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1.
The current study investigated the short-term physiological implications of plant nitrogen uptake of urea amended with the urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT) under both greenhouse and field conditions. 15N labelled urea amended with 0.0, 0.01, 0.1 and 0.5% nBTPT (w/w) was surface applied at a rate equivalent to 100 kg N ha–1 to perennial ryegrass in a greenhouse pot experiment. Root, shoot and soil fractions were destructively harvested 0.75, 1.75, 4, 7 and 10 days after fertilizer application. Urease activity was determined in each fraction together with 15N recovery and a range of chemical analyses. The effect of nBTPT amended urea on leaf tip scorch was evaluated together with the effect of the inhibitor applied on its own on plant urease activity.nBTPT-amended urea dramatically reduced shoot urease activity for the first few days after application compared to unamended urea. The higher the nBTPT concentration the longer the time required for shoot activity to return to that in the unamended treatment. At the highest inhibitor concentration of 0.5% shoot urease activity had returned to that of unamended urea by 10 days. Root urease activity was unaffected by nBTPT in the presence of urea but was affected by nBTPT in the absence of urea.Transient leaf tip scorch was observed approximately 7–15 days after nBTPT + urea application and was greatest with high concentrations of nBTPT and high urea-N application rates. New developing leaves showed no visual sign of tip necrosis.Urea hydrolysis of unamended urea was rapid with only 1.3% urea-N remaining in the soil after 1.75 days. N uptake and metabolism by ryegrass was rapid with 15N recovery from unamended urea, in the plant (shoot + root) being 33% after 1.75 days. Most of the 15N in the soil following the urea+0.5% nBTPT application was still as urea after 1.75 days, yet 15N plant recovery at this time was 25% (root+shoot). This together with other evidence, suggests that if urea hydrolysis in soil is delayed by nBTPT then urea can be taken up by ryegrass as the intact molecule, albeit at a significantly slower initial rate of uptake than NH4 +-N. Protein and water soluble carbohydrate content of the plant were not significantly affected by amending urea with nBTPT however, there was a significant effect on the composition of amino acids in the roots and shoots, suggesting a difference in metabolism.Although nBTPT-amended urea affected plant urease activity and caused some leaf-tip scorch the effects were transient and short-lived. The previously reported benefit of nBTPT in reducing NH3 volatilization of urea would appear to far outweigh any of the observed short-term effects, as dry-matter production of ryegrass is increased.  相似文献   

2.
The development of management techniques to improve the poor N use efficiency by lowland rice (Oryza sativa L.) and reduce the high N losses has been an important focus of agronomic research. The potential of an Azolla cover in combination with urea was assessed under field conditions in Laguna, Philippines. Two on-station field experiments were established in the 1998–1999 dry season and eight on-farm experiments per season were carried out in the 2000–2001 wet and dry seasons. Treatment combinations consisting of N levels applied alone or combined with Azolla were evaluated with respect to floodwater chemistry, 15N recovery, crop growth, and grain yield. A full Azolla cover on the floodwater surface at the time of urea application prevented the rapid and large increase in floodwater pH and floodwater temperature. As a consequence, the partial pressure of ammonia (NH3), which is an indicator of potential NH3 volatilization, was significantly depressed. 15N recovery was higher in plots covered with Azolla where the total 15N recovery ranged between 77 and 99%, and the aboveground (grain and straw) recovery by rice ranged between 32 and 61%. The tiller count in Azolla-covered plots was significantly increased by 50% more than the uncovered plots at all urea levels. Consequently, the grain yield was likewise improved. Grain yields from the 16 on-farm trials increased by as much as 40% at lower N rates (40 and 50 kg N ha–1) and by as much as 29% at higher N rates (80 and 100 kg N ha–1). In addition, response of rice to treatments with lower N rates with an Azolla cover was comparable to that obtained with the higher N rates without a cover. Thus, using Azolla as a surface cover in combination with urea can be an alternative management practice worth considering as a means to reduce NH3 volatilization losses and improve N use efficiency.  相似文献   

