共查询到20条相似文献,搜索用时 31 毫秒
1.
The contribution of bacteria and fungi to NH 4+ and organic N (N org) oxidation was determined in a grassland soil (pH 6.3) by using the general bacterial inhibitor streptomycin or the fungal inhibitor cycloheximide in a laboratory incubation study at 20°C. Each inhibitor was applied at a rate of 3 mg g ?1 oven‐dry soil. The size and enrichment of the mineral N pools from differentially (NH 415NO 3 and 15NH 4NO 3) and doubly labelled ( 15NH 415NO 3) NH 4NO 3 were measured at 3, 6, 12, 24, 48, 72, 96 and 120 hours after N addition. Labelled N was applied to each treatment, to supply NH 4+‐N and NO 3?‐N at 3.15 μmol N g ?1 oven‐dry soil. The N treatments were enriched to 60 atom % excess in 15N and acetate was added at 100 μmol C g ?1 oven‐dry soil, to provide a readily available carbon source. The oxidation rates of NH 4+ and N org were analysed separately for each inhibitor treatment with a 15N tracing model. In the absence of inhibitors, the rates of NH 4+ oxidation and organic N oxidation were 0.0045 μmol N g ?1 hour ?1 and 0.0023 μmol N g ?1 hour ?1, respectively. Streptomycin had no effect on nitrification but cycloheximide inhibited the oxidation of NH 4+ by 89% and the oxidation of organic N by more than 30%. The current study provides evidence to suggest that nitrification in grassland soil is carried out by fungi and that they can simultaneously oxidize NH 4+ and organic N. 相似文献
2.
Determination of the labile soil carbon (C) and nitrogen (N) fractions and measurement of their isotopic signatures (δ 13C and δ 15N) has been used widely for characterizing soil C and N transformations. However, methodological questions and comparison of results of different authors have not been fully solved. We studied concentrations and δ 13C and δ 15N of salt‐extractable organic carbon (SEOC), inorganic (N–NH 4+ and N–NO 3?) and organic nitrogen (SEON) and salt‐extractable microbial C (SEMC) and N (SEMN) in 0.05 and 0.5 m K 2SO 4 extracts from a range of soils in Russia. Despite differences in acidity, organic matter and N content and C and N availability in the studied soils, we found consistent patterns of effects of K 2SO 4 concentration on C and N extractability. Organic C and N were extracted 1.6–5.5 times more effectively with 0.5 m K 2SO 4 than with 0.05 m K 2SO 4. Extra SEOC extractability with greater K 2SO 4 concentrations did not depend on soil properties within a wide range of pH and organic matter concentrations, but the effect was more pronounced in the most acidic and organic‐rich mountain Umbrisols. Extractable microbial C was not affected by K 2SO 4 concentrations, while SEMN was greater when extracted with 0.5 m K 2SO 4. We demonstrate that the δ 13C and δ 15N values of extractable non‐microbial and microbial C and N are not affected by K 2SO 4 concentrations, but use of a small concentration of extract (0.05 m K 2SO 4) gives more consistent isotopic results than a larger concentration (0.5 m ). 相似文献
3.
To evaluate the pathways and dynamics of inorganic nitrogen (N) deposition in previously N-limited ecosystems, field additions of 15N tracers were conducted in two mountain ecosystems, a forest dominated by Norway spruce ( Picea abies) and a nearby meadow, at the Alptal research site in central Switzerland. This site is moderately impacted by N from agricultural and combustion sources, with a bulk atmospheric deposition of 12 kg N ha −1 y −1 equally divided between NH 4+ and NO 3−. Pulses of 15NH 4+ and 15NO 3− were applied separately as tracers on plots of 2.25 m 2. Several ecosystem pools were sampled at short to longer-term intervals (from a few hours to 1 year), above and belowground biomass (excluding trees), litter layer, soil LF horizon (approx. 5-0 cm), A horizon (approx. 0-5 cm) and gleyic B horizon (5-20 cm). Furthermore, extractable inorganic N, and microbial N pools were analysed in the LF and A horizons. Tracer recovery patterns were quite similar in both ecosystems, with most of the tracer retained in the soil pool. At the short-term (up to 1 week), up to 16% of both tracers remained extractable or entered the microbial biomass. However, up to 30% of the added 15NO 3− was immobilised just after 1 h, and probably chemically bound to soil organic matter. 16% of the NH 4+ tracer was also immobilised within hours, but it is not clear how much was bound to soil organic matter or fixed between layers of illite-type clay. While the extractable and microbial pools lost 15N over time, a long-term increase in 15N was measured in the roots. Otherwise, differences in recovery a few hours after labelling and 1 year later were surprisingly small. Overall, more NO 3− tracer than NH 4+ tracer was recovered in the soil. This was due to a strong aboveground uptake of the deposited NH 4+ by the ground vegetation, especially by mosses. 相似文献
4.
