首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
Maintaining and/or conserving organic carbon (C) and nitrogen (N) concentrations in the soil using management practices can improve its fertility and productivity and help to reduce global warming by sequestration of atmospheric CO2 and N2. We examined the influence of 6 years of tillage (no-till, NT; chisel plowing, CP; and moldboard plowing, MP), cover crop (hairy vetch (Vicia villosa Roth.) vs. winter weeds), and N fertilization (0, 90, and 180 kg N ha−1) on soil organic C and N concentrations in a Norfolk sandy loam (fine-loamy, siliceous, thermic, Typic Kandiudults) under tomato (Lycopersicon esculentum Mill.) and silage corn (Zea mays L.). In a second experiment, we compared the effects of 7 years of non-legume (rye (Secale cereale L.)) and legume (hairy vetch and crimson clover (Trifolium incarnatum L.)) cover crops and N fertilization (HN (90 kg N ha−1 for tomato and 80 kg N ha−1 for eggplant)) and FN (180 kg N ha−1 for tomato and 160 kg N ha−1 for eggplant)) on soil organic C and N in a Greenville fine sandy loam (fine-loamy, kaolinitic, thermic, Rhodic Kandiudults) under tomato and eggplant (Solanum melogena L.). Both experiments were conducted from 1994 to 2000 in Fort Valley, GA. Carbon concentration in cover crops ranged from 704 kg ha−1 in hairy vetch to 3704 kg ha−1 in rye in 1999 and N concentration ranged from 77 kg ha−1 in rye in 1996 to 299 kg ha−1 in crimson clover in 1997. With or without N fertilization, concentrations of soil organic C and N were greater in NT with hairy vetch than in MP with or without hairy vetch (23.5–24.9 vs. 19.9–21.4 Mg ha−1 and 1.92–2.05 vs. 1.58–1.76 Mg ha−1, respectively). Concentrations of organic C and N were also greater with rye, hairy vetch, crimson clover, and FN than with the control without a cover crop or N fertilization (17.5–18.4 vs. 16.5 Mg ha−1 and 1.33–1.43 vs. 1.31 Mg ha−1, respectively). From 1994 to 1999, concentrations of soil organic C and N decreased by 8–16% in NT and 15–25% in CP and MP. From 1994 to 2000, concentrations of organic C and N decreased by 1% with hairy vetch and crimson clover, 2–6% with HN and FN, and 6–18% with the control. With rye, organic C and N increased by 3–4%. Soil organic C and N concentrations can be conserved and/or maintained by reducing their loss through mineralization and erosion, and by sequestering atmospheric CO2 and N2 in the soil using NT with cover crops and N fertilization. These changes in soil management improved soil quality and productivity. Non-legume (rye) was better than legumes (hairy vetch and crimson clover) and N fertilization in increasing concentrations of soil organic C and N.  相似文献   

2.
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   

3.
Summary Long-term experiments (97–98 weeks) were carried out in macrocosm systems simulating the complexity of coniferous forest soil. The macrocosms were partially sterilized by freezing, thawing and drying, then re-inoculated with microbes alone or microbes + soil fauna. Removable microcosms containing birch litter, spruce litter, or humus were inserted into the substrate humus in the macrocosms. Two experiments used organic matter only, and in the third there was mineral soil below the humus. The macrocosms were incubated in climate chambers that simulated both summer and winter conditions. At 4- to 6-week intervals the substrates were irrigated for analyses of pH, total N, NH 4 + –N, NO 3 – –N, and PO 4 3– –P in the leachates. At the end of each growing season a destructive sampling was performed, including analyses of KCl-extractable N and P.Leaching of NH 4 + and PO 4 3– from both the litter and the total systems was significantly enhanced by the soil fauna. There were also differences in mineralization of N and P between the refaunated systems, apparently due to divergent development of the faunal communities. In general, fauna affected KCl-extractable nutrients from the litter positively, although this effect was less evident than in the leaching water. In the humus and mineral soil the fauna significantly increased the release of N and P, especially in the later stages of the experiments. Soil pH was higher in the presence of fauna, but there was no difference in the pH of the leachates. Not only invertebrate-microbial interactions, but also mutual relationships among fauna were important in the nutrient dynamics.  相似文献   

