华北潮土冬小麦-夏玉米轮作包气带氮素淋溶机制

合理水氮管理可以实现作物目标产量和品质、维持土壤肥力和降低环境污染。然而,自20世纪90年代以来,我国农田过量施氮和大水漫灌等问题突出,引起农业面源污染日趋加重,地下水硝酸盐污染成为一个普遍现象。本文以华北潮土区冬小麦-夏玉米体系为研究对象,采用数据整合和文献分析的方法,阐明了典型农田硝态氮淋溶的时空特征及影响因素,研究了地表裂隙和土壤大孔隙对硝态氮淋溶的影响,定量了氮素在地表-根层-深层包气带-地下水的垂直迁移通量及过程。结果表明,农户常规管理的冬小麦-夏玉米轮作体系氮素盈余较高(299～358kg·hm~(-2)·a~(-1)),导致土壤根区和深层包气带累积了大量的硝态氮。冬小麦季硝态氮的迁移主要受灌溉影响,以非饱和流为主,且迁移距离较短;春季单次灌溉量低于60 mm,可以有效控制水和硝态氮淋溶出根区。冬小麦耕作和灌溉引起的地表裂隙对水氮运移的贡献不大。雨热同期的夏玉米季,土壤水分经常处于饱和状态,再降雨就可以导致硝态氮淋溶出根层进入深层包气带。夏玉米季极易发生硝态氮淋溶事件(占全年总淋溶事件的81%左右),硝态氮淋溶量占全年总淋溶量的80%左右,且单次淋溶事件的淋溶量较高。大孔隙优先流对夏玉米季根区硝态氮淋溶的贡献率在71%左右,这些硝态氮脱离了作物根系吸收范围,反硝化作用对硝态氮去除具有一定作用。在华北气候-土壤条件下,特别应注意冬小麦收获后土壤不应残留过多硝态氮,以避免夏玉米季降雨发生大量淋溶;夏玉米季需要注意施氮与作物需氮的匹配。由于夏玉米追肥困难,生产上提倡一次性施肥措施,控释肥应该能够发挥更大作用。未来气候变化,导致夏季极端高强度降雨事件的频率增加,将会加剧包气带累积硝态氮通过饱和流或优先流向地下水的迁移。合理的水氮管理是从源头上减少硝态氮向深层包气带和地下水迁移的主要措施。     

The leaching potential as a land quality of two Dutch soils under current and potential management conditions

Within the field of land evaluation, crop productivity as well as environmental effects should be investigated for specific land use types. The leaching potential is introduced as an environmental land quality and is expressed in terms of a downward flux from the root zone. The frequency distribution and the amount of this downward flux were calculated for each period of the year using the SWANY model, which simulates soil water flow, evapotranspiration and crop growth. Two examples for the use of this land quality are presented for potato production under different irrigation regimes on a coarse-textured Humic Podzol and under different groundwater control regimes on a median-textured Calcaric Fluvisol in the Netherlands.

The simulation results showed that irrigation increases crop yields for the Humic Podzol, but also increases the leaching potential. Restricted irrigation resulted in similar crop production levels, but in only part of the additional downward flux from the root zone. For the Calcaric Fluvisol, drainage provided higher crop yields and a slightly lower leaching potential due to an increase in crop uptake.     

Salt—Water Dynamics in Soils：Ⅲ.Effect of Crop Planting

Through a simulation test conducted with soil columns (61.8cm in diameter) in field condition,effect of crop planting upon the regulation of salt-water dynamics in soils was studied by monitoring of salt-water dynamics in situ,using soil salinity sensors and tensiometers.The results indicated that the amount of water absorbed by crops from the soil was generally larger than the decrement of water consumption from soil surface evaporation reduced by the crop covering the soil surface and improving the soil structure,therefore,under the conditions of crop growing and non-irrigation,water content in soil profile was less than that without crop growing,and the gradient of negative pressure of soil water in soil profile especially in the root zone was enlarged,thus causing the water flowing from subsoils into root zone and increasing the groundwater moving upwards into soil layer via capillary rise,so that the groundwater evaporation increased.Consequently,under the condition of crop growing,the salt was mainly accumulated towards the root zone rather than to the top soil.the accumulating rate of salt in groundwater via capillary rise of soil water to subsoils was increased thereby.     

