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1.
Manipulation of quality and mineralization of tropical legume tree prunings by varying nitrogen supply 总被引:5,自引:1,他引:4
The effect of N supply on the quality of Calliandra calothyrsus and Gliricidia sepium prunings was studied in a glasshouse over a 7-month growing period. Increasing the concentration of N supplied from 0.625 to 10.0 mM NO3-N resulted in increased N concentration but decreased polyphenol concentration, protein-binding capacity and C:N ratio of prunings from both species. Lignin concentration was not consistently altered by the N treatment. Mineralization of N from the prunings was measured over a 14-week period under controlled leaching and non-leaching conditions. The results indicated a strong interaction between legume species and concentration of N supply in their influence on N mineralization of the prunings applied to the soil. Differences in the %N mineralized were dictated by the quality of the prunings. The (lignin + polyphenol):N ratio was the pruning quality factor which could be used most consistently and accurately to predict N mineralization of the legume prunings incubated under leaching conditions, and the relationship was best described by a linear regression. Under non-leaching conditions, however, the protein-binding capacity appeared to be the most important parameter in determining the patterns of N release from the prunings studied. The relationship between the N mineralization rate constant and the protein-binding capacity was best described by a negative exponential function, y=0.078 exp(–0.0083x). The present study also indicated that the release of N from legume prunings containing a relatively high amount of polyphenol could be enhanced by governing the N availability conditions under which the plant is grown, for example whether or not it is actively fixing nitrogen. Estimates of pruning N mineralization after 14 weeks with the difference method averaged 6% (leaching conditions) and 22% (nonleaching conditions) more than with the 15N method for all legume prunings studied. The recovery of pruning by maize (4–38%) was well correlated with the % pruning N mineralized suggesting that incubation data closely reflect the pruning N value for a given catch crop under non-leaching conditions. 相似文献
2.
S. Promsakha Na. Sakonnakhon B. Toomsan G. Cadisch E. M. Baggs P. Vityakon V. Limpinuntana S. Jogloy A. Patanothai 《Plant and Soil》2005,272(1-2):183-199
It is generally thought that grain legume residues make a substantial net N contribution to soil fertility in crop rotation systems. However, most studies focus on effects of residues on crops immediately sown after the legume crop while in fact in many tropical countries with a prolonged dry season there is a large gap before planting the next crop with potential for nutrient losses. Thus the objectives of this study were* to improve the efficiency of groundnut (Arachis hypogaea L.) stover-N (100 kg N ha –1) recycling by evaluating the effect of dry season stover management, i.e. surface application and immediate incorporation after the legume crop or storage of residues until next cropping in the rainy season. N dynamics (litterbags, mineral N, microbial biomass N, N 2O emissions) were monitored and 15N labelled residues were applied to assess the fate of residue N in the plant–soil (0–100 cm) system during two subsequent maize crops. Recycling groundnut stover improved yield of the subsequent maize (Zea mays L.) crop compared to treatment without stover. A higher N recycling efficiency was observed when residues were incorporated (i.e. 55% total 15N recovery after second maize crop) than when surface applied (43% recovery) at the beginning of the dry season. This was despite the faster nitrogen release of incorporated residues, which led to more mineral N movement to lower soil layers. It appears that a proportion of groundnut stover N released during the dry season was effectively captured by the natural weed population (54–70 kg N ha –1) and subsequently recycled particularly in the incorporation treatment. Despite the presence of weeds major leaching losses occurred during the onset of the rainy season while N 2O emissions were relatively small. There was a good correlation between soil microbial biomass N and first crop maize yield. Incorporation of groundnut residues led to small increases in economic yield, i.e., 3120 versus 3528 kg ha –1 over two cropping cycles in the surface versus incorporation treatments respectively, with corresponding residue 15N uptakes of 4 and 8%, while 15N recovery in water stable aggregates (9–15%) was not significantly different. In contrast, when stover was removed and applied before the first crop, yield benefits were highest with cumulative maize yields of 4350 kg ha –1 and residue utilization of 12%. However, N recycling efficiency was not higher than in the early incorporation treatment due to an asynchrony of N release and maize N demand during the first crop. 相似文献
3.
