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1.
The effects of 15N-labelled ammonium nitrate, urea and ammonium sulphate on yield and uptake of labelled and unlabelled N by wheat (Triticum aestivum L. cv. Mexi-Pak-65) were studied in a field experiment. The dry matter and N yields were significantly increased with fertilizer N application compared to those from unfertilized soil. The wheat crop used 64.0–74.8%, 61.5–64.7% and 61.7–63.4% of the N from ammonium nitrate, urea and ammonium sulphate, respectively. The fertilizer N uptake showed that ammonium nitrate was a more available source of N for wheat than urea and ammonium sulphate. The effective use of fertilizer N (ratio of fertilizer N in grain to fertilizer N in whole plant) was statistically similar for the three N fertilizers. The application of fertilizer N increased the uptake of unlabelled soil N by wheat, a result attributed to a positive added N interaction, which varied with the method of application of fertilizer N. Ammonium nitrate, urea and ammonium sulphate gave 59.3%, 42.8% and 26.3% more added N interaction, respectively, when applied by the broadcast/worked-in method than with band placement. A highly significant correlation between soil N and grain yield, dry matter and added N interaction showed that soil N was more important than fertilizer N in wheat production. A values were not significantly correlated with added N interaction (r=0.719). The observed added N interaction may have been the result of pool substitution, whereby added labelled fertilizer N stood proxy for unlabelled soil N.  相似文献   

2.
We studied the effects of 15N-labelled ammonium nitrate and urea on the yield and uptake of labelled and unlabelled N by wheat (Triticum aestivum L., cv. Mexi-Pak-65) in a field experiment. The dry matter and N yields were significantly increased with fertilizer N application compared to those from unfertilized soil. The wheat crop used 33.6–51.5 and 30.5–40.9% of the N from ammonium nitrate and urea, respectively. Splitting the fertilizer N application had a significant effect on the uptake of fertilizer N by the wheat. The fertilizer N uptake showed that ammonium nitrate was a more available source of N for wheat than urea. The effective use of fertilizer N (ratio of fertilizer N in grain to fertilizer N in whole plant) was statistically similar for the two N fertilizers. The application of fertilizer N increased the uptake of unlabelled soil N by wheat, a result attributed to a positive added N interaction, which varied according to the fertilizer N split; six split applications gave the highest added N interaction compared to a single application or two split applications for both fertilizers. Ammonium nitrate gave 90.5, 33.5, and 48.5% more added N interaction than urea with one, two, and six split N applications. A values were not significantly correlated with the added N interaction (r=0.557). The observed added N interaction may have been the result of pool substitution, whereby added labelled fertilizer N replaced unlabelled soil N.  相似文献   

3.
Summary The uptake of labelled and unlabelled N by wheat was measured in a field experiment using 15N-labelled ammonium nitrate fertilizer. The dry matter yield and N yields were significantly increased with fertilizer N application compared to those from unfertilized soil. The uptake of applied N by wheat ranged between 25 and 34%. Fertilizer N application increased the uptake of unlabelled soil N which was attributed to a positive priming effect or added N interaction. The added N interaction observed by applying 20, 60, and 120 kg fertilizer N was 11.4, 19.1, and 27.9 kg, corresponding to 26, 44 and 64%, respectively of the N taken up from unfertilized soil. The A values did not alter with the increase in fertilizer N application. The observed added N interaction may have been the result of pool substitution whereby added labelled fertilizer N stood proxy for unlabelled soil N. A significant correlation coefficient (r=0.996**) between the uptake of soil N and the dry matter yield showed that soil N was more important than fertilizer N in wheat production.  相似文献   

4.
Summary We used 15N technology to investigate N2 fixation by Sesbania speciosa and Sesbania rostrata and its transfer to a lowland rice crop after incorporation of the Sesbania spp. into soil as green manure. During the first 50 days after establishment in November–December 1989, S. speciosa and S. rostrata produced 1126 and 923 kg dry matter ha-1 respectively. They gathered 31 and 23 kg N ha-1 respectively, of which 62%±5% and 55%±3% respectively, came from N2 fixation. Both these species produced a greater biomass during September–October 1989, with S. rostrata producing more than S. speciosa. These results reflected differential responses by the plants to different day lengths at different times of the year. Furthermore, the dry matter yield and %N of 15N-labelled S. speciosa were smaller than those of the unlabelled plants, possibly due to inhibition of N2 fixation in root nodules by the chemical N fertilizers added during labelling. These differences were not so pronounced in the stem-nodulated S. rostrata. The increased grain yield of rice fertilized with N in the form of chemical fertilizer or green manure was a result of an increased number of panicles per hill. The rice crop manured with S. speciosa produced a lower grain yield, with a lower grain weight than that manured with S. rostrata. This was due to a low uptake of soil N by rice manured with S. speciosa. Recovery of N from the green manure in rice straw with S. speciosa was significantly higher than from rice manured with S. rostrata, because of the higher applied N uptake by rice manured with the former.  相似文献   

