Nitrate in upper groundwater on farms under tillage as affected by fertilizer use,soil type and groundwater table

Indicators are needed to check whether policies on protection of groundwater are effective and if regulations are complied with. We evaluated various indicators at different scales, both in space and in time, and at different degrees of complexity. Groundwater was sampled on 34 arable farms for 3 years. Nitrate concentration in upper groundwater was low on clay soil. On sandy soil, peat layers reduced the nitrate concentration with about 80 mg/l on average. Sandy soils with high groundwater tables had nitrate concentrations that were less than half of those at sandy soils with low groundwater tables. The relationship between different fertilization variables and nitrate in groundwater was investigated for sandy soils without peat layers. N surplus poorly correlated with nitrate concentrations in groundwater when individual sampling points were studied, but clearly increased when data were averaged at the farm level. Soil mineral nitrogen correlated best with nitrate concentrations in groundwater. The relationships show that especially on well drained soil drastic measures will be inevitable to reach good water quality.     

Long-term effects of balanced fertilization on grass forage yield,quality and nutrient uptake,soil organic C and N,and some soil quality characteristics

Many soils in the Parkland region of the Canadian Prairie contain insufficient amounts of plant-available S and N for high crop yields. Two field experiments (Experiment 1 1980–2005 and Experiment 2 1996–2005) were conducted on a Dark Gray Chernozem (Boralfic Boroll) loam soil at Canwood in north-central Saskatchewan, Canada, to determine the effects of long-term N, S and/or K fertilization to grass on mean forage dry matter yield (DMY), nutrient (N, S and K) concentration and nutrient uptake (averaged over years), and root mass, soil pH, total organic C (TOC) and N (TN), light fraction organic matter (LFOM), C (LFC) and N (LFN), mineralizable C and N, and extractable ammonium-N and nitrate-N in May 2006 (after 26 or 10 growing seasons). Experiment 2 additionally compared the effects of ‘hay-on’ (cut hay not removed) versus ‘hay-off’ (hay removed) on the plant and soil parameters. Experiment 1 had annual treatments of no fertilizer, N, NS and NSK fertilizers from 1980 to 2005, and Experiment 2 received no fertilizer, N, S and NS fertilizers from 1996 to 2005 under ‘hay-on’ and ‘hay-off’ conditions. While DMY, nutrient uptake and root mass were little affected by application of N or S alone compared with the unfertilized treatment, they were substantially increased by application of both N and S together. Co-application of N, S and K fertilizers increased DMY, nutrient uptake and root mass compared with NS application in Experiment 1. Nitrogen concentration in forage was highest in the N only treatment, followed by NS, and then nil, S or NSK treatments. The concentration of K in forage decreased in the order of treatments: NSK > nil or S treatment > N or NS; and of S: NS or S treatment > NSK treatment > nil treatment > N only treatment. Nutrient uptake was influenced more by forage DMY than nutrient concentration. In Experiment 2, DMY and N and K uptakes were greater under ‘hay-on’ than ‘hay-off’ conditions. Soil pH to 15-cm depth was decreased by NSK fertilization. The amounts of TOC, TN, LFOM, LFC, LFN, and mineralizable C and N in the 0–10 cm soil were increased considerably by the co-application of N and S fertilizers. The increase in soil C correlated well with the increase in DMY or root mass resulting from balanced fertilization. Not removing hay resulted in substantially increased LFOM, LFC and LFN contents in soil. The accumulation and downward movement of nitrate-N in the soil profile was decreased with NS application compared with N alone. In conclusion, application of N and S fertilizers together to soil deficient in both N and S produced high forage yield, nutrient uptake and root mass while also reducing soil pH, increased C and N sequestration in soil, and minimized accumulation and downward movement of nitrate-N in the soil profile.     