Abstract Nitrogen (N) fertilizers increase yield and quality of grass forage, and may also alter soil chemical properties. A field experiment was conducted in south‐central Alberta to determine the effect of long‐term application of ammonium nitrate to bromegrass on concentration and downward mobility of soluble NO 3‐N, extractable NH 4‐N, P, Ca, Mg, and K, and total C and N in a Thin Black Chernozemic loam soil. The fertilizer was applied annually in early spring for 16 years at 0 to 336 kg N/ha. There was little accumulation of NO 3‐N in the soil at N rates of 112 kg/ha or less. However, at rates higher than 112 kg N/ha there was accumulation of NO 3‐N in the 15–30 and 30–60 cm layers, but very little in the 90–120 cm depth. The NH 4‐N accumulated in the 0–5 cm layer when the fertilizer was applied at rates between 168 to 280 kg N/ha and in the 5–10 cm layer at N rates exceeding 280 kg/ha. There was a decline in extractable P in soil with N application up to 84 kg N/ha rate, while it increased with high N rates. The increasing amounts of applied N resulted in a decline in extractable soil Ca, Mg and K, and this decrease was more pronounced in the 0–5,5–10,10–15, and 15–30 cm layers for K, 0–5 and 5–10 cm layers for Ca, and 0–5, 5–10, and 10–15 cm layers for Mg. There was a build‐up of total C and N in the surface soil with increasing rate of applied N. 相似文献
5.
The assumption in using the chloroform fumigation technique for microbial biomass determination is that microbes are killed or at least inactivated by the treatment. Problems associated with transformations of the N released on or during fumigation have so far only been associated with the fumigation-incubation method. A laboratory and a field study were carried out to investigate the possible N transformations during biomass determination by the fumigation-extraction method. Labelled NH 4NO 3 (either the NO 3−, NH 4+ or both pools were 15N enriched) was applied to the soil and biomass determinations made at intervals subsequently. The size and enrichment of the ammonium (NH 4+), and nitrate (NO 3−) pools were determined before and after chloroform fumigation. The 15N enrichment of the NH 4+ pool after fumigation could only be explained if immobilisation of ammonium occurred at some time during the 24 h fumigation period. The extent of this immobilisation was calculated. In addition, there was evidence that nitrification occurred during the fumigation procedure at the start of the laboratory study and throughout the field study. The laboratory and field study differed mainly in the dynamics related to NO 3− uptake and release. There was evidence for uptake of NO 3− by the microbial biomass with and without utilization. We conclude that the 15N enrichment in the microbial biomass cannot be accurately determined when N transformations and release of non-utilized N occurs during fumigation. The possible immobilisation of mineral N during fumigation will affect the magnitude of the factor used to convert measured microbial biomass N to actual microbial biomass N in soil. 相似文献
6.
Improving manure management to benefit both agricultural production and the environment requires a thorough understanding of the long‐term effects of applied manure on soil properties. This paper examines the effect of 25 annual solid cattle manure applications on soil organic carbon (OC), total N (TN), and KCl‐extractable NO 3‐N and NH 4‐N under both non‐irrigated and irrigated conditions. After 25 annual manure applications, OC and TN contents increased significantly with the rate of manure application at the top two sampling depths (0–15 cm and 15–30 cm), and the increases were not affected by the irrigation treatment. The NO 3 content increased at all sampling depths with greater increases observed under non‐irrigated conditions, while NH 4 content was not affected by manure application rates or the irrigation treatment. The changes in OC and TN at the surface (0–15 cm) and 15–30 cm depth were dependent on the cumulative weight of manure added over the years. The relationships between cumulative manure OC added and soil OC content and between cumulative manure TN added and soil TN content were linear and not affected by the irrigation treatment. For every ton of manure OC added, soil OC increased by 0.181 g kg –1 in the topsoil (0–15 cm). Similarly, for every ton of manure TN added, surface soil TN increased by 0.192 g kg –1. The linear relationship between manure C added and soil C content suggests that the soil had a high capacity for short‐term C sequestration. However, the total amount of NO 3‐N in the soil profile (0–150 cm) was affected by both the manure application rates and the irrigation treatment. A large amount of NO 3 accumulated in the soil, especially under non‐irrigated conditions. The extremely high level of NO 3 in the soil increases the potential risk of surface and groundwater pollution and losses to atmosphere as N 2O. 相似文献
7.