3.
Field experiments were carried out in 1987 on winter wheat crops grown on three types of soil. 15N-labelled urea, 15NH4NO3 or NH4 15NO3 (80 kg N ha-1) was applied at tillering. The soils (chalky soil, hydromorphic loamy soil, sandy clay soil) were chosen to obtain a range of nitrogen dynamics, particularly nitrification. Soil microbial N immobilization and crop N uptake were measured at five dates. Shortly after fertilizer application (0–26 days), the amount of N immobilized in soil were markedly higher with labelled urea or ammonium than that with nitrate in all soils. During the same period, crop 15N uptake occurred preferentially at the expense of nitrate. Nitrification differed little between soils, the rates were 2.0 to 4.7 kg N ha-1 day-1 at 9°C daily mean temperature. The differences in immobilization and uptake had almost disappeared at flowering and harvest. 15N recovery in soil and crop varied between 50 and 100%. Gaseous losses probably occurred by volatilization in the chalky soil and denitrification in the hydromorphic loamy soil. These losses affected the NH4 + and NO3 - pools differently and determined the partitioning of fertilizer-N between immobilization and absorption.  相似文献   

4.
Destain  J. P.  Francois  E.  Guiot  J.  Goffart  J. P.  Vandergeten  J. P.  Bodson  B. 《Plant and Soil》1993,155(1):367-370
Since 1986, the fate of fertilizer N (NH4NO3 or NaNO3) applied in field conditions on two main arable crops, winter wheat (Triticum aestivum) and sugar beet (Beta vulgaris), has been studied using 15N. Up to a rate of 200 kg ha-1 of N, mean recovery of fertilizer by winter wheat was 70%, provided it had been split applied. Single application (with or without dicyandiamid) was less effective. For sugar beet, in 1990, 1991 and 1992, 40% of fertilizer N was found in the crop at harvest when NH4NO3 had been broadcast at 100 to 160 kg N ha-1 at sowing time. For the same N rate, recovery was 50% when row applied near the seeds and 60% for 80 kg N ha-1. For the two experimental crops, residual fertilizer N in soil was exclusively organic. It ranged from 15 to 30% of applied N and was located in the 30 cm upper layer. Losses were generally lower with winter wheat (12%) than with sugar beet (20–40%) and could be ascribed to volatilization and denitrification. Soil derived N taken up by the plant was site and year dependent.  相似文献   

5.
Erratic rainfall in rainfed lowlands and inadequate water supply in irrigated lowlands can results in alternate soil drying and flooding during a rice (Oryza sativa L.) cropping period. Effects of alternate soil drying and flooding on N loss by nitrification-denitrification have been inconsistent in previous field research. To determine the effects of water deficit and urea timing on soil NO3 and NH4, floodwater NO3, and N loss from added 15N-labeled urea, a field experiment was conducted for 2 yr on an Andaqueptic Haplaquoll in the Philippines. Water regimes were continuously flooded, not irrigated from 15 to 35 d after transplanting (DT), or not irrigated from 41 to 63 DT. The nitrogen treatments in factorial combination with water regimes were no applied N and 80 kg urea-N ha–1, either applied half basally and half at 37 DT or half at 11 DT and half at 65 DT. Water deficit at 15 to 35 DT and 41 to 63 DT, compared with continuous soil flooding, significantly reduced extractable NH4 in the top 30-cm soil layer and resulted in significant but small (<1.0 kg N ha–1) soil NO3 accumulations. Soil NO3, which accumulated during the water deficit, rapidly disappeared after reflooding. Water deficit at 15 to 35 DT, unlike that at 41 to 63 DT, increased the gaseous loss of added urea N as determined from unrecovered 15N in 15N balances. The results indicate that application of urea to young rice in saturated or flooded soil results in large, rapid losses of N (mean = 35% of applied N), presumably by NH3 volatilization. Subsequent soil drying and flooding during the vegetative growth phase can result in additional N loss (mean = 14% of applied N), presumably by nitrification-denitrification. This additional N loss due to soil drying and flooding decreases with increasing crop age, apparently because of increased competition by rice with soil microorganisms for NH4 and NO3.  相似文献   

