Nitrogen balance in and export from agricultural fields associated with controlled drainage systems and denitrifying bioreactors

Nitrate loss from drainage tiles across the cornbelt of the upper midwestern US is a result of intensive agriculture with limited crop diversity, extensive periods of fallow soil, and the need for high fertilizer applications to corn, all located on a hydrologically modified landscape. Two methods proposed to reduce tile nitrate export are managed or controlled drainage to limit tile flow and bioreactors to enhance denitrification. Nitrogen budgets and tile flow monitoring were conducted over two- to three-year periods between 2006 and 2009. We estimated N budgets in a seed corn-soybean rotation farming system near DeLand, east-central Illinois, USA, with free (FD) and controlled drainage (CD) patterned tile systems. In addition, wood chip filled trenches (bioreactors) were installed below the CD structures, one lined with plastic and one unlined. We measured daily tile flow and nitrate-N (NO₃-N) concentrations and calculated cumulative N loss from the tile water at both FD and CD areas for a period of three cropping years. We also monitored the tile flow and nitrate concentration in inlet and outlet of the bioreactor associated with a CD system and evaluated the efficiency of the bioreactor for two cropping years. Most components of the N balance were unaffected by CD (yields and therefore N harvested, surface soil denitrification), and there was a negative N balance in the soybean cropping year (?165 and ?163 kg N ha^?1 at FD and CD areas, respectively), whereas seed corn cropping in the following year resulted in positive N balances (29 and 34 kg N ha^?1 at FD and CD areas, respectively). For two years, the overall N balances were ?136 and ?129 kg N ha^?1 at FD and CD areas, respectively, consistent with other recent corn belt studies showing a small net depletion of soil organic N. Controlled drainage greatly reduced tile N export, with a three-year average loss of 57.2 kg N ha^?1 yr^?1 from FD compared to 17 kg N ha^?1 yr^?1 for CD. There was high uncertainty in denitrification measurements and thus the fate of missing N in the CD system remained unknown. Nitrate reduction efficiency of the bioreactor varied greatly, with periods where nearly 100% of the nitrate was denitrified. The overall efficiency of the bioreactor associated with the CD system in reducing the tile N load was 33%. When nitrate was non-limiting, the nitrate removal rate of the bioreactor was 6.4 g N m^?3 d^?1. Little N₂O emission was found from the bioreactor bed and is not thought to be a problem with these systems. Both the tile bioreactor and controlled drainage greatly reduced tile nitrate export in this leaky seed corn and soybean agricultural field.     

Land use and stream nitrogen concentrations in agricultural watersheds along the central coast of California

In coastal California nitrogen (N) in runoff from urban and agricultural land is suspected to impair surface water quality of creeks and rivers that discharge into the Monterey Bay Sanctuary. However, quantitative data on the impacts of land use activities on water quality are largely limited to unpublished reports and do not estimate N loading. We report on spatial and temporal patterns of N concentrations for several coastal creeks and rivers in central California. During the 2001 water year, we estimated that the Pajaro River at Chittenden exported 302.4 Mg of total N. Nitrate-N concentrations were typically <1 mg N l(-1) in grazing lands, oak woodlands, and forests, but increased to a range of 1 to 20 mg N l(-1) as surface waters passed through agricultural lands. Very high concentrations of nitrate (in excess of 80 mg N l(-1)) were found in selected agricultural ditches that received drainage from tiles (buried perforated pipes). Nitrate concentrations in these ditches remained high throughout the winter and spring, indicating nitrate was not being flushed out of the soil profile. We believe unused N fertilizer has accumulated in the shallow groundwater through many cropping cycles. Results are being used to organize landowners, resource managers, and growers to develop voluntary monitoring and water quality protection plans.     

