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1.
Yield and N uptake of tomato(Lycopersicum esculentum Mill．)and pepper(Capsicum annuum L．)crops in five successive rotations receiving two compound fertilizers (12-12-17 and 21-8-1l N-P2O5-K2O)were studied to determine 1) crop responses，2)dynamics of NO3-N and NH4-N in different soillayers，3)N balance and 4)system-level N efficiencies．Five treatments (2fertilizers，2 fertilizer rates and a control)，each with three replicates，were arranged in the study．The higher N fertilizer rate，300 kg N ha^-1(versus 150 kg N ha^1)，returned higher vegetable fruit yields and total aboveground N uptake with the largest crop responses occurring for the low-N fertilizer(12-12-17)applied at 300 kg N ha^-1 rather than with the high-N fertilizer(21-8-11)．Ammonium-N in the top 90 cm of the soil profile declined during the experiment，while nitrate-N remained at a similar level throughout the experiment with the lower rate of fertilizer N．At the higher rate of N fertilizer there was a continuous NO3-N accumulation of over 800 kg N ha^-1．About 200 kg N ha^-1 Was applied with irrigation to each crop using NO3-contaminated groundwater．In general，about 50％ of the total N input was recovered from all treatments．Pepper、relative to tomato，used N more efficiently with smaller N losses，but the crops utilized less than 29％of the fertilizer N over the two and a half-year period．Local agricultural practices maintained high residual soil nutrient status．Thus，optimization of irrigation is required to minimize nitrate leaching and maximize crop N recovery．  相似文献   

2.
A soil column method was used to compare the effect of drip fertigation （the application of fertilizer through drip irrigation systems, DFI） on the leaching loss and transformation of urea-N in soil with that of surface fertilization combined with flood irrigation （SFI）, and to study the leaching loss and transformation of three kinds of nitrogen fertilizers （nitrate fertilizer, ammonium fertilizer, and urea fertilizer） in two contrasting soils after the fertigation. In comparison to SFI, DFI decreased leaching loss of urea-N from the soil and increased the mineral N （NH4^＋-N ＋ NO3^--N） in the soil. The N leached from a clay loam soil ranged from 5.7% to 9.6% of the total N added as fertilizer, whereas for a sandy loam soil they ranged between 16.2% and 30.4%. Leaching losses of mineral N were higher when nitrate fertilizer was used compared to urea or ammonium fertilizer. Compared to the control （without urea addition）, on the first day when soils were fertigated with urea, there were increases in NH4^＋-N in the soils. This confirmed the rapid hydrolysis of urea in soil during fertigation. NH4^＋-N in soils reached a peak about 5 days after fertigation, and due to nitrification it began to decrease at day 10. After applying NH4^＋-N fertilizer and urea and during the incubation period, the mineral nitrogen in the soil decreased. This may be related to the occurrence of NH4^＋-N fixation or volatilization in the soil during the fertigation process.  相似文献   

3.
长期施肥对华北平原一种潮土有机氮组成的影响   总被引：8，自引：0，他引：8  
In order to illustrate the change of nitrogen （N） supply capacity after long-term application of manure and chemical fertilizer, as well as to properly manage soil fertility through fertilizer application under the soil-climatic conditions of the North China Plain, organic N forms were quantified in the topsoil with different manure and chemical fertilizer treatments in a 15-year fertilizer experiment in a Chinese calcareous alluvial soil. Soil total N （TN） and various organic N forms were significantly influenced by long-term application of chemical fertilizer and manure. TN, total hydrolysable N, acid-lnsoluble N, amino acid N and ammonium N in the soil increased significantly （P 〈 0.05） with increasing manure and fertilizer N rates, but were not influenced by increasing P rates. Also, application of manure or N fertilizer or P fertilizer did not significantly influence either the quantity of amino sugar N or its proportion of TN. Application of manure significantly increased （P 〈 0.05） hydrolysable unknown N, but adding N or P did not. In addition, application of manure or N fertilizer or P fertilizer did not significantly influence the proportions of different soil organic N forms.  相似文献   