6.
免耕稻田氮肥运筹对土壤NH3挥发及氮肥利用率的影响   总被引:2,自引:0,他引:2  
马玉华  刘兵  张枝盛  郑大  周亮  曹凑贵  李成芳 《生态学报》2013,33(18):5556-5564
通过大田试验,设置5种不同的施肥比例(基肥:分蘖肥:拔节肥:穗肥-2:2:3:3(R1)、3:2:2:3(R2)、4:2:2:2(R3)、4:3:1:2(R4)与0:0:0:0(CK)),研究氮肥运筹对稻田NH3挥发和氮肥利用率的影响。结果表明,(1)相对于不施肥,施肥显著提高了稻田NH3挥发量。氮肥施用后,NH3挥发损失量占施氮量的6.2%-8.5%,其中,以分蘖期NH3挥发损失量最大,齐穗期次之,苗期和拔节期最小。施肥处理间,处理R1稻田累积NH3挥发量最小,显著低于其它施肥处理,比处理R2、R3和R4分别低9.1%(P<0.05)、10.9%(P<0.05)和17.7%(P<0.05)。(2)相关分析表明,田面水NH4+、pH值和土壤NH4+和pH值均与稻田土壤NH3挥发通量呈显著或者极显著相关;(3)处理R1水稻氮肥利用率相对于处理R2、R3和R4增加了28.4%(P<0.05)、55.4%(P<0.05)和74.9%(P<0.05)。研究表明,氮肥后移能有效降低免耕稻田NH3挥发,提高水稻的氮肥利用率。  相似文献   

7.
Summary The fate of 100 kg N ha–1 applied as15N-urea and its modified forms was followed in 4 successive field-grown wetland rice crops in a vertisol. The first wet season crop recovered about 27 to 36.6% of the applied N depending upon the N source. In subsequent seasons the average uptake was very small and it gradually decreased from 1.4 to 0.5 kg N ha–1 although about 18 to 20, 12 to 17 and 14 to 18 kg ha–1 residual fertilizer N was available in the root zone after harvest of first, second and third crops, respectively. The average uptake of the residual fertilizer N was only 7.6% in the second crop and it decreased to 4.5% in the third and to 3.2% in the fourth crop although all these crops were adequately fertilized with unlabelled urea. The basal application of neem coated urea was more effective in controlling the leaching loss of labelled NH4+NO3–N than split application of uncoated urea. In the first 3 seasons in which15N was detectable, the loss of fertilizer N through leaching as NH4+NO3–N amounted to 0.5 kg ha–1 from neem-coated urea, 1.5 kg from split urea and 4.1 kg from coal tar-coated urea. At the end of 4 crops, most of the labelled fertilizer N (about 69% on average) was located in the upper 0–20 cm soil layer showing very little movement beyond this depth. In the profile sampled upto 60 cm depth, totally about 13.8 kg labelled fertilizer N ha–1 from neem-coated urea, 12.7 kg from coal-tar coated urea, and 11.8 kg from split urea were recovered. The average recovery of labelled urea-N in crops and soil during the entire experimental period ranged between 42 and 51%. After correcting for leaching losses, the remaining 47 to 56% appeared to have been lost through ammonia volatilization and denitrification.  相似文献   

8.
Labelled fertilizer N applied to winter wheat as Na15NO3 and (15NH4)2SO4 at a total N dressing of 100kg ha−1 was used in a microplot balance study to investigate the fate of each split fraction at three growth stages: end of tillering, heading and beginning of flowering. Results indicated that while the percentage utilization of the applied N by the grain and total crop increased considerably from the first to the third split application, these values diminished steadily in the straw. Grain recovery values for the first, second and third split applications were 34.2%, 51.5% and 55.7% for the NO3 and 32.3%, 48.4% and 52.5% for the NH4 carrier, respectively. The corresponding recovery values for the whole plant were 54.6%, 67.8% and 69.9% for the NO3 and 51.7%, 63.5% and 66.1% for the NH4 carrier. A greater proportion of the fertilizer N applied at the end of tillering stage was found in the vegetative plant components as compared with the grain. The reverse occurred for the N applied at the heading and at the beginning of the flowering stages. The residual fertilizer N found in the soil amounted to 18.0%, 10.4% and 11.6% of the applied NO3−N and to 22.5%, 12.7% and 15.2% of the applied NH4−N for the respective split applications. No differences were found for each split application between the two carriers as far as the unaccounted fertilizer N was concerned. The losses were 26.6%, 22.3% and 18.6% of the applied N for the three split applications, respectively. The application of fertilizer N did not lead to any increase in soil N uptake by the crop.  相似文献   

