Nitrate Concentrations In Soil Water Research Articles

The GANE Roof Project: The impact of reduced N & S deposition and experimental warming in an acid grassland

A field-based system used to quantify the response of acid grassland to reduced atmospheric nitrogen and sulphur deposition, and to investigate the effects of elevated soil temperature on acid grassland development is described. The system is based on 12 retractable roofs, covering undisturbed experimental plots of acid grassland and three controls. Nine roofs are used to exclude natural precipitation and three roofs used to retain emitted IR radiation at night. An irrigation system has been developed to simulate natural precipitation, allowing for the application of specific treatment regimes of ambient, reduced nitrogen and reduced nitrogen/sulphur deposition beneath the nine rain exclusion plots. Plant, soil parameters, leachate chemistry and gaseous fluxes are being monitored and initial results on soil water chemistry are described. Warming appeared to enhance nitrate concentrations in soil water but this was not sustained beyond the first year of treatment. In contrast, the deposition reduction treatments decreased soil water nitrate concentrations within a few weeks of reducing deposition. This was not observed for other solutes such as sulphate or ammonium suggesting a more direct link between deposition of nitrate and leaching losses.

Indicators of nitrate in wetland surface and soil-waters: interactions of vegetation and environmental factors

Abstract. This paper describes a new bio-indicator method for assessing wetland ecosystem health; as such, the study is particularly relevant to current legislation such as the EU Water Framework Directive, which provides a baseline of the current status of surface waters. Seven wetland sites were monitored across northern Britain, with model construction data for predicting eco-hydrological relationships collected from five sites during 1999. Two new sites and one repeat site were monitored during 2000 to provide model test data. The main growing season for the vegetation, and hence the sampling period, was May–August during both years. Seasonal mean concentrations of nitrate (NO3-) in surface and soil water samples during 1999 ranged from 0.01 to 14.07 mg N l–1, with a mean value of 1.01 mg N l–1. During 2000, concentrations ranged from trace level (<0.01 mg N l–1) to 9.43 mg N l–1, with a mean of 2.73 mg N l–-1. Surface and soil-water nitrate concentrations did not influence plant species composition significantly across representative tall herb fen and mire communities. Predictive relationships were found between nitrate concentrations and structural characteristics of the wetland vegetation, and a model was developed which predicted nitrate concentrations from measures of plant diversity, canopy structure and density of reproductive structures. Two further models, which predicted stem density and density of reproductive structures respectively, utilised nitrate concentration as one of the independent predictor variables. The models were tested where appropriate using data collected during 2000. This approach is complementary to species-based monitoring, representing a useful and simple tool to assess ecological status in target wetland systems and has potential for bio-indication purposes. Keywords: bio-indicators, surface water, water quality, wetland vegetation

Productivity and soil nutrient relations of bedwork watermeadows in southern England

Irrigation (or ‘floating’) of watermeadows in Europe was economically important before the 20th century because it enhanced grazing sward productivity in the spring. Today, few operational systems remain, but interest in floating as a technique is returning as concern grows over floodplain management, the fate of nutrients and the sustainability of agricultural production systems. Investigations into grass productivity, phosphorus and nitrogen relations were undertaken at a surviving watermeadow system, the Britford Site of Special Scientific Interest, Salisbury, England (1995–2001) and at an experimental site at Norwich, England (1998–2001). Irrigation significantly increased late-winter and early-spring grass productivity at Britford in the order of 60–80% over 5 weeks compared with un-irrigated controls. Phosphorus travelled across the system; some included with the clay fraction in suspended sediment, but available phosphorus in the topsoil reduced across the meadows by between one-half and one-third. Nitrate in irrigation water was utilised, but the meadow system did not reduce concentrations of dissolved nitrate. Increased nitrate concentration in soil-water is attributed to mineralisation after drainage. Annual nitrogen cycle process modelling suggests the present levels of production and soil organic matter accumulation are attributable to environmental eutrophication. A conceptual model is presented for enhanced spring growth following floating and it is concluded that, while temperature is the trigger that enhances productivity early in the season, this is achieved by enhancing the mineralisation of soil organic matter and release of available nitrogen. There was no evidence that watermeadows act as a sink for nitrogen mobile in surface waters but there was significant uptake of topsoil available phosphorus.

