Inorganic Nitrogen Leaching Research Articles

Long term response and adaptation of farmland water, carbon and nitrogen balances to climate change in arid to semi-arid regions

Climate change poses a challenge for resource utilization and environmental pollution issues caused by agricultural production, especially in arid to semi-arid regions. Farmland water, carbon and nitrogen balances are closely related to these resource and environmental issues. Thus, the Agro-Hydrological & chemical and Crop systems simulator was used to assess the response of water, carbon and nitrogen balances to climate change in a spring wheat farmland of arid to semi-arid Northwest China and to propose adaptation strategies. Five Global Climate Models from the Coupled Model Intercomparison Project 6 and two Shared Socioeconomic Pathways (SSP1–2.6 and SSP5–8.5) were used to establish scenarios with the Agro-Hydrological & chemical and Crop systems simulator to simulate farmland water, carbon and nitrogen balances for the 2025–2100 period. Various irrigation amounts and nitrogen fertilization rates were tested as compensation strategies. Results indicated that climate change could negatively affect farmland water, carbon and nitrogen balances, especially under the SSP5–8.5 scenario. Precipitation showed an increasing trend, thus percolation increased and soil water consumption decreased from 2025 to 2100. However, for the carbon budget, although the soil carbon dioxide emissions tend to decrease, the net primary production was also significantly reduced, which resulted in declining the net ecosystem carbon budget under future climatic conditions. In addition, higher temperature and increased precipitation enhanced soil inorganic nitrogen leaching and nitrous oxide emissions but reduced ammonia volatilization from 2025 to 2100. Overall, the soil total nitrogen loss was increased over time, whereas crop nitrogen uptake was significantly reduced. In relation to the SSP1–2.6 scenario, the SSP5–8.5 scenario accelerated the increase rates of soil water percolation and total nitrogen loss over time, as well as the decrease rates of crop nitrogen uptake and net primary production over time. The negative effects caused by climate change can be mitigated by reducing irrigation and increasing nitrogen fertilization. For the SSP1–2.6 scenario, 30% irrigation reduction and 30% nitrogen fertilization increase can effectively decrease soil water percolation and the related nitrogen losses while crop nitrogen uptake, net primary production and net ecosystem carbon budget increase in relation to the current management (irrigation = 240 mm and nitrogen fertilization = 200 kg ha–1). For SSP5–8.5 the strategy with 45% irrigation reduction and 45% nitrogen fertilization increase can also decrease nitrogen losses and increase crop nitrogen uptake, net primary production and net ecosystem carbon budget.

Nutrients status and soil microbial biomass C and N in charcoal production sites of derived savannah forest of southwestern Nigeria

Deforestation and other anthropogenic activities, including charcoal production affect several microbial activities and nutrients availability and status in the savannah forest soil of southwestern Nigeria. However, understandings of the microbial activities and soil nutrients availability in these sites have not been thoroughly studied. Therefore, the study aims to clarify the charcoal production effects on the microbial biomass carbon and nitrogen, nutrients status of charcoal production sites and the surrounding soils. Soil samples were collected to determine the microbial biomass contents in carbon and nitrogen (BC and BN), organic carbon of the soil (SOC), total nitrogen (TN), ammonium and nitrate nitrogen [(NH4+-N) and (NO3N)] in the soil layers between 0–15, 15–30 and 30 – 45 cm, under different locations of charcoal production and non-production sites (CPS and NPS) respectively. We found out that SOC, TN, C/N ratio, Bc and BN and the ratios of Bc/SOC and BN/TN were significantly higher in the NPS than in the CPS. The SOC, TN, BC and BN and the ratios of Bc/SOC and BN/TN declined significantly (P ˂ 0.05) with increase in depth in the two sites under different locations. However, NH4+-N and NO3N contents in the NPS were significantly lower compared to the CPS. The results of the analysis indicate better soil nutrients in term of SOC and TN in the NPS than CPS. It is therefore posited that NPS is healthier and can sustain soil microbial activities than CPS. Although, NPS is lower in inorganic nitrogen contents determined, CPS has the potential to reduce leaching of inorganic nitrogen and increases its availability in the derived savannah agro-ecological region of southwestern Nigeria. Effort must be made to mitigate the large-scale conversions of the native derived savannah forests for traditional charcoal production that contributes to environmental pollution; it is therefore useful to consider biochar strategy in order to mitigate global warming and manage soil health and productivity.