9.
Although the variation in natural 15N abundance in plants and soils is well characterized, mechanisms controlling N isotopic composition of organic matter are still poorly understood. The primary goal of this study was to examine the role of NH3 volatilization from ungulate urine patches in determining 15N abundance in grassland plants and soil in Yellowstone National Park. We additionally used isotopic measurements to explore the pathways that plants in urine patches take up N. Plant, soil, and volatilized NH315N were measured on grassland plots for 10 days following the addition of simulated urine. Simulated urine increased 15N of roots and soil and reduced 15N of shoots. Soil enrichment was due to the volatilization of isotopically light NH3. Acid-trapped NH315N increased from –28 (day 1) to –0.3 (day 10), and was lighter than the original urea-N added (1.2). A mass balance analysis of urea-derived N assimilated by plants indicated that most of the N taken up by plants was in the form of ammonium through roots. However, isotope data also showed that shoots directly absorbed 15N – depleted NH3-N that was volatilized from simulated urine patches. These results indicate that NH3 volatilization from urine patches enriches grassland soil with 15N and shoots are a sink for volatilized NH3, which likely leads to accelerated cycling of excreted N back to herbivores.  相似文献   

10.
The role of nitrification-denitrification in the loss of nitrogen from urea applied to puddled soils planted to rice and subjected to continuous and intermittent flooding was evaluated in three greenhouse pot studies. The loss of N via denitrification was estimated indirectly using the15N balance, after either first accounting for NH3 volatilization or by analyzing the15N balance immediately before and after the soil was dried and reflooded. When urea was broadcast and incorporated the loss of15N from the soil-plant systems depended on the soil, being about 20%–25% for the silt loams and only 10%–12% for the clay. Ammonia volatilization accounted for an average 20% of the N applied in the silt loam. Denitrification losses could not account for more than 10% of the applied N in any of the continuously flooded soil-plant systems under study and were most likely less than 5%. Intermittent flooding of soil planted to rice did not increase the loss of N. Denitrification appeared to be an important loss mechanism in continuously flooded fallow soils, accounting for the loss of approximately 40% of the applied15N. Loss of15N was not appreciably enhanced in fallow soils undergoing intermittent flooding. Apparently, nitrate formed in oxidized zones in the soil was readily denitrified in the absence of plant roots. Extensive loss (66%) of15N-labeled nitrate was obtained when 100 mg/pot of nitrate-N was applied to the surface of nonflooded soil prior to reflooding. This result suggests that rice plants may not compete effectively with denitrifiers if large quantities of nitrate were to accumulate during intermittent dry periods.  相似文献   

11.
During vegetative regrowth of Medicago sativa L., soil N, symbiotically fixed N2 and N reserves meet the nitrogen requirements for shoot regrowth. Experiments with nodulated or non-nodulated plants were carried out to investigate the changes in N flows originating from the different N sources and in xylem transport of amino acids during regrowth. Exogenous N uptake, N2 fixation and endogenous N remobilization were estimated by 15N labelling and amino acids in xylem sap were analysed. Removal of shoots resulted in great declines of exogenous N flows derived either from N2 or from NH4NO3 during the first week of regrowth, thereafter recovery increased linearly. Mineral N uptake as well as N2 fixation occurred mainly between the 10th and 18th day after removal of shoots while exogenous N assimilation in intact plants remained at a steady level. Nitrogen remobilization rates in defoliated plants increased by at least three to five-fold, especially during the first 10 days following shoot removal. Compared to control plants, contents of amino acids in xylem sap, during the first 10 days of regrowth, were reduced by about 72% and 82% in NH4NO3 grown and in N2 fixing plants, respectively. Asparagine was the main amino acid transported in xylem sap of both treated plants. Its relative contents during this period significantly decreased from 75% to 59% and from 67% to 36% respectively in non-nodulated plants and in nodulated ones. This decline was accompanied by compensatory increase in the relative contents of aspartate and glutamine.  相似文献   

