for combined bioenergy production and depollution. In this article, a dynamic model for anaerobic digestion of microalgae is developed with the aim of improving the management of such a coupled system. This model describes the dynamics of inorganic nitrogen and volatile fatty acids since both can lead to inhibition and therefore process instability. Three reactions are considered: Two hydrolysis-acidogenesis steps in parallel for sugars/lipids and for proteins, followed by a methanogenesis step. The proposed model accurately reproduces experimental data for anaerobic digestion of the freshwater microalgae Chlorella vulgaris with an organic loading rate of 1 gCOD L(-1) d(-1). In particular, the three-reaction pathway allows to adequately represent the observed decoupling between biogas production and nitrogen release. The reduced complexity of this model makes it suitable for developing advanced, model-based control and monitoring strategies.

Nitrogen dynamics in soil management systems. I - flux of inorganic nitrogen (NH4+ and NO3-)

In agricultural systems the N-NH4+ and N-NO3- contents is significantly affected by soil management. This study investigated the dynamics of inorganic nitrogen (N; NH4+ and NO3-) in an experimental evaluation of soil management systems (SMSs) adopted in 1988 at the experimental station of the ABC Foundation in Ponta Grossa, in the Central South region of the State of Paraná. The objective of this study was to evaluate the changes in N-NH4+ and N-NO3- flux in the surface layer of a Red Latosol arising from SMSs over a 12-month period. The experiment was arranged in a completely randomized block design in split plots, in three replications. The plots consisted of the following SMSs: 1) conventional tillage (CT); 2) minimum tillage (MT); 3) no-tillage with chisel plow every three years (NT CH); and 4) continuous no-tillage (CNT). To evaluate the dynamics of inorganic N, the subplots represented samplings (11 sampling times, T1 - T11). The ammonium N (N-NH4+) and nitric N (N-NO3-) contents were higher in systems with reduced tillage (MT and NT CH) and without tillage (CNT) than in the CT system. In the period from October 2003 to February 2004, the N-NH4+ was higher than the N-NO3- soil content. Conversely, in the period from May 2004 to July 2004, the N-NO3- was higher than the N-NH4+ content. The greatest fluctuation in the N-NH4+ and N-NO3- contents occurred in the 0-2.5 cm layer, and the highest peak in the N-NH4+ and N-NO3- concentrations occurred after the surface application of N. Both N-NH4+ and N-NO3- were strongly correlated with the soil organic C content, which indicated that these properties vary together in the system.

Ingestion and excretion of nitrogen by larvae of a cabbage armyworm: the effects of fertilizer application

1 Insect frass has significant impacts on decomposition and soil nitrogen dynamics. Although the frass contains various forms of nitrogen that may differently influence nitrogen dynamics in the decomposition process, how the nitrogen form in the insect frass is influenced by host plant quality remains poorly understood. 2 The present study examined the effects of application of fertilizer on leaf quality of Brassica rapa L. var. perviridis Bailey (Brassicaceae), and on the consumption, frass excretion and frass quality of its insect pest Mamestra brassicae (L.) (Lepidoptera: Noctuidae), with a particular focus on the dynamics of inorganic nitrogen. 3 Brassica rapa increased total nitrogen concentration, and accumulated inorganic nitrogen [i.e. leaf nitrate-nitrogen (NO3−-N) and ammonium-nitrogen (NH4+-N)] in the leaves in response to the application of fertilizer. 4 Although leaf consumption and frass excreted by M. brassicae was not affected by fertilizer treatment, frass quality was influenced by host plant quality as altered by fertilizer applications. Frass contained high concentrations of total nitrogen, NO3−-N, and NH4+-N under high fertilizer treatment. In particular, the larvae excreted much more NH4+-N than ingested. The relationship between host plant quality and insect frass quality, as well as the potential implications for decomposition and nutrient dynamics, are discussed.