Nitrogen fertilizer rate and crop management effects on nitrate leaching from an agricultural field in central Pennsylvania

Eighteen pan lysimeters were installed at a depth of 1.2 m in a Hagerstown silt loam soil in a corn field in central Pennsylvania in 1988. In 1995, wick lysimeters were also installed at 1.2 m depth in the same access pits. Treatments have included N fertilizer rates, use of manure, crop rotation (continuous corn, corn-soybean, alfalfa-corn), and tillage (chisel plow-disk, no-till). The leachate data were used to evaluate a number of nitrate leaching models. Some of the highlights of the 11 years of results include the following: 1) growing corn without organic N inputs at the economic optimum N rate (EON) resulted in NO3--N concentrations of 15 to 20 mg l(-1) in leachate; 2) use of manure or previous alfalfa crop as partial source of N also resulted in 15 to 20 mg l(-1) of NO3--N in leachate below corn at EON; 3) NO3--N concentration in leachate below alfalfa was approximately 4 mg l(-1); 4) NO3--N concentration in leachate below soybeans following corn was influenced by fertilizer N rate applied to corn; 5) the mass of NO3--N leached below corn at the EON rate averaged 90 kg N ha(-1) (approx. 40% of fertilizer N applied at EON); 6) wick lysimeters collected approximately 100% of leachate vs. 40-50% collected by pan lysimeters. Coefficients of variation of the collected leachate volumes for both lysimeter types were similar; 7) tillage did not markedly affect nitrate leaching losses; 8) tested leaching models could accurately predict leachate volumes and could be calibrated to match nitrate leaching losses in calibration years, but only one model (SOILN) accurately predicted nitrate leaching losses in the majority of validation treatment years. Apparent problems with tested models: there was difficulty estimating sizes of organic N pools and their transformation rates, and the models either did not include a macropore flow component or did not handle macropore flow well.     

Fertilizer vs. organic matter contributions to nitrogen leaching in cropping systems of the Pampas: 15N application in field lysimeters

Nitrogen (N) export from soils to streams and groundwater under the intensifying cropping schemes of the Pampas is modest compared to intensively cultivated basins of Europe and North America; however, a slow N enrichment of water resources has been suggested. We (1) analyzed the fate of fertilizer N and (2) evaluated the contribution of fertilizer and soil organic matter (SOM) to N leaching under the typical cropping conditions of the Pampas. Fertilizer N was applied as ¹⁵N-labeled ammonium sulfate to corn (in a corn/soybean rotation) sown under zero tillage in filled-in lysimeters containing two soils of different texture representative of the Pampean region (52 and 78 kg N ha^-1, added to the silt loam and sandy loam soil, respectively). Total fertilizer recovery at corn harvest averaged 84 and 64% for the silt loam and sandy loam lysimeters, respectively. Most fertilizer N was removed with plant biomass (39%) or remained immobilized in the soil (29 and 15%, for the silt loam and sandy loam soil, respectively) whereas its loss through drainage was negligible (<0.01%). We presume that the unaccounted fertilizer N losses were related to volatilization and denitrification. Throughout the corn growing season, subsequent fallow and soybean crop, which took place during an exceptionally dry period, the fertilizer N immobilized in the organic pool remained stable, and N leaching was scarce (7.5 kg N ha^-1), similar at both soils, and had a low contribution of fertilizer N (0–3.5%), implying that >96% of the leached N was derived from SOM mineralization. The inherent high SOM of Pampean soils and the favorable climatic conditions are likely to propitiate year-round production of nitrate, favoring its participation in crop nutrition and leaching. The presence of ¹⁵N in drainage water, however, suggests that fertilizer N leaching could become significant in situations with higher fertilization rates or more rainy seasons.     

Crop uptake and leaching losses of15N labelled fertilizer nitrogen in relation to waterlogging of clay and sandy loam soils