再生水灌溉区农田包气带及地下水中硝酸盐分布特征及来源研究

本文通过对华北平原典型再生水灌溉区(河北省石家庄洨河流域)的包气带土壤、地表水和地下水进行采样分析,对硝酸盐在多种环境介质中的来源与环境行为进行了研究,识别了再生水灌溉区地下水硝酸盐污染来源,明确了不同灌溉条件对包气带土壤中硝酸盐迁移的影响。在受到城市再生水严重影响的洨河流域,地下水中的硝酸盐浓度分布范围在4.0 mg·L?1到156.6 mg·L?1之间,已经形成了距离河道2 km、深度70 m的硝酸盐高值区域,经过计算硝酸盐的垂向扩散速率为每年1～2 m。硝酸盐与氯离子的相关性表明,城市再生水是再生水灌溉区包气带、地表水和地下水中硝酸盐的主要来源。利用Geoprobe获取利用不同灌溉水农田土壤剖面样品,研究再生水对厚包气带NO3?-N垂向分布影响,再生水灌溉区和地下水灌溉区中包气带土壤的NO3?-N的平均含量为137.0 mg·kg-1和107.7 mg·kg-1,最高含量523.2 mg·L?1和725.9 mg·L?1,分别出现1.20 m和0.85 m深度,分布规律有着明显的差别。包气带土壤硝酸盐与氯离子的相关性分析表明,再生水灌溉区土壤硝酸盐主要来源于城市再生水,而地下水灌溉区可能来源于农田氮肥。地下水年龄和硝酸盐之间关系表明,地下水中1975年以前补给的硝酸盐浓度低于1975年以后补给,地下水硝酸盐污染与包气带氮入渗的历史过程密切相关。在华北平原特殊的地质水文背景下,农田面源污染对地下水的影响有限,但再生水灌溉区地下水硝酸盐污染的风险较高。     

农用地土壤重金属超标评价与安全利用分区

土地资源是大自然馈赠给人类的独特珍品,承载万物。开展区域农用地土壤重金属超标评价与安全利用分区、分类利用管控,促进区域土地资源合理、高效利用是新常态下耕地保护的基本要求。该文分不同p H值区间、8种不同地类,基于现行土壤环境质量评价和食品安全评价的众多标准集成土壤环境质量现状评价标准,以江苏省某市为例,运用单因子指数法、内梅罗综合指数法和潜在生态危害指数法开展土壤重金属超标评价,进而提出了安全利用等级划分方案和分区、分类利用与管理的管控策略。结果表明:将研究区农用地分为安全、基本安全、低风险、中风险和高风险5种综合分区,分别采取优先保护、综合监控、预警防控和限制利用等措施,以精细化管理思想为出发点,从源头控制、农艺措施调控、种植作物调整、地类转换以及土壤修复、综合整治等方面提出了各综合分区的安全利用管控策略。因此,开展区域农用地土壤重金属超标评价与安全利用分区研究为确保土地资源合理利用保护耕地提供了重要思路。     

Effektive Durchwurzelungstiefe,Sickerwasserbildung und Nitratverlagerung in tiefgründigen Lößböden eines Trockengebietes

Effective rooting depth, percolation water, and nitrate leaching in deeply developed loess soils of a water‐shortage area In 14 deeply developed loess soils, high amounts of mineral nitrogen (N) were measured within the first meter, whereas several nitrate depth profiles up to more than three meters resulted in low and medium nitrate values. The maximum depth of water uptake was measured in two years on four representative sites with regard to soil and crop properties. The maximum depth of water uptake was always considerably deeper than 200 cm, with a maximum of 290 cm (alfalfa). It is assumed that roots take up nitrogen even in this depth. The calculation of the effective rooting depth resulted in noticeably higher values (for wheat between 160 cm and 185 cm) than those given by the ”︁German Instructions for Soil Mapping” (AG Boden, 1994), the ”︁Regulations of the German Organisation for Water Management and Land Improvement” (DVWK, 1995) or the ”︁German Institute for Standardization” (DIN, 1998). As a result of low annual precipitation (normally less than 600 mm), only a minor part of the high amounts of nitrate within the root zone was leached into deeper soil layers. We conclude that it is not possible to predict the potential groundwater pollution with nitrate on the basis of the mineral N content in the first meter of the soil profile.     