The turnover of organic matter determines the availability of plant nutrients in unfertilized soils, and this applies particularly to the alkaline saline soil of the former Lake Texcoco in Mexico. We investigated the effects of alkalinity and salinity on dynamics of organic material and inorganic N added to the soil. Glucose labelled with 14C was added to soil of the former Lake Texcoco drained for different lengths of time, and dynamics of 14C, C and N were investigated with the Detran model. Soil was sampled from an undrained plot and from three drained for 1, 5 and 8 years, amended with 1000 mg 14C‐labelled glucose kg ?1 and 200 mg NH 4+‐N kg ?1, and incubated aerobically. Production of 14CO 2 and CO 2, dynamics of NH 4+, NO 2– and NO 3–, and microbial biomass 14C, C and N were monitored and simulated with the Detran model. A third stable microbial biomass fraction had to be introduced in the model to simulate the dynamics of glucose, because > 90 mg 14C kg ?1 soil persisted in the soil microbial biomass after 97 days. The observed priming effect was mostly due to an increased decay of soil organic matter, but an increased turnover of the microbial biomass C contributed somewhat to the phenomenon. The dynamics of NH 4+ and NO 3– in the NH 4+‐amended soil could not be simulated unless an immobilization of NH 4+ into the microbial biomass occurred in the first day of the incubation without an immediate incorporation of it into microbial organic material. The dynamics of C and a priming effect could be simulated satisfactorily, but the model had to be adjusted to simulate the dynamics of N when NH 4+ was added to alkaline saline soils. 相似文献
8.
Several studies show that increases in soil temperature result in higher N mineralization rates in soils. It is, however, unclear if additional N is taken up by the vegetation or accumulates in the soil. To address this question two small, forested catchments in southern Norway were experimentally manipulated by increasing air temperature (+3°C in summer to +5°C in winter) and CO 2 concentrations (+200 ppmv) in one catchment (CO 2T-T) and soil temperature (+3°C in summer to +5°C in winter) using heating cables in a second catchment (T-T). During the first treatment year, the climate treatments caused significant increases in soil extractable NH 4 under Vaccinium in CO 2T-T. In the second treatment year extractable NH 4 in CO 2T-T and NO 3 in T-T significantly increased. Soil solution NH 4 concentrations did not follow patterns in extractable NH 4 but changes in soil NO 3 pools were reflected by changes in dissolved NO 3. The anomalous behavior of soil solution NH 4 compared to NO 3 was most likely due to the higher NH 4 adsorption capacity of the soil. The data from this study showed that after 2 years of treatment soil inorganic N pools increased indicating that increases in mineralization, as observed in previous studies, exceeded plant demand and leaching losses. 相似文献
9.
The dynamic of different soil C and N fractions in a Cambisol under succession fallow was investigated from June 1996 until May 2001. Mineral soil samples (0 – 10 and 10 – 30 cm) were analyzed for their concentrations of organic C (C org), total N (N t), hot water extractable C and N (HWC and HWN), and KCl extractable C and N (C org(KCl), N org(KCl), NH 4+‐N, NO 3–‐N). The values of all C and N fractions revealed a distinct depth gradient. While the concentrations of C org increased after set aside significantly from 7.7 to 8.9 g kg –1 at 0 – 10 cm, those at 10 – 30 cm depth decreased from 7.2 to 6.1 g kg –1. N t remained rather constant throughout the whole observation period. The HWC concentrations increased from 0.33 to 0.49 g kg –1, while HWN decreased slightly at 0 – 10 cm with time. In contrast, both HWC and HWN increased at 10 – 30 cm soil depth. HWC showed close significant correlations to C org, and HWN to N t as well as to NH 4+‐N and NO 3–‐N, respectively. In comparison to hot water‐extractable C and N, C org(KCl) and N org(KCl) accounted only about one tenth of those and showed a decreasing trend with time of succession. C : N ratio of the KCl fraction was in the same order of magnitude as the HWC : HWN ratio, except the last phase of the experiment where hot water extract values increased above 10. 相似文献
10.
