Nitrate Concentrations In Soil Water Research Articles

Nutrient leaching potential along a time series of forest water reclamation facilities in northern Idaho

Forest water reclamation is a decades-old practice of repurposing municipal reclaimed water using land application on forests to filter nutrients and increase wood production. However, long-term application may lead to nutrient saturation, leaching, and potential impairment of ground and surface water quality. We studied long-term effects of reclaimed water application on nutrient leaching potential in a four-decade time series of forest water reclamation facilities in northern Idaho. Our approach compared reclaimed water treated plots with untreated control plots at each of the forest water reclamation facilities. We measured soil nitrifier abundance and net nitrification rates and used tension lysimeters to sample soil matrix water and drain gauges to sample from a combination of matrix and preferential flow paths. We determined nutrient leaching as the product of soil water nutrient concentrations and model-estimated drainage flux. There was more than 450-fold increase in nitrifier abundance and a 1000-fold increase in net nitrification rates in treated plots compared with control plots at long-established facilities, indicating greater nitrate production with increased cumulative inputs. There were no differences in soil water ammonium, phosphate, and dissolved organic nitrogen concentrations between control and effluent treatments in tension lysimeter samples. However, concurrent with increased nitrifier abundance and net nitrification, nitrate concentration below the rooting zone was 2 to 4-fold higher and nitrate leaching was 4 to 10-fold higher in effluent treated plots, particularly at facilities that have been in operation for over two decades. Thus, net nitrification and nitrifier abundance assays are likely indicators of nitrate leaching potential. Inorganic nutrient concentrations in drain gauge samples were 2 to 11-fold higher than lysimeter samples, suggesting nutrient losses occurred predominantly through preferential flow paths. Nitrate was vulnerable to leaching during the wet season under saturated flow conditions. Although nitrogen saturation is a concern that should be mitigated at long-established facilities, these forest water reclamation facilities were able to maintain average soil water nitrate concentrations to less than 2 mg L−1, so that nitrogen and phosphorous are effectively filtered to below safe water standards.

High greenhouse gas emissions after grassland renewal on bog peat soil

Drained agriculturally used peatlands are hotspots for greenhouse gas (GHG) emissions, especially carbon dioxide (CO2) and nitrous oxide (N2O). To reduce GHG emissions and simultaneously maintain intensive grassland use, raising water levels by subsurface irrigation (SI) is controversially discussed. Both, intensive grassland use and installations of SI may require grassland renewal. We investigated an experimental intervention site (INT) (SI target water levels: -0.30 m) and a deeply drained reference site (REF), both intensive grassland on deep bog peat. After installation of the SI system, a mechanical grassland renewal took place at INT. At both sites, CO2 (eddy covariance), N2O and methane (manual closed chamber technique) were measured. Additionally, soil water was analyzed for nitrogen species. Here, we report on the initial year of GHG measurements including grassland renewal and rising water levels. Overall, GHG emissions were strongly influenced by grassland renewal at INT. Despite progressively rising water levels, soil moisture in the upper centimeters was low and thus grass growth was slow, resulting in an almost complete loss of harvest. This resulted in a net ecosystem carbon balance (NECB) of 4.64 ± 1.03 t C ha−1 containing only 0.57 ± 0.09 t C ha−1 harvest at INT, while NECB at REF was 6.08 ± 1.74 t C ha−1 including harvest from five grass cuts. Methane fluxes were negligible at both sites. Nitrous oxide emissions dominated the GHG balance at INT. With 144.5 ± 45.5 kg N2O–N ha–1 a–1, they were much higher than at REF (3.9 ± 3.1 kg N2O–N ha–1 a–1) and any other values published so far. Peak fluxes occurred when nitrate concentrations in soil water were extremely high, soil moisture was increased, and vegetation development was struggling. This study highlights the risk of grassland renewals on peat soils regarding yield losses as well as high GHG emissions.

