MAGNITUDE OF NITROGEN-FIXATION BY LENTIL AT DIFFERENT RATES OF PHOSPHORUS USING N-15 TECHNIQUE

Two lentil cultivars, UJ1 and ILL, have been introduced into the farming system of the Middle East. The influence of P on their potential to fix N-2 under drought conditions is lacking. A factorial field experiment was carried out at Taibeh (500 mm yr(-1)) and Muru (300 mm yr(-1)), where three rates of P, two lentil cultivars and barley were included. Phosphorus was the main plot, while lentil and barley were grown randomly in the subplots. A typical experiment treated with unlabeled 100 kg N ha(-1) with similar P rates was conducted at the Taibeh site. Both cultivars on each site did not differ significantly at different levels of P regarding the biological yield. At each P level, both cultivars derived similar nitrogen percentages from atmosphere (per cent Ndfa), except at Taibeh with the intermediate rate of P, where ILL derived (66.1 %) compared to UJ1 (40.3 %). At Taibeh, the average percentages of N in the grain and straw were 4.17 % and 1.14 %, respectively, and were significantly higher than at the Muru site (3.38 %, 1.29 %). The relatively drought-like conditions at Muru reduced percentage Ndfa to approximate to 28 but this was increased by P addition. Nitrogen addition reduced partitioning of N (N index) from approximate to 0.70 % to; approximate to 0.55 % and decreased P percentage in the grain from approximate to 0.40 % to approximate to 0.31 % and in straw from 0.11 % to 0.07 % due to early maturation. In spire of the indigenous Rhizobium efficiency to fix N-2, only 52.0 % and 42.3 % of the plant N was derived from the atmosphere at Taibeh and Muru, respectively, causing depletion of soil N reservoir.