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1.
Information on N cycling in dryland crops and soils as influenced by long-term tillage and cropping sequence is needed to quantify soil N sequestration, mineralization, and N balance to reduce N fertilization rate and N losses through soil processes. The 21-yr effects of the combinations of tillage and cropping sequences was evaluated on dryland crop grain and biomass (stems + leaves) N, soil surface residue N, soil N fractions, and N balance at the 0–20 cm depth in Dooley sandy loam (fine-loamy, mixed, frigid, Typic Argiboroll) in eastern Montana, USA. Treatments were no-tilled continuous spring wheat (Triticum aestivum L.) (NTCW), spring-tilled continuous spring wheat (STCW), fall- and spring-tilled continuous spring wheat (FSTCW), fall- and spring-tilled spring wheat–barley (Hordeum vulgare L.) (1984–1999) followed by spring wheat–pea (Pisum sativum L.) (2000–2004) (FSTW-B/P), and spring-tilled spring wheat–fallow (STW-F). Nitrogen fractions were soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), potential N mineralization (PNM), NH4-N, and NO3-N. Annualized crop grain and biomass N varied with treatments and years and mean grain and biomass N from 1984 to 2004 were 14.3–21.2 kg N ha−1 greater in NTCW, STCW, FSTCW, and FSTW-B/P than in STW-F. Soil surface residue N was 9.1–15.2 kg N ha−1 greater in other treatments than in STW-F in 2004. The STN at 0–20 cm was 0.39–0.96 Mg N ha−1, PON 0.10–0.30 Mg N ha−1, and PNM 4.6–9.4 kg N ha−1 greater in other treatments than in STW-F. At 0–5 cm, STN, PON, and MBN were greater in STCW than in FSTW-B/P and STW-F. At 5–20 cm, STN and PON were greater in NTCW and STCW than in STW-F, PNM and MBN were greater in STCW than in NTCW and STW-F, and NO3-N was greater in FSTW-B/P than in NTCW and FSTCW. Estimated N loss through leaching, volatilization, or denitrification at 0–20 cm depth increased with increasing tillage frequency or greater with fallow than with continuous cropping and ranged from 9 kg N ha−1 yr−1 in NTCW to 46 kg N ha−1 yr−1 in STW-F. Long-term no-till or spring till with continuous cropping increased dryland crop grain and biomass N, soil surface residue N, N storage, and potential N mineralization, and reduced N loss compared with the conventional system, such as STW-F, at the surface 20 cm layer. Greater tillage frequency, followed by pea inclusion in the last 5 out of 21 yr in FSTW-B/P, however, increased N availability at the subsurface layer in 2004.  相似文献   

2.
Core lysimeters containing undisturbed coarse sandy soil (from grassland) were amended with a high rate of anaerobically digested sewage sludge (equivalent to >1,000 t ha–1). Water, at a rate equivalent to the mean weekly rainfall for the soil, was applied to amended and control lysimeters for 30 weeks and the leachate analysed for anions and cations. Lysimeters were also destructively sampled at intervals throughout the experiment and soil samples were analysed for extractable NH4+-N, NO3–-N and PO43–-P. Ammonium N leached for about 11 weeks from the amended lysimeters, then abruptly stopped. A similar amount of NO3–-N leached, but leaching was continuing when the experiment finished. The control lysimeters leached as much NO3–-N as those that were amended, but no NH4+-N. The amended lysimeters also leached NO2–-N. Negligible PO43–-P, but large amounts of SO42– were leached from the amended lysimeters. Concentrations of extractable NH4+-N and PO43–-P were very high in the amended soils, but NO3–-N concentrations remained low throughout the experiment, indicating that nitrification rates were low and/or that denitrification rates were high.  相似文献   