Influence of a riparian wetland on nitrate and herbicides exported from an agricultural field

Agrochemicals are a major source of nonpoint pollution. Forested corridors along stream channels (riparian zones) are thought to be potential sites for removal of agricultural contaminants from ground and surface waters. First-order riparian wetlands are reputed to be especially effective at groundwater remediation. The study site is a fairly typical (for eastern Maryland) small, first-order stream in an agricultural watershed. Preferential flow supplies most of the stream water within the riparian headwater wetland. This upstream area also contains the highest average stream N and pesticide loads in the entire first-order riparian system. Zones of active groundwater emergence onto the surface display high concentrations of nitrate throughout the soil profile and in the exfiltrating water, whereas inactive areas (where there is no visible upwelling) show rapid attenuation of nitrate with decreasing depths. Atrazine degradation products appear to penetrate more readily through the most active upwelling zones, and there is a correlation between zones of high nitrate and high atrazine metabolite levels. Deethylatrazine/atrazine ratios (DAR) seem to indicate that stream flow is dominated by ground water and that much of the ground water may have reached the stream via preferential flow. Remediative processes appear to be very complex, heterogeneous, and variable in these systems, so additional research is needed before effective formulation and application of riparian zone initiatives and guidelines can be accomplished.     

土壤水盐与玉米产量对地下水埋深及灌溉响应模拟

引黄水量的削减将进一步加剧宁夏银北灌区农业用水短缺问题,合理应用地下水进行灌溉对保障作物产量具有重要意义。为探究地下水灌溉条件下土壤水盐与作物生长的互馈机制,该研究修正了HYDRUS-1D的土壤蒸发模块,并嵌入可模拟作物生长与产量的EPIC模块,以此提高该模型在农田水文过程模拟中的适用性。采用2008年银北灌区不同水质灌水处理的玉米田间试验数据对模型进行了率定与验证。进一步应用该模型探寻地下水灌溉条件下,土壤水盐动态及玉米产量对地下水埋深变动及灌溉的响应规律。结果表明,玉米产量随地下水埋深增大呈现先增后减趋势,为保障玉米产量应将地下水适宜埋深控制在140~155 cm,且灌水量不宜低于现状灌水量,即玉米生育期内灌3水,每次900 m3/hm2。该研究对干旱银北灌区农业生产具有重要意义。     

Nitrogen Uptake Efficiency and Growth of Bell Pepper in Relation to Time of Exposure to Fertilizer Solution

Irrigation of high‐value vegetable crops on sandy soils with poor water‐retention capacities may result in fertilizer nitrogen (N) displacement below the effective root zone prior to complete crop uptake. As a result, fertilizer N‐uptake efficiency (FUE) of vegetable crops is often relatively low, thereby increasing the potential risk of groundwater contamination. The objective of this study was to determine how time of exposure of the root zone to the N fertilizer (which is referred to as “fertilizer residence time” or t _R), as related to irrigation management, affects N uptake, FUE, growth, and yield of bell pepper (Capsicum annuum L.). Plants were grown in PVC columns with 45 kg of soil equipped with a drainage valve in the bottom of the column. Weekly irrigation with dissolved fertilizers (potassium nitrate; KNO₃) was applied 1, 3, or 7 d before weekly removal of residual soil N by leaching. Weekly N uptake rates were calculated by comparing total N recovery between unplanted (reference) and planted columns. At 77 d after planting, increasing the t _R from 1 to 3 or 7 d increased the weekly N uptake from 1.4 to 10.8 and/or 13.3 kg N ha^?1, respectively. Total calculated plant N accumulations were 19, 72, and 106 kg N ha^?1 for the 1‐, 3‐, and 7‐d t _R treatments, with overall FUE values being 8, 31, and 45%, respectively. It is concluded that during initial growth crop, uptake capacity is limiting, and more frequent (daily) fertilizer injection into the irrigation water may be required to enhance FUE. It is proposed also that via sound or innovative irrigation management practices, fertilizer retention in the root zone can be enhanced, thereby improving crop growth, yield, and FUE while reducing production cost and potential environmental impacts.     