5.
Summary A pot experiment was conducted to study the availability of soil and fertilizer N to wetland rice as influenced by wheat straw amendment (organic amendment) and to establish the relative significance of the two sources in affecting crop yield. Straw was incorporated in soil at 0.1, 0.2, and 0.3% before transplanting rice. Inorganic N as 15N-ammonium sulphate was applied at 30, 60, and 90 g g-1 soil either alone or together with wheat straw in different combinations. After harvesting the rice, the plant and soil samples were analyzed for total N and 15N. Straw incorporation significantly decreased the dry matter and N yield of rice, the decrease being greater with higher rates of straw. The reduction in crop yield following the straw incorporation was attributed mainly to a decrease in the uptake of soil N rather than fertilizer N. The harmful effects of organic matter amendment were mitigated by higher levels of mineral N addition. The uptake of applied N increased and its losses decreased due to the straw incorporation. Mineral N applied alone or together with organic amendment substantially increased the uptake of unlabelled soil N. The increase was attributed to a real added N interaction.  相似文献   

6.
To evaluate the impact of top-pruning time on fertilizer N use efficiency (NUE) of flue-cured tobacco, we adopted 15N tracing technique and conducted a 2-year experiment from 2014 to 2015 in eastern China. The experiment included three top-pruning points of time: 5th, 25th and 45th day after flowering (DAF), abbreviated, respectively, as TP5, TP25 and TP45. The amounts of plant N derived from fertilizer (Ndff) and soil (Ndfs) were observed during 0–55th DAF. Results showed that top-pruning slowed down the increase of Ndff in tobacco organs, particularly in the leaf, but accelerated the increase of Ndfs dramatically. The proportion of Ndff (%) accounted for the total N reduced dramatically after top-pruning. This reduction might attribute to the selectivity of plant to different N sources as influenced by top-pruning while had little relationship with soil N supply, according to the analysis on the soil total mineral N and mineral 15N. The average NUE for the 2 years was 32%, 41% and 47%, respectively, for TP5, TP25 and TP45, showing significant (p < 0.05) differences. We concluded that the tobacco preferred to uptake soil N rather than fertilizer N after top-pruning; thus, optimizing the top-pruning time might be one of the approaches to improve the in-season NUE of flue-cured tobacco.  相似文献   

7.
Abstract

A field study with maize (Zea mays L.) was conducted in the 1988/89 cropping season to investigate the fate of 15NO3-N-labelled NH4 15NO3 applied at 40, 80 and 120 kg N ha?1 (unlabelled N applied at 0, 80, 160 and 240 N ha?1) with and without lime. The investigations were conducted in northern Zambia at Misamfu Regional Research Centre, Kasama on a Misamfu red sandy loam soil. The experimental design was a split plot arrangement with four replications with main plots receiving 0 and 2 Mg ha?1 dolomitic limestone, while subplots received fertilizer N at various rates. Significant (p < 0.001) grain and DM yield responses to applied N up to 160 kg ha?1 were observed. At higher rates little or no crop responses were observed and fertilizer use efficiency declined. Partitioning of amounts of total N and 15N in plants was in the order of seed = tassel > leaf> cob = earleaf> stem. Fertilizer N rates showed a highly significant (p < 0.001) effect on plant uptake of labelled N. Lime and its interaction with N rates had no effect on all measured parameters. Leaching of NO3-N fertilizer to lower soil depths was in proportion to the rate of N applied, with highly significant (p < 0.001) differences among soil depths. Although higher concentrations of fertilizer-15N were recovered in the 0–20 cm depth the recovered portion at lower soil depths was still significant. Total recovery of labelled N by plant and by soil after crop harvest averaged 75, 55 and 54% of originally applied fertilizer-15N at 40, 80 and 120 kg N ha?1, respectively. Corresponding unaccounted for 15N was 25, 45 and 46%. The most probable loss mechanism could have been by leaching to depths greater than 60 cm, gaseous losses to the atmosphere and root assimilation.  相似文献   