3.
土地混合使用制度下土壤硝态氮分布的地理空间制图研究   总被引：5，自引：0，他引：5  
Mapping the spatial distribution of soil nitrate-nitrogen (NO3-N) is important to guide nitrogen application as well as to assess environmental risk of NO3-N leaching into the groundwater. We employed univariate and hybrid geostatistical methods to map the spatial distribution of soil NO3-N across a landscape in northeast Florida. Soil samples were collected from four depth increments (0-30, 30-60, 60-120 and 120-180 cm) from 147 sampling locations identified using a stratified random and nested sampling design based on soil, land use and elevation strata. Soil NO3-N distributions in the top two layers were spatially autocorrelated and mapped using lognormal kriging. Environmental correlation models for NO3-N prediction were derived using linear and non-linear regression methods, and employed to develop NO3-N trend maps. Land use and its related variables derived from satellite imagery were identified as important variables to predict NO3-N using environmental correlation models. While lognormal kriging produced smoothly varying maps, trend maps derived from environmental correlation models generated spatially heterogeneous maps. Trend maps were combined with ordinary kriging predictions of trend model residuals to develop regression kriging prediction maps, which gave the best NO3-N predictions. As land use and remotely sensed data are readily available and have much finer spatial resolution compared to field sampled soils, our findings suggested the effcacy of environmental correlation models based on land use and remotely sensed data for landscape scale mapping of soil NO3-N. The methodologies implemented are transferable for mapping of soil NO3-N in other landscapes.  相似文献   

4.
Soil and crop management practices may alter the quantity, quality, and placement of plant residues that influence soil C and N fractions. We examined the effects of two tillage practices [conventional till (CT) and no-till (NT)] and five crop rotations [continuous spring wheat (Triticum aestivum L.) (CW), spring wheat–fallow (W–F), spring wheat–lentil (Lens culinaris Medic.) (W–L), spring wheat–spring wheat–fallow (W–W–F), and spring wheat–pea (Pisum sativum L.)–fallow (W–P–F)] on transient land previously under 10 years of Conservation Reserve Program (CRP) planting on the amount of plant biomass (stems + leaves) returned to the soil from 1998 to 2003 and soil C and N fractions within the surface 20 cm in March 2004. A continued CRP planting was also included as another treatment for comparing soil C and N fractions. The C and N fractions included soil organic C (SOC), soil total N (STN), microbial biomass C and N (MBC and MBN), potential C and N mineralization (PCM and PNM), and NH4-N and NO3-N contents. A field experiment was conducted in a mixture of Scobey clay loam (fine-loamy, mixed, Aridic Argiborolls) and Kevin clay loam (fine, montmorillonitic, Aridic Argiborolls) in Havre, MT, USA. Plant biomass yield varied by crop rotation and year and mean annualized biomass was 45–50% higher in CW and W–F than in W–L. The SOC and PCM were not influenced by treatments. The MBC at 0–5 cm was 26% higher in W–W–F than in W–F. The STN and NO3-N at 5–20 cm and PNM at 0–5 cm were 17–1206% higher in CT with W–L than in other treatments. Similarly, MBN at 0–5 cm was higher in CT with W–L than in other treatments, except in CT with W–F and W–P–F. Reduction in the length of fallow period increased MBC and MBN but the presence of legumes, such as lentil and pea, in the crop rotation increased soil N fractions. Six years of tillage and crop rotation had minor influence on soil C and N storage between croplands and CRP planting but large differences in active soil C and N fractions.  相似文献   

5.
坡缕石包膜对尿素氮行为的影响   总被引：2，自引：1，他引：2  
采用静态吸收和土柱淋溶试验方法,分析对比了3种不同用量坡缕石包膜尿素与普通尿素施入土壤后对尿素氮行为的影响,结果表明:在土壤中施用坡缕石包膜尿素较普通尿素减少10.38%～26.24%的氨挥发损失,减少5.88%～27.74%的氮素(NO3--N+NH4+-N)淋溶损失,20%的坡缕石包膜尿素能显著提高土柱土壤NH4+-N含量,3种坡缕石包膜尿素都能极显著提高土柱土壤NO3--N含量.坡缕石包膜后能减少尿素氨的挥发,降低NH4+-N和NO3--N的淋失,提高土壤NH4+-N和NO3--N含量,以20%的坡缕石包膜尿素的综合生态效应最好.  相似文献   