Response of surface and subsurface water quality to land use changes

Modern agricultural production systems need to reduce their environmental contamination potential. Within the test site of the FAM Research Network on Agroecosystems, the existing agricultural system was modified from intensive to sustainable land use practices. The aim of this study was to quantify the long-term effects of these new practices on the surface and subsurface water quality at the Research Station Scheyern in Bavaria, Germany. Nutrient concentrations in soil water and ground water were monitored by soil hydrological stations and in multilevel wells. Water and material fluxes were observed in a brook and in the tile drain system over a 4-year period. Nitrate concentrations in soil water were affected by soil types, relief position and fertilization (farming system). Highest concentrations were found in soils under potatoes and integrated crop production (ICP), lowest under organic farming (OF). Since monitoring began in 1994, nitrate concentrations below the root zone decreased continuously from 25–50 to 5–30 mg NO 3 − l −1. Temporal variable concentrations within the root zone were stabilized by plant uptake and lateral subsurface flow in deeper soil horizons. Lower material inputs to soils were confirmed by decreasing nitrate and chloride concentrations in drain water and diffuse lateral input to the Brook West. Nitrogen loading into the brook decreased up to 50% whereas in the upper regional ground water, values greater than 50 mg NO 3 − l −1 still reflect former nutrient loads. Surface water phosphorous load was also strongly affected by agricultural practice. The lateral inputs area into the brook from the farm showed that phosphate loading decreased up to 25% (from 0.37 to 0.09 kg P ha −1 a −1). However, concentrations of dissolved reactive ortho-phosphate (DRP) remained high, due to remobilization from the brook's sediment. Our results have shown that adapted land use practice can reduce groundwater and surface water loads effectively. The anti-erosion program (mulching, minimum tillage, fallow strips and others) minimized lateral loads to the surface water and optimized fertilization and intercropping, whereas ecofarming mainly reduced the leakage potential of soils. The slow response in the groundwater is strongly affected by the mean transit time, whereas lateral subsurface flow and buffering effects of soils and sediments determine the dynamics within brooks and ponds.

Effects of land-use on the activity and diversity of methane oxidizing bacteria in forest soils

Methane is an important greenhouse gas and CH 4 oxidation in soil represents a significant sink for this gas. High capacity CH 4 oxidation potentials and molecular profiles of CH 4 oxidizing bacteria in soil were compared for five land-use treatments at a fully replicated experimental site within the Gisburn Forest Experiment, to assess the effects of land-use on both the potential activity of CH 4 oxidizing bacteria and their diversity. Forestry land-use was found to have a highly significant effect on CH 4 oxidation potentials. Highest CH 4 oxidation potentials were found in soils collected under stands of oak, in grassland plots, and in one soil under Norway spruce. A negative relationship between soil water nitrate concentration and CH 4 oxidation capacity was evident across the experimental site, with the high nitrate soils under stands of alder exhibiting little or no capacity for CH 4 oxidation even at optimal temperature and water content. Molecular profiles indicated that a diverse range of bacteria with the potential to oxidize CH 4 were present in all soils, however no clear correlation with CH 4 oxidation potential was identified.

Nitrogen deposition and leaching from two forested catchments in Southwest China--preliminary data and research needs.

