[en] Five groundnut cultivars were grown at an upland site in Khon Kaen to study the residual benefit of the stover to a following maize crop. Nitrogen fixation was estimated in the groundnuts using the ¹⁵N isotope dilution technique. Three independent estimates were made of the residual nitrogen benefit to maize crop when the groundnut stover was either removed or returned. It was found that the maize crop grain N and dry weights were up to 87% and 65% greater respectively in the plots where the stover was returned as compared with the plots where the stover was removed. In a second experiment the increases in grain yields and total N in rice grown after incorporation of groundnut stover were significant but not so dramatic as with maize. However, ¹⁵N analysis of the rice grain and stover indicated that over 30% of the nitrogen in the rice corp was supplied by the groundnut stover. This work indicated the considerable ability of local groundnut varieties to fix atmospheric nitrogen and the benefits possible from returning and incorporating legume residues to the soil in the upland and lowland cropping systems of Northeast Thailand

[en] Determination of atmospheric N₂ fixation by difference method and ¹⁵N technique in soybean plant. An experiment using a randomized block design with four replicates has been carried out to determine the percentage (%) and content (mg N/plant) of N derived from fixation (N-dffix) of soybean. The methods used were the difference method and the ¹⁵N technique. Data from this experiment showed that both methods could be used to determine atmospheric N₂ fixation, but in certain circumstances the ¹⁵N methods is superior to the difference method. (author). 11 refs

[en] DiNitrogen-fixing capacity of four species of leguminous trees of Sri Lanka (Abarema bigemina, Adenanthera bicolor, Humboldtia laurifolia and Pericopsis mooniana) by analyzing their xylem sap and by taking acetylene reducyion (AR) measurements of nodulated roots of all species, except A.bicolor which had no nodules. Based on the results of the study on P.mooniana, a method to determine the C₂H₂/N₂ conversion factor by analysing the total NH₂ compounds is being developed

[en] Determination of atmospheric N₂ fixation by difference method and N¹⁵ in technique in soybean plant. An experiment using a randomized bloc design with four replicites has been carried out to determine the percentage (%) and content (mg N/plant) of N derived from fixation (N-dffix) of soybean. The methods used were the difference methods and the ¹⁵N technique. Data from this experiment showed that both methods could be used to determine atmospheric N₂ fixation, but in certain circumstances N¹⁵ method in superior to the difference method. (author). 11 refs

[en] In order to quantify the biological nitrogen fixation (BNF) and to evaluate the mycorrhiza effect in the BNF, an experiment was carried on by applying ¹5^N-ammonium sulphate and mycorrhiza fungi to the soil. The treatments included legumes: mucuna negra(Stizolobium atterrinum Piper et Tracv) and caupi (Vigna unguiculoata L. Walp). Two control plants: non nodulating soybean (Glycine max L.Merril) and rice (Oryza sativa), were used for measuring the fixed N in the legumes by isotope dilution method. Both legumes and control plants assimmilated the same ammounts of nitrogen from the soil and fertilizer. The greater N content in the legumnes was determined as coming from the fixed nitrogen. Rice and non nodulating soybean showed to be good controls for measuring biological nitrogen fixation using isotopic dilution method. The values of fixed nitrogen for legumes calculated using rice as control plant were slightly greater than those with non nodulating soybean, nevertheless there were no significant statistical differences between the values. The mucuna fixed more N than caupi in both mycorrhiza treatments (76.7, 66.6 and 56. 7 per cent of N fixed, respectively). The mycorrhiza increased dry matter yield (13.84 per cent), accumulation of N in the plant(14.85 per cent N) and the biological N fixation (16.06 per cent N-fixed) in caupi