8.
Summary Using 15N, the fate of N applied to wetland rice either as Azolla or urea was studied in a field at the International Rice Research Institute (IRRI). In bigger plots nearby, yield response and N uptake were also determined with unlabelled N sources. Azolla microphylla was labelled by repeated application of labelled ammonium sulfate. Labelled and unlabelled N were used alternately in applications of Azolla or urea 0 and 42 days after transplanting, in order to determine the effect of the time of application on the availability of Azolla N. The quantities of Azolla N incorporated were 23% more than those of urea N (30 kg N ha–1) in the isotope plots or 7% less in the yield response plots. Grain yield and total N uptake by the rice plants in the yield-response plots were higher in the urea-treated plots than in the Azolla-treated plots, but the physiological effect of Azolla N (grain yield response/increase in N uptake) was higher than that of rea. The labelled N balance was studied after the first and second crops of rice. Losses of labelled N after the first crop were higher from urea (30%–32%) than from Azolla (0%–11 %). Losses in N applied as a side dressing 42 days after transplanting were less than those of N applied basally. No further losses of 15N occurred after the first crop. The recovery of Azolla 15N in the first crop of rice was 39% from the basal application and 63% from the side dressing. The recovery of urea 15N was 27% from the basal application and 48% from the side dressing. Recoveries of residual N from both Azolla and urea during the second rice crop were similar. Laboratory incubation of the Azolla used and the changes in labelled exchangeable N in the soil showed that at least 65% of Azolla N (4.7% N content) was mineralized within 10 days.  相似文献   

9.
Summary A pot experiment was conducted to compare the yields from five commercially cultivated varieties (Bas-198, Bas-370, Bas-Pak, Bas-385, and IR-6) of rice (Oryza sativa L.) and to establish the relative significance of soil N and fertilizer N (15N-labelled ammonium sulphate) in affecting crop performance. Another aim was to study the interaction of fertilizer N and soil N as influenced by different rice varieties. Among the five varieties tested, Bas-Pak gave the maximum dry matter and N yield. The N-use efficiency (percentage of applied N taken up by the plants) of different varieties ranged between 33.7 and 43.7%, Bas-Pak being the most efficient. Significant losses of fertilizer N occurred from the soil-plant system. The maximum N loss (52.1% of applied N) was observed with IR-6 and the minimum loss (39.2%) with Bas-Pak. A substantial increase in the uptake of soil N following the application of fertilizer and an interaction between the two N sources were observed with all varieties except Bas-385. The interaction was attributed to greater root proliferation following the application of fertilizer. It was concluded that a varietey with greater potential to use soil N is likely to give a better yield and that, of the two N sources, the availability of soil N was more important in determining the yield performance of different varieties of rice.  相似文献   

10.
Summary The dynamics of basally applied 15N-labeled ammonium sulfate in inorganic and organic soil fractions of five wetland rice soils of the Philippines was studied in a greenhouse experiment. Soil and plant samples were collected and analyzed for 15N at various growth stages. Exchangeable NH4 + depletion continued after 40 days after transplanting (DAT) and corresponded with increased nitrogen uptake by rice plants. Part of the applied fertilizer was fixed by 2:1 clay minerals, especially in Maligaya silty clay loam, which contained beidellite as the dominant clay mineral. After the initial fixation, nonexchangeable 15N was released from 20 DAT in Maligaya silty clay loam, but fixation delayed fertilizer N uptake from the soil. Part of the applied N was immobilized into the organic fraction. In Guadalupe clay and Maligaya silty clay loam, immobilization increased with time while the three other soils showed significant release of fertilizer N from the organic fraction during crop growth. Most of the immobilized fertilizer N was recovered in the nondistillable acid soluble (alpha-amino acid + hydrolyzable unknown-N) fraction at crop maturity. Between 61% and 66% of applied N was recovered from the plant in four soils while 52% of fertilizer N was recovered from the plant in Maligaya silty loam. Only 20% – 30% of the total N uptake at maturity was derived from fertilizer N. Nmin (mineral N) content of the soil before transplanting significantly correlated with N uptake. Twenty-two to 34% of applied N was unaccounted for possibly due to denitrification and ammonia volatilization.  相似文献   