広島県東部海域における溶存態無機窒素動態とノリの色落ちへの影響

2004 年 4 月～2008 年 3 月に，広島県東部海域で溶存態無機窒素（DIN）の動態調査を行い，1～3 月に慢性的に起こるノリの色落ちの原因について考察した。この海域では 12 月頃より西部から東部にかけて次第に高塩分化し，一方で東部に形成される河川水由来の低塩分水塊が西部まで達しなくなることがわかった。このような海況の変化と区画漁場内での DIN およびノリ色調の分布から，本海域のノリの色落ちは，河川水流入の減少と西から東への水塊の移動によって，河川由来の DIN がノリ漁場へ到達しにくくなることにより起こると考えられた。

THE EFFECT OF AGROTECHNICAL INTERVENTIONS ON SEASONAL CHANGES OF INORGANIC NITROGEN CONTENT IN THE SOIL

We researched the influence of soil cultivation and fertilization on changes of nitrate, ammonium and inorganic nitrogen content in soil during the monitored vegetation periods (2004/2005 – 2005/2006). This experiment was realized on experimental bases of Slovak University of Agriculture in Nitra – Dolna Malanta on the winter/summer wheat (Triticum aestivum), variety Bonita, with red clover as its before-crop. In the field trial we used two types of tillage, B1 – conventional tillage up to the depth of 0,25 m and B2 – disc ploughing up to 0,15 m, with three variants of fertilization, 0 – unfertilized control, PH – fertilization according to its content in soil and PZ – fertilization according to its content in soil + plough down of post harvest residues. Samples of the soil were taken from the two soil depth (0,0- 0,3 m and 0,3-0,6 m) and in each vegetation period there were 8 takings of soil samples in four repetitions. During monitored vegetation period this dynamics was changeable. The content of nitrate nitrogen in the soil in autumn was about 40 % higher than content of ammonium nitrate. This tendency changed in spring, when the average content of ammonium nitrogen was higher than the content of nitrate nitrogen on average about 60 %. The cultivation had significant influence on dynamics of inorganic nitrogen. The average content of inorganic nitrogen in conventional tillage up to the depth of 0,25 m was 8,43 mg.kg-1 and in disc ploughing it was 7,60 mg.kg-1. The influence of fertilization on changes of inorganic nitrogen was significantly important. Monitored ways of fertilization within the content of nitrates in the soil had the following averages: in unfertilized soil 7,48 mg.kg-1, in fertilized soil NPK 8,20 mg.kg-1 and in the soil fertilized with plough down of post harvest residues 8,37 mg.kg-1. In the first and second variety of soil cultivation we found out a low increase of average concentration of nitrates in the fertilized soil in comparison with unfertilized one. High significant influence on dynamics of nitrate nitrogen in the soil had date of sample takings and also depth. In the first depth (0,0-0,3 m) the level of nitrate nitrogen was 9,18 mg.kg-1 and in the second depth (0,3-0,6 m) it was 6,85 mg.kg-1.

Soil Inorganic Nitrogen and Microbial Biomass Carbon and Nitrogen Under Pine Plantations in Zhanggutai Sandy Soil

The dynamics of soil inorganic nitrogen (NH + 4 -N and NO − 3 -N) and microbial biomass carbon (Cmic) and nitrogen (Nmic) under 30-year-old fenced Pinus sylvestris L. var. mongolica Litvin (SF), unfenced P. sylvestris L. var. mongolica Litvin (SUF), and unfenced Pinus densiflora Siebold et Zucc. (DUF) plantations in the Zhanggutai sandy soil of China were studied during Apr. to Oct. 2004 by the in situ closed-top core incubation method. All mentioned C and N indices in each stand type fluctuated over time. The ranges of inorganic N, Cmic, and Nmic contents in the three stand types were 0.7–2.6, 40.0–128.9, and 5.4–15.2 μg g −1, respectively. The average contents of soil NH + 4 -N and Cmic under the three 30-year-old pine plantations were not different. However, soil NO − 33 -N and total inorganic N contents decreased in the order of SUF ≥ SF ≥ DUF, the Nmic content was in the order of SF = SUF > DUF, and the Cmic: Nmic ratio was in the order of SUF = DUF > SF. Seasonal variations were observed in soil inorganic N, microbial biomass, and plant growth. These seasonal variations had certain correlations with microbe and plant N use in the soil, and their competition for NH + 4 -N was mostly regulated by soil N availability. The influence of tree species on inorganic N and Nmic were mainly because of differences in litter quality. Lack of grazing decreased the Cmic:Nmic ratio owing to decreased carbon output and increased the ability of soil to supply N. The soil N supply under the P. sylvestris var. mongolica plantation was lower than under the P. densiflora plantation.