Effects of molecular weight of polyaspartic acid on nitrogen use efficiency and crop yield.

In the past decades, ever-increasing fertilizer use has led to a continuous increase in agricultural output. However, serious waste of resources occurs because of the low utilization of fertilizers. Polyaspartic acid (PASP) is a biodegradable polymer that can be used as a fertilizer synergist in agricultural production to improve the nutrient utilization capacity of plants. For polymers, the molecular weight (MW) often affects their effectiveness. However, little information is available on the effects of PASP MW in agriculture, especially on nitrogen leaching and plant element uptake. This work was conducted to identify the effect of PASPs with three different MWs - PASP-1 (MW: 5517), PASP-2 (MW: 6934), and PASP-3 (MW: 7568) - on nitrogen leaching, lettuce growth, and wheat cultivation. The results revealed that PASP favored plant growth and nitrogen accumulation in the soil, independent of crop species. PASP with a higher MW improved yields and the agronomic characteristics of lettuce and wheat. Furthermore, apparent amelioration of nitrogen use efficiency for lettuce (7.6%, 12.8%, and 15.0%) and wheat (4.6%, 8.1%, and 9.2%) was observed in the treatments with PASP addition. The effects and merits of PASPs on preventing ammonium nitrogen leaching and improving lettuce and wheat productivity were as follows: PASP-3 > PASP-2 > PASP-1. The MW of PASP is an essential factor affecting inorganic nitrogen leaching and crop productivity, and PASP with a higher MW (7568) is recommended for application in agriculture. © 2022 Society of Chemical Industry.

Alteration of soil-surface electrochemical properties by organic fertilization to reduce dissolved inorganic nitrogen leaching in paddy fields

Dissolved inorganic nitrogen (DIN) adsorbed onto soil colloids plays an important role in soil N leaching, but previous studies have not clearly defined the mechanisms of this process in paddy soils under organic fertilization. In this study, we investigated how ongoing fertilization can change soil DIN leaching via affects on soil-surface electrochemical properties and physical properties, and the main influences of soil properties on DIN leaching were characterized. Five fertilization regimes applied during a 5-year field experiment were employed to study this mechanism, i.e., no fertilizer, chemical fertilizer, chemical fertilizer plus hog manure, hog manure, and chemical fertilizer plus oil cake. Increasing levels of applied manure decreased DIN leaching from the soil profile, especially for NH4+, the main form of DIN in the leachate and soil. Compared to chemical fertilizer, organic fertilization changed the surface electrochemical and physical properties more effectively with regards to decreased soil bulk density (9.84–20.49 %, P < 0.05) and specific surface area (26.38–44.88 %, P < 0.05), as well as enhanced water-holding capacity (19.05–42.86 %, P < 0.05) and the number and density of soil-surface charges (7.97.55–98.44 %, P < 0.05). Furthermore, organic fertilization significantly increased the NH4+ adsorbed by soil. Structural equation modeling showed that soil-surface electrochemical properties had the greatest impact (β = –0.88, P < 0.05) on the NH4+ content of the leachate when compared with the soil NH4+ adsorption capacity and physical properties. The increase in the soil-surface charge, surface charge density, surface potential, and surface electric field strength under organic fertilization increased soil NH4+ retention in soil (P < 0.001), and thus, these changes decreased the risk of NH4+ leaching. Our results suggest that continuous substantial organic fertilization may mainly decrease early DIN leaching from cultivated paddy soils in the Dongting Lake area by altering soil-surface electrochemical properties, where soil-surface electrochemical properties can be set as an internal factor to predict soil ion migration in agriculture systems, such as the Dongting Lake area or other similar regions.

