Phosphorus deficiency is a major limiting
factor for symbiotic nitrogen fixation and grain yield of
legume crops in the tropics. Eight cowpea genotypes of wide
use in Cuba, were grown in hydroponics solutions; supplying
from 50 to 500 µM of P/plant/week. Nitrogen nutrition was
dependent upon symbiotic N2-fixation on adding of 4
mmoles NO3/plant/week. Shoot growth was severely limited
by P deficiency, while dry weight of roots increased in both
groups of plants. Nodule formation was severely decreased
by P deficiency, while specific nodule activity was increased
in the atmospheric N2 fixing plants. Growth response of N2
plants was higher than that of NO3- fed plants due to P use
efficiency, and revealed a the great large N2-fixation
potential of the specie.