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1.
PurposeHulunbuir steppe has flat terrain and wide riparian zone of rivers and lakes on it. Owing to climate change, these riparian zones are often submerged or dried. This not only results in the instability of biodiversity in these regions but also affects the soil biogeochemical cycles. Soil C:N:P ecological stoichiometry plays a vital role in predicting and understanding the balance of multiple chemicals in ecological interactions. However, few studies have examined the soil C:N:P ecological stoichiometry in riparian zones of Hulunbuir steppe under different submergence states. Our objectives were to explore whether submergence frequencies impact soil C:N:P stoichiometry and identify the key factors. Materials and methodsFour study sites were selected along the Hui river in Hulunbuir steppe, and three plots of different submergence frequencies, high (HF-sub, 5 to 7 times per year), moderate (MF-sub, 2 to 3 times per year), and low (LF-sub, unflooded or flooded once per year), were selected for each study site. Soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), their ecological stoichiometric ratios (soil C:N, N:P, and C:P), soil ammonia nitrogen (NH4+-N), nitrate nitrogen (NO3?-N), available phosphorus (AP), soil pH, electrical conductivity (EC), soil moisture content (SMC), soil bulk density (SBD), porosity, and hardness were measured and analyzed. Results and discussionThe results indicated that soil C:N:P ecological stoichiometry was notably affected by submergence frequency across the four study sites (P?<?0.05). SOC, TN, TP, and their stoichiometric ratios changed regularly with the submergence frequency change, whereas their trends were inconsistent at different drainage basins. Soil C:N decreased with the decrease in submergence frequency but kept in a narrow scope, whereas the N:P and C:P were changed greatly under different submergence frequencies. Further analysis found that these significant variations in N:P and C:P were mainly due to the changes in soil TP which suggested there might be a P limitation in the riparian zones. The results of redundancy analysis (RDA) and path analysis indicated that soil AP and NO3?-N were the key indirect factors affecting soil C:N:P ecological stoichiometry under different submergence frequencies, and SMC was an indirect factor. ConclusionsWe demonstrated that the soil C:N:P ecological stoichiometry was significantly affected by the submergence frequency in the riparian zones of Hulunbuir steppe. Soil N:P and C:P were more susceptible to change than C:N under different submergence frequencies. If the contents of soil AP and NO3?-N were appropriate, soil C:N:P ecological stoichiometry will be more beneficial to regulating the cycle and balance of soil nutrient elements in the riparian zones, which can promote the riparian zones to provide better ecological functions. 相似文献
2.
PurposeThis study examined the usefulness of 15N natural abundance (δ15N) with in situ core incubation to quantify the predominant N transformation processes in a natural suburban forest of subtropical Australia, which was subjected to prescribed burning. Materials and methodsIn situ core incubation for 3 days with 20 ml water, or 160.79 ml of 60 mg L?1 NO3?-N surface application, and in situ core with 160.79 ml water but without incubation were set up in Toohey forest for sampling three times as before (once) and after (twice) a prescribed burning. The δ15N of NH4+-N and NO3?-N in the top 5 cm soil before and after the incubation, and δ15N of NO3?-N in the 5–10 cm soil before incubation were compared with each other to examine the soil N mineralisation, nitrification, denitrification, and nitrate leaching processes. Results and discussionThe significant decrease in δ15N of NH4+-N after incubation under 20 ml water treatment was ascribed to soil N mineralisation, and the significant decrease in δ15N of NH4+-N and significant increase in δ15N of NO3?-N after incubation with elevated water and nitrate inputs were associated with N mineralisation and nitrification, respectively, 2 months after the burning. The 160.79 ml water treatment also triggered nitrification in the baseline soil cores in both samplings after the burning. Water was crucial to stimulate soil N mineralisation and nitrification, but excessive water depleted labile N pools and reduced N mineralisation and nitrification. Burning effects were hard to separate from the seasonal impacts on soil N cycling processes. ConclusionsThe δ15N in soil mineral N pools was sensitive to indicate soil N mineralisation and nitrification processes. Soil water and labile N were determining factors for N transformations in the soil. It is suggested that δ15N combined with soil inorganic N concentrations and net N transformation rates could be used to identify primary N transformation processes. More frequent samplings would be needed to differentiate burning impacts from the seasonal impacts on soil N cycling processes. 相似文献
3.