Pathways and dynamics of 15NO 3− and 15NH 4+ applied in a mountain Picea abies forest and in a nearby meadow in central Switzerland

To evaluate the pathways and dynamics of inorganic nitrogen (N) deposition in previously N-limited ecosystems, field additions of 15N tracers were conducted in two mountain ecosystems, a forest dominated by Norway spruce ( Picea abies) and a nearby meadow, at the Alptal research site in central Switzerland. This site is moderately impacted by N from agricultural and combustion sources, with a bulk atmospheric deposition of 12 kg N ha −1 y −1 equally divided between NH 4 + and NO 3 −. Pulses of 15NH 4 + and 15NO 3 − were applied separately as tracers on plots of 2.25 m 2. Several ecosystem pools were sampled at short to longer-term intervals (from a few hours to 1 year), above and belowground biomass (excluding trees), litter layer, soil LF horizon (approx. 5–0 cm), A horizon (approx. 0–5 cm) and gleyic B horizon (5–20 cm). Furthermore, extractable inorganic N, and microbial N pools were analysed in the LF and A horizons. Tracer recovery patterns were quite similar in both ecosystems, with most of the tracer retained in the soil pool. At the short-term (up to 1 week), up to 16% of both tracers remained extractable or entered the microbial biomass. However, up to 30% of the added 15NO 3 − was immobilised just after 1 h, and probably chemically bound to soil organic matter. 16% of the NH 4 + tracer was also immobilised within hours, but it is not clear how much was bound to soil organic matter or fixed between layers of illite-type clay. While the extractable and microbial pools lost 15N over time, a long-term increase in 15N was measured in the roots. Otherwise, differences in recovery a few hours after labelling and 1 year later were surprisingly small. Overall, more NO 3 − tracer than NH 4 + tracer was recovered in the soil. This was due to a strong aboveground uptake of the deposited NH 4 + by the ground vegetation, especially by mosses.

Dynamics of Inorganic Nitrogen in Nitrate and Glucose-amended Alkaline–saline Soil

Induction of assimilatory NO3 ) reduction through the application of an easily decomposable substrate in alkaline–saline soils of the former lake Texcoco (Mexico) resulted in a fast immobilization of NO3 ) in excess of N required for metabolic activity and the release of large concentrations of NO2 ) and smaller amounts of NH4 + . We postulated that this was regulated by the amounts of NO3 ) and glucose added, and affected by the specific characteristics of soil from the former lake Texcoco. This was investigated by spiking soils of different electrolytic conductivity (EC) 56.0 dS m )1 (soil A of Texcoco) and 11.6 dS m )1 (soil B of Texcoco) with different concentrations of NO3 ) and glucose while dynamics of CO2 ,N H 4 + , NO2 ) and NO3 ) were monitored in an aerobic incubation for 7 days. For comparison reasons (control) an agricultural soil with low EC (0.3 dS m )1 ) was included as well. In the agricultural soil, 67% of the added glucose mineralized within 7 days, but only 15% in soil A of Texcoco and 20% in soil B of Texcoco. The application of NO3 ) to the agricultural soil added with glucose increased cumulative production of CO2 1.2 times, 1.5 times in soil A of Texcoco and 1.8 times in soil B of Texcoco. Concentration of NO2 ) increased to >100 mg NO2 ) -N kg )1 when 1000 mg glucose-C kg )1 and 500 mg NO3 ) -N kg )1 were added to soil A and B of Texcoco, but remained <3 mg NO2 ) -N kg )1 in the agricultural soil. The ratio between the cumulative production of CO2 and the decrease in concentration of NO3 ) was approximately one in soil A and B of Texcoco, but 10 in the agricultural soil after 3 days. It was found that micro-organisms in the alkaline– saline soil of the former lake Texcoco were capable of immobilizing large quantities of NO3 ) when an easy decomposable substrate was available in excess of what might be required for metabolic activity while producing large concentrations of NO2 ) , but these phenomena were absent in an agricultural soil. In soil of Texcoco, concentrations of NO2 ) and NH4 + increased with increased salinity and availability of NO3 ) . This ability to remove large quantities of NO3 ) under these conditions and then utilize it at a later time might benefit micro-organisms of the N limited alkaline–saline soils of Texcoco.