Summary Homozygous mutant lines of field bean selected for (a) improved yielding potential and (b) altered plant architecture and/or physiological response were tested for symbiotic nitrogen fixing ability under field conditions in comparison with their parent cultivar.15N-tracer techniques were applied to determine %N derived from atmosphere. Data were collected on assimilate and nitrogen accumulation and distribution among various plant parts during two stages of reproductive growth.Symbiotic nitrogen fixation was closely correlated with total plant top biomass and nitrogen yield. A similar close association was found between crop yield and nitrogen harvest index. Both harvest indices tended to be negatively correlated with stage of maturity and with the amount of N derived from air per unit of area. The generally high %N derived from symbiotic N2 fixation and its comparatively small variability implies that this parameter may be difficult to improve inVicia faba under field conditions.It is concluded, that the main genetic potential for improving the amount of biological nitrogen fixation in this crop depends upon factors that promote high photosynthetic productivity and efficient N-use under appropriate agronomic conditions and with effective rhizobial associations. The establishment of rational ideotypes with a possitive impact on yield appears to be of practical significance for increasing the amount of symbiotically fixed nitrogen. 相似文献
4.
A mixed pasture comprising of buffel grass and a legume siratro was studied under field condition for a two-year period to know the fodder yield increase, nitrogen fixation and nitrogen balance with and without the inoculation of VA mycorrhiza to grass and Rhizobium to legume component.15N dilution technique was followed using labelled ammonium sulphate. The data showed that during the first year of the above study combined inoculation of VA mycorrhiza and Rhizobium to grass and legume respectively significantly increased the total dry matter (DM) (23,900 kg ha–1 yr–1) and total N content (308 kg ha–1 yr–1) of the mixed pasture over the uninoculated mixture. However, the above increase due to combined inoculation was maximum during second year with respect to DM yield (28,200 kg ha–1 yr–1), but the total N harvested through grass-legume mixture was comparatively lower than the first year (297 kg ha–1 yr–1). The amount of biologically fixed N was highest in the first year (79 kg ha–1 yr–1) and showed a very drastic reduction at the end of second year (39 kg ha–1 yr–1). A positive nitrogen balance was observed in the grass-legume mixture irrespective of inoculation of VA mycorrhiza and/or Rhizobium. 相似文献
5.
Estimates of the residual nitrogen benefit of groundnut to maize in Northeast Thailand 总被引:4,自引:1,他引:3
Four cultivars of groundnut were grown in upland soil in Northeast Thailand to study the residual benefit of the stover to a subsequent maize crop. An N-balance estimate of the total residual N in the maize supplied by the groundnut was made. In addition three independent estimates were made of the residual benefits to maize when the groundnut stover was returned to the land and incorporated. The first estimate (Estimate 1) was an N-balance estimate. A dual labelling approach was used where 15N-labelled stover was added to unlabelled microplots (Estimate 2) or unlabelled stover was added to 15N-labelled soil microplots (Estimate 3). The nodulating groundnut cultivars fixed between 59–64% of their nitrogen (as estimated by the 15N isotope dilution method using non-nodulating groundnut as a non-fixing reference) producing between 100 and 130 kg N ha-1 in their stover. Although the following maize crop suffered from drought stress, maize grain N and dry weights were up to 80% and 65% greater respectively in the plots where the stover was returned as compared with the plots where the stover was removed. These benefits were comparable with applications of 75 kg N ha-1 nitrogen in the form of urea. The total residual N estimates of the contribution of the nodulated groundnut to the maize ranged from 16.4–27.5 kg N ha-1. Estimates of the residual N supplied by the stover and fallen leaves ranged from 11.9–21.3 kg N ha-1 using the N-balance method (Estimate 1), from 6.3–9.6 kg N ha-1 with the labelled stover method (Estimate 2) and from 0–11.4 kg N ha-1 with the labelled soil method. There was closest agreement between the two 15N based estimates suggesting that apparent added nitrogen interactions in these soils may not be important and that N balance estimates can overestimate the residual N in crops following legumes, even in very poor soils. This work also indicates the considerable ability of local groundnut cultivars to fix atmospheric nitrogen and the potential benefits from returning and incorporating legume residues to the soil in the upland cropping systems of Northeast Thailand. The applicability of the 15N methodology used here and possible reasons for the discrepancies between estimates 1, 2 and 3 are discussed. 相似文献
6.