ABSTRACTPlant nitrogen (N)-acquisition strategy affects soil N availability, community structure, and vegetation productivity. Cultivated grasslands are widely established to improve degraded pastures, but little information is available to evaluate the link between N uptake preference and forage crop biomass. Here an in-situ 15N labeling experiment was conducted in the four cultivated grasslands of Inner Mongolia, including two dicots ( Medicago sativa and Brassica campestris) and two monocots ( Bromus inermis and Leymus chinensis). Plant N uptake rate, shoot- and root biomass, and concentrations of soil inorganic-N and microbial biomass-N were measured. The results showed that the root/shoot ratios of the dicots were 2.6 to 16.4 fold those of the monocots. The shoot N concentrations of the dicots or legumes were 40.6% to 165% higher than those of the monocots or non-legumes. The four forage crops in the cultivated grassland preferred to uptake more NO 3?-N than NH 4+-N regardless of growth stages, and the NH 4+/NO 3? uptake ratios were significantly lower in the non-legumes than in the legumes (p < 0.05). Significant differences in the NH 4+-N rather than NO 3?-N uptake rate were observed among the four forages, related to plant functional types and growth stages. The NH 4+ uptake rate in the perennial forages exponentially decreased with the increases in shoot-, root biomass, and root/shoot ratio. Also, the plant NH 4+/NO 3? uptake ratio was positively correlated with soil NH 4+/NO 3? ratio. Our results suggest that the major forage crops prefer to absorb soil NO 3?-N, depending on soil inorganic N composition and belowground C allocation. The preferential uptake of NO 3?-N by forages indicates that nitrate-N fertilizer could have a higher promotion on productivity than ammonium-N fertilizer in the semi-arid cultivated grassland. 相似文献
4.
PurposeMany studies have shown the simulated effects of nitrogen (N) deposition on soil microbial community composition by adding N directly to the forest floor but have ignored the N retention process by the canopy. This study was conducted to compare the responses of soil microbial biomass and community composition between soil application of N (SAN) and foliage application of N (FAN). Materials and methodsA pot experiment was designed with (1) two N application methods (SAN and FAN), (2) three N application levels (5.6, 15.6 and 20.6 g N m?2 year?1), and (3) two tree species (Schima superba Gardn. et Champ. and Pinus massoniana Lamb.) following a nested factorial design. Soil microbial biomass and community composition were determined using phospholipid fatty acids (PLFAs) techniques after 1 and 1.5 years of treatments. Results and discussionNitrogen addition increased (P?<?0.05) soil NH4+-N content and soil NO3?-N content and decreased (P?<?0.05) soil pH and soil microbial (bacterial, fungal, and actinomycete) biomass for both N application methods. Compared with the SAN treatment, the FAN treatment had higher (P?<?0.05) pH and lower (P?<?0.05) contents of soil NH4+-N and soil NO3?-N. Soil microbial biomass and community composition were significantly different between the different N addition levels under the SAN treatment, but they showed no significant difference (P?<?0.05) between the different N addition levels under the FAN treatment. The soil microbial biomass in the S. superba soil was higher (P?<?0.05) than that in the P. massoniana soil for the FAN treatment, with the opposite trend observed under the SAN treatment. Moreover, redundancy analysis showed that soil microorganisms were significantly correlated with soil pH, soil water content, NH4+-N, and NO3?-N. ConclusionsThe results showed that N addition affected soil properties, microbial biomass, and the composition of microbial communities; however, the FAN treatment had less influence on soil properties and soil microorganisms than did the SAN treatment over short time scales, and the extent of this effect was different between coniferous and broadleaf trees. 相似文献
5.
