Abstract
In India, wheat crops receive 1-2 irrigations in the majority of the areas where the soil, in general, is low in N resulting in low average productivity. Azospirillum and vesicular arbuscular mycorrhiza (VAM) have been reported to increase wheat yield through enhanced nutrient supply, but the information regarding the performance of these bio-fertilizers at different levels of N and soil moisture in the field, particularly in India, is lacking. Hence, an investigation was conducted at New Delhi, India, during the winter seasons of 1993-1994 and 1994-1995 to evaluate the impact of (i) irrigation and (ii) bio-fertilizers alone or in association with fertilizer N on yield and N and P uptake by wheat. Two irrigations applied at crown root initiation and flowering stages of wheat recorded maximum grain and straw yield as well as crop nutrient uptake. The Azospirillum population in the rhizosphere of wheat or mycorrhizal infection in wheat roots did not increase much with irrigation, but both decreased with application of fertilizer N. Azospirillum and VAM, alone or in combination, increased grain yield of wheat as well as N and P uptake in grain significantly over uninoculated controls, both at 0 and 60 kg N ha-1 levels. The Azospirillum population in the rhizosphere of wheat and mycorrhizal infection in wheat roots increased with applied bio-fertilizers at both 0 and 60 kg N ha-1 levels, but the magnitude of increase was greater under the unfertilized condition. In general, combined application of Azospirillum and VAM recorded higher values of all the parameters under study, compared to their sole applications.