[en] A Field experiment was conducted at the Chiang Mai field crops research center to study the response and nitrogen fixation of soybeans on nitrogen fertilizer supplementation at early pod-filling stage. Two soybean genotypes SJ5 and NW1 were used in this study. Experimental design was split plot in RCB. Supplemental nitrogen was added at pod-filling stage in the rate of 0, 3, 6 and 9 kg N/ria. ¹⁵ N labelled ¹⁵(N H₄)₂ SO₄ was added for 4 plants per treatment in the 3 x 5 m² subplot. The harvesting area was 2.2 x 4.0 m². The cultural practices followed the recommended standards of the farmer, by mixing the seeds with Rhizobium inoculant. Basal fertilizer was added at the rate of 3 - 9 - 6 (N - P₂ O₅ - K₂ O) kg/ria at planting. The results showed that soybean NW1 seed yield increase 26% to the addition of supplemental nitrogen at 3 kg N/ria whereas SJ5 gave no response for all 3 rates of nitrogen addition. There was a significant response in both genotypes in terms of seed protein. The seed protein for both genotypes increased with the incremental addition of supplemental nitrogen at rate of 9 kg N/ria, average about 3.6%. ¹⁵ N isotope dilution method indicated that no fixation occurred with N supplementation for both genotypes. But the percent fertilizer use efficiency (% FUE) significantly decreased with rates of N supplementation. The % FUE of NW1 was lower than SJ5 due to the short maturity. Total N yield for each vegetative part of SJ5 was no significantly different with the three rates of N addition. Total N yield in grain of NW1 increased with increasing of supplemental nitrogen. It is therefore concluded that nitrogen applied to the plant at pod-filling is the growth factor, to promote production and seed quality of NW1 in Chiang Mai

[en] A field experiment was conducted for long term rice-soybean cropping system at Chiang Mai Field Crop Research Center, to estimate nitrogen fixation of soybean and residual benefit of the soybean stover to a following rice crop. Nitrogen fixation was estimated in the soybean using ¹⁵ N dilution technique and non nodulated groundnut as a standard crop. To estimate the residual nitrogen benefit to the rice crop was calculated by nitrogen-15 yield of rice where the soybean stover was either removed or returned. In the first year soybean fixed 48.42% of their nitrogen which producing 50.31 KgN/ha. Residual effect of soybean stover returned was 36.72% of nitrogen in rice which equal 50.62 KgN/ha. come from the soybean returned (stover plus root and nodule under the ground where the soybean stover was returned). The residual nitrogen-15 in the second year was too low to detect. No nitrogen fertilizer applied to the following rice plot where the soybean stover was returned, grain dry matter yield were up to 12% (1^st year) and 27% (2^nd year) grater than in the plots where the soybean stover was removed produce the highest grain dry matter yield which were higher 14 - 29% than the plots where the soybean stover was removed

[en] This study was performed at the ''San Jorge'' experimental farm of the Instituto Colombiano Agropecuario (ICA), Bogota, Colombia. The study was performed to investigate the effect of timing of application of nitrogen fertilizer on the productivity of, and the efficiency of utilization of ¹⁵N-labelled fertilizer by, a potato crop (Solanum tuberosum L.), cv. Tequendama. The crop was fertilized with 100, 200 and 100 Kg/ha^-1 of N, P₂O₅ and K₂O respectively. The N fertilizers were either added as ¹⁵N labelled urea (2.955 at.% ¹⁵N excess) or as labelled ammonium sulphate (2.071 at.% ¹⁵N excess). In all treatments with nitrogen, a total of 100 Kg N ha^-1 was added, but the nitrogen was added either in two or three split doses (only one dose being labelled with ¹⁵N) at the following times: at planting, 35 days after emergence (DAE) and/or 60 DAE. It was found that: a) Nitrogen fertilization increased tuber production from 24 to 43 t/ha^-1; b) The tubers constituted approximately 80% of total plant dry matter and 70% of the total nitrogen and fertilizer N accumulated by the plant; c) The fertilizer use efficiency varied between 49 and 68%, and the highest efficiency occurred when the nitrogen was split in three doses; d) The urea and ammonium sulphate gave similar results in all parameters evaluated; e) When the total nitrogen difference method was applied to interpretation of the results the fertilizer use efficiency was overestimated by 15 to 30%

[en] A study carried out to evaluate the effects on N fixation in groundnut of four rates of K applied as KCl (60% K₂O) at planting or in split application (at planting and 35 days) at a ratio of 60:40% is presented. 4 refs, 1 tab

[en] A bibliography with 298 references on the use of the stable nitrogen isotope ¹⁵N in the research on the biological fixation of dinitrogen is presented. The literature pertaining to this bibliography covers the period from 1975 to the middle of 1985. (author)