Abstract Simple microdiffusion methods are described for determination of NH 4 +, NO 3 ‐, and NO 2 ‐ in soil extracts. These methods involve diffusion of NH 3 in a 473‐mL (1‐pint) wide‐mouth Mason jar, the diffused NH 3‐N being collected in 3 mL of boric acid‐indicator solution in a 60 mm (dia.) Petri dish suspended from the Mason jar lid, for quantitative determination by titrimetry (0.0025 M H 2SO 4). Magnesium oxide is used to liberate NH 4 +; Devarda's alloy is used to reduce NO 3‐ and NO 2 ‐ to NH 4 +; and sulfamic acid is used to eliminate NO 2 ‐. Depending upon the volume of soil extract (10–50 mL), diffusion at room temperature (a20°C) was complete in 18–72 h with orbital shaking, and in 24–86 h without shaking. The methods gave quantitative recovery of NH 4 +, NO 3 ‐, and NO 2 ‐added to soil extracts. A potential source of interference in the methods involving use of Devarda's alloy is the liberation of NH 4 +‐N from alkali‐labile organic‐N compounds. 相似文献
11.
We performed a series of experiments in controlled conditions to assess the potential of hardwood‐derived biochar either as a source or as a removing additive of macronutrients [nitrate‐nitrogen (NO 3‐N), ammonium‐N (NH 4‐N), potassium (K), phosphorus (P), and magnesium (Mg)] in solution. In addition, a 3‐year field trial was carried out in a commercial nectarine orchard to evaluate the effect of increasing soil‐applied biochar rates on tree nutritional status, yield, fruit quality, soil pH, soil NO 3‐N, and NH 4‐N concentration and soil water content. In controlled conditions, the concentrations of K, P, Mg, and NH 4‐N in solution were significantly increased and positively correlated with biochar rates. Biochar was ineffective in removing NO 3‐N, K, P, and Mg from enriched solutions, while at the rate of 40 g L ?1 biochar removed almost 52% of the initial NH 4‐N concentration. In a mature, irrigated, fertilized, commercial nectarine orchard (Big Top/GF677) on a sandy‐loam soil in the Italian Po Valley, soil‐applied biochar at the rates of 5, 15, and 30 t ha ?1 were effective in reducing the leached amount of NH 4‐N in the top 0.25 m soil layer over 13 months, as estimated by ion exchange resin lysimeters. Nevertheless, independent of the rate, biochar did not affect soil pH, soil N mineral availability, soil moisture, tree nutritional status, yield, and fruit quality. We conclude that, unless an evident constraint is identified, in non‐limiting conditions ( e.g., water availability and soil fertility), potential benefits from biochar application in commercial orchards are hidden or negligible. 相似文献
12.
To improve our knowledge of how nutrient cycling in Mediterranean environments responds to climate change, we evaluated the effects of the continuous changes in soil nitrogen (N) pools during natural wetting and drying events. We measured soil N pools (microbial biomass [MB-N], dissolved organic nitrogen [DON], NH 4+ and NO 3−) and N ion exchange resins at weekly intervals for one year in two contrasting Mediterranean ecosystems. All soil N fractions in both ecosystems showed high intraseasonal and interseasonal variability that was greater in inorganic soil fractions than in organic N soil fractions. MB-N, DON and resin-NH 4+ showed increased concentrations during wetting events. Only the soil NO 3− and resin-NO 3− showed the opposite trend, suggesting a different response to water pulses compared to the other soil variables. Our results show that N pools are continuously changing, and that this high variability is not associated with the total amount of organic matter and labile soil carbon (C) and N soil fractions found in each ecosystem. The highest variability was found for inorganic N forms, which suggests that organic N forms are more buffered in soils exposed to wetting-drying cycles. Our results suggest that the changes in wetting-drying cycles expected with global climate change may have a significant impact on the availability and turnover of organic and inorganic N. 相似文献
13.