4.
氮肥用量对太湖水稻田间氨挥发和氮素利用率的影响   总被引：28，自引：0，他引：28  
Ammonia volatilization losses, nitrogen utilization efficiency, and rice yields in response to urea application to a rice field were investigated in Wangzhuang Town, Changshu City, Jiangsu Province, China. The N fertilizer treatments, applied in triplicate, were 0 （control）, 100, 200, 300, or 350 kg N ha^-1. After urea was applied to the surface water, a continuous airflow enclosure method was used to measure ammonia volatilization in the paddy field. Total N losses through ammonia volatilization generally increased with the N application rate, and the two higher N application rates （300 and 350 kg N ha^-1） showed a higher ratio of N lost through ammonia volatilization to applied N. Total ammonia loss by ammonia volatilization during the entire rice growth stage ranged from 9.0% to 16.7% of the applied N. Increasing the application rate generally decreased the ratio of N in the seed to N in the plant. For all N treatments, the nitrogen fertilizer utilization efficiency ranged from 30.9% to 45.9%. Surplus N with the highest N rate resulted in lodging of rice plants, a decreased rate of nitrogen fertilizer utilization, and reduced rice yields. Calculated from this experiment, the most economical N fertilizer application rate was 227 kg ha^-1 for the type of paddy soil in the Taihu Lake region. However, recommending an appropriate N fertilizer application rate such that the plant growth is enhanced and ammonia loss is reduced could improve the N utilization efficiency of rice.  相似文献   

5.
中国南方大棚蔬菜地氮平衡与损失   总被引：28，自引：0，他引：28  
High rates of fertilizer nitrogen (N) are applied in greenhouse vegetable fields in southeastern China to maximize production;however,the N budgets of such intensive vegetable production remain to be explored.The goal of this study was to determine the annual N balance and loss in a greenhouse vegetable system of annual rotation of tomato,cucumber,and celery at five N (urea) application rates (0,348,522,696,and 870 kg N ha-1 year-1).Total N input to the 0-50 cm soil layer ranged from 531 to 1 053 kg ha-1,and N fertilizer was the main N source,accounting for 66%-83% of the total annual N input.In comparison,irrigation water,wet deposition,and seeds in total accounted for less than 1% of the total N input.The fertilizer N use efficiency was only 18% under the conventional application rate of 870 kg N ha-1 and decreased as the application rate increased from 522 to 870 kg N ha-1.Apparent N losses were 196-201 kg N ha-1,of which 71%-86% was lost by leaching at the application rates of 522-870 kg N ha-1.Thus,leaching was the primary N loss pathway at high N application rates and the amount of N leached was proportional to the N applied during the cucumber season.Moreover,dissolved organic N accounted for 10% of the leached N,whereas NH3 volatilization only contributed 0.1%-0.6% of the apparent N losses under the five N application rates in this greenhouse vegetable system.  相似文献   

6.
氮肥形态和用量对蔬菜生长与硝态氮累积的影响   总被引：31，自引：0，他引：31  
Experiments were carried out on a vegetable field with Peking cabbage (Bvassica pekinensis (Lour.) Rupr.), cabbage (Bvassica chinensis var. oleifera Makino and nemoto), green cabbage (Brassica chinensis L.), spinach (Spinacia oleracea L.) and rape (Brassica campestris L.) to study the effects of N forms and N rates on their growth and nitrate accumulation. The results indicated that application of ammonium chloride, ammonium nitrate, sodium nitrate and urea significantly increased the yields and nitrate concentrations of Peking cabbage and spinach. Although no significant difference was found in the yields after application of the 4 N forms, nitrate N increased nitrate accumulation in vegetables much more than ammonium N. The vegetable yields were not increased continuously with N rate increase, and oversupply of N reduced the plant growth, leading to a yield decline. This trend was also true for nitrate concentrations in some vegetables and at some sampling times. However, as a whole, the nitrate concentrations in vegetables were positively correlated with N rates. Thus, addition of N fertilizer to soil was the major cause for increases in nitrate concentrations in vegetables. Nitrate concentrations were much higher in roots, stems and petioles than in blades at any N rate.  相似文献   