4.
Summary The chloroform fumigation-incubation method (CFIM) was used to measure the microbial biomass of 17 agricultural soils from Punjab Pakistan which represented different agricultural soil series. The biomass C was used to calculate biomass N and the changes occurring in NH4 +-N and NO3 –-N content of soils were studied during the turnover of microbial biomass or added C source. Mineral N released in fumigated-incubated soils and biomass N calculated from biomass C was correlated with some N availability indexes.The soils contained 427–1240 kg C as biomass which represented 1.2%–6.9% of the total organic C in the soils studied. Calculations based on biomass C showed that the soils contained 64–186 kg N ha–1 as microbial biomass. Immobilization of NCO3 –-N was observed in different soils during the turnover of microbial biomass and any net increase in mineral N content of fumigated incubated soils was attributed entirely to NH4 +-N.Biomass N calculated from biomass C showed non-significant correlation with different N availability indexes whereas mineral N accumulated in fumigated-incubated soils showed highly significant correlations with other indexes including N uptake by plants.  相似文献   

5.
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   

6.
Under a Mediterranean climate, denitrification losses were quantified for 2 years on a sandy loam soil with an irrigated maize crop. The effect of pig slurry application at two different rates (165 and 495 kg N ha–1, respectively, for PS1 and PS3) was compared with that of urea (U) applied at 165 kg N ha–1 and with a control treatment (P0) without fertilizer. After application, the denitrification rate (DR) increased in PS1 and PS3 respect to P0 and decreased to the levels of the control treatment after 5 days. In July and August (the irrigation period) the DR increased considerably in all treatments with maximum values for the PS3 treatment (0.134 g N m–2 day–1 in the first year and 0.147 g N m–2 day–1 in the second year). The differences in DRs between each treatment could be explained by the pattern of water filled pore space, NO3– concentration of the soil solution and the soil temperature during the maize growing season. In the first year denitrification losses in the 0–10 cm layer were 1.90, 2.49, 2.87 and 4.00 g N m–2 for P0, U, PS1 and PS3, respectively, while in the second year the losses were 1.21, 2.28, 2.47 and 3.42 g N m–2. Finally, a simple predictive model (SOILN) was evaluated and found to give acceptable results.  相似文献   

7.
Samples of strongly acid forest litter and humus from beneath Sitka spruce, heather, Scots pine and larch from two sites in north-east Scotland were incubated aerobically at 20°C in the laboratory. At the Glen Tanar site, spruce litter and larch humus showed significant nitrification and ammonification whereas spruce humus and Scots pine humus produced only NH4+-N. Heather humus showed no net mineralization. At the Fetteresso site, application of fertilizer N, P and K to Sitka spruce up to 3 yr previously, significantly stimulated the production of NO3−-N in both litter and humus.Amendment of the samples with organic N as peptone caused significant increases in NO3−-N production in those samples that already showed nitrification. The increases in NO3−-N generally represented a low proportion of the added peptone-N. Amendment with NH4+-N as (NH4)2SO4 either had no effect or significantly reduced NO3−-N production (in larch humus). The results suggest the occurrence of heterotrophic nitrification in some of these forest samples.Net immobilization of NH4+-N was typically greater in NH4+-N amended than in peptone amended samples, except for heather humus which showed complete immobilization of both N sources.Total mineral N produced at the end of the aerobic incubation was correlated (P < 0.01) with NH4+-N produced during a 30-day anaerobic incubation at 30°C. Net NO3−-N production was greater in litter than in the corresponding humus samples and was correlated (P < 0.001) with initial organic N soluble in 1 m KCl.  相似文献   

8.
Crop rotations and tillage practices influence the quantity and quality of soil organic N (SON). We evaluated the impact of crop rotations and tillage practices on SON and mineralizable N at a depth of 0–15 cm in six field experiments, varying in duration over 8–25 years, that were being conducted in three Chernozemic soil zones in Saskatchewan, Canada. In a Brown Chernozem, continuous wheat increased SON at 0–15 cm by 7–17 kg N ha–1year–1 more than fallow/wheat. In a Dark Brown Chernozem, continuous cropping increased SON by 30 kg N ha–1year–1, compared with cropping systems containing fallow once every 3 years; and, in a Rego Black Chernozem, the increase in SON was 29 kg N ha–1 year–1, compared with cropping systems containing fallow once every 4 years. The increase in SON due to increased cropping frequency was accompanied by an increase in the proportion of mineralizable SON in the Brown Chernozem, but not in the Dark Brown and Black Chernozems. In the Brown Chernozemic soil zone, no-tillage management increased SON, compared with conventional tillage, varying from 16 kg N ha–1year–1 to 28 kg N ha–1year–1. In the Dark Brown Chernozemic soil zone, it increased SON by 35 kg N ha–1year–1 and, in the Black Chernozemic soil zone, by about 40 kg N ha–1year–1. Increases in SON at a depth of 0–7.5 cm due to no-tillage management was accompanied by a greater increase in the mineralizable N for Hatton fine sandy loam, Melfort silty clay and Indian Head clay than for other soils, indicating that the material responsible for the increased SON due to no-tillage was more labile than the soil humus N. However, the increased SON under no-till in Swinton loam, Sceptre clay and Elstow clay loam was not associated with an increase in the mineralizable N, indicating that this increased SON was no more susceptible to decomposition than the soil humus N. Therefore, increases in SON under improved management practices, such as conservation tillage and extended crop rotations, do not necessarily increase the potential soil N availability.  相似文献   