Effects of contrasting biochars on the leaching of inorganic nitrogen from soil

The use of excessive nitrogen (N) fertilizers usually causes soil N leaching, eutrophication, and water pollution. Nevertheless, biochars may play an important role in decreasing N losses from soil to waterways. The objectives of this study were to explore the effect of contrasting biochars on the leaching of key inorganic N species during the N transformation processes in a biochar-amended soil. A column leaching experiment was carried out through a soil treated with 2% (w/w) application rate of dead pig-derived biochar (DPB), ultrasonic-modified dead pig-derived biochar (UPB), or Platanus orientalis branch-derived biochar (POB). The DPB contained 5% N, which was much greater than that in the POB (1% N). The amount of ammonium and nitrate N (NH4+-N and NO3−-N) in the leachate samples from the soil treated with different biochars were collected and analyzed periodically. After 20 weeks of incubation, the cumulative NH4+-N leaching loss from the control treatment was 1.87, 2.00, and 2.07 times greater than that from the POB-, DPB-, and UPB-treated soils (P < 0.05). Biochar application reduced NH4+-N leaching from the soil, likely because of NH4+ ion retention and adsorption on biochar surface areas and pore spaces. The cumulative NO3−-N in the leachate from the biochar-amended soil was significantly lower than that of the untreated control, in the order of POB < UPB = DPB < untreated control. With the application of DPB and UPB, the cumulative inorganic N (especially NO3−-N) leaching loss was significantly higher by up to 50%, compared with the POB treatment (P < 0.05). The suppression of nitrate leaching may be due to microbial N immobilization, resulting from the addition of different biochars. It is apparent that the ultrasonic modification process of DPB caused no further inhibition of inorganic N leaching from the soil via incorporating the UPB. Despite the relatively high N concentration in the DPB, 2% of DPB dosage reduced inorganic N leaching from the amended soil. Therefore, regardless of the biochar N concentrations, biochars could be used to improve N fertilizer use efficiency by reducing N leaching loss from soils.

Simultaneous and Efficient Capture of Inorganic Nitrogen and Heavy Metals by Polyporous Layered Double Hydroxide and Biochar Composite for Agricultural Nonpoint Pollution Control.

Agricultural nonpoint pollution has been recognized as the main source of aquatic contaminants worldwide, such as inorganic nitrogen (ION) and heavy metals (HMs). It is an important challenge to simultaneously and efficiently immobilize soil ION and HMs in farmland. Herein, we present a polyporous Mg/Fe-layered double hydroxide and biochar composite (Mg/Fe-LDH@biochar) with the efficient coadsorption capacity of ION and HMs for the mitigation of agricultural nonpoint pollution toward aquatic systems. The Mg/Fe-LDH@biochar showed strong adsorption toward ION (i.e., NH4+-N and NO3--N) and HMs (i.e., Cu, Zn, Ni, Pb, and Cd), with maximum capacity of 98.53 mg of NH4+-N/g, 27.09 mg of NO3--N/g, 295.80 of mg Cu/g, 141.70 mg of Zn/g, 75.59 mg of Ni/g, 1264.10 mg of Pb/g, and 126.30 mg of Cd/g, respectively. More attractively, by deionized water extraction, the adsorbed ION on the composite was more easily rereleased, with a desorption percentage of about 42.33 ± 6.87% NO3--N and 1.42 ± 0.78% NH4+-N, than that of HMs (<1.0%). This difference is primarily related with the strength of bonding forces of ION and HMs when adsorbed on Mg/Fe-LDH@biochar, in the sequence of NO3--N (van der Waals force and electrostatic attraction) < NH4+-N (hydrogen bonding) < HMs (ionic/coordinate bonding). Finally, to examine the performance of Mg/Fe-LDH@biochar for practical applications in farmland, column leaching experiments were successfully conducted by stimulated rainfall events. The addition of Mg/Fe-LDH@biochar into soils could greatly reduce the leaching of ION and HMs simultaneously, with reduction ratios of >60, >40, and >90% for NH4+-N, NO3--N, and HMs, respectively, at 3.0% addition. Moreover, there was no leaching risk of Fe ions into the water body from Mg/Fe-LDH@biochar-amended soils.