Nutrient cycling in a cropping system with potato, spring wheat, sugar beet, oats and nitrogen catch crops. II. Effect of catch crops on nitrate leaching in autumn and winter

The Nitrate Directive of the European Union (EU) forces agriculture to reduce nitrate emission. The current study addressed nitrate emission and nitrate-N concentrations in leachate from cropping systems with and without the cultivation of catch crops (winter rye: Secale cereale L. and forage rape: Brassica napus ssp. oleifera (Metzg.) Sinksk). For this purpose, ceramic suction cups were used, installed at 80 cm below the soil surface. Soil water samples were extracted at intervals of ca 14 days over the course of three leaching seasons (September – February) in 1992–1995 on sandy soil in a crop rotation comprising potato (Solanum tuberosum L.), spring wheat (Triticum aestivum L.), sugar beet (Beta vulgaris L.) and oats (Avena sativa L.). Nitrate-N concentration was determined in the soil water samples. In a selection of samples several cations and anions were determined in order to analyze which cations primarily leach in combination with nitrate. The water flux at 80 cm depth was calculated with the SWAP model. Nitrate-N loss per interval was obtained by multiplying the measured nitrate-N concentration and the calculated flux. Accumulation over the season yielded the total nitrate-N leaching and the seasonal flux-weighted nitrate-N concentration in leachate. Among the cases studied, the total leaching of nitrate-N ranged between 30 and 140 kg ha^–1. Over the leaching season, the flux-weighted nitrate-N concentration ranged between 5 and 25 mg L^–1. Without catch crop cultivation, that concentration exceeded the EU nitrate-N standard (11.3 mg L^–1) in all cases. Averaged for the current rotation, cultivation of catch crops would result in average nitrate-N concentrations in leachate near or below the EU nitrate standard. Nitrate-N concentrations correlated with calcium concentration and to a lesser extent with magnesium and potassium, indicating that these three ion species primarily leach in combination with nitrate. It is concluded that systematic inclusion of catch crops helps to decrease the nitrate-N concentration in leachate to values near or below the EU standard in arable rotations on sandy soils.     

Effects of applied nitrogen on soil nitrate-nitrogen content after harvest of winter barley

Seven field trials were conducted on winter barley to define relationships between rate of applied N, the amount of nitrate-N present in the soil after harvest and the ratio of soil nitrate-N to grain yield. Applying N up to the economic optimum rate (estimated from yield and N rate data from individual trials) was associated with small increases in soil nitrate-N after harvest (the mean increase was 4 kg N ha^–1). Where the optimum N rate was exceeded, soil nitrate-N levels increased to a greater extent. In every trial, the ratio of soil nitrate-N to yield showed a minimum at a fertilizer N rate below the economic optimum. However, the value of the ratio was always lower at the optimum N rate (mean value 6.0 kg N t^–1) than at the zero-N treatment (mean value 8.9 kg N t^–1) and the difference between the minimum value (mean 5.6 kg N t^–1) and that found at the optimum N rate was small.Overall, application of fertilizer N up to the economic optimum rate for practical purposes could be regarded as consistent with the objective of minimising the risk of nitrate leaching per hectare and per tonne of grain in the trials.     

Vegetable cultivation under greenhouse conditions leads to rapid accumulation of nutrients,acidification and salinity of soils and groundwater contamination in South-Eastern China

Vegetable cultivation during winter season is economically profitable, but the impact of the intensive production on soil and water quality remains to be studied. The objectives of this study were to investigate the seasonal dynamics of soil nutrients, acidification and salt accumulation in vegetable fields in South-Eastern China. Various vegetables were grown either under open-field conditions or under two different alternating open-field and greenhouse conditions with three replications. Soil samples were collected periodically and analyzed for pH, plant available nitrogen (N), phosphorous (P), potassium (K), electrical conductivity (EC), and urease activity. Water samples from wells located in or near the plots were collected and analyzed for nitrate. Soil nitrate, available phosphate and salt concentrations declined in summer under open-field conditions and significantly increased from December to May under greenhouse conditions. Exchangeable K also decreased in summer season, but did not increase in the spring. Under alternating open-field and greenhouse conditions, nutrient accumulation, soil salinity and acidification were significantly higher for soil used for vegetable cultivation for 2 years (2-y-plot) than that for only half year (0.5-y-plot). The accumulation of nitrate significantly correlated with soil EC and soil acidification. Thirty-two percent of groundwater samples from the 2-y-plot showed a nitrate concentration higher than 50 mg NO₃ l⁻¹. Conversely, no groundwater sample of 0.5-y-plot showed such high nitrate concentration. It can be concluded that the nitrate accumulation in soil used for vegetable cultivation under alternating open-field and greenhouse conditions not only causes soil salinization and soil acidification but also presents a high pollution potential for groundwater.     

