Hydrochemical and stable isotopic assessment of nitrate contamination in an alluvial aquifer underneath a riverside agricultural field

Major ions and stable isotopic (δD_water, δ¹⁸O_water, δ¹⁵N_nitrate, δ¹⁸O_nitrate) measurements in concert with hydrochemical modeling were used in order to elucidate the sources and geochemical processes controlling nitrate contamination of shallow alluvial groundwater underneath a riverside agricultural field in the Buyeo area, Korea. Beneath vegetable fields in the sandy soil, the mean nitrate concentration of groundwater was 148.6 mg/L, which is significantly higher than in groundwater (mean 28.8 mg/L) beneath silty soils underneath rice paddy fields. Nitrogen isotope data indicate that synthetic fertilizers are the predominant source of groundwater nitrate in the study area. Denitrification during recharge through rice paddy soils appears to be responsible for the lower nitrate concentrations in groundwater beneath the silty soil zone. The relationship between nitrogen and oxygen isotope data of nitrate also suggests mixing of two different groundwater bodies with nitrates from the silt zone and the sand zone. Geochemical mass balance modeling on hydrochemical data indicates that various agricultural chemicals such as urea, lime, magnesium sulfate and potassium chloride dissolve in vegetable fields of the sandy zone, resulting in significant enrichment of various solutes such as K⁺, Ca²⁺, Mg²⁺, NO₃⁻, SO₄²⁻ and Cl⁻. As a consequence of over-utilization of synthetic nitrogen fertilizers, the sand zone is characterized by very high nitrate concentrations in the groundwater. This study suggests that a reduction of over-fertilization especially on vegetable fields in the riverside sand zone is required to minimize the nitrate contamination of groundwater. This study also shows that combination of geochemical and isotopic techniques with simple mass balance modeling provides information about the causes and processes of nitrate contamination of groundwater underneath a riverside agricultural field. The study also provides sustainable measures to optimize fertilization rate as an important basis of eco-friendly agriculture.     

餐饮业食品中亚硝酸盐含量调查研究

为了解餐饮业中熟食制品、香肠和腌菜中亚硝酸盐残留量情况,采用随机抽样的方法,对样品中亚硝酸盐的残留量进行检测。结果表明：检测的60份样品的亚硝酸盐残留量合格率为91.67%;腌菜类的亚硝酸盐含量较低,而香肠的亚硝酸盐含量最高。     

硝酸钙在底泥修复中的作用机理及

受污染底泥的修复已经成为水环境修复中的重要组成部分，在底泥中注入硝酸钙则是近十多年来发展起来的一种污染底泥原位处理技术。全面分析了硝酸钙在底泥修复中去除有机物、抑制磷的释放以及消除水体黑臭现象的机理，并介绍了这一技术在国内外的研究和应用状况。研究成果表明：在底泥中注入硝酸钙的技术已从实验室和中试研究阶段发展到了实际的工程动作阶段，并且在有机物PAHS的降解和硫化物的去除方面已经得到了很好的效果。     

Nitrate leaching in a silage maize field under different irrigation and nitrogen fertilizer rates

Quantification of the interactive effects of nitrogen (N) and water on nitrate (NO₃) loss provides an important insight for more effective N and water management. The goal of this study was to evaluate the effect of different irrigation and nitrogen fertilizer levels on nitrate-nitrogen (NO₃-N) leaching in a silage maize field. The experiment included four irrigation levels (0.7, 0.85, 1.0, and 1.13 of soil moisture depletion, SMD) and three N fertilization levels (0, 142, and 189 kg N ha⁻¹), with three replications. Ceramic suction cups were used to extract soil solution at 30 and 60 cm soil depths for all 36 experimental plots. Soil NO₃-N content of 0-30 and 30-60-cm layers were evaluated at planting and harvest maturity. Total N uptake (NU) by the crop was also determined. Maximum NO₃-N leaching out of the 60-cm soil layer was 8.43 kg N ha⁻¹, for the 142 kg N ha⁻¹ and over irrigation (1.13 SMD) treatment. The minimum and maximum seasonal average NO₃ concentration at the 60 cm depth was 46 and 138 mg l⁻¹, respectively. Based on our findings, it is possible to control NO₃ leaching out of the root zone during the growing season with a proper combination of irrigation and fertilizer management.     