ABSTRACTIn order to formulate a nitrogen (N) management strategy under continuous full amount of straw returning (CFSR) for double cropping rice production, long-term (2013–2016) paddy field experiments were conducted in double cropping rice production area in the Jiangxi province, China. Five N fertilizer treatments under CFSR were tested, that is, (i) no N fertilizer application (CK); (ii) conventional N fertilizer application (165kg N ha ?1 and 195 kg N ha ?1 in early and late rice variety with the ratio of basal dressing to topdressing as 6:4, respectively) (CNF 6:4); (iii) recommended N fertilizer application (135 kg ha ?1 N and 165 kg ha ?1 N in early and late rice variety with the ratio of basal dressing to topdressing as 4:6, 6:4, and 8:2, respectively) (RNF 4:6, RNF 6:4, and RNF 8:2). Nitrogen fertilizer treatments under CFSR had 5.70% and 8.93% higher soil total nitrogen (TN), 1.32% and 0.80% higher available nitrogen (AN), 16.55% and 22.94% higher NH 4+-N, and 13.10% and 7.93% higher NO 3--N than CK treatments in early and late rice variety, respectively. There were no differences in soil TN, AN, NH 4+-N, and NO 3--N contents between CNF6:4 and RNF6:4 treatments, while CNF6:4 treatment showed higher or significantly higher soil N contents than RNF4:6 and RNF8:2 treatments. N fertilizer treatment under CFSR showed 88.9% and 43.20% higher grain yield and 62.15% and 42.52% higher panicle numbers than CK treatments in early and late rice variety, respectively. Compared with CNF6:4, RNF treatments did not significantly reduce grain yield and yield components in early and late rice variety, respectively, except for RNF8:2. Compared with RNF6:4 and 8:2, RNF4:6 showed higher rice grain yield, while no obvious differences in yield components were obtained among all RNF treatments. We concluded that N fertilizer under CFSR was helpful to improve soil N contents and double rice grain yield and panicle numbers. Appropriate reduction of N application (18% and 15% reduction in early and late rice variety, respectively) on the basis of adjusting ratio of basal dressing to topdressing as 4:6 and 6:4 did not significantly reduce soil TN and double rice grain yield and yield components, especially, the 40% basal N dressing and 60% N topdressing was beneficial to increase double rice grain yield under CFSR. 相似文献
6.
PurposeNitrogen (N) is an important nutrient for re-vegetation during ecosystem restoration, but the effects of cover restoration on soil N transformations are not fully understood. This study was conducted to investigate N transformations in soils with different cover restoration ages in Eastern China. Materials and methodsSoil samples were collected from four degraded and subsequently restored lands with restoration ages of 7, 17, 23, and 35 years along with an adjacent control of degraded land. A 15N tracing technique was used to quantify gross N transformation rates. Results and discussionCompared with degraded land, soil organic carbon (SOC) and total N (TN) increased by 1.60–3.97 and 2.49–5.36 times in restoration land. Cover restoration increased ammonium and nitrate immobilization, and dissimilatory nitrate reduction to ammonium (DNRA) by 0.56–0.96, 0.34–2.10, and 0.79–3.45 times, respectively, indicating that restoration was beneficial for N retention. There were positive correlations between SOC content and ammonium and nitrate immobilization and DNRA, indicating that the increase in soil N retention capacity may be ascribed to increasing SOC concentrations. The stimulating effect of SOC on ammonium immobilization was greater than its effect on organic N mineralization, so while SOC and TN increased, inorganic N supply did not increase. Autotrophic and heterotrophic nitrification increased with increasing SOC and TN concentrations. Notably, heterotrophic nitrification was an important source of NO3??N production, accounting for 47–67% of NO3??N production among all restoration ages. ConclusionsThe capacity of N retention was improved by cover restoration, leading to an increase in soil organic carbon and total N over time, but inorganic N supply capacity did not change with cover restoration age. 相似文献
7.