6.
Extraction of soil nitrate nitrogen (NO3 ?-N) and ammonium nitrogen (NH4 +-N) by chemical reagents and their determinations by continuous flow analysis were used to ascertain factors affecting analysis of soil mineral N. In this study, six factors affecting extraction of soil NO3 ?-N and NH4 +-N were investigated in 10 soils sampled from five arable fields in autumn and spring in northwestern China, with three replications for each soil sample. The six factors were air drying, sieve size (1, 3, and 5 mm), extracting solution [0.01 mol L?1 calcium chloride (CaCl2), 1 mol L?1 potassium chloride (KCl), and 0.5 mol L?1 potassium sulfate (K2SO4)] and concentration (0.5, 1, and 2 mol L?1 KCl), solution-to-soil ratio (5:1, 10:1, and 20:1), shaking time (30, 60, and 120 min), storage time (2, 4, and 6 weeks), and storage temperature (?18 oC, 4 oC, and 25 oC) of extracted solution. The recovery of soil NO3 ?-N and NH4 +-N was also measured to compare the differences of three extracting reagents (CaCl2, KCl, and K2SO4) for NO3 ?-N and NH4 +-N extraction. Air drying decreased NO3 ?-N but increased NH4 +-N concentration in soil. Soil passed through a 3-mm sieve and shaken for 60 min yielded greater NO3 ?-N and NH4 +-N concentrations compared to other treatments. The concentrations of extracted NO3 ?-N and NH4 +-N in soil were significantly (P < 0.05) affected by extracting reagents. KCl was found to be most suitable for NO3 ?-N and NH4 +-N extraction, as it had better recovery for soil mineral N extraction, which averaged 113.3% for NO3 ?-N and 94.9% for NH4 +-N. K2SO4 was not found suitable for NO3 ?-N extraction in soil, with an average recovery as high as 137.0%, and the average recovery of CaCl2 was only 57.3% for NH4 +-N. For KCl, the concentration of extracting solution played an important role, and 0.5 mol L?1 KCl could fully extract NO3 ?-N. A ratio of 10:1 of solution to soil was adequate for NO3 ?-N extraction, whereas the NH4 +-N concentration was almost doubled when the solution-to-soil ratio was increased from 5:1 to 20:1. Storage of extracted solution at ?18 °C, 4 °C, and 25 °C had no significant effect (P < 0.05) on NO3 ?-N concentration, whereas the NH4 +-N concentration varied greatly with storage temperature. Storing the extracted solution at ?18 oC obtained significantly (P < 0.05) similar results with that determined immediately for both NO3 ?-N and NH4 +-N concentrations. Compared with the immediate extraction, the averaged NO3 ?-N concentration significantly (P < 0.05) increased after storing 2, 4, and 6 weeks, respectively, whereas NH4 +-N varied in the two seasons. In conclusion, using fresh soil passed through a 3-mm sieve and extracted by 0.5 mol L?1 KCl at a solution-to-soil ratio of 10:1 was suitable for extracting NO3 ?-N, whereas the concentration of extracted NH4 +-N varied with KCl concentration and increased with increasing solution-to-soil ratio. The findings also suggest that shaking for 60 min and immediate determination or storage of soil extract at ?18 oC could improve the reliability of NO3 ?-N and NH4 +-N results.  相似文献   