7.
中国洞庭湖区稻田土壤氮素淋溶损失的系统研究   总被引：5，自引：0，他引：5  
A two-year lysimeter study was conducted to study the effects of different fertilizers and soils on nitrogen leaching loss in a double rice cropping system by considering three major types of paddy soils from the Dongting Lake area. The results showed that N concentration in the leachate did not differ significantly among the treatments of urea, controlled release N fertilizer and pig manure and that all these fertilizers produced higher total nitrogen (TN) concentrations in the leachate compared to the case where no fertilizer was applied. The TN leaching loss following urea treatment accounted for 2.28%, 0.66%, and 1.50% of the amount of N applied in the alluvial sandy loamy paddy soil (ASL), purple calcareous clayey paddy soil (PCC), and reddish-yellow loamy paddy soil (RYL), respectively. Higher TN loss was found to be correlated with the increased leachate volume in ASL compared with RYL, and the lowest TN loss was observed in the PCC, in which the lowest leachate volume and TN concentration were observed. Organic N and NH4+ -N were the major forms of N depleted through leachate, accounting for 56.8% and 39.7% of TN losses, respectively. Accordingly, soil-specific fertilization regimens are recommended; in particular, the maximum amount of fertilizer should be optimized for sandy soils with a high infiltration rate. To avoid a high N leaching loss from rice fields, organic N fertilizers such as urea or coated urea should primarily be used for surface topdressing or shallow-layer application and not for deep-layer application.  相似文献   

8.
氮肥施用对冬小麦籽粒产量和氮素表观损失的影响   总被引：16，自引：0，他引：16  
Excessive nitrogen （N） fertilizer application to winter wheat is a common problem on the North China Plain. To determine the optimum fertilizer N rate for winter wheat production while minimizing N losses, field experiments were conducted for two growing seasons at eight sites, in Huimin County, Shandong Province, from 2001 to 2003. The optimum N rate for maximum grain yield was inversely related to the initial soil mineral N content （Nmin） in the top 90 cm of the soil profile before sowing. There was no yield response to the applied N at the three sites with high initial soil mineral N levels （average 212 kg N ha^-1）. The average optimum N rate was 96 kg N ha^-1 for the five sites with low initial soil Nmin （average 155 kg N ha^-1） before sowing. Residual nitrate N in the top 90 cm of the soil profile after harvest increased with increasing fertilizer N application rate. The apparent N losses during the wheat-growing season also increased with increasing N application rate. The average apparent N losses with the optimum N rates were less than 15 kg N ha^-1, whereas the farmers＇ conventional N application rate resulted in losses of more than 100 kg N ha^-1. Therefore, optimizing N use for winter wheat considerably reduced N losses to the environment without compromising crop yields.  相似文献   

9.
长期稻草还田对土壤球囊霉素和土壤C、N的影响   总被引：7，自引：0，他引：7  
A long-term experiment was conducted to investigate how long-term fertilization and rice straw incorporation into soil affect soil glomalin, C and N. The combined application of chemical fertilizer and straw resulted in a significant increase in both soil easily extractable glomalin （EEG） and total glomalin （TG） concentrations, as compared with application of only chemical fertilizer or no fertilizer application. The EEG and TG concentrations of the NPKS （nitrogen, phosphorus, and potassium fertilizer application ＋ rice straw return） plot were 4.68% and 5.67% higher than those of the CK （unfertilized control） plot, and 9.87% and 6.23% higher than those of the NPK （nitrogen, phosphorus, and potassium fertilizer applied annually） plot, respectively. Application of only chemical fertilizer did not cause a statistically significant change of soil glomalin compared with no fertilizer application. The changes of soil organic C （SOC） and total N （TN） contents demonstrated a similar trend to soil glomalin in these plots. The SOC and TN contents of NPKS plot were 15.01% and 9.18% higher than those of the CK plot, and 8.85% and 14.76% higher than those of the NPK plot, respectively. Rice straw return also enhanced the contents of microbial biomass C （MBC） and microbial biomass N （MBN） in the NPKS plot by 7.76% for MBC and 31.42% for MBN compared with the CK plot, and 12.66% for MBC and 15.07% for MBN compared with the NPK plots, respectively. Application of only chemical fertilizer, however, increased MBN concentration, but decreased MBC concentration in soil.  相似文献   