PurposeThis study aimed to investigate the benefits of retaining harvest residues on the dynamics of soil C and N pools following clear-cut harvesting of a slash pine plantation in South East Queensland of subtropical Australia. Materials and methodsImmediately following clear-cut harvesting, macro-plots (10?×?10 m) were established on a section of the plantation in a randomised complete block design with four blocks and three treatments: (1) residue removal (RR0), (2) single level of residue retention (RR1) and (3) double level of residue retention (RR2). Soils were sampled at 0, 6, 12, 18 and 24 months following clear-cutting and analysed for total C and N, microbial biomass C (MBC) and N (MBN), hot water–extractable organic C (HWEOC), hot water–extractable organic N (HWEON), NH4+–N and NOx?–N. Results and discussionThe study showed that although soil total C decreased in the first 12 months following clear-cutting, harvest residue retention increased soil total C and N by 45% (p?<?0.001) and 32% (p?<?0.001), respectively, over the 12–24 months. NH4+–N, HWEOC, HWEON and MBC showed initial surges in the first 6 months irrespective of residue management, which declined after the 6th month. However, residue retention significantly increased HWEOC and HWEON over the 12–24 months (p?<?0.001). ConclusionsThis study demonstrated that harvest residue retention during the inter-rotation period can minimise large changes in C and nutrient pools, and can even increase soil C and nutrient pools for the next plantation rotation. 相似文献
8.
The concentration and amounts of NO 3-N and TN transported in surface, accelerated subsurface, and subsurface runoff and stream flow draining a 20 ha pasture watershed were measured over a period of 3 yr. A slight decrease and increase of NO 3-N and particulate N concentrations, respectively, were obtained with increased flow of the runoff types and stream, due to dilution and increased sediment transport, respectively. The concentration of NO 3-N in surface, accelerated subsurface and subsurface runoff and stream flow averaged for the 3 yr was 0.3, 6.6, 4.8, and 4.6 mg 1 ?1, respectively, amounting to 0.5, 9.4, 11.6, and 16.8 kg ha ?1 yr ?1, respectively, transported annually. Although NO 3-N accounted for only a minor proportion of the TN transported in surface runoff (10%) it was the main form of N (75%) transported in the other runoff types and in streamflow. Subsurface runoff contributed the major proportion of stream discharge (63%), and NO 3-N (69%), particulate N (44%) and TN (65%) loading of the stream. The results are discussed in terms of non-point pollution of surface waters by NO 3-N. 相似文献
9.
Abstract A sandy soil was amended with various rates (20 – 320 g air-dry weight basis of the amendments per kg of air-dry soil) of chicken manure (CM), sewage sludge (SS), and incinerated sewage sludge (ISS) and incubated for 100 days in a greenhouse at 15% (wt/wt) soil water content. At the beginning of incubation, NH 4-N concentrations varied from 50 – 280 mg kg ?1 in the CM amended soil with negligible amounts of NO 3-N. Subsequently, the concentration of NH 4-N decreased while that of NO 3-N increased rapidly. In soil amended with SS at 20 – 80 g kg ?1 rates, the NO 3-N concentration increased sharply during the first 20 days, followed by a slow rate of increase over the rest of the incubation period. However, at a 160 g kg ?1 SS rate, there were three distinct phases of NO 3-N release which lasted for160 days. In the ISS amended soil, the nitrification process was completed during the initial 30 days, and the concentrations of NH 4-N and NO 3-N were lower than those for the other treatments. The mineralized N across different rates accounted for 20 – 36%, 16 – 40%, and 26 – 50% of the total N applied as CM, SS, and ISS, respectively. 相似文献
10.