9.
Summary Field studies to determine the effect of different rates of fertilization on emission of nitrous oxide (N2O) from soil fertilized with anhydrous ammonia showed that the fertilizer-induced emission of N2O-N in 116 days increased from 1.22 to 4.09 kg ha–1 as the rate of anhydrous ammonia N application was increased from 75 to 450 kg ha–1. When expressed as a percentage of the N applied, the fertilizer-induced emission of N2O-N in 116 days decreased from 1.6% to 0.9% as the rate of fertilizer N application was increased from 75 to 450 kg N ha–1. The data obtained showed that a 100% increase in the rate of application of anhydrous ammonia led to about a 60% increase in the fertilizer-induced emission of N2O.Field studies to determine the effect of depth of fertilizer injection on emission of N2O from soil fertilized with anhydrous ammonia showed that the emission of N2O-N in 156 days induced by injection of 112 kg anhydrous ammonia N ha–1 at a depth of 30 cm was 107% and 21 % greater than those induced by injection of the same amount of N at depths of 10 cm and 20 cm, respectively. The effect of depth of application of anhydrous ammonia on emission of N2O was less when this fertilizer was applied at a rate of 225 kg N ha–1.  相似文献   

10.
Litterfall, decomposition, and N release in 5-year-old and 8-year-old plantations of Casuarina equisetifolia (Forst.) in the dry tropical region of the Vindhyan plateau were studied during 1989–1990. Maximum litterfall occurred in May. The total litterfall ranged from 7.2 to 9.9t ha-1 year-1 in the 5-year-old stand and from 11.3 to 12.7t ha-1 year-1 in the 8-year-old stand over the 2-year period. Photosynthetic branchlets contributed 87–95% to the total litter. The relative decomposition rates of litter components of the ash-free mass were highest in the rainy months (4.7 to 9.9mg g-1 day-1) followed by winter (2.8 to 3.6 mg g-1 day-1) and lowest in the summer months (1.7 to 3.0 mg g-1 day-1). Similar patterns were observed for N release. The annual decay constant was highest for cone litter and lowest for photosynthetic branchlets. During decomposition, the photosynthetic branchlets showed N immobilization in November and April, the twig litter in March, and the roots in January and February. N release per unit area (g m-2) was maximum from the photosynthetic branchlets (5.3–6.3) followed by cones (4.4) > roots (3.4) > twigs (2.6–3.2). The combination of the litter C:N ratio, moisture, and temperature with the relative decomposition rate in a multiple regression analysis explained 66–84% of the variability in mass loss and 58–66% of the variability in N release.  相似文献   

11.
A 3-year study was conducted to determine the effects of broiler litter relative to inorganic fertilizer on soil nutrient content and quality in an upland Loring silt loam soil. Treatments included annual broiler litter rates of 0, 2.2, 4.5, 5.6, 6.7, 10.1, and 13.4 Mg ha?1 y?1 and commercial fertilizer rates of 34, 68, 90, 112, 134, and 168 kg nitrogen (N) ha?1 y?1. Broiler litter application linearly increased soil total carbon (C), microbial biomass C, extractable soil phosphorus (P), potassium (K), soil cation exchange capacity (CEC), and the stability of soil aggregate. At the highest broiler litter rate, the stability of soil aggregate was 34% greater than inorganic fertilizer. Application of broiler litter or fertilizer N at rate greater than 6.7 Mg ha?1 or 90 kg N ha?1, respectively, exceeded plant N utilization potential as evidenced by higher end-of-season soil residual nitrate (NO3)-N. Broiler litter is more effective in improving soil physical, chemical, and biological components than conventional fertilizer.  相似文献   