A pot experiment was conducted to determine the effects of the application of 13C (1.256 atom%) and 15N (1.098 atom%) dual-labeled maize residue compost (MRC) on the nitrogen and carbon uptake by radish, komatsuna, and chingensai
as compared with the effect of inorganic fertilizer (IF). The vegetables were grown over three consecutive growing seasons
over 4 months; compost was applied at the rate of 24 g kg–1 soil. Nonlabeled nitrogen fertilizer was applied to the compost treatments in the second and third crops to compare the effects
of blends of compost with N fertilizer to fertilizer alone. The N uptake and yield of vegetables were significantly higher
with the recommended inorganic N treatment. The vegetables took up significantly (P < 0.05) lower amounts of N from MRC than from IFs during the three cultivations. The values of the N uptake derived by fertilizer
application to the plant exhibited significant differences among different vegetables. Nitrogen recovered by komatsuna and
chingensai from MRC was 7.3 (6.6%), 2.7 (1.8%), and 2.3, (1.7%) in the first, second, and third crops, respectively. Radish,
komatsuna, and chingensai recovered significant amounts of C from MRC in the first and second crops, with negligible C recovery
in the third crop. The initial loss of fertilizer C in soil at the first crop indicates that the microbial decomposition decoupled
substantial amounts of 13C/15N-labeled compounds early in plant development, thus giving the microorganisms a preemptive competitive advantage in the acquisition
of easily available 13C/15N-labeled substrates. It is concluded that a combination of compost and inorganic N did not supply sufficient plant-available
N to increase vegetables yields or N uptake over those of fertilizer alone. The data suggested that higher productivity of
vegetables might be achieved after the accumulation of a certain amount of residual compost N. 相似文献
7.
In an experiment with sorghum on a medium deep red soil (Udic Rhodustalf) at Patancheru, India, where15N-labeled urea was applied at different rates during the 1981 rainy season, the apparent (ARF) and isotope recovery fractions
(15NRF) were appreciably different, particularly at lower rates of fertilizer application. The fertilizer rates were corrected
for losses of fertilizer nitrogen, that were estimated from the differences in the amounts of15N recovered in the soil and the crop, and the known amounts of15N applied. Introducing these ‘effective’ fertilizer rates, the apparent discrepancy between ARF and15NRF could be explained if it were assumed that the15N immobilized in the organic soil fraction was not remineralized during the course of the growing season. In the difference
method, the equivalent amount of nitrogen at natural abundance released in exchange for fertilizer nitrogen (5 atom % xs15N) immobilized in the organic nitrogen fraction is treated as ‘fertilizer nitrogen’, since no distinction is made between14N and15N. In the isotope-dilution method, the nitrogen at natural abundance mineralized during biological interchange is not considered
fertilizer nitrogen, and therefore the assumed effective amount of fertilizer nitrogen available to the crop is less than
in the difference method. 相似文献
8.
Nitrogen cycling in low input legume-based agriculture,with emphasis on legume/grass pastures 总被引:3,自引:0,他引:3
Low input legume-based agriculture exists in a continuum between subsistence farming and intensive arable and pastoral systems. This review covers this range, but with most emphasis on temperate legume/grass pastures under grazing by livestock. Key determinants of nitrogen (N) flows in grazed legume/grass pastures are: inputs of N from symbiotic N2 fixation which are constrained through self-regulation via grass/legume interactions; large quantities of N cycling through grazing animals with localised return in excreta; low direct conversion of pasture N into produce (typically 5–20%) but with N recycling under intensive grazing the farm efficiency of product N: fixed N can be up to 50%; and regulation of N flows by mineralisation/immobilisation reactions. Pastoral systems reliant solely on fixed N are capable of moderate-high production with modest N losses e.g. average denitrification and leaching losses from grazed pastures of 6 and 23 kg N ha–1 yr–1. Methods for improving efficiency of N cycling in legume-based cropping and legume/grass pasture systems are discussed. In legume/arable rotations, the utilisation of fixed N by crops is influenced greatly by the timing of management practices for synchrony of N supply via mineralisation and crop N uptake. In legume/grass pastures, the spatial return of excreta and the uptake of excreta N by pastures can potentially be improved through dietary manipulation and management strategies. Plant species selection and plant constituent modification also offer the potential to increase N efficiency through greater conversion into animal produce, improved N uptake from soil and manipulation of mineralisation/immobilisation/nitrification reactions. 相似文献
9.