Optimized number of suction cups required to predict annual nitrate leaching under varying conditions in Denmark

Nitrate concentrations in soil water leaving the root zone measured by suction cups combined with water transport modeling is a commonly used practice in Denmark for calculating nitrate leaching. Two suction cups installed in one plot giving one water sample and replicated four times, (eight total suction cups) to reduce variability between samples. For practical reasons, it would be beneficial to minimize the number of suction cups used yet maintain reliable predictions. To assess the variability in reducing suction replicates, this study analyzed data from five research sites across Denmark representing annual field nitrate leaching predictions for different combinations of soil, weather conditions, crops, N-fertilizer rates, and winter soil cover, covering a total of 173 annual nitrate leaching experiments. The analysis was conducted having different nitrate leaching predictions using different numbers of replicates of suction cup measurements. Linear regression was used to identify the different influences of leaching year (hydrological year), N rate applied, soil characteristics, and crop sequence on nitrate leaching. The analyses were set up on three 2-yr and two 3-yr field experiments in five different sites. Crop effects showed that cereals and winter cover sown in autumn 2017 had significantly more nitrate leaching than in 2015 and 2016 leaching years due to high precipitation rates in the autumn. Furthermore, decreasing the number of suction cup replicates from four (eight total) to three replicates (six total) did not have a significant effect on nitrate leaching prediction. In contrast, decreasing replicates from four to two (four total) and one (two total) replicates did show a significant difference. Therefore, using three replicates is a viable solution for future sampling strategies and a good trade-off between costs and accuracy.

Rate and Timing of Meat and Bone Meal Applications Influence Growth, Yield, and Soil Water Nitrate Concentrations in Sweet Corn Production

Using local resources and minimizing environmental impacts are two important components of sustainable agriculture. Meat and bone meal (MBM), tankage, is a locally produced organic fertilizer. This study was conducted to investigate the response of sweet corn (Zea mays L. var. saccharata Stuart.) and soil water nitrate (NO3-N) concentration to MBM application at two locations, Waimānalo and Poamoho, on the island of O’ahu. The objectives were to determine effects of six application rates (0, 112, 224, 336, 448 and 672 kg N ha−1) and two application timings (preplant and split application) on: (1) sweet corn growth, yield, and quality, and (2) soil water nitrate concentration within and below the root zone. The split-plot was designed as four replicates randomly arranged in a complete block. Plant growth of roots and shoots, yield, and relative leaf chlorophyll content of sweet corn increased with increasing application rates of MBM in both locations. At Poamoho, yield was 13.6% greater in preplant versus split application. Nitrate-nitrogen losses were reduced by 20% at Waimānalo and 40% at Poamoho when MBM was applied in split applications. These findings suggest that MBM is an effective nitrogen source for sweet corn and a split application of MBM may reduce the potential for pollution.

Autumn-based vegetation indices for estimating nitrate leaching during autumn and winter in arable cropping systems

Nitrate leaching losses from arable cropping systems cause severe damage to environmental services worldwide. There is a considerable need for methods that allow rapid, easy and area covering detection of nitrate leaching to guide nitrogen (N) management. We used three years of data from the 5th cycle of a long-term crop rotation experiment in Denmark to quantify the relationships between nitrate leaching in autumn and winter and field conditions in autumn as defined by three vegetation indices [VIs; Ratio Vegetation Index (RVI), Normalized Difference Vegetation Index (NDVI), Ratio Red Edge (RRE)] in autumn. Following cereal crops, cover crops significantly reduced nitrate leaching in autumn and winter, whereas this was only the case for one out of the three years after faba bean. In autumn and winter, a negative relationship was found between nitrate leaching and cover crop aboveground biomass or aboveground N, and the thresholds were ∼2 Mg ha−1 for aboveground cover crop biomass and 60 kg N ha−1 for aboveground cover crop N, above which nitrate leaching was low and stable. A significant positive linear relationship was found between nitrate leaching and soil water nitrate concentration in autumn and winter with a slope of 4.0 kg N ha−1 per mg L−1 of nitrate-N in the soil. Although all three VIs showed significant negative relationships with nitrate leaching during autumn and winter, the sensitivities of RVI and NDVI to estimated nitrate leaching were lost sharply when nitrate leaching exceeded 100 kg N ha−1 and 50 kg N ha−1, while RRE exhibited consistent low noise equivalent values for the nitrate leaching in autumn and winter. These results provide evidence for the scope of assessing risk of nitrate leaching from agricultural soils based on newly launched satellite remote sensing platforms with NDVI and red edge bands. To maximize the application of these technologies it will be necessary to combine remote sensing with information on cropping systems and biophysical conditions.