The response of terrestrial ecosystems to elevated atmospheric CO 2 is related to the availability of other nutrients and in particular to nitrogen (N). Here we present results on soil N transformation dynamics from a N-limited temperate grassland that had been under Free Air CO 2 Enrichment (FACE) for six years. A 15N labelling laboratory study (i.e. in absence of plant N uptake) was carried out to identify the effect of elevated CO 2 on gross soil N transformations. The simultaneous gross N transformation rates in the soil were analyzed with a 15N tracing model which considered mineralization of two soil organic matter (SOM) pools, included nitrification from NH 4+ and from organic-N to NO 3− and analysed the rate of dissimilatory NO 3− reduction to NH 4+ (DNRA). Results indicate that the mineralization of labile organic-N became more important under elevated CO 2. At the same time the gross rate of NH 4+ immobilization increased by 20%, while NH 4+ oxidation to NO 3− was reduced by 25% under elevated CO 2. The NO 3− dynamics under elevated CO 2 were characterized by a 52% increase in NO 3− immobilization and a 141% increase in the DNRA rate, while NO 3− production via heterotrophic nitrification was reduced to almost zero. The increased turnover of the NH 4+ pool, combined with the increased DNRA rate provided an indication that the available N in the grassland soil may gradually shift towards NH 4+ under elevated CO 2. The advantage of such a shift is that NH 4+ is less prone to N losses, which may increase the N retention and N use efficiency in the grassland ecosystem under elevated CO 2. 相似文献
14.
Abstract A new soil extractant (H 3A) with the ability to extract NH 4, NO 3, and P from soil was developed and tested against 32 soils, which varied greatly in clay content, organic carbon (C), and soil pH. The extractant (H 3A) eliminates the need for separate phosphorus (P) extractants for acid and calcareous soils and maintains the extract pH, on average, within one unit of the soil pH. The extractant is composed of organic root exudates, lithium citrate, and two synthetic chelators (DTPA, EDTA). The new soil extractant was tested against Mehlich 3, Olsen, and water for extractable P, and 1 M KCl and water‐extractable NH 4 and NO 2/NO 3. The pH of the extractant after adding soil, shaking, and filtration was measured for each soil sample (5 extractants×2 reps×32 soils=320 samples) and was shown to be highly influential on extractable P but has no effect on extractable NH 4 or NO 2/NO 3. H 3A was highly correlated with soil‐extractable inorganic N (NH 4, NO 2/NO 3) from both water (r=0.98) and 1 M KCl (r=0.97), as well as being significantly correlated with water (r=0.71), Mehlich 3 (r=0.83), and Olsen (r=0.84) for extractable P. 相似文献
15.
Low temperatures and high soil moisture restrict cycling of organic matter in arctic soils, but also substrate quality, i.e. labile carbon (C) availability, exerts control on microbial activity. Plant exudation of labile C may facilitate microbial growth and enhance microbial immobilization of nitrogen (N). Here, we studied 15N label incorporation into microbes, plants and soil N pools after both long-term (12 years) climate manipulation and nutrient addition, plant clipping and a pulse-addition of labile C to the soil, in order to gain information on interactions among soil N and C pools, microorganisms and plants. There were few effects of long-term warming and fertilization on soil and plant pools. However, fertilization increased soil and plant N pools and increased pool dilution of the added 15N label. In all treatments, microbes immobilized a major part of the added 15N shortly after label addition. However, plants exerted control on the soil inorganic N concentrations and recovery of total dissolved 15N (TD 15N), and likewise the microbes reduced these soil pools, but only when fed with labile C. Soil microbes in clipped plots were primarily C limited, and the findings of reduced N availability, both in the presence of plants and with the combined treatment of plant clipping and addition of sugar, suggest that the plant control of soil N pools was not solely due to plant uptake of soil N, but also partially caused by plants feeding labile C to the soil microbes, which enhanced their immobilization power. Hence, the cycling of N in subarctic heath tundra is strongly influenced by alternating release and immobilization by microorganisms, which on the other hand seems to be less affected by long-term warming than by addition or removal of sources of labile C. 相似文献
16.