Simplifying Dynamic River Water Quality Modelling: A Case Study of Inorganic Nitrogen Dynamics in the Crocodile River (South Africa)

The ultimate goal of this study is to develop a simple dynamic river water quality model that can be applicable in a data limited situation and is compatible with typical activated sludge models, so that the model can be used in integrated modelling of wastewater and river water quality in the future. A simplified river water quality model was formulated based on a conceptual hydraulic sub-model and simplification of an existing river water quality model. The simplified water quality was derived from the River Water Quality Model No. 1, which is one of the most comprehensive basic river water quality models available in literature. The applicability of the simplified model in data limited situations was investigated using a case study of inorganic nitrogen (nitrate and ammonia) in the Crocodile River (South Africa). The model was calibrated and validated on the basis of independent data collected for four years (1987–1990). The results show that the model can adequately describe the seasonal dynamics of inorganic nitrogen in the Crocodile River. The sensitivity of the model output to the model inputs was also analysed, and the results indicate that the model is most sensitive to the microbial biomass (nitrifier) followed by hydraulic parameters. The relation of river flow versus concentration of inorganic nitrogen in the downstream section of the river was also examined in order to identify the main source and critical time for nitrate pollution.

EFFECT OF LONG-TERM GREEN FALLOW ON INORGANIC NITROGENCONTENT IN THE SOIL

The impact of fallow management on the dynamics of inorganic nitrogen and pH was evaluated in the field experiment established on Ortic Luvisol during 1996 – 2000. The green fallow was maintained on the field for 6 years without tillage except of mowing. The trial included the following variants of management: 1. uncut green fallow, 2. cut green fallow, biomass remained on the field, 3. cut green fallow, biomass was removed from the field. The soil samples were collected from a 0 to 0,3 m of depth to do analyses of nitrogen and pH. During the growing season (spring, summer and autumn aspects) the contents of ammonia nitrogen, nitrate nitrogen and pH were measured. In each treatment the ammonium nitrogen predominated and with its ratio to total nitrogen ranged around 70 %. In studied variants the significance in nitrate nitrogen content was found only between 2nd and 3rd variant. However, statistically highly significant differences were found between spring and autumn sampling. A year had the most significant effect on changes of inorganic nitrogen, especially amount of rainfall that influenced significantly the activity of nitrification process. The mean values of nitrate nitrogen were influenced by acid soil pH reaction.

Simulation model for the effects of climate change on temperate grassland ecosystems

We studied the responses of temperate grasslands to climate change using a grassland ecosystem model which simulates seasonal dynamics of shoots, roots, soil water, mycorrhizal fungi, saprophytic microbes, soil fauna, inorganic nitrogen, plant residues and soil organic matter. Forty-year simulations were made for several climate change scenarios. The model was driven with observed weather and with combinations of elevated atmospheric CO 2, elevated temperature, and either increased or decreased precipitation. Precipitation and CO 2 level accounted for most of the variation among climate change treatments in the responses of soil, plants, animals and microbes. Elevated temperature extended the growing season but depressed photosynthesis in the summer, with little net effect on annual primary production. Doubling CO 2 (1) caused persistent increases in primary production, in spite of greater nitrogen limitation, and (2) led to greater storage of carbon in plant residues and soil organic matter. The increased carbon storage was not great enough to keep pace with the present rate of increase in atmospheric CO 2.