Summary Ammonium nitrate fertilizer, labelled with¹⁵N, was applied in spring to winter wheat growing in undisturbed monoliths of clay and sandy loam soil in lysimeters; the rates of application were respectively 95 and 102 kg N ha⁻¹ in the spring of 1976 and 1975. Crops of winter wheat, oilseed rape, peas and barley grown in the following 5 or 6 years were treated with unlabelled nitrogen fertilizer at rates recommended for maximum yields. During each year of the experiments the lysimeters were divided into treatments which were either freelydrained or subjected to periods of waterlogging. Another labelled nitrogen application was made in 1980 to a separate group of lysimeters with a clay soil and a winter wheat crop to study further the uptake of nitrogen fertilizer in relation to waterlogging. In the first growing season, shoots of the winter wheat at harvest contained 46 and 58% of the fertilizer nitrogen applied to the clay and sandy loam soils respectively. In the following year the crops contained a further 1–2% of the labelled fertilizer, and after 5 and 6 years the total recoveries of labelled fertilizer in the crops were 49 and 62% on the clay and sandy loam soils respectively. In the first winter after the labelled fertilizer was applied, less than 1% of the fertilizer was lost in the drainage water, and only about 2% of the total nitrogen (mainly nitrate) in the drainage water from both soils was derived from the fertilizer. Maximum annual loss occurred the following year but the proportion of tracer nitrogen in drainage was nevertheless smaller. Leaching losses over the 5 and 6 years from the clay and sandy loam soil were respectively 1.3 and 3.9% of the original application. On both soils the percentage of labelled nitrogen to the total crop nitrogen content was greater after a period of winter waterlogging than for freely-drained treatments. This was most marked on the clay soil; evidence points to winter waterlogging promoting denitrification and the consequent loss of soil nitrogen making the crop more dependent on spring fertilizer applications.     

Effects of differentiated applications of fertilizer N on leaching losses and distribution of inorganic N in the soil

Summary Nitrogen fertilizer was applied to field plots at rates of 0, 50, 100, 150 and 200 N kg/ha yr, in order to determine the effects of differentiated N applications on drainage water and groundwater quality. Water samples, collected monthly or bimonthly from 1974 to 1983, were analysed for inorganic and total N content. In order to see the impact of residual N on leaching losses, soil samples were collected to a depth of 2 m in the N0, N100 and N200 plots, usually in September and April. Leaching of nitrate was moderate to the N100 level but increased substantially with increasing fertilization, up to 91 N kg/(ha-yr) for the highest application rate (N200), during the wet year of 1980/81. The losses were greatest during the fall, mainly due to high levels of N remaining in the soil after harvest combined with high precipitation. The N content of the groundwater did not show any significant correlation to the fertilization intensity. A buildup of inorganic N in the soil occurred only when excessive amounts of fertilizer were applied (N200), while the contents of the N0 and N100 treatments fluctuated around states of balance, approximately 45 and 70 N kg/ha respectively. Spring rape followed by winter wheat showed a great ability to reduce N contents in the tile effluent from highly fertilized plots (N150 and N200), even though the plots had received excessive amounts of fertilizer for several years. Results of this experiment in central Sweden demonstrate the importance of applying nitrogen fertilizer in balance with crop needs and of maintaining a growing crop cover as much of the time as possible in order to minimize water pollution.     

太湖地区稻田土壤养分淋洗特征

通过排水采集器(Lysimeter)模拟试验,研究了太湖地区不同施肥水平下稻季农田养分淋洗特点。结果表明,施肥后田面水NH4^+-N浓度升高很快,2～3d达到峰值,最高值达26．2mg·L^-1,随后下降很快,这一周期约7～10d,渗漏水中NH4^+-N浓度很低,稻季NH4^+-N淋洗的氮仅占施肥量的0．008％～0．074％,渗漏液中NO3^--N含量随着氮肥用量的增加而增加,其浓度范围在0～7．14mg·L^-1,在土壤剖面中呈上低下高的趋势,稻季氮素的淋洗仍以NO3^--N为主,净淋洗量在3．2～8．3kg·hm^-2之间,占总施肥量的1．40％～2．78％,田面水磷浓度在施磷肥后1d即达最高值,随后下降,下层渗漏液中T-P含量很低,几乎不受施肥量的影响,猪粪能促进磷的迁移。     

Nitrogen use and carbon sequestered by corn rotations in the northern corn belt,U.S