10.
A soil column method was used to compare the effect of drip fertigation (the application of fertilizer through drip irrigation systems, DFI) on the leaching loss and transformation of urea-N in soil with that of surface fertilization combined with flood irrigation (SFI), and to study the leaching loss and transformation of three kinds of nitrogen fertilizers (nitrate fertilizer, ammonium fertilizer, and urea fertilizer) in two contrasting soils after the fertigation. In comparison to SFI, DFI decreased leaching loss of urea-N from the soil and increased the mineral N (NH4+-N + NO3--N) in the soil. The N leached from a clay loam soil ranged from 5.7% to 9.6% of the total N added as fertilizer, whereas for a sandy loam soil they ranged between 16.2% and 30.4%. Leaching losses of mineral N were higher when nitrate fertilizer was used compared to urea or ammonium fertilizer. Compared to the control (without urea addition), on the first day when soils were fertigated with urea, there were increases in NH4+-N in the soils. This confirmed the rapid hydrolysis of urea in soil during fertigation. NH4+-N in soils reached a peak about 5 days after fertigation, and due to nitrification it began to decrease at day 10. After applying NH4+-N fertilizer and urea and during the incubation period, the mineral nitrogen in the soil decreased. This may be related to the occurrence of NH4+-N fixation or volatilization in the soil during the fertigation process.  相似文献   

11.
The leaching of nitrate-N under autumn-sown arable crops was measured using hydro-logically isolated plots, about 0.24 ha in area, from 1984–1988. Fluxes of water and nitrate moving over the soil surface (surface runoff), at the interface between topsoil and subsoil (interflow), and in the subsoil (drainflow) were monitored in plots with mole-and-pipe drain systems (drained plots); surface runoff and interflow only were monitored in ‘undrained’ plots. Half the drained and undrained plots were direct-drilled, and on the other half seedbeds were prepared by tillage to 200 mm. Tillage increased the total leaching loss of nitrate by 21 % compared with direct drilling in drained plots. About 95% or the nitrate moving from the soil was present in the water intercepted by the subsoil drains in these plots. In undrained plots less water and nitrate were collected in total; more of the nitrate was present in interflow on ploughed plots and in surface runoff in direct-drilled land. Losses of nitrate for the whole experiment from 1978-1988 were analysed. This showed that, between the harvest of one crop and the spring application of fertilizer to the next, loss of nitrate-N from ploughed land (Lp) was approximated by Lp=22+Fkg N ha?1, where F was the autumn fertilizer-N applied. After fertilizer was applied in spring, loss of nitrate-N depended on rainfall such that for 100 mm rainfall about 30% of the fertilizer-N was lost by leaching. About 18% more nitrate-N was lost from direct-drilled land than from ploughed land in spring, but the total loss was generally small compared to that over winter. The apparent net mineralization of organic-N was measured in 1988. In autumn and winter there was little effect of tillage treatment (26 and 31 kg N ha?1 on direct drilled and tilled plots respectively). However, over the year 83 kg N ha?1 were mineralized in tilled plots, and 67 kg N ha?1 in direct-drilled plots. Five factors governing the leaching of nitrate are assessed and this identified that fertilizer nitrogen application to the seedbed of winter sown crops and the mineralization of nitrogen from the residues of the previous crop are the most significant factors for nitrogen leaching in the UK.  相似文献   