7.
After removal of the above-ground plant debris three different soil layers were taken from a typical coniferous forest and its adjacent orchard in Numata City, Japan. The potentials of soil CH4 uptake at two initial CH4 concentrations were studied under aerobic conditions in the laboratory, along with inhibition of soil CH4 oxidation by urea-N or KNO3-N addition. Due to long-term N inputs, the CH4 uptake of the upper mineral layer of the orchard soil was 25.4% and 87.7% lower than that of the surface forest soil at 2.4 and 12.6 l l–1 CH4, respectively. Methane uptake of the forest soil decreased with increasing soil depths at two CH4 levels. However, maximal CH4-consuming activity occurred in the 9- to 23-cm depth of the orchard soil at 12.6 l l–1 methane. Nitrogen additions in the form of KNO3 or urea at the rate of 200 g N g–1 soil substantially reduced soil CH4 uptake in the upper and sub-surface mineral layers at both sites, except that the addition of KNO3-N had no apparent inhibitory effect on the CH4 uptake in the 9- to 23-cm depth of the orchard soil. A strong inhibitory effect of NO3– addition on the CH4 uptake, in contrast to NH4+, occurred in the surface forest soil. The use of KNO3-N, as compared to urea or urea plus a nitrification inhibitor (dicyandiamide), resulted in a lower potential to cause inhibition of CH4 oxidation in the 0- to 23-cm depth of the orchard soil.  相似文献   

8.
Improved fallows with leguminous trees have been developed in Southern Africa as a viable alternative to inorganic fertilizers but the changes in soil properties that are responsible for crop productivity improvement and implications of mixing litter and fresh leaves from the same tree species on soil fertility are not fully understood. Our objectives were to quantify (1) some changes in soil properties that are responsible for crop production improvement under improved fallow systems; (2) the N mineralization patterns of mixtures of litter and fresh leaves from the same tree species. The treatments used in the study were 2-year planted Sesbania sesban (sesbania) and Cajanus cajan (cajanus) and controls of natural fallow, continuous fertilized and unfertilized maize. At fallow clearing sesbania contributed 56 kg N ha–1 through litter and fresh leaves. Sesbania (fresh leaves + litter) showed high N mineralization after 10 weeks compared to the mixture of cajanus fresh leaves with litter. Maize yields were significantly correlated with preseason NO3–-N and total inorganic-N content of the top 20-cm soil layer. Soil penetrometer resistance at 4 weeks after planting was lowest in the sesbania land-use system (2.2 Mpa), whereas the highest percentage of water-stable aggregates at fallow clearing and crop harvest was in sesbania (83%) and cajanus (77%), respectively. The improved soil conditions and N contribution of sesbania and cajanus fallows to the subsequent maize crop was evidenced by increased maize yields of between 170–200% over maize without fertilizer.  相似文献   

9.
Availability and leaching of dissolved inorganic N (DIN = NH4+ + NO3-) in soil were measured in a periodically flooded forest of the Central Amazon floodplain (várzea) during one terrestrial phase. Special emphasis was on the effects of a legume and a non-legume tree species. NH4+-N accounted for more than 85% of DIN even at the end of the terrestrial phase although it decreased throughout the experimental period. While extractable NO3–-N was always low in the soil (less than 15% of DIN), the amount of leached NO3–-N was in the same range as NH4+-N. Under the legume trees mean DIN contents of the topsoil were higher than under the non-legume trees. DIN leaching from the topsoil (0–20 cm) was significantly higher under the legume trees than at the other sites, also indicating a higher N availability. Therefore, despite considerable leaching legume trees may be an important source of N supporting a high biomass production of the várzea forest.  相似文献   

10.
Soil nitrogen mineralization as affected by water and temperature interactions   总被引：10，自引：0，他引：10  
Summary The hypothesis that water and temperature interact to influence the rate of soil N mineralization was studied in laboratory incubation experiments with two contrasting soils. Small sample rings (10 mm tall, 50 mm diameter) were packed to uniform bulk density with 1–2 mm aggregates of Plano silt loam and Wacousta silty clay loam. Samples were brought to five different water potentials (–0.1, –0.33, –0.5, –1.0, –3.0 bars) using pressure-plate techniques, and the undisturbed sample rings were then incubated at 10–35°C for 3, 10 or 14 days. The concentration of soil exchangeable NH4 +-N and NO3 –-N was measured at the end of each incubation period on replicate samples. The Q10 of N mineralization was approximately 2 for all tested water potentials. Soil N mineralization was linearly related to water content or log water potential, but no water-temperature interaction was evident. The Q10 was constant with water content, and the scaled water content-N mineralization relationship was constant with temperature. We recommend the use of scaling approaches for assessing interactive effects between water and other environmental factors on N turnover in soils.  相似文献   