Assessing the impact of the Nitrate Directive on farming systems using a bio-economic modelling chain

Bio-economic models can be used to assess the impact of policy and environmental measures through economic and environmental indicators. Focusing on agricultural systems, farmers’ decisions in terms of cropping systems and the associated crop management at field scale are essential in such studies. The objective of this paper is to present a study using a bio-economic model to assess the impact of the Nitrate Directive in the Midi-Pyrenees region (France) by analyzing, at the farm scale, farm income and three environmental indicators: nitrate leaching, erosion and water consumption. Two scenarios, the 2003 CAP reform (baseline scenario) and the Nitrate Directive (policy scenario), with a 2013 time horizon, were developed and compared for three representative arable farm types in the Midi-Pyrenees region. Different types of data characterizing the biophysical context in the region (soil, climate), the current cropping systems (rotation, crop management) and farm resources (irrigated land, labor) were collected to calibrate and run the models. Results showed that the implementation of the Nitrate Directive may not affect farm income. However, significant modifications to cropping systems and crop allocation to soil types were simulated. Contrary to expectations, nitrogen leaching at the farm scale did not change. Overall water consumption increased and soil erosion decreased due mainly to a modification in cropping patterns and management by soil type. This study provides an example of unanticipated effects of policy and trade-offs between environmental issues.     

Nitrate leaching assessment in a long-term experiment under supplementary irrigation in humid Argentina

Applying high rates of nitrogen (N) fertilizer to crops has two major disadvantages: (1) the low N fertilizer use efficiency and (2) the loss of N by leaching, which may cause groundwater nitrate (NO₃⁻) pollution, especially in humid areas.The objectives of this study were to adjust and validate the LEACH-W model simulations with data observed in the field; to quantify nitrate concentrations in the soil solution; to estimate N loss by leaching; and to determine the moments during the year when greatest nitrate transport events occur beyond the rooting profile.A randomized complete block design with four replications was established on a typic Argiudoll. Crop fertilization treatments consisted of three N rates (0, 100, and 200 kg N ha⁻¹) using urea and ammonium nitrate solution (UAN) as the N source. Corn (Zea mays L.) was planted and ceramic soil-water suction samplers were installed to depths of 1, 1.5 and 2 m. Drainage was estimated by the LEACH-W model, which adjusted very well the actual volume of water in the soil profile. Nitrogen losses were statistically analyzed as repeated measure data, using the PROC MIXED procedure.Losses of nitrate-nitrogen (NO₃⁻-N) during the study increased as the rate of N applied increased. At all depths studied, statistically significant higher values were found for 200 N compared to 100 N and 0 N, and for 100 N compared to 0 N (p < 0.001).The greatest NO₃⁻-N losses through leaching occurred during crop growth. Significant differences (p < 0.05) were found between cropping and fallow in the three treatments and depths studied for seasons 4 and 5; these two seasons produced the highest drainage volumes at all depths.     

Nitrate leaching and soil nitrate content as affected by irrigation uniformity in a carrot field

High value crops such as carrot planted in coarse soils of the Southern San Joaquin Valley in California are prime candidates for nitrate leaching through irrigation nonuniformity. A 2-year study was carried out to explore the impact of irrigation uniformity on nitrate leaching. Irrigation uniformity was measured using catchcans. Soil nitrate (NO₃-N) and ammonium (NH₄-N) contents were measured from soil sampled at different depths and times during two growing seasons. Nitrate leaching was determined using ion-exchange resin bags at 1-m depth sampled three times during each season. Although, soil NO₃-N as well as seasonal irrigation was significantly higher along the lateral irrigation pipe than between the sprinklers, nitrate leaching was not significantly higher. As expected, soil nitrate content decreased as percolation increased for both years. Nitrate leaching, as estimated by anion-exchange resin bags, was positively correlated to soil NO₃-N content but was not correlated to irrigation depth, irrigation uniformity, or deep percolation. Field variation in saturated hydraulic conductivity (K_s), soil organic matter (OM), and soil water retention at field capacity had limited effect on NO₃-N and NH₄-N distributions in the profile and on nitrate leaching. The results of this experiment suggest that irrigation nonuniformity has less impact on nitrate movement than suggested by earlier studies.     