Increased nitrogen deposition has resulted in increased nitrogen pools and nitrogen leaching in European and North American forest soils. The development in Asia in general, and China in particular, suggests increased deposition of reduced nitrogen from changes in agricultural practices and of oxidized nitrogen from rapid growth of the transportation sector. Decreased nitrogen retention in forested areas in the future may cause increased NO3– leaching and, thus, acidification and eutrophication in surface waters. The differences in climate, ecosystems, land use, and deposition history make direct application of knowledge from studies in Europe and North America difficult. In Southwest China the potential for nitrogen mobilization from forest soils may be high because of the warm and humid climate, resulting in high decomposition rates of soil organic matter. However, there are very few data available for quantifying the suspected potential for increased nitrogen leaching in forest ecosystems. Here we present data from two forested catchments, dominated by Masson pine (Pinus massoniana), near Guiyang and Chongqing, respectively, in Southwest China. The present nitrogen deposition is moderate, estimated in the range from 10 to 40 kg N ha–1 year–1. The C/N ratios of the soils are generally below 15. Nitrate concentrations in soil water are rather variable in space, with highest values of several hundred microequivalents per liter. The turnover rate of nitrogen in the forest ecosystem is quite high compared to the atmospheric deposition rate. At present, nitrate runoff from the catchments is low and intermediate in Guiyang and Chongqing, respectively. More research is needed to improve our ability to predict future nitrogen leaching from subtropical Asian coniferous forests.

Are differences in root growth of nitrogen catch crops important for their ability to reduce soil nitrate-N content, and how can this be measured?

An experiment was made to measure root growth of nitrogen catch crops, to investigate whether differences in root growth among plant species are related to their ability to deplete the soil nitrate-N pool. Large differences were observed in root growth parameters. Monocot species had rooting depth penetration rates in the range of 1.0 to 1.2 mm d−1 °C−1, whereas the non-legume dicot species had rates between 1.5 and 2.3 mm d−1 °C−1. Substantial differences were also found in the lag time from sowing until significant root growth was observed. The estimated temperature sum needed for the crops to reach a rooting depth of 1.0 m varied from 750 d °C for fodder radish to 1375 d °C for Italian ryegrass. The depth distribution of the root system varied strongly, and at a depth of 1.0 m the non-legume dicot species generally had root intensities (number of root intersections m−1 line on the minirhizotrons) 12 times as high as the monocot species. The amount of nitrate left in the topsoil (0–0.5 m) was only weakly correlated to a few of the measured plant and root parameters, whereas nitrate left in the subsoil (0.5–1.0 m) was clearly correlated to several root parameters. Subsoil nitrate residues were well correlated to root intensity, but showed even stronger correlations to more simple estimates of rooting depth. In the deepest soil layer measured (1.0–1.5 m), the soil water nitrate concentration was reduced from 119 μg L−1 without a catch crop to 61 μg L−1 under Italian ryegrass and to only 1.5 μg L−1 under fodder radish. The results show that to identify the important differences in root growth among catch crops, root growth must be measured in deep soil layers. In this study, none of the measurements made aboveground or in the upper soil layers were well related to subsoil nitrate depletion.

Nitrate leaching in an organic dairy/crop rotationas affected by organic manure type, livestock densityand crop

Abstract. In dairy farming systems the risk of nitrate leaching is increased by mixed rotations (pasture/arable) and the use of organic manure. We investigated the effect of four organic farming systems with different livestock densities and different types of organic manure on crop yields, nitrate leaching and N balance in an organic dairy/crop rotation (barley–grass‐clover–grass‐clover–barley/pea–winter wheat–fodder beet) from 1994 to 1998. Nitrate concentrations in soil water extracted by ceramic suction cups ranged from below 1 mg NO3‐N l−1 in 1st year grass‐clover to 20–50 mg NO3‐N l−1 in the winter following barley/pea and winter wheat. Peaks of high nitrate concentrations were observed in 2nd year grass‐clover, probably due to urination by grazing cattle. Nitrate leaching was affected by climatic conditions (drainage volume), livestock density and time since ploughing in of grass‐clover. No difference in nitrate leaching was observed between the use of slurry alone and farmyard manure from deep litter housing in combination with slurry. Increasing the total‐N input to the rotation by 40 kg N ha−1 year−1 (from 0.9 to 1.4 livestock units ha−1) only increased leaching by 6 kg NO3‐N ha−1. Nitrate leaching was highest in the second winter (after winter wheat) following ploughing in of the grass‐clover (61 kg NO3‐N ha−1). Leaching losses were lowest in 1st year grass‐clover (20 kg NO3‐N ha−1). Averaged over the four years, nitrate concentration in drainage water was 57 mg l−1. Minimizing leaching losses requires improved utilization of organic N accumulated in grazed grass‐clover pastures. The N balance for the crop rotation as a whole indicated that accumulation of N in soil organic matter in the fields of these systems was small.