11.
In the coastal sage scrub (CSS) community of southern California, Artemisia californica and other native shrubs are gradually being replaced by invasive annual grasses, especially Bromus madritensis ssp. rubens. This decline may be attributed, in part, to local atmospheric N deposition, which causes elevated soil NO3 –. Unaffected soils have low N with a relatively higher concentration of NH4 + than NO3 –. The objectives in this study were: (1) to compare the short-term uptake of 15NO3 – and 15NH4 + by B. madritensis and A. californica and (2) to discern whether 15NO3 – or 15NH4 + uptake is influenced by the mycorrhizal status of either plant species. Analysis of 15N concentrations indicated that both A. californica and B. madritensis took up more 15NO3 – than 15NH4 +, but overall, B. madritensis took up 6–15 times more of both forms of 15N than A. californica. Mycorrhizal A. californica had an increased 15NH4 + concentration in roots but not shoots. In B. madritensis, the only mycorrhizal response was a reallocation of 15NO3 –, with mycorrhizal plants retaining a higher proportion of 15NO3 – in roots. Overall, arbuscular mycorrhizae had a small effect on 15N uptake in this short-term study. However, the ability of B. madritensis to take up so much 15N may explain in part why it has been so successful in replacing A. californica in CSS.  相似文献   

12.
The aim of the study was to determine the effect of adding two tropical earthworm species, Rhinodrilus contortus and Pontoscolex corethrurus, to mesocosms on the availability of mineral N (NH4 + and NO3 – concentrations), soil microbial biomass (bio-N), and the decomposition rates of three contrasting leaf litter species, in a glasshouse experiment. The mesocosms were filled with forest soil and covered with a layer of leaf litter differing in nutritional quality: (1) Hevea brasiliensis (C/N=27); (2) Carapa guianensis (C/N=32); (3) Vismia sp., the dominant tree species in the second growth forest (control, C/N= 42); and, (4) a mixture of the former three leaf species, in equal proportions (C/N=34). At the end of the 97-day experiment, the soil mineral N concentrations, bio-N, and leaf litter weight loss were determined. Both earthworm species showed significant effects on the concentrations of soil NO3 – (p<0.01) and NH4 + (p<0.05). Bio-N was always greater in the mesocosms with earthworms (especially with R. contortus) and in the mesocosms with leaf litter of H. brasiliensis (6 µg N g–1 soil), the faster decomposing species, than in the other treatments (0.1–1.6 µg N g–1). Thus, earthworm activity increased soil mineral-N concentrations, possibly due to the consumption of soil microbial biomass, which can speed turnover and mineralization of microbial tissues. No significant differences in decomposition rate were found between the mesocosms with and without earthworms, suggesting that experiments lasting longer are needed to determine the effect of earthworms on litter decomposition rates.  相似文献   