保水剂底施对沙子剖面水分和硝态氮运移的影响研究

【目的】解决沙土地区漏水漏肥的核心问题,建立保水防渗漏新技术体系,促进沙土地区农业可持续发展。【方法】基于保水剂的吸水保肥等物理化学特点,以保水剂和土壤混合物底施为技术方法,选用聚丙烯酸钠和壤土为材料,采用沙柱模拟试验,研究了不同施用厚度的保水剂-土壤混合物对剖面水分运移及硝态氮淋洗的影响。【结果】聚丙烯酸钠在壤土中的质量分数为1%时,可以对水分有效截流;混合物底施,以0.9～1.5 cm厚度为最佳;淋溶试验表明硝态氮主要集中在表层和保水剂层,占比为87.2%,有效防止了硝态氮的下移。【结论】保水剂壤土混合物底施,可以起到显著的水分养分截流作用,本试验中聚丙烯酸钠质量分数1%及1 cm厚度时,可获得较好效果。     

光强对生菜硝酸盐累积的影响

以意大利耐抽苔生菜为试验材料,研究了5个梯度(75,150,225,450,550mol/s·m2)光照强度处理对其叶绿素相对含量、干重等生理指标和硝酸盐累积的影响。结果表明,光照强度显著的影响植株生长及各测定指标。叶绿素含量与光强呈正相关;地上部分和地下部分硝酸盐的累积与光强呈负相关;光合速率的日变化出现第一个波峰的时间要比田间作物滞后;分析各指标后表明最适合生菜生长的光照强度为450mol/(s·m2),达到了低硝酸盐的累积与生长品质的统一。     

地下水中硝酸盐氮污染修复技术综述

介绍了地下水中硝酸盐氮的来源和危害,较全面地阐述了地下水中硝酸盐氮的物理、化学、生物修复技术的研究情况,比较了各种方法的优缺点,并对其发展趋势进行了简单的论述。     

农业机械化及农业产业化在建设社会主义新农村中的作用

建设社会主义新农村是党中央统筹城乡发展的重大战略决策,是我国现代化进程中的重大历史任务。建设社会主义新农村,必须以农村经济建设为中心,建设现代农业。农业机械化是构成农业综合生产能力的重要组成部分,是现代农业的重要物质基础,是农业现代化的重要内容和标志。加快发展农业机械化,是建设社会主义新农村的内在要求与必由之路,必须把它摆在重要的位置。全面建设社会主义新农村,也为农业机械化提出了更新、更高、更快的发展要求。本文着重就农业机械化及农业产业化在建设社会主义新农村中的作用进行探讨。     

同步滴灌施肥条件下根际土壤水氮分布试验研究

通过室内土槽试验,探讨了停灌后不同时间,同步施肥滴灌对土壤水分及土壤硝态氮在土壤剖面分布的影响。结果表明:停灌后,各处理土壤水分以滴头为中心沿径向向四周扩散;由于水分在横向及纵向运动,上下层土壤水势梯度随径向距离增加而逐渐减少。停灌后,氮浓度3、2 g/L处理硝态氮的含量与径向距离及土层深度成反比;氮浓度0 g/L处理硝态氮的含量随径向距离及土层深度增加先增大后减小,氮浓度0 g/L处理硝态氮在深度分布表现为"上低中高下稳定"抛物线分布。     

Assessment of groundwater quality and its variations in the capture zone of a pumping well in an agricultural area