Irrigation and Nitrogen Fertilizer Rate Impacts on Soil Nitrate in Potato Production

ABSTRACT

Parts of the Kern County have high nitrate levels in groundwater. A State Water Resources Control Board commissioned report has indicated that crop land agriculture is the main source of nitrates in the groundwater. Annual rainfall is less than 20 cm, thus irrigation is necessary for optimum crop production. A project was undertaken to evaluate current nitrogen fertility and irrigation scheduling in potato production and their contribution, or lack thereof, to nitrate movement in the soil profile and potential nitrate contamination of groundwater. A line-source sprinkler plot area was established to create soil moisture regimes of 120% of target, target (optimum soil moisture for potato growth) and 80% of target. Pre-plant and post-harvest soil samples were collected to a depth of 2 meters. Plant, root and tuber samples were collected and analyzed for nitrogen content. Soil moisture and irrigation amounts were monitored. Plant dry matter and tuber yield increased with each N rate increase. The high N rate increased plant growth disproportionally to the increased tuber yield. Appropriate irrigation scheduling did not produce water movement beyond the effective potato rooting zone. Excessive irrigation moved soil nitrate deeper into the soil profile.     

长期施肥对农田土壤氮素关键转化过程的影响

当前,如何合理施肥、提高作物产量、维持土壤肥力、并兼顾生态环境效应是农业研究的主要挑战之一。本文综述了长期施肥对农田土壤氮素关键转化过程的影响,主要从土壤氮转化过程的初级转化速率角度综述肥料(有机肥和化学氮肥)对土壤氮素关键转化过程的影响。土壤氮素矿化-同化循环是自然界氮循环过程中两个至关重要的环节,是决定土壤供氮能力的重要因素。总体而言,长期施用氮肥,尤其是有机肥能显著提高初级矿化-同化周转速率;长期施肥可以刺激自养硝化作用,且有机肥的刺激作用更明显;施用化学氮肥和有机肥均能提高反硝化速率,且有机肥的刺激作用高于化学氮肥。有机肥一直被提倡和实践用来改善土壤肥力和提高土壤固碳能力,无论是单施有机肥还是有机-无机配施,均能有效地减轻硝酸盐污染,改善土壤肥力并提高作物产量。但是有机肥的施用并不是多多益善,有机肥过多施用也会增加氮损失的风险。因此,本文综述了长期施肥对农田土壤氮素关键转化过程初级转化速率的影响,讨论了各个氮转化过程之间的联系,以期增强人们对长期施肥措施影响农田土壤氮素循环的理解,并为合理施用氮肥、提高氮肥利用率、减少与氮相关的环境污染提供理论依据。     

Sodicity‐induced land degradation and its sustainable management: problems and prospects

Currently at least 20 per cent of the world's irrigated land is salt‐affected. However, projections of global population growth, and of an increased demand for food and fibre, suggest that larger areas of salt‐affected soil will need to be cropped in the future. About 60 per cent of salt‐affected soils are sodic, and much of this land is farmed by smallholders. Ameliorating such soils requires the application of a source of calcium (Ca²⁺), which replaces excess sodium (Na⁺) at the cation exchange sites. The displaced Na⁺ is then leached from the root zone through excess irrigation, a process that requires adequate flows of water through the soil. However, it must now be recognized that we can no longer conduct sodic soil amelioration and management solely with the aim of achieving high levels of crop productivity. The economic, social, and environmental impacts of different soil‐amelioration options must also be considered. A holistic approach is therefore needed. This should consider the cost and availability of the inputs needed for amelioration, the soil depth, the level to which sodicity needs to be reduced to allow cropping, the volume and quality of drainage water generated during amelioration, and the options available for drainage‐water disposal or reuse. The quality and cost of water available for post‐amelioration crops, and the economic value of the crops grown during and after amelioration should also be taken into account, as should farmers' livelihoods, the environmental implications of amelioration (such as carbon sequestration), and the long‐term sustainable use of the ameliorated site (in terms of productivity and market value). Consideration of these factors, with the participation of key stakeholders, could sustainably improve sodic soil productivity and help to transform such soils into a useful economic resource. Such an approach would also aid environmental conservation, by minimizing the chances of secondary sodicity developing in soils, particularly under irrigated agriculture. Copyright © 2006 John Wiley & Sons, Ltd.     

