Quantifying N2-Fixed by Groundnut (Arachis hypogaea L.) as Compared to Some Summer Legumes Using 15N Methodology with Different Reference Crops

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Adlan, M.A. M.
Mukhtar, N. O.
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Faculty of Agriculture, University of Khartoum, Shambat, Sudan
Using the 15N methodology, one cultivar of groundnut repeated once (as groundnut 1 and 2) and one cultivar of each of the summer legumes guar, pigeon pea and mungbean were studied (a) to determine the amounts of nitrogen fixed by these legumes using different reference crops and (b) to compare N-fixation by groundnut to that of the above mentioned summer legumes. The reference crops used were, sorghum, soybean and a non-nodulating groundnut isoline. Each of the studied legumes and reference crops was grown at the Gezira Research Station Farm, in a microplot of 2.4 m2 situated at one side of a main-plot of 24 m2. The N2 fixing legumes guar, mung bean, and pigeon pea and sorghum were given 20 kg N/ha as urea at 5.0% 15N atom excess, and the reference crops of soybean and non-nodulating groundnut were given 100 kg N/ha at 1.0% 15N atom excess. 14N/15N ratios were determined in plants sampled from the microplots. The results showed that pigeon pea and guar could compete well with groundnut as N2-fixers. Levels of fixation (%Ndfa) were 79% (108 kg N/ha), 77% (138 kg N/ha) and 80% (70 kg N/ha) of the total crop's N need for guar, groundnut and pigeon pea, respectively. Mungbean fixed about 12% (6 kg N/ha) of its N need. The variation in the amounts of N2 fixed in kg/ha is dependent on the total plant N yield of each legume which was 160-180, 139, 87 and 68 for groundnut, guar, pigeon pea and mung bean, respectively. The non-nodulating groundnut was a superior reference crop over sorghum and soybean. Thus, the studied reference crops can be listed in a descending order of excellence as follows: non-nodulating groundnut > sorghum > soybean.
Page(s):12 (3), 357-369, 19 Ref.