Effects of input level and crop diversity on soil nitrate-N,extractable P,aggregation, organic C and N,and nutrient balance in the Canadian Prairie

A field experiment was conducted from 1995 to 2006 on a Dark Brown Chernozem (Typic Boroll) loam soil at Scott, Saskatchewan, Canada to determine the influence of input level and crop diversity on accumulation and distribution of nitrate-N and extractable P in the soil profile, and soil pH, dry aggregation, organic C and N, and nutrient balance sheets in the second 6-year rotation cycle (2001–2006). Treatments were combinations of three input levels (organic input under conventional tillage—ORG; reduced input under no-till—RED; and high input under conventional tillage—HIGH), three crop diversities (fallow-based rotations with low crop diversity—LOW; diversified rotations using annual cereal, oilseed and pulse grain crops—DAG; and diversified rotations using annual grain and perennial forage crops—DAP), and six crop phases including green manure (GM), chem-fallow or tilled-fallow (F). Amount of nitrate-N in 0-240 cm soil was usually highest under the HIGH input-LOW crop diversity treatment and lowest under the ORG input-DAP crop diversity treatment. The distribution of nitrate-N in various soil depths suggested downward movement of nitrate-N up to 240 cm depth, especially with LOW crop diversity compared to DAP crop diversity, and with HIGH input. In some years, the ORG input systems had higher nitrate-N than the RED or HIGH input systems, which was attributed to low extractable P in soil for optimum crop growth and reduced nutrient uptake with ORG input management. Extractable P in soil was higher by a small margin for HIGH or RED input relative to ORG input in the 0–15 cm layer, suggesting little downward movement of P. Crop diversity did not affect extractable soil P due to the low baseline levels of P in this soil. The proportion of fine dry aggregates (<1.3 mm, erodible fraction) in 0–5 cm soil was highest with LOW crop diversity-HIGH input system, and lowest with DAG diversity-RED input system. The opposite was true for large aggregates (>12.7 mm). Wet aggregate stability was higher for RED input compared to ORG and HIGH input, which was attributed to the increase in the concentration of organic C in aggregates in the RED input system. Amount of light fraction organic matter (LFOM), light fraction organic C (LFOC) and light fraction organic N (LFON) in 0–15 cm soil was higher for RED input compared to ORG and HIGH inputs, and higher for DAG and DAP crop diversities than for LOW crop diversity. Soil N and P were usually deficient under ORG input management, but large amounts of N and P were unaccounted for, or in surplus, under RED and HIGH inputs, despite a marked increase in plant N and P uptake and crop yield compared to ORG input. Overall, our findings suggest that soil quality can be improved and nutrient accumulation in the soil profile can be minimized by increasing cropping frequency, reducing/eliminating tillage, and using appropriate combinations of fertilizer input and diversified cropping.     

Movement and transformations of fertigated nitrogen below trickle emitters and their effects on pH in the wetted soil volume

