Nodulation and symbiotic nitrogen fixation by genotypes of blackgram [Vigna mungo (L.) Hepper] as affected by fertiliser nitrogen

Abstract

Intercropping with legumes and non-legumes is commonly practised in many parts of the world to maximise productivity per unit area of land. In India, blackgram or urd [Vigna mungo (L.) Hepper] is a popular pulse legume component of intercropping farming systems. Often, however, potential production is compromised, particularly in high fertiliser input systems, because blackgram competes with the non-legume component of the system for nitrogen in the soil.

In order to identify lines of blackgram that could obtain the majority of their nitrogen requirements from symbiotic fixation of atmospheric nitrogen rather than from uptake of soil nitrogen, 50 genotypes were screened for tolerance to (applied) nitrogen in soil. The parameters used to appraise tolerance were extent of root nodulation, the amount of nitrogen fixed, nitrate reductase activity in roots and nodules, and nitrite content of roots and nodules. There were 2 nitrogen treatments applied as urea, viz. 40 (N40) and 120 (N120) kg N per ha.

There were 3 genotypes whose nitrogen-fixing effectiveness was apparently unimpaired by applications of nitrogen to the soil. Genotype NC-59308 nodulated and fixed atmospheric nitrogen satisfactorily at both the lower and higher levels of applied nitrogen. At N40, genotypes EC-48215 and PLU-726 formed a great abundance of large nodules effective in nitrogen fixation; even at N120, both lines had better symbioses than the majority of the 50 blackgram lines originally screened. These 3 genotypes are deemed worthy of further examination for their suitability for intercropping systems. How this might be done is discussed.