Maize Stover Biochar Accelerated Urea Hydrolysis and Short-term Nitrogen Turnover in Soil

The study was carried to determine the labile carbon contents in biochar pyrolyzed under different temperatures and its effect on urea hydrolysis rate. Corn stovers were pyrolyzed at highest temperature of 300°C, 500°C and 700 °C to produce fresh biochar. Soil incubation experiment was conducted with biochar application rate of 0% and 2% with presence of urea. The results showed that biochars accelerated urea hydrolysis, and high temperature pyrolyzed biochar have more significant effect on soil pH enhances and acceleration of urea hydrolysis than biochar pyrolyzed at low temperature. Moreover, biochar produced at 300°C contains relative high concentration of labile carbon, and 43-64% of labile carbons were oxidized within 40 days incubation. The labile carbon in biochars also leaded microbes thrives and resulted in accelerate short-term N turnover. i.e. at early stage of incubation, fresh biochar increased mineralization of soil N by 79-449 mg•kg−1, and matured biochar by 30-61 mg•kg−1, but microbial immobilization effect was observed in fresh biochar-amended soil at the end of incubation. We concluded that aged biochar is suitable for simultaneous soil amendment with urea rather than newly produced biochar as it can promote available N accumulation in short time thus increase the risk of inorganic nitrogen leaching loss.

Increased nitrogen leaching following soil freezing is due to decreased root uptake in a northern hardwood forest

The depth and duration of snow pack is declining in the northeastern United States as a result of warming air temperatures. Since snow insulates soil, a decreased snow pack can increase the frequency of soil freezing, which has been shown to have important biogeochemical implications. One of the most notable effects of soil freezing is increased inorganic nitrogen losses from soil during the following growing season. Decreased nitrogen retention is thought to be due to reduced root uptake, but has not yet been measured directly. We conducted a 2-year snow-removal experiment at Hubbard Brook Experimental Forest in New Hampshire, USA to determine the effects of soil freezing on root uptake and leaching of inorganic nitrogen simultaneously. Snow removal significantly increased the depth of maximal soil frost by 37.2 and 39.5 cm in the first and second winters, respectively (P < 0.001 in 2008/2009 and 2009/2010). As a consequence of soil freezing, root uptake of ammonium declined significantly during the first and second growing seasons after snow removal (P = 0.023 for 2009 and P = 0.005 for 2010). These observed reductions in root nitrogen uptake coincided with significant increases in soil solution concentrations of ammonium in the Oa horizon (P = 0.001 for 2009 and 2010) and nitrate in the B horizon (P < 0.001 and P = 0.003 for 2009 and 2010, respectively). The excess flux of dissolved inorganic nitrogen from the Oa horizon that was attributable to soil freezing was 7.0 and 2.8 kg N ha(-1) in 2009 and 2010, respectively. The excess flux of dissolved inorganic nitrogen from the B horizon was lower, amounting to 1.7 and 0.7 kg N ha(-1) in 2009 and 2010, respectively. Results of this study provide direct evidence that soil freezing reduces root nitrogen uptake, demonstrating that the effects of winter climate change on root function has significant consequences for nitrogen retention and loss in forest ecosystems.