11.
Summary Soil N dynamics and barley yields (Hordeum vulgare L.) were compared in pot experiments using surface samples from a Gray Luvisol under three cropping systems at Breton, Alberta: (1) an agroecological 8-year rotation including cereals, forage, and fababeans (Vicia faba L.) as green manure, from wich two plots were selected, one following fababeans, and the second following 3 years of forage; (2) a continuous grain system, with fertilizer N at 90 kg ha-1 year-1; and (3) a classical Breton 5-year rotation [following oats (Avena sativa L.)] involving forage and cereals, without returning crop residues to the land, selecting one plot with PKS treatment and a second as control. The fertilizer N equivalent for the cropping system; AN value and A value (analogous to AN), but in fertilizer 15N units, soil biomass, and C and N mineralization were monitored. In the first agroecological plot (after fababeans), grain and total plant biomass production were 116% greater than from the continuous grain treatment. Barley plants in the two agroecological plots derived 48.5% and 37.8%, respectively, of their N requirement from non-labelled soil N sources not present in the continuous grain plot. At crop maturity, the recovery of 15N microbial biomass was 1.5 times higher in soil from the first agroecological plot than from the continuous grain plot. The fertilizer N equivalent was 2670 mg pot-1 (485 kg ha-1) for the first and 1850 mg pot-1 for the second agroecological treatment. Fertilizer N equivalent values exceed net amounts of N mineralized by a factor of 4. Recovery by the barley crop of 15N added at 55 mg pot-1 was more efficient in the agroecological treatments (45%–51%) than in the continuous grain or classical Breton treatments (35%–37%). It was concluded (1) that past soil history may be associated more with the ability of barley plants to compete for available N, and hence the use of N, than with net soil N mineralization; and (2) an increased supply of N to crops following the incorporation of fababean residues, manure application, and the soil N-conserving effect of growing legumes were all partly responsible for the observed differences in soil fertility.  相似文献   

12.
The effect of acetylene (provided by wax-coated calcium carbide, CaC2) on N transformations in a red-brown earth was measured in a field experiment with irrigated wheat by determining the change in the concentration and 15N enrichment of the organic N and mineral N pools with time. The study was conducted in the Goulburn-Murray Irrigation region of south-eastern Australia using 0.3 m by 0.3 m microplots fertilized with 15N-labelled urea (10 g N m-2; 5 atom% 15N). Acetylene was effective in slowing the nitrification of both unlabelled and labelled N. Nitrate derived from the added fertilizer reached a maximum 19 days after sowing in the treatment without CaC2, whereas little nitrate accumulated in the 8 g CaC2 m-2 treatment. There was significant immobilization of the urea N by 19 days after sowing in all treatments, but the extent of immobilization was not affected by the acetylene. The addition of acetylene slowed net mineralization of labelled and unlabelled N from the organic N pool, and resulted in increased accumulation of both unlabelled and labelled N in wheat tops.  相似文献   

13.
Summary The common bean (Phaseolus vulgaris L.) is generally regarded as a poor N2 fixer. This study assessed the sources of N (fertilizer, soil, and fixed N), N partitioning and mobilization, and soil N balance under field conditions in an indeterminate-type climbing bean (P. vulgaris L. cv. Cipro) at the vegetative, early pod-filling, and physiological maturity stages, using the A-value approach. This involved the application of 10 and 100 kg N ha-1 of 15N-labelled ammonium sulphate to the climbing bean and a reference crop, maize (Zea mays L.). At the late pod-filling stage (75 days after planting) the climbing bean had accumulated 119 kg N ha-1, 84% being derived from fixation, 16% from soil, and only 0.2% from the 15N fertilizer. N2 fixation was generally high at all stages of plant growth, but the maximum fixation (74% of the total N2 fixed) occurred during the interval between early (55 days after planting) and late podfilling. The N2 fixed between 55 and 75 days after planting bas a major source (88%) of the N demand of the developing pod, and only about 11% was contributed from the soil. There was essentially no mobilization of N from the shoots or roots for pod development. The cultivation of common bean cultivars that maintain a high N2-fixing capacity especially during pod filling, satisfying almost all the N needs of the developing pod and thus requiring little or no mobilization of N from the shoots for pod development, may lead to a net positive soil N balance.  相似文献   