Optimal fertilizer nitrogen (N) rates result in economic yield levels and reduced pollution. A soil test for determining optimal fertilizer N rates for wheat has not been developed for Quebec, Canada, or many other parts of the world. Therefore, the objectives were to determine: 1) the relationship among soil nitrate (NO ? 3)- N, soil ammonium (NH + 4)- N and N fertilizer on wheat yields; and 2) the soil sampling times and depths most highly correlated with yield response to soil NO ? 3-N and NH + 4-N. In a three year research work, wet and dried soil samples of 0- to 30- and 30- to 60-cm depths from 20 wheat fields that received four rates of N fertilizer at seeding and postseeding (plants 15 cm tall) were analyzed for NH + 4-N and NO ? 3 -N using a quick-test (N-Trak) and a standard laboratory method. Wheat yield response to N fertilizer was limited, but strong to soil NO ? 3-N. 相似文献
11.
Three mulch treatments were tested for their ability to control erosion on a sloping site. Additionally, the choice of mulch can also enhance revegetation success and improve soil organic matter input. This study aimed to investigate the effects of three mulching treatments, hydro-seeding, granite mulch and forest mulch, on soil C and N pools at different positions on highly erodible slope with approximately 30 % gradient. Soil moisture, total C (TC), total N (TN), hot water-extractable organic C (HWEOC), hot water-extractable total N (HWETN), microbial biomass C and N (MBC and MBN), inorganic N and potentially mineralisable N were measured. All variables were significantly higher in soils amended with forest mulch than those with hydro-seeding and granite mulch, for the same slope positions. Soil moisture was significantly higher in the lower slope position than middle and upper slope positions in hydro-seeding and granite mulch treatments, whereas no slope effect was observed on soil moisture under the forest mulch application. In the forest mulch treatment, the upper slope position had higher soil TC, TN, HWEOC, HWETN, MBC, MBN, NO 3 ?-N and total inorganic N than the middle and lower slope positions. Five years following mulch application, forest mulch still exerted a significant influence on soil fertility compared to the other treatments and the influence on soil moisture suggests that this treatment would be the most effective in the control of water-driven soil erosion on this steep site. 相似文献
12.
Fine-textured soil cores were saturated with KNO 3 solutions, withdrawn at periodic in tervals and examined for mineral N forms. Reduction of NO 3? was correlated with time using a first-order rate function. Instantaneous initial NO 3?-N reduction rates were determined by taking derivatives of the rate function and setting t = 0. Duplicate experiments gave maximum NO 3?-N reduction rates of 1.0 μ N/g soil/h or ? 100 kg NO 3?-N/ha/day. Calculated NO 3? reduction rates increased with depth down to 30 cm. Net NO 3?-N reduction ceased between 48 and 96 h after which net NO 3?-N production of 0.016 to 0.29 μg N/g soil/h (～1.5 kg N/ha/day/0 to 20 cm) occurred. Net NH 4+-N mineralization ranged from about 0.03 to 0.05 μg N/g soil/h (3.5 to 4.0 kg N/ha/day/0 to 30 cm). Both instantaneous initial NO 3?-N loss rates and N mineralization rates are similar to results of laboratory studies elsewhere on similar soil types. This procedure for estimating N-transformations may be useful where other techniques are either not adequate or not feasible for field use. 相似文献
13.