Diversified crop rotation may improve production efficiency, reduce fertilizer nitrogen (N) requirements for corn (Zea mays L.), and increase soil carbon (C) storage. Objectives were to determine effect of rotation and fertilizer N on soil C sequestration and N use. An experiment was started in 1990 on a Barnes clay loam (U.S. soil taxonomy: fine-loamy, mixed, superactive, frigid Calcic Hapludoll) near Brookings, SD. Tillage systems for corn-soybean ( Glycine max [L.] Merr.) rotations were conventional tillage (CS) and ridge tillage (CSr). Rotations under conventional tillage were continuous corn (CC), and a 4-year rotation of corn-soybean-wheat ( Triticum aestivum L.) companion-seeded with alfalfa ( Medicago sativa L.)-alfalfa hay (CSWA). Additional treatments included plots of perennial warm season, cool season, and mixtures of warm and cool season grasses. N treatments for corn were corn fertilized for a grain yield of 8.5 Mg ha(-1) (highN), of 5.3 Mg ha(-1) (midN), and with no N fertilizer (noN). Total (1990-2000) corn grain yield was not different among rotations at 80.8 Mg ha(-1) under highN. Corn yield differences among rotations increased with decreased fertilizer N. Total (1990-2000) corn yields with noN fertilizer were 69 Mg ha-1 under CSWA, 53 Mg ha(-1) under CS, and 35 Mg ha(-1) under CC. Total N attributed to rotations (noN treatments) was 0.68 Mg ha(-1) under CSWA, 0.61 Mg ha(-1) under CS, and 0.28 Mg ha(-1) under CC. Plant carbon return depended on rotation and N. In the past 10 years, total C returned from above- ground biomass was 29.8 Mg ha(-1) under CC with highN, and 12.8 Mg ha(-1) under CSWA with noN. Soil C in the top 15 cm significantly increased (0.7 g kg(-1)) with perennial grass cover, remained unchanged under CSr, and decreased (1.7 g kg(-1)) under CC, CS, and CSWA. C to N ratio significantly narrowed (-0.75) with CSWA and widened (0.72) under grass. Diversified rotations have potential to increase N use efficiency and reduce fertilizer N input for corn. However, within a corn production system using conventional tillage and producing (averaged across rotation and N treatment) about 6.2-Mg ha(-1) corn grain per year, we found no gain in soil C after 10 years regardless of rotation.     

地表处理方式对日光温室辣椒水分利用效率及土壤硝态氮、速效磷分布的影响

研究了不同地表处理方式对日光温室辣椒水分利用效率及土壤氮磷分布的影响.结果表明:地表覆盖秸秆 地膜处理的辣椒产量水分利用效率和经济水分利用效率最高,分别达33·04kg·m-3和50·22元·m-3;其次是地表覆盖地膜处理,分别达18·81kg·m-3和28·57元·m-3.不同地表处理方式对0～20cm土壤的硝态氮含量有显著影响,地表覆盖秸秆和覆盖秸秆 地膜处理,分别为31·98mg·kg-1和31·96mg·kg-1,小于对照处理(50·33mg·kg-1);地表覆盖地膜和使用保水剂处理的硝态氮含量较低.与对照相比,各处理辣椒对氮肥的利用均有所增加,耕层硝态氮积累减少.在0～20cm耕层内,地表覆盖地膜处理的速效磷含量最低,为0·72mg·kg-1,其次是地表覆盖秸秆 地膜处理,为0·92mg·kg-1.地表覆盖秸秆 地膜和地表覆盖地膜处理增加了当季作物对肥料的利用率,减少了肥料的损失,提高了产量.     

Using NCSWAP to simulate seasonal nitrogen dynamics in soil and corn

The objective of this study was to determine if a re-calibrated version of the computer model NCSWAP (version 36) could accurately predict corn growth and soil N dynamics in conventionally tilled (CT) and no-till (NT) corn supplied with legume green manure or ammonium nitrate as N sources. We also attempted to ascertain the reasons for limitations in the model's ability to simulate corn growth and soil N dynamics found by our colleagues in a previous study and to propose potential improvements. The model was calibrated to accurately simulate total available N (N in plant above-ground biomass plus soil nitrate in the 0 to 45 cm profile) for a control and a fertilizer CT treatment in the 1992 growing season. To do so, input values defining the quantities of active soil organic N had to be reduced to 19% of the values proposed by the model developers and a solute transport factor defining the mobile vs. immobile fractions of soil nitrate adjusted from 0.8 to 0.2. The discrepancies between the proposed values and the lower values employed in this study might be due to the uncertainties in quantitatively describing soil N mineralization processes and the way they are handled in the model, as well as the lack of a component simulating macroporous-influenced water flow and solute transport in the model. With the current version, until one knows how to predict what these values are, the model needs to be re-calibrated for each experimental site and condition and thus is of limited value as a general model.With no further adjustment of input values, model validation success was mixed. The model accurately predicted total available N for treatments in the second year of the experiment that had the same N source and tillage as the treatments used for the calibration year but with the different weather and growing conditions. However, total available N was underpredicted where legume green manure was the N source and overpredicted with no-till cultivation. The model was accurate in simulating seasonal corn growth for nearly all the treatments, judged by nonsignificant mean difference (MD) values and highly significant correlation coefficients (r). Prediction of seasonal soil nitrate concentration was less accurate compared to total available N and corn growth variables. Potential improvements in the model's simulation of a no-till system as well as for predicting corn harvest yield and seasonal soil nitrate concentration where N deficiency occurs were discussed.     