Agricultural activities are frequently associated with water contamination. The spreading and storage of fertilizers, for instance, may result in groundwater contamination due to pollutants leaching into an aquifer. Nitrates and fecal bacteria are two important contaminants associated with agriculture. Thus, the development of efficient strategies for groundwater protection in agricultural areas requires an assessment of these two contaminants. Given this perspective, groundwater quality monitoring was carried out over the whole capture zone of a municipal well located in an agricultural area in the St.-Lawrence Lowlands in Québec. Thirty-eight piezometers were installed within the roughly 2 km² capture area of the well to measure physico-chemical parameters such as major ions, field measured parameters (pH, electrical conductivity, dissolved oxygen, water level, temperature), and isotopic ratios, bacteriological parameters (Heterotrophic Plate Count—HPC, enterococci, total coliforms, Escherichia coli) and their variations in space and time. Groundwater was sampled from the pumping well and the piezometers during 25 field campaigns in 2005, 2006 and 2007. The results demonstrate the impact of agricultural activities on nitrate contamination. They indicate high spatial and temporal variations in nitrate concentrations, from 6 to 125 mgNO₃⁻/L within the capture area, with 40% of the samples exceeding the Québec drinking water limit of 45 mgNO₃⁻/L. Nitrate pollution in the municipal well exceeded 45 mgNO₃⁻/L during 2005, but no bacteriological contamination was observed. The results also show a high variability of nitrate concentration with depth within the capture zone. Electrical conductivity appears as a good indicator of the presence of nitrate and calcium ions in this capture zone. Correlations between nitrate, calcium and chloride suggest that these ions come from the same source of fertilizer. Nitrate isotopic composition suggests that nitrate in groundwater originates from both chemical and organic fertilizers. The bacteriological results show that the extracted volume of water during sampling of a piezometer has a significant impact on the bacteria count. The variability of bacteriological pollution is important in space and time, showing a higher contamination during summer. Only 2% of the raw water samples exhibit contamination exceeding the drinking water standard for treated water. Total coliforms seem to be a good precursor of E. coli or enterococci contamination. Globally, the physico-chemical and bacteriological groundwater quality within the studied capture area and the pumping well shows contamination by nitrates, but low contamination levels by fecal bacteria.     

Cattle accumulation and the commercialization of the traditional livestock industry in Botswana

The unfenced ranges of Botswana support large cattle herds, which are operated on a commercial basis, and small herds, which are managed in order to meet family subsistence needs. The distinctive herding practices and sales strategies associated with large and small herds are suited to the variable amounts of human labour, cash and saleable animals at the disposal of herd owners. If they are to operate permanently on a commercial basis, small herds must grow in size. The process of commercialization will not, therefore, alleviate overstocking on communal rangelands and the majority of small herd owners are not likely to endorse any programme of voluntary destocking.     

Salt and water transport in unsaturated soil for non-conservative systems

An analytical solution is developed for one-dimensional salt and water transport in soil systems with a steady intake velocity. Both water and solutes are non-conservative in the sense that they are removed by plant roots. Additionally, the solute (or any water-transported entity) may be lost through a first order reaction. The unique feature of the solution is the coupling of unsaturated flow to solute uptake by the use of a “reflection coefficient” describing selective uptake by the roots. Hydrodynamic dispersion is included in the initial formulation, but is assumed negligible in actual calculations. Four numerical examples illustrate the utility of the solution. In the first example the effects of rooting pattern are shown for two different discretely-layered uptake functions. Example two shows results of changes in the magnitude of the first order reaction coefficient while in the third example, computations are made for differences in the reflection coefficient including changes with depth. The final comparison shows the effect of varying leaching coefficients.     

Modelling point and diffuse source pollution of nitrate in a rural lowland catchment using the SWAT model

The assessments of potential environmental impacts of point and diffuse source pollution at regional scales are necessary to achieve the sustainable development of natural resources such as land and water. Nutrient related diffuse source pollutant inputs can enhance crop growth and improve soil eutrophication. However, excessive nutrient input can result in the impairment of water quality. The objectives of this study were to evaluate the long-term impact of point and diffuse source pollution on nitrate load in a lowland catchment using the ecohydrological model SWAT (Soil and Water Assessment Tool) and to determine the contribution of point and diffuse sources to nitrate load in the entire catchment.The study area Kielstau catchment has a size of approximately 50 km² and is located in the North German lowlands. The water quality is not only influenced by the predominating agricultural land use in the catchment as cropland and pasture, but also by six municipal wastewater treatment plants. Diffuse entries as well as punctual entries from the wastewater treatment plants are implemented in the model set-up. The model was first calibrated and then validated in a daily time step. The values of the Nash-Sutcliffe efficiency for the simulations of flow and nitrate load range from 0.68 to 0.75 for the calibration period and from 0.76 to 0.78 for the validation period. These statistical results revealed that the SWAT model performed satisfactorily in simulating daily flow and nitrate load in lowland catchment of Northern Germany. The results showed that diffuse sources are the main contributor to nitrate load in the entire catchment accounting for about 95% of the total nitrate load, while only 5% results from point sources. The model results also indicated that agriculture is the dominant contributor of diffuse sources and the percentage of agricultural land area is considerably positively correlated to nitrate load at the different subbasins. The area covered by forest is found to be negatively correlated with nitrate load.     