Comparison of the modeling results of nitrate concentrations in soil water below the root zone in the local and regional scale

The article presents a comparative analysis of the modeling results of nitrate concentrations in water below the root zone of the soil in the local and regional scale. In this research, the field-scale DNDC (Denitrification – Decomposition) and the regional-scale GROWA–DENUZ (ger. Großräumiges wasserhaushalt – Denitrifikation im durchwurzelten Boden) models were applied to the study area of the shallow aluvial aquifer of the Spodnje Savinjska dolina in the central part of Slovenia. Using the concept of Hydrological Response Unit (HRU) and Cohen Kappa statistical analysis of the degree of agreement and assessment of the reliability of the results of spatial modeling of nitrate in soil water below the root zone, we determined and interpreted the areas of maximum agreement and disagreement of model results. A good agreement was found at the highest modeled concentrations of nitrate in soil water, whereas the greatest deviations were detected primarily in the lower part of the range. The main reasons for disagreement were differences in the estimation of the denitrification conditions in the anaerobic environments of gley-soils with the shallow groundwater and differences in fertilisation scenarios and agricultural practices.

Decomposer diversity increases biomass production and shifts aboveground-belowground biomass allocation of common wheat

Biodiversity is well known to enhance many ecosystem functions, but empirical evidence for the role of soil biodiversity for plant biomass production and allocation is scarce. Here we studied the effects of animal decomposer diversity (1, 2, and 4 species as well as a control without any decomposers) on the biomass production and aboveground-belowground biomass allocation of common wheat using two earthworm and two Collembola species using an additive design in two soil management types (organic and mineral fertilizer treatments) in a microcosm experiment. Shoot (+11%), spike (+7%), and root biomass (+56%), increased significantly with increasing decomposer diversity, and these effects were consistent across the two soil management types. Notably, decomposer diversity effects were stronger on root than on shoot biomass, significantly decreasing the shoot-to-root ratio (−27%). Increased plant biomass production was positively correlated with a decomposer richness-induced increase in soil water nitrate concentrations five weeks after the start of the experiment. However, elevated soil nitrate concentrations did not cause significantly higher plant tissue nitrogen concentrations and nitrogen amounts, suggesting that additional mechanisms might be at play. Consistent decomposer diversity effects across soil management types indicate that maintaining soil biodiversity is a robust and sustainable strategy to enhance crop yield.

Long-term soil hydrological data of a Pleistocene region in North-East Germany

Long-term soil hydrological studies were carried out at the ZALF Muencheberg Experimental Station. Muencheberg is located in a Pleistocene end moraine landscape in NE Germany about 50 km east of Berlin and 40 km west of the Oder river, the border with Poland. The soils are formed on Pleistocene parent material, classified as Haplic Albeluvisol with a Bt horizon mostly beginning at about 70 cm depth. From 1994-1999 the site was used as arable land managed by different farming systems (integrated, integrated with irrigation, ecological and low input). From 2000 to 2005 the effect of different tillage systems (plough and no till) was investigated. Furthermore, soil water was extracted by use of suction cups for analysing the soil water nitrate concentrations. The data were used for quantifying deep drainage rates and nitrate losses as described in (Schindler and Mueller, 2008 and Schindler et al., 2010). All basic data (soil water content, tension, precipitation, potential evapotranspiration and soil water nitrate concentrations) are accessible via DOI 10.4228/ZALF.1995.282.

Increased concentrations of nitrate in forest soil water after windthrow in southern Sweden

In January 2005, south-west Sweden was hit by a severe storm that caused large damage to the forests through massive windthrow. The aim of this study was to assess the effect of this windthrow on nitrate concentrations in the soil water below the root zone on 33 forest monitoring plots within the Swedish Throughfall Monitoring Network (SWETHRO). These sites were damaged to different extents by the storm. The analysis showed increased levels of nitrate concentrations in the soil water as a consequence of storm damaged forest. The present study concerned forest ecosystems with relatively low levels of nitrogen deposition, as compared with forests analysed in previous studies. The maximum soil water nitrate concentrations occurred 1–4years after the storm. After 5–6years, the concentrations were back at the same levels as before the storm event. It was not possible to demonstrate a significant correlation between increased nitrate concentrations in the soil water after the storm and the level of nitrogen deposition at the site. The potential impact on ground- and surface waters due to elevated nitrate concentrations in soil water after storm events is discussed.