Transport of phosphorus,nitrogen, and carbon by the Apure River,Venezuela

The concentrations and transport of carbon, nitrogen, and phosphorus were studied in the Apure River, Venezuela, over a period of 21 months. The drainage basin, which is in western Venezuela, encompasses 167,000 kM², most of which has low relief and supports tropical savanna vegetation. Average runoff for the period of study was 361 mm/year. Discharge-weighted mean concentrations were 188 ug/l for total P, 957 ug/l for total N, and 9.8 mg/l for organic C. Annual transport was 0.68 kg· ha^-1· year^-1 for total P, 3.45 kg · ha^-1· year^-1 for total N, and 35.4 kg · ha^-1 · year^-1 for organic C. Particulate matter accounted for 68% of P, 54% of N, and 37% of C transport. The yield of carbon from the Apure watershed agrees well with empirical predictions, based mostly on the temperate zone, for watersheds of similar size and water yield.Seasonal patterns in chemistry are tied strongly to the hydrologic cycle. When the wet season begins, rising water flushes organic matter from side channels and produces a sharp increase in particulate C and N. Particulate P, which is associated more with mineral material, also increases during rising water. All dissolved constituents except inorganic C also increase over the rising-water phase. As the river inundates the floodplain, the concentration of nitrate declines, whereas the concentrations of dissolved organic C and N continue to rise. At high water the floodplain appears to store sediments that are later remobilized. During low water, all fractions except dissolved inorganic C tend to be at minimum concentration.Soluble reactive P, total dissolved P, dissolved inorganic C, and dissolved organic C were successfully modelled as hyperbolic functions of discharge. No significant relationships were found between concentration and discharge for any particulate fraction because the flushing and storage mechanisms affecting these fractions occurred within specific hydrologic phases, rather than as a smooth function of discharge. No significant relationships were found for any nitrogen fraction. For nitrate, and thus for total dissolved N, of which nitrate is a major component, poor conformance to standard models is explained by association of key mechanisms (e.g. uptake) with specific hydrologic phases. Particulate components and nitrate in this sense violate the continuity assumptions implicit in the standard models.     

Phytoremediation Potential of Selected Plants for Nitrate and Phosphorus from Ground Water

The phytoremediation potential of three aquatic plants namely, water lettuce(Pistia stratioes), water hyacinth (Eichhornia crassipes), and water spinach (Ipomoea aquatica) for nitrate N and phosphorus from nutrient treated ground water was assessed. A total of twelve treatment combinations including four levels of nitrate (expressed as nitrate N 0, 20, 40, and 60 mg/l) and three levels of phosphorus (0, 20, and 40 mg/l) were treated for the total volume of 1 and 20 liters of water respectively, for Pistia stratiotes and Eichhornia crassipes. For Ipomoea aquatica ten treatment combinations with five levels of nitrate N (0, 10, 20, 40, and 50 mg/l) and two levels of phosphorus (0 and 5 mg/l) were treated to 3 liters of water. The design used was a two factor factorial with three replicates. Water was analyzed at weekly interval for nitrate N and phosphorus. Pistia stratiotes, Eichhornia crassipes and Ipomoea aquatica had the potential to remove nitrate N between 61.5–91.8%, 40–63.5%, and 29.3–75% during the period of six, three and three and weeks, respectively. In addition, 90–99%, 75–97.2%, and 75–83.3% of phosphorus was removed from water by Pistia stratiotes, Eichhornia crassipes and Ipomoea aquatica respectively, during the same period.     