12.
Effects of enhanced N, S and NS Acid additions, up to approximately 100 kg N and S ha?1 y?1, are described for a 15-year-old Sitka spruce forest growing on an acid peat in Scotland. Groups of 10 trees, replicated over 4 blocks, have been treated at canopy height on approximately 50 or 100 occasions with 2 mm precipitation equivalent, between April and November, since 1996. Relative stem volume increment (RSVI) has been consistently higher in the NS Acid treated trees compared with control or N treated trees since the second year of treatment, although no dose response was found. Litterfall was also considerably increased in the NS Acid treatments and showed a clear dose effect but was not correlated with RSVI. Base cation concentrations in soil waters, collected using zero tension lysimeters reflected the presence or absence of the spray treatments and showed a dose related increase in response to NS Acid inputs. Treatment with 2NS Acid increased NH4-N and NO3-N by an order of magnitude. Results after 4 years of treatment showed a positive growth and litterfall response to NS Acid inputs but no effect of N alone. Enhanced stemwood growth may be linked to the higher base cation and phosphate concentrations measured in the soil water in the presence of NS Acid and S treatments.  相似文献   

13.
Summary Soil enzyme activities (acid and alkaline phosphatase, arylsulfatase, -glucosidase, urease and amidase) were determined (0- to 20-cm depth) after 55 years of crop-residue and N-fertilization treatment in a winter wheat (Triticum aestivum L.)-fallow system on semiarid soils of the Pacific Northwest. All residues were incorporated and the treatments were: straw (N0), straw with fall burn (N0FB), straw with spring burn (N0SB), straw plus 45 kg N ha–1 (N45), straw plus 90 kg N ha–1 (N90), straw burned in spring plus 45 kg N ha–1 (N45SB), straw burned in spring plus 90 kg N ha–1 (N90SB), straw plus 2.24 T ha–1 pea-vine residue and straw plus 22.4 T ha–1 of straw-manure. Enzyme activities were significantly (P<0.001) affected by residue management. The highest activities were observed in the manure treated soil, ranging from 36% (acid phosphatase) to 190% increase in activity over the control (N0). The lowest activities occurred in the N0FB (acid phosphatase, arylsulfatase and -glucosidase) and N90 treated soils (alkaline phosphatase, amidase and urease). Straw-burning had a significant effect only on acid phosphatase activity, which decreased in spring burn treated soil when inorganic N was applied. Urease and amidase activity decreased with long-term addition of inorganic N whereas the pea vine and the manure additions increased urease and amidase activity. There was a highly significant effect from the residue treatments on soil pH. Arylsulfatase, urease, amidase and alkaline phosphatase activities were positively correlated and acid phosphatase activity was negatively correlated with soil pH. Enzyme activities were strongly correlated with soil organic C and total N content. Except for acid phosphatase, there was no significant relationship between enzyme activity and grain yield.Journal Paper No. 8072 of the Agricultural Experimental Station, Oregon State University, Corvallis, OR 97331, USA  相似文献   

14.
Legumes grown for grain may or may not contribute net N benefits to soil and succeeding crops. An experiment was conducted to assess N2 fixation attributes of six mungbean cultivars and two groundnut cultivars (Tainan 9 and Non-nod), which determine their residual benefit to the subsequent maize. Nodule number and dry weight of mungbeans peaked early (at 45 days) and declined thereafter strongly. In groundnut nodulation peaked later and declined only by 50% towards the final harvest. The N2-fixing groundnut produced higher total dry matter yield than mungbeans; however, mungbeans produced higher seed yields. Dry matter harvest index and nitrogen harvest index (NHI) were higher in mungbeans (average 0.44 and 0.69) than groundnut (0.23 and 0.47, respectively, in Tainan 9). The percentage of nitrogen derived from air (%Ndfa, 15N isotope dilution) ranged from 54% to 62% in mungbeans, similar to that of groundnut (64%). However, Tainan 9 fixed more N2 (82 kg N ha–1) than mungbeans (35–50 kg N ha–1) and resulted in a positive soil net N balance (+22 kg N ha–1) while negative values were found for Non-nod groundnut and mungbeans (–3 to –12 kg N ha–1). Maize grown after groundnut Tainan 9 had the highest total dry weight and total N uptake. This was equivalent to maize grown in fallow plots, which received 60–90 kg N ha–1, while the respective benefits after mungbeans were 30–60 kg N ha–1. Maize yield was directly related to the amount of residue N returned. Thus, the combination of high N yield, residue quality, %Ndfa and low NHI proved most beneficial to soil fertility and the succeeding crop.  相似文献   