Reprint of “Nitrogen field balances and suction cup-measured N leaching in Danish catchments”

In Denmark suction cup-measured nitrate concentrations in soil water and N leaching have been used as a means for monitoring the impact of changes in the consumption of commercial fertilizer and improved utilisation of nitrogen in manure by agriculture. The measurements are a part of the Danish Agricultural Monitoring Programme (NOVANA) and are carried out in five small agricultural dominated catchments covering differences in climate, soil types and farming practices within the country. Statistical analyses allowing for annual variations in climate showed that nitrate concentrations in root zone water from loamy and sandy catchments decreased by, respectively, 23 and 48% during 1991–2003, after which no further decrease occurred until 2010/11. The aim of this study is to describe how the year to year variations in percolation and field balance characterise N leaching for 30 soil water stations in the period 1991–2010. A general linear model for annual observations of N leaching, N leaching=3479+0.140×percolation+0.080×surface N balance−1.737 year, explained 29% of the variation. When N leaching was calculated as a mean for each soil water station for the period 1991–2010, the field N balance explained about 44% of the variation in leaching between the 16 soil water stations located in loamy catchments. A lower proportion, 36%, was recorded for the 14 soil water stations located in sandy catchments, but the signature increased to 60% if an outlier field, having a large excess input of manure, was omitted. From these results for Danish catchments, we conclude that field N balances are able to predict the risks of leaching provided that measurements are integrated over 30 soil water stations or a relatively long monitoring period. However, the data showed that the leaching responses to the field balance are different for loamy and sandy soils and depend on farm type.

Comparing annual and perennial crops for bioenergy production – influence on nitrate leaching and energy balance

AbstractProduction of energy crops is promoted as a means to mitigate global warming by decreasing dependency on fossil energy. However, agricultural production of bioenergy can have various environmental effects depending on the crop and production system. In a field trial initiated in 2008, nitrate concentration in soil water was measured below winter wheat, grass‐clover and willow during three growing seasons. Crop water balances were modelled to estimate the amount of nitrate leached per hectare. In addition, dry matter yields and nitrogen (N) yields were measured, and N balances and energy balances were calculated. In willow, nitrate concentrations were up to approximately 20 mg l−1 nitrate‐N during the establishment year, but declined subsequently to <5 mg l−1 nitrate‐N, resulting in an annual N leaching loss of 18, 3 and 0.3 kg ha−1 yr−1 N in the first 3 years after planting. A similar trend was observed in grass‐clover where concentrations stabilized at 2–4 mg l−1 nitrate‐N from the beginning of the second growing season, corresponding to leaching of approximately 5 kg ha−1 yr−1 N. In winter wheat, an annual N leaching loss of 36–68 kg ha−1 yr−1 was observed. For comparison, nitrate leaching was also measured in an old willow crop established in 1996 from which N leaching ranged from 6 to 27 kg ha−1 yr−1. Dry matter yields ranged between 5.9 and 14.8 Mg yr−1 with lowest yield in the newly established willow and the highest yield harvested in grass‐clover. Grass‐clover gave the highest net energy yield of 244 GJ ha−1 yr−1, whereas old willow, winter wheat and first rotation willow gave net energy yields of 235, 180 and 105 GJ ha−1 yr−1. The study showed that perennial crops can provide high energy yields and significantly reduce N losses compared to annual crops.

