ROOT-HAIR INFECTION AND NODULATION OF 4 GRAIN LEGUMES AS AFFECTED BY THE FORM AND THE APPLICATION TIME OF NITROGEN-FERTILIZER

The effects of application of combined nitrogen fertilizer (ammonium n itrate or urea) on root-hair infection and nodulation of four grain le gumes were studied. Young roots of each legume were inoculated with th eir compatible rhizobia. The application of the two forms of combined N either at the early stages of plant growth and/or at the time of nod ule formation depressed root-hair curling, infection and nodulation. I nfection of hairs on the primary roots was more sensitive to the N fer tilizer than hair infection of secondary roots in both Vicia faba and Pisum sativum. The nodule number and total fresh mass of the four legu mes were drastically affected by fertilizer application. The combined N added both at early and at later stages significantly reduced the no dulation of V. faba, Phaseolus vulgaris and Vigna sinensis. The inhibi tory effect of urea on nodulation of P. sativum was only observed when the fertilizer was applied at the late stages of plant growth. It is concluded that, although the nodulation of the four legumes was suppre ssed by combined N, the initial events of Rhizobium-legume symbiosis ( infection of roots and nodule initiation) are more sensitive to combin ed N than the stages after nodule formation.