Estimated historical and current nitrogen balances for Illinois

The Midwest has large riverine exports of nitrogen (N), with the largest flux per unit area to the Mississippi River system coming from Iowa and Illinois. We used historic and current data to estimate N inputs, outputs, and transformations for Illinois where human activity (principally agriculture and associated landscape drainage) have had a dominant impact. Presently, approximately 800,000 Mg of N is added each year as fertilizer and another 420,000 Mg is biologically fixed, primarily by soybean (Glycine max L. Merr.). These annual inputs are greater than exports in grain, which results in surplus N throughout the landscape. Rivers within the state export approximately 50% of this surplus N, mostly as nitrate, and the remainder appears to be denitrified or temporarily incorporated into the soil organic matter pool. The magnitude of N losses for 1880, 1910, 1950, and 1990 are compared. Initial cultivation of the prairies released large quantities of N (approximately 500,000 Mg N year(-1)), and resulted in riverine N transport during the late 19th century that appears to have been on the same order of magnitude as contemporary N losses. Riverine flux was estimated to have been at a minimum in about 1950, due to diminished net mineralization and low fertilizer inputs. Residual fertilizer N from corn (Zea mays L.), biological N fixed by soybean, short-circuiting of soil water through artificial drainage, and decreased cropping-system diversity appear to be the primary sources for current N export.     

Effect of winter cover crops on soil nitrogen availability,corn yield,and nitrate leaching

Biculture of nonlegumes and legumes could serve as cover crops for increasing main crop yield, while reducing NO3 leaching. This study, conducted from 1994 to 1999, determined the effect of monocultured cereal rye (Secale cereale L.), annual ryegrass (Lolium multiflorum), and hairy vetch (Vicia villosa), and bicultured rye/vetch and ryegrass/vetch on N availability in soil, corn (Zea mays L.) yield, and NO3-N leaching in a silt loam soil. The field had been in corn and cover crop rotation since 1987. In addition to the cover crop treatments, there were four N fertilizer rates (0, 67, 134, and 201 kg N ha(-1), referred to as N0, N1, N2, and N3, respectively) applied to corn. The experiment was a randomized split-block design with three replications for each treatment. Lysimeters were installed in 1987 at 0.75 m below the soil surface for leachate collection for the N 0, N 2, and N 3 treatments. The result showed that vetch monoculture had the most influence on soil N availability and corn yield, followed by the bicultures. Rye or ryegrass monoculture had either no effect or an adverse effect on corn yield and soil N availability. Leachate NO3-N concentration was highest where vetch cover crop was planted regardless of N rates, which suggests that N mineralization of vetch N continued well into the fall and winter. Leachate NO3-N concentration increased with increasing N fertilizer rates and exceeded the U.S. Environmental Protection Agency's drinking water standard of 10 mg N l(-1) even at recommended N rate for corn in this region (coastal Pacific Northwest). In comparisons of the average NO3-N concentration during the period of high N leaching, monocultured rye and ryegrass or bicultured rye/vetch and ryegrass/vetch very effectively decreased N leaching in 1998 with dry fall weather. The amount of N available for leaching (determined based on the presidedress nitrate test, the amount of N fertilizer applied, and N uptake) correlated well with average NO3-N during the high N leaching period for vetch cover crop treatment and for the control without the cover crops. The correlation, however, failed for other cover crops largely because of variable effectiveness of the cover crops in reducing NO3 leaching during the 5 years of this study. Further research is needed to determine if relay cover crops planted into standing summer crops is a more appropriate approach than fall seeding in this region to gain sufficient growth of the cover crop by fall. Testing with other main crops that have earlier harvest dates than corn is also needed to further validate the effectiveness of the bicultures to increase soil N availability while protecting the water quality.     