Modelling inorganic nitrogen leaching in nested mesoscale catchments in central Germany

ABSTRACTWater quality models are increasingly used to predict nutrient losses from anthropogenically impacted catchments, but comprehensive model calibration and transfer of model parameters are often difficult. The objectives of this study are (i) to assess the Hydrological Predictions for the Environment (HYPE) model for simulating runoff and inorganic nitrogen (IN) leaching in nested and spatially heterogeneous mesoscale catchments in central Germany and (ii) to investigate the temporal and spatial variations of IN leaching. A multi‐site and multi‐objective calibration approach using the parameter estimation tool PEST was employed. Results showed that parameters related to evapotranspiration were most sensitive for runoff simulation. The nitrogen balance was controlled by plant uptake and denitrification. Runoff was well reproduced for both calibration (1994–1999) and validation (1999–2004) periods at all three gauging stations, with the lowest Nash–Sutcliffe efficiency (NSE) of 0·86 and bias (PBIAS) of less than 15%. In addition, the model was tested successfully to predict the dynamics of soil water storage during extreme climatological events. IN concentrations showed increase in magnitude and decrease in dynamics from upstream to downstream of the catchment, reflecting the combined effects of nutrient inputs and IN in‐stream retention. The dynamics of monthly IN loads were well represented by the model during the whole simulation period, with the lowest NSE and PBIAS of 0·69 and 33%, respectively. Results revealed seasonal dynamics of IN leaching due to the combined effects of hydrological and biogeochemical processes, which is consistent with runoff dynamics. This indicates the controlling role of hydrology on nitrogen transport processes. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Role of arthropod communities in bioenergy crop litter decomposition†

The extensive land use conversion expected to occur to meet demands for bioenergy feedstock production will likely have widespread impacts on agroecosystem biodiversity and ecosystem services, including carbon sequestration. Although arthropod detritivores are known to contribute to litter decomposition and thus energy flow and nutrient cycling in many plant communities, their importance in bioenergy feedstock communities has not yet been assessed. We undertook an experimental study quantifying rates of litter mass loss and nutrient cycling in the presence and absence of these organisms in three bioenergy feedstock crops-miscanthus (Miscanthus x giganteus), switchgrass (Panicum virgatum), and a planted prairie community. Overall arthropod abundance and litter decomposition rates were similar in all three communities. Despite effective reduction of arthropods in experimental plots via insecticide application, litter decomposition rates, inorganic nitrogen leaching, and carbon-nitrogen ratios did not differ significantly between control (with arthropods) and treatment (without arthropods) plots in any of the three community types. Our findings suggest that changes in arthropod faunal composition associated with widespread adoption of bioenergy feedstock crops may not be associated with profoundly altered arthropod-mediated litter decomposition and nutrient release.

Growth response and nitrogen use physiology of Fraser fir (Abies fraseri), red pine (Pinus resinosa), and hybrid poplar under amino acid nutrition

Plants can assimilate amino acids from soils. This has been demonstrated in controlled environments and soils of various forest ecosystems. However, the role of root-absorbed amino acids in plant nitrogen nutrition is still poorly understood. We investigated the agroecological performance and nutrient use physiology of two conifers (Abies fraseri and Pinus resinosa) and one hardwood species (hybrid poplar) under amino acid fertilization. Arginine fertilizer (arGrow® Complete) was applied at varying rates (0, 56, 112, 224, and 336 kg N/ha) and compared to an inorganic control treatment (ammonium sulfate 112 kg N/ha). Parameters monitored included tree growth response, foliar nitrogen concentration, and inorganic nitrogen leaching below the rootzone. Results obtained indicate a significant growth and foliar nitrogen response to amino acid treatments, with increasing amino acid application leading to greater growth and foliar nitrogen. However, rates two to three times higher than that of the inorganic control were necessary to provide similar growth and foliar nitrogen responses. These observations were suggested to be due to competition with soil microbes for organic nitrogen, growth inhibition due to the presence of large concentrations of amino acids, or adsorption to cation exchange sites. Amino acid applications did not increase the leaching of inorganic nitrogen due either to the binding of positively charged arginine cations to exchange sites or rapid mineralization followed by plant assimilation. Mineral nitrogen collected in leachate samples increased with the application rate suggesting at least some mineralization in high amino acid application rates. We conclude that growth response and nitrogen use physiology of these species when treated with arginine are largely controlled by soil processes including microbial competition and adsorption. Further studies are being conducted to confirm these hypotheses.