13.
Fertilization produces many nutrient patches that have been confirmed to affect root growth. However, it is not clear how nutrient transformation and microbial community composition are affected in an inorganic nutrient patch. In this experiment, a nitrogen enrichment patch was formed by the diffusion of a urea fertilizer layer in a specially-designed container. Responses of nitrogen transformation and microbial community composition to the nitrogen enrichment patch were investigated at different incubation times. Results showed that nitrogen status and microbial community composition were slightly affected in the control patch (CK patch). In the nitrogen enrichment patch, however, soil pH was significantly increased in most soil layers close to the urea fertilizer layer; NO2−-N was the predominant form of mineral N, and its transformation to NO3−-N was delayed. Microbial community composition shifted significantly, especially before day 28 of incubation. Principal components analysis (PCA) of phospholipid fatty acids (PLFAs) patterns showed that the microbial community presented different sensitivity to high nitrogen concentration. Fungi (18:2ω6,9) showed the least sensitivity to high concentrations of NO2−-N and NO3−-N. Gram-positive bacteria showed the most sensitivity to NO2−-N. Gram-negative bacteria (cy17:0, cy19:0, 18:1ω9, and 18:1ω7) and actinomycetes (10Me17:0 and 10Me18:0) presented similar responses to NO2−-N and NO3−-N. Results of this study indicate that changes in nitrogen transformation and microbial community composition are likely to occur in nitrogen enrichment patches, but the extent of those changes depend on the microbial species and the distance of soil layers from the urea layer.  相似文献   

14.
 The objectives of this work were to evaluate the inhibitory action on nitrification of 3,4-dimethylpyrazole phosphate (DMPP) added to ammonium sulphate nitrate [(NH4)2SO4 plus NH4NO3; ASN] in a Citrus-cultivated soil, and to study its effect on N uptake. In a greenhouse experiment, 2 g N as ASN either with or without 0.015 g DMPP (1% DMPP relative to NH4 +-N) was applied 6 times at 20-day intervals to plants grown in 14-l pots filled with soil. Addition of DMPP to ASN resulted in higher levels of NH4 +-N and lower levels of NO3 –-N in the soil during the whole experimental period. The NO3 –-N concentration in drainage water was lower in the ASN plus DMPP (ASN+DMPP)-treated pots. Also, DMPP supplementation resulted in greater uptake of the fertilizer-N by citrus plants. In another experiment, 100 g N as ASN, either with or without 0.75 g DMPP (1% DMPP relative to NH4 +-N) was applied to 6-year-old citrus plants grown individually outdoors in containers. Concentrations of NH4 +-N and NO3 –-N at different soil depths and N distribution in the soil profile after consecutive flood irrigations were monitored. In the ASN-amended soil, nitrification was faster, whereas the addition of the inhibitor led to the maintenance of relatively high levels of NH4 +-N and NO3 –-N in soil for longer than when ASN was added alone. At the end of the experiment (120 days) 68.5% and 53.1% of the applied N was leached below 0.60 m in the ASN and ASN+DMPP treatments, respectively. Also, leaf N levels were higher in plants fertilized with ASN+DMPP. Collectively, these results indicate that the DMPP nitrification inhibitor improved N fertilizer efficiency and reduced NO3 – leaching losses by retaining the applied N in the ammoniacal form. Received: 31 May 1999  相似文献   

15.
Summary Mineral-N dynamics have been measured over a period of 3 years in PK- and NPK-treated plots (4 m2) laid out on an area of poorly drained, reseeded, blanket peat in the north of Scotland. Mineral-N, present in the peat almost entirely as NH in4 sup+ , accumulated in winter, reaching 42 kg N ha–1 in the surface 10 cm in April before the application of 112.5 kg N ha–1 as NH4NO3 or urea. In situ incubation of peat cores isolated to prevent leaching, and with grass tops removed, confirmed that net mineralization occurred between November and April, with the greatest rate, 1.2 kg N ha–1 day–1, recorded between March and April. During the period May to early June, immobilization of N predominated and rates of net immobilization ranged between 0.2 and 0.8 kg N ha–1 day–1. This coincided with a poor uptake into herbage, less than 16% of soil mineral N and fertilizer NH4NO3 in June of the first 2 years. The largest counts (most probable number) of ammonifying bacteria in the surface 5 cm were recorded in July for aerobes (27.1×109 litre–1) and August for anaerorbes (7.1×109 litre–1). N fertilizer increased these counts significantly (P<0.05) to 56×109 aerobes and 13×109 anaerobes. During July and August, in 2 out of the 3 years, mineralization predominated over immobilization and mean net rates of up to 0.9 kg N ha–1 were recorded.  相似文献   