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
17.
Abstract Plant growth in saline soils is regulated by the availability of nitrogen (N). High soil nitrate (NO 3)‐N can lead to poor water quality. Many workers think that NO 3‐N as a source for N can contribute to better plant growth in saline soils. The purpose of this work was to determine the necessity of NO 3‐N and the ratio of NO 3/ammonium (NH 4) in the N fertilizer which gives higher productivity of the biomass yield of corn. Corn ( Zea mays L.) plants (Var. LG11) were grown under saline soil conditions (8.5 dS m ‐1), soils taken from the Euphrates valley (ACSAO Research Station) at Deir‐Ez‐Zor, east of Syria, from the surface layer of soil (0–25 cm). Five levels of N were applied in two forms, ammonium sulfate [ 15(NH 4) 2SO 4] with enrichment (1.5% a) as the NH 4‐N form and calcium nitrate [Ca(NO 3) 2] as the NO 3‐N form, besides fixed amounts of phosphorus (P) and potassium (K) for all N treatments. The corn plants were harvested at the flowering stage (56 days old), oven dried, weighed, and analyzed for total N and 15N recovery. The results indicated that the dry matter weight for treatments which received a combination of NH 4‐N and NO 3‐N gave higher dry matter yield than a single treatment of one source of N. But, NO 3‐N was more effective in improving yield than NH 4‐N. Nitrogen recoveries on the basis of added and absorbed N derived from fertilizer were significantly more affected by NO 3‐N than NH 4‐N. 相似文献
18.
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
19.
Inorganic nitrogen (N) in soils is a primary component of soil‐plant N buffering. This study was conducted to determine if non‐exchangeable ammonium‐nitrogen (NH 4‐N) could serve as an index of potentially mineralizable organic N which is an important sink in N buffering. Four long‐term winter wheat ( Triticum aestivum L.) experiments that had received annual fertilizer N at 0 to 272 kg N ha ‐1 were used. Soils from these experiments were extracted by four 10 mL portions of 2M potassium chloride (KC1) at room temperature followed by extraction with 20 mL of 2M hot KC1. Extraction at 100°C for four hours using 3 g soil and 20 mL 2M KC1 was found to be the most effective. Hot KC1‐extractable NH 4‐N minus room temperature KCl‐extractable NH 4‐N was considered non‐exchangeable NH 4‐N. Non‐exchangeable NH 4‐N was correlated with the long‐term N rates, and believed to be a reliable index of potentially mineralizable organic N. The relationship was linear for NH 4‐N where the lowest N rate had the lowest extractable N. The mean non‐exchangeable NH 4‐N concentration ranged from 8.42 to 16.34 mg kg ‐1; whereas, nitrate‐nitrogen (NO 3‐N) ranged from 0.07 to 1.87 mg kg 1. Total inorganic N extracted was similar to that mineralized in a 42‐day aerobic water saturated incubation. In addition, using a linear‐plateau model, extractable NH 4‐N was highly correlated with long‐term average yield (R 2=0.92). For the soils evaluated, this method provided a rapid measure of potentially mineralizable N. 相似文献
20.
Soil microbial organisms are central to carbon (C) and nitrogen (N) transformations in soils, yet not much is known about the stable isotope composition of these essential regulators of element cycles. We investigated the relationship between C and N availability and stable C and N isotope composition of soil microbial biomass across a three million year old semiarid substrate age gradient in northern Arizona. The δ15N of soil microbial biomass was on average 7.2‰ higher than that of soil total N for all substrate ages and 1.6‰ higher than that of extractable N, but not significantly different for the youngest and oldest sites. Microbial 15N enrichment relative to soil extractable and total N was low at the youngest site, increased to a maximum after 55,000 years, and then decreased slightly with age. The degree of 15N enrichment of microbial biomass correlated negatively with the C:N mass ratio of the soil extractable pool. The δ13C signature of soil microbial biomass was 1.4‰ and 4.6‰ enriched relative to that of soil total and extractable pools respectively and showed significant differences between sites. However, microbial 13C enrichment was unrelated to measures of C and N availability. Our results confirm that 15N, but not 13C enrichment of soil microbial biomass reflects changes in C and N availability and N processing during long-term ecosystem development. 相似文献
|