12.
The objective of this experiment was to assess the effects of organic or chemical nutrient solutions on the growth and composition of lettuce (Lactuca sativa L.) in greenhouse production. Hoagland and Arnon nutrient solution, an organic hydroponics solution, and no fertilization were factored with lettuce cultivars of different phenotypes, iceberg, romaine, loose head, and loose leaf. Lettuce growth was higher with Hoagland and Arnon solution than with the organic fertilizer or with no fertilization. The organic fertilizer increased growth above no fertilizer applied. Hoagland and Arnon solution gave the highest concentration of nitrogen, potassium, magnesium, and iron in the lettuce whereas lettuce grown with the organic fertilizer had the highest phosphorus. Plant nutrient accumulation differed slightly among the cultivars. Hoagland and Arnon solution produced high nitrate in leaves. Nitrate concentrations with organic or no fertilization were low. Loose head or loose leaf cultivars had higher nitrate than romaine or iceberg.  相似文献   

13.
不同氮源与镁配施对甘蓝产量、品质和养分吸收的影响   总被引：5，自引：0，他引：5  
采用田间试验和室内分析相结合的方法,研究不同氮源与镁配施对甘蓝(Brassica oleracea L.)产量、品质和养分吸收的影响。试验在等氮条件下设4个氮源,分别为不施氮肥、100%铵态氮、50%铵态氮+50%硝态氮、100%硝态氮;设4个硫酸镁施用量,分别为0、75 kg·hm-2、150 kg·hm-2、300 kg·hm-2。结果表明,100%硝态氮与中量(150 kg·hm-2)镁配施处理的甘蓝产量比不施肥处理、100%铵态氮与中量镁配施处理和50%铵态氮+50%硝态氮与中量镁配施处理分别增产56.9%、14.7%和5.2%。施用100%硝态氮处理的甘蓝产量略高于50%硝态氮+50%铵态氮处理,比施用100%铵态氮处理和不施肥处理分别增产13.0%和44.2%。施用低量(75kg·hm-2)镁肥的甘蓝产量比不施镁肥增产9.3%,而增加镁肥用量对甘蓝产量没有显著影响。施用100%硝态氮、50%铵态氮+50%硝态氮和100%铵态氮处理的甘蓝硝酸盐含量比不施氮肥处理分别增加84.4%、63.4%和6.9%。100%硝态氮与高量(300 kg·hm-2)镁肥配合施用的甘蓝硝酸盐含量比不施肥处理、100%铵态氮与高量镁肥配施处理和50%铵态氮+50%硝态氮与高镁肥配施处理分别增加101.4%、82.3%和14.1%。施用高量镁肥处理甘蓝硝酸盐含量比不施肥处理增加11.2%。随着硝态氮比例增加,甘蓝维生素C、还原糖、总氨基酸含量相应增加,镁肥施用量对甘蓝维生素C、还原糖、总氨基酸含量影响明显。随着硝态氮比例增加,甘蓝对磷、钾和钙吸收量显著增加;随着镁施用量增加,磷、钾和镁吸收量相应增加。不同氮源与镁肥相互作用对甘蓝维生素C含量,氮、磷、钾、钙和镁养分吸收均有明显的影响。本研究表明,50%硝态氮和50%铵态氮混合与适量镁肥配合施用,既能增加甘蓝产量,提高维生素C、还原糖和总氨基酸含量,又能减少硝酸盐含量,提高甘蓝品质。  相似文献   

14.
The responses of lettuce (Lactuca sativa L. ‘Arroyo’) to organic nitrogen (N) fertilizers were investigated in a greenhouse. Fertilizers were blood meal (BLO), feather meal (FM), cottonseed meal, alfalfa meal, sewage sludge, compost, cow manure, a chemical fertilizer, and a treatment without fertilizer. Amounts of N from fertilizers were 100, 200, 400, or 800?mg per pot. Lettuce yield was higher for plants receiving fertilizers than with no fertilizer and increased with increased N applications, but high applications of BLO or FM suppressed yields. Nitrogen and nitrate increased in leaves as N supply increased with all fertilizers. Small changes in leaf nutrient contents other than N occurred among or with increased application of the various fertilizers. The soil carbon dioxide release and ammonia volatilization were high from fertilizers with high N concentrations. Organic fertilizers with high N increased lettuce growth at lower applications than those with low N content.  相似文献   