Nitrate leaching losses under Miscanthus grass planted on a silty clay loam soil

Abstract. Nitrate leaching under newly planted Miscanthus grass was measured for three years. The crop received either no fertilizer‐N or an annual spring application of 60 kg or 120 kg N ha‐1. During three winters soil water was collected from porous cup probes installed 90 cm deep. Nitrate leaching was calculated from the mean drain flow recorded in two drain gauges multiplied by the mean nitrate‐N concentration in the soil water solutions collected. In the first year soil water nitrate concentrations were high on all treatments and N losses were 154, 187 and 228 kg ha‐1 respectively on the unfertilized treatment and those that received 60 or 120 kg N ha‐1. Leaching losses in the second and third years were, in turn, 8, 24 and 87 kg ha‐1 and 3, 11 and 30 kg ha‐1 for the unfertilized treatment and for the 60 and 120 kg N ha‐1 treatments respectively. Leaching losses were closer to those recorded under extensively managed grassland than arable land. The large losses in the first year were probably due to the previous agricultural management at the site and excessive inputs of N on the fertilized plots. In the second and third year, lower drainage volumes may also have influenced losses. The results show that Miscanthus, once established, can lead to low levels of nitrate leaching and improved groundwater quality compared with growing arable crops.

The effect of crop, N‐level, soil type and drainage on nitrate leaching from Danish soil

Abstract. Nitrate leaching measurements in Denmark were analysed to examine the effects of husbandry factors. The data comprised weekly measurements of drainage and nitrate concentration from pipe drains in six fields from 1971 to 1991, and weekly measurements of nitrate concentration in soil water, extracted by suction cups at a depth of 1 m, from 16 fields in 1988 to 1993. The soils varied from coarse sand to sandy clay loam.The model used for analysing the data was: Y= exp (1.136–0.0628 clay+ 0.00565N +crop) D0.416, with R2= 0.54, where Y is the nitrate leaching (kg N/ha per y), clay is the % clay in 0‐25 cm depth (%), N is the average N‐application in the rotation (kg/ha/y) and D is drainage (mm/y). The most important factor influencing leaching was the crop type. Grass and barley undersown with grass showed low rates of leaching (17‐24 kg/ha/y). Winter cereal following a grass crop, beets, winter cereals following cereals and an autumn sown catch crop following cereals showed medium rates of leaching (36‐46 kg/ha/y). High rates of leaching were estimated from winter cereals following rape/peas, bare soil following cereals and from autumn applications of animal manure on bare soil (71‐78 kg/ha/y). Estimates of leaching from soil of 5, 12 and 20% clay were 68, 44 and 26 kg/ha/y, respectively. Leaching was estimated to rise significantly with increasing amounts of applied N.The model is suitable for general calculations of the effects of crop rotation, soil type and N‐application on nitrate leaching from sandy soil to sandy clay loarns in a temperate coastal climate.

Effects of enhanced nitrogen deposition in a spruce forest at Klosterhede, Denmark, examined by moderate NH 4NO 3 addition