It was the aim of this study to determine the way in which low temperature modifies the effect of a competing grass on nitrogen fixation of a forage legume. White clover (Trifolium repens L.) was grown in monoculture or in different planting ratios with timothy (Phleum pratense L.) or perennial ryegress (Lolium perenne L.) in growth chambers at either 7.5/5°C (LoT) or 15/10°C (HiT) average day/night temperatures, and with 2.5 or 7.5 mM
15N-labelled nitrate in the nutrient solution.Competition with grass led to a marked increase in the proportion of clover nitrogen derived from symbiosis (% Nsym). This increase was slower at LoT where % Nsym was reduced considerably; it was closely related to the reduction in the amount of available nitrate as a result of its being utilized by the grass.Nitrogen concentration in white clover herbage and dry matter yield per clover plant were reduced, for the most part, when a competing grass was present. The amount of nitrogen fixed per plant of white clover decreased markedly with temperature. Low temperature consequently accentuated competition for nitrate. The capacity of white clover to compete successfully was limited by its slower growth and nitrogen accumulation. 相似文献
10.
Soil carbon distribution with depth, stable carbon isotope ratios in soil organic matter and their changes as a consequence of the presence of legume were studied in three 12-year-old tropical pastures (grass alone —Brachiaria decumbens (C4), legume alone —Pueraria phaseoloides (C3) and grass + legume) on an Oxisol in Colombia. The objective of this study was to determine the changes that occurred in the13C isotope composition of soil from a grass + legume pasture that was established by cultivation of a native savanna dominated by C4 vegetation. The13C natural abundance technique was used to estimate the amount of soil organic carbon originating from the legume. Up to 29% of the organic carbon in soil of the grass + legume pasture was estimated to be derived from legume residues in the top 0–2-cm soil depth, which decreased to 7% at 8–10 cm depth. Improvements in soil fertility resulting from the soil organic carbon originated from legume residues were measured as increased potential rates of nitrogen mineralization and increased yields of rice in a subsequent crop after the grass + legume pasture compared with the grass-only pasture. We conclude that the13C natural abundance technique may help to predict the improvements in soil quality in terms of fertility resulting from the presence of a forage legume (C3) in a predominantly C4 grass pasture. 相似文献
11.
Four different methods: direct15N2 exposure, legume leaf labeled with15N,15N dilution and total N balance were applied to assess the nitrogen transfer (NT) from alfalfa to companion timothy. Evidence of NT was obtained in all cases, which represents about 3% of total N fixed by alfalfa or 10% of N content in timothy at the first cycle of growth. All the three15N methods gave identical results, while the conventional calculation of NT from the difference of N content in timothy from mixture and monoculture resulted in an over-estimation. The advantages and disadvantages of each method as applied to field conditions are discussed.Contribution No 1158 from the Plant Research Centre. 相似文献
12.