The movement and transformations of ammonium-, urea- and nitrate-N in the wetted volume of soil below the trickle emitter was studied in a field experiment following the fertigation of N as ammonium sulphate, urea and calcium nitrate. Effects on soil pH in the wetted volume were also investigated.During a fertigation cycle (emitter rate 2lh^–1) applied ammonium was concentrated in the surface 10 cm of soil immediately below the emitter and little lateral movement occurred. In contrast, because of their greater mobility in the soil, fertigated urea and nitrate were more evenly distributed down the soil profile below the emitter and had moved laterally in the profile to 15 cm radius from the emitter. The conversion of applied N to nitrate-N was more rapid when urea rather than ammonium-N was applied suggesting that the accumulation of large amounts of ammonium below the emitter in the ammonium sulphate treatment probably retarded nitrification.Following their conversion to nitrate-N, both fertigated ammonium sulphate and urea caused acidification in the wetted soil volume. Acidification was confined to the surface 20 cm of soil in the ammonium sulphate treatment, however because of its greater mobility, fertigation with urea (2lh^–1) resulted in acidification occurring down to a depth of 40 cm. Such subsoil acidity is likely to be very difficult to ameliorate. Increasing the trickle discharge rate from 2lh^–1 to 4lh^–1 reduced the downward movement of urea and encouraged its lateral spread in the surface soil. As a consequence, acidification was confined to the surface (0–20 cm) soil.     

Crop and soil nitrogen responses to phosphorus and potassium fertilization and drip irrigation under processing tomato

Shortage of water or nutrient supplies can restrict the high nitrogen (N) demand of processing tomato, leaving high residual soil N resulting in negative environmental impacts. A 4-year field experiment, 2006?C2009, was conducted to study the effects of water management consisting of drip irrigation (DI) and non-irrigation (NI), fertilizer phosphorus (P) rates (0, 30, 60, and 90?kg P?ha^?1), and fertilizer potassium (K) rates (0, 200, 400, and 600?kg?K?ha^?1) on soil and plant N when a recommended N rate of 270?kg?N?ha^?1 was applied. Compared with the NI treatment, DI increased fruit N removal by 101?%, plant total N uptake by 26?%, and N harvest index by 55?%. Consequently, DI decreased apparent field N balance (fertiliser N input minus plant total N uptake) by 28?% and cumulative post-harvest soil N in the 0?C100?cm depth by 33?%. Post-harvest soil N concentration was not affected by water management in the 0?C20?cm depth, but was significantly higher in the NI treatment in the 20?C100?cm depth. Fertilizer P input had no effects on all variables except for decreasing N concentration in the stems and leaves. Fertilizer K rates significantly affected plant N utilization, with highest fruit N removal and plant total N uptake at the 200?kg?K?ha^?1 treatment; therefore, supplementing K had the potential to decrease gross N losses during tomato growing seasons. Based on the measured apparent field N balance and spatial distribution of soil N, gross N losses during the growing season were more severe than expected in a region that is highly susceptible to post-harvest soil N losses.     

Denitrification in shallow groundwater in a coastal agricultural area in Japan

In a coastal agricultural area in the central part of Japan (Shizuoka), we found decreasing nitrate concentration with depth in a shallow groundwater, where the depth to water table varied between 0.6 and 1.2 m below ground surface. High nitrate concentrations (5–29 mg N L^–1) were often observed in the upper layer (0–2 m) of the groundwater, but the concentration decreased to less than 1 mg N L^–1 in the deeper layer. Ammonium was scarcely detected, and the concentration of dissolved oxygen was usually low (< 1 mgO₂ L^–1) in the groundwater. Nitrate in the groundwater often had very heavy nitrogen stable isotope ratios (>20{}). There was a negative relationship between nitrogen stable isotope ratio of nitrate and its concentration. When nitrate was injected into the groundwater with acetylene and bromide (a conservative tracer), nitrate concentration decreased to 20% of the initial level within 5 days, accompanied by the increase in nitrite and nitrous oxide concentration and a little change in bromide concentration. These results indicate that microbial denitrification plays a potential role in the decrease of nitrate in shallow groundwater at the study site.     