16.
The restoration of drained peat bogs in Northwest (NW) Europe is an important task of soil protection, but needs to cope with warmer and drier summers. Our examination took place in the Pietzmoor bog (Schneverdingen, NW Germany) that had been drained for fuel peat extraction until the 1970s and rewetted since then. We determined carbon dioxide (CO2) efflux in situ and in laboratory incubations. Also, we analyzed pore water for dissolved organic carbon (DOC), total and dissolved organic N (DON), nitrate (NO3–) and ammonium (NH4+) concentration. In Schneverdingen, the summer 2003 was record-breaking hot (mean temperature June to August elevated > 3 K compared to long-term average) and dry (precipitation during the same period < 59% of long-term average). In July 2003, the water table in the Pietzmoor subsided to > 42 cm below the surface in July 2003, when in situ soil CO2 efflux was up to 23.4 g m–2 d–1 compared to 15.7 g m–2 d–1 in September. Prior to March 2003, DOC concentrations in pore water were < 180 mg l–1 and NH4+ was the dominant fraction of mineral N. In July 2003, DOC concentration rose to 249 g l–1, DON concentrations more than doubled, and NO3– became the dominant fraction of mineral N. Due to the increased future likelihood of hot and dry summers in NW Germany, peat bog restoration efforts need take care that a water table close to the surface is maintained.  相似文献   

17.
A laboratory incubation experiment was conducted to demonstrate that reduced availability of CO2 may be an important factor limiting nitrification. Soil samples amended with wheat straw (0%, 0.1% and 0.2%) and (15NH4)2SO4 (200 mg N kg–1 soil, 2.213 atom% 15N excess) were incubated at 30±2°C for 20 days with or without the arrangement for trapping CO2 resulting from the decomposition of organic matter. Nitrification (as determined by the disappearance of NH4+ and accumulation of NO3–) was found to be highly sensitive to available CO2 decreasing significantly when CO2 was trapped in alkali solution and increasing substantially when the amount of CO2 in the soil atmosphere increased due to the decomposition of added wheat straw. The co-efficient of correlation between NH4+-N and NO3–-N content of soil was highly significant (r =0.99). During incubation, 0.1–78% of the applied NH4+ was recovered as NO3– at different incubation intervals. Amendment of soil with wheat straw significantly increased NH4+ immobilization. From 1.6% to 4.5% of the applied N was unaccounted for and was due to N losses. The results of the study suggest that decreased availability of CO2 will limit the process of nitrification during soil incubations involving trapping of CO2 (in closed vessels) or its removal from the stream of air passing over the incubated soil (in open-ended systems).  相似文献   

18.
华北山前平原农田土壤硝态氮淋失与调控研究   总被引：11，自引：5，他引：6  
本文依托中国科学院栾城农业生态系统试验站小麦-玉米一年两熟长期定位试验, 应用土钻取土和土壤溶液取样器取水的方法, 研究了不同农田管理措施下土壤硝态氮的累积变化, 计算了不同氮肥处理通过根系吸收层的硝态氮淋失通量。结果表明, 小麦-玉米生长季土壤硝态氮累积量和淋失量随着施氮量的增加显著增加, 相同氮肥水平下增施磷、钾肥增加了作物的收获氮量, 施磷肥增加的作物收获氮量最高可达123kg·hm-2·a-1, 施钾肥增加的作物收获氮量最高为31 kg·hm-2·a-1。不同灌溉水平下0~400 cm 土体累积硝态氮随着灌溉量的增加而降低, 控制灌溉(小麦季不灌水, 玉米季灌溉1 水)、非充分灌溉(小麦季灌溉2~3 水, 玉米季按需灌溉)、充分灌溉(小麦季灌溉4~5 水, 玉米季按需灌溉)各处理剖面累积硝态氮量分别为1 698 kg·hm-2、1148 kg·hm-2 和961 kg·hm-2。与非充分灌溉和充分灌溉处理相比, 控制灌溉在100~200 cm 土层硝态氮累积量显著高于其他层次, 2003~2005 年间控制灌溉剖面增加的硝态氮量占施肥总量的23%; 非充分灌溉处理剖面增加的硝态氮量占施肥总量的22%; 充分灌溉处理剖面增加的硝态氮量占施肥总量的47%。免耕措施降低了作物产量, 影响土壤水的运移, 增加了硝态氮的淋失风险。根据作物所需降低氮素投入(N 200 kg·hm-2·a-1), 增施磷、钾肥, 控制灌溉量是减少华北山前平原地区硝态氮淋失, 保护地下水的有效措施。  相似文献   

