Quantification of the contribution of biological nitrogen fixation to tropical green manure crops and the residual benefit to a subsequent maize cropusing N-15-isotope techniques
Mg. Ramos et al., Quantification of the contribution of biological nitrogen fixation to tropical green manure crops and the residual benefit to a subsequent maize cropusing N-15-isotope techniques, J BIOTECH, 91(2-3), 2001, pp. 105-115
In this study the contribution of biological N-2 fixation (BNF) to legumino
us green manures was quantified in the field at different sites with differ
ent N-15 methodologies. In the first experiment, conducted on a Terra Roxa
soil in Cuba, the BNF contribution to three legumes (Crotalaria juncea, Muc
una aterrima and Canavalia ensiformis) was quantified by applying N-15-labe
lled ammonium sulphate to the soil. The second experiment was planted in a
very low fertility sandy soil near Rio de Janeiro, and the N-15 natural abu
ndance technique was applied to quantify BNF in C. juncea, M. niveum and so
ybean. In both studies the advantages of using several non-N-2-fixing refer
ence plants was apparent and despite the much greater accumulation of the C
. juncea in the experiment performed on the fertile soil of Cuba, the above
ground contributions of BNF at both sites were similar (40-80 kg N ha(-1))
and greater than for the other legumes. In a further experiment the possib
le contribution of root-derived N to the soil/plant system of two of the le
gumes was quantified using a N-15-leaf-labelling technique performed in pot
s. The results of this study suggested that total below-ground N could cons
titute as much as 39 to 49% of the total N accumulated by the legume crops.
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