15.
Biomass productivity and nutrient cycling in a Bambusa bambos plantation aged 4, 5, and 6 years were studied. The dry matter production of above-ground biomass increased progressively with age. Nutrient quantities in bamboo stands were in a range of 1–2 t ha-1 for N and K, 0.5–1 t ha-1 for Ca and Mg, and 0.1–0.2 t ha-1 for P. Nutrient concentrations increased with the age of the plantation. About 10% year-1 the nutrients present in the biomass of the bamboo stand are recycled to the soil by litter fall.  相似文献   

16.
氮肥用量及其分施比例对棉花氮利用和土壤氮平衡的影响   总被引：1，自引：0，他引：1  
The Yellow River valley is one of the three largest cotton production areas in China.An experiment was performed in cotton fields of Anyang,China from 2013 to 2014 to investigate the effects of nitrogen(N) application rate and the ratio between basal and topdressing N fertilizer on N balance in a soil-plant system,N use efficiency,and cotton yield.Five N application rates as treatments were applied with the same split application ratio.Half of the N(50% basal fertilizer) was applied at pre-planting and the other half(50% topdressing fertilizer) at the initial flowering stage.These treatments were:zero N(N0,control),90 kg N ha~(-1)(N90(5/5)),180 kg N ha~(-1)(N180(5/5)),270 kg N ha~(-1)(N270(5/5),a reduced N rate),and 360 kg N ha~(-1)(N360(5/5),a conventional N rate).Additional 2 split application ratios as treatments were applied with the same N rate of 270 kg N ha~(-1).The split application ratios between basal N and topdressing N were 30%:70%(N270(3/7)) and 70%:30%(N270(7/3)).Results demonstrated that soil NH_4-N content in the 0–60 cm layer and NO3-N content in the 0–20 cm layer increased with increased N rate at the squaring and boll-opening stages and then decreased to lower levels at the initial flowering and harvest stages.Soil NO_3-N content in the 20–60 cm layer after the initial flowering stage increased with the increase of topdressing N rate.Soil apparent N surplus varied at different growth stages,while the soil apparent N surplus over the entire growth period exhibited a positive relationship at N rates over 180 kg ha~(-1).Seed cotton yield of N270(3/7) was the highest of all treatments.Plant N uptake,N agronomic efficiency,and apparent N recovery efficiency of N270(3/7) were significantly higher than those of N270(5/5) and N270(7/3) in both growing seasons.These suggest both economic and ecological benefits in cotton production in the Yellow River valley could be created,by appropriately reducing total N application rate and increasing the ratio of topdressing to basal N fertilizer at the initial flowering stage.  相似文献   

17.
This study was based on laboratory incubations of mor humus from two N fertilized stands of Norway spruce in Sweden (Skogaby and Stråsan), which had received repeated N additions (100 kg N ha−1 yr−1 as (NH4)2SO4 at Skogaby and 35, 73 and 108 kg ha−1 yr−1 as NH4NO3 at Stråsan) during 8 and 24-29 years, respectively. The aim was to investigate long-term N effects on the mineralization of C and production of DOC. Mor humus (Oe and Oa) was incubated in columns at 20 °C for 49 days. Columns were leached once a week with artificial throughfall solution, which was analyzed for DOC, total N, NH4+-N and NO3−-N. Prior to each leaching event, CO2 evolution from the columns was determined. C-to-N ratios in the N-treated Oe layers at Stråsan (21-24) and Skogaby (24) were significantly lower than those of the controls (Stråsan, 32; Skogaby, 28). The cumulative amount of CO2-C showed a significant treatment effect in the Oe layer at Skogaby, i.e. 18 and 29 mg C g−1 C in the N treatment and control, respectively. At Stråsan, the cumulative CO2-C was significantly lower in the N3 treatment compared to the control in both layers (33 compared to 74 mg C g−1 C in the Oe layer and 16 compared to 35 mg C g−1 C in the Oa layer). Neither the DOC nor the DON production showed any significant treatment effects at the two sites. However, DOC was lower in the fertilized Oe layer at Skogaby throughout the incubation. The leaching of DON was highest in the Oe layers at both sites, and DON increased with time at Skogaby while there was a decreasing trend at Stråsan. The DOC-to-DON ratio tended to be lower in the fertilized Oe layers at both sites. The NH4+ leaching at Skogaby decreased in the N-treated Oe and Oa layers. At Stråsan, NH4+ from the Oe layer increased in N2 and control. The NO3− leaching was low and constant in both Skogaby layers. At Stråsan, NO3− increased in the Oe layer of N1. Cumulative CO2 was positively correlated to C-to-N ratio (r2=0.71,p<0.01) and to cumulative DOC (r2=0.63,p<0.05) in the Oe layer at Stråsan. Our conclusion was that long-term N additions caused decreased C-to-N ratios and decreased CO2 evolution rates. The correlation between CO2 and C-to-N ratio in the Oe layers at Stråsan may be due to a changed quality of the fertilized forest floor material and presence of more N efficient microorganisms.  相似文献   

