Cultivar differences in nitrogen assimilation, partitioning and mobilization in rain-fed grown lentil

A field experiment was carried out to assess the source of nitrogen (N-2 fixation, soil and fertilizer), N assimilation, partitioning and mobilization in rain-fed lentil at various growth stages using N-15 isotopic dilution method. The study was conducted on five lentil cultivars differing in seed size: Horani and ILL16 (small size), Idlib and ILL5883 (medium size) and Kurdi (large size). Small-seeded cultivars formed more nodules than those of large seeds. The percentage of N-2 fixation (%Ndfa) ranged from 58% to 68% according to lentil cultivar, whereas, the actual amounts of fixed N-2 were from 111 to 154 kg N ha(-1). The highest rate of N-2 fixation (3.11 kg N ha(-1) day(-1)) occurred between flower-bud initiation and maximum flowering in ILL5883. There was a strong cultivar effect on both N-2 fixation and soil N uptake beyond flowering, and the plants were characterised by either current N-2 fixation and soil N uptake, mainly by soil N uptake, or by negligible N assimilation from either source. The results showed net mobilization of N (43% to 94%) from shoots and roots to pods. It was concluded that when both soil and atmospheric N-2 sources are limited, translocation of N from the pre-existing N pool in vegetative tissues becomes the major source of N for pod filling, and vice versa. However, this phenomenon was affected considerably by plant cultivar. After pod removal, annual N-2 fixation returned to the soil in plant residues ranged from 10 to 83 kg N ha(-1). However, when all aboveground parts are harvested, soil N balance became negative in all cultivars. (C) 1997 Elsevier Science B.V.