Estimation of N2 fixation in winter and spring sown chickpea and in lentil grown under rainfed conditions using 15 N

A field experiment was conducted under rainfed conditions to asses N2 fixation in one cultivar of lentil and in two cultivars of chickpea (Gab 1 for winter and spring sowing, and Baladi for spring sowing). Moreover, the effect of P fertilizer on dry matter production, percentages and amounts of different N sources was studied using 15 N isotope dilution method. Wheat was used as a reference crop. The rate of N2 fixation affected by several factors such as plant species, cultivar, date of sowing, P-fertilizer and the growing season. The highest amount of N2 fixation obtained in winter sown chickpea was 126 Kg N ha-1. Whereas, that of spring sowing for the same cultivar was 30 Kg N ha-1. For Baladi cultivar, the highest amount of N-fixed was 55 Kg N ha-1. While it was 104 Kg N ha-1 in lentil. Generally, N2 -fixation affected positively by P-application. In the first growing season, N2-fixation increased from 33 to %58 by P application in spring sown chickpea (Baladi), and from 20 to %35 in spring sown chickpea (Gab 1). Whereas, no significant differences were observed upon P application in winter sown chickpea and in lentil. In the second growing season, P-fertilizer increased the percentage of N2 fixation from 54 to %64 in winter sown chickpea, and from 45 to %64 in spring sown chickpea (Gab 1), and from 49 to %60 in spring sown chickpea (Baladi). While, in lentil it was from 66 to %72. The rate of N2 fixation in winter sown chickpea was clearly higher than that of spring sowings. Moreover, this last one absorbed more N from the soil. Our results indicate the importance of winter sown chickpea in terms of N2 fixation, seed yield and the reduction of soil N-uptake, besides a positive P-fertilizer response, especially when suitable rain fall occurs during the season. Moreover, the importance of these results from agronomical point of view was discussed. (author). 24 refs., 6 figs., 7 tabs