Nitrogen field balances and suction cup-measured N leaching in Danish catchments

In Denmark suction cup-measured nitrate concentrations in soil water and N leaching has been used as a means for monitoring the impact of changes in consumption of commercial fertilizer and improved utilisation of nitrogen in manure by agriculture. The measurements are a part of the Danish Agricultural Monitoring Programme (NOVANA) and are carried out in five small agricultural dominated catchments covering differences in climate, soil types and farming practices within the country. Statistical analyses allowing for annual variations in climate showed that nitrate concentrations in root zone water from loamy and sandy catchments decreased by, respectively, 23 and 48% during 1991–2003, after which no further decrease occurred until 2010/11. The aim of this study is to describe how the year to year variations in percolation and field balance characterise N leaching for 30 soil water stations in the period 1991–2010. A general linear model for annual observations of N leaching, N leaching=3479+0.140×percolation+0.080×surface N balance−1.737 year, explained 29% of the variation. When N leaching was calculated as a mean for each soil water station for the period 1991–2010, the field N balance explained about 44% of the variation in leaching between the 16 soil water stations located in loamy catchments. A lower proportion, 36%, was recorded for the 14 soil water stations located in sandy catchments, but the signature increased to 60% if an outlier field, having a large excess input of manure, was omitted. From these results for Danish catchments, we conclude that field N balances are able to predict the risks of leaching provided that measurements are integrated over 30 soil water stations or a relatively long monitoring period. However the data showed that the leaching responses to the field balance are different for loamy and sandy soils and depend on farm type.

Effect of nitrogen fertilization on nitrate leaching in relation to grain yield response on loamy sand in Sweden

High rates of nitrogen (N) fertilizer may increase N leaching with drainage, especially when there is no further crop response. It is often discussed whether leaching is affected only at levels that no longer give an economic return, or whether reducing fertilization below the economic optimum could reduce leaching further. To study nitrate leaching with different fertilizer N rates (0–135kgNha−1) and grain yield responses, field experiments in spring oats were conducted in 2007, 2008 and 2009 on loamy sand in south-west Sweden. Nitrate leaching was determined from nitrate concentrations in soil water sampled with ceramic suction cups and measured discharge at a nearby measuring station. The results showed that nitrate leaching per kg grain produced had its minimum around the economic optimum, here defined as the fertilization level where each extra kg of fertilizer N resulted in a 10kg increase in grain yield (85% DM). There were no statistically significant differences in leaching between treatments fertilized below this level. However, N leaching was significantly elevated in some of the treatments with higher fertilization rates and the increase in nitrate leaching from increased N fertilization could be described with an exponential function. According to this function, the increase was <0.04kgkg−1 fertilizer N at and below the economic optimum. Above this fertilization level, the nitrate leaching response gradually increased as the yield response ceased and the increase amounted to 0.1 and 0.5kgkg−1 when the economic optimum was exceeded by 35 and 100kgNha−1, respectively. The economic optimum fertilization level depends on the price relationship between grain and fertilizer, which in Sweden can vary between 5:1 and 15:1. In other words, precision fertilization that provides no more or no less than a 10kg increase in grain yield per kg extra N fertilizer can be optimal for both crop profitability and the environment. To predict this level already at fertilization is a great challenge, and it could be argued that rates should be kept down further to ensure that they are not exceeded due to overestimation of the optimum rate. However, the development of precision agriculture with new tools for prediction may reduce this risk.

Soil carbon accumulation and nitrogen retention traits of four tree species grown in common gardens

Tree species effects on soil carbon (C) accumulation are uncertain, especially with respect to the mineral soil C, and the consistency of such effects across soil types is not known. The interaction between C accumulation and nitrogen (N) retention among common tree species has also been little explored. Effects of four tree species on soil C and N stocks and soil water nitrate concentration below the root zone were evaluated in a common garden design replicated at eight sites in Denmark. The tree species were beech (Fagus sylvatica L.), oak (Quercus robur L.), larch (Larix leptolepis Kaempf), and Norway spruce (Picea abies (L) Karst.). After four decades, there were significant differences in forest floor C stocks among all four species, and C stocks increased consistently in the order oak<beech≪Norway spruce<larch along the soil texture gradient of the sites. Forest floor N stocks only differed significantly between conifers and broadleaves. The observed differences in forest floor C and N stocks were attributed to differences in litter turnover rates among the tree species. Mineral soil C stocks were significantly higher in stands of Norway spruce than in stands of oak and beech while mineral soil N stocks did not differ significantly. Total soil C stocks were thus significantly higher under conifers than under broadleaves. Even though forest floor C and N stocks decreased with finer texture, the C–N stoichiometry in forest floors was quite similar across sites. A significant difference in soil water nitrate concentration at 70–90cm depth was found only between beech and oak. Nitrate concentrations were highest on fine-textured soils with high pH and low C/N ratio as well as on a site with high local N emissions. Nitrate concentrations were negligible on sandy acidic soils with high C/N ratio. We conclude that tree species may establish consistent differences in soil C and N stocks and N retention traits even along soil texture gradients.