The fate and effects of increased N deposition were investigated by experimental manipulation in a mature Norway spruce plantation at Klosterhede, western Denmark. The ambient N deposition was 15–20 kg N ha −1 yr −1. Addition of 35 kg N ha −1 yr −1 as ammonium nitrate to a 500-m 2 plot was carried out by handspraying monthly for 4 years. During the first year the spray was labeled with 15N. Tree growth was depressed by 4 successive spring or summer droughts throughout the treatment years. The nitrogen concentration in needles increased in the third year of treatment and critical low P concentrations (0.6–1 mg P g −1) developed possibly as a combined effect of drought and N stress on roots and mycorrhizae. Reduced retranslocation of N was indicated by increased concentration and flux of N in needle litterfall. Increased uptake of N was observed in all parts of the trees and the fraction of the input N taken up was increased from 32 to 43%, whereas the fraction immobilized in the soil was decreased from 40 to 33% of the input N. The decomposition remained unchanged, whereas the net N mineralization was increased 85% over the control. The effect on net mineralization may have resulted from saturation of the immobilization process rather than from an increase in gross mineralization. Soil respiration was not affected, indicating that microbial activity did not respond. Nitrification and denitrification were not important in either control or treated soils. Soil solution chemistry responded promptly to nitrogen applications. Nitrate concentrations increased at all depths, and nitrate leaching increased from < 0.3 to 4.2 kg N ha −1 yr −1 by the third year. Reduced biological control on nitrate leaching was indicated by increased nitrate concentration in soil water at the end of the growing season. Ammonium concentrations increased down to 15 cm depth, but all ammonium was retained in the system. Despite the increased nitrate leaching, 92% of the total inputs were retained. No changes in concentrations of other major ions due to the N additions were detectable. The effects of the successive droughts on growth and nutrient cycling caused significant interaction on the response to N addition. Continuation of the N addition treatment will be necessary to observe the full response of the simulated deposition increase in this forest.

Nitrate in soil water in three Norway spruce stands in southwest Sweden as related to N-deposition and soil, stand, and foliage properties

N-cycling was studied at three Norway spruce (Piceaabies (L.) Karst.) sites located within a distance of 30 km in southwest Sweden. Nitrate concentrations in soil water at 50-cm depth differed substantially between the three sites, annual site means being 0, 1, and 9 mg N•L−1. Using simulated runoff, the leaching of inorganic N from the two sites with the highest concentrations was estimated at, respectively, 7–8 and 19–30 kg•ha−1 during the hydrological year 1991–1992. The N-deposition measured as throughfall was 31 kg•ha−1 on the second site, suggesting that it was close to being N-saturated. The differences in nitrate concentration and estimated leaching across sites were not related to differences in forest growth or suggested symptoms of forest decline, such as canopy defoliation and nutrient deficiency. Nitrate concentrations were unrelated to N-deposition in an open field, but positively related to N-deposition in throughfall. However, the difference in N-leaching between the two main sites was much larger than the difference in N-deposition in throughfall. The difference in leaching seemed related to soil conditions. The soil with the highest leaching had the largest potential nitrification and a low C/N ratio (17–20) in the upper part of the profile. Nitrate concentrations in the soil water were positively related to the concentrations of arginine and 15N in foliage, which supports the use of these two variables as indicators of forests approaching N-saturation.

Effect of Different Organic Manures and Garden Waste Compost on the Nitrate Dynamics in Soil, N Uptake and Yield of Winter Wheat

ABSTRACT The different ratios of organic to inorganic nitrogen of organic fertilizers affect the nitrate dynamics in soil as well as the yield of crops. To examine this, winter wheat was cultivated on loess in Therwil near Basel (Switzerland). The plots were amended with stacked, composted and rotted manure, garden waste compost, slurry or mineral fertilizer (mineral control). In additional treatments, a top dressing with slurry was applied. Nitrate concentration in soil water was measured with ceramic cups. The N uptake of winter wheat was determined at three growing stages: tillering, flowering and at harvest. The nitrate dynamics in soil water were not significantly influenced by the different organic manures. Only the top dressing with slurry led to slightly enhanced nitrate concentration in the soil water. After sowing in autumn and the following winter period, the organically fertilized plots showed the same nitrate concentrations in soil water in 110 cm depth as the minerally fertilized control. This indicates a similar potential of nitrogen losses in all treatments. The different organic manures strongly affected the winter wheat plants both in the rate of N uptake during the growing season and in the growth rate. However, a high potential of the plants to compensate in later growing stages led to comparable yields in all organically manured treatments. The increased yield in the top dressed plots compared to the plots without top dressing was about 7%.