Nitrogen Fluxes in Silage Maize Production: Relationship between Nitrogen Content at Silage Maturity and Nitrate Concentration in Soil Leachate

A challenge with respect to environmental soundness of agricultural production is the development of suitable indicators, which support an improved understanding and measurement of agricultural activities on environmental quality. The objective of this study was to investigate whether N concentration (Nc) of silage maize at silage maturity, a routinely recorded quality parameter, can serve as an indicator of nitrate concentration in the soil leachate (NO₃C). The study was based on a 5-year experiment (1997–2001), conducted on sandy soil in Northern Germany. The experiment involved four mineral N fertilization rates (0, 50, 100, 150 kg N ha⁻¹) and three slurry treatments (0, 20, 40 m³ ha⁻¹). The water and N balance model HERMES was applied to simulate the N flows within the soil–plant system. The model performed satisfactorily for aboveground biomass accumulation, N uptake, soil mineral N, and nitrate leaching. Statistical analysis of the relationship between measured crop N concentration (Nc, g N kg⁻¹) at silage maturity and simulated mean nitrate concentration (NO₃C, mg NO₃1⁻¹) of the leachate (October–March) revealed a significant impact of rainfall amount during spring/summer. Two exponential functions were estimated to describe the relationship for (i) ℈wet’ years: NO₃C = 3.4253 × exp(0.3426 × Nc), and (ii) ℈dry’ years: NO₃C = 6.8538 × exp(0.1811 × Nc). While in ℈dry’ years nitrate concentration exceeded the drinking water threshold even at very low N concentrations, the risk of high nitrate concentrations was negligible in ℈wet’ years. It is concluded that the newly developed indicator can provide a useful tool for assessing the potential risk of groundwater nitrate contamination in silage maize production.     

Reduced nitrate concentrations in shallow ground water under a non-fertilised grass buffer strip

In this paper the suitability of a buffer strip to reduce nitrate concentrations in the upper groundwater was tested for a sandy arable soil in The Netherlands during two consecutive leaching seasons. The bufferstrip was a 3.5 m wide unfertilised grass strip adjacent to a ditch on an arable field. In total 24 groundwater wells were installed in 4 transects perpendicular to the ditch to determine Cl, NO₃ and δ¹⁵N concentrations. Piezometers were installed to assess the groundwater flow, which was in the direction of the ditch with small downward leakage across a peat layer at about 3 m depth. Nitrogen was dominantly present as nitrate (NO₃). The NO₃-N concentrations under the bufferstrip were significantly lower than under the adjacent arable field. The lower concentrations were due to dilution, uptake by grass and denitrification. Nitrate was actively removed in the bufferstrip, since the Cl/NO₃ ratios were higher in the bufferstrip than in the remainder of the field. Furthermore, δ¹⁵N data indicated that denitrification occurred in the groundwater and increased with decreasing distance to the ditch. NO₃-N loads to the ditch were estimated at 8.5 kg ha⁻¹yr⁻¹, which is relatively low for this area. We can, however, not determine whether these relatively low NO₃-N loads were causally related to the reduced NO₃-N concentrations in the bufferstrip. Nevertheless, the results of the present study are promising and justify additional research on the efficiency of bufferstrips to reduce NO₃ concentrations in shallow groundwater, and subsequently reduce NO₃ loading of surface water, under Dutch conditions.     

Nitrogen losses and fertilizer N use efficiency in irrigated porous soils

Porous soils are characterized by high infiltration, low moisture retention and poor fertility due to limitation of organic matter and nitrogen (N). However, wherever irrigated and properly managed, these are among the most productive soils in the world. For sustained productivity and prevention of N related pollution problems, fertilizer N management in porous soils needs to be improved by reducing losses of N via different mechanisms. Losses of N through ammonia volatilization are not favoured in porous soils provided fertilizer N is applied before an irrigation or rainfall event. Ammonium N transported to depth along with percolating water cannot move back to soil surface where it is prone to be lost as NH₃. Under upland conditions nitrification proceeds rapidly in porous soils. Due to high water percolation rates in porous soils, continuous flooding for rice production usually cannot be maintained and alternate flood and drained conditions are created. Nitrification proceeds rapidly during drained conditions and nitrates thus produced are subsequently reduced to N₂ and N₂O through denitrification upon reflooding. Indirect N-budget estimates show that up to 50% of the applied N may be lost via nitrification-denitrification in irrigated porous soils under wetland rice.High soil nitrate N levels and sufficient downward movement of rain water to move nitrate N below the rooting depth are often encountered in soils of humid and subhumid zones, to a lesser extent in soils of semiarid zone and quite infrequently, if at all in arid zone soils. The few investigations carried out with irrigated porous soils do not show substantial leaching losses of N beyond potential rooting zone even under wetland rice. However, inefficient management of irrigation water and fertilizer N particularly with shallow rooted crops may lead to pollution of groundwater due to nitrate leaching. At a number of locations, groundwater beneath irrigated porous soils is showing increased nitrate N concentrations. Efficient management of N for any cropping system in irrigated porous soils can be achieved by plugging losses of N via different mechanisms leading to both high crop production and minimal pollution of the environment.     