14.
Summary Considerable effort has been spent in developing chemical indices to predict N mineralization. However, in spite of numerous studies, the relationship between the index value and plant N uptake has not been as apparent as hoped, and therefore, additional work is required to evaluate the ability of promising new indices to predict the extraction of mineralizable N from soil. The objective of the present study was to evaluate the use of phosphate borate and hot KCl to extract immobilized 15N-labeled fertilizer, applied 1 and 2 years previously. Soil samples (0–15 cm) were collected on 12 June 1989 from field soil fertilized in either 1987 or 1988 with 15N-labeled urea. In the laboratory, net N mineralization over 51 days and the amount of N extracted by the phosphate borate and hot KCl methods were determined. In the field, the amount of residual fertilizer and soil plus fixed N in soybeans (Glycine max) at the V5 growth stage were determined on 12 June 1989. The extractability ratio (ER*) and the mineralizable extractability ratio (MER) were higher for mineralizable N and phosphate borate N for fertilizer applied in 1988 than 1987, while ER* and MER values for the hot KCl were similar for both application dates. These results suggest that compositional changes occurred which influenced the extractability and mineralization of residual fertilizer applied 1 and 2 years previously, and that the phosphate borate was able to predict these changes while the hot KCl method was not.  相似文献   

15.
Pot experiments were conducted with two soils, from Rottenhaus and Seibersdorf in Austria, to ascertain whether the rate of fertilizer N application and the test crop would influence the amount of N available in the soil as assessed by the A-value method. 15N-labelled fertilizer was applied at rates of 10, 25, 40, 60, and 100 mg N kg-1 soil, corresponding approximately to 20, 50, 80, 120 and 200 kg N ha-1 respectively, and two crop species, barley (Hordeum vulgareL.) and non-nodulating soybean (Glycine max L.) were used to determine the soil A N value under the various fertilizer regimes. The results showed that the Rottenhaus soil had a higher A N value than the Seibersdorf soil, suggesting that the former was more fertile than the latter. The A N values of both soils were significantly affected by the level of N application. When grown in the same soil, the two test crops showed significantly different fertilizer use efficiency and per cent N derived from fertilizer when the rate of N application exceeded 20 kg ha-1. Thus, the A N value as determined by the two test crops differed significantly for the same soil when the rate of N application was greater than 20 kg/ha. The difference was greater when the soil fertility level was high. The dependence of the A N value on the level of N application and the species of crop seriously compromises the suitability of this method for determining plant-associated N2 fixation. Hence, considerable caution is required when using this method to estimate plant-associated N2 fixation.  相似文献   

16.
Summary Leptochloa fusca (L.) Kunth (kallar grass) has previously been found to exhibit high rates of nitrogen fixation. A series of experiments to determine the level of biological nitrogen fixation using 15N isotopic dilution were carried out in nutrient solution and saline soil. In the nutrient solution, E. coli inoculated plants were taken as non-nitrogen-fixing control. It was observed that nearly 60%–80% of the plant N was derived from atmospheric fixation. Estimations based on the N difference method gave much lower values (18%–35%). In experiments with saline soil which was initially sterilized with chloroform fumigation, a mixed culture of N2-fixing rhizospheric isolates from kallar grass roots was inoculated and planted to kallar grass. Uninoculated treatments were regarded as controls. The soil was previously labelled with 15N by adding cellulose and (15NH4)2SO4. The results of these studies showed fixation values of 6%–32% when estimated by 15N dilution, whereas by the N difference method 54% of the plant N was estimated to be derived from fixation. This discrepancy is due to the increase in root proliferation due to inoculation, which results in greater uptake of soil N. The distribution of 15N in different fractions of the soil-N indicted isotopic dilution due to bacterial fixation of atmospheric N2.  相似文献   