Environmentally Sustainable Nitrogen Fertilizer Management for ‘Tifton 85’ Hay Production in Sandy Soils

ABSTRACTNitrogen is a critical element for sustainable forage production but N surpluses in sandy soils could result in nitrate leaching and water contamination. Our objective was to identify a N application rate that optimizes yield and quality of ‘Tifton 85’ bermudagrass (Cynodon Rich. spp.) with minimal N leaching losses in a typical Florida sandy soil. Four N application rates (30, 50, 70, and 90 kg N ha−1 per harvest) and an unfertilized (0 N) control in a Tifton 85 bermudagrass hay field were evaluated. Suction lysimeters were installed in each plot at 30 and 100 cm below the soil surface to measure soil water nitrate concentration. Nitrogen application at the recommended rate of 90 kg N ha−1 per harvest produced the greatest total dry matter yield (DMY) (∼22 Mg ha−1 yr−1), but a modeled optimum DMY of ∼18 Mg ha−1 yr−1 occurred at 57 kg N ha−1 per harvest. Nitrogen application increased herbage nutritive value, but the difference was not significant above 30 kg N ha−1 per harvest. Treatments with N rates ≤ 50 kg N ha−1 per harvest had leachate nitrate concentration below the maximum contaminant limit (MCL) of 10 mg L−1. However, N rates ≥ 70 kg N ha−1 per harvest had leachate nitrate concentration that exceeded the MCL, suggesting a risk of impacting groundwater quality. The results demonstrate that although Tifton 85 bermudagrass is an efficient N remover, there is potential for N leaching in sandy soils. Therefore, site‐specific evaluation of appropriate N management is critical.

Assessing the risk of N leaching from forest soils across a steep N deposition gradient in Sweden

Nitrogen leaching from boreal and temporal forests, where normally most of the nitrogen is retained, has the potential to increase acidification of soil and water and eutrophication of the Baltic Sea. In parts of Sweden, where the nitrogen deposition has been intermediate to high during recent decades, there are indications that the soils are close to nitrogen saturation. In this study, four different approaches were used to assess the risk of nitrogen leaching from forest soils in different parts of Sweden. Nitrate concentrations in soil water and C:N ratios in the humus layer where interpreted, together with model results from mass balance calculations and detailed dynamic modelling. All four approaches pointed at a risk of nitrogen leaching from forest soils in southern Sweden. However, there was a substantial variation on a local scale. Basing the assessment on four different approaches makes the assessment robust.

Monitoring and modelling draining and resident soil water nitrate concentrations to estimate leaching losses

Abstract Quantifying nitrogen (N) losses below the root zone is highly challenging due to uncertainties associated with estimating drainage fluxes and solute concentrations in the leachate. Active and passive soil water samplers provide solute concentrations but give limited information on water fluxes. Mechanistic models are used to estimate leaching, but require calibration with measured data to ensure their reliability. Data from a drainage lysimeter trial under irrigation in which soil profile nitrate (NO3−) concentrations were monitored using wetting front detectors (passive sampler) and ceramic suction cups (active sampler) were compared to NO3− concentrations in draining and resident soil water as simulated by the research version of the Soil Water Balance model (SWB-Sci). SWB-Sci is a daily time-step, cascading soil water and solute balance model that provides draining NO3− concentrations by accounting for incomplete solute mixing. As hypothesized, suction cup concentrations aligned closely with resident soil water concentrations, while wetting front detector concentrations aligned closely with draining soil water NO3− concentrations. These results demonstrate the power of combining monitoring and modelling to estimate NO3− leaching losses. Access to measured draining and resident NO3− concentrations, especially when complemented with modelled fluxes, can contribute greatly to achieving improved production and environmental objectives.