Pipeline right‐of‐way construction activities impact on deep soil compaction

A 762‐mm‐diameter pipe 1,886 km long was installed to transfer crude oil in the USA from North Dakota to Illinois. To investigate the impact of construction and restoration practices on long‐term soil productivity and crop yield, vertical soil stresses induced by a Caterpillar (CAT) pipe liner PL 87 (475 kN vehicle load) and semi‐trailer truck (8.9 kN axle load) were studied in a farm field. Soil properties (bulk density and cone penetration resistance) were measured on field zones within the right‐of‐way (ROW) classified according to construction machine trafficking and subsoil tillage (300‐mm‐depth tillage and 450‐mm‐depth tillage in two repeated passes) treatments. At 200 mm depth from the subsoiled surface, the magnitude of peak vertical soil stress from trafficking by the semi‐truck trailer and CAT pipe liner PL 87 was 133 kPa. The peak vertical soil stress at 400 mm soil depth appeared to be influenced by vehicle weight, where the Caterpillar pipe liner PL 87 created soil compaction a magnitude of 1.5 greater than from the semi‐trailer truck. Results from the soil bulk density and soil cone penetration resistance measurements also showed the ROW zones had significantly higher soil compaction than adjacent unaffected corn planted fields. Tillage to 450 mm depth alleviated the deep soil compaction better than the 300‐mm‐depth tillage as measured by soil cone penetration resistance within the ROW zones and the unaffected zone. These results could be incorporated into agricultural mitigation plans in ROW construction utilities to minimize soil and crop damage.     

Assessment of the Intrinsic Vulnerability of Agricultural Land to Water and Nitrogen Losses via Deterministic Approach and Regression Analysis

A set of indices was developed in order to classify the vulnerability of agricultural land to water and nitrogen losses (LOS), setting a basis for the integrated water resources management in agricultural systems. To calibrate the indices using multiple regression analysis, the simulation results of Groundwater Loading Effects of Agricultural Management Systems (GLEAMS) model for combinations of different soil properties, topography, and climatic conditions of a reference field crop were used as “observed values.” GLEAMS quantified (1) the annual losses of the percolated water beneath the root zone, (2) the annual losses of the surface runoff, (3) the annual losses of the nitrogen leaching beneath the root zone, and (4) the annual losses of nitrogen through the surface runoff, which were used to calibrate the following indices LOSW-P, LOSW-R, LOSN-PN, and LOSN-RN, respectively. All the simulations to gain the LOS indices were carried out for the same reference field crop, the same nitrogen fertilization, and the same irrigation practice, in order to obtain the intrinsic vulnerability of agricultural land to water and nitrogen losses. The LOS indices were also combined to derive nitrogen concentrations in the percolated and in the runoff water. Finally, the connection of LOS indices with the groundwater was performed using an additional equation, which determines the minimum transit time of the percolated water to reach the groundwater table.     

蔬菜地土壤磷饱和度及其对磷释放和水质的影响

为了解蔬菜地土壤磷素的积累对水环境的影响,我们在浙江省选择了33个代表性蔬菜地,采集和分析了土壤、地表水和地下水样的磷素状况,从土壤磷饱和度的角度,研究了浙江省主要蔬菜土壤磷积累状况及其对地表和地下水水质和土壤磷释放潜力的影响。结果表明,半透膜渗析法测得的磷释放量与土壤磷积累呈正相关,磷释放量随土壤磷饱和度的提高而增加。蔬菜地土壤磷饱和度的增加可显著提高地表水体和地下水中磷的浓度,当土壤磷饱和度小于25%左右时,水体中磷浓度随土壤磷饱和度增加较为缓慢;但当磷饱和度大于25%时,水体中磷浓度随土壤磷饱和度提高迅速上升。地表水中磷浓度主要与表层土壤磷饱和度有关;地下水中磷浓度主要受深层土壤磷饱和度的影响,与表层土壤磷饱和度的相关性较小。土壤磷饱和度可很好地表征土壤磷释放和对环境的潜在影响。     

