Nitrogen Requirements at Different Growth Stages of Short‐duration Pigeonpea (Cajanus cajanL. Millsp)1

Abstract The response to N fertilization of a short‐duration pigeonpea genotype, ICPL 87, was studied in the field to assess the scope for genetically improving symbiotic N2fixation by pigeonpea. The field study was undertaken during 1985, 1986 and 1987 growing seasons on Vertisol and Alfisol at ICRISAT Center (peninsular India), Inceptisol at Gwalior (central India) and Entisol at Hisar (northern India) in as non‐limiting environmental conditions as possible. Nitrogen fertilizer was applied to the soil at various growth stages to determine when N becomes most limiting. There was a significant response in grain yield to fertilizer N applied at flowering in Vertisol but not in Alfisol, Inceptisol or Entisol. This suggests that biological N2fixation by short‐duration pigeonpea was not adequate to meet N requirements of the crop grown in Vertisol but that it was probably adequate in the other three soil types. These results are discussed in relation to the nodulation and acetylene reductase activity of pigeonpea and also N mineralization potential of different soils. It can be concluded that there is a need for genetic improvement of N2fixing ability of short‐duration pigeonpea grown on heavy textured soils such as Vertisols.