18.
为了研究氮沉降对次生林土壤碳氮组分和酶活性的影响,以华西雨屏区湿性常绿阔叶次生林为对象,从2014年1月起进行野外定位模拟氮沉降试验,分别设置对照(CK,+0 g/(m^2·a))、低氮(LN,+5 g/(m^2·a))和高氮(HN,+15 g/(m^2·a))3个氮添加水平。在氮沉降进行27个月后,按照腐殖质层和淋溶层表层进行取样,测定不同土层土壤总有机碳(TOC)、可浸提溶解性有机碳(EDOC)、易氧化碳(ROC)、全氮(TN)、硝态氮(NO_3^-—N)和铵态氮(NH_4^+—N)含量以及蔗糖酶、脲酶、酸性磷酸酶和多酚氧化酶活性。结果表明:模拟氮沉降显著增加该次生林腐殖质层土壤的TOC和NH_4^+—N含量,显著增加腐殖质层和淋溶层表层土壤的NO_3^-—N含量,腐殖质层土壤C/N显著升高。淋溶层表层土壤TOC、NH_4^+—N、C/N以及2层土壤的EDOC、ROC、TN和NH_4^+—N/NO_3^-—N均无显著影响。2层土壤的多酚氧化酶活性均随着氮添加量的升高而降低,其中淋溶层表层达到显著差异。模拟氮沉降对蔗糖酶、脲酶和酸性磷酸酶活性均无显著影响。腐殖质层中,NH_4^+—N和NO_3^-—N含量与TOC含量存在极显著正相关关系。2层土壤的多酚氧化酶活性均与NO_3^-—N含量呈极显著负相关。结果说明,模拟氮沉降使该次生林中原本较高的腐殖质层土壤TOC含量进一步显著增加,并且促进土壤无机氮的积累,而模拟氮沉降对多酚氧化酶的抑制作用更加有利于土壤有机质的积累。  相似文献   

19.
The results of 40 long-term liming experiments in Scots pine and Norway spruce stands on mineral soil sites of varying fertility are reviewed in this paper. Limestone was broadcast at a dose of 2 t ha–1 at the end of the 1950s and sampling was carried out at the end of the 1970s. Liming resulted in considerable accumulation (10 to 50% increase) of organic matter in the humus layer, but no changes in the mineral soil. The C/N ratio of the humus increased on the most productive sites. Liming brought about a long-term decrease in acidity of the humus layer on all site types, as well as a decrease in the mineral soil (0 to 10 cm) of the least productive ones. There was also a corresponding increase in base saturation. There was considerable accumulation of B and Mn in the humus layer. Sulphur was found to have been immobilized to a considerable extent in the humus layer, presumably as Al sulfate. Liming at fairly low doses (e.g. 2 t ha–1) thus seems to be sufficient to counteract any future increases in soil acidification without bringing about any adverse effects (apart from perhaps B levels) on the nutrient status of the soil.  相似文献   

20.
Summary Nitrogen fixation in seven groundnut genotypes was measured by 15N-isotope dilution using a non-nodulating cultivar of groundnut as the nonfixing reference plant. Nitrogen fixation varied between 100 kg N ha–1 in genotype J-11 and 153 kg N ha–1 in Robut 33-1. The amount of plant-available soil N was small, so that 86%–92% of plant nitrogen was derived from N2-fixation. Thus differences in N2-fixation between genotypes closely reflected differences in their total N accumulation.ICRISAT Journal Article no. 600  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号