15.
Results are presented from a 3 year investigation into nitrate leaching from isolated 0.4 ha grassland plots fertilized with 250, 500 and 900 kg N ha?1 a?1. Cumulative nitrate leaching over the 3 years was equivalent to 1.5%, 5.4% and 16.7% of the fertilizer applied at 250, 500 and 900 kg N ha?1 rates respectively. Over a whole drainage season, mean nitrate leachate concentrations at 250 kg N ha?1 did not exceed 4 mgl?1, although maximum values of 13.3 mgl?1 were observed. In contrast, at 900 kg N ha?1, the mean nitrate leachate concentration in two of the years exceeded 90 mgl?1. Mineral nitrogen balances constructed for the 1979 growing season indicated that leaching at 250 kg N ha?1 was low because net mineralization of soil organic nitrogen was small, and crop nitrogen uptake almost balanced fertilizer application. Although the pattern of nitrate leaching suggested that by-passing occurred in the movement of water down the soil profile, it was not possible to confirm this using simulation models of leaching. Possible reasons for this, including the occurrence of rapid water flow down gravitationally drained macropores, are discussed.  相似文献   

16.
Abstract

Nitrogen (N) can leach in porous golf greens, especially when they are flushed with high rates of irrigation. Drain water often discharges to the surface, possibly endangering surface waters with eutrophic concentrations of nitrogen. A greenhouse study was initiated to study the effects of fertilizer source and rate and irrigation schemes on leaching of nitrate and ammonium nitrogen. Simulated golf green columns were sodded with bermudagrass. Treatments were 3 fertilizer sources (20‐20‐20, ammonium nitrate, and a sulfur‐coated urea), 3 rates (zero control, 12, and 24 kg ha?1), and 2 irrigation schemes. The first was a daily rate of 0.6 mm (N.I.), and the second was the same daily rate with several flushes of 11.5 cm each (FL). Essentially no nitrogen leached for the N.I. scheme, whereas the FL treatment resulted in significant leaching of nitrate‐N. Ammonium‐N leached to a much less extent than nitrate‐N. The nitrate‐N concentration “break through” occurred earlier, the peaks were higher, and the flushes were more prominent for 20‐20‐20 and ammonium nitrate than for the sulfur‐coated urea. The sulfur‐coated urea had a gradual nitrate‐N concentration peak that tapered off slowly. The percent N leached of that applied was higher for the flushes, and all sources were the same for flushes and the high N rate (about 20%). At the low N rate and flushes, the percent leached was highest for ammonium nitrate (10.2%), 20‐20‐20 was intermediate (4.3%), and sulfur‐coated urea was the lowest (0.14%). These data show that fertilizer sources and rates can make a difference in nitrate‐nitrogen leaching but only when significant leaching is taking place as with flushing.  相似文献   

17.
《Journal of plant nutrition》2013,36(4-5):743-751
While nitrogen (N) form affects growth and yield of many vegetables crops, previous studies suggested that N-form may affect lettuce (Lactuca sativa L.) quality more than growth and yield. The objectives of this research were to evaluate the effect of the N-source used as injection material on the field performance and sensory attributes of three lettuce types. Three lettuce types (Romaine, butterhead and looseleaf) where grown with plasticulture and sidedressed with weekly injections of calcium nitrate, potassium nitrate, or ammonium nitrate, each at a rate of 7 kg N ha?1 week?1. All lettuce type reached marketable size 49 days after transplanting. N-source effect on marketable yield and head number was not significant (P>0.05). After harvest, lettuce samples were prepared for sensory evaluation. In a quiet session, panelists (n=36) were instructed to rate each sample for bitterness, sweetness, crunchiness, and overall preference on a 9-cm Hedonic scale. Sensory ratings were similar for all three lettuce types. Panelist found that crunchiness of calcium nitrate-fed plants (4.8 cm) was significantly (P=0.05) higher than that of plants receiving potassium nitrate (4.4 cm) or ammonium nitrate (4.2 cm). These results suggest that while growers may use ammonium nitrate because of its cost, they should consider using calcium nitrate to enhance lettuce crunchiness.  相似文献   