12.
A field study was conducted on a clay soil (Andaqueptic Haplaquoll) in the Philippines to directly measure the evolution of (N2+N2O)−15N from 98 atom %15N-labeled urea broadcast at 29 kg N ha−1 into 0.05-m-deep floodwater at 15 days after transplanting (DT) rice. The flux of (N2+N2O)−15N during the 19 days following urea application never exceeded 28 g N ha−1 day−1. The total recovery of (N2+N2O)−15N evolved from the field was only 0.51% of the applied N, whereas total gaseous15N loss estimated from unrecovered15N in the15N balance was 41% of the applied N. Floodwater (nitrate+nitrite)−N in the 5 days following urea application never exceeded 0.14 g N m−3 or 0.3% of the applied N. Prior cropping of cowpea [Vigna unguiculata (L.) Walp.] to flowering with subsequent incorporation of the green manure (dry matter=2.5 Mg ha−1, C/N=15) at 15 days before rice transplanting had no effect on fate of urea applied to rice at 15 DT. The recovery of (N2+N2O)−15N and total15N loss during the 19 days following urea application were 0.46 and 40%, respectively. Direct recovery of evolved (N2+N2O)−15N and total15N loss from 27 kg applied nitrate-N ha−1 were 20% and 53% during the same 19-day period. The failure of directly-recovered (N2+N2O)−15N to match total15N loss from added nitrate-15N might be due to entrapment of denitrification end products in soil or transport of gaseous end products to the atmosphere through rice plants. The rapid conversion of added nitrate-N to (N2+N2O)−N, the apparently sufficient water soluble soil organic C for denitrification (101 μg C g−1 in the top 0.15-m soil layer), and the low floodwater nitrate following urea application suggested that denitrification loss from urea was controlled by supply of nitrate rather than by availability of organic C.  相似文献   

13.
Mahmood  T.  Malik  K.A.  Shamsi  S.R.A.  Sajjad  M.I. 《Plant and Soil》1998,199(2):239-250
Denitrification and total N losses were quantified from an irrigated field cropped to maize and wheat, each receiving urea at 100 kg N ha-1. During the maize growing season (60 days), the denitrification loss measured directly by acetylene inhibition-soil cover method amounted 2.72 kg N ha-1 whereas total N loss measured by 15N balance was 39 kg ha-1. Most (87%) of the denitrification loss under maize occurred during the first two irrigation cycles. During the wheat growing season (150 days), the denitrification loss directly measured by acetylene inhibition-soil cover and acetylene inhibition-soil core methods was 1.14 and 3.39 kg N ha-1, respectively in contrast to 33 kg N ha-1 loss measured by 15N balance. Most (70-88%) of the denitrification loss under wheat occurred during the first three irrigation cycles. Soil moisture and NO 3 - -N were the major factors limiting denitrification under both crops. Higher N losses measured by 15N balance than C2H2 inhibition method were perhaps due to underestimation of denitrification by C2H2 inhibition method and losses other than denitrification, most probably NH3 volatilization.  相似文献   

14.
Rates of N uptake by spring wheat as ammonium and as nitrate, and rates of nitrification, gross N immobilization and gross N mineralization were measured in a pot experiment during 84 days of growth in a clay soil. Soil treatments included an unfertilized control and addition of 15NH4NO3 or NH4 15NO3 in the absence and presence of N-serve 24E. Incorporation of ammonium into the soil organic N pool was considerably higher in the presence compared to the absence of nitrapyrin, but the processes contributing to this effect could not be positively identified. Both dry matter and grain yield as well as N uptake by wheat were enhanced in the presence of the inhibitor in N fertilized soil, despite the increased immobilization of N. On the other hand, inhibitor application had a detrimental effect on yield and N uptake by wheat in unfertilized soil. Both ammonium and nitrate forms of inorganic N were absorbed by wheat, but nitrate uptake was dominant in the absence of the inhibitor. The uptake of N as ammonium was higher and the uptake of N as nitrate was less, both in absolute and proportional terms, in the presence compared to the absence of inhibitor. In addition, the proportion of N taken up as ammonium was higher than the proportion of N as ammonium in the available N pool up to day 56 in the inhibitor treatment, which indicated a preference for ammonium uptake by wheat. Evidence was obtained which suggested that several factors may have contributed to the positive response of wheat to inhibitor application in N fertilized soil, including reduced N losses, higher gross N mineralization and a physiological response due to the proportional increase in uptake of inorganic N as ammonium.  相似文献   

