Effects of single and double-strain rhizobial inocula on some legumes under field conditions

ABSTRACT

Two field experiments were conducted to evaluate the response of winther [faba bean, pea, berseem miskawy and chickpea] and summer legumes [cowpea as well as two soybean cultivars, namely Clark and Crawford] to single - or double - strain rhizobial inoculation. Plant growth [height, dry weight and N - contents], nodulation [numbers and dry weights of nodules] and in vitro N2 - ase activity of intact roots and / or detached nodules were determined as paramenters for plant response to rhizobial inoculation. Uninoculated plants formed considerable numbers of nodules. Plants incoulated with double -strain inocula produced significantly higher numbers and weights of nodules. Nodule numbers and dry weights of faba bean either inoculated or not were markedly higher than those of the other legumes. The nitrogenase activity of intact roots of winter legumes increased due to rhizobial inoculation particulary with the copmposite inocula. In terms of the N2 - ase activity per unit dry weight, roots of pea were superior among the winter legumes. Plant heights, dry matter production and N - contents responded to inoculation and the response was more pronounced with double - strain inoculation. Inoculation increased the nodule production of summer legumes, although the effect was statistically insignificant in the majority of cases. The lowest N2 - ase activity of the excised nodules was recorded for the ruininoculated plants. Inoculation, with the double - strain inocula in particular, enhanced such acivity. Again, inoculation either with single - or douuble - strain inocula resulted in taller and heavier plants of higher N- contents