17.
Agricultural systems that receive high amounts of inorganic nitrogen (N) fertilizer in the form of either ammonium (NH4+), nitrate (NO3−) or a combination thereof are expected to differ in soil N transformation rates and fates of NH4+ and NO3−. Using 15N tracer techniques this study examines how crop plants and soil microbes vary in their ability to take up and compete for fertilizer N on a short time scale (hours to days). Single plants of barley (Hordeum vulgare L. cv. Morex) were grown on two agricultural soils in microcosms which received either NH4+, NO3− or NH4NO3. Within each fertilizer treatment traces of 15NH4+ and 15NO3− were added separately. During 8 days of fertilization the fate of fertilizer 15N into plants, microbial biomass and inorganic soil N pools as well as changes in gross N transformation rates were investigated. One week after fertilization 45-80% of initially applied 15N was recovered in crop plants compared to only 1-10% in soil microbes, proving that plants were the strongest competitors for fertilizer N. In terms of N uptake soil microbes out-competed plants only during the first 4 h of N application independent of soil and fertilizer N form. Within one day microbial N uptake declined substantially, probably due to carbon limitation. In both soils, plants and soil microbes took up more NO3− than NH4+ independent of initially applied N form. Surprisingly, no inhibitory effect of NH4+ on the uptake and assimilation of nitrate in both, plants and microbes, was observed, probably because fast nitrification rates led to a swift depletion of the ammonium pool. Compared to plant and microbial NH4+ uptake rates, gross nitrification rates were 3-75-fold higher, indicating that nitrifiers were the strongest competitors for NH4+ in both soils. The rapid conversion of NH4+ to NO3− and preferential use of NO3− by soil microbes suggest that in agricultural systems with high inorganic N fertilizer inputs the soil microbial community could adapt to high concentrations of NO3− and shift towards enhanced reliance on NO3− for their N supply.  相似文献   

18.
The fate of fertilizer N applied with different irrigation amounts in tobacco fields was quantitatively studied by applying 15N double-labelled NH4NO3 in lysimeters. The 15N (fertilizer N originating from the fertilizer applied in 2011) in tobacco plants, 15N in soils and 15N loss were observed continuously from 2011 to 2014. The results showed that 21.6% of 15N was utilized by tobacco plants, 72.1% remained in the 0–60 cm soil layer and 6.3% was lost from the soil–plant system after the first season’s harvest (2011) of flue-cured tobacco. During the four seasons from 2011 to 2014, cumulative utilization of 15N by tobacco plants was 34.3%, while 54.2% remained in the 0–60 cm soil layer, and 11.5% was lost via mechanisms such as leaching and volatilization. The fate of 15N in terms of accumulation in plants and soils or losses from the soil–plant system from 2012 to 2014 was greatly affected by the fertilizer and irrigation management strategies in 2011. The results of this investigation suggest that the major amount of fertilizer N applied during the first season remains available in the soil for utilization by tobacco plants after 4 years.  相似文献   

19.
Summary The legume Medicago sativa (+Rhizobium melilott) was grown under controlled conditions to study the interactions between soluble P in soil (four levels), or a mycorrhizal inoculum, and the degree of water potential (four levels) in relation to plant development and N2 fixation. 15N-labelled ammonium sulphate was added to each pot for a qualitative estimate of N2 fixation, in order to rank the effects of the different treatments.Dry-matter yield, nutrient content and nodulation increased with the amount of plant-available P in the soil, and decreased as the water stress increased, for each P-level. The mycorrhizal effect on dry matter, N yield, and on nodulation was little affected by the water potential. Since P uptake was affected by the water content in mycorrhizal plants, additional mechanisms, other than those mediated by P, must be involved in the mycorrhizal activity.There was a positive correlation between N yield and nodulation for the different P levels and the mycorrhizal treatment at all water levels. A high correlation between plant unlabelled N content and atom% 15N excess was also found for all levels of P. In mycorrhizal plants, however, the correlation between unlabelled N yield and 15N was lower. This suggests that mycorrhiza supply plants with other N sources in addition to those derived from the improvement on N2 fixation.  相似文献   

20.
Summary An attempt has been made to estimate quantitatively the amount of N fixed by legume and transferred to the cereal in association in intercropping systems of wheat (Triticum aestivum L.) — gram (Cicer arietinum L.) and maize (Zea mays L.) —cowpea (Vigna unguiculate L.) by labelling soil and fertilizer nitrogen with 15N. The intercropped legumes have been found to fix significantly higher amounts of N as compared with legumes in sole cropping if the intercropped cereal-legume received the same dose of fertilizer N as the sole cereal crop. But when half of the dose of the fertilizer N applied to sole cereal crop was received by intercropped plants, the amount of N fixed by legumes in association with cereals was significantly less than that fixed by sole legumes. Under field conditions 28% of the total N uptake by maize (21.2 kg N ha–1) was of atmospheric origin and was obtained by transfer of fixed N by cowpea grown in association with maize. Under greenhouse conditions gram and summer and monsoon season cowpea have been found to contribute 14%–20%, 16% and 32% of the total N uptake by associated wheat and summer and monsoon maize crops, respectively. Inoculation of cowpea seeds with Rhizobium increased both the amount of N fixed by cowpea and transferred to maize in intercropping system.  相似文献   

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