The contribution of nitrogen by promiscuous soybeans to maize based cropping the moist savanna of Nigeria 总被引:1,自引:0,他引:1
Agronomic results indicate that maize grain yields generally are higher when the crop is planted following soybean than in continuous maize cultivation in the moist savanna agroecological zones of West Africa. Many factors have been hypothesized to explain this phenomenon, including enhanced N availability and the so-called `rotational effect'. There is, however, hardly any quantitative information on the residual N benefits of promiscuous soybeans to subsequent cereal crops grown in rotation with soybean. Three IITA promiscuous soybean breeding lines and two Brazilian soybean lines were grown in 1994 and 1995 at Mokwa in the southern Guinea savanna, Nigeria, to quantify the nitrogen contribution by soybeans to a succeeding crop of maize grown in rotation with soybean for two consecutive years, 1996 and 1997 using two methods of introducing 15N into soil (fresh 15N labelling and its residual 15N) and three maize cultivars (including one cultivar with high N use efficiency) used as reference plants. The nodulating soybeans fixed between 44 and 103 kg N ha–1 of their total N and had an estimated net N balance input from fixation following grain harvest ranging from –8 to 43 kg N ha–1. Results in 1996 and in 1997 showed that maize growing after soybean had significantly higher grain yield (1.2 – 2.3-fold increase compared to maize control) except for maize cultivar Oba super 2 (8644-27) (a N-efficient hybrid). The 15N isotope dilution method was able to estimate N contribution by promiscuous soybeans to maize only in the first succeeding maize crop grown in 1996 but not in the second maize crop in 1997. The first crop of maize grown after soybean accumulated an average between 10 and 22 kg N ha–1 from soybean residue, representing 17–33% of the soybean total N ha–1. The percentage 15N derived from residue recovery in maize grown after maize was influenced by the maize cultivars. Maize crop grown after the N-efficient hybrid cultivar Oba Super 2 (844-27) had similar 15N values similar to maize grown after soybeans, confirming the ability of this cultivar to use N efficiently in low N soil due to an efficient N translocation ability. The maize crop in 1997 grown after maize had lower 15N enrichment than that grown in soybean plots, suggesting that soybean residues contributed a little to soil available N and to crop N uptake by the second maize crop. The differential mineralization and immobilization turnover of maize and soybean residues in these soils may be important and N contribution estimates in longer term rotation involving legumes and cereals may be difficult to quantify using the 15N labelling approaches. Therefore alternative methods are required to measure N release from organic residues in these cropping systems. 相似文献
13.
E. S. Jensen 《Plant and Soil》1987,101(1):29-37
The seasonal patterns of growth and symbiotic N2 fixation under field conditions were studied by growth analysis and use of15N-labelled fertilizer in a determinate pea cultivar (Pisum sativum L.) grown for harvest at the dry seed stage.
The patterns of fertilizer N-uptake were almost identical in pea and barley (the non-fixing reference crop), but more fertilizer-N
was recovered in barley than in pea. The estimated rate of N2 fixation in pea gradually increased during the pre-flowering and flowering growth stages and reached a maximum of 10 kg N
fixed per ha per day nine to ten weeks after seedling emergence. This was the time of early pod-development (flat pod growth
stage) and also the time for maximum crop growth rate and maximum green leaf area index. A steep drop in N2 fixation rate occurred during the following week. This drop was simultaneous with lodging of the crop, pod-filling (round
pod growth stage) and the initiation of mobilization of nitrogen from vegetative organs. The application of fertilizer-N inhibited
the rate of N2 fixation only during that period of growth, when the main part of fertilizer-N was taken up and shortly after. Total accumulation
of fixed nitrogen was estimated to be 244, 238 and 213 kg N ha−1 in pea supplied with nil, 25 or 50 kg NO
3
−
−N ha−1, respectively. About one-fourth of total N2 fixation was carried out during preflowering, one fourth during the two weeks of flowering and the remainder during post-flowering.
About 55% of the amount of N present in pods at maturity was estimated to be derived from mobilization of N from vegetative
organs. “Starter” N (25 or 50 kg NO
3
−
−N ha−1) did not significantly influence either dry matter and nitrogen accumulation or the development of leaf area. Neither root
length and root biomass determined 8 weeks after seedling emergence nor the yield of seed dry matter and nitrogen at maturity
were influenced by fertilizer application. 相似文献
14.
In this study, an approach involving a double isotope (15N and 34S) labelling technique was used to examine which of five reference crops (Eucalyptus camaldulensis, Cassia siamea, Cassia spectabilis, Lolium perenne and Eucalyptus grandis) would be suitable for measuring N fixed by Gliricidia sepium and Leucaena leucocephala. The rationale is that the ratio of fertilizer-derived S to soil-derived S in a suitable reference crop is similar to that measured in the nitrogen fixing tree (NFT) since the N ratios in the two crop types cannot be measured directly. E. camaldulensis and E. grandis were found to be suitable reference crops because they absorbed fertilizer and soil S in the same ratio as G. sepium and L. leucocephala. 相似文献
15.