Evaluation of the RZWQM for the Simulation of Water and Nitrate Movement in Level-Basin,Fertigated Maize

This study concerns the evaluation of the root zone water quality model (RZWQM) to simulate the seasonal water and nitrate movement in a level basin irrigated corn field under three different nitrogen (N) fertilizer treatments. The three N treatments, superimposed over a split basal dose applied before and at planting, were: a single broadcast application of 150 kg N/ha as urea (100% amidic form), a single fertigation application of the same N as UAN (50% amidic, 25% ammonium and 25% nitrate) with the first irrigation, and multiple UAN fertigations with three irrigations. Certain variety-specific maize crop parameters in the model were obtained by fitting these parameters to field data from the single fertigation treatment. The model was then evaluated on water and N results for the treatments. The model adequately simulated the water and nitrate transport for the season, with the seasonal averages of measured and predicted values differing by less than 5%. The most significant differences between measured and simulated water and nitrate occurred near the soil surface (15 cm depth), mostly during the days when the soil was extremely wet following irrigations. With the soil hydraulic properties estimated by simple means, the model tends to overestimate downward water fluxes and related nitrate transport through a compacted layer; however, it is found to be a useful tool to study the relative impacts of alter- nate nitrogen fertilizer and irrigation practices on root zone water quality.     

Crop yields under the traditional cropping patterns in a middle-belt savanna agro-ecological zone of Nigeria

A farming systems study was carried out from 1983 through 1985 among the rural farmers of the Middle-Belt agro-ecological zone of Benue State in Nigeria. The study aimed at providing the baseline data needed for evaluating the traditional cropping patterns and for assessing the magnitude of their effects on yields and returns from farms. Crop yields were found to be affected by several components of traditional cropping systems: fallow length, crop combinations in inter-cropping patterns, crop sequences and dates of planting. Variation of crop performance is such that the development in the area of well articulated farming systems research through ‘on the farm’ experimentation will provide a framework for improving the farmers' yields through modifications to the farming system.     

不同灌水模式对土壤水分和硝态氮分布的影响

通过2年带防雨棚微区试验研究了传统灌水施肥与水肥异区交替灌水施肥对土壤中水分和硝态氮分布的影响。结果表明:土壤水分和硝态氮分布与灌水方式和灌水量有关。无论灌水量高低,第1次灌水后,水肥异区的施肥沟与灌水沟在0~60 cm土层土壤水分和硝态氮含量存在差异。第2次灌水后,施肥沟与灌水沟之间土壤水分含量的差异会随灌水量增加而缩小,而二沟之间0~60 cm土层中硝态氮含量的差异则随灌水量的增加而增加。同时,土壤中表层及亚表层硝态氮含量随灌水量的增加而增加。考虑到减少水分的深层渗漏和提高肥料的有效性,在交替灌水时必须控制灌水量,建议灌水量在450~600 m3/hm2为佳。     

A scaling based estimation of soil unsaturated hydraulic properties at a field scale

This paper deals with the prediction of the soil water retention h(S) and the soil unsaturated hydraulic conductivity K(S) functions of a clay-loam soil at a field scale (1 ha) where the variable S represents water saturation. The Van Genuchten model and the corresponding Mualem-Van Genuchten model were used to predict h(S) and K(S) functions respectively. The field data (tensiometric and neutron probe measurements) used in this study were provided by the soil water balance (four neutron sites, 0.35 to 1.55 m soil layer) of a soybean crop over a 78 days growing season. The advantages of the scaling approach for describing the field variability of the h(S) function were confirmed. The scaling approach accounted for 73% of the field variability of the soil matrix potential. A simple procedure was proposed in order to predict the K(S) function using scaling theory. This was done by simultaneously applying a ``zero flux method' and ``deep flux method' to compute the soil water balance and fit the saturated hydraulic conductivitiy (K _sat), the only unknown parameter in K(S). Received: 15 November 1995