Soil nitrate-N levels required for high yield maize production in the North China Plain

High profile nitrate-nitrogen (N) accumulation has caused a series of problems, including low N use efficiency and environmental contamination in intensive agricultural systems. The key objective of this study was to evaluate summer maize (Zea mays L.) yield and N uptake response to soil nitrate-N accumulation, and determine soil nitrate-N levels to meet N demand of high yield maize production in the North China Plain (NCP). A total of 1,883 farmers’ fields were investigated and data from 458 no-N plots were analyzed in eight key maize production regions of the NCP from 2000 to 2005. High nitrate-N accumulation (≥172 kg N ha⁻¹) was observed in the top (0–90 cm) and deep (90–180 cm) soil layer with farmers’ N practice during maize growing season. Across all 458 no-N plots, maize grain yield and N uptake response to initial soil nitrate-N content could be simulated by a linear plus plateau model, and calculated minimal pre-planting soil nitrate-N content for maximum grain yield and N uptake was 180 and 186 kg N ha⁻¹, respectively, under no-N application conditions. Economically optimum N rate (EONR) decreased linearly with increasing pre-planting soil nitrate-N content (r ² = 0.894), and 1 kg soil nitrate-N ha⁻¹ was equivalent to 1.23 kg fertilizer-N ha⁻¹ for maize production. Residual soil nitrate-N content after maize harvest increased exponentially with increasing N fertilizer rate (P < 0.001), and average residual soil nitrate-N content at the EONR was 87 kg N ha⁻¹ with a range from 66 to 118 kg N ha⁻¹. We conclude that soil nitrate-N content in the top 90 cm of the soil profile should be maintained within the range of 87–180 kg N ha⁻¹ for high yield maize production. The upper limit of these levels would be reduce if N fertilizer was applied during maize growing season.     

Simulating nitrate leaching in bare fallow soils: a model comparison

In Western Europe, agriculture is one of the major contributors to the pollution of ground- and surface waters. Environmental concern has created the need for protection of these waters against eutrophication, caused by nutrient losses from e.g. agricultural sources. Leaching models may be used to predict nitrate-N losses to the environment and a plethora of such leaching models already exist. Four nitrate leaching models (Burns model, SLIM, SACFARM and ANIMO), with varying degree of complexity and parameter requirements, were used to simulate leaching in a bare fallow soil on a number of fields in the Wijlegem catchment in Flanders, Belgium. The models' performance was evaluated both statistically and graphically. Although all models predicted nitrate content in the soil profile within acceptable limits, the slightly adjusted Burns model appeared to simulate both the nitrate nitrogen and the water content best for the calibration field. Similar results were obtained for the evaluation field experiments: the Burns_– model simulated the moisture and nitrate content fairly well, while SLIM performed well in simulating the nitrate content. In conditions with limited data availability, simple (management) models, needing only a limited number of parameters to be measured or calibrated, may yield better simulation results than complex mechanistic models.     