Productivity enhancement of salt‐affected environments through crop diversification

Recent trends and future demographic projections suggest that the need to produce more food and fibre will necessitate effective utilization of salt‐affected land and saline water resources. Currently at least 20 per cent of the world's irrigated land is salt affected and/or irrigated with waters containing elevated levels of salts. Several major irrigation schemes have suffered from the problems of salinity and sodicity, reducing their agricultural productivity and sustainability. Productivity enhancement of salt‐affected land and saline water resources through crop‐based management has the potential to transform them from environmental burdens into economic opportunities. Research efforts have led to the identification of a number of field crops, forage grasses and shrubs, aromatic and medicinal species, bio‐fuel crops, and fruit tree and agroforestry systems, which are profitable and suit a variety of salt‐affected environments. Several of these species have agricultural significance in terms of their local utilization on the farm. Therefore, crop diversification systems based on salt‐tolerant plant species are likely to be the key to future agricultural and economic growth in regions where salt‐affected soils exist, saline drainage waters are generated, and/or saline aquifers are pumped for irrigation. However, such systems will need to consider three issues: improving the productivity per unit of salt‐affected land and saline water resources, protecting the environment and involving farmers in the most suitable and sustainable crop diversifying systems to mitigate any perceived risks. This review covers different aspects of salt‐affected land and saline water resources, synthesizes research knowledge on salinity/sodicity tolerances in different plant species, and highlights promising examples of crop diversification and management to improve and maximize benefits from these resources. Copyright © 2008 John Wiley & Sons, Ltd.     

Legume-based farming in Southern Australia: developing sustainable systems to meet environmental challenges

Development of legume-based farming systems has resulted in Australian agriculture being globally competitive. There is now political pressure for agriculture to become accountable for ‘off-site’ environmental consequences. Farming systems relying on annual species are unsustainable because of a mismatch between the supply and demand of water and N, resulting in N leakage to streams or groundwater. Rainfall in excess of plant requirements coupled with N build-up, permeable soils, limited opportunities for reduction and proximity to surface or groundwater present risks for leakage of NO₃-N. We present examples of N leakage from legume systems in southern Australia, where rainfall exceeds 450 mm yr⁻¹, and the evidence suggesting that leakage contributes to stream and groundwater pollution. N build-up in autumn through mineralisation of organic-N from legume-based systems often exceeds 100 kg N ha⁻¹ and N leakage losses can be 15-35 kg N ha⁻¹ yr⁻¹. Stream and groundwater N pollution issues are emerging. Surface water quality problems are already apparent in Victoria although the contribution from legumes, N fertilisers and point sources remains unresolved. Examples of groundwater problems where legumes are a contributing factor have been recorded in New South Wales (NSW), South Australia (SA), Western Australia (WA) and Victoria. In Victoria, areas at risk of N groundwater contamination are found along the Great Dividing Range and in southern Victoria. Groundwater pollution causes concern because once problems are found they take decades to reverse. Stores of N in the unsaturated zone combined with limited N monitoring in groundwater suggests that early detection is unlikely. Solutions for reducing off-site consequences are outlined and include management to prevent water and N leakage happening, capture of N before it reaches waterways or groundwater and low input systems including land retirement. For scientists interested in N fixation and biological mediation, future research areas include increasing the proportion of perennials in farming systems, better control of N supply and demand through improved technology and us of N fertiliser, use of nitrification inhibitors and studies of the potential for N immobilisation and reduction through denitrification, both within and below the root zone. Integrated management strategies that address environmental implications from point/micro-scale to paddock and catchment scales are needed as are considerations of other environmental consequences. Research priorities will change from maximising N fixation for profitability towards balancing profitability and environmental goals for more sustainable systems.     