15.
The effect of incorporating cattle slurry in soil, either by mixing or by simulated injection into a hollow in soil, on the ryegrass uptake of total N and 15NH4 +-N was determined in three soils of different texture. The N accumulation in Italian ryegrass (Lolium multiflorum L.) from slurry N and from an equivalent amount of NH4 +-N in (15NH4) SO4 (control) was measured during 6 months of growth in pots. After this period the total recovery of labelled N in the top soil plus herbage was similar in the slurry and the control treatments. This indicated that gaseous losses from slurry NH4 +-N were insignificant. Consequently, the availability of slurry N to plants was mainly influenced by the mineralization-immobilization processes. The apparent utilization of slurry NH4 +-N mixed into soil was 7%, 14% and 24% lower than the utilization of (NH4)2SO4-N in a sand soil, a sandy loam soil and a loam soil, respectively. Thus, the net immobilization of N due to slurry application increased with increasing soil clay content, whereas the recovery in plants of 15N-labelled NH4 +-N from slurry was similar on the three soils. A parallel incubation experiment showed that the immobilization of slurry N occurred within the first week after slurry application. The incorporation of slurry N by simulated injection increased the plant uptake of both total and labelled N compared to mixing the slurry into the soil. The apparent utilization of injected slurry NH4 +-N was 7% higher, 8% lower and 4% higher than the utilization of (NH4)2SO4-N in the sand, the sandy loam and the loam soil, respectively. It is concluded that the spatial distribution of slurry in soil influenced the net mineralization of N to the same degree as did the soil type.  相似文献   

16.
During three rice-growing seasons in Uruguay, field experiments were conducted to study the contribution of cyanobacterial inoculation and chemical N fertilization to rice production. Neither grain yield nor fertilizer recovery by the plant were affected by inoculation with native cyanobacterial isolates. A low fertilizer use efficiency (around 20%) was observed when labelled (NH4)2SO4 was applied at sowing. Recovery of applied 15N by the soil–plant system was 50%. Inoculation did not modify 15N uptake by the plant when the fertilizer was three-split applied either. The total N-fertilizer recovery was higher when the fertilizer was split than when applied in a single dose. Plant N-fertilizer uptake was higher when the fertilizer was applied at tillering. Uptake of 15N from cyanobacteria by rice was studied in a greenhouse pots experiment without chemical nitrogen addition. Recovery of 15N from labelled cyanobacteria by rice in greenhouse growth conditions was similar to that of partial recovery of (NH4)2SO4 applied at sowing in the field. Cyanobacterial N mineralization under controlled conditions was fast as cyanobacterial N was detected in plants after 25 days. Moreover 40 days after inoculation non-planted and inoculated soil had more inorganic N than the non-inoculated one.  相似文献   

17.
Fertilization rates and clay fixed ammonium in two Quebec soils   总被引:5,自引:0,他引:5  
Clay fixed NH4 + can provide a significant sink for fertilizer N, as well as a source of N for plant uptake. Knowledge or soil NH4 + fixing capacity and release for crops is necessary to develop long-term fertilizer programs. Field experiments with corn (Zea mays L.) were carried out to investigate soil NH4 + fixing capacity and subsequent release as influenced by fertilizer rates using 15N in a Ste. Rosalie clay (fine, mixed, frigid, Typic Humaquept) and a Chicot sandy clay loam (fine-loamy, mixed, frigid, Typic Hapludalf). With high N rates increased NH4 + fixation occurred only in the Ste. Rosalie soil. At the end of the first growing season, fertilizer N recovery as clay fixed NH4 + for high and normal rates of fertilizer in the Ste. Rosalie soil was 17.8% and 28.7%, respectively and the recovery for the high and normal rates in the Chicot soil was 4.6 and 10.5%, respectively. Significant amounts of clay fixed NH4 +-N were released in the soil profile in the second year after 15N application on the Chicot soil. Recently clay fixed fertilizer NH4 +N was released more rapidly than that of the native fixed NH4 +, from the surface layer of the Ste. Rosalie soil. The fertilizer fixed NH4 + seems to be in a more labile N pool than the native fixed NH4 +-N in the Chicot soil.  相似文献   