Crop yield, nitrogen uptake and nitrate-nitrogen accumulation in soil as affected by 23 annual applications of fertilizer and manure in the rainfed region of Northwestern China

Application of chemical fertilizers and farmyard manure affects crop productivity and improves nutrient cycling within soil–plant systems, but the magnitude varies with soil-climatic conditions. A long-term (1982–2004) field experiment was conducted to investigate the effects of nitrogen (N), phosphorus (P), and potassium (K) fertilizers and farmyard swine manure (M) on seed and straw yield, protein concentration, and N uptake in the seed and straw of 19-year winter wheat (Triticum aestivum L.) and four-year oilseed (three-year canola, Brassica napus L. in 1987, 2000 and 2003; one-year flax, Linum usitatisimum L. in 1991), accumulation of nitrate-N (NO₃-N) in the soil profile (0–210 cm), and N balance sheet on a Huangmian soil (calcaric cambisols, FAO) near Tianshui, Gansu, China. The two main plot treatments were without and with farmyard swine manure (M); sub-plot treatments were control (Ck), N, NP, and NPK.␣The average seed yield decreased in the order MNPK ≥ MNP > MN ≥ NPK ≥ NP > M > N > Ck. The average effect of manure and fertilizers on seed yield was in the order M > N > P > K. The seed yield increase was 20.5% for M, 17.8% for N, 14.2% for P, and 2.9 % for K treatment. Seed yield response to fertilizers was much greater for N and P than for K, and it was much greater for no manure than for manure treatment. The response of straw yield to fertilization treatments was usually similar to that of seed yield. The N fertilizer and manure significantly increased protein concentration and N uptake plant. From the standpoint of increasing crop yield and seed quality, MNPK was the best fertilization strategy. Annual applications of N fertilizer and manure for 23 successive years had a marked effect on NO₃-N accumulation in the 0–210 cm soil profile. Accumulation of NO₃-N in the deeper soil layers with application of N fertilizer and manure is regarded as a potential danger, because of pollution of the soil environment and of groundwater. Application of N fertilizer in combination with P and/or K fertilizers reduced residual soil NO₃-N significantly compared with N fertilizer alone in both no manure and manure plots. The findings suggest that integrated and balanced application of N, P, and K fertilizers and␣manure at proper rates is important for protecting soil and groundwater from potential NO₃-N pollution and for maintaining high crop productivity in the rainfed region of Northwestern China.     

Source identification of nitrate on Cheju Island, South Korea

Stable isotopes of nitrogen were used to identify sources of nitrate contamination to groundwater on Cheju, a subtropical island off the southernmost tip of the Korean peninsula. The δ¹⁵N ranges of potential animal waste and fertilizer N sources on the island were similar to those previously reported in the USA, Europe, and Africa. A total of 108 soil pore water samples were collected between January and October 1998 from fertilized soils below soybean fields and citrus groves. Low concentrations of nitrate below fertilized soybean fields indicated that it is highly unlikely that these fields contribute significant N to the groundwater problem on Cheju. The low average δ¹⁵N value of +1.9 ± 2.1‰ in pore-water nitrate and the even lower δ¹⁵N values after the fertilizer flush suggest that low levels of mineralized N are released from the bean roots or nodules. Located in the western region, the bean fields received less rainfall than the citrus groves in the southern region. Pore-water below citrus trees contained considerably higher nitrate levels, and the δ¹⁵N values became cyclically enriched after the initial fertilizer flush. Although denitrification can be expected in warm, wet soils high in organic-C content in the southern region of Cheju, it was not supported by pore-water or groundwater chemistry. Isotopic enrichment in soil pore-water is caused primarily by volatilization of ammonium-based fertilizers. Since isotopic fractionation in the soils did not exceed +4‰, source identification was possible. The dominant sources of nitrate contamination to Cheju groundwater were identified as commercial N-fertilizer applications to citrus, and, in the Seogwipo municipality, human or animal wastes.     