植被缓冲带在水源地面源污染治理中的作用

在山地丘陵区遭遇高强度降雨时,常常发生水土流失;水流携带泥沙下泄,过量施入农田的肥料、农药等化学物质随之进入河流、水库、湖泊等地表水和地下水水体,进而造成水体富营养化等面源污染,危害水源地安全。为梳理植被缓冲带能够控制水土流失、阻控污染物移动、解决水源地面源污染问题,明确该项技术措施减少和治理水源地面源污染的机制,为水源地面源污染防治和水环境改善提供参考。在概括介绍植被缓冲带的类型、功能的基础上,对该项技术措施减少和治理水源地面源污染的机制进行讨论。植被缓冲带治理水源地面源污染的机制主要有:①植物在生长过程中自身对氮磷等物质的吸收;②利用植被固结土壤,减少水土流失;③植被覆盖、拦蓄能够延长径流在地面的停留时间而增加水分入渗、减少氮磷等物质随地表径流流失;④植物根系参与土壤中多种物理、化学和生物过程,加速碳、氮、磷等物质的形态转化。针对水源地面源污染特点和植被缓冲带的建设技术及其应用要点,提出相关建议,并对今后该技术的发展进行了展望。     

Use of long-term monitoring data to derive a relationship between nitrogen surplus and nitrate leaching for grassland and arable land on well-drained sandy soils in the Netherlands

The decrease in nitrogen (N) use in agriculture led to improvement of upper groundwater quality in the Sand region of the Netherlands in the 1991–2009 period. However, still half of the farms exceeded the European nitrate standard for groundwater of 50 mg/l in the 2008–2011 period. To assure that farms will comply with the quality standard, an empirical model is used to derive environmentally sound N use standards for sandy soils for different crops and soil drainage conditions. Key parameters in this model are the nitrate-N leaching fractions (NLFs) for arable land and grassland on deep, well-drained sandy soils. NLFs quantify the fraction of the N surplus on the soil balance that leaches from the root zone to groundwater and this fraction represents N available for leaching and denitrification. The aim of this study was to develop a method for calculating these NLFs by using data from a random sample of commercial arable farms and dairy farms that were monitored in the 1991–2009 period. Only mean data per farm were available, which blocked a direct derivation of NLFs for unique combinations of crop type, soil type and natural soil drainage conditions. Results showed that N surplus leached almost completely from the root zone of arable land on the most vulnerable soils, that is, deep, well-drained sandy soils (95% confidence interval of NLF 0.80–0.99), while for grassland only half of the N surplus leached from the root zone of grassland (0.39–0.49). The NLF for grassland decreased with 0.015 units/year, which is postulated to be due to a decreased grazing and increased year-round housing of dairy cows. NLFs are positively correlated with precipitation surplus (0.05 units/100 mm for dairy farms and 0.10 units/100 mm for arable farms). Therefore, an increase in precipitation due to climate change may lead to an increase in leaching of nitrate.     

Enhancement of area‐specific land‐use objectives for land development

Maps of land‐use classes and soil series were analysed to identify areas having specific priorities with respect to agricultural land‐use analysis. Remote sensing data supported by field investigations was used to generate land‐use and soil maps. Present relationships between soils and associated land cover/use are analysed and patterns in these relationships are identified using GIS techniques. Relationships observed on the basis of a priori knowledge of the area and the available statistics are compared and these relationships in the field and through interviews with farmers are correlated. This allows three land‐use analysis objectives to be formulated: crop management improvement; crop selection; and conservation. The results can be used to focus the efforts of planning and extension services in the area. The method was tested using a participatory rural appraisal in eighteen villages in which the areas for the three land‐use analysis objectives were identified. The findings are that the areas identified for crop management improvement require knowledge about management practices for a specific crop to optimize yield and water use. Most areas identified for crop selection are occupied by smallholder subsistence farmers with insufficient water for irrigation, and a lack of contact with the extension service. In these areas, identifying suitable crops to minimize risk and allow subsistence for the resource‐poor farmers may be the priority. In areas identified for conservation the question to be addressed is whether to grow a crop at all, or to encourage alternative activities. Copyright © 2004 John Wiley & Sons, Ltd.