Abstracts of Nippon Dojo-Hiryogaku Zasshi

Abstracts of Nippon Dojo-Hiryogaku Zasshi

Predicting dissolved inorganic nitrogen leaching in European forests using two independent databases

Regional-scale databases can be particularly useful for identifying relationships between dissolved inorganic nitrogen (N) leaching in forests and environmental drivers, which in turn allow an assessment of the risk of ecosystem damage, such as forest acidification and eutrophication of downstream water bodies. However, detecting the ‘signal’ of a significant correlate to N leaching against a background of wide variability in other factors requires a large number of sites, and the validation of models developed requires a similarly large number of independent sites. Here we use two large and fully independent databases of forest ecosystems across Europe to develop and validate indicators of N saturation and leaching. One database was used for model development and the other for validating these models. Among 35 variables considered, the most significant indicators of N leaching in the model development database were: the flux of dissolved inorganic N in deposition, mean annual temperature, mean altitude, the site drainage (plot vs catchment), needle- and litter-N concentration, organic horizon C:N ratio, and subsoil pH. Altitude was not a consistent predictor (it was significant in the development database but not in the validation database), and needle and litter N concentration, plot vs catchment, and subsoil pH all showed high intercorrelation with N deposition and so were not significant in models already including N deposition. The most consistent and useful indicators of N leaching were throughfall N deposition, organic horizon C:N ratio and mean annual temperature. Sites receiving low levels of N deposition (< 8 kg N ha − 1 y − 1 ) showed very low output fluxes of N and were simulated separately from more polluted forests. In general, the models successfully predicted N leaching (mean of ± 5 kg N ha − 1 y − 1 between observed and predicted) from forests at early to intermediate stages of nitrogen saturation but not from nitrogen-saturated sites. Thus, simple relationships developed from combining (1) external drivers (deposition, temperature) and (2) site conditions (nitrogen status of soils) can successfully estimate nitrogen leaching from forests that have not yet been highly damaged by N deposition.

Manipulation of Snow in Small Headwater Catchments at Storgama, Norway: Effects on Leaching of Inorganic Nitrogen

We have manipulated the winter-time soil temperature regime of small headwater catchments in a montane heathland area of southern Norway to study the possible effects on concentrations and fluxes of inorganic nitrogen in runoff. The experiments included extra insulation of soils in two catchments to prevent subzero temperatures during winter, and removal of snow in two other catchments to promote soil frost. Increased soil temperatures during winter increased the springtime concentrations and fluxes of ammonium (NH4) and nitrate (NO3) in runoff. By contrast, snow removal with development of significant soil frost showed no systematic effects on mean concentrations or fluxes of inorganic N. The results from our experiments suggest that warmer soils during winter caused by exceptionally mild winters, or alternatively a heavy snowpack, imply a greater risk for inorganic N leaching in this region than a possible increase of soil frost events because of reduced snow cover.

Bracken effects on inorganic nitrogen leaching from an upland podzol

AbstractLeaching of inorganic N species to stream waters from upland areas of the UK is increasing, reflecting the increases in atmospheric deposition of nitrogen species due to increased levels of vehicular emissions. Bracken cover in UK uplands is also increasing overall (Taylor, 1986), and the architectural nature of bracken has been shown to both increase deposition of atmospheric constituents to soils and change their chemical and physical nature. We have tested the nutrient status of upland podzols from the Lake District, Cumbria, UK, from under both moorland grass and bracken. The results show reduced levels of base cations and nitrate throughout the profile and decreases in the organic matter content of surface horizons as a consequence of bracken encroachment. We also report increased ammonium concentrations in lower soil horizons under bracken, possibly leading to increased leaching to stream waters. These results suggest either increased leaching of soil nutrients due to bracken encroachment or increased storage of nutrients within the bracken rhizome system. Results also suggest changes in either microbial activity or the microbial community of podzols, possibly due to the allelopathic nature of bracken. This may have caused changes in the soil nutrient dynamics, possibly accounting for some of the changes seen. We hypothesize that increased bracken cover within the British uplands has the potential to increase leaching of inorganic nitrogen to upland streams.