Field Investigation of Water Movement and Nitrate Transport under Perched Water Table Conditions

Increasing amounts of potentially hazardous chemicals such as nitrate (NO 3 − ) arising from various agricultural operations are polluting soil and water ecosystems worldwide. In the present study, the perching process and the simultaneous movement of water and nitrate through lateritic soils under perched water table conditions were investigated through two field experiments. The piezometric head and soil matric suction at five depths as well as the perched water table fluctuations in nine vadose zone wells were monitored daily. Also, a 20 mm pulse of calcium nitrate was displaced in two experimental plots (called ‘plot I’ and ‘plot II’) by maintaining a constant depth of water throughout the leaching period, and the leaching of nitrate was monitored at six soil depths and in all the observation wells at suitable time intervals. The results of saturated hydraulic conductivity and bulk density at different depths in plot II suggested that the soil profile is heterogeneous. The analysis of hydraulic head and soil matric suction data revealed that the top 1·25 m of the soil profile responds rapidly to rainfall in both the plots, with plot I more permeable than plot II. Relatively long perching conditions at 1·71 m depth in both the plots indicated the presence of a more effective water-resisting layer at this depth. The maximum nitrate concentration in soil water was found after 8–12 h of leaching at shallower depths (up to 0·33 m) and after 12–18 h at greater depths. The enhanced rate of nitrate leaching in both the plots indicated the presence of macropores in the soil profile. Lateral flow due to perching conditions was also found to considerably affect the contamination process in lateritic soils. Furthermore, the dispersion coefficients of nitrate based on the breakthrough curves were found to range between 0·004 and 1·67 m 2 /day, suggesting heterogeneity in the soil profile. Finally, it is concluded that the relatively shallow aquifers of the lateritic region are vulnerable to nitrate contamination due to the current practice of nitrogenous fertiliser application in agricultural fields. Long-term and large-scale field studies under actual field conditions, together with simulation modeling, are recommended to generalise the flow and transport behaviour in lateritic soils.

Estimating deep drainage and nitrate leaching from the root zone under sugarcane using APSIM-SWIM

The Burdekin Delta (BD) is located on the dry-tropical coastal strip in North Queensland, Australia. It is one of Australia's premier sugar producing districts with approximately 40,000 ha of land under sugarcane. Because the BD borders the Great Barrier Reef World Heritage Area (GBRWHA), industry, community, regulatory, and environmental organisations are interested in ascertaining the magnitude of deep drainage and nitrate leaching from the root zone and potential implications for the GBRWHA. Direct measurement of deep drainage and nitrate leaching is difficult, and modelling is likely to play an ever-increasing role in guiding experimental work and decision-making. Here, we describe the collection of drainage and nitrate-leaching related data collected over two cropping seasons at a specific field site within the BD and its use in the calibration and application of a drainage and nitrate-leaching model created within the Agricultural Production Systems Simulator (APSIM) modelling framework with constituent crop-growth, soil–water, and nitrogen transformation modules (Sugar, APSIM-SWIM, Soiln2). Model application indicated that the simulated amount of drainage and nitrate leached over a cropping season compared favourably to that derived from inferred drainage and observed soil–water nitrate concentrations. Subsequent investigation of fertilizer management options using the model identified the timing and amount of both irrigation and fertilizer application as key parameters over which management control might be exploited to minimise deep drainage and flux of nitrate to groundwater.

Statistical Analysis of Nitrate Movement through the Soil in Central Kansas

An earlier investigation by the Kansas Geological Survey in central Kansas studied the movement of nitrate from fertilizer through soil into the groundwater. Nitrate concentrations in soil water were measured on samples collected at three locations during a three-year span, from sets of lysimeters buried at different depths. Although patterns seemed apparent in the resulting measurements, no statistical analyses were performed to test their significance; this re-study of the data uses analyses of variance to test for differences in nitrate concentration attributable to time and to depth in the soil. The mean nitrate concentration of samples collected in the first year of the experiment was significantly higher than the means of second and third year samples at all three locations, perhaps reflecting the confounding influence of a previous flooding experiment. ANOVAs of depth across years determined few significant differences in nitrate concentration with depth. The wintertime gap in measurements and unequal sampling through time precludes formal time-series analyses, but graphs of concentration versus time show that peak concentration occurs at later times with increasing depth, and that maximum concentration decreases with depth. These statistical analyses support the conclusions from the original investigation.