19.
 Efficient N-fertiliser management during the corn (Zea mays L.) phase in corn-forage rotation requires information on temporal dynamics of N release from forage biomass. The influence of forage phase, in corn-forage rotation, and no- versus conventional-till on (1) in situ temporal dynamics of soil nitrate-N (NO3-N) during corn phase and (2) corn grain yield was investigated in this study. The data used were collected from a crop rotation (corn-forage) experiment, with superimposed tillage treatments, established on a silt loam soil in 1988 and continued until 1994. The cropping treatments were continuous conventionally cultivated (CT) corn, rotations involving corn and forages (alfalfa, Medicago sativa L.; and bromegrass, Bromus inermis L.) and continuous minimally tilled corn with under-seeded red clover (Trifolium pratense L.). The forages were grown for 6 years and corn was re-introduced in these plots under no- and conventional-till systems. Soil NO3-N in the top 30 cm depth, determined six times during the corn phase, was significantly influenced by previous forage species and tillage system. Regression analysis indicated soil NO3-N under continuous CT corn did not show significant temporal changes. In the rotations, soil NO3-N after tillage or herbicide treatment, i.e. in no-till, increased with time until 45 days after tillage (DAT), reached a plateau between 45 and 65 DAT, and then decreased with time. During the plateau, soil NO3-N in rotation plots ranged from 17 to 33 mg kg–1 compared to 15.7 mg kg–1 in the continuous CT corn. Tillage increased soil NO3-N concentration in alfalfa plots whereas an opposite trend existed in the bromegrass plots. Soil NO3-N in the rotation plots increased at rates ranging from 0.71 to 1.63 mg kg–1 day–1. The interaction involving forage species and the temporal dynamics of soil NO3-N accounted for 68–77% of variability in corn grain yield. Received: 14 July 1998  相似文献   

20.
 The within-field variability of soil mineral nitrogen (Nmin) in a grazed grassland of 8000 m2 was examined. NO3 –-N concentrations were characterized by a high spatial variability. This can be explained by the uneven deposition of animal excreta. All NH4 +-N as well as NO3 –-N values were lognormally distributed, before and after the grazing season. At the end of the grazing season the largest part of the variability of NO3 –-N was found for NO3 –-N concentrations measured within a distance of a few metres. A high variability for NO3 –-N over very short distances was also indicated by a large nugget variance. During the grazing season, observed mean Nmin values increased from 22 to 132 kg N ha–1. Regions with clearly higher NO3 –-N concentrations could be identified. These zones matched with the drinking place and the entrance of the pasture, places which were more frequently visited than others. High residual N levels in autumn led to relatively high losses of N, mostly by leaching, during the subsequent drainage period. Knowing the variability of Nmin, the number of samples needed to estimate the average Nmin in a field could be calculated for different probabilities and various degrees of precision. From the spatial distribution of the Nmin concentrations and the restrictions imposed by the new European decree, adapted fertilizer strategies can be proposed at least for places where systematically higher Nmin concentrations can be expected. Received: 14 December 1999  相似文献   

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