Testing the INCA model in a small agricultural catchment in southern Finland

Abstract. Nutrient leaching from agricultural production is still recognised as a major environmental problem in Finland. To estimate agricultural nitrogen loading under changing land-use and climate conditions, the Integrated Nitrogen Model for Catchments (INCA) was applied in Savijoki, a small (15.4 km2) agricultural catchment, which represents the intensively cultivated areas in south-western Finland. Hydrological calibration and testing of the INCA model was first carried out in Savijoki during 1981–2000. In spite of heterogeneous soil and land-use conditions, INCA was able to reproduce the overall hydrological regime in the stream. The model was calibrated further in respect of nitrogen processes during 1995–2000. The model was able, reasonably well, to simulate the overall annual dynamics of the inorganic N concentrations in the stream water and the annual N export from the catchment. The average simulated NO3-N export was 550 kg N km–2 yr–1 and the observed one (constituting more than half of the annual total N export) was 592 kg N km–2 yr–1. For NH4-N, the simulated export was somewhat higher than that measured but NH4-N was only 4% of the total N export. In spite of some underestimation of flow and N concentration during extreme hydrological conditions, the INCA model proved to be a useful tool for analysing flow pattern and inorganic nitrogen leaching in a small agricultural catchment, characterised by a rapid response to rainfall. Keywords: nitrogen, integrated modelling, hydrology, catchment, agriculture

Subsurface drip irrigation in raised bed tomato production. I. Nitrogen and phosphate losses under current commercial practice

The leaching of inorganic nitrogen and phosphate was studied at field sites that utilised subsurface drip irrigation (SDI) for commercial production of processing tomatoes. Irrigation expended for the establishment of crops, at emergence, accounted for 34% of the seasonal total in a Rochester clay (site 1) and 25% in a Binabbin clay (site 2). In the period after emergence and up to crop harvests, irrigation and rainfall amounted to 88% and 105% of calculated crop evapotranspiration for site 1 and site 2, respectively. Drainage between the commencement of irrigation and crop harvests amounted to 66 mm below 2 m at site 1 and 60 mm below 0.9 m at site 2. Total irrigation caused a 2- and 5-fold depletion of soil chloride at site 1 (within 2 m) and site 2 (within 0.9 m), respectively. The drainage and chloride depletion showed that irrigation regimes at these sites were conducive to the leaching of fertiliser inputs. It was calculated that ~32 kg NO–3-N + NH+4-N/ha and 7 kg HPO2–4-P/ha was leached below 2 m during irrigation at site 1. At site 2, ~75 kg NO–3-N + NH+4-N/ha was leached below 0.9 m during irrigation.Post harvest amounts of inorganic nitrogen and phosphate at site 1 and site 2 indicated that fertiliser applications exceeded total crop uptake of both compounds. Post harvest quantities of inorganic nitrogen and phosphate at several other commercial locations (sites 3, 4, 5, 6) showed that excessive fertiliser use was not restricted to site 1 and site 2. At site 1, between an early autumn harvest and early spring, when vegetable beds were fallow, the leaching losses of post harvest amounts of both compounds below 2 m were 137 kg NO–3-N + NH+4-N/ha and 11 kg HPO2–4-P/ha. The irrigation and fertiliser management practices at all sites were similar to those reported for studies of SDI production of other vegetable and grain crops. Altogether, these results indicated that the effects of SDI combined with excessive fertiliser inputs in current commercial practice may cause the leaching of significant amounts of nitrogen and phosphate to groundwater depths.