The Impact of Rotational Practice on Nitrate Leaching Losses in Organic Farming Systems in the United Kingdom

ABSTRACT The characteristics of organic farming involve the application of husbandry practices which are consistent with limiting nitrate leaching from agricultural land. The high losses of nitrate associated with ploughing of grass-clover leys are balanced by lower losses during the subsequent years of the arable and grassland phases of the rotation. Nitrate leaching data are presented from a monitoring programme carried out on 10 field sites on three commercial organic farms in the UK during the period 1988–92. Fields in arable and grassland phases of the farm rotations were monitored. Nitrate leaching was estimated from the nitrate concentration in soil water (sampled using porous ceramic cup samplers installed at 0.9 m soil depth) integrated with cumulative net drainage. The rotations operated on the farms were 5 to 8 years duration, including grass/clover for grazing and conservation, winter and spring wheat, winter and spring oats and potatoes. Average annual losses from these rotations calculated using the data derived from the monitored fields ranged between 10–21 kg Nha−1 yr−1. It is concluded that organic farming systems in the UK may have a valuable role to play in limiting nitrate leaching and should be considered for use in water protection zones.

Long-term conservation tillage and liquid dairy manure effects on corn. II. Nitrate concentration in soil water

Deterioration of ground and surface water quality has often been associated with failure to properly account for nitrogen (N) from manure and legumes in crop production. The objective of this study was to evaluate the effects of tillage, N source, and frequency of liquid manure application on NO 3-N concentration of soil water under the root zone of corn ( Zea mays L.). The experiment was conducted on a silt loam soil in southeast Minnesota, USA. Tillage and N treatments were initiated in 1982 and remained constant during the study. Tillage systems were chisel plowing plus secondary tillage with a field cultivator (CP) and no-tillage (NT). Nitrogen treatments were unfertilized control, inorganic fertilizer applied annually at 235 kg ha −1 for NT and 191 kg ha −1 for CP, and manure application of 284±20 kg ha −1 N (total N) annually and biennially (application every other year). Soil water for NO 3-N analysis was sampled weekly from 1.5-m depth using suction samplers during the 1989 and 1990 growing seasons. For these two years, mean soil water NO 3-N concentrations were 66 mg l −1 for annual inorganic fertilizer, 50 mg l −1 for annual manure and 11 mg l −1 for biennial manure treatments. Differences in NO 3-N concentrations between annual manure and annual inorganic fertilizer treatments, and between annual manure and biennial manure treatments were statistically significant ( P=0.05). Mean NO 3-N concentrations averaged over annual inorganic fertilizer and annual manure treatments were 69 mg l −1 for CP and 50 mg l −1 for NT. With small supplemental fertilizer N, biennial manure application offers an alternative to annual application to minimize N leaching.

Nitrate leaching from a Sitka spruce plantation and the effect of fertilisation with phosphorus and potassium

Mature Sitka spruce ( Picea sitchensis (Bong.) Carr.) plantations in the Beddgelert area of North Wales have comparatively large concentrations and leaching rates of soil water nitrate. To determine whether elimination of any phosphorus or potassium deficiency in the trees can result in increased demand for N and reduce nitrate leaching rates, P and K fertiliser was applied at two rates (P1K1 and P2K2) in a randomized block experiment. Soil water nitrate concentrations dropped significantly in the P2K2 treatment, compared with the Control, for two growing seasons following application of the fertiliser. There was no significant effect of the P1K1 treatment. Demand for N, P and K by the trees was estimated using root bioassay techniques. Three months after application of the fertiliser, uptake of all three nutrients from solution by excised roots was significantly lower in the P1K1 treatment, and very significantly lower in the P2K2 treatment, compared with the Control. These results imply that at least part of the demand for P and K in the trees had been satisfied by increased uptake of the applied fertiliser, resulting in an increased uptake of N. Foliar analysis confirmed that additional N was present in the trees in the P2K2 treatment. Fertiliser application is a technique which could reduce nitrate leaching rates. Only at sites where nitrate is a major component of the total inorganic anion concentration will reduction in nitrate concentration reduce acidification rates significantly.