18.
Results are presented from a 3-year investigation into nitrate leaching from grassed monolith lysimeters treated with double (15NH415NO3) or single (15NH4NO3) labelled ammonium nitrate at three rates, 250, 500 and 900 kg N ha?1 a?1. Over the 3 years of the experiment, 0.14%, 3.1% and 18.1% of the applied fertilizer was recovered in the leachate at 250, 500 and 900kg N ha?1 respectively. This represented 9%, 39% and 75% of the overall nitrate leaching at the three application rates. A significant proportion of the fertilizer leached as nitrate at the three application rates was derived, via nitrification, from the fertilizer ammonium. Increasing fertilizer applications caused a rise in the leaching of both soil and fertilizer derived nitrogen, although whether the increase reflected a true priming effect was not clear.  相似文献   

19.
Pollution of ground water caused by excessive and uncontrolled use of nitrogen fertilizer is worrying. A recent example of such pollution has been observed in an agricultural basin in the province of Nevsehir, Turkey, where up to 900 kg ha?1 nitrogen fertilizer is used for growing potatoes in sandy soils under irrigation. Using nitrogen fertilizer in amounts that guarantee large yields without polluting ground water is essential. We present results of field experiments and numerical simulations involving 15N-labelled nitrogen fertilizer leaching. In the field, we monitored the movement of water and the distributions of nitrogen species within the soil–water–plant continuum. The detailed dynamics of the nitrogen cycle within the system were simulated. Simulations included calibration and validation of the nitrogen version of the LEACHM model (LEACHN, version 3) and long-term applications of the model. The model’s predictions of nitrogen fluxes under long-term use of fertilizer and irrigation were analysed. Nearly half of the applied ammonium-N was converted to nitrate-N during the growing season. With increasing additions of N the rate of plant uptake declined, while leaching increased significantly, and the fraction of nitrogen remaining in the soil profile increased only moderately. In long-term applications, a significant fraction of the applied fertilizer tended to accumulate after the first year in soil as the residual nitrogen not taken up by the crop. Accumulated residual nitrogen is converted to nitrate-N and leached rapidly from the soil profile during the wet season following the harvest. To reduce leaching of the residual nitrate, the rates, frequencies and timings of fertilizer application and irrigation must be scheduled in accordance with the plant growth periods and the hydraulic regime of the soil.  相似文献   

20.
Drained and undrained grassland lysimeter plots were established in 1982 on a clay loam of the Hallsworth series at a long-term experimental site in south-west England. The plots were continuously grazed by beef cattle, and received fertilizer at either 200 or 400 kg N ha-1 per annum to the existing permanent sward, or at 400 kg N ha-1 to a new sward, reseeded to perennial ryegrass following cultivation. Drainage water was monitored at V-notch weirs and sampled daily for the analysis of nitrate-N. Seven years of data are presented (five years for the reseeded swards). On the drained plots a large proportion of the rainfall was routed preferentially down large pores to the mole drains, whilst on the undrained plots, drainage was mainly by surface runoff. The average quantities of nitrate N leached per year were 38.5, 133.8 and 55.7 kg ha-1 from the old sward that received 200 and 400 kg N ha-1, and from the reseed that received 400 kg N ha-1 fertilizer, respectively. Ploughing and reseeding resulted in a two-fold reduction in leaching, except during the first winter after ploughing, and twice as much leaching occurred after a hot, dry summer as after a cool, wet one. Nitrate concentrations in drainage from either drained or undrained plots were rather insensitive to rainfall intensity, such that concentration was a good predictor of nitrate load for a given drainage volume. The drainage volume determined the proportion of the leachable N that remained in the soil after the winter drainage period. Initial (peak) concentrations of nitrate N ranged, on average, from 55 mg dm-3 for the drained old sward that received 400 kg N ha-1 fertilizer, to 12 mg dm-3 for the undrained sward at 200 kg N ha-1 fertilizer input. Concentrations of nitrate N in drainage from similar, unfertilized plots rarely exceeded 1 mg dm-3. The results suggest that manipulating the nitrate supply can lessen leaching and that the route of water through soil to the watercourse determines the maximum nitrate concentration for a given load.  相似文献   

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