Abstract To determine the relationships between microbial biomass nitrogen (N), nitrate–nitrogen leaching (NO 3-N leaching) and N uptake by plants, a field experiment and a soil column experiment were conducted. In the field experiment, microbial biomass N, 0.5 mol L ?1 K 2SO 4 extractable N (extractable N), NO 3-N leaching and N uptake by corn were monitored in sawdust compost (SDC: 20 Mg ha ?1 containing 158 kg N ha ?1 of total N [approximately 50% is easily decomposable organic N]), chemical fertilizer (CF) and no fertilizer (NF) treatments from May 2000 to September 2002. In the soil column experiment, microbial biomass N, extractable N and NO 3-N leaching were monitored in soil treated with SDC (20 Mg ha ?1) + rice straw (RS) at five different application rates (0, 2.5, 5, 7.5 and 10 Mg ha ?1 containing 0, 15, 29, 44 and 59 kg N ha ?1) and in soil treated with CF in 2001. Nitrogen was applied as (NH 4) 2SO 4 at rates of 220 kg N ha ?1 for SDC and SDC + RS treatments and at a rate of 300 kg N ha ?1 for the CF treatment in both experiments. In the field experiment, microbial biomass N in the SDC treatment increased to 147 kg N ha ?1 at 7 days after treatment (DAT) and was maintained at 60–70 kg N ha ?1 after 30 days. Conversely, microbial biomass N in the CF treatment did not increase significantly. Extractable N in the surface soil increased immediately after treatment, but was found at lower levels in the SDC treatment compared to the CF treatment until 7 DAT. A small amount of NO 3-N leaching was observed until 21 DAT and increased markedly from 27 to 42 DAT in the SDC and CF treatments. Cumulative NO 3-N leaching in the CF treatment was 146 kg N ha ?1, which was equal to half of the applied N, but only 53 kg N ha ?1 in the SDC treatment. In contrast, there was no significant difference between N uptake by corn in the SDC and CF treatments. In the soil column experiment, microbial biomass N in the SDC + RS treatment at 7 DAT increased with increased RS application. Conversely, extractable N at 7 DAT and cumulative NO 3-N leaching until 42 DAT decreased with increased RS application. In both experiments, microbial biomass N was negatively correlated with extractable N at 7 DAT and cumulative NO 3-N leaching until 42 DAT, and extractable N was positively correlated with cumulative NO 3-N leaching. We concluded that microbial biomass N formation in the surface soil decreased extractable N and, consequently, contributed to decreasing NO 3-N leaching without impacting negatively on N uptake by plants. 相似文献
14.
Switchgrass ( Panicum virgatum L.) is a perennial biofuel crop with a high production potential and suitable for growth on marginal land. This study investigates the long-term planting effect of switchgrass on the dynamics of soil moisture, pH, organic carbon (SOC), total nitrogen (TN), nitrate nitrogen (NO 3–-N) and ammonium nitrogen (NH 4+-N) for soils to a depth of 90-cm in a sandy wasteland, Inner Mongolia, China. After crop harvesting in 2015, soil samples were collected from under switchgrass stands established in 2006, 2008, and 2009, native mixture, and a control that was virgin sand. Averaged across six layers, soil moisture and pH was significantly higher under the native mixture than switchgrass or virgin sand. However, SOC and TN were significantly higher under the 2006 switchgrass stand when compared with all other vegetation treatments and the control. The SOC and TN increased from 2.37 and 0.26 g kg ?1, respectively, for 2009 switchgrass stand, and to 3.21 and 0.42 g kg ?1, respectively, for 2006 switchgrass stand. Meanwhile, SOC and TN contents were 2.51 and 0.27 g kg ?1, respectively, under the native mixture. The soil beneath switchgrass and native mixture showed the highest NO 3–-N and NH 4+-N, respectively. The soil moisture increased with depth while SOC, TN, and NO 3–-N decreased. An obvious trend of increasing moisture, SOC, TN, and mineral N was observed with increasing switchgrass stand age. Thus, growing switchgrass on sandy soils can enhance SOC and TN, improve the availability of mineral N, and generate more appropriate pH conditions for this energy cropping system. 相似文献
15.