Soil surface N balances and soil N content in a clay-loam soil under Irish dairy production systems

This study evaluated the effect of a dairy system involving grazing over the winter on a soil surface N balance (SSB) and soluble N content in a clay loam soil in comparison with early spring calving systems. The SSBs were calculated for each paddock within three dairy systems for 2 years. Inputs included N entering the soil in fertilizer, slurry, excreta, atmospheric deposition and biological N fixation. Outputs consisted of N leaving the soil in harvested and grazed herbage. Nitrogen surplus was calculated as a difference between N inputs and outputs. Soluble N was assessed in soil extracts at three depths to 0.9 m. The management of the systems resulted in N surplus from 113 to 161 kg N ha^?1 year^?1 and N use efficiency of the soil component from 63 to 72 % without significant variation between the systems. The dairy system had no effect on soil N content as its variation was likely buffered by inherent soil properties (heavy texture, high C, pH) and the presence of shallow groundwater. The biochemical anaerobic reduction processes (i.e. denitrification) likely ensured soil oxidised N consistently low (<20 kg ha^?1). Consequently, the system involving grazing over the winter on these soils did not create an additional environmental pressure via N losses to groundwater and N₂O emissions compared with early spring calving systems. The size of soil inorganic N pools was mainly controlled by the hydrological factors and soil temperature, which are the most important factors controlling microbial activity, biochemical processes and leaching.     

Leaching of nitrate from cropped rainfed terraces in the mid-hills of Nepal

Intensification of crop production in the mid-hills of Nepal has led to concerns that nitrogen loss by leaching may increase. This study estimated the amount of N leached during two years from rainfed terraces (bari-land) at three locations in Nepal. Maize or upland rice grown in the monsoon season was given either no nutrient inputs or inputs via either nitrogen fertilizer or farmyard manure. Nitrate concentration in soil solution was measured regularly with porous ceramic cup samplers and drainage estimated from a simple soil water balance. Estimated losses of nitrogen by leaching ranged from 0 to 63.5 kg N ha^–1 depending on location and the form of nitrogen applied. Losses from plots receiving no nutrient inputs were generally small (range: 0–35 kg N ha^–1) and losses from plots where nitrogen was applied as manure (range: 2–41 kg N ha^–1) were typically half those from plots with nitrogen applied as fertilizer. Losses during the post-monsoon crops of finger millet were small (typically <5% of total loss) although losses from the one site with blackgram were larger (about 13%). The highest concentrations of nitrate in solution were measured early in the season as the monsoon rains began and immediately following fertilizer applications. Leaching losses are likely to be minimised if manure is applied as a basal nutrient dressing followed by fertilizer nitrogen later in the season.     

Compensatory fertilization of Scots pine stands polluted by heavy metals

The results from four compensatory fertilization experiments located at different distances (0.5, 2, 4 and 8 km) along a heavy metal deposition gradient extending from the Harjavalta Cu-Ni smelter in SW Finland are presented. The experiments were established in middle-age Scots pine stands growing on dryish sites of sorted glaciofluvial sediments. The soil type in all the experiments is ferric podsol. The treatments in the experiments consisted of liming, a powdered slow-release mineral mixture and stand-specific fertilization which comprised at least methylene urea and ammonium nitrate.Monitoring of deposition and soil solution and studies on soil chemical and microbiological properties, on the nutrient status of trees and needle litterfall, on fine root dynamics and on the growth of the tree stands were carried out during a 5-year period.There was a severe shortage of exchangeable Ca and Mg in the organic layer of the most polluted stands. Although the uppermost mineral soil layer had relatively high exchangeable Ca and Mg concentrations, the trees were not able to utilize these nutrient reserves presumably due to the toxic effects of Cu and Ni on the plant roots and mycorrhizas.The treatments that included limestone markedly decreased the Cu and Ni concentrations in the soil solution and soil organic layer, presumably due to immobilisation through precipitation or absorption. The Ca and Mg concentrations correspondingly increased, which certainly contributed to the partial recovery of fine root and stand growth. The powdered mineral mixture and the combination of methylene urea and ammonium nitrate had no short-term effect on the microbial biomass and activity. All the fertilizer treatments increased volume growth in the most polluted stand. The stand-specific fertilization increased needle mass in heavily polluted stands, but the response of the needle mass to fertilizer treatments was low in the less polluted stands. No clear evidence was found to support the role of nutrient status in tree resistance.