Effect of plant genotype and nitrogen fertilizer on symbiotic nitrogen fixation by soybean cultivars
Summary Isotopic as well as non-isotopic methods were used to assess symbiotic nitrogen fixation within eight soybean [Glycine max (L.) Merr.] cultivars grown at 20 and 100 kg N/ha levels of nitrogen fertilizer under field conditions.The15N methodology revealed large differences between soybean cultivars in their abilities to support nitrogen fixation. In almost all cases, the application of 100 kg N/ha resulted in lower N2 fixed in soybean than at 20 kg N/ha in the first year of the study. However, N2 fixed in one cultivar, Dunadja, was not significantly affected by the higher rate of N fertilizer application. These results were confirmed by measurements of acetylene reduction activity, nodule dry weight and N2 fixed as measured by the difference method. Further proof of differences in N2 fixed within soybean cultivars and the ability of Dunadja to fix similar amounts of N2 at 20 and 100 kg N/ha was obtained during a second year experiment. Dunadja yield was affected by N fertilizer and produced larger yield at 100 kg N/ha than at 20 kg N/ha. This type of cultivar could be particularly useful in situations where soil N levels are high or where there is need to apply high amounts of N fertilizer.The present study reveals the great variability between legume germplasms in the ability to fix N2 at different inorganic N levels, and also the potential that exists in breeding for nitrogen fixation associative traits. The15N methodology offers a unique tool to evaluate germplasms directly in the field for their N2 fixation abilities at different N fertilizer levels. 相似文献
16.
15N-labelled ammonium nitrate was applied to spring barley growing on a Cambisol soil in western Switzerland. Immobilization, plant uptake and disappearance of inorganic nitrogen were followed at frequent intervals. Fertilizer nitrogen disappeared shortly after its application, mainly through immobilization by soil microorganisms and absorption by the crop. Some of the added nitrogen was probably denitrified as a result of humid conditions during the first days after fertilizer application. At the end of the growing season, 31% of the added nitrogen was recovered from the aerial barley plants, and 56% was immobilized by microorganisms. Most of the fertilizer nitrogen not used by the crop was immobilized in the upper 0–30 cm soil layer. This prevented downward movement of nitrate and limited nitrogen losses. Fertilizer efficiency was mainly determined by the competition between crop uptake and microbial immobilization. Careful consideration of the time of fertilization, taking into account plant growth and weather conditions, can result in an increase in fertilizer efficiency and minimal pollution. 相似文献
17.
Use of isotope dilution to measure nitrogen fixation associated with the roots of sorghum and millet genotypes 总被引:2,自引:0,他引:2
Summary Genotypes of sorghum and millet have previously been found to have different amounts of root-associated acetylene reduction activity. Isotope dilution experiments using15N have been carried out to evaluate the amount of nitrogen fixed by bacteria which is incorporated into the different genotypes when grown in vermiculite in the glasshouse. Isotope dilution result indicated that the content of shoot nitrogen derived from biological nitrogen fixation varied by up to 27% between sorghum genotypes and 17% between millet genotypes. Considerable isotope dilution also resulted from uptake of non-exchangeable-N (as NH
4
+
) in the vermiculite. It is possible that the genotypic differences in isotope dilution may reflect differences in the ability of plants to take up non-exchangeable-N, and that vermicultite is therefore an unsuitable growth medium for such studies.Published as Journal Article No. 493 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru P.O., Andhra Pradesh 502 324, India. 相似文献
18.