ABSTRACT A study was carried out to determine the influence of nitrogen (N) sources on the growth, nitrate (NO 3 ?) accumulation, and macronutrient concentrations of pakchoi ( Brassica chinensis L.) in hydroponics. Plants were supplied with NO 3 ? and two amino acids (AA), glutamic acid (Glu), and glutamine (Gln), at six NO 3 ?-N/AA-N molar ratios: (1) 100:0, (2) 80:20, (3) 60:40, (4) 40:60, (5) 20:80, (6) 0:100. The total N concentration was 12.5 mmol/L for all treatments in nutrient solutions. Both AAs reduced plant growth with decreasing NO 3 ?-N/AA-N ratios, but the reduction was for Gln than for Glu. At 80:20 NO 3 ?-N: Gln-N ratio, the Gln had no significant effect on pakchoi fresh weights. Decreasing NO 3 ?-N/AA-N ratios reduced NO 3 ? concentrations in the plant, regardless of AA sources. Adding an appropriate portion of AA-N to nutrient solutions for hydroponic culture increased concentrations of N, phosphorus (P), and potassium (K) in pakchoi shoots. Substituting 20% or less of NO 3 ?-N with Gln-N in hydroponic culture will increase the pakchoi quality by reducing NO 3 ? concentration and increasing mineral nutrient concentrations in shoots without significant reduction of crop yields. 相似文献
16.
Extraction of soil nitrate nitrogen (NO 3 ?-N) and ammonium nitrogen (NH 4 +-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 NO 3 ?-N and NH 4 +-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 (CaCl 2), 1 mol L ?1 potassium chloride (KCl), and 0.5 mol L ?1 potassium sulfate (K 2SO 4)] 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 NO 3 ?-N and NH 4 +-N was also measured to compare the differences of three extracting reagents (CaCl 2, KCl, and K 2SO 4) for NO 3 ?-N and NH 4 +-N extraction. Air drying decreased NO 3 ?-N but increased NH 4 +-N concentration in soil. Soil passed through a 3-mm sieve and shaken for 60 min yielded greater NO 3 ?-N and NH 4 +-N concentrations compared to other treatments. The concentrations of extracted NO 3 ?-N and NH 4 +-N in soil were significantly ( P < 0.05) affected by extracting reagents. KCl was found to be most suitable for NO 3 ?-N and NH 4 +-N extraction, as it had better recovery for soil mineral N extraction, which averaged 113.3% for NO 3 ?-N and 94.9% for NH 4 +-N. K 2SO 4 was not found suitable for NO 3 ?-N extraction in soil, with an average recovery as high as 137.0%, and the average recovery of CaCl 2 was only 57.3% for NH 4 +-N. For KCl, the concentration of extracting solution played an important role, and 0.5 mol L ?1 KCl could fully extract NO 3 ?-N. A ratio of 10:1 of solution to soil was adequate for NO 3 ?-N extraction, whereas the NH 4 +-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 NO 3 ?-N concentration, whereas the NH 4 +-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 NO 3 ?-N and NH 4 +-N concentrations. Compared with the immediate extraction, the averaged NO 3 ?-N concentration significantly ( P < 0.05) increased after storing 2, 4, and 6 weeks, respectively, whereas NH 4 +-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 NO 3 ?-N, whereas the concentration of extracted NH 4 +-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 NO 3 ?-N and NH 4 +-N results. 相似文献
17.
A 56-day aerobic incubation experiment was performed with 15-nitrogen (N) tracer techniques after application of wheat straw to investigate nitrate-N (NO 3-N) immobilization in a typical intensively managed calcareous Fluvaquent soil. The dynamics of concentration and isotopic abundance of soil N pools and nitrous oxide (N 2O) emission were determined. As the amount of straw increased, the concentration and isotopic abundance of total soil organic N and newly formed labeled particulate organic matter (POM-N) increased while NO 3-N decreased. When 15NO 3-N was applied combined with a large amount of straw at 5000 mg carbon (C) kg ?1 only 1.1 ± 0.4 mg kg ?1 NO 3-N remained on day 56. The soil microbial biomass N (SMBN) concentration and newly formed labeled SMBN increased significantly ( P < 0.05) with increasing amount of straw. Total N 2O-N emissions were at levels of only micrograms kg ?1 soil. The results indicate that application of straw can promote the immobilization of excessive nitrate with little emission of N 2O. 相似文献
18.