不同施肥对雷竹林径流及渗漏水中氮形态流失的影响

雷竹经营过程中化肥的大量施用,是产区水体污染的主要原因之一,养分管理技术可有效控制面源污染。为了探明减量施肥和有机肥施用对雷竹不同氮形态流失的影响,2012年在浙江省临安市雷竹产区设置了4种施肥处理:对照(CK);常规施肥(CF);减量无机(DI);减量有机无机(DOI),试验于5月18日、9月7日、11月9日分别施用肥料总量的40%,30%和30%,施肥后均进行浅翻,深度5 cm左右。通过建立径流场和土壤渗漏水收集装置,同时在试验田附近布置量雨筒,观察2012年不同氮形态浓度及流失负荷随降雨量的动态变化。研究结果表明:不同施肥处理径流水硝态氮、水溶性有机氮(WSON)以及颗粒态氮的浓度分别在3.82-6.82 mg/L、0.89-1.85 mg/L和0.89-1.83 mg/L,其占总氮的百分比分别为60.9%-68.2%、16.0%-18.1%和15.1%-21.6%。不同施肥处理渗漏水中硝态氮、铵态氮及WSON的浓度分别在26.2-92.5 mg/L、0.50-6.42 mg/L和6.57-12.6 mg/L,其占总氮的百分比分别为75.8%-82.9%、1.50%-6.36%和11.2%-20.6%。不同施肥处理径流水的氮总流失负荷,减量无机和减量有机无机相对于常规施肥来说减少了46.9%和23.1%;不同施肥处理的渗漏水的氮总流失负荷,减量无机和减量有机无机相对于常规施肥来说减少了19.1%和52.1%,可见减量施肥和减量有机无机减少氮流失的效果显著。     

Denitrification activity,wood loss,and N2O emissions over 9 years from a wood chip bioreactor

Loss of nitrate in subsurface drainage water from agricultural fields is an important problem in the Midwestern United States and elsewhere. One possible strategy for reducing nitrate export is the use of denitrification bioreactors. A variety of experimental bioreactor designs have been shown to reduce nitrate losses in drainage water for periods up to several years. This research reports on the denitrification activity of a wood chip-based bioreactor operating in the field for over 9 years. Potential denitrification activity was sustained over the 9-year period, which was consistent with nitrate removal from drainage water in the field. Denitrification potentials ranged from 8.2 to 34 mg N kg^?1 wood during the last 5 years of bioreactor operation. Populations of denitrifying bacteria were greater in the wood chips than in adjacent subsoil. Loss of wood through decomposition reached 75% at the 90–100 cm depth with a wood half-life of 4.6 years. However, wood loss was less than 20% at 155–170 cm depth and the half-life of this wood was 36.6 years. The differential wood loss at these two depths appears to result from sustained anaerobic conditions below the tile drainage line at 120 cm depth. Pore space concentrations of oxygen and methane support this conjecture. Nitrous oxide exported in tile water from the wood chip bioreactor plots was not significantly higher than N₂O exports in tile water from the untreated control plots, and loss of N₂O from tile water exiting the bioreactor accounted for 0.0062 kg N₂O-N kg^?1 NO₃-N.     

Drainage and nitrate leaching in a crop rotation under different N-fertilizer strategies: application of capacitance probes

Quantification of drainage and nitrate leaching from cropping systems is necessary to optimize N-fertilizer application and determine the impact on groundwater quality. The objectives of this work were to (i) assess the use of capacitance probes for the continuous determination of the volume of drainage water and the amount of nitrate leached in a crop production system, and (ii) compare the effect of different N-fertilizer strategies to control nitrate leaching in a crop rotation in humid Mediterranean climate. A factorial (control and three fertilizer strategies) experiment was conducted during three cropping seasons in Navarra (Spain). Wheat (Triticum aestivum L.) was planted in 2002, barley (Hordeum vulgare L.) in 2003, and rapeseed (Brassica napus L.) in 2004. Daily soil water content measurements based on capacitance probes were used to calculate drainage at 1 m depth, by applying the water balance equation. Nitrate leaching was calculated as the drainage volume multiplied by the nitrate concentration of the soil solution extracted in ceramic cups. The results revealed distinct behaviour in three crop phases, viz.: (i) from planting to GS-25, with high risk of drainage and nitrate leaching, (ii) from GS-25 to the end of the drainage period, with little drainage and leaching, and (iii) from then to harvest, when no drainage or nitrate leaching took place. Drainage and soil mineral N content before planting were the main factors determining the amount of N leached. Splitting N-fertilizer application and the use of nitrification inhibitors are not likely to have a significant impact on subsequent N-leaching losses, provided that the N-fertilizer application is adjusted to crop N needs corrected by soil N supply.     