A plant mixture of white clover (Trifolium repens L.), red clover (Trifolium pratense L.), and ryegrass (Lolium perenne L.) was established in the spring of 1991 under a cover-crop of barley. Treatments were two levels of nitrogen (400 and 20 kg N ha-1) and two cutting intensities (3 and 6 cuts per season). Fixation of atmospheric derived nitrogen was estimated by two 15N dilution methods, one based on application of 15N to the soil, the other utilising small differences in natural abundance of 15N.Both methods showed that application of 400 kg N ha-1 significantly reduced dinitrogen fixation, while cutting frequency had no effect. Atmospheric derived nitrogen constituted between 50 and 64% of harvested clover nitrogen in the high-N treatment, while between 73% and 96% of the harvested clover nitrogen was derived from the atmosphere in the low-N treatment. The amounts of fixed dinitrogen varied between 31–72 kg N ha-1 and 118–161 kg N ha-1 in the high-N and low-N treatment, respectively. The highest values for biological dinitrogen fixation were estimated by the enriched 15N dilution method.Estimates of transfer of atmospheric derived nitrogen from clover to grass obtained by the natural 15N abundance method were consistently higher than those obtained by the enriched 15N dilution method. Neither mineral nitrogen application nor defoliation frequency affected transfer of atmospheric derived nitrogen from clover to grass.Isotopic fractionation of 14N and 15N (B value) was estimated by comparing results for nitrogen fixation obtained by the enriched 15N dilution and the natural 15N abundance method, respectively. B was on average +1.20, which was in agreement with a B value determined by growing white clover in a nitrogen free media. 相似文献
19.
F. Azam 《Plant and Soil》1990,125(2):255-262
A pot experiment was conducted to study the effect of organic and inorganic nitrogen (N) sources on the yield and N uptake
of rice from applied and native soil-N. The residual effect of these N sources on a succeeding wheat crop was also studied.
Organic N was applied in the form of 15N-labelled Sesbania aculeata L., a legume, and inorganic N in the form of 15N-labelled ammonium sulphate. The two sources were applied to the soil separately or together at the time of transplanting
rice.
Recovery of N by rice from both the applied sources was quite low but both sources caused significant increases in biomass
and N yield of rice. Maximum increase was recorded in soil treated with organic N. The residual value of the two materials
as source of N for wheat was not significant; the wheat took up only a small fraction of the N initially applied. Loss of
N occurred from both applied N sources, the losses being more from inorganic N.
Both applied N sources caused a substantial increase in the availability of soil-N to rice and wheat; most of this increase
was due to organic N and was attributed to the so-called ‘priming’ effect or ANI (added nitrogen interaction) of the applied
material. 相似文献
20.
Summary Lucerne is an important forage legume in the south and south-east of Sweden on well-drained soils. However, data is lacking on the apparent amount of nitrogen derived through N2 fixation by field-grown lucerne. This report provides basic information on the subject. The experiment was performed in a lucerne ley grown 40 km north of Uppsala. The input of nitrogen through fixation to the above-ground plant material of an established lucerne (Medicago sativa L.) ley was estimate by15N methodology during two successive years. The amount of fixed N was 242 kg N ha–1 in 1982 and 319 kg N ha–1 in 1983. The proportion of N derived from the atmosphere (%Ndfa) was 70% and 80% for the two years respectively. The first harvest in both years contained a lower proportion fixed N. Both N2 fixation and dry matter production were enhanced during the second year, particularly in the first harvest. The Ndfa was 61% in the first harvest in 1982, compared to 72% Ndfa during the same period in 1983. This demonstrates the strong influence of environment on both dry matter production and N2 fixation capacity of the lucerne.In addition anin situ acetylene reduction assay was used in 1982 to measure the seasonal distribution of the N2 fixation and in 1983 to study the effect of soil moisture on the N2 fixation process. The seasonal pattern showed great dependence on physiological development and harvest pattern of the lucerne ley. The maximum rate of N2 fixation occurred at the bud or early flower stage of growth and was followed by a rapid decline as flowering proceeded. After harvest the nitrogenase activity markedly decreased and remained low during at least two weeks until regrowth of new shoots began. Irrigation doubled the nitrogenase activity of the lucerne in late summer 1983, when soil moisture content in the top soil was near wilting point. No changes in nitrogenase activity did occur in response to watering earlier during the summer, when the soil matric potential was around –0.30 MPa. 相似文献