Nitrate leaching from sheep-grazed grass/clover and fertilized grass pastures

SUMMARYNitrate leaching from sheep-grazed pastures was measured over three winters between 1987 and 1990 at a lowland site in Wales. Losses from replicated plots of ryegrass/white clover (Lolium perenne/Trifoliwn repens) pasture that received no N fertilizer and from pure ryegrass pasture receiving 150–200 kg fertilizer-N/ha per year were determined using suction cup samplers. In Year 1, the average clover content of the grass/clover swards (April-September) was equivalent to 35% of total dry matter but declined during the course of the experiment and was only 4% in Year 3. Concentrations of nitrate and quantities of N leached from separate sampling positions exhibited a wide range of values and conformed to a log-normal distribution. In the first two winters, mean nitrate concentrations in soil water and quantities leached from grass/clover plots were greater than those from fertilized grass plots. In Year 3 the loss from the N-fertilized plots was higher and exceeded that from the grass/clover treatment. Total quantities of N leached during the three winters ranged from 6 to 33 kg N/ha from grass/clover plots and from 2 to 24 kg N/ha from fertilized grass plots. At no time did mean nitrate concentrations from either treatment exceed 11 mg N/litre. These values probably underestimate the true loss as the distribution of the main sets of water samplers did not provide adequate coverage of those areas of the plots where sheep congregated and which received high returns of excreta. These positions were characterized by particularly high leaching losses. Differences between losses from the two treatments and between years could only be partly explained by the decline in clover content and differences in stocking rates.

Nutrient balance in forests of northern Tasmania. 2. Alteration of nutrient availability and soil-water chemistry as a result of logging, slash-burning and fertilizer application

In situ measurements of nitrogen mineralization and nutrient mobility in severely perturbed forest soils (the forest was clear-felled, slash-burnt and then fertilizer amended) were compared with those in the undisturbed forest. Nitrification was absent in all soils. Nitrate concentrations in soil-water were low and probably not responsible for cation movement. Cation concentrations in soil-water were immediately increased by fire and by fertilizer additions and decreased continuously after these perturbations. Addition of strong-acid anions (SO 4 2−) in fertilizer increased cation movement. Soil-water sampled at 10 cm depth was often coloured and contained high concentrations of oxidizable organic carbon; lower concentrations were found in samples collected from 30 cm depth. Uptake and mineralization of N were increased by logging and slash-burning. N-mineralization was promoted further by the addition of fertilizer-N and was reduced by the addition of P, or N and P together. Nutrient losses are exacerbated by fertilizer additions and restricted by the lack of nitrification, by nutrient uptake by soil microorganisms and vegetation, and probably by the formation of complexes between organic anions and cations in the soil profile.

Nitrogen renovation by denitrification in forest sewage irrigation systems

Nitrogen renovation in a forest spray-irrigation system was monitored by soil and groundwater nitrate, and chloride concentrations, for 14 months. Nitrate concentrations in soil water in the spray zone increased to 37 gm −3 NO 3−N but were less than 0·1 gm −3 NO 3−N in the wetland. The results indicate that approximately 98% of the nitrogen applied to the site was removed and it can be inferred that denitrification was the main pathway of loss.

Description of nitrogen movement in the presence of spatially variable soil hydraulic properties

Spatial variation in soil hydraulic properties has been recognized as a limitation in the accurate application to the field of most numerically based, finite differenced models of nitrogen transport and transformation. Most of these models are formulated with the assumption that one relationship exists over the field between hydraulic conductivity (K), water content (θ) and soil water pressure (h). Calculated water contents and water fluxes arising from these input relationships form the basis for calculation of nitrogen transport and distribution within the soil profile. Several studies have observed that K-θ relationships are variable over orders of magnitude in normal agricultural field soils. This study measured the K-θ-h variation in an agricultural field and used the results to represent the extremes of water and solute flow regimes in a nitrogen transport model. The K-θ relationship was measured at 100 field locations at 7 depths and the results summarized by scaling methods to estimate spatial variability. The field was also the site of a corn growth-nitrogen fertility experiment that was designed to allow measurement of crop yield, soil water content, soil water nitrate concentrations and other data needed for evaluation of the nitrogen model. Conceptual approaches, field experiments and comparison of field data with results of the modeling exercise are presented.