18.
Leaching of nitrate (NO3 ) below the root zone and gaseous losses of nitrogen (N) such as ammonia (NH3) volatilization, are major mechanisms of N loss from agricultural soils. New techniques to minimize such losses are needed to maximize N uptake efficiency and minimize production costs and the risk of potential N contamination of ground and surface waters. The effects of cellulose (C), clinoptilolite zeolite (CZ), or a combination of both (C+CZ) on NH3 volatilization and N transformation in a calcareous Riviera fine sand (loamy, siliceous, hyperthermic, Arenic Glossaqualf) from a citrus grove were investigated in a laboratory incubation study. Ammonia volatilization from NH4NO3 (AN), (NH4)2SO4(AS), and urea (U) applied at 200 mg N kg–1 soil decreased by 2.5-, 2.1- and 0.9-fold, respectively, with cellulose application at 15 g kg–1 and by 4.4-, 2.9- and 3.0-fold, respectively, with CZ application at 15 g kg–1 as compared with that from the respective sources without the amendments. Application of cellulose plus CZ (each at 15 g kg–1) was the most effective in decreasing NH3 volatilization. Application of cellulose increased the microbial biomass, which was responsible for immobilization of N, and thus decreased volatilization loss of NH3–N. The effect of CZ, on the other hand, may be due to increased retention of NH4 in the ion-exchange sites. The positive effect of interaction between cellulose and CZ amendment on microbial biomass was probably due to improved nutrient retention and availability to microorganisms in the soil. Thus, the amendments provide favorable conditions for microbial growth. These results indicate that soil amendment of CZ or CZ plus organic materials such as cellulose has great potential in reducing fertilizer N loss in sandy soils.  相似文献   

19.
The seasonal course of nitrogen uptake, incorporation and remobilization in different shoot components of winter oilseed rape (Brassica napus L.) was studied under field conditions including three rates of 15N labelled nitrogen application (0, 100 or 200 kg N ha-1) and two irrigation treatments (rainfed or watered at a deficit of 20 mm). The total amount of irrigation water applied was 260 mm, split over 13 occasions in a 7-week-period ranging from 1 week before onset of flowering until 4 weeks after flowering.Nitrogen application and irrigation increased plant growth and nitrogen accumulation. Irrespective of N and irrigation treatment more than 50% of total shoot N was present in the stem when flowering started. At the end of flowering, pod walls were the main N store containing about 30–40% of shoot N. The quantities of N remobilized from stems and pod walls amounted in all treatments to about 70% of the N present in these organs at mid-flowering. At harvest, stem and pod walls each contained about 10% of total shoot N, the remaining 80% being incorporated into seeds. The main component contributing to the response of seed N accumulation to nitrogen application and irrigation was pods in axillary racemes. Up to 20 kg N ha-1, corresponding to about 10% of final shoot N content, was lost from the plants by leaf drop.Irrigation increased the recovery at harvest of applied N from 30% to about 50%, while the level of N application did not affect the N recovery. 15N labelled (fertilizer derived) nitrogen constituted a greater proportion of the N content in old leaves than in young leaves and increased with age in the former, but not in the latter. Relative to soil N, fertilizer derived N also contributed more to the N content of vegetative than to that of reproductive shoot components. Small net changes in shoot N content after flowering reflected a balance between N import and export, leading to continuous dilution of 15N labelled N with unlabelled N.  相似文献   

20.
Young saplings of Pinus sylvestris L. were exposed to gaseous NH3 at 53 or 105 g m–3 for one year in open-top chambers. Saplings received 15N-labelled (NH4)2SO4 via the soil. To examine the importance of foliar N uptake, changes in the concentration of total and labelled N in the needles were followed. Increase in needle biomass and N concentration were found in trees exposed to NH3, confirming that atmospheric NH3 acted as a N fertilizer. NH3 had a greater and quicker effect than (NH4)2SO4: compared with the growth in ambient air, the N concentration in the needles exposed to NH3 had increased by 49% in four months, while the increase after highest N-fertilization (200 kg N ha–1 y–1) was only 8%. The small contribution of NH4 + fertilization to the total N concentration was not due to a deficient N uptake: the 15N concentration in the needles increased significantly with time. On the other hand, NH3 uptake in shoots may have a negative effect on the NH4 + root uptake. The relation between plant N and atmospheric NH3 concentration was non-linear and possible reasons for this observation are discussed. Fumigation with NH3 significantly decreased the ratios of K/N and P/N, showing that fumigation disrupted the nutrient balance.  相似文献   

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