Soil Acidification Induced by Ammonium Sulphate Addition in a Norway Spruce Forest in Southwest Sweden

The contributions of different acidifying processes to the total protonload (TPL) of the soil in control plots (C) and ammonium sulphate treatedplots (NS) were studied in a Norway spruce stand in Southwest Sweden during 1988–1998. The annual deposition of inorganic nitrogen and sulphate was on average 18 kg N and 20 kg S ha-1. In addition the NS treated plots received 100 kg N and 114 kg S ha-1 annually. The amounts of nutrients added to the ecosystem by wet and dry deposition and the leaching at 50 cm depth were calculated. The net atmosphericproton load, the proton load by nitrogen transformations in the soil, the sulphate sorption/desorption in the soil and the excess base cation accumulation in biomass were calculated. There was no leaching of inorganic nitrogen from control plots during the study period. The net atmospheric proton deposition, originating from sulphuric and nitric acid deposition, was the main contributor to TPL in control plots. The addition of ammonium sulphate increased the leaching of ammonium, nitrate, sulphate, magnesium and calcium but not of potassium. The TPL in NS plots was about ten times that in control plots. The nitrogen transformation processes were the main contributors to TPL to NS soil, in the beginning by ammonium uptake and later also by nitrification. The pH decreased by 0.4 units in the mineral soil. The between-year variation in TPL during the eleven year period in C plots (200–1500 molc ha-1 yr-1) and in NS plots (1000–13000 molc ha-1 yr-1) was mainly dependent on the sorption or release of sulphate. Both in C and NS, the TPL was buffered mainly by dissolving solid aluminium compounds, most probably some Al(OH)3 phase.

Climate change as a confounding factor in reversibility of acidification: RAIN and CLIMEX projects

Abstract. The RAIN and CLIMEX experiments at Risdalsheia, southernmost Norway, together cover 17 years (1984-2000) of whole-catchment manipulation of acid deposition and climate. A 1200 m2 roof placed over the forest canopy at KIM catchment excluded about 80% of ambient acid deposition; clean rain was sprinkled under the roof. A climate change treatment (3.7°C increase in air temperature and increase in air carbon dioxide concentrations to 560 ppmv) was superimposed on the clean rain treatment for four years (1995-1998). Sea-salt inputs and temperature are climate-related factors that influence water chemistry and can confound long-term trends caused by changes in deposition of sulphur and nitrogen. The RAIN and CLIMEX experiments at Risdalsheia provided direct experimental data that allow quantitative assessment of these factors. Run-off chemistry responded rapidly to the decreased acid deposition. Sulphate concentrations decreased by 50% within three years; nitrate and ammonium concentrations decreased to new steady-state levels within the first year. Acid neutralising capacity increased and hydrogen ion and inorganic aluminium decreased. Similar recovery from acidification was also observed at the reference catchment, ROLF, in response to the general 50% reduction in sulphate deposition over southern Norway in the late 1980s and 1990s. Variations in sea-salt deposition caused large variations in run-off chemistry at the reference catchment ROLF and the year-to-year noise in acid neutralising capacity was as large as the overall trend over the period. These variations were absent at KIM catchment because the sea-salt inputs were held constant over the entire 17 years of the clean rain treatment. The climate change experiment at KIM catchment resulted in increased leaching of inorganic nitrogen, probably due to increased mineralisation and nitrification rates in the soils. Keywords: acid deposition, global change, water, soil, catchment, experiment, Norway.

Modelling the response of soil and runoff chemistry to forest harvesting in a low deposition area (Kangasvaara, eastern Finland)

Abstract. A simple dynamic soil model developed to analyse the effects of atmospheric deposition and nutrient cycling on terrestrial ecosystems, SMART 2, was applied to the Kangasvaara catchment in eastern Finland. Given the historical deposition and forest growth patterns and reasonable values for the input parameters, SMART 2 was calibrated successfully to reproduce present-day soil and Kangasvaara catchment on the soil and runoff water chemistry under a future deposition scenario (GRP scenario). These impacts were also compared to the effects of further reducing the deposition of sulphur and nitrate under the maximum feasible reduction (MFR) scenario. The model demonstrates the consequences of breaking the nutrient cycle, and predicts that final cutting results in increased leaching of inorganic nitrogen and base cations from the cut part of the catchment for about 10 years. The resulting concentrations in the stream will depend on the ability of the buffer zones surrounding the stream to capture and utilize these nutrients.