Sandy loam soil, with added glucose, was incubated anaerobically under N 2 and subjected to repeated 1-h C 2H 2 reduction assays. In the presence of 1% glucose the addition of 50 μg NH 4+ ?N/g or of 20 μg NO ?3 N/g (untreated soil contained 1.2 μg NH +4?N and 7.10 μg NO ?3-N/g) caused at least some suppression of nitrogenase activity. Activity developed when the KCl-extractable soil inorganic nitrogen concentration dropped below 35 μg/g. In the presence of 0.1 or 0.05% glucose the addition of 5 μg NH +4?N/g caused some suppression of nitrogenase activity. However, activity developed when the soil NH 4+-N concentration dropped below about 4 μg/g. With 0.1% glucose and 5 μg added NO ?2 N/g, activity did not develop until the soil NO ?2 -N concentration dropped to zero. Added NO ?3 N was rapidly reduced and denitrified to NO ?2- N, N 2O-N and NH +4 N and furthermore caused some inhibition of CO 2 evolution. The data from NH 4?-addition experiments are consistent with a nitrogenase repression/ derepression threshold of 4 and 35μg NH +4-N/g at 0.05 and 1% glucose concentrations, respectively. The data from NO ?2- and NO ?3-addition experiments suggest a combination of repression and toxicity effects in the presence of added NO ?3 N. 相似文献
19.
ABSTRACT Controlled-release fertilizers (CRF) are used to reduce leaching of nutrients, especially nitrate-nitrogen (NO 3 ?-N) to groundwater, caused mainly by application of soluble N fertilizers to sandy soils in Florida. A leaching column study was conducted to evaluate N release and transformation from a CRF (CitriBlen) over a 16-week period when it was applied on the soil surface or incorporated into the soil. When one pore volume of water was applied to column weekly or biweekly, the CRF released urea-N slowly over time with three peaks of release on 3–4, 8, and 12 week after application. Both ammonium-nitrogen (NH 4 +-N) and NO 3 ?-N were leached in large amounts on week 2, likely from soluble forms of N. Cumulatively, the most leached N at the end of study was in the NH 4 + form, followed by the NO 3 ? form. The sum of all N forms leached and volatilized accounted for 53–69% of total N applied. Total N recovery was 70% and 93% of total N applied for surface and sub-surface application of the fertilizer, respectively. It was indicated that the better recovery rate found with sub-surface application may have been due to minimized N loss by volatilization. Sub-surface application of fertilizer resulted in more than three times NH 4 +-N remained in soil, compared with surface application. On average for both application treatments throughout 16-week period, 5.8 h was required for ammonification and 4.7 d for nitrification to occur after N release from the fertilizer. Characterization of CRFs for specific soil type, leaching volume and cycle, and application manner as well as knowledge of N requirement of the crop will allow for the Best Management Practices of these fertilizers, thus obtaining optimum yields and minimizing nutrient losses from CRFs. 相似文献
20.
In this study, the concentrations and loads of different forms of nitrogen [nitrate nitrogen (NO 3-N), total Kjeldahl nitrogen (TKN), and total nitrogen (TN)] in the headwater catchment of the Mero River (NW Spain) were analyzed. The TN concentrations were relatively low (mean: 2.57 mg L ?1). Nitrate was the predominant form of N in the Mero catchment, accounting for 76.65 percent of the TN concentration. Measured NO 3-N concentrations were always lower than the maximum allowed drinking water concentration. An annual TN load of 61.2 Mg was computed, representing an export of 0.94 Mg km ?2 y ?1, whereas annual exports NO 3-N and TKN were of 0.79 and 0.15 Mg km ?2 y ?1, respectively. 相似文献
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