根系分区交替灌溉条件下水肥供应对番茄果实硝酸盐含量的影响

为了研究根系分区交替灌溉条件下灌水量和氮、磷、钾肥及有机肥用量对番茄果实硝酸盐含量的影响,采用五元二次正交旋转组合设计,通过盆栽试验,建立了番茄果实中硝酸盐含量与水肥因子的数学模型,并对各单一因素的效应及两两因素的耦合效应进行了分析。结果表明,在其他因子为中间水平时,番茄果实中的硝酸盐含量,随灌水量呈先降低后增加的变化规律;随施氮量和施磷量呈先增加后降低的变化趋势;随有机肥用量呈逐渐增加的趋势;但不受钾肥用量的影响。交互效应表现为,施磷量与有机肥用量、施氮量与施磷量间的相互作用会促使番茄果实硝酸盐含量提高;灌水量与施钾量和有机肥量、施氮量与施钾量间的相互作用有利于降低番茄果实硝酸盐累积。耦合效应表现为,除不施有机肥时随灌水量增加番茄果实硝酸盐含量显著增加外,对于其它任何有机肥及钾肥施用水平,果实硝酸盐含量皆随灌水量增加呈先减小后增加趋势;灌水量高于中水平时,番茄果实硝酸盐含量随着钾肥与有机肥用量的增加而减少。不论施磷量与施钾量如何变化,番茄果实硝酸盐含量皆随施氮量呈现先增加后减小的变化趋势,降低氮肥用量同时提高磷肥用量有利于降低番茄果实硝酸盐累积,而提高施钾量仅在施氮量高于中水平时能显著降低番茄果实硝酸盐含量。适当增加磷肥用量、减小有机肥用量能显著降低番茄果实硝酸盐的累积。     

Monitoring nitrogen leaching for the evaluation of the Dutch minerals policy for agriculture in clay regions

This paper presents the results of the Dutch monitoring program for agriculture in the clay regions for the period 1996-2000 and evaluates the monitoring strategy. A wide range of farms (25 to 85%) had a NO3--N concentration in tile drainwater higher than the EU standard of 11.3 mg/l. The low figure is related to wet winters; the high, to dry winters. Arable farms are more prone to NO3- leaching than dairy farms. On arable farms, about 25% of the N surplus leached to groundwater and tile drainwater, on dairy farms this was about 15%. N in tile drainwater has shown to be the best indicator for monitoring the effects of farming practice changes in the clay regions. The average NO3--N concentration in tile drainwater was 18.8 and 3.2 mg/l in borehole water on farms where both were monitored. It is known that N use has a relationship with NO3- in tile drainwater and not with NH4+ and organic N. The presented results indicate that crop rotation and precipitation strongly influence NO3- concentration in tile drainwater.     

基于水量平衡下灌区农田系统中氮素迁移及平衡的分析

本文以于河套灌区典型灌域（前旗北疙堵乡塔布村）为研究对象,通过分析农田系统中水量平衡和氮素平衡,建立农田系统中氮素平衡和水分平衡的联立模型,并用此模型分析典型区域内农田系统中氮素随水分迁移的规律。分析表明：应用水量和氮平衡模型分析灌区农田系统中氮迁移及平衡,可以反映出农业面源污染物（氮）在整个农田系统中的去向,化肥使用量的降低和灌水量的减少,将有效的减少农田系统中氮素的输入量;秋灌—秋浇期间,玉米、番茄和葵花作物对氮的吸收率分别为17%、18%和32%,3种土壤中残留量分别为57%、60%和58%。依据河套灌区年施肥60万t计算,土壤残留量达到17.2万t。在秋灌-秋浇期间从黄河引入的氮总量达到